Fore to aft rocker.Why is it needed?

[PAR]

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.

[PAR]

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.

[lewisboats]

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

Originally Posted by alan white

Read it again. You are correct only if all dimensions are doubled.
I said, "...a 48 ft boat having exactly the same beam and depth..."
In other words, the longer boat has thesame depth and beam as the shorter boat and the stability is doubled even when the LB ratio goes from 3:1 to 6:1.

[alan white]

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.

[George 2659]

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

Originally Posted by PAR

Yes, in short that's correct Ben2go, an 8' beam 24' boat will be a plow all right. 6' of beam will be a dramatic improvement, but still not great efficiency. Anything less then 6' will progressively shown increasingly more efficiency gains, the narrower you get.

Again, length is the only way to get more interior volume and still retain a high level efficiency.

Shown is Floom (RYD-29.6a) one of my riverboat designs. The first (lefthand) version is 7' beam on 33' length, making for a boat with nearly 5:1 beam/length ratio. It's very efficient considering what it is. Her sister (RYD-29.6c) is her well fed sibling and 9' of beam. This extra beam does offer a lot more interior volume, but at a huge cost in efficiency. Her beam/length ratio is 3.6:1 and more in keeping with modern trends. Her dry weight alone nearly doubles with this extra beam, you just imagine how much more power it takes to push her.

[PAR]

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

[Easy Rider]

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

[PAR]

The rocker controls the speed range of these boats.

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.

[Easy Rider]

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