Capsized Atlantic 57 Salvaged

[Delancey]

What about running rigging? I'm thinking with lighter displacement they would be same or smaller on a multi when compared to typical medium displacement keel boat with the same sail area. Yes? No? Maybe?

[a64pilot]

I'm going to assume that rigging is larger on a multi because heeling a mono unloads the rig, what unloads a mono's rig?

[44'cruisingcat]

Originally Posted by s/v Beth

Great idea- but what happens when the spectra gets old?

Umm, you'd renew it? It would need replacing fairly often in fact. But you'd only be looking at a very short length of rope.

[LTDsailing]

Originally Posted by a64pilot

Stupid question as I'm not a Cat sailor, just barely a sailor actually.

I've often wondered why an overload device isn't fitted to the main sheet?

Interestingly, this feature is incorporated in the new Gun Boat designs. You are able to adjust the main sheet load. Very cool idea.

[colemj]

Originally Posted by Delancey

What about running rigging? I'm thinking with lighter displacement they would be same or smaller on a multi when compared to typical medium displacement keel boat with the same sail area. Yes? No? Maybe?

Unless racing, the running rigging is typically spec'd so that it fits common rope clutches, winches, blocks, etc. This does tend to make it oversized. Happens on monos also.

Then again, the majority of the production catamarans being made now can hardly be considered lighter displacement than their mono brethren…

Mark

[2Hulls]

Originally Posted by a64pilot

I'm going to assume that rigging is larger on a multi because heeling a mono unloads the rig.....

Why do you think that? Heeling doesn't unload the rig. At best, it can only keep it from continually increasing.

2 Hulls Dave

[Blue Stocking]

In the 70s I sailed a Paul Lindenberg cat, 48 x 19, that had a pendulum switch, controlling a solenoid, controlling a modified jam cleat for releasing the mainsheet. I never used it, always handed the sheet. Another captain, sailing it with about 20 day charter guests, tacked in a breeze, weight didn't change side, rolled Calypso right over Hamilton Harbour, Bermuda. Stuff the mast in the mud.

[a64pilot]

Originally Posted by 2Hulls

Why do you think that? Heeling doesn't unload the rig. At best, it can only keep it from continually increasing.

2 Hulls Dave

Agreed, it does not un-load, that was a bad choice of words, your correct.

[Polux]

Originally Posted by Blue Stocking

In the 70s I sailed a Paul Lindenberg cat, 48 x 19, that had a pendulum switch, controlling a solenoid, controlling a modified jam cleat for releasing the mainsheet. I never used it, always handed the sheet. Another captain, sailing it with about 20 day charter guests, tacked in a breeze, weight didn't change side, rolled Calypso right over Hamilton Harbour, Bermuda. Stuff the mast in the mud.

I guess he was not using that system either Probably similar to the ones that are used on the racing solo trimarans, anyway the system is released by heel not by a given force.

[2Hulls]

Originally Posted by a64pilot

Agreed, it does not un-load, that was a bad choice of words, your correct.

Roger. I thought that was the case.

But back to your question mono vs multi heeling vs not heeling and rig loads. Multis DO heel - just not as much. But the physics is no different than monos. Both will heel an amount directly related to the load on the rig. The rig does not know the difference whether there's a little heel or a lot - it just feels the force that is balanced by the counter force applied by the hull(s) that balances the wind and water forces. So, I think, standing rigging design is irrelevant to amount of heel and should rely only on the correct engineering for the forces involved. Because of their narrower beam, mono rigs are usually far more complex than multi rigs simply because the multi rig designer can exploit the wider angles available to him/her. For example, on my boat there are just two shrouds and a forestay and one set of spreaders with one set of diamonds. As simple as a Hobie 18 (without the rotating mast).

2 Hulls Dave

[a64pilot]

Dave,
Only point I was trying to make is if you hit a mono with a big gust of wind, you may knock her down with X amount of force, but hit a similar sized multi with a big gust of wind, I assume it takes a lot more than the same amount of force to capsize a multi, than it takes to knock down a mono, and if that is correct, then a multi's rigging is in a position to have more force placed on it than a mono.
Mono knockdowns I don't think are anywhere near as rare as a cruising Cat being
capsized

Would seem logical that a multi's rigging should be stronger than a mono, good thing you have that wide beam to make things stronger

[2Hulls]

Originally Posted by a64pilot

Only point I was trying to make is if you hit a mono with a big gust of wind, you may knock her down with X amount of force, but hit a similar sized multi with a big gust of wind, I assume it takes a lot more than the same amount of force to capsize a multi, than it takes to knock down a mono, and if that is correct, then a multi's rigging is in a position to have more force placed on it than a mono.

