First off, thanks to all for keeping the discussion collegial on the first chapter on motion comfort, let’s keep that going right to the end of the series so we end up with something really useful for those trying to make the critical decision of how many hulls will be best for their type of cruising.
When writing this chapter I assumed well designed and built boats. There are a lot of dangerous boats out there, regardless of number of hulls, that simply should not be taken offshore, but that’s another article.
Now let’s take a look at seaworthiness and dive right in at the deep end with capsize risk.
Monohull fanboys love to come at this one simplistically to get a win, but the reality is more complicated since we need to think not just about being capsized by wind but also waves, often a bigger danger.
Wind Capsize Risk
Still, let’s start with wind:
Interesting article making placing the data side by side for the hull types. The stability data for a catamaran, which should include wind speeds and reefing plans, should be stated in the owners manual, which in general I have found to be in place for new builds and coded charter cats in the UK. It may be that when buying second hand, this data is missing, hence potential purchasers of second hand cats should insist that the owners manual is included in the sale or that the seller includes such critical information.
Hi Alastair,
Good to hear that you have generally found the reefing information in the owners manual, and a great recommendation that buyers of second hand boats should insist of seeing the manual.
Thanks for continuing this series John, great information here.
Reefing at prescribed wind speeds is the rule of law on our boat. The reality is that nearly all modern cats and tris actually perform better and are more comfortable when you set the reefs at those wind speeds so there is really no excuse. On our Dragonfly 32, we will still see boat speeds of 8-10 knots broad reaching with a 2nd reef in the mainsail and a full jib in 18-25 knots of wind and it’s very calm and comfortable.
Thunderstorms and squalls are our biggest fear on our boat so we typically take the mainsail down if we are getting in close proximity (typically less than 5 miles) to any storm cell. If we are sailing at night with the possibility of any storm activity, we set the 2nd mainsail reef (we being my wife and I).
So far, we have been successful reefing our full battened mainsail at downwind angles in wind speeds ranging from 18-26 knots. Downwind angles for us are 140-160 degrees TWA. The wide platform of our boat will allow me to center the traveller and pull some mainsheet in to stall and depower the mainsail and I have the ability to ease the leeward shroud to minimize interference with the upper portion of the mainsail. You must also have someone on the helm who is very attentive to maintaining the sailing angle and/or a reliable autopilot. It’s interesting that Quorning Boats (the Dragonfly builder) stresses to turn up to an upwind or close reaching angle any time you reef. The Dragonfly trimarans all have what I would call a “mild” square top mainsail and that is what can potentially get hung up when you are trying to set a reef sailing downwind, thus centering the traveller and keeping some mainsheet in (not tight) to minimize this interference. In truthfulness, I’ve not have to do this in anything over 26 knots of breeze so even more important to set the appropriate reefs at prescribed wind speeds.
I agree with John’s recommendations on getting the boat through the “death zone” (I hate that term) safely during a bear away. I’ve raced small catamarans (Prindle 19, Tornado, and currently A-Class catamaran) since the early 90’s. For those boats, when you got to the weather mark in big breeze and had to turn down to downwind, the safest bet was to stop, blow the mainsheet traveller and most of the mainsheet, and then turn down with the jib still sheeted tight. With the advent of curved daggerboards and rudder winglets (at least on the A-Class catamarans), the maneuver is a lot less risky and in up to 17-18 knots, you can get through nearly full powered up. The foiling multihulls have it even easier if the sailor has his technique right. We are seeing some performance cruising multihulls now sporting curved daggerboards to provide some lift to the forward sections of the boat but so far I’ve not seen any rudder winglets and for practical purposes they may not make sense since you have to maintain them at the correct angle of attack and they are magnets for weed and debris in the water.
Hi Bob,
Great real world information that should be invaluable to any multihull owner, or prospective buyer, thanks.
Also, good point about stalling the main by overtiming it. I have to admit I had never really thought of that, or at least not quite in that way, until you mentioned it in connection with the jib in another comment. Always more to learn.
