how do cats handle big waves?

I think this video can contribute to the discussion:
http://www.youtube.com/watch?v=eiRgKXs92fc

It contains nearly everything that has been discussed about here:
- self-righting monohull
- Search and Rescue power catamaran
- surf waves.
You're free to make your conclusions, folks.

What I see is a monohull which takes takes a bad blow by the surf, capsizes but stays afloat and ultimately gets upright again, offering safety to it's crew.

On the other side, the SAR cat ends up very sadly. Once a cat flips over, it's really over.

Cheers.

 

I don't think that little power cat with the narrow beam is the kind of cat we're talking about here, but I will definitely agree... once the cat goes over, it doesn't right.

There's no coming back from a capsize.

At the same time, no boat will ever be in the surf unless disabled or there is a navigation error. Storms in deep water produce different waves from thos pictured in the video and in surf.

 

Hi Daiquiri,

Those are planing cats, probably 2.5 - 3.5m wide, and is totally different from a displacement cat.

Also, if I'm not mistaken those small ski boats are responsible for the most accidents, someone did post some stats a while back.

If you have like a 9m x 6m displacement cat I'm sure it would be very different. Here is a similar type vessel that I was thinking about. This boat is still quite narrow and have slim hulls.
http://www.youtube.com/watch?v=MA4XnO97MVY
and
http://www.youtube.com/watch?v=grDqbKohm1g

 

I agree guys, the cat in my video is not very wide. But even with a wider displacement cat the problem with surf waves would remain, imho. Yes, it will surely be initially very resistant to rolling moments, much more than a monohull. But if the surf action manage to turn the boat sideways to the wave front, the final result is only a matter of the surf height, be it a cat or a mono.

By the way, these are interesting stories, too:
http://www.allianz-yachts.co.uk/info/catamarancapsize
http://www.sfgate.com/cgi-bin/article.cgi?f=//a/2010/07/04/BAN41E9JJ6.DTL

As I see it, both hull types evidently can be capsized, if the conditions are right. The main difference between the two then becomes: what happens after the boat has capsized the first time? Is it safer to be on board a crippled self-righting monohull, floating upright with broken rig - or having to swim in the water attached to a capsized (but floating) cat?

It's all imho, of course.

 

What I suspect will happen to a wide cat is it would proably be pushed sideways, to flip one would take some effort. That is why in the case of a rescue vessel you also would want relative large motors - to keep the bows into the waves if need be and for short turning radiusses.

Of course there is the wave that can flip any size boat, but is it practical to go too big in size ? South Africans are nutty enough to do beach/surf launches with those skiboats. Anything wider adds a lot to the capsize resistance it will have.

Those planing cats in the vid are probably 5 to 6m long, if they were that wide they may not capsize so easily. Add length and you have a boat that will handle waves even better.

Also, the guys does surf sailing with hobies, and yes they do capsize, but keep in mind the boat size and the sail size, a whole different set of things to watch out for.

I'm still of the opinion a wide displacemnt cat and of appropriate length would make a stunning rescue vessel. I said 9m, but of course a 14m cat would be a lot more comfy in those waves.

It could be interesting to see how a wide displacement cat lives up to surf... I may take mine out when it's done (one day) and have a play. Start with small waves and venture into the larger. If it breaks then it's poorly made and may not stand up to the really big storms.

Of course something with a 5m bridgedeck clearance would solve a lot of problems...

 

I think the question is, how long would that monohull have lasted if it had been stuck in a position of continued breaking waves? His hatches were open, he would have gone to the bottom if he had been rolled a couple of more times.
And do you think the rescue boat situation would have been any different had it been a monohull power boat? A monohull power boat would have been much less stable upside down, or swamped.

 

The waves weren't that bad. Sufficient HP and skill takes a skiff thru that, NP. Thos self-bailing Australian surf rescue rowboats with good crew wud have had no problem with that rescue (do we have anything like that in States? I don't know. A jetski?. The cat not able to maintain headway and getting cockeyed is exactly what I was talking about (but in MUCH more vicious seas). That little thing was definately out of its league. A 17' Achilles could dart around in that surf for play. Not enuf HP to tow the sailboat well, unless out of the surf, but culd effect a snatch and go of crew.
I agree with Fanie on the dispalcement cats - they do much better here, at least.

 

There's an assumptions here, I think-- that the monohull will remain watertight. Further, once the mono loses its rig, it will be much more likely to capsize repeatedly, with attendant injury and damage. If conditions are such that the crew cannot cut away the rig, it will likely stove in the hull. I don't know why the cat crew would be more likely to be in the water than the mono crew.

As far as beaching a boat in a heavy surf, the cat, I think, will be much more likely to survive the exercise. The first thing that happens when a keelboat grounds in the surf, if the keel isn't driven up through the hull, is that the boat falls over on its side, and all control is lost, the boat fills and pounds itself into pieces. Cats don't have a single deep keel to trip over, have a much better chance of remaining upright, and pointed in the right direction, because they are naturally more inclined to run straight. (The downside of this is that they are harder to tack than a keelboat.)

