In Part 1 I wrote about why rigging a proper end boom preventer is vital when sailing off the wind. In this post I'm going to share how we have made rigging a preventer easy on Morgan's Cloud.
This is information that will help you set up your boat so that you can, like us, always have a proper preventer rigged when the boom is far enough out to make it possible.
But first, let's start off with a short video to demonstrate how easy it is to use this system in practice.
Now, let's dig into the details and look at the two parts of our system, which I have named the boom line and the deck line.
Nice description of the proper method of rigging a preventer, John. We just got back from an awesome trip racing on a friends boat in the RORC Caribbean 600, and now I know we were doing it all wrong (dock line tied off at mid-boom, through a turning block aft of the shrouds to a winch). Funny thing about Ultrex Plus, though- when I Googled the term, looking for comparable line from other companies, the first link was from the National Library of Medicine- http://www.ncbi.nlm.nih.gov/pubmed/9788107
Who knew it had more than one use!
Glad the post helped.
And on the link, what can I say but Yikes, who knew?
That looks a lot like the preventer I rigged on our last boat, a 24′ gaff yawl. The only significant difference is that rather than screw extra fittings into the wooden boom, I simply made an eye-splice right round it. The loop passed through the eyebolt used for the clew lashing, but this was just to help locate it, all significant load would be around the spar and not on the bolt.
This is quite a common approach on traditionally-rigged craft; most of the high-load attachments involve a strop passed right round the spar rather than trusting fittings screwed or bolted onto it. Seems very sensible to me.
Thanks for the comment, that makes a lot of sense to me.
As Helen mentioned on Facebook, we have used pretty much this approach since reading Eric Hiscock in the 1970’s
The line along each side of the book is made fast to a cleat near the gooseneck. That way it is a good grabrail/harness attachment when working on our (rather high) boom.
We keep it a bit simpler by simply tying the preventer off at the bow, with the mainsheet eased off, then tensioning the mainsheet. Less control, but simpler.
I wonder about the best line? We use 1/2″ nylon, breaking strain about 4000 lbs. (47 foot boat) The few gybes we have had were quite tame, with the line stretching a lot, in up to about 25 knots. We have no experience in extreme winds.
I think, (but am not sure) that a pretty elastic line is preferable to a lower stretch.
To take your points in reverse order, I think you are right that having a bit of give in the system is a good idea, although I think that using nylon might be a bit too much of a good thing since when caught aback the boom is going to move a lot before being restrained, so I would go with Dacron, which still has some stretch, rather than nylon.
While, as most readers know, I’m a big fan of simplicity, I really don’t like the idea of cleating off the preventer on the foredeck for two reasons:
I would strongly suggest installing a block forward and then bringing the preventer aft to a winch, as recommended in the post. Also, after doing that, you will have about doubled the length of the preventer, so probably a good time to change from nylon to Dacron.
Could you please post a picture of your forward attachment on the bow and describe in more detail what a MOORING FAIRLEAD is? That would be helpful. I am thinking of using padeyes with backing plates on port and starboard about 5′ aft of the bow.
Great post. I am building one now.
I have added a photo of our bow area showing the enclosed fairleads.
I get that its the round pad eye. But you have gotten me even more curious to see how you have the line led. It appears to go straight up. Please show the rest of your set up. I am working on the boom lines and want to install padeyes or fair lead ASAP.
Your web site is really great and I am learning a lot from you and the people who post here.
No, it’s not the round pad eye that we use. We pass the line through the fairleads—the oval holes in the toe rail that you can see each side in the small shot I added next to the “Notes that will help” heading. The deck line is rove from the winch forward, through the fairlead (inboard to outboard) and thence back to the boom line. You can see this in the large pic with the caption that starts “Note the snatch block…
As I say in the post, if you are not blessed with nice rounded enclosed fairleads like this, you will need to add two strong blocks up forward to accomplish the same function.
Is it viable to consider attaching a large snatch block to the forward cleat with jackline webbing (or perhaps spectra line) as the turning block?
Also: Any thoughts about doing double duty on the preventer line – to also act as the pole foreguy? Thinking it would reduce clutter on the deck… Problem I see is when flying both genoa and main deep on the same side…
Yes, I think that might be a very good alternative, as long as the cleat and its attachments are strong enough to take the load. I’m going to guess that on most good quality boats they will be since said cleats should be designed to take full mooring and anchoring loads.
As to double duty. It’s certainly an idea, but, as you say, what happens if, say, you are goose-winged and decide to gybe and leave the jib on the pole, as we often do? I guess there may be ways to do this, but my gut says that since the preventer is such an important piece of safety gear, maybe we shouldn’t be using it for other things since so doing always adds the risk that we will be tempted to say, “oh, the preventer line is in use for someone else and we are not going to be on this gybe long…”
We use a similar system but with a continuous line that runs through blocks at the bow and along each side deck. After attaching the leeward end of it to the appropriate permanently installed boom line we haul in on the windward side.
This means less rope on the side decks and no need for an extra winch on the leeward side since a sheeting winch to windward will normally be unused anyway.
This could also used as a fore guy for the pole but it’s often already in use.
Sounds like a good system, and, as you say, solves the winch problem on many boats.
I like the idea of this arrangement, and would like to implement it, but wonder if I am missing something in the application:
The author says, “After attaching the leeward end of it to the appropriate permanently installed boom line we haul in on the windward side.”
What does one do to set up the preventer on the opposite tack? If I am right, the bitter end is now tied to the boom line on the opposite side of the boat. It seems that the only way to rig the preventer on the new tack is to go forward and bring the line aft to the winch to tension it AFTER the boom is on the opposite side of the boat. I am hoping I am mistaken because it sounds like good option and cure for the single cockpit winch situation that I have on my boat. Although running backs would keep the windward winch busy unless I installed clutches.
Good point, I think your analysis is right.
