Capsized Atlantic 57 Salvaged

[2Hulls]

Originally Posted by valhalla360

The rigging must be stronger on catamarans due to shock loads. If you hit a monohul with a gust, she rolls over a bit and then when the gust eases, she rolls back up. With a catamaran, it just stands up to the wind unless you reach the extreme where she capsizes or something breaks. Even with slightly wider shroud angles, the forces are significantly higher in most cases.

I'll have to disagree with you on this. Just because a mono rolls over a bit more doesn't mean the added forces in a gust did not exist. Extra load on the rig had to exist to cause the extra heeling and raising all that ballast. Only when it rolls far enough to decrease the effective sail area do the forces reach an equilibrium at a higher heel angle. The multi will also heel a little more in the same gust, and then roll back up as the gust subsides and/or accelerate using the extra force.

2 Hulls Dave

[valhalla360]

Originally Posted by 2Hulls

I'll have to disagree with you on this. Just because a mono rolls over a bit more doesn't mean the added forces in a gust did not exist. Extra load on the rig had to exist to cause the extra heeling and raising all that ballast. Only when it rolls far enough to decrease the effective sail area do the forces reach an equilibrium at a higher heel angle. The multi will also heel a little more in the same gust, and then roll back up as the gust subsides and/or accelerate using the extra force.

2 Hulls Dave

The force of the gust does exist but the mono bleeds it off by rolling. The cat tries to stand up to it.

It's similar to crumple zones on a car. A cat is like an old solid body on frame car. If you hit a brick wall, the entire car comes to a stop almost instantly imparting a huge amount of force on the occupants (F=ma and a is huge). In newer crumple zone cars, they spread that same load out over a longer time period and reduce the force applied (by spreading it out over time, a is drastically reduced and therefore the force is reduced).

When a gust first hits a mono that is fully upright, there is very little resistance to heeling so the initial force is converted mostly into rolling. Then it gradually loads up the rigging until it reaches equilibrium.

When a gust hits a cat, there is just the slightest amount of heeling and then the rigging must resist the full force of the wind.

[Polux]

Originally Posted by valhalla360

The force of the gust does exist but the mono bleeds it off by rolling. The cat tries to stand up to it.

...

That is very clear if we look at the two stability curves:

[s/v Beth]

In spite of all the above arguments, it becomes clear that if you take two similar sized boats going 5knts in wind and there is a microburst that brings 60 knts of wind within a minute, the cat is more likely to flip. The mono will broach, then pop back up as soon as the wind abates.
This happens more often than people think. It has happened to me at least twice, but I sail around mountains a lot, were I think these types of winds seem to live...
BTW- I saw one of them coming (day) and one of them I didn't see (night, in fog)

[Polux]

Originally Posted by s/v Beth

In spite of all the above arguments, it becomes clear that if you take two similar sized boats going 5knts in wind and there is a microburst that brings 60 knts of wind within a minute, the cat is more likely to flip. The mono will broach, then pop back up as soon as the wind abates.
This happens more often than people think. It has happened to me at least twice, but I sail around mountains a lot, were I think these types of winds seem to live...
BTW- I saw one of them coming (day) and one of them I didn't see (night, in fog)

It is not in spite...what you says is in accord with the above arguments. But on a extreme sea the cat with no sails or minimum sails will be able to resist better to a capsize....it is also in accordance with the above.

Off course after being capsized the monohull will be able to right itself up, the cat even if more dificult to capsize, if capsized, will stay capsized.

Vantages and disadvantages on both sides. Now regarding cats and trimarans in what regards stability, the advantages are all on the trimaran side.

[2Hulls]

Actually, I think we're in violent agreement. The offered graph above relates to required forces, not effects of comparable forces, so it's irrelevant.

For comparable sail areas of a mono vs multi, the instantaneous forces in a gust are equal. They have to be. The mono decreases these forces over time as it heels but sacrifices acceleration which may be limited by hull speed anyway. For the multi the forces do not decrease as much over time because they heel less, but they are never greater just because it doesn't heel as far.* They can't be. The forces just stay up longer and get used for acceleration, not inhibited by hull speed. They can never be greater than those initially experienced by the mono. In fact, the forces on the mono are more dynamic and cyclic. On and off.