 

The internet is not king

Its time to get reading guys.

First get Jim Brown's book and then Chris White's book. These two do a great job of covering this issue much better than anywhere else.

The problem is that you can't really compare mono and multi directly. Dacquiri makes the reasonable query "Wrecked mono or capsized cat" but it isn't that simple. It takes an awful lot less energy to capsize a 38 ft light mono than a 38ft light cat. This is a function of their stability curves. Calculation shows a multi has far more area under its stability curve. Also the mono is far more likely to be rolled because of its low roll moment of inertia (the same reason tightrope walkers carry a long pole) All this points to the fact that a mono must be self righting because it is much more likely to be rolled.

As for the videos - I am not sure what they mean. The Hobie one is trivial. I can take lots of videos of mono dinghies and multi dinghies wiping out. It doesn't mean much for a cruising cat or mono which due to the scale effect is a hugely different matter. The surf rescue is another case in point - this is an old video of a mono that gets rolled easily (low roll moment) and a thin cat with high CG also getting rolled. The cat is a trailer boat and as such is limited to 8 ft beam. We have a sailing trailer cat of similar length in Australia that capsize regularly but it doesn't condemn the type - just the design.

As for the Achilles - I bought one from a surf club and it has self righting ropes for when the crew is dumb enough to get flipped. So even a flat inflatable gets flipped too.

Rather than waste time debating - get sailing and calculating. Cats will capsize and monos will too. I have a bit of a problem with monohullers and multihullers when they both get too one eyed. Both boats have their problems and you should sail them accordingly. If you are silly enough to be inside when hit by a microburst then you should jump for the sheet or at least have it led inside with you. Racing multis have a dump line inside that you can reach inside that releases the sheet. Its is a good idea for those that push hard shorthanded. Don't forget the inverted flotation and grab bag accessibility. Plan for your own boat's Achilles heel and deal with it properly - not by pointing out the problems in others choices.

cheers

Phil

 

Hi Phil,

The question was asked why rescue services are not using displcement cats since there could be a lot of advantages in doing so. The comparassons made to other hull shapes was made to point the differences and probable advantages out. I guess one gets a bit one eyed when you feel you have to defend another view - however it is still every one's choice what boat he wants or have - knowing what your boat's Achilles heel is may be to your advantage, which is why we have these arguments about hull shapes and the application of them.

People make choices for funny reasons. I had a guy telling me he would rather buy a mono because he needs to put only one motor on it, where for a cat he would have to put two motors on and he doesn't think a cat would work with only one motor.

Had the mono in the video have two motors the cost of a motor would justify the damages from that one roll - and the outcome could have been very different.

The reason for bringing the hobie in surf up is to point out how easy maneuverable a light cat can be even in breaking waves. If a rescue vessel have similar agile characteristics it would be an advantage, similar to the reason why they use jet ski's to rescue people off the coast.

 

design is about more than survival safety

The cat in the video is a Shark cat and they were designed to go on a trailer. So they have to be less than 8 foot wide. Cats always run into this problem when asked to trail. Be that as it may there are very few easily trailerable rescue boats of any configuration that could better its seaworthiness. Many of these rescue boats are launched at boat ramps in Australia (near shallow bars) so they can't be a beamy square cat. So the designer starts of with set criteria and does their best.

Sure we could design a "better" cat but not when it has to be trailed and fit in a normal boat shed like the rescue cat at my local rescue station. The operators have to understand the limitations of the design and deal with them.

cheers

Phil

 

If you consider the 2m500 allowed width for trailing then it means for a cat that is 1m200 per hull. With some hinged folding beams the hulls could be moved apart after launch, and folding open doesn't have to take long, a winch can do that or even a hydraulic system. Even folded it could be as stable as the planing cat.

The hulls may not be very wide, but inside offers enough space for a bit of equipment and it's out of the elements, which may well count in favor of a critical patient.

The hulls can be trailed back to front, so once rolled off the trailer and free the motors can be started and be underway while the boat folds open.

The space between the hulls can be a trampoline in the front and another between the beams. These can hang between the hulls when trailing, and once the beams are in place the trampolines can also then be tensioned.

With all the expertise on the forum re 'boat design' I'm almost sure a better solutution can be designed.

 

A lot of posts while I was flying...

Mark says

"I know that you could roll my boat - I could, too."

But he hasn't. Why not??

Because he uses good seamanship, keeps his boat properly maintained and uses it in the conditions for which it was designed. When he is in extreme weather he gets frightened, but the boat copes better than he expects.

Is that a good assessment??

And isn't that exactly what would happen if he used a multihull?? So no real practical difference between a monohull powerboat and a sailing catamaran.