One thought, you could have two lines, as we do, but just cross them over so that the boom end was on the leeward side and the winch end to windward. That way you could use the windward winch but still be able to set up for a jibe more easily with the new preventer to go on the new (after the jibe) windward winch as soon as the jib sheet was transferred during the jibe.
Good post, thanks.
I have a similar setup, but with preventers permanently rigged cleated off by the cockpit with a short line which gets chocked round the end of the boom anytime downwind is likely. Usually singlehanded, leaving the cockpit is seen as bad form 🙂 It’s only a 33′ boat so it’s easy to get a little tension by easing the mainsheet more than you want, cleating off the preventer then tensioning the main a bit again .
One feature not mentioned is how useful they can be in light airs, my topping lift is cleated off to the backstay so by adjusting that, the mainsheet and a preventer you can lock off the boom wherever you want, a simple way to get the weight of the boom off the mainsail to make it a bit fuller in downwind light airs.
Very good point about how useful a preventer is in stopping the boom from slamming around in light air, thanks.
Nice write up and well thought through. A couple of thoughts:
I would suggest that this method of preventing is easiest executed on bigger boats like yours or on racing (or ex-racing) boats with winch farms aft. They either have the winches already at hand or (bigger boats) have the territory to execute changes like a brake grouping which demand exquisite placement in the lining up of leads etc.
For those of us with only one winch (per side) I have a couple of suggestions. When setting up the preventer without a winch available, let the boom go out farther than wished, tighten up the preventer, by hand is likely with no winch available, and secure it, likely on a cleat. Then tighten up the preventer by pulling in on the mainsheet bringing the boom end aft and firming up the preventer.
As well, it might be advised, for those hand tightening the preventer, this might be a place for low stretch lines: there will already be some slack in the set-up. For systems where you can apply load by winch regular Dacron (or maybe even nylon braid) of sufficient strength would be fine and give a little bounce softening shock loads.
As for using cleats, all your caveats are well taken, but I would suggest many of us in the 40 foot range will end up with the preventer on cleats. With care quite high loads can be bled off of a cleat while maintaining control of the line. To follow, I would suggest it is a rare cockpit cleat that could handle these loads. They are generally designed to take loads after a few turns on a winch (with the ubiquitousness of self tailing winches there is a lamentable lack of cleats at all). This will leave many with only midship’s or stern cleats having the necessary strength to take the loads being discussed unless one finds property appropriate for a cleat where one can also install substantial backing plates.
I would question the wisdom of a brake for this kind of job. If you have a brake, tendency would be to use it to secure the preventer, at least at times when you want the winch for other uses. Brakes are not, to my casual observation, made to handle shock loads such as you are discussing and are often installed individually with 2 bolts, even when ganged together. (I notice yours are built 3 brakes as one set with 4 bolts more widely spaced.) Moreover, in a fire drill, even if the brake holds, you have to free up the winch and load up the preventer line on the winch before you can even think of releasing the brake. A good cure for this would be to never throw the brake on the preventer and always have the load carried by the winch.
Finally, again likely for smaller boats, one may need only one boom line. Secured with a loop (rather than padeyes on either side) it can rotate to be deployed to either side. Being a smaller boat, I can reach the tail lead forward from the side decks, even with the boom out, without it getting cross- wise with mainsheet etc.
Thanks for another nice contribution to boating safety.
Dick Stevenson, s/v Alchemy
All good points and tips, as usual, thanks.
One thought jumps to mind. What is it with yacht designers and builders that they give a bunch of young gorillas on a race boat all the huge winches they could ever need and then give us aging shorthanded cruisers just two, often undersized, cockpit winches—just nuts! In my opinion the absolute minimum number of winches in the cockpit of any boat over 30-feet is 4 (two each side) and they should be sized to work well for a small light woman.
John, picking up on your remark that winches should be manageable by small women. I’m considering replacing mine, with larger diameter, perhaps with self tailing, partly with this in mind.
What is an adequate diameter – 4.5 inches, 6″, 8″? (The maximum diameter I can go up to is 5.5″)
And is self tailing very helpful for a small woman?
I don’t think diameter is the real issue, the key is the power ratio of the winch. I would check with Harken on the right winch size and then go up one size from whatever they say for your size boat.
As to self tailing, I think that that feature is probably one of the most important and useful sailboat gear inventions of my lifetime, particularly for short handed boats—don’t leave home without it,
Many thanks John. A friend also on this site tells me (in private) that tailless winches work great for his wife. Guess I’ll splash the cashoola..
You might like to consider the WinchRite electric winch handle.
A friend with an arthritic shoulder has recently bought one and reckons it has changed his life.
Makes sense to me: it means every winch on board has the potential to be powered at relatively little cost.
Have any of you used one long term?
Excellent post and we use a similar system with a few minor differences aboard Asmara Sky, our Oyster 53. I decided not to have the preventer permanently attached to either side of the boom as I worried that it would “slap” in the wind under way and/or at anchor. Have you had this problem or did my careful analysis lead to its usual erroneous conclusion?
I wondered exactly the same thing but after three years in use, including an Arctic voyage with a lot of wind both at anchor and at sea, I’m happy to report no problems at all with slap. I think part of the secret is using high modulus rope for the boom line so that it’s nice and easy to tension with the shock cord.
Our lines along the boom are attached by eye splices to U-bolts as in John’s photo above.
Fwd end ties off to a cleat on the side of the boom. I make this TIGHT, so it is a handy grabrail. No issue with slapping in 9 years, including some very windy anchorages.
Great article John. I had been previously thinking about how best to set up the preventer lines. This nails it for me. Thanks
My pleasure, great to hear that it works for you.
I installed a Wichard Boom Brake on our 42” yacht sailed shorthanded. It is a very good safety equipment for crew and rig. Two solid pad-eyes are fitted close to the toe rail just behind the stations. On the couch roof I got a dedicated Spinlock clutch holding the line. The total cost adds up – but it works really well. With the right tension on the line – I can forget the main sheet when jibing or tacking. The mast slowly moves across.
