# length/beam ratio of around 20

Discussion in 'Multihulls' started by PetterM, Apr 21, 2015.

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### hump101Senior Member

In that graph, is the monohull form the same displacement as the catamaran form, or half the catamaran displacement?

Alternatively, is that the "per hull" residuary resistance, cat and mono alike?

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### Gary BaigentSenior Member

Actually I was thinking about square and oversquare modern trimarans, and trimaran foilers. But for catamarans (moden - not some narrow beast from the 1950s) with 50/50, 60/40 or more beam length, FLYING or partially flying the windward hull skimming the surface - what is that Ad Hoc? A monohull without the ballast? Same applies to trimaran and especially tri foilers.

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Well, here is the data and you can decide

Aaahh..i see. So a hydrofoil, for example, we just ignore the hull that it is supporting and say the "boat" is just a set of foils and nothing else as the hull is not in the water. Hey great stuff...why didn't i think of that!!

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### hump101Senior Member

That data is the characteristics of a single hull, not of how displacement relates to this for a catamaran form, so doesn't answer the question.

It is common practice to run the catamaran hulls such that each hull is at the same waterline as the monohull form, then to compare the resistance of a single catamaran hull to the single monohull. This provides a direct comparison between the frictional and residual resistance of a single hull form in mono and catamaran arrangements, but ignores the fact that the catamaran is displacing twice as much as the monohull. I am interested to know what your data represents.

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### Gary BaigentSenior Member

Why didn't you? Because Ad Hoc, you are you.
Still haven't answered what a conventional catamaran with no lifting foils, flying a hull is - meaning one hull out of the water or skimming surface and one immersed leewward hull. Kind of sounds like a monohull configuration in that position to me. And any wave interference from the leeward hull? Yeah, right - as we say in NZ.

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### Mr EfficiencySenior Member

The only data I am interested in is the 'residual' resistance of two given hulls as a catamaran at various spacings, compared to just one hull on its own, alone, all 3 hulls being identical.

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Well, do you understand what the Length displacement ratio, or in the table L/Vol^1/3 means?

You clearly don't understand irony either!

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### Mr EfficiencySenior Member

Situation normal here !

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### Gary BaigentSenior Member

Oh, the ponderous attempt at subtle irony.
Or do you only know about power boats?

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So if it is on one hull, you mean it is a monohull?...oh wait...If it is not a monohull it is then...er...um..a catamaran? Hmmm..pesky questions eh?!!

I think you don't understand your own question. (Nothing new there from previous debates).

That's the trouble with trying to sound important and knowledgeable on technical matters....flying hulls...one hull...etc....the science doesn't change because you elect to use different words.

In general yes. But hydromechanics doesn't differentiate between power or sail. It is 3 dimensional hull shape moving through the water. That's it! Endless pontification wont change the laws of physics.

I realise this doesn't help you as you can only debate with verbose woolly grandiose sounding words rather than actual facts. But each to their own.

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### Mr EfficiencySenior Member

Has such a warm fuzzy feel to it, this thread.

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Agreed. The usual pointless trolling as always by the usual suspects. But that'll go over your head again, like the last one.

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### Mr EfficiencySenior Member

It's like The Love Boat here, imo

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### Gary BaigentSenior Member

"Indeed."

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### redreubenredreuben

Made popcorn, opening beer and sitting comfortably.

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