Modern cats

[UpOnStands]

Originally Posted by arsenelupiga

hum.... there is around 3000 lagoons out there, probably half not in charter, many circling globe, and I heard of 2 capsizes when sailing/motoring.

relax. Most cats are sailed very conservatively and the number of capsizes is extremely small. From memory the designer was comparing light displacement to heavy displacement hulls in a general way.

[44'cruisingcat]

Originally Posted by arsenelupiga

hum.... there is around 3000 lagoons out there, probably half not in charter, many circling globe, and I heard of 2 capsizes when sailing/motoring. One delivery of L 380 in winter and the other with only mainsail up and motoring when caught in large gust between islands.

And then unknown number at moorings/berths in cyclones when gusts > 150 kn. That is when houses go flying...

Very few lagoons, Wharrams,Orams, Schionnings,leopards... you name it, ever capsize. If you eliminate racing from the equation, even less.

But for some reason you find certain invertebrates who've never owned a boat are fanatical about capsizes, and constantly try to whip up hysteria. I'd suggest it's driven by jealousy.

[UpOnStands]

Heresy!
Take 2 cases. You want to lift the left side of a complex structure (2 boxes joined by a bridgedeck).
Case 1: The structure pivots on the extreme outer edge of the right side box which is unpinned.
Case 2. The structure pivots on a bearing that passes through the center of the right side box.

Case 1 yields higher lift load than case 2.

Is a floating catamaran case 1 or case 2?
From the Marchaj figure it seems that he assumes its case 1.
The equation is RM = Gz*Disp*gravity.
The key sticking points are how to determine the center of gravity and what load is actually being lifted. Pinned or unpinned?
The basic shape of the stability curve remains the same (maybe, have not checked).
Over to the experts.

[PaulinOz]

Originally Posted by Polux

I give up. How can you be asking that after all those explanations and links regarding catamaran stability?

If you decrease the displacement you decrease stability YES
If you increase beam you increase stability YES
...........................
Why is this so dificult to understand for some?

Take a deep breath mate.

Quote myself :"By the way this is rhetorical, most of us already know the answer."

a rhetorical question: to make a statement rather than to elicit information.

Quote UpOnStands : "If you increase displacement by adding toys you decrease your performance. yes/no"

If your definition of a vessels performance is it's sailing speed the answer may be yes.

However if by performance you are referring to a given design being able to perform to its designed specification, as long as the addition of the toys is not overloading it, then my answer would be NO.

It will not effect the vessels designed performance.

By way of an example adding the following:
11kw generator, a 220kg dinghy & motor, 270 lt /hour water maker, 2 x extra freezers and another 800 amp/hours of battery capacity.Will not effect the designed performance of my condo cat, but if loaded onto a light weight racer will severely effect its ability to operate to it's designed performance.

Then again what one man calls toys maybe another's necessities of life.

That's an argument for another thread though.

[UpOnStands]

Originally Posted by PaulinOz

By way of an example adding the following:
11kw generator, a 220kg dinghy & motor, 270 lt /hour water maker, 2 x extra freezers and another 800 amp/hours of battery capacity.Will not effect the designed performance of my condo cat, but if loaded onto a light weight racer will severely effect its ability to operate to it's designed performance.

not sure it had "performance" to begin with
Grace, and space, but down on pace.

[Training Wheels]

Originally Posted by Polux

I give up. How can you be asking that after all those explanations and links regarding catamaran stability?

If you decrease the displacement you decrease stability YES

If you increase beam you increase stability YES

Today performance cats and condo cats have about the same beam. The Lagoon 450 has even more than an Outremer 45 and it is not efficient to increase more the beam.

After a given beam ratio, on a given cat, the only way to increase stability is to add displacement.

The Lagoon 450 has almost the double of the displacement than the Outremer 45 with a smaller beam therefore the Outremer 45 has about half the stability of a Lagoon 450.

On a cat RM (righting moment) = D (Displacement)X B/2 being the beam measured at the hull's center line.

Stability index that take into consideration the stability in proportion with sail area don't take into account that the boats can be reefed or that in extreme situations can be sailed in bare poles.

Even if considering the stability index, considering full sail, performance cats are easier to capsize due to a bigger SA/D. As I have showed the beams of modern performance cats are not bigger than the ones of condocats.

That is the reason why a same sized condo cat is much more dificult to capsize than a performance cat cruiser.

That is the reason why on the last year all big cruising cats capsized by gusts are performance cats and also the reason why during the same period o condo cats where capsized by gusts.

Why is this so dificult to understand for some?

