40 foot displacement hull cruising at 15 knots -- Impossible?

[ranger58sb]

Originally Posted by valhalla360

It's a myth that you can't generate big HP out of gas engines.

The result is there has been almost no development into gas engines in excess of around 350-400hp.

Yep, don't think anyone said it couldn't be done (or at least I didn't mean to imply that)...

Just that big, new, modern gas engine availablity (discounting Merlins and the big Packard versions and so forth...) tails off at a point somewhere around 502 cubic inches or so (IIRC)...

-Chris

[ALAIN97133]

Originally Posted by jsc7

I have read that using a "slender" design it is possible to exceed the normal hull speed limitation (https://en.wikipedia.org/wiki/Hull_speed), but there are never any specifics or formulas that I have seen that tell by how much that speed can be exceeded and under what conditions. If I have a design goal of a 40 foot displacement hull cruising at 15 knots is that impossible? For example, if we imagine a 40-foot boat with an 8-foot beam weighing 12,000 pounds, wave-piercing prow and a 300 HP gas engine are we getting there, or is it just not going to happen?

Hi! Have a look at the 60 foot IMOCA architecture. They're real fast They keep 30 knots over several hours & 20 knots over several days. If your cruise program is a downwind 'round the world cruise along the trade winds belt, a light displacement 40 footer with fine entries, wide stern & lifting keel/centerboard (Foils?) would be a good bet: Downwind, with twin rudders, keel or centerboard raised, you could keep your spinnaker up when most people wouldn't !
Hugo Boss with regular centerboards since replaced with lifting foils as on Gitana
IMOCA | XS Sailing
Cheers !

[Adelie]

Originally Posted by ALAIN97133

Hi! Have a look at the 60 foot IMOCA architecture. They're real fast They keep 30 knots over several hours & 20 knots over several days. If your cruise program is a downwind 'round the world cruise along the trade winds belt, a light displacement 40 footer with fine entries, wide stern & lifting keel/centerboard (Foils?) would be a good bet: Downwind, with twin rudders, keel or centerboard raised, you could keep your spinnaker up when most people wouldn't !
Hugo Boss with regular centerboards since replaced with lifting foils as on Gitana
IMOCA | XS Sailing
Cheers !

OP is talking about power vessels not sailboats.

[ALAIN97133]

Originally Posted by Adelie

OP is talking about power vessels not sailboats.

I know, the warming of our planet is a communist plot ! We need more power boats
Also: To reach/keep 20 knots on a power boat, you need a big engine/bank account while to reach/keep 20 knots on a sailboat you also need a big brain... & a big bank account

[valhalla360]

Originally Posted by ALAIN97133

Hi! Have a look at the 60 foot IMOCA architecture. They're real fast They keep 30 knots over several hours & 20 knots over several days. If your cruise program is a downwind 'round the world cruise along the trade winds belt, a light displacement 40 footer with fine entries, wide stern & lifting keel/centerboard (Foils?) would be a good bet: Downwind, with twin rudders, keel or centerboard raised, you could keep your spinnaker up when most people wouldn't !
Hugo Boss with regular centerboards since replaced with lifting foils as on Gitana
IMOCA | XS Sailing
Cheers !

And those aren't displacement vessels.

I used to have a tunnel hull inflatable with a 40hp outboard that I clocked at just over 60mph but that's not a 40ft displacement hull.

[sailorcherry]

Sure it's possible, not 15 but we have done 13 (not offshore surfing)
Hooked is 42.5' loa, 13.25' b, 7.4'd and 18000lbs. Tall three spreader mast. Held 13kts steady crossing the SF bay small bay swells on the beam, beam reach full white canvas. Again 13.5kts double reefed main and cruising spinnaker along the city front. Sistership Scarlet O'Hara reported over 17 kts offshore racing with full crew. Other S43s report 14-16 in bluewater.