By tightening the line on the winch it acts like a “solid presenter”. It works both as a prevent and a boom brake. I find this arrangement very useful when reefing – it keeps the boom under control, the same goes when I take the main down. At anchor or at the marina I get the rig quiet since it stops the boom from moving.
Yes, boom brakes are useful pieces of kit, however they are not a substitute for a proper end-boom preventer as we explain in part 1 of this post.
John and others using this system,
Thank you. This is most helpful as we set up our new (to us) boat….
I understand the desirability of running the preventer as far forward as possible – less stress on the whole system. However, with this system if you use the preventer to control the jibe, easing it out as you sheet in (and ultimately jibe) the boom, doesn’t the preventer come across the stays while it’s still loaded? Is it no big deal if the preventer is tensioned against the stays? Or do I misunderstand – are you not using the preventer to help control the jibe, but rather you are simply releasing it prior to commencing the jibe?
Good question and something I should have made more clear in the post. No, we don’t use the preventer to control the boom in the jibe. We do that the old way by trimming the mainsheet into the centre line before the jibe and then easing it out afterward. As you say, We release the preventer before the jibe starts.
Although they are not a substitute for a preventer, one of the advantages of boom brakes (discussed at length in this comment stream) is that they control the boom throughout the jibe. Although, having said that, even with a boom brake I would be nervous of jibing without first trimming the sheet since so doing will impose very large loads on the brake due to the geometry. But I should add that I have never used a boom brake so that is theory only.
What do you think about making an eye splice on the end of the boom line and the deck line and then using a soft dyneema shackle to join them? Alternatively, making your boom line out of Dyneema and put a soft shackle in the end of it to secure to an eye splice in a double braid deck line. It seems this might be stronger and quicker than a bowline.
Sure, you could do that. The way we are set up, speed is not required, and anyway I can tie a bowline pretty quickly, so I have never bothered with anything more complicated.
I should be grateful for comments on this proposal for a combined vang and preventer. A friend has a Class 40 with the gooseneck virtually at deck level making a kicking strap impossible. The Class 40’s use a line strung along the boom with a block running free along it. This block is attached with a line to each toerai leading aft to the cockpit. Providing the line is not too tight ( I would aim for a 10° angle at each end with the boom) the forces should be manageable, and the strain on the boom will be at each end rather than in the middle. The running block can take up the best position according to the position of the boom. This seems to offer the best of all worlds, good mechanical leverage to hold the boom down, prevention of unplanned gybes, and giving two for the price of one.
Have I missed something?
Incidentally, I plan to drill for threaded rod, with a UHMW PE sleeve at each end of the boom, with eye nuts to take the line.
I look forward to any comments.
The thing that immediately jumps out at me is that the compression load on the boom and the line along it, as well as the fittings attaching it, will be multiplied logarithmically and inversely to the angle the line makes with boom ends.
In addition, this will not change the loads on the block at or near the toe rail, that I discuss at length in part one.
Now let’s assume that the peak load on the block at the rail is about 3000 pounds on your boat (probably conservative and half of our boat) then the load on the boom line you are proposing is going to be about four times that or 12,000 pounds!
And here’s a really scary thought. If say the deck block lets go (for all the reasons I detail in part 1 of this post) the boom is going to fly across trailing the line you have added as a really nice garrotte…or dodger remover.
In summary, I just can’t see a benefit here. While you may have reduced the chances of a broken boom, due to removing the centre point loading, you have increased other loads a lot, and nothing has changed in the loads imposed on the deck blocks.
To me, this is not a substitute for a preventer as specified in the post above. And the key thing is that if you set up as we are, rigging a boom end preventer is easy and quick, so why risk something else that actually increases loads?
By the way, the I think the reason that Open 40s make this work is their extreme beam in relation to boom length, which reduces all the loads.
Thanks Bill for the contribution and ideas you provided regarding rigging of a boom preventer. You did so under refit, but since it is really a preventer theme, I pull it toward the right section. Have decided to go for a dyneema loop at the boom end as preventer line anchor and lash it to something to stop it from sliding off or forward on the book.
Thanks for the response which I need to consider at leisure – with my calculator to hand! I shall start with estimating the loads on the mainsail, transfer to boom, and then look at the loads on the vang and its attachment point to the deck. One easy part of the calculation is the loads on the boom ends as the vectors are basic trig. If the angle that the line makes with the boom is 10° then the multiplier is about 5.7, and I suspect that the actual angle would be greater, probably 20°. I have no concerns about the deck fitting pulling out as I have access to all of the deckhead and no problem fitting substantial backing plates. One planning factor that I have is that there is no kicker, so vangs are a necessity. I’m sure you can see the attraction of combining vangs and preventers, a big reduction in clutter. However, your response has motivated me to do a proper analysis of the loads. If I cannot be sure that the system is absolutely robust, then I’ll not implement it. I read Tony Gooch’s paper on heavy weather sailing on the OCC website recently, and noted that he uses, or used, vangs on Taonoui.
You will find all that you need o make this calculation in part 1 of the two part series.
One important point, as outlined in that post, in making you calculations, you need to take into account what the loads are and what happens if you are caught aback all standing in any of the scenarios outlined in said post—that’s what a proper preventer is for. Sizing for general working conditions is not adequate.
When you make your calculation based on the above, you will find, as I did in part one, that the loads are truly eye popping.
Also, no, I am no fan of trying to combine the vang and preventer functions. The two pieces of gear have different purposes and should be separate.
In collecting data, you might refer to the CCA’s (Cruising Club of America) web site for their fleet surgeom’s description of a preventer/vang very similar to what we use in everyday sailing life on Alchemy. I believe it to be similar to what you are considering. He includes in his description an analysis of the safety aspects which I believe to be very pertinent to any decisions in this area. I find an end of boom just too cumbersome for everyday use, which for us has been mostly day sailing European ports for the last few years. That said I always like the boom prevented and our side decks preventer/vang serves this function as well as serving as a boom vang. It is very easy and simple and, for me, a safety devise used is better than a better design not used. We are prepared, when offshore and conditions call for it, to easily deploy an end of boom preventer.