*Due to increases in apparent wind speed due to acceleration, the multi may experience higher loads than initially felt by both vessels. But this effect is not germane to the discussion.

In spite of all the above arguments, it becomes clear that if you take two similar sized boats going 5knts in wind and there is a microburst that brings 60 knts of wind within a minute, the cat is more likely to flip. The mono will broach, then pop back up as soon as the wind abates.
This happens more often than people think. It has happened to me at least twice, but I sail around mountains a lot, were I think these types of winds seem to live...

No, cats don't flip more often than people think. By your accounting, you've been knocked down twice but I've flipped none.

2 Hulls Dave

[Polux]

Originally Posted by 2Hulls

Actually, I think we're in violent agreement. The offered graph above relates to required forces, not effects of comparable forces, so it's irrelevant.

For comparable sail areas of a mono vs multi, the instantaneous forces in a gust are equal. They have to be. The mono decreases these forces over time as it heels....
2 Hulls Dave

Well, any agreement is a good one, even a violent one

That is the same that saying that on a gust the forces on two equal sails, one of them completely lose and the other tightly sheeted are the same.

They are not, the sheeted sail will resist wind and will be subjected to a huge force, as well as the mast. The lose one will go with the wind and little force will be made on the mast.

Regarding the effect of heel on the diminishing of force on the sails on a boat hit by a gust, it will not be as substantial or comparable between the lose sail and the sheeted one, but the principle would be the same.

But I really don't understand your argument since you agree that the mono decreases forces as it heels. So, what are you considering "instantaneous forces": 1/100 of a second? Both sailboats will start to heel as soon as they are hit by the gust, the difference is that the mono, as the Stability curves show, will heel a lot more and a lot faster. if the gust is strong enough the monohull will be knocked down and the wind will pass over the hull not hitting the sails anymore. When the gust passes the mono will right itself up. If the gust is strong enough the cat will be knocked out too, and that on a cat means a capsize.

As the stability curves shows the cat can take more wind without being knocked out, but sometimes (not many happily) the gusts are just too strong and unexpected and cats are knocked down and capsize.

[clockwork orange]

Originally Posted by a64pilot

Back in the 70's? There was a beach cat, not Hobie, that had a Styrofoam ball at the top of the mast.

Lots of beach cats today have masthead floats, in fact i installed a Hobie "mama bob" float this year on my Pacific cat 19, its the largest of 3 sizes they make i think. I used to own a Macgregor 36 cat that originally came with a masthead float but most people removed them because the boats were very unlikely to capsize and this proved to be correct in practice even though they only had a 2:1 length/beam ratio.

Steve.

[2Hulls]

Originally Posted by Polux

That is the same that saying that on a gust the forces on two equal sails, one of them completely lose and the other tightly sheeted are the same.

No, then they aren't "equal".

They are not, the sheeted sail will resist wind and will be subjected to a huge force, as well as the mast. The lose one will go with the wind and little force will be made on the mast.

Yes, but that's not relevant to the discussion. To make a fair comparison of rig loading we need to consider two equal sail areas, including sheeting variables.

Regarding the effect of heel on the diminishing of force on the sails on a boat hit by a gust, it will not be as substantial or comparable between the lose sail and the sheeted one, but the principle would be the same.

True, but we are not considering two unequal sails due to variable sheeting.

But I really don't understand your argument since you agree that the mono decreases forces as it heels. So, what are you considering "instantaneous forces": 1/100 of a second? Both sailboats will start to heel as soon as they are hit by the gust, the difference is that the mono, as the Stability curves show, will heel a lot more and a lot faster. if the gust is strong enough the monohull will be knocked down and the wind will pass over the hull not hitting the sails anymore. When the gust passes the mono will right itself up. If the gust is strong enough the cat will be knocked out too, and that on a cat means a capsize.

As the stability curves shows the cat can take more wind without being knocked out, but sometimes (not many happily) the gusts are just too strong and unexpected and cats are knocked down and capsize.

The original argument was that a cat sustains more forces on the rig because it doesn't heel. What I have shown is that this is not correct. Unrelated, the stability curves show that a cat can sustain more forces prior to capsize, i.e. it takes more forces to cause a capsize than it takes to knockdown a mono. But this is not relevant whatsoever to comparing rig loading of two vessels experiencing the same forces - the same gust - that produce neither a capsize nor a knockdown.

