how much can a catamaran carry?

[georgebanker]

is there any general rule? ie. 10% of displacement, before performance suffers?

[Jeff_H]

Depends on the cat. The lower performance to begin with the more weight that can be tollerated as a percentage of boat weight, but the greater the increase of capsize in a gust because cats partially get their stability by dispursing the force of the wind through accelleration.

Jeff

[sailphoto]

I am not a cat expert but have been told by cat owner whom I helped load his boat that he carries almost all provisions as far out on the beams as possible so that the weight acts as windward ballast helping to translate the weight into "ballast" and thereby aiding acceleration mentioned by jeff_H. Mathematically it makes sense to me.

[sailingdog]

Originally Posted by sailphoto

I am not a cat expert but have been told by cat owner whom I helped load his boat that he carries almost all provisions as far out on the beams as possible so that the weight acts as windward ballast helping to translate the weight into "ballast" and thereby aiding acceleration mentioned by jeff_H. Mathematically it makes sense to me.

I doubt that really has much effect, as the weight put towards the end of the beam in the leeward hull would probably counteract the weight in the windward hull. It would also seem to me, that by putting the weight out to the extreme beam ends, you'll tend to increase the lateral pitching moment of the boat—much as adding weight to the bow or stern of a monohull increase the tendency to hobbyhorse...but I'm not a naval architect, so I can say for sure. If this is true, that is probably a really bad idea.

That said, the amount of weight that will start to detrimentally effect a catamaran's performance has a lot to do with the design and size of the catamaran. An ultra-lightweight racing catamaran will be more quickly affected than a heavy cruising catamaran.

As a general rule, most cruising catamarans have far more stowage space than can reasonably used before the boat's performance starts to suffer.

[KeelHaulin]

Originally Posted by sailingdog

I doubt that really has much effect, as the weight put towards the end of the beam in the leeward hull would probably counteract the weight in the windward hull. It would also seem to me, that by putting the weight out to the extreme beam ends, you'll tend to increase the lateral pitching moment of the boat—much as adding weight to the bow or stern of a monohull increase the tendency to hobbyhorse...but I'm not a naval architect, so I can say for sure. If this is true, that is probably a really bad idea.

Actually, putting weight on the outer hulls of a cat or tri should tend to stabilize the roll and improve stability. I would say this is so because the furhter you move mass from the CG horizontally the higher the moment of inertia becomes. In the case of a Cat/Tri I don't think there would be as much of a 'hobbyhorse' effect because it is a different situation than a monohul pitching fore/aft. The hobbyhorse of a monohull is due to the reduced bouyancy in the extreme ends of the boat and this is not the case with a Cat/Tri. On the downside you might tend to increase the loads on the structure of a Tri if too much weight is on the outer hulls and not in the center section; but I think you are better off carrying weight in the hull sections of a Cat as that is where all of the bouyant force is located anyway. I'm sure you could calculate out an ideal loading for each boat; but it would take some time/calcs to find the correct distribution.

JMHO/HTH...
Everything I have read says that while multihulls have much more stowage space, their windward performance drops off rapidly if you are carrying too much gear/provisions.