View Full Version : Design Review #233

07-30-2013, 03:07 PM
The Spirit of Tradition Yawl.......

I guess Maynard must be on holiday ;)....Someone should have asked some hard questions about this submission. I know Bob knows better but he gracefully skirted the questionable issues.

Yes, young designers are to be encouraged, but they also must be told when they get it wrong......And there is a bunch wrong here. First the lines, those weird aft sections are not only ugly looking, I doubt they make any sense hydrodynamicly (reducing CP rather than increasing it). The whole thing looks un-fair and un-fairable, not to mention un-buildable. Besides the skeg being structurally inadequate(or impossible to build adequately as drawn), the rudder is far too small (IMO). The main mast step looks totally inadequate, it needs to be longer and have more deeper floors under it to spread the loads.

Finally the machine screw connection between the clamp and the endgrain of the laminated transverse frame is no good. Under extreme stress that 3/8" screw will just split out the top of the frame....useless. She's a glued boat so you want glue area at this vital connection. A big laminated hanging knee lapped onto the side of the frame and a corresponding deck beam, bonded and bolted horizontally to both, and with athwart-ships bolts through the clamp, would be one solution. A knee block on the frame face (with bolts) lapped onto a deck beam is another possibility. At BKYD we used to fit what we called "tie-blocks" at this connection. They were laminated blocks of wood bolted and bonded to the frame head and the clamp, and usually bonded a plywood bulkhead as well. The important part is to lock the framehead to the clamp, so that it will not move.

Generally this is a nice looking if somewhat plain (for her size and cost) yacht. The designers just need to take a few more turns round the design spiral and address the sticky issues in more detail. Otherwise it's a great issue......

Tom Lathrop
08-02-2013, 08:16 AM

Not expecting to ever come in contact with such a boat, I just admired the aspect of it and passed on to other parts of the issue. Needed a magnifying glass to find the screws you mentioned and saw just below that some even smaller #10 by 2 1/2" screws which I would not expect to find in a structural position on a large yacht. The unfairness of the aft sections is not obvious but will take your word for it. The skeg does look small but then, the AC boats ride on things that are about the size of a good kitchen griddle these days.

Tom Lathrop

Ian McColgin
08-02-2013, 07:29 PM
I'm not in a position to address the construction concerns TR raises, though one would not expect these designers to be massivly wrong.

I think the design issues he mentions were indeed addressed in the article, but perhaps more gently, as:

"It's be interesting to see a diagonal that passes through the turn of the bilge."


"I think it's harder to engineer a skeg that will actually lend meaningful support and protection to the rudder than to design a sturdy and dependable spade."

08-04-2013, 01:16 PM
Below is the body plan published in WB#233 and a body plan I drew by hand many years ago. When drawing lines it must be remembered that what you are doing is fairing a surface, not just connecting a bunch of points. To my eye the unhappiness (in the Rockport sections) starts between stations 4 and 5 at the 24" Butt. One section (4) runs straight, while the next (5) has a big hollow and the surface is suddenly curved.....that can't happen IPL. The baggy-bulge along the 36" Butt, especially at station 8, is just really bumpy, not close to fairing into the rest of the hull. Look at my drawing and note that each section is closely related to those fore and aft of it, so that the beginnings and ends of surface changes are not apparent, it all blends into one fair surface.......



David Cockey
08-21-2013, 10:02 PM
Perhaps the lines were distorted for publication. Simple enough to do with the lines in electronic form - just nudge a few of the control points.

08-22-2013, 11:06 AM
Perhaps the lines were distorted for publication. Simple enough to do with the lines in electronic form - just nudge a few of the control points.

Dave, first I think these lines are "preliminary" and drawn by hand. I think they're preliminary because there are so few lines and they are not faired properly. They don't match in all views. It's not a few points bumped out of place, it's sections that aren't fair but waterlines and butts that are (that can't be). Second, why would a designer do such a thing? The only thing a designer has to sell is his or her skill at design. The fundemetal skill of design is being able to produce a fair and attractive set of hull lines. Publishing these fair and attractive lines is what will sell your work to those that understand and are more likely in a position to buy something.......

08-22-2013, 12:22 PM
I noted in another thread that the review had nothing good to say, he mocks the lack of shelter, the inboard shrouds, but said it in very praising terms. I have to commend Bob Stephens for his writing skillls.

I agree with Bob that the rudder is way out of date, and I have broken the steering on a skeg hung rudder, on a boat designed by a group related to these guys. As you can guess, shortening the steering chain and adjusting the cables in 35 degree weather and force 5 winds does not engender praise for the designers or very well known steering suppliers