Dick Stevenson, s/v Alchemy
Phyllis and I have been rigging an end boom preventer inshore and offshore each and every time the boom was far enough out to require it for over 20 years. With a proper set up, as detailed in the above post, it a matter less than a minute. Well worth it is my view.
I shot a video today to demonstrate actual use. If I didn’t make some dumb video-newbie-mistake it will appear soon.
Thanks for your info. I did answer 2 days ago, but for some reason the comment doesn´t seem to have registered. I shall certainly check out the CCA website and assume that the referenced article is available to non-members?
Did I make clear in my original post the concept of the line along the boom which allows the block to take up an optimal position? I am having some trouble deciding what the primary load (effectively the load on the deck fitting) to be used in the calculation should be. Probably quite a complicated equation beyond my capabilities to solve. The potential loads that I can identify are: upwards, as for the kicking strap, and towards the stern if taken aback or the boom end dips into the water.
If wished, I can describe my way of setting up my preventer/boom vang if the previous descriptions above need elaborating, particularly the attachment to the boom.
Please note that John has some reservations with regard to my approach.
My best, Dick
I am, as you know and say, no fan of the article you linked to. In fact I would go as far as to say that, although I’m sure the author is well intentioned, it is ill informed and dangerous.
While, as you and I agreed last time we went through this debate, that the system detailed may be safe in the hands of experienced sailors like you and Ginger who understand it’s limitations and the colossal loads it imposes and who rig a proper preventer when required, to propose said system as a replacement for a proper end boom preventer (or even call it a preventer) when offshore in big breeze and waves shows that the author has very little understanding of the forces involved in the reasons for rigging a preventer in the first place that I detailed in part one.
You only have to take a quick glance at the photos in said report to see that the boom will break at the control line attachment point if, for example, the end even brushed a wave top, a quite common occurrence offshore, and that is just one scenario that would result in disaster and potential injury with the system proposed.
After giving it a lot of thought, I am now of the firm opinion that for those that wish to restrain the boom in this way, a boom brake as Colin details is a far better solution because it will bleed off the load when the system is stressed.
I have looked at the article you recommended. Very clear and a frightening confirmation of how dangeeous the boom is if not controlled. The system is almost identical to that which I had installed, except that my original had the preventer to the boom end and the pulpit. My planned system fulfills the functions of preventer and kicker (vang), as I have removed the kicker. The mechanics of a kicker are, in my opinion, so poor as to be almost useless. My concern was that a mid- or part-boom attachment would act like a hinge in the event of an unplanned jibe, or other misfortune, with a strong chance of breaking the boom. The use of the “Affenleine” or monkey rope (I have no idea why it is nicknamed this) should move the stress on the boom to its ends. I still have to satisfy myself that the various forces can be managed. The one area where I still have to decide is the boom end attachments for the line – Dyneema 8mm single braid, with a free-running block, and a short strop P and S with a violin block and a double block at each toerail, each running back to a jammer. I may decide to replace the violin blocks with aluminium rings and lose 1x mechanical advantage, the reason being that they are much lighter and the lazy vang will be less noisy/damaging.
In any event, a lash-up system will be tested next month before I start drilling holes in the boom.
I shall certainly report on the success or failure of my system, and would appreciate any photos of your system.
I have done some calculations, and although I am no mathematician or engineer, I think they are a reasonable estimate.
The force on my proposed preventer system, assuming the block is more or less in the middle of the boom, would be 840 kgs in a 20 knot breeze (from your Harken calculator). I estimate that the angle formed by the Affenleine (the line along the boom) would be 20°, but will use 15° as more conservatine estimate. The forces on the boom attachments, at each end would be 3,245 kgs (2,456 for a 20° angle). I don´t see any problem with a deck fixing well able to handle the 840 kgs load. Dyneema 10 mm has a breaking strain of 8,500 kgs, so would have a sufficient safety factor as Affenleine. Maybe scale up to 12 mm to cover the loss of strength in the splices. The one area where I still have to find a solution is the boom attachments. Two sailing friends, at the moment off on their annual cruise, who are engineers will be consulted on my proposals. I may even listen to their advice.
In any event, I shall report back on the success or failure of my system. I have gained so much useful information from the AAC website, it will be nice if I can repay some of this.
840 kg may be a realistic working load, but when sizing something like a preventer, working load is no where near enough. Engineers always add a safety factor on such systems, typical a factor of 5 to 10. If you crank that in, I suspect your conclusions will be very different.
The key is that the system must be able to withstand things like the boom dipping into a wave in a broach. I have no idea what that force is, but consider the about three to one leverage alone (boom end to floating block position) and it’s a lot more than 840 kg, perhaps an order of magnitude more—then add the loads imposed by the geometry of the floating line.
We are talking loads here that in broach will surely either break the boom, or tear the attachment point out of the deck, backer plate and all.
Keep in mind in all of this that when I wrote part one, no one (including our resident engineers) challenged my arithmetic or scenarios. All of the arguments against a proper end boom preventer were based on saying it was too much trouble to rig…gotta tell you something.
The potential vulnerability of the boom is certainly one of John’s misgivings for this system and is an element I pay attention to. My thinking is as follows:
My boom is quite robust and the original design had the preventer/vang point loaded to a bale at the base of the boom (and then going to the side decks and aft in a 2-1 part system). I assume most Valiant’s are still operating like that. I pay a good deal of attention to the Valiant web site and have never heard of any boom failures/damage and they do lots of miles in open water. That said I have switched to a three fall lashing over an 18 inch length of boom to spread out the load and I use nylon for the lashing to give some small degree of bounce. The actual preventer/vang connects at the end of the falls about 6-8 inches from the boom and is a 4 part polyester braid to the side deck and then going back to a brake at the side of the cockpit. It is 4-1 to allow me some additional leverage for its use as a vang and even then (in heavier winds) I let the boom out farther than needed, vang it, and then bring in the boom with the mainsheet to really get the boom vanged well and the sail flat (ter). It being 4-1, it is a fairly long line and even though polyester, will give way to some degree if the boom kisses the water.