Interesting that Quorning want you to turn up in the wind to reef. Despite my huge respect for them, I still think you are right in your approach. Point being that if reefing down wind is not our standard practice we can get in a situation where we have too much sail up to turn into the wind and so are stuck with the boat going every faster and no way out of the situation.
If I remember right, this happened to the super-cat Play Station on one of her early voyages. They got away with it, but apparently the crew saw God.
Whereas if you reefing down wind is our default we will have it cracked and so can do it in most any situation.
I also think that not having to round up makes us more likely to reef frequently because it’s just so much less scary. The result often is that we will, like you two, have less sail up more of the time.
Also, great tip on just taking the main down with T-storms coming. The ultimate safety move.
As to the weather mark, as a 505 sailor I totally get that. Always a trick one. On the 505 the key move was to get the board mostly up during the rounding. Forget that and a swim was pretty much guaranteed.
Regarding our downwind reef technique, for a lot of folks it may seem counterintuitive to center the traveller and pull in some mainsheet at deep angles but what this does is present less projected sail area reducing the load on the sail. The main thing I am trying to achieve is to keep the top of the sail clear of the rigging. That said we will have the preventer attached and again it requires a steady hand on the helm and control of the boat to keep the boat in the safe zone. It’s good to practice the steps in lighter air so it becomes very familiar.
Bob, also as an owner of Dragonfly 32, mine is the touring version, I confirm that I have found reefing downwind to be effective. Drawing the boom towards the centreline using the mainsheet and preventer is an effective way to keep the sail under control, away from the rig (mostly) and to de-power it. I will take some convincing that easing the leeward shroud is a good idea – I would prefer to use the boom position and the load on the leech to minimise interference.
Hi Simon,
To clarify, I typically ease the leeward shroud about 24”-36” on the control line so with the 4:1 purchase on the control system, it is only a 6”-9” ease on the shroud. We will do it when sailing at 120-160 TWA’s to keep the leeward shroud from chafing the mainsail and for the above to take pressure off the square top when setting a reef downwind. The caveat is to remember to tighten it back up if you turn back upwind but even if you don’t it does not cause any problems.
I just love the preventer and barber hauler systems on the Dragonfly’s. You can really dial in to very close to perfect sail trim in nearly all conditions with these trimming tools and probably the best feature is mainsail preventer can just about eliminate mainsail flopping in lighter air and chop sailing downwind.
Cheers,
Bob
Very, very interesting article.
I wonder if in terms of capsize risk a Pacific Proa (like Russel’s Brown Jzerro for example) could be assimilated to a trimaran or it’s a complete different beast.
You calculate the data for a proa exactly the same way as for a cat or a tri, and then you see what comes out of the math. There’s such a huge variety of them – some inherently stable, some requiring movable ballast or active management to stay upright – that it’s impossible to generalize.
Hi Michele,
My guess , and it is just that, would be that a since the smaller hull is always to windward and the proa not generally as beamy as a tri the stability curve and relationship to wind pressure and heal angle would be more like a cat than a trimaran and therefore less forgiving than the latter, and probably even less forgiving than a cat. Anyway, Proas are interesting but in my view special interest only and not really viable cruising boats.
Hi John,
Capsize risk has long been an interest of mine too but in a very different context. Many large traditional vessels have met their ends due to wind induced capsize. These vessels are generally not as susceptible to wave induced capsized by shear size but they also tend to have very heavy tophampers and not great GZ curves. To make this more complicated, depending on flag state, sometimes good information is available to the master and at other times, it is nothing more than a number like GM. Roger Long who you mention stands out as being someone who really helped the industry (and is a nice guy too). I just wish I could find a copy of the study he worked on when they were coming up with sailing school vessel stability criteria in the US but it seems to be hard to find.
