Stern shapes on displacement motor-cruisers

[fcfc]

For mackid068
You are obviously confusing superstructure design and hull design )
See :
http://www.beneteaupower.com/swift/newphotos/14.html
http://www.stadtdesign.com/images/photos/stline-w.jpg

Guess which one has a hull tank optimized for displacement speed, single 75 hp engine and ocean ulimited capability (CE category A). The other is a (semi)planning hull with twin 370 hp, and CE category B (Vawes under 13 ft).

A clue:
http://www.swifttrawler.com/newphotos/16.html
http://www.stadtdesign.com/images/photos/P431_stand.jpg

[mackid068]

Beneteau is the faster (semi-planing) one. It can also go up to 25 kts. I think. FCFC you're probably (DEFINATELY) right.

[fcfc]

Back to the initial post:

Displacement speed is not precise enough, because wether you are at .9, 1.1, or 1.3 sqrt(lwl), you would need a different stern for max efficiency.

The faster (relatively speaking, we are still in displacement mode) the boat is, the further should be LCB and LCF. and higher the Cp.
So as the speed of best efficiency increase, the stern should be fuller.

More. at 1.3, having an immersed transom at 0 speed (area about 0 - 5 of max section) and cleared from water at speed (not too deep) is beneficial.

Now, if you should have straight, concave or convex (S form) buttocks is another matter.

[artemis]

Check out the designs of William Atkin - http://www.atkinboatplans.com - in his Seabright Skiff designs (or any SeaBright Skiff designs for that matter.

[D'ARTOIS]

fcfc - you are talking gibberish - the stadtline is and has never invented for use at open sea - you are comparing a DC3 with a Superconny....

[fcfc]

It is truly possible that the open ocean was not the primary market for the stadline. But according to the architect web site, this boat carries a category A CE certification, which is labelled as "Unlimited ocean".

The goal of the message was only to point that superstructure design/style implies nothing for the hull design. (more or less euro look on a displacement hull, and trawler style superstructures on a planning hull).

[D'ARTOIS]

You overestimate the CE certification's value too much. The Stadtline is a boat I know very well and this boat is not fit to cruise open sea if no changes are made to the design and certain safety measurements are undertaken. That it does fit some (theoretical) requirements of the certification issue does not mean that this boat is physically capable to fare in open sea without some drastic changes. The boat was never designed with long seapassages in mind - the IJsselmeer and Waddenzee, yes, but only under normal weather conditions. This is not one of he best designs from VdS and Partners, although the looks are not too bad.