Fore to aft rocker.Why is it needed?

It's more about weight and shapes permisable. The ratios are handy ways of comparing things.

You'll be hard pressed to provide standing headroom in a 24' LWL boat, offer elbow room and reasonable sailing qualities, all in a shoal draft boat that length. I'd strongly consider some other for of rig then a junk if sailing qualities are desired.

These are the lines to RYD-29.6 and it should be clear why she's efficient. She meets you shoal draft and standing headroom requirements, but clearly has way to much windage for even considering sail power.

 

This is a 24' power cruiser of mine. It's got 8' of beam and typical proportions for what she is. It's a full plane hull form and runs to 37 knots on 175 HP and has a dry hull weight of 3,500 pounds.

I have a larger version of this cruiser theme (28') that is a full displacement mode cruiser. It needs only 30 HP to reach top speed and sips fuel like a bird drinks water. Both have standing headroom, but wouldn't be considered for anything other then a steadying sail.

 

My apologies...you are correct in that I missed the doubling factor over all...though I still think you gain more than double...just can't prove it

 

It's interesting that you don't add stability by doubling each of the three parameters. Like doubling height, which would actually make a short boat LESS stable. So it seems you might be right, in that the other two parameters (length and width) more than compensate, or at least doubling beam has more effect that just doubling stability.

 

I was trying to reply to your posting on the Floom Design (RYD-29.6), but seem to have pushed a wrong button. Hope this reaches you anyway: Very fine looking ships indeed! But is there any more information on these designs? Want to build a solar-driven boat that would function as a 'mother ship' for the various sailing boats we're using in the family.

The roof of these boats would give space for solar panels, and the hulls look a lot prettier than the Mark V39 I was considering or the Mundoo3. Did not really understand the side of the cabin: is there space to walk on the outside, or is that rail just sitting there?

Best,

George, Uppsala Sweden

 

Yes George, I received your email, will respond tomorrow . . .

 

ben2go,

http://www.atkinboatplans.com/
Look at "Wader" for disp speeds and "Marcia" for 15 knots. The rocker controls the speed range of these boats.

Easy Rider

 

Actually the rocker on Marcia is for steering and the hook controls the speed on Marcia. With Wader, the rocker is for a "clean exit", controls displaced volume and again for steering.

 

PAR,

I've been looking at Marcia for a long time and never noticed the hook. Perhaps you have bigger drawings of her. I had to zoom way in w my 27" computer and turn it sideways to see the hook. The hook would even make it more likely she'd do well w OB power but I'd want her as an open skiff and I'd loose a lot of weight fwd without the cabin so a 400# OB aft and the loss of cabin fwd may be too much change for the design. I could put fuel fwd but I'd definitely not put the helm fwd on a 15 knot flat bottomed boat. And w Wader's full disp rocker my 60hp OB would be way too much power. Oh well ....too busy to build anything now anyway. Thank's for your observation PAR.

Easy Rider