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Hello, everyone!

I'm new in general. I have been looking around and found lots saying about stability and speeds but nothing about comparing displacements. So how do the hull designs compare in terms of:
-dead weight to full load weight with same total loading capacity and same power or engine.

If you can link to some papers, that would be great also.
Sorry, if this has been asked before.
 

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I see but isn't structural mass still a good measure?

I saw multihulls are said to capsize forward, as I understand it this is because of the sail and mast. This is rather a mechanical problem and design of a specific ship. For example if the mast is much taller than ship length than it will capsize in the direction of the wind. A solution would be making the ship longer or maybe devide the center hull into forward and aft hulls (diamond).

I wonder are there actually any ships in diamond configuration?
 

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Well, I read that post, but my question was for a general understanding of the matter.

Yes, a heavier boat is often more stable...but if the weight is added in the wrong place, then it can make the boat far less stable.
I understand but it's always difficult to do it right in practice.
Finding the center of gravity of your boat... Can I assume it's usually designed to be where the mast is or somewhere along it?

As for a multihull with four hulls in a diamond configuration... doesn't make much sense at all. First, the load carrying capacity would be much lower
Well, if the hulls are used as feet for deck structures like the SWATH....
So they all could be of the same design, and with the big deck structure it's easier to have them rigidly fixed. Virtually a big ship on four feets. I guess it would be very big for better deck to hull structure ratios, and many tension structures.

It is pretty easy to badly engineer a multihull... look at the "Tin Can" trimaran.
Yeah, concentrating the forces you want to reduce in one point is counter productive. :laugher

Finally, I'd point out that many multihull capsizes are actually not capsizes per se but caused by the boat pitchpoling after stuffing the bows into the back of a wave. This is one reason it is generally wise to leave a multihull a bit aft-heavy.
I also read in the wikipedia about that but somehow I don't quite get that bit.
Is there a visual explanation around?

However, unlike a monohull, a multihull is generally pretty light and doesn't have the inertia to resist accelerating during a gust, so it is a huge disadvantage to have the slightly lower amount of sail area up.
This is similar to vessels being to fast and lift off, too. I would imaging adding controlable hydrofoilers/wings to increase downward force for increased resistance in bad sea may help.
Or maybe watertaking bags underwater for increased mass but with no boyancy (or the reverse...maybe not). Don't mind my random ideas.

Cruising sized multihulls also have enormous initial stability... an order of magnitude greater than that of a similarly sized monohull. This tends to damp out any but the greatest movement.
How about underwater control surface. (Let's ignore port draft restrictions)
Hmm, reading all this I have the impression that ship technology isn't as advanced as aeronautics yet. But then aeronautics get lots of development money.

Btw. thanks for all the insights.
 

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I see, thanks.

It seem someone has already registrated a patent on something similar:
International patent WO 94/20359
It's a trimaran with spaces midship of the hulls allowing waves to go through, hence, decreasing wave pressure to the hull (I think).

On another point, it's been said that multihulls have bad manoeuvering.
Is there any ship using a rudder at the keel to improve that?
(similar to canards for aircrafts; future ship will probably use propulsors, though)
Also would an arrow arrangement for a trimaran improve manoeuverabiliy?
 

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An arrow configuration for a trimaran would be a disaster.

On many trimarans, the forward buoyancy is really supplied by the amas, not the main hull.
I didn't realize that. I guess it's a trade off for the necessary bow design of multihulls.

Also, at anchor, my trimaran moves with the wind, not the current, so at places like St. Augustine, as the other boats orient north-south, I found that I was oriented east-west, and other boaters do not anticipate this when anchoring nearby.
I see. Yeah, relatively more boyancy makes it too light for the elements.
I would be nice to have it transform to a monohull. :lol:

Anyway, now I know and understand lots more thanks to all your explanations and illustrations. I'm satisfied for now. Thanks a lot.
 

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I have one questions regarding sails. Since I don't think it's enough to start a new thread and may give answer to multihull problems I decided to just post here.

Is there a difference in wind force when a sail is loose and has more 'volume' compared to a straight one, but with same cross area?
 
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