There is also the fact that I requested from my sailmaker to have my boom end rise more than most when my deep reefs are set. And with my after shrouds, the boom end does not get outboard that dramatically. I have watched the boom end in rolling conditions and never seen it get close to the water. That said there are always “rogue” conditions.
My system is a bit of a compromise, but one that allows me to have the boom prevented at (almost) all times, day sailing or offshore. This in itself is a big safety plus. The vang on the side deck also allows me much storage under the boom (for me a nesting dinghy) that would not be possibly with a conventional vang to the base of the mast.
And, as said before, offshore, when conditions warrant, an end of boom preventer is ready at hand.
Keep us informed as you go along.
My best, Dick Stevenson, s/v Alchemy
All makes sense…in the light of your second last sentence. Like I said, safe in the hands of the experienced and well informed.
Good advice from the skipper of the “other” Alchemy, for which I thank you. We have no vang, but there is sufficient space and lashing possibilities to put the nesting tender on the pilothouse roof, and the method you describe would work for us to provide enough clearance to get same result, plus the advantages of “the side vang”, a system I’ve used in heavy air in my rather differently deployed ’70s IOR racer to good effect.
A couple of clarifications to my earlier comments and your replies, for which I thank you. The boom end in water case should not involve any leverage, as the boom is supported at both ends by the Affenleine. The free-running block transfers the boom end load to the deck fitting. I have no intention of using the working load of 840 kgs as the basis for the system, it was merely a first look at what scale of forces might be involved. A multipoint attachment, say two large U-bolts, with substantial backing plates might do it. Another thought is that in the event of being caught aback, if the boom is well held, then the main will remain at a large angle to the wind and the force on it will be small. Of course if the boat suffers a massive broach, then the mast and main will be almost flat on the water and again not experience much force. Racers may do it but to allow this to happen on a cruising boat would seem to me gross negligence. The other point which all this discussion about force vectors does not seem to have illuminated is the inefficiency of the classic kicking strap. I haven´t run the numbers through the Harken calculator, but I suspect that the results would be surprising.
I started sailing dinghies in the early 50´s and did my first offshore race in the mid-60´s when boom roller-reefing was the standard, and we had to use a claw or vangs to flatten the mainsail.
I have just added a short video to this chapter to show how quick and easy it is to deploy a proper end boom preventer when set up to do so, as we are—less than 2 minutes, soup to nuts.
I would also (once more) strongly urge any of you that are considering any alternatives to an end-boom to bow preventer to carefully read, or reread, part one, including the comments from engineers, so that you are really clear on the colossal loads that many of these alternatives place on the gear.
We now have good enough internet so as to see the video which was fun, informative, and a great way to convey methods of operation. Nicely done.
I would want to underline a couple of things you did during the video that may go un-noticed: one you gave your knot a jerk to work it up tight and, secondly, you left a nice amount of tail, both important elements to ensuring the knot accomplishes its goal.
I would also wish to suggest to those starting to put together their own system that the connection of the preventer to the boom end must be bulletproof. I am wary of padeyes (even thru-bolted and well backed up as I assume MC’s to be) such as I see on your boom end. I do not trust them without back-up lines or lashings. Further, the protruding bails are going to do a great deal more damage to a head than a gently curved boom if the worst occurs.
On Alchemy, our preventer line goes around the boom end (kept from migrating by going through the outhaul bail) and is lead forward to a position easily accessed from the side deck in just the way you get yours from the gooseneck. This makes for a much stronger connection to the boom end and does away with 2 padeyes and the 6-8 bolts and holes and back up materials and the attendant installation. This also allows us to only need one preventer line on the boom (easily accessed/deployed on either side deck with our mid boom 3 position mainsheet connection- boom end might even be easier). As a bonus, although the boom end can never be deemed safe, all efforts to make it safer should be considered and it can certainly be kept from imitating a head bashing mace from olden times.
My best, Dick Stevenson, s/v Alchemy
Thanks for the kind comments on the Video.
While I have no worries about the pod eyes on our boom since they are massive and way over the strength of the rest of the system, I agree on the benefits of lashing. In fact I say that (based on an earlier comment of yours) in the post above.
2 follow-up questions, maybe already addressed in the numerous comments preceding.
1- how about using only 1 line on the boom, that could be used for both sides; the line would have to run close to the bottom of the boom (mine is on the bottom), but maybe if the attachment point is at the bottom it’s less resilient than if attached to the side?
2- how about using carabiners as the boom attachment, to be used for disconnecting the preventer in an emergency? I’m using my preventer in weak winds to stabilize the boom against the wake generated by those *&&^$#@^%* large motor yachts and had to gybe quickly in some cases. As a single handler I’m under the impression that going off the cockpit and trying to untie a bowline that may have become tight would take too much time in some situations.
1. One line would foul the mainsheet and vang, at least on our boat.
2. Sure, you can use carabiners (make sure they are strong) but do recognize they will bang into the side of the boat, unless you are very quick to trim the preventer, and do your paint no good. I have never had trouble untying a bowline that was loaded, but if you really don’t like bowlines, maybe a soft shackle? Also, you can still jibe with the old preventer on, we do it all the time, just slack it right off.
I have spent a fair amount of time on a boat with a single line for a preventer. It worked just fine on this boat but it had end boom sheeting and no vang. The preventer was actually attached directly to the boom bail which seemed to work fine.
Regarding the use of biners for attachment, we are down to only 1 biner on board and have replaced everything else with soft shackles as John suggests. We even attach things like our topping lift with one as the noise of the metal one was driving me nuts. I have never had a soft shackle come undone when I didn’t want it to and I have never had one jam on me. We do still use a lot of bowlines which are very easy to undo if you break their back.
Your suggested system is the one I have used for decades on 2 different boats, one with mid boom sheeting and one with end boom.