I like to look at a graph of wind loading laid over the GZ curve when looking at it statically although it is very rarely presented this way. The wind loading curve is a gross simplification but it is still helpful. If you look at it, you see it goes to 0 at a heel angle of 90° which of course is not accurate (there is some difference in mathematical convention here), the wind is still pushing on a lot of boat. The good news is that it is more accurate at the lower angles of heel where it actually matters.
Once you get to the point where the wind moment hits only at a single point, any more wind and you will capsize. It is interesting where these hit as it is at an angle significantly less than the AVS. What this means is that in a perfectly steady wind with no seaway, once you reach this heel angle, the boat will capsize despite having significant remaining AVS unless the wind is suddenly removed.
To me, the really interesting/scary thing happens somewhere around 90° heel angle. If the boat has an AVS above this, an infinite amount of wind cannot capsize it (theoretically only as the hull windage is assumed to vanish here which it doesn’t in practice). However, if the AVS is below this, it is always susceptible to a wind induced capsize. How susceptible is due to what the actual GZ curve looks like and how much windage there is.
I quickly put together 3 graphs that show this. The 120° AVS boat has no worries of a wind induced capsize if it is kept watertight. The 90° AVS boat is extremely close so a small wave or something could push it over the edge. The 75° AVS boat is definitely susceptible to wind induced capsize. You can do this same thing with a multihull but you need to more carefully calculate windage as the projected area of a cat or tri up on edge is quite high.
There are a few things that I always try to keep in mind from this:
Agreed to your conclusions. I hope this is not too off topic.
Eric
Next graph
Final graph
Hi Eric,
A very good point that a boats with an AVS of under say 120 can reach what one might call the capsize vulnerability point (CVP) at heel angles that seem safe. I did know that (kinda) from reading Roger’s stuff, but it did not really sink in until I read his full analysis of the Bayesian sinking, and even then I’m not sure I fully “got it” until I read your comment above. Thank you, it’s important, particularly (as you point out) when thinking about internal ballasted centre board boats. Definitely something I need to think about more.
While on the subject, in recent years I have learned, much to my surprise, that we are generally much safer going to sea on a well found 40 foot yacht than many much larger sailing vessels—definitely counter intuitive. This was exposed by “Pride of The Sea” and “Tall Ships Down” in relation to traditional vessels but I suspect (and hope) that the Bayesian sinking is going to bring the same sort of scrutiny to super yachts, and particularly allowing them to be classed with very low AVS numbers, just because they are big.
In my own case reading Roger’s stuff on Bayesian made me think a lot about the super yacht I went to Greenland on, and not in a good way, particularly the location of her engine room venting coupled with the difficulty of easing her heavily loaded sheets quickly in a gust. And worst of all, the unreliability of reefing her huge mainsail using an in-boom system. Add it all together and I’m very happy that on that trip the skipper basically handled her as a motorboat with a little main rolled out for steading.
Hi John,
Yes, I definitely think there is truth in bigger is not necessarily safer. A lot of large vessels have marginal stability, really poor downflood angles and the ingress points are not ones that can be shut off quickly. These vessels also take a long time to turn into the wind or run off and all sail handling is slow. Plus, there is no ability for the crew to manhandle things when they go wrong, everything must be done with a purchase or leverage and there are some things that simply require a dockside crane or other piece of machinery. Just like small boats, extreme weather events are rare and the chances of everything lining up to actually cause a problem that is newsworthy are also relatively rare. There are also plenty of unbelievably sea worthy large boats out there, it is just that size is no guarantee.
My own personal comfort zone is somewhere around 100° AVS on large vessels (say 100’+ and displacement >150 tons) that haven’t had significant modifications since the calculations and maybe 110° for smaller vessels and I definitely like more. In the US this is complicated as many of the vessels fall under regulations that are more based on a comparison to the rig size so boats with really poor stability are allowed as long as they have very little sail area but these vessels are actually quite susceptible in squalls as even that sail area is way too much. In many of the accidents with traditional vessels, it is found that the AVS had significantly decreased from when it was last calculated. This applies to smaller vessels as well and I can definitely see one of the smaller centerboarders that has had 1kW+ of solar bimini added, a dinghy in davits, a furling mainsail, 3 headsails on furlers, etc. being at the point where they could be capsized by a wind level that they would expect to see many times during their life and only by having no sail up and not being broadside do they not have issues. Some people are fine with those margins, I am not as I know I make mistakes and want the boat to be forgiving.