Many of you know that for many years I have been on the committee that writes the stability standards for all recreational craft, both power and sail. We spent far more time worrying about the stability and buoyancy of powerboats with large open cockpits than we did discussing multihulls, because we knew that not only did boats like Mark's have very limited stability in roll, but were also very prone to flooding (as I mentioned earlier in this thread). Naval architects accept that a boat is stable in waves whose height does not exceed the boat's beam. So wide boats are much more stable when lying ahull in beam seas than narrower ones - the number of hulls or even displacement is irrelevant.

For those that are not from the UK, the Royal National Lifeboat Institution is the UK's largest charity and does much of the work that coastguards do in other countries. Their crews are all volunteers. They get no government funding.

The RNLI don't use multihulls, nor do they use conventional non-self-righting monohulls. For several reasons, including the need for big engines with plenty of power to tow fishing boats and coasters, while they often get smashed against the sides of distressed ships.

I suggest you read this wikipedia link http://en.wikipedia.org/wiki/Penlee_lifeboat_disaster

It will help explain why the RNLI now use the boats they do.

They also use RIBs for inshore work. The Dutch equivalent to the RNLI have used surf catamarans as an alternative to RIBs

I have to say I think the Stolkraft type catamaran is an awful concept. There are similar looking designs used as fishing boats in the UK as well. Many fishermen like a boat that rolls, it is easier to work than on one with a jerky motion and the roll can be used to help haul pots or jig. (Which is why many traditional pre-engine fishing boats were deliberately designed to roll). One of my 30ft Sagitta catamarans is being used as a commercial fishing boat in the UK. Under sail only, there is no engine on board. (The owner reads this forum.)

Years ago a Heavenly Twins catamaran was hit by a breaching whale when in mid Atlantic. The whale landed in the cockpit and smashed it, yet the HT made it safe to shore. I had a narrow escape myself when sailing off Costa Rica and a whale breached right behind our boat.

On capsize prevention. Many, many multihulls capsize because the sheets could not be freed, yet I still see many, many multihulls with very poor deck layouts. Having a boat that is stable in high winds is not really any safer if, once the stability limit is reached, sheets cannot be released quickly and easily by any of the crew. And to my mind that means mainsheets in particular should not be run through a stopper because the risk of a snarl up is too great.

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

"When he is in extreme weather he gets frightened, but the boat copes better than he expects." I don't really know. Yes, I have been petrified but I keep the boat in an aggressive attitude (attack) and (usually!) avoid getting in spots where the sea has control.
My back deck has been nearly completely pooped but I have large freeing port area (13'10" beam x 14' length deck under water on the diagonal, i.e., half under water, half nearly full of water) and I estimate four seconds for complete drain. Flooding doesn't scare me so much unless there is the second wave threat of compounding the situation or hitting me while I'm down. Four second drain is enuf to be ready for the next but I do fear capsize by broach and pitchpole.
I realize that this is a cat thread but I think this is relevant - sometimes the thing that keeps me in control is the prop being deep in the water. When it ventilates, I am not in control. Also 493 HP is enough for most circumstances but there are times when I would like to leap to the opening between waves and can't. Higher gear reduction, larger four blade prop and more HP would be nice if our weather were always as crappy as it has been this year.
"...mainsheets in particular should not be run through a stopper because the risk of a snarl up is too great." I'm going to be a sailor before you guys are done with me. (I wouldn't have thought of that, e.g..)
Is there no way to right a capsized cruising cat, partially flooding one hull and righting with crew leverage or ???
One last thing, I've done some amazing things (and seen more amazing things) in inflatables. Do you believe that RIBS are better in seas..or just more comfortable?

 

There are two main ways to capsize - wind-induced and wave-induced. Wind-induced capsize is to a large degree under the control of the crew, based on how much sail they have up.

Wave-induced capsize was considered in the study by the Wolfson Unit. Their study, and similar ones by other researchers, have shown that the most important factor in determining wave-induced capsize is the size of the beam compared to the height of the wave.

The beam of a cat makes the probability of being rolled much less than for a monohull in the same sea state. Because of the dynamics of how the wave affects each of the hulls in turn, a trimaran effectively has its beam cut in half for this purpose, and so is generally more susceptible than a cat. But still less susceptible than a monohull.

So the short answer to your question is a the cat will remain inverted if it capsizes, but it is less likely to be rolled in the first place than a monohull. The attraction is the greater probability of staying upright.

The hazard level is the probability of the event happening times the consequences of the event. The cat has basically one catastrophic consequence - capsize. The monohull has one less catastrophic possibility - recovery to upright after being rolled - and one more catastrophic possibility - sinking. Those who are attracted to cats believe the lower probability of being rolled, combined with the capsize consequence is less hazardous than the higher probability of the monohull being rolled times the chances of recovery vs sinking.