I loop the securing line to the end of the boom (running it through the outhaul bail to keep it from migrating) and bring the tail to mid-boom. This allows the whole boom end to take the load and means no fitting is necessary. Mid-boom is always accessible from the side decks while setting up the preventer so tying the long line is done the same as John does in his video, just done on the side deck rather than at the gooseneck.
I tie in the long line rather than using a biner.
Eric’s comments about using an end boom mainsheet bail for the preventer makes me a bit nervous as the geometry of a sheet bail is for downward pull, not the side forces that a preventer might exert.
My best, Dick Stevenson, s/v Alchemy
Thank you for this post. I installed the preventor this spring and it is the best bit of kit I’ve added in years. I use it all of the time, and when I have crew with me they happily go forward to rig it. It literally takes all of the boom g worry away. My&’ boat is a Dana 24. I used Ropeye padeyes on each side of I the boom – soft rope and no dissimilar metals to worry about and dyneema boom lines with a Tylaska spool shackle – very easy to undo and soft materials. The deck line is led through the forward enclosed fairleads and then through a block and to the cockpit. I only have single cockpit winches so I substituted my footblock for a Harkin double footblock with lockoffs. This is the weekest point in the system, however my winches are self-tailing and backed with a good cleat so I only use the lock offs as a brake to transfer the deck lines from the winch to the cleat (and the jib line back to the winch). Thank you again.
Thanks for the kind words and it sounds like you have taken our system up a notch.
Thanks for all the answers to my questions; the soft shackle solution kept escaping my mind and now it will remain fixed there. I experimented with the recommended system and decided it wouldn’t do for me on my Dana 24:
– The narrow passageways make it somewhat a contorsionist exercise for me on the lee side. And the Dana 24 is not as stable a working platform in a swell as a bigger boat. While I don’t hesitate to move around the boat when need arises, why not use a solution that saves you a trip, if the system is good? Especially when single-handling.
– I don’t know about you guys, but I can’t untie a tight bowline while keeping the deck line secure, with just one hand. Using teeth is not fair play 🙂 I want a solution fulfilling the “one hand for thee, one hand for the boat” rule.
I decided to stick with the solution of just one line each side, running back to cockpit level with biner or soft shackle attaching to the boom end. IMO this works because the small size of the Dana is turned into an advantage: I can reach the boom end without overextending myself dangerously out of the cockpit. I think. This setup was used by the Sockdolager crew on their cruise across the Pacific. I’ll reconsider the 2-part solution, which I still think is good, if (ever) I buy a bigger boat.
Makes sense to me.
Great video. question, how do you terminate the bitter end of your preventer lines at the cockpit? Do they share a winch? If so, do they go through a clutch?
The preventer lines share the staysail winch. This works because any time the boom is far enough out to use a preventer the wind is too far aft to use the staysail.
The result is that we don’t need a clutch, but for boats that are not blessed with as many winches as we are, running the preventer lines through a substantial clutch could be a good option, as long as the clutch is positioned so a winch can be used to tension the preventer or bleed off load if the sail is caught aback.
I dont understand why my mainsheet bail, connected with a heavy thru boom bolt is insufficient. it was sized ,I azssume, to withstand a full jibe. shouldn’t it be as strong as a bolted on padeye? I sail a morgan 382 with end boom sheeting.
You may be right that main sheet bail will be strong enough. However, you do need to look at said bail critically: very often the bail is designed to take maximum load vertically and not horizontally. Also the main sheet load is often distributed over two bails, so just using one for the preventer may not be a good idea.
The other issue is that many production booms are minimally specified with cost, rather than strength, as the driving criteria. Point being that I would not assume that the mainsheet bail(s) can take a full on crash jibe, many can’t.
I guess the core point in all of this is that a preventer needs to be sized for the kinds of scenarios that I detailed in part one of this post.
I broke my boom bail this summer , in a relatively benign accidental jibe.
Previously, the original boom had been replaced by a heavier section- I guess because that boom broke.
The new boom was from a respected brand name and is heavier then the original boom. I agree with you, the mainsheet bails normally provided by boom manufacturers are generally inadequate for heavy shock loads.
Fortunately I could jerry rig the mainsheet bail by lashing line around the boom, and it got me back from “The Labrador”.
I have the boom home in the workshop now, and will repair and/or upgrade the bails this winter.
So the boat has an upgraded boom, heavier than the boom supplied by the original boat builder,
and the bails on this boom failed, guess you are right when you say the booms and bails are minimally specified…
The boom manufacturer does offer a heavier bail then those originally supplied.
As well I will follow your lead and permenently attach a boom line for the preventer.
But I don’t like those harken pad eyes you have attached to the ends of the boom, to me they have brain damage written all over them.
Rather I think I will drill two 3/4″ holes in the end of the boom and attach a single boom line thru these, side to side.
Good article though, I learn something almost every time I read your site.
That’s great real world data, thank you, although I’m sorry you had to prove the theory that way.
In our case, being a centre cockpit boat, with a high boom, the danger from those pad eyes is probably minimal, but I agree that a soft attachment is probably a better idea.
I subscribed to this site yesterday and this page just paid for my subscription. I’ve been struggling with a design for rigging a preventer for the loose footed main on my 40 catamaran (oh the horror!). Until now, I’ve been rigging a line from mid boom to a mid-ship cleat with a modified trucker’s hitch, fearing all the while that if the fertilizer ever really hit the fan, the cleat or boom was likely to break.
After reading this article, it is now obvious that I need to rig a line through a pad eye at the end of the boom (already there!) forward to the block on the lee bow that is otherwise used for a spinnaker guy, through the spinnaker guy fair-leads on the coachroof and back to a winch. I’ll give it a try with a recently retired spinnaker halyard for the preventer line and see how it works.
Thanks very much, that made my day.
It’s preventer installation time and your advice is needed. First up is mounting what you call the boom line at the aft end of the boom. We need a proper way to eliminate the play between the curved surface of the boom and the flat surface of the pad eye. Is there an acceptable shim or a pad eye with a curved back, or what?
