catamaran stability

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voyager35

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I own a 45ft Dereck Kelsall designed and built cat from 1987.
I was on a nice beam reach heading south to Ireland a few weeks ago and there was a steep beam sea around 2 meters may be a bit more at times This put quite a heal on the boat at times which got me thinking about how much the stability of a cat would be affected by a beam sea. I normally reef at set wind speeds but do multihulls need reefing earlier in these sort of conditions
 
voyager35 said:
I normally reef at set wind speeds but do multihulls need reefing earlier in these sort of conditions
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Monohull sailor here. I usually reef when I feel it needs done, never at set wind speed. You are relying on only one variable and living in an environment with at least two, usually a lot more and one can be the vomit.
 
Sandy said:
Monohull sailor here. I usually reef when I feel it needs done, never at set wind speed. You are relying on only one variable and living in an environment with at least two, usually a lot more and one can be the vomit.
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Cats are sailed by numbers. The feedback on loads is just not there otherwise.
 
Oh dear. Some weird ansers.

Yes, obviously waves add heel, the motion can start the rotation, and coming off a steep wave the wind will get under the deck. Steep waves reduce stability. They don't have to be breaking and there does not need to be a specific relationship of size to beam. It's a complex relationship, but generarlly you will feel a slight hesitation of the boat to come back down after a large wave passes. The best answer is to learn to sail on beach cats.

Yes, catamarans do have considerable feel, it's just lost on people who have not sailed them enough. It's all there, it's just different. Watch a beach cat sailor balance on one hull for 1/2 mile; he has the feel.
 
I have a 40' monohull. Crossing Biscay on a beam reach, I had a single reef at sunset, trotting along nicely with 7+ knots through the water and 18 or 20 knots of wind.

I stood on deck, viewed the empty horizon with satisfaction and asked myself, "shall I put in a second reef?" "No," I thought to myself, "I can always put it in later."

During the night, the wind gusted between 20 knots and 30 knots, the motion of the boat became far more aggressive and I was too scared to get on deck and reef further. It would probably have been fine once the boat was turned into wind, but I was distinctly uncomfortable. As a solo sailor I would say that night's darkness adds several knots - perhaps as many as 10 - to the perceived scariness of the conditions.

The boat is fine with 2 reefs with winds in excess of 30 knots.

I believe my boat carries quite a lot of sail area, relative to her displacement. She is a Van De Stadt Caribbean 40.

HTH, HAND, etc.
 
I would say that OP if he was concerened re the heel that yes it is time to reef or at least ease the main sail. The stability of a cat is from the distance centre of gravity to centre of buoyancy. Across the beam) As the boat heels on a wave this distance will be reduced. So resistance to heel by sail pressure reduces. ol'will
 
A 2m sea is nothing - if the seas are 100m apart. You do mention steep beam sea - if you are twitchy why risk it - put in a reef.

The last time I was twitchy I was sailing on a beam reach with steep seas - an overly large wave approached and 3 dolphins surfed down the front of the wave - and I was looking up at them - I panicked (and did not take a picture) but put a reef in.

38' cat, 22'6" beam, mini keels.

Many, cruising, cats have the sail controls far too far apart - you need to walk to ease the main. We have all our sail controls within reach of the helm (a lesson from racing hard - when you are sailing to the limits you need total control - This is absent on a cruising cat as the assumption is, lots of crew, and you don't drive a cruising cat to its limits (the crew will not react and possibly will not like it - they are there to enjoy, not break records.). We carry on our racing background - hence having control of all sails at the helm.

We can average 10knots over 100nm. To achieve this peak speeds are 18-20 knots - a lot can go wrong, and quickly.

Jonathan
 
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The danger is when sailors or cockpit designers think of multihulls as more stable, comfortable versions of monohulls. Cockpit style can override the demands of vigorous sailing. The designer may have known better, but the marketing people push changes. I've seen good multihulls ruined by marketing people. I once questioned a designer about his changes, and he said "we build these for a different kind of sailor." I think (know) he meant either charter or dock queen.

Multihulls require different thinking to design and to sail.
 
thinwater said:
Oh dear. Some weird ansers.

Yes, obviously waves add heel, the motion can start the rotation, and coming off a steep wave the wind will get under the deck. Steep waves reduce stability. They don't have to be breaking and there does not need to be a specific relationship of size to beam. It's a complex relationship, but generarlly you will feel a slight hesitation of the boat to come back down after a large wave passes. The best answer is to learn to sail on beach cats.

Yes, catamarans do have considerable feel, it's just lost on people who have not sailed them enough. It's all there, it's just different. Watch a beach cat sailor balance on one hull for 1/2 mile; he has the feel.
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Having been an owner of two cruising cats then flipped back to mono I would say the feel of a cat is considerably less than a mono, but that's just a detail.
The rule of thumb is just that. It applies to mono or cat
The behaviour of cats in beam on big waves can vary dramatically. Mini keels will slide in a roll threatening situation. If you have both dagger boards down in the same situation the ability to slip sideways is much diminished. Note that we had both types of cats so have had some experience of this. We would lift the leeward board in big beam seas. If the windward hull lifted it would allow us to slip sideways
The scariest moment in my sailing career was in a cat with mini keels with circa 30 kts, 5m ground swell and crossing a sea mount. The monster steam roller of a rouge wave that hit us beam on sent us sliding sideways before we broke over the back of the wave. We were very close to going over. If we had have had daggerboards I am certain we would have flipped
 
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Yet another issue

Cats in general sail flat, don't get the idea it is flat - light ones bounce around a lot and do heel to wind (a bit) and a bit more to swell.