I have talked to a few people who have been part of some of the wind induced capsizes a decent amount and it definitely seems to me like they had no idea how little margin was left in some of their normal sailing. I believe that this is due to not understanding the implications of the AVS angle being when there are no overturning forces and not realizing that the point of no return occurs much earlier if the wind continues. If you look at the Pride incident, they only had the staysail and double reefed main up which is not a large portion of what you might call their normal sail area of 4 lowers and was an extremely small portion of their overall sail area they could fly. On a boat like that, I would expect that to be pretty close to full on storm canvas and yet it was still significantly too much. For anyone who wants to look at this incident more, it is interesting to note the difference in what the implied cause of loss is in Tall Ships Down versus Pride of the Sea. Tall Ships Down gives what I would consider to be Tom Gillmer’s (the boat’s designer) version and Pride of the Sea gives closer to what Roger Long’s version is and they are quite different and somewhat contradictory.
One other random thought. As I learned more about this, I came to see bulwarks quite differently. If you assume that the top of the bulwarks is defined by aesthetics and windage and can’t move up, the boat with short bulwarks and high deck has a much better stability curve than one with tall bulwarks and a low deck. Under 100′ or so, I simply don’t think you can have bulwarks that are high enough that the extra safety they provide is worth it compared to a low bulwark to give your foot a place to go and good railings/lifelines.
Eric
John, I had an interesting incident years ago with my Ranger 33. I motored down the East River in light winds, and approaching the Battery a breeze developed so we made sail and continued around into the Hudson. I went below to make lunch and suddenly we got hit by a huge gust (clear weather) that knocked the boat WAY over. As I rushed up the companionway my friend, an excellent seaman, was bringing the boat into the wind when we got hit by another strong gust from the other side. Each gust only lasted a few seconds, but I noticed that a cooler that had been on the starboard settee now resided on the port settee, not on the cabin sole, indicating either a 90 degree knockdown or a major knockdown quick enough to catapult the cooler across without landing on the sole.
On a couple of occasions I have seen the effect of gusts heeling the boat (as you say) maybe 50 degrees only.
Hi Leonard,
Interesting, particularly about the cooler. One of the things that I intentional left out of the above article was dynamic stability including capsize inertia, but in your case with the violence of the experience those factors would have come into play, rather than the more simplistic static stability that I used in the comparisons above. That’s a long way of saying that my guess is that you did not go all the way to 90 degrees, but rather, as you say, the speed of what happened was the factor that made the cooler end up on the opposite settee.
Hi John,
Thanks for this.
I fear waves much much more than wind in terms of capsize risk, in fact a lot more than anything else on our mono. This article sure did not change that.
I fear what an important wave, not even necessarily a rogue one, which by definition I think would need to be 2-2.2 times the other waves we would be in, could do to our boat if other serious conditions are already upon us: winds in the 40s, minimal canvas out, significant heeling, 4-6 meter waves… How bad a would a wave have to be? Of course, it remains a healthy fear, one that is tamed and looked at from a scientific perspective and rooted into deep respect for the ocean and what it can do. This fear that I have won’t ever prevent us from adventuring. Hopefully, I never get the answer to how big the waves needs to be it if you understand what I mean. But I wonder about it when I read dreadful accounts of boats that did capsize and recovered or met their demise, offering mere survival to their crew to tell the tale. It’s a combination of factors, but let’s face it, it’s always a LOT about the waves; how big the wall of waters were.