Secondly, our boat has no fully enclosed fairlead at or near the bow. Is it reasonable to install one? I’ve only seen a stainless Bullseye fairlead which mounts directly to the deck with the equivalent of (2) #12 screws/bolts and accepts a 5/8″ line. I’ve also seen the ‘Antal’ low friction (3/4″) ring with Dyneema loop which has an unacceptably low SWL (safe working load) of 3,300 lbs. which attaches to a deck mounted pad eye. Is the any reason not to trust the SS fairlead? Is there another preferred means of achieving the goal?
Our boat is roughly the size of yours. It’s a Passport 470 AC.
Looking forward with much appreciation to your counsel.
Earle and Helen
S/Y Leaning Out
The best way to mount any piece of flat hardware to a curved surface is to make a shim from epoxy resin mixed with high density filler. Wax everything the epoxy will touch and then mount the fitting with enough epoxy mix under it so it squeezes out all around. Do not screw the fitting down completely, but only until there is about 1/4″ clearance at the least. Remove the excess with a putty knife. When dry, remove everything and you will have a perfect epoxy shim, then mount as normal with Tefgel on the bolts. (You can also use Tefgel as a release agent instead of wax.)
You could also attach the block to the boom end with Spectra line, as detailed in the post and comments.
As to a bow fitting, that bullseye is way too flimsy for your boat, so it will probably be best to mount an appropriately sized pad eye and then attach a strong enough block.
As to size, your boat (30,000 lbs) is actually quite a bit smaller than MC (48,000) and the rig smaller, so you probably don’t need the system to be as strong as ours. I would calculate your mainsheet load for 20 knots (see post) and them multiply by a safety factor of 5. Do keep in mind that the load on the block at the bow will be nearly double that on the preventer line.
What would be your suggestions for a preventer/ vang on an Achilles 24 with roller reefing.
If you are offshore in the boat, I think I would recommend a preventer like ours, only scaled to smaller rope, although you probably don’t want to go below 1/2″ or so, due to handling issues.
For a vang, I really like solid vangs and there are several good options at that size.
Thanks for your reply, but a solid vang will not work on roller reefing as I need to use a boom claw.
Of course, sorry. Having said that, have you considered getting rid of the roller furling boom? We used those back in the sixties but most of us converted to slab because it produces so much better set and is easier to use.
This may be a catamaran-specific thing, but I think I’ll share it anyway, since it does meet the “simplicity” requirement. Avoids more lines under foot on the side deck, which I find unsafe at times. I also keep a few carabiners and climbing slings.
I keep 2 lines in the cockpit about 1-boat length long that I think of as “jack lines” in the utility sense, not as the tether clip points they are generally called. On one end is an eye and a carabiner.
* Preventer. Clip the boom end bail, lead through the mid-ships cleat and back to a winch. No need to go farther forward on a cat because of the beam. Adjustable, and should you need to release it, it can be let fly with out tangles. I can still reach the boom-end when it is out.
* Genoa or spinnaker sheet down haul. Same, except I clip a climbing rescue pulley through the biner (like a snatch block).
*MOB recovery. Get a life sling to the person, clip the biner to the sling, and lead the line up through a rescue pulley clipped to the boom bail (sail is down), through a snatch block on the rail (there is a spinnaker/reacher track there), and up to a winch. Very fast.
I have also used it for little emergencies; recently I had a davit tackle failure (yup, I’d been too lazy to trice-up), and that line plus sling/biner/pulley allowed me to rig a lift in seconds, avoiding damage to the dingy.
The point is I have learned it is very handy to keep a pair of multi-purpose lines stashed in the cockpit, pre-rigged with a biner and snatch block. I’m sure there are other combinations for other boats, based on the same multi-function contingency thinking. Without thinking, I know I can grab on of the lines (I know how long it is) and a biner/sling/pully and rig something fast.
Good point that a couple of spare lines ready to hand are a good idea. We do the same, although the two lines we keep in the cockpit are normally purposed as guys for the pole, but can be used for most anything else. Our’s have wichard snap shackles, which we prefer to carabiners.
We also have three snatch blocks on deck at all times. Normally they guide the preventer deck line around the dinghy (2) and take the pole after-guy, but they can be pressed into service for most anything.
More on dragging recovery coming in the spring.
I’m going to disagree on snap shackles for my applications. I only like snap shackles where there is a high probability I will have to release it under load (spinnaker sheets) and tack). Thus, I have only a few on the boat.
* A carabiner takes a fraction of a second to hook securely, only one hand needed. Same to release, if no load. When I rigged the dingy tackle, for example, I had only one hand in a bouncy sea. A biner was instant. Same with MOB; I want to be able to stab and clip the harness the first time. Rock climbing wire gate biners are particularly fast this way (most marine biners are pitiful this way).
* Cannot release under load. This is a good thing from most MOB uses. Climbers do not own shackles that are releasable, for obvious reasons. And not important from most applications (you don’t release them until the load is off).
The greatest down side of a common biner is that it can clip other things if it runs across them, such as lifelines and stays.
I guess I would say “Horses for courses”. I use the Kong Tango climbing carabiner for the boat end of our tethers, but for sailing type applications I prefer a snap shackle. And for the situations where I want no chance at all of an unplanned release I like a Tylaska snap shackle. While I agree that climbing gear has many good uses on a boat, I also like to leverage the great gear developed by generations of racing sailors operating at the pinnacle of this sport.
Thank you John – fantastic website – I became a member two or three weeks ago and literally can not stop reading. I have only recently got my license which is limited to 12nm so it is not just for ocean voyaging experts;) On the topic – boom hitting someone’s head has always been my biggest nightmare – thank you for sharing your system – I used to just cleat the line aft sometimes with slack and thought how smart I was;) Amazing website many thanks – Alex
Thanks for the kind words. You are smart to worry about the boom. I don’t have solid stats, but I’m pretty sure that being hit by the boom or the mainsheet in a crash jibe is the most common serious injury and fatality modality in sailing.