2 Hulls Dave

[thinwater]

Some misconceptions:

Masthead float. Other than racers flying aggressive sail, cats will only capsize in violent conditions that would remove the mast, were a float fitted.

Fuse. Is the capsize load on the mainsheet determined...
a. hard on the wind.
b. reaching.
c. based upon dynamic loads or sustained loads.
In practice, this just does not work. However their are commercial models... that don't work.

Snap shackle quick-release. That is served by cam cleats on the mainsheet and traveler. And it wouldn't work down-wind anyway.

Ratio arguments. Mostly from monohull sailors.... But this goes deep into wave conditions and hull forms. No single number solves the problem.

Wave induced capsize. This is probably the only one cruising cats worry about. Wind can be managed, but monstrous breaking waves are a hazard to everyone.


The reality is that prudent cat sailors don't worry over capsize much.

[Polux]

Originally Posted by 2Hulls

...
The original argument was that a cat sustains more forces on the rig because it doesn't heel. What I have shown is that this is not correct. Unrelated, the stability curves show that a cat can sustain more forces prior to capsize, i.e. it takes more forces to cause a capsize than it takes to knockdown a mono. But this is not relevant whatsoever to comparing rig loading of two vessels experiencing the same forces - the same gust - that produce neither a capsize nor a knockdown.

2 Hulls Dave

I believe you have not showed anything by the simple reason I believe you are wrong and I believe it will be easy to prove:

Just imagine two boats with an equal rig, a cat and a monohull, subjected to a gust that will knock down the monohull and will not capsize the cat. Obviously, being the monohull knocked down the wind is not making any effect on the sail or on the mast, but will be hitting with full force the sail on the cat that due to the bigger stability is able to counter act it with a relatively small angle of heel. The mast on the cat will be subjected to a much bigger effort than the one on the monohull.

[Polux]

Originally Posted by thinwater

Some misconceptions:

Masthead float. Other than racers flying aggressive sail, cats will only capsize in violent conditions that would remove the mast, were a float fitted.
...

Even if capsized cats are not frequent that is not true that happens only to cats sailed aggressively or in violent conditions that would break the mast. Reality shows that. most of the ones that are capsized were by violent and unexpected gusts.

I don't want to turn this thread on a capsized cats thread neither I am interested in other thing than reality and that is that capsized cruising cats are relatively rare, but if you make a search you will find some, most of them capsized on the conditions I described and will see that not all were performance cats or where being sailed aggressively. Most capsizes did not happened on extreme conditions but due to strong gusts.

[colemj]

Originally Posted by Polux

Even if capsized cats are not frequent that is not true that happens only to cats sailed aggressively or in violent conditions that would break the mast.

I think what he meant was that if a float were attached to the masthead of most cruising cats, the act of capsizing would break the mast - thus rendering the float useless anyway.

Mark

[colemj]

Originally Posted by s/v Beth

In spite of all the above arguments, it becomes clear that if you take two similar sized boats going 5knts in wind and there is a microburst that brings 60 knts of wind within a minute, the cat is more likely to flip. The mono will broach, then MAYBE pop back up as soon as the wind abates

A lot of mono's out sailing in light conditions would probably have hatches and companionways open.

Mark

[thinwater]

Originally Posted by colemj

I think what he meant was that if a float were attached to the masthead of most cruising cats, the act of capsizing would break the mast - thus rendering the float useless anyway.

Mark

Correct. Sometimes the mast survives, but it would NEVER survive on a full grown cruising cat if there were a float and any wave action.

And let us review Chris's observations:
To summarize:
1) Neither captain thought capsize was even a possibility until way too late
2) Both boats were under autopilot, which had the helm all the way through the capsize
3) The main sheet was never eased or released

Niether capsize should have happened. Period. A responsible multihull skipper would never sail through a squall on autopilot with significant sail up. I've sailed cats though lots of squalls, and you just don't do that. Autopilot is for settled conditions. Thus, capsize will only happen when the waves are wild, in which case a float only INCREASES the likelyhood of capsize (weight and windage) and insure the rig is coming off.

There are many things you can do to keep a cat on her feet, but most involve multiple boat handling procedures.