[xamdawson7]

hi all,

imagine this:

• A mono hull boat is 62meters long;

• it's devided into 2 sections from point 0: stern is at 43m forward, and bow is at 19m aft.

• at 0 it has a maximum beam of 30m (from strbrd to port), to then reach 0 at stern and bow.

let's exclude the superstructure.... what stability issues would it encounter (many i am sure), but what exactly? how do you counter them? would you need a deeper draft?

thanks!

[SharkyFHB]

Would this vessel need to be concerned with parametric rolling?

http://www.lr.org/NR/rdonlyres/1D750.../Parametric.pd

You can google the topic for more info.. DNV, the class of our ships, has held seminars on the topic..
Believe it is a fairly new subject now being further understood and researched.

Sharky

[xamdawson7]

Well that was the main idea, but what about the smoothness of the ride?

Would such a large beam for a mono hull cause a lot of oscillations at beam extemities?

[KCook]

I'm haven't studied displacement hull forms much. But for hulls that run higher speeds it's typical practice to have the maximum beam back in the rear half of the hull. Your setup sounds like it's counter to that? Intuition tells me putting the maximum beam near the bow will result in an odd, or uncomfortable, motion in a seaway. But that is only intuition speaking, nothing more.

Whole different speed realm! But hydroplane race boats do have their sponsons in front. So max beam is forward. They get away with that, but the dynamics are very different for their speeds and water conditions.

Kelly Cook

[CODOG]

Originally Posted by xamdawson7

hi all, imagine this:

• it's devided into 2 sections from point 0: stern is at 43m forward, and bow is at 19m aft.

Are we talking the right way round here ? Bow aft, stern fwd etc ?. What you are describing is an egg shape in plan view. It would help us to help you by understanding which way the craft would actually be travelling Also, is this beam at waterline ? I for one am intrigued by such a vessel.

[xamdawson7]

yes, Bow aft, stern fwd. the vessel therfore will move with the maximum beam closer to the aft side. it is easier if you plot it on a napkin.

The hull is basically 2 triangles put together, joining opposite to each other.
So one triangle facing west with hight 19 and base 30. The other triangle facing east with hight 43 and base 30. Both starting at the same point.

whether it remains pointy is up to you. the idea is a little more complex, then the diamond shape described. But the diamond shape will do for now.

the shape is only in plane view. once you reach the waterline you can do whatever you want with it, to get it as hydrodynamically stable and fuel efficient as possible, while still keeping it in perfect equilibrium for the beam extremities.

[KCook]

the shape is only in plane view. once you reach the waterline you can do whatever you want with it, to get it as hydrodynamically stable and fuel efficient as possible

That pretty well throws the door open. For example, US aircraft carriers have flight decks with a very different plan shape from their waterline shape.

Kelly

[CODOG]

Originally Posted by xamdawson7

yes, Bow aft, stern fwd. the vessel therfore will move with the maximum beam closer to the aft side. it is easier if you plot it on a napkin

My brain hurts

[AMG]

Originally Posted by CODOG

My brain hurts

And I avoided to take it in...

[xamdawson7]

I'm glad to hear that!

If you knew the particulars of it all it would be a continuos head rush!
I thank and appreciate all your helpful comments and suggestions.

[CODOG]

Well, I thought about it, and although I'm still bemused about a craft that is designed to move in reverse, I can get my head around your kite / egg shaped 2:1 length / beam ratio'ed deck plan on a monohull....if you can allow out-riggers.
I can imagine a fairly conventional displacement hull capped with your kite shaped deck, but with the outer points of the kite folded down into the water to form the outriggers. Think paper plane with the wing tips folded downward. The upper hull topsides would be heavily rolled over outwards to blend into the underside of the 'kite', and the outer tips (now outriggers) would be similarly blended and shaped to provide bouyancy during lateral roll. Its arguable that a narrower (say 6:1 length / beam ratio) main hull can support your undescribed superstructure on its own, but the outriggers would assist stability in heavy seas with minimal drag.
I still think it would go better with the bow (pointy bit) fwd though

[KCook]

Err .... CODOG .... didn't you just describe a trimaran?

[CODOG]

Originally Posted by KCook

Err .... CODOG .... didn't you just describe a trimaran?

If hes allowed the bow at the stern and the stern at the bow, surely I'm allowed a three pointed monohull ?

[xamdawson7]

i always meant .... bow, fwd ... stern, aft..... (i'm such an idiot, i got caught in the moment)

i am so so, so, so sorry... must have been a brain fart, when i wrote the opposite!

ps: so that means your not allowed a trimaran any more

[KCook]

Originally Posted by CODOG

If hes allowed the bow at the stern and the stern at the bow, surely I'm allowed a three pointed monohull ?

You mean Wally hasn't already patented the three pointed monohull?