Rigging a Proper Preventer—Part 2

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.

  1. Six Reasons To Leave The Cockpit Often
  2. Don’t Forget About The Sails
  3. Your Mainsail Is Your Friend
  4. Hoisting the Mainsail Made Easy—Simplicity in Action
  5. Reefs: How Many and How Deep
  6. Reefing Made Easy
  7. Reefing From The Cockpit 2.0—Thinking Things Through
  8. Reefing Questions and Answers
  9. A Dangerous Myth about Reefing
  10. Mainsail Handling Made Easy with Lazyjacks
  11. Topping Lift Tips and a Hack
  12. 12 Reasons The Cutter Is A Great Offshore Voyaging Rig
  13. Cutter Rig—Should You Buy or Convert?
  14. Cutter Rig—Optimizing and/or Converting
  15. Cruising Rigs—Sloop, Cutter, or Solent?
  16. Sailboat Deck Layouts
  17. The Case For Roller-Furling Headsails
  18. UV Protection For Roller Furling Sails
  19. In-Mast, In-Boom, or Slab Reefing—Convenience and Reliability
  20. In-Mast, In-Boom, or Slab Reefing —Performance, Cost and Safety
  21. The Case For Hank On Headsails
  22. Making Life Easier—Roller Reefing/Furling
  23. Making Life Easier—Storm Jib
  24. Gennaker Furlers Come Of Age
  25. Swept-Back Spreaders—We Just Don’t Get It!
  26. Q&A: Staysail Stay: Roller Furling And Fixed Vs Hanks And Removable
  27. Rigid Vangs
  28. Rigging a Proper Preventer, Part 1
  29. Rigging a Proper Preventer—Part 2
  30. Amidships “Preventers”—A Bad Idea That Can Kill
  31. Keeping The Boom Under Control—Boom Brakes
  32. Downwind Sailing, Tips and Tricks
  33. Downwind Sailing—Poling Out The Jib
  34. Setting and Striking a Spinnaker Made Easy and Safe
  35. Ten Tips To Fix Weather Helm
  36. Running Rigging Recommendations—Part 1
  37. Running Rigging Recommendations—Part 2
  38. Two Dangerous Rigging Mistakes
  39. Rig Tuning, Part 1—Preparation
  40. Rig Tuning, Part 2—Understanding Rake and Bend
  41. Rig Tuning, Part 3—6 Steps to a Great Tune
  42. Rig Tuning, Part 4—Mast Blocking, Stay Tension, and Spreaders
  43. Rig Tuning, Part 5—Sailing Tune
  44. 12 Great Rigging Hacks
  45. 9 Tips To Make Unstepping a Sailboat Mast Easier
  46. Cruising Sailboat Spar Inspection
  47. Cruising Sailboat Standing Rigging Inspection
  48. Cruising Sailboat Running Rigging Inspection
  49. Cruising Sailboat Rig Wiring and Lighting Inspection
  50. Cruising Sailboat Roller Furler and Track Inspection
  51. Download Cruising Sailboat Rig Checklist
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Ray Dunn

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!

Ray

Pete

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.

Neil McCubbin

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.

Larry

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.

Larry

Thanks John,
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.

Bill Balme

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…

pat synge

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.

Larry

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.

PaddyB

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.

Dick Stevenson

Dear John,
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

Nick Kats

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?
Thanks,
Nick

Nick Kats

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..

pat synge

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?

Derek H

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?

Thanks.

Derek H

Neil McCubbin

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.

stephen Poulson

Great article John. I had been previously thinking about how best to set up the preventer lines. This nails it for me. Thanks

Terje Moglestue

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.

Colin Farrar

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?

Colin Farrar

Mark

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.

Bill Attwood

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.
Yours aye,
Bill

Petter :-)

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.
Greetings!

Bill Attwood

Hi John
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.
Yours aye,
Bill

Dick Stevenson

Bill,
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

Bill Attwood

Hi Dick,
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.
Yours aye,
Bill

Dick Stevenson

Hi Bill,
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

Bill Attwood

Hi Dick
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.
Yours aye,
Bill

Bil Attwood

Hi John,
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.
Yours aye,
Bill

Dick Stevenson

Hi Bill,
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

Marc Dacey

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.

Bill Attwood

Hi John.
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.
Yours aye,
Bill

Dick Stevenson

Hi John,
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

Richard Dykiel

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.

Eric Klem

Hi Richard,

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.

Eric

Dick Stevenson

Hi Richard,
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

Margot Young

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.

Richard Dykiel

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.

Jim_G

hi John,
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?

Thanks, Jim

terry thatcher

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.

Ed Finn

John
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.
Ed

CaptainCrabby

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.

Thank you!

Earle

Hi John,
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

BERTT

Hi John,
What would be your suggestions for a preventer/ vang on an Achilles 24 with roller reefing.

BERTT

Hi John,
Thanks for your reply, but a solid vang will not work on roller reefing as I need to use a boom claw.

Drew Frye

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.

Drew Frye

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.

Alex

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

Carl G Neumann

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?
Thanks, Carl

Carl G Neumann

Opps! Sorry John. I meant I was on port tack

Terry Thatcher

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.

Peter Sweitzer

Hi John,
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.
https://youtu.be/91_jEjQdlBU
https://l-36.com/soft_shackles.php?menu=4
https://youtu.be/7TGwkWBYgX8

Chuck B

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?

Rob Gill

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.
Rob

Vesa Ikonen

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.