Also, your missing the point on "beam". Beam in these calculations is the centerline beam of the hulls, not the ultimate beam. Performance cats have much narrower hulls, condomarans much wider hulls.
Also, you need to do some refreshing on your algebra.

[sailjumanji]

Originally Posted by Pizzazz

Thus, if you load up a light catamaran it will be more stable (at least initially, until it flips, then it would be even more stable .

Ok, it's a cat thread. These always migrate to some non-cat owners claim that cats flip, or can't sail upwind, or whatever. But of course "flipped stable" is better in a survival situation than sunk sitting on bottom (mono).

But regarding your statement, my issue with the whole "heavier is more stable", is that my experience is that a light boat tends to accelerate when hit with a gust, which moves the apparent wind and has the effect of unloading the sails somewhat. The tipping effort is turned into speed. Was the same for the Corsair 28 that we raced a lot, and our Seawind that has done a lot of bay and offshore races as well (in some pretty gnarly conditions, and we've never flown a hull on it, but typically push pretty hard and have a very good race record.)

Now if you load up the same cat with weight, then you reduce the acceleration aspect - and associated unloading. Static conditions, yeah, I'll agree with you that adding weight to the hulls would reduce the tipping moment. (Which is why I fill up my water tank when expecting a hurricane.) But if a boat is sailing, then conditions aren't static. So I think you are tending to overstate the stability advantage of the heavier boat.

[PaulinOz]

Originally Posted by UpOnStands

not sure it had "performance" to begin with
Grace, and space, but down on pace.

Lots of Food and Beer, without much fear.

[UpOnStands]

Originally Posted by Polux

After a given beam ratio, on a given cat, the only way to increase stability is to add displacement.
Why is this so dificult to understand for some?

How about a little rewrite to make understanding easier.
"Assuming that the beam of a built catamaran cannot be increased, the only way to increase its design stability after launch is to increase its displacement."

[UpOnStands]

Originally Posted by PaulinOz

Lots of Food and Beer, without much fear.

Good one, why go sailing unless it makes you happy?

[Seaslug Caravan]

Originally Posted by 44'cruisingcat

Very few lagoons, Wharrams,Orams, Schionnings,leopards... you name it, ever capsize. If you eliminate racing from the equation, even less.

What do you consider as very few?

Let me remind you of some recent non racing capsize events.





[IMG]http://static-sailfeed.s3.amazonaws.com/wp-
content/uploads/2013/03/Queequeg.jpg[/IMG]



[IMG]http://media.graytvinc.com/images/690*388/missing+catamaran+050417.jpg[/IMG]

plenty more where they came from

We haven't mentioned Chris White or the multiple flips whilst swinging to a mooring in the recent storm events.

[UpOnStands]

Originally Posted by Seaslug Caravan

Let me remind you of some recent non racing capsize events.

Exactly how many of those were not due to poor seamanship?
As in, too much sail up for the conditions.
According to your philosophy, a 50 foot cat could fly no more than 10 square feet of sails (total) because we must expect that the captain is a fool, the deckhands untrained, and the boat will experience a 1 in 500 year hurricane.

[sailjumanji]

Originally Posted by UpOnStands

How about a little rewrite to make understanding easier.
"Assuming that the beam of a built catamaran cannot be increased, the only way to increase its design stability after launch is to increase its displacement."

Or you could reduce the sail area, or go to a square top mainsail design (that tends to blow off and depower in high wind, as per personal experience). And wouldn't reducing weight aloft also increase stability? So add swap-out to carbon fiber mast to the list.

[UpOnStands]

Originally Posted by sailjumanji

Or you could reduce the sail area, or go to a square top mainsail design (that tends to blow off and depower in high wind, as per personal experience). And wouldn't reducing weight aloft also increase stability? So add swap-out to carbon fiber mast to the list.

'Fraid not. Polux is (as far as I can make out) now talking about the design stability as expressed by the Marchaj graph. It ignores the sails and exactly how the overturning force is applied to the boat.
The Warram heuristic (I called it a kludge but its more properly a heuristic) also ignores factors like the use of CF masts, Dyneema rigging, etc etc.

[44'cruisingcat]

Originally Posted by Seaslug Caravan

What do you consider as very few?

Let me remind you of some recent non racing capsize events.





[IMG]http://static-sailfeed.s3.amazonaws.com/wp-
content/uploads/2013/03/Queequeg.jpg[/IMG]



[IMG]http://media.graytvinc.com/images/690*388/missing+catamaran+050417.jpg[/IMG]

plenty more where they came from

We haven't mentioned Chris White or the multiple flips whilst swinging to a mooring in the recent storm events.

A half dozen globally in the past several years.... that's few enough for me, if not for you. If you ever get a boat get a mono.