Hi John, my preventers are rigged as on Morgan’s Cloud. I was sailing downwind in 18-20 knts almost on the lee on STB tack and needed to work to starboard to get into a harbor sheltered area to drop my main. Waves were 3’ and I was solo sailing my 36’ boat. I released the preventer so I could jibe, but it was a violent jibe anyway. How should I have executed that properly?
Hum, I’m confused. If you were on starboard tack and needed to work to starboard surely that would just require sharpening up and no jibe? Perhaps you were on port tack (boom out to starboard)?
Anyway, the secret to this kind of situation, and particularly when short or single handed is anticipation and sea room to do what’s required. In this case Phyllis and I always sharpen up a bit before removing the preventer so that there is no chance for a crash jibe. So the key is to perform the jibe while we still have sea room to sharpen up before the jibe without getting too close to land. Another trick we often use when entering confined waters is to put in one or two reefs, even if not required by the wind speed, well ahead of time. This makes it much easier to jibe our very large mainsail.
Opps! Sorry John. I meant I was on port tack
So, the Platino disaster has really got me thinking. I would like to start using dyneema line for my preventer deck lines, but it sounds as if that means I can no longer use a bowline to tie them to the boom lines. Please give me your thoughts about splicing an eye at the end of the deck line and then attaching that to my boom line with a soft shackle. I have never used soft shackles, so I don’t know if they are reliable and unlikely to open. Thanks.
I really don’t know if a soft shackle is reliable enough for this purpose. I guess, if it were me, I would go with the Tylaska shackle I recommend in the chapter above. I just really like the fact that these shackles can be locked with a half turn of the pin.
I understand the idea of using bowlines, j-hooks, or double rolling hitch to attach snubber to chain. With all respect, I really think you should have a deeper look at Dyneema soft shackles. A properly made and sized soft shackles on a snubber has a breaking strength considerably higher than the chain. They will not rust, stronger than a comparable metal shackle or cable, are very easy to make, easier to install than a knot, and will not come undone on its own. I’ve attached a few links to show my reasoning.
I don’t have anything against soft shackles. In fact I have several on Morgan’s Cloud. I don’t use them for anchor snubbers because I like to be able to use any old piece of rope, so it’s good for me to be constantly practicing the double rolling hitch.
As to our preventer, I like the J-hook because I can snap it closed with one hand a lot faster than I can manipulate a soft shackle
After reading these excellent preventer articles and comments, I’m still confused about one thing. My mainsheet is not attached at the end of the boom. So, is it better to rig the preventer to where the mainsheet attaches and avoid accidental bending of the boom (i.e. sleepily winching on the sheet), or is it better to rig the preventer to the end of the boom for mechanical advantage and helping should the boom dip into the water?
If it were me in that situation, I would go for a compromise with the preventer say 1/3 of the distance from the aft mainsheet bail to the end of the boom, aft from the mainsheet bail.
Chuck, sounds like we have the same set-up as you, and although John’s advice sounds eminently sensible we have chosen end boom attachment. We figure the risk of the boom being bent out of shape can be mitigated:
1) With my mercantile marine training, I insist on a full handover for the person coming on watch, including sails, setting and any preventer set (I have recently done a few deliveries where the norm was a cursory “see yah later”).
2) With a preventer set, we leave the winch handle in the (electric) mainsheet winch. It would be almost impossible to bend the boom with the manual winch handle, without at least wondering why there was so much strain.
3) We have a tri-sail, jib and a code-0, so if we did damage the boom we should still be able to sail efficiently with it lowered to the deck, for later repair.
4) We have comprehensive insurance and human error is accidental. So providing we can show evidence of a sensible maintenance schedule being adhered to (we have a rig check done before going offshore) we are covered for the cost of any subsequent repair.
So for better or worse, we have the view that bending the boom is of less consequence than a preventer breaking with a consequent crash gybe.
Hi Rob and Chuck,
All sounds good, and I like the idea of leaving the handle in the electric winch to disable it.
One thought, I’m not sure that once the attachment point for the preventer in out past say 2/3 of the boom length, that moving it out to the end makes much difference to the load on it in a crash gibe.
If I’m right about that, then, assuming that Chuck’s main sheet bails are aft of centre or the boom (rare if they were not), moving the preventer attachment a further third aft, of the remaining distance to the boom end, should not appreciably change the force on it in a gibe, but will make a big difference if someone starts cranking on the mainsheet.
Any thoughts from you engineers out there?
Well, if you double the lever arm, you double the mechanical advantage. It works in a linear fashion:
Fa * a = Fb * b, where Fa, Fb are the forces at the ends of the lever, and a,b the distances from the pivot point.
The Mechanical Advantage is:
MA = Fb/Fa = a/b.
This means that moving the distance between the sheet bail and the connection point of the preventer by 10%, the force also changes by 10%.
If the sheet is connected, say, 3 meters from the pivot (gooseneck) and a force of say 1kN is applied, a preventer at 4 meters distance must oppose it with 0,75 kN to equal.
(We get 1 kN * 3m = 3 kNm = 0,75 kN * 4m = 3 kNm)
Practically, this means that moving the preventer a few inches here or there makes little difference to the forces the attachment points see – but obviously big ones if the distance grow significantly.
As the forces with which the preventer and the sheet poses on the boom are opposite, a fairly big bending moment is created on the boom with a fairly small distance between the preventer and sheet.
Booms probably are not designed to withstand significant, opposing forces bending them sideways.
In summary, although the preventer will see smaller forces the further aft it is connected, I personally would be careful not to set it very far from the furthest connection point of the sheet.
How far is too far?
That depends on a number of things and should be considered case by case with real measurements, but to be on the safe side, I would guess (!) that perhaps 10-15% of the distance from gooseneck to furthest sheet bail would sound reasonable.
That makes sense, thanks for the fill on that.