# When does a monohull become a multihull??

Discussion in 'Boat Design' started by Abby cat, Jan 1, 2017.

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### TANSLSenior Member

Mr Efficiency, what I mean is that a pear can not be transformed into an apple. What do you think if I ask: when a pear turns into an apple ?.
If you define well what is a pear and, on the other hand, what is an apple, the answer is obvious : never. If you do not do it, the question does not make sense.
So, what is a monohull?, what is a multihull?. See Ad Hoc and Ike answers, they can help in this deep scientific discussion.

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### Abby catJunior Member

TANSL
yea but you can blur the lines between if it is a mono or a multi depending on what the definition is.
If you are using the definition of single footprint while the boat is level you could lower the deck between the hulls of a cat until it just pierces the water when it is sitting level at stationary, but when dynamic lift and heeling moments come into the equation, there is two footprints therefore can be both??

Thanks

Nick

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### TANSLSenior Member

I think we could talk about a multihull working like a mono, or quite the opposite, I do not care much.
Cheers.

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### CT249Senior Member

The traditional answer, as others have already pointed out, is that a monohull has no "air gap" when at rest or upright.

But it's an odd question to ask in some ways. It's a bit like asking how to enter a Formula One car into a famous motorcycle race by finding a way around the definition of "motorcycle", or like using rollerskates to win a footrace marathon because you wear some cunning shoes that "just happen" to have wheel-like devices on them instead of tread. My old club has a definition of "youth" that could be stretched to allow 30 year olds to sail in its youth regatta - would you be happy if Glen Ashby used that as justification to enter and beat the kids?

If your way worked then all that would happen is that Notices of Race would become longer, more complex and full of tighter definitions. Volunteers would have to work longer and harder at drafting them. Sailors would have to work longer and harder at reading them. Races could be decided in the courts instead of on the water. Does that sound good to you?

Wouldn't it be better to admit that the Hobart is a monohull race just as the world motorcycling championships is a motorbike race, just as the Texel cat race is a race for cats and not for kitefoilers, and just like the singlehanded transatlantic race is just for singlehanded boats? If you would be unhappy with someone sailing with a full crew in the OSTAR because there was a loophole in the NoR, sailing a kitefoiler in a beachcat event or sailing as an adult in a junior event, why would you be happy with a multi in the Hobart?

It's odd that some multi sailors don't accept that mono sailors have the right to their own events, just as every other form of sporting equipment has its own events, and just as people who do many other forms of recreation have events just for specific equipment. The claims that mono sailors discriminate against multis are incorrect - the mono sailors are being discriminated against by those who claim that they, alone of perhaps all sportspeople, cannot run events just for certain types of gear.

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### Squidly-DiddlySenior Member

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### CT249Senior Member

The traditional answer, as others have already pointed out, is that a monohull has no "air gap" when at rest or upright.

But it's an odd question to ask in some ways. It's a bit like asking how to enter a Formula One car into a famous motorcycle race by finding a way around the definition of "motorcycle", or like using rollerskates to win a footrace marathon because you wear some cunning shoes that "just happen" to have wheel-like devices on them instead of tread. My old club has a definition of "youth" that could be stretched to allow 30 year olds to sail in its youth regatta - would you be happy if Glen Ashby used that as justification to enter and beat the kids?

If your way worked then all that would happen is that Notices of Race would become longer, more complex and full of tighter definitions. Volunteers would have to work longer and harder at drafting them. Sailors would have to work longer and harder at reading them. Races could be decided in the courts instead of on the water. Does that sound good to you?

Wouldn't it be better to admit that the Hobart is a monohull race just as the world motorcycling championships is a motorbike race, just as the Texel cat race is a race for cats and not for kitefoilers, and just like the singlehanded transatlantic race is just for singlehanded boats? If you would be unhappy with someone sailing with a full crew in the OSTAR because there was a loophole in the NoR, or sailing a kitefoiler in a beachcat event, why would you be happy with a multi in the Hobart?

It's odd that some multi sailors don't accept that mono sailors have the right to their own events, just as every other form of sporting equipment has its own events, and just as people who do many other forms of recreation have events just for specific equipment. The claims that mono sailors discriminate against multis are incorrect - the mono sailors are being discriminated against by those who claim that they, alone of perhaps all sportspeople, cannot run events just for certain types of gear.

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### Mr EfficiencySenior Member

Well, it is not hard to find planing cats that have zero tunnel clearance at rest, therefore have one continous "footprint". They may not have been designed that way, but through weight increases finish up that way. However, with increasing speed the boat can rise sufficiently that the tunnel is no longer in contact with solid water, though still maybe aerated water and spray

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### Angéliqueaka Angel (only by name)

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Some pics or videos or drawings of it ? - Otherwise we might get stuck in just theorie . .

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### upchurchmrSenior Member

This is a waste of time, by someone with an agenda.
Does anyone else actually care?

I liked CT249's discussion, but he is being too nice.

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### Angéliqueaka Angel (only by name)

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### Abby catJunior Member

if no-one cared there would be no responses.

"Someone with an agenda."??

I was just curious and thought I would pose a question.

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### Angéliqueaka Angel (only by name)

Apparently you missed the word actually and the ? as it was a question by Upchurchmr to all posters . . . :idea:

Seems to me you were just curious which the answers might be to your question of which yourself thought the answer was ridiculous !

(at least to me that's what it looks like you mean by ‘‘rediculus’’ in the pic's URL) - (Note: I don't mind the 2 typos in ‘‘rediculus’’)

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### rxcompositeSenior Member

If I build the hull with corrugated GI sheet, will it be a super super multihull?

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### Easy RiderSenior Member

I've said "If a duck can swim all around the hulls it's a multihul."

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### Angéliqueaka Angel (only by name)

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They're quick and easy to build, but as Rx says, are those Monos or Super Super Multihulls ? . .

Edit: added P.S. - It's as E.R. says, a duck can't swim all around all these many many "hulls", so the boats are not Super Super Multihulls . .

Here some more advanced plans for a one sheet steel boat . . :idea:

Though not adapted to corrugated GI sheet yet, as this would add some wetted surface, as well as some build difficulties . .

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