In the deep of this subject, I expected maybe a mention about the relation between capsizing risk and length. I know you are comparing mono and multihulls, but very few multihulls, if we are talking about offshore sailing, are under 40 feet. Much shorter monos have proven their seaworthiness. But I’m curious, does added length both on multihulls and monohull, provide the same protection? I think they could be compared toe to toe there: is an added feet in lenght a lot more beneficial on a cat than on a mono when it comes down to considering capsize risk?
On capsizing, a capsized cat is pretty much game over out there, although it nearly never happens. A capsized mono is an absolute nightmare where people break bones, stay stuck under heavy objects, die from the capsizing event itself or drown. However, it’s not necessarily final. Depending on the shape of the boat and it’s center of gravity, the lower the better, if a narrow boat, only one tenth of the force of the capsize energy could be necessary to recover from that belly up situation. John Lacey, the naval architect, came up with that post FastNet of 79. That’s where I console myself with our old 70s racing hull shape from William H. Tripp Jr. when I think of the worse the waves can offer us out there. Although it for sure is more than one tenth of the capsize energy for our boat, it’s less than some large sail boat. I also think about this when stocking up, everything heavy as close to the keel as can be and tied up… Cuz, why not always plan for the worse?
I’ll go read your articles on survival after capsize, I feel it’s right up my dark alley of prepping for the worse.
As always, receive my best John,
Marie
Hi Marie,
I cover most all of that in the heavy weather book, so would rather not get into it here. I will also be covering survival after capsize in all types in the next chapter.
Great article, thanks for sharing. Was caught in a sudden increase in wind yesterday with too much sail out on Lake Superior. Luckily there was no damage, but did create some unwanted excitement. Thanks again.
One small correction for the multihull section: “Heeling angle is not an effective warning of impending disaster.”. That is not quite corrrect. Heel angle, indicated by windward hull rising, is absolutely an effective warning on a cruising catamaran. We have by the numbers warning (apparent wind speed), rig load warning (if you have shroud and/or mainsheet load sensors) and windward hull underbody exposure warning. Each of these in isolation or together indicate need to reef and/or alter course.
The death zone on a multihull is that 20-30 degree zone (at about 60-80* apparent wind angle) where turning into the wind increases apparent wind speed and increases the centrifugal force trying to trip the boat and where bearing away accelerates the boat too quickly with too much sideways force on the sails. Multihull cruising sailors need to be aware of this zone and either head up or bear away to avoid it.
Another correction: dumping the sheets, especially the mainsheet, is absolutely the wrong thing to do when more the 60* off the wind. The reason being that easing the mainsheet powers up the sail. When sailing off the wind the proper gust response is 1) bear away hard and 2) bring in the mainsheet. Only when less than 50* apparent wind angle is dumping the main sheet the correct response.
We survived a 60 knot storm cell on our 54′ catamaran with full jib and full main by thankfully being close hauled when the wind increased from 15-60 knots. We didn’t ease any sheets, just steered up to 20* apparent wind angle and feathered the sails. That was 30 minutes of anxiety!
The modern design fashion for very sharp reverse bows is not a forgiving feature as it reduces the amount of flotation with immersion. We are very thankful for our old-fashioned rounded destroyer bows – a little more drag at low speeds but heaps of volume.
Hi Tom,
I agree with nearly all of your points and in my earlier comment about releasing mainsheet tension and/or the traveller when making the turn from upwind (TWA less than 50 degrees) to downwind, I should have clarified that I never turn to dead downwind for the same reason you state above. The turn is typically to around 120-130 TWA which (at least on the boats I’ve sailed) keeps the AWA typically no less than 90 degrees and IME keeps the eased mainsail depowered. After the turn is made safely I immediately re-trim the mainsheet. I would bet John’s experience as a 505 sailor would be similar. If on our Dragonfly 32 we are sailing downwind (TWA greater than 100 degrees) and the breeze builds to where we want to add a reef, we will turn down to at least 150-160 degrees TWA without easing the mainsheet and then center the traveller and bring some mainsheet back in to further depower the sail (and reduce twist) before easing the halyard and pulling on the reef lines.
