Yacht Motoring Speeds ??

Thanks the pics, very interesting - does higher motoring speeds change the underwater hull form or is it still a sailing hull that motors quickly?

 

More points for Fanie, somebody!

 

Its a bit hard to tell from the screen shots, but the underneath hull form is optimised for sailing, except at the stern, where a V shape encourages planing under power, or downwind.

The other feature that aids power performance is the pronounced lifting strakes on the bottom chine.

These would only affect sailing at larger angles of heel, and since these types of hull are optimised for about 6 degrees maximum heel, the lifting strakes would only affect sailing in heavy weather. As there would be plenty of pressure in heavy weather, the strakes should not compromise sailing performance significantly (might even help)


Fanie - its not just the speed of getting out - its the speed of getting back.
a) To be first in line at the ramp
b) To get rid of rebellious, sick, injured, scared or inept crew
c) To get out of the way of the big squall line coming over the horizon or pending nightfall (its dark and scary)


but it means you can power to the peacefull far way places that would take all day to get to at 10 knots, and you can catch that &^$^)&^ steel 60 footer that failed to give way, and throw eggs at the skipper.

 

The Kirkena picture shows it throwing a disconcertingly big bow disturbance. I'd bet that it will take a lot of horsepower to put up that kind of fuss. Going to piss off any other boaters in the vicinity too. Looks like something one might observe while watching an underway navy destroyer.

 

I've seen you mention this a number of times.

How do you plan to sail upwind in anything over 5 knots of breeze with only 6 degrees of maximum heel? Ditto close and beam reaching?

 

I am not sure what you are getting at here. Optimum heel is not maximum heel.

With say, Lasers, Tasers and Catamarans, with similar small heel optimum angles, you downsize sail are as much as possible when required, to avoid unnecessary heel. When there is plenty of pressure, you sail accordingly.

 

Sorry fro my misunderstanding, but you said maximum heel:

I don't know how you downsize sail on your Laser or beach cat, but I don't know of any way to do it efficiently if the wind comes up.

You say "sail accordingly". I guess that was my original question. What is "sailing accordingly" that will limit the heel to 6 degrees?

 

Hmm, I can see where the confusion came about

"optimised for about 6 degrees maximum heel." is really bad english. I was trying to convey that over 6 degrees, you are sailing at a non optimum angle. I sure dont know any way of limiting heel to 6 degrees in heavy weather.

Allowing for less than perfect prose in a sailing forum, I reckon you meant "I know how you downsize sail on your Laser or beach cat, but I don't know of any way to do it efficiently if the wind comes up.?"

Because you can wind the sail around the Laser mast, or put a smaller one one on a cat - but once you are out there, thats not easy to do.

So, when I say "sail accordingly" I mean that you dont give a stuff about optimum heel angles, you just vang off and watch out for the gusts like any other yacht in rough weather.

The righting tables on the design I posted show several hundred pounds of bouyancy at 90 degrees with water ballast, so even in knockdowns, you expect to bounce right up.

Aint the written word wonderfull ?