A new wooden yacht build, strip planking technique technique impresses

I just became aware of a local (to me) wooden yacht build. The use of double diagonal, strip planking looks impressive as an "easy" and robust way of building, especially for relatively inexperienced amateurs.


An interesting interview with the builders here

 

I think cold molded planking is a great way to go. Like making custom plywood in place. I was wondering if there was a way to vacuum bag each layer.

If you can split the strips out, even better, because otherwise, that's a lot of saw dust.

-Will

 

Add some foam and it gets better, especially fairing & structural design flexibility. (Our boat, Schooner Creek build, is going 20+ years). Eric Jespersen in British Columbia is currently building an electric motorboat using the same technique. The hull layup goes fast.

http://www.wyliedesigngroup.com/wyl...es/Jelek, Losing Weight, Pro Boat Builder.pdf

 

Double or more diagonal planking has been around for quite a while. I don't understand why they have old school framing in a cold molded hull though. It defeats the advantages of light weight construction with cold molded.

 

True enough, although having some frames in key places, like where bulkheads or panting beams go can be a big help when the interior starts being built.
The modern use of epoxy with various schemes of cold molding/diagonal/strip construction can sure produce an immensely strong and rigid structure.

 

Everything in the interior of our boat except for cushions, lights, toilet, sheet, drawers, electrical and the like is structural. The interior is very open, to the point that more than a few knowledgeable people have come below, and immediately climb out, look at the outside, look below and look outside again- the size of the interior seems bigger than the boat should have. There is a streak of conservatism that goes with wooden boats that seems to demand things like traditional supports inside. Does anyone hear know of, say, a 30 sq m done with double diagonal epoxy or a uni directional glass / wood / u d glass / foam / u d glass / wood / u d glass layup? Would that open up the interior some?

 

That seems like an odd sequence of lamination. Glass between the foam and wood is unnecessary. I used to race a 34' one tonner built with triple diagonal mahogany over stringers and a few bulkheads. It had no glass at all and the hull was 1/2' thick. It was built in 1974, people thinking it is not a good construction method are not conservative but Luddites. Fairey Marine was building laminated hulls designed by Uffa Fox in the early 50s.

 

In fact the 30sqm "skerry cruiser" has been built in modern materials for a long time. Reimers Bijoux 1 is considered the modern standard, and can be had in monolithic glass poly/vinylester, diverse sandwiches, and cold molded mahogany from several manufacturers. Some years ago the class association commissioned a new digital version of the original plans wich were used to build a new mold.
Pictures:
CNC cut plug: Bergner Bootsbau - Fotos https://www.bergner-bootsbau.de/30erSchaere_bau.html
New mold and foam core boat: Bergner Bootsbau - Fotos https://www.bergner-bootsbau.de/30erSchaere_2.html
Cold molded version: Schärenkreuzer | Michelsen-Werft http://www.michelsen-werft.de/gallery/70.html

Brand new class approved linesplan (first hull should launch this year), WRC glass sandwich, mahogany veneered on the outside for looks: 30er Schärenkreuzer - die neueste Kreation aus der Bootswerft am Mattsee. Zeitlose Faszination – ... https://www.steiner-nautic.at/de/segelboote/index.asp?dat=30er-Schaerenkreuzer

Now, before we start piling it on the designer of the boat in the videos, remember how hard it is to make a living from plans. People drawn to boats that look like that aren't necessarily looking for light weight, they want "really strong", "belt and suspenders", "it has to look right to me" hulls. If they don't feel good about that, they won't buy, or even worse, they buy and modify, then complain it doesn't perform as advertised.

That beeing said, double or triple diagonal veneers over strip is a method that's rarely used at its full structural potential, probably because it's not worth doing. There is a sweet spot balancing build effort, cost and structural benefits, but it's very hard to hit that spot, since it only works for specific hull shapes (long and thin light displacement), and in specific market conditions.

 

My impression is that they were more interested in the design being authentic than being optimal. The way they built there is more wood in the boat but less wood in the mold. They met as crew on a restored classic and this is their first build. The result being an overly strong boat that weighs as much as 100 year old boats is what they want.

 

IIRR, the idea was that the multiple layers of uni e glass allowed for fine tuning load paths within the hull, and easing fairing time.

Why specifically do you think it’s an odd lamination sequence?

FWIW, Amati weighs in at ~9600 lbs.

 

There is no advantage to have glass between the foam and wood. It will add weight with little effect in strength. The glass fibers should be installed where the maximum tension/compression stresses are: the skins.

 

Thanks for the links! I try to keep abreast of what is going on with the 30 sq m skerry cruisers, but easier said than done.

To your last paragraph, exactly! Amati is 40’ loa, 10.5 boa, 8’ bwl, 8.5’ depth (fin). I asked Bob Perry to blend a 30 sq m skerry cruiser and an IMS mk 1, and the result, I think, proves your point. She came in ~10% more weight than a carbon hull, but ~ 30% of the cost in 1999. We looked at a computer/machine sculpted foam hull, but the cost for only that was more than a completed boat at Schooner Creek.

FWIW, the wood veneers are 1/4” each, and the Klegecell foam is 1/2”. I’ve forgotten how many ounces the uni e glass weight was. She was formed over temporary male forms. I wish I had pics of the hull lamination, but we couldn’t get down to the boatyard until after 4 weeks after the start of construction and they’d already flipped the hull over by the time we got down there. Wood was Port Orford Cedar.

 

I get your point, but sometimes there are other concerns involved. In my experience building windsurfers, there was a point where hand laminating thicker uni e glass made fairing more difficult and time consuming, but that was in the dark ages of the 80’s. Fairing time for Amati was greatly reduced with the COVE method, which, given that labor costs are the biggest part of a boat building budget, gave great savings on that front- each layer required less fairing time, especially the klegecell, and the last layer of cedar required almost no fairing at all.

I also remember e glass/epoxy sticking to foam better than wood to foam, at least with stringers, although it weighed more. The thought at the time with Amati was that the wood was considered core inside e glass, and the two wood cores were considered skins to the Klegecelll, which in a general way was where windsurfing laminations were going at the time with multiple layers of different densities of foam in the board laminations, taking some stress off of the core foam, and the epoxy bond to the foam. A fat 40’ carbon boat and Amati hit the same rock at the same speed , and we had no water at all in the boat. The carbon/foam boat needed pumps. We were 10% heavier, granted, but cost 1/3. Good trade off for us at least.

My $.02, at least.

 

I agree, glass between foam and wood not necessary.
Your point about "stringers" is right on target.
All engineering/testing has shown that in that/those construction methods that the weight used for longitudinal members is much more contributing to strength and rigidity than transverse framing, and still saves weight in comparison.
In the old days using lots of frames was the only way to "pull-in" and secure carvel planking such that the boat could maintain its shape, (and with the floor timbers to keep each half of the hull together).
If one wishes to maintain the weight, then increasing hull thickness is better than maintaining the framing schedule of a carvel built hull.

 

what wood was used for the one tonner?