Like you I’ve also survived some high winds (thankfully typically short lived) summer thunderstorms hove to at an upwind angle on my A-Cat with the traveller fully eased, but keeping the mainsheet tension on. On that boat, if the wind picked up to over 30 knots, it would probably get knocked over no matter what (180 lbs total boat weight,18’ overall length, 29’ tall mast, and 7’6” beam).
I’ll qualify the above in that I’ve never had to do these maneuvers in over 30 knots of sustained wind. Experiencing gale force conditions is hopefully a situation I will continue to avoid for the rest of my sailing life.
I’d like to add some comments about reverse bow designs as the bow design is part of the overall package in the performance and stability of the boat. At least on the higher performance catamarans I have sailed, there is actually more volume in the reverse bow design (look at the lower section profile) than there is in older straight or destroyer looking bows (like the older Nacras, Prindle 19, and Tornado). I still actively race A-Class catamarans and it is now rare that pitchpole induced capsizes occur with the current reverse bow designs on the boats. As a Dragonfly 32 owner (but with the older conventional amas), I’ve noted that Jens Quorning went to the reverse bow design first on the amas of the DF 28 and DF32 and then followed by the DF 40 (on those boats, the center hulls retained a plumb bow design) and now on the new DF 36 (the center hull on this boat is reverse bow). The stated design goal was to get more volume in the forward sections of the amas allowing you to either push the boat harder or giving you a better safety margin against the boat tripping over the leeward ama and when you see the boats sailing in big breeze, it appears to be very effective. The following links showing a Dragonfly 28 Evolution and a Dragonfly 40 sailing upwind and reaching in 25–30 knots of wind and severe sea state (short period waves) seem to bear that out:
https://www.youtube.com/watch?v=IQAFcQkbRn8
https://www.youtube.com/watch?v=bbvsTsaBqoE
You still have to obey proper reefing guidelines as no matter what bow design you have, pushing too much sail area downwind in big breeze is very risky. A lot of naysayers on reverse bows bring up pictures of boats being pushed off wind at their limits while racing. I believe the reality is they are safer if the boat is managed properly in terms of sail area for the breeze the boat is being sailed in. I will agree they are wetter but that can be a moot point dependent on the number of hulls and the beam and length of the boat. I will be very interested in seeing video of the newer Dragonfly 36 sailing in big breeze and waves with the reverse bow on the center hull.
Functionally I think we are seeing a similar thing in the high performance offshore monohull world with the development of scow type bows in the Mini-Transat, Open 40, and IMOCA classes. Whether that trickles down to offshore cruising monohulls remains to be seen. The scow type bows looks to be potentially a better solution than a reverse bow for a monohull application in terms of improving safety and performance. But it sure is ugly!
Cheers,
Bob
Hi Tom and Deb,
I get your points, that said I stick by my warning that healing angle is not a reliable indicator on cats. Sure, a skilled and experience sailor of cats will note the heal angle and that may help them react to a not too extreme situation. But in the case of a sudden high gust that’s not going to work reliably since the difference in healing from normal sailing ~5° and 10° after which stability starts to fall off fast, is just too narrow to be used reliably as a capsize warning given that in a gust wind pressure increases by the square of wind speed.
The key concept here is that of a reliable indicator, and healing fails that test on a cat. Or to put it another way relying on heal angle will work…until one day in a strong gust it does not.
Also, while centrifugal force may play a small role I don’t think it’s significant.
And sure, if you are undercanvased in a bear away in the death zone not easing the sheet may work, but given that the apparent wind will come forward as the boat accelerates, again, I don’t believe that’s as a reliable as holding course and dumping (not easing) the main and possibly the jib to unload everything, before changing course, probably to windward.
And yes, as I will cover in the next chapter on storm tactics, fore-reaching while feathering, what you were doing, can be a very good tactic on multihulls.
And I generally agree on the drawbacks of reverse bows, on cats. I’m still thinking about trimarans, but my guess is it’s far from open and shut.