Yes, I think you're correct. Because of the higher stability more force is req'd to capsize a multi vs knockdown a mono - all other things being equal. But the force on the rigging is a function of the rigging design - including the wider angles from vertical. The case could be that multi rigging piece parts don't need to be as robust as a comparable mono rig just because of the wider angles. A real NA would have to help us here with specific examples to analyze. But, yes, more total force on the multi rig as a unit can exist because of the higher stability before the force get relieved via capsize. This is one reason why multis can be faster, right?

2 Hulls Dave

[Doe818]

Originally Posted by valhalla360

For a boat of a given length, if you increase the beam (ie: change the L/B ratio), it's not typically done in a vacume. If you keep the mast/sail area the same, you don't gain any performance advantage. So the typical response is to put a taller mast and bigger sails on the wider beam boat. Also as you go wider, you need more bridge deck clearance, so the ceneter of gravity for the boat is higher.
- The capsize moment looks good because the extra beam directly helps that.
- Pitchpole moment is slightly worse due to the higher center of gravity but other wise unchanged by the wider beam but the taller mast creates a larger moment arm.

Theoretically, you could put a short mast on a wider beam boat but it will be slow and whats the point in widening the boat, just stay with the shorter mast on the 2-1 ratio boat that is reasonably safe already.

Probably also worth clarifying what " effective" beam actually is on catamarans when it comes to stability... It is not the overall or extreme beam of the boat that counts, it is the distance between the center lines of each hull that is everything... For example, take an 8m overall beam on an Atlantic 57 vs an 8m overall beam on say a similar sized lagoon type of boat or similar, the distance between the hull center lines will be vastly different even though both boats have a similar overall beam, the A57 will have more static stability which allows her to be made light and with a powerful rig and still remain within stability limits. Worth keeping in mind when checking out the latest crop of smaller cats with big king size walkaround bunks in the aft hulls...

[Polux]

Originally Posted by Doe818

Probably also worth clarifying what " effective" beam actually is on catamarans when it comes to stability... It is not the overall or extreme beam of the boat that counts, it is the distance between the center lines of each hull that is everything... For example, take an 8m overall beam on an Atlantic 57 vs an 8m overall beam on say a similar sized lagoon type of boat or similar, the distance between the hull center lines will be vastly different even though both boats have a similar overall beam, the A57 will have more static stability which allows her to be made light and with a powerful rig and still remain within stability limits. Worth keeping in mind when checking out the latest crop of smaller cats with big king size walkaround bunks in the aft hulls...

Stability on a cat is not different than a mono in the way it is created. What counts is the boat CG, the boat CB and distance between them when the boat heels plus the weight of the boat. Giving the much bigger beam the arm (GZ: the horizontal distance between CG and CB) is much bigger at smaller angles of heel on a cat than on a monohull (well, it is always much bigger till the Max GZ, than it comes sharply down).

Increasing beam and lowering CG increases the GZ (arm). The third factor is weight that is multiplied by the arm to given RM.

That's why condo cats capsize less then sportive cats: The beam is not that different, they are heavier and because they don't intend to be sportive, they carry smaller rigs. The two factors combined contribute to a cat more difficult to capsize then a lighter one with a bigger rig. CG is also important but unless ballast is carried on the keels the difference would not be that much between a condo cat and a more sportive cat, unless we are talking really about a very sportive one with a small low central cabin or no central cabin at all, like the Sig 45.

[valhalla360]

Originally Posted by Doe818

Probably also worth clarifying what " effective" beam actually is on catamarans when it comes to stability... It is not the overall or extreme beam of the boat that counts, it is the distance between the center lines of each hull that is everything... For example, take an 8m overall beam on an Atlantic 57 vs an 8m overall beam on say a similar sized lagoon type of boat or similar, the distance between the hull center lines will be vastly different even though both boats have a similar overall beam, the A57 will have more static stability which allows her to be made light and with a powerful rig and still remain within stability limits. Worth keeping in mind when checking out the latest crop of smaller cats with big king size walkaround bunks in the aft hulls...

True to a degree but not a huge difference unless you go to extreme hull shapes. It's actually not the centerline of the hulls unless they are symetrical (most cruising are). It's the center of bouyancy which may not fall on the hull centerline if they use asymetrical hulls.

Also the extra weight of the cruising cat will typically counter any small advantage of extra effective beam that a lightweight performance boat will gains from pushing the underwater volume outboard (in terms of capsize resistance) Though of course the light weight performance boat will still outperform assuming it isn't loaded down, it is unlikely to be significantly more capsize resistant.

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.