But big swells don't occur in many cruising locations and, in my ignorance, I might suggest you need to sail in water with a big fetch, sustained and big winds with breaking seas to get swells (plus wind) that are going to be a big issue. Most charter fleets, where many would be introduced to the pleasures of a cat simply don't have big swells. These locations might have strong winds - and the rules are the same as for a mono reef down before you ask yourself - should you reef down. Big swells simply add a new and unknown environment.

I cannot comment on dagger boards - no experience - except on small cats with no accomodation.

I mentioned that when you are hitting speeds in the upper teens - things can go wrong - quickly. We broke a bobstay shackle with our 45m^2 screecher and lost a halyard (stripped the braided cover off) on a bigger screecher on a 43' cat (that I was crewing on). We had to cut the halyard to get the sail down - in both cases unlike a mono - retreiving a big headsail by hand is not something ever done on a multi - so having had mono experience stands in good stead.

Oddly multis don't have toe rails - which indicates how designers and builders view them - totally unnecessary (I'd challenge the assumption - short handed wrestling with a big sail - toe rails offer some comfort.

I'd agree with Geem - cats lack feel, compared to most monos - or the feel is totally different. The indicator is speed, whereas on a mono it would be heel and dumping the main.

Jonathan
 
It is not the size of the swell that is important. My experience of multihulls is that it is the steepness of wave setup, that is important.
They tend to follow the angle of the wave, especially if little or no sideways resistance.
Only time I have been worried was with tidal convergences to the North of the Channel Isles with short very steep seas from all directions, and the height was only 2-3metres. Boat is/was 4.2 m beam 10m long and weighs in at 6 tons.
All boats give you a feeling of whether it is "safe" in time and experience. Lowering the central point of sail area, gives a better feeling,whether it is a 100' monohull or a 30' cat.
 
Speaking as yet another monohull sailor with opinions on the subject, I would say that reefing by numbers is a good policy to adopt by anyone who is concerned about their ability to make their own judgement in a multihull. A 2-metre sea doesn't sound much but can be quite disturbing. If it were me I think I would add a decent margin of error in such conditions, reefing at perhap one wind force earlier. Even in a monohull, most experienced sailors will reef to the sea conditions as well as the wind.
 
I've never sailed on a cat so no personal experience. What did surprise me watching the Ruby Rose videos was the comment that the charter company owning the cat they are sailing on bans having sails up at 25 kts or above. They comment that on old Ruby Rose mono they would have been sailing in far stronger winds, as would we.
 
Mudisox said:
Only time I have been worried was with tidal convergences to the North of the Channel Isles with short very steep seas from all directions, and the height was only 2-3metres. Boat is/was 4.2 m beam 10m long and weighs in at 6 tons.
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Must have been an old one. Apart from the American Gemini, they're not made with that sort of low beam to length ratio any more. The Gemini is not an open water boat.
 
The other lesson, applicable to many boats, is to avoid steep beam seas. If nothing else, the are uncomfortable. Either head up or bear off a little. On a long passage, this can often be combined with working changes in wind direction; a straight line is often not the fastest fastest or safest course.
 
Thank you some interesting reply's confirming my thoughts that reefing sooner in the steep beam seas we encountered that day would be prudent, My cat is set up with the sheets directly in front of the helm but i dont fancy the odds on releasing them to prevent a capsize as a wave lifts the windward hull, with a 1000 sq feet of sail to control and at 10 ton plus weight the sheet loads are very high.
When i first sailed the boat it felt dead in the water and the instruments seemed to be the main reference to what the boat was doing , but with more miles i am beginning to feel the boat but it is a lot more subtle than a monohull.
An odd feature of my boat is that it has a single pivoting centerboard that draws 2,4 meters. it means upwind performance is pretty good but it does concern me that it could trip the boat in extreme conditions. It can obviously be lifted but then it is only the strength of the hinge pin stopping it from twisting and the damage it could do if it was torn off when lifted up in a storm dosnt bear thinking about
 
voyager35 said:
Thank you some interesting reply's confirming my thoughts that reefing sooner in the steep beam seas we encountered that day would be prudent, My cat is set up with the sheets directly in front of the helm but i dont fancy the odds on releasing them to prevent a capsize as a wave lifts the windward hull, with a 1000 sq feet of sail to control and at 10 ton plus weight the sheet loads are very high.
When i first sailed the boat it felt dead in the water and the instruments seemed to be the main reference to what the boat was doing , but with more miles i am beginning to feel the boat but it is a lot more subtle than a monohull.
An odd feature of my boat is that it has a single pivoting centerboard that draws 2,4 meters. it means upwind performance is pretty good but it does concern me that it could trip the boat in extreme conditions. It can obviously be lifted but then it is only the strength of the hinge pin stopping it from twisting and the damage it could do if it was torn off when lifted up in a storm dosnt bear thinking about
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In fact, there should not be too much load on the pin. The pressure is against the sides of the trunk. The trunk needs to be very strong and well braced.
 
Graham376 said:
I've never sailed on a cat so no personal experience. What did surprise me watching the Ruby Rose videos was the comment that the charter company owning the cat they are sailing on bans having sails up at 25 kts or above. They comment that on old Ruby Rose mono they would have been sailing in far stronger winds, as would we.
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You don’t need much wind at all if you have a lot of sail up like here. This is the Gunboat 60 in racing mode. About 206m2 on a 16.5 ton boat.

1632607242285.jpeg
 
thinwater said:
In fact, there should not be too much load on the pin. The pressure is against the sides of the trunk. The trunk needs to be very strong and well braced.
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Yes that is what we have, the problem is that when the board is pivoted up the head that gives all the strength is no longer in the trunk so if a lot of pressure is applied to the board (ie from a wave ) there is very little apart from the pivot pinto stop it twisting
 
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