Thanks David.

I would be reasonably confident about planking the bow. When I built Havoc I did two skins, diagonal planking – but when it came to the bow, some of the diagonal planks had to be tapered to