Graeme,

The NZ scow is a workboat - and therefore well suited to being a workhorse tender. The slab sides would be good for coming alongside for loading/unloading. Query: how would you plank the bow? Double diagonal 2 x 3mm perhaps? Or commercially available bendy ply? I wouldn't use more than 5mm ply for the rest, but I'd put stringers on edge halfway down the topsides, which would come in handy to lodge the thwarts on. Will it sail? Certainly, there's nothing wrong with sailing scows. With the very high stability and load capacity that it has, I'll put in a plea to not make it too beamy. I'm going to stick to my guns and declare that 3ft 6in beam with 7ft oars is spot-on for a working tender

PS to make a model of the SibLing tender, I'd scale up the three drawings of the plywood layouts, and take them to a copyshop to be printed on card - equivalent to getting the plywood CNC cut.

When I last used stitched-and-glue with polyester resin I just used the resin 'as mixed' and it did the job. The inside didn't look all that pretty, but it stuck and held well. That of course was some years back.

Since then I've thickened resins with a variety of fillers, and even used fine sawdust which worked but was a bit coarse. I've heard of people using wheat flour, as used in baking. and had some success. It's worth having some filler if the ply edge joins are not a tight fit, but many books show big fillets which add weight. I tended to brush pure resin and then a very small fillet of peanut butter consistency filler pressed in with an old knife before the tape. 

There ae many books on the subject, but they tend to use expensive fillers.

Cheers, Slieve.

Graeme,

now that I seem to have landed on the Medium Boy (“Weight” will be dropped from now on), I can develop the panels. This is of course quicker than with the 5-plank ‘Halibut’ design. However, my QCAD program is a 2-D program, not made for designing boats, so there is no ‘develop-button’ in it (AFAIK). Luckily, since I use the simple cylindrically developed shapes here, with constant deadrise, I can do it by using old skills from high school. I think that Medium Boy deserves a PDF write-up with both lines and some hints on how to build the thing.

The topsides for the Trim Boy and Medium Boy will be identical. Only the bottom and transoms will vary in width, but their curved sides (edges?) will have the same shape, which, as said, is the same curve as on that of the lower edge of the topsides.

Question to those of you who have used stitched-and-glue with polyester resin: Did you add some thickening agent to the polyester resin, as we do with epoxy? If ‘yes’, what did you use?

Arne

PS:
I drew ‘the Boys’ to only 229cm to avoid running out of plywood when developing the side planks (which I did on Halibut). When the planks are being developed I will make full use of the 2.40 or 2.44m sheet of plywood, which means that the flare of the bow transom can be increased a little (the shape of that transom itself must then be adjusted a little).

Arne’s evolution of a 3-plank pram is really interesting and instructive. There seems to be a sort of convergence going on, towards something “normal”. I rather like Trim Boy, but I suppose Medium Boy is the more sensible.

What is “doing my head in” is trying to relate and compare these different evolving designs, when one is a not-to-scale sketch on a cereal packet with a few measurements, one is a CAD drawing with lines, body sections and some measurements, and the third is a plywood pre-cut kitset with no measurements given.  And having to shuffle from web page to web page.

I have tried to take measurements off the computer screen and relate them to the 2.4m length of a sheet of plywood, giving the red figures as guesstimates. Open to correction.

And perhaps the two most important parameters which I can not express quantitatively.

• 
  1.      Rocker. KISS doesn’t have enough. Siblim T achieves it by immersing the bow transom
• 2.      Looks. The “Boys” are fast catching up with KISS. Siblim T lags behind – that big immersed bow transom still doesn’t quite do it for me – though in the end, if it performs well, I suppose it will become an acquired taste - in fact its starting to make some sense - these are very small boats and I am beginning to understand how difficult it is to get displacement, without getting too much beam, or immersing the stern too much - or the bottom looking like a banana.

I do wish I had the software and the skill to run them all through the same process, lay out the body sections and profiles all to the same scale etc to get a good and fair comparison.

Dear little KISS - she's probably only any good as a one-person dinghy.

Thanks so much, Slieve and Arne and David. This is instructive for me, and for many others too I should imagine.

Now I have landed on the ‘Medium Weight Boy’. This is what I regard as a sensible compromise between the fat and the trim version.
With a beam of 122cm (Fat Boy: 144cm), its displacement on the blue waterline is 190dm³, so should carry a payload of around 160kg. This puts this version in the 2 + 1 person category. The bottom plank will be 88cm wide on its widest, and the waterline beam will be 101cm (= 6.3 times the draft), so I feel safe in this version without ending up with FAT BOY’s perverse beam.

To get away with only two sheets of plywood, it might be necessary to build the transoms from two pieces, but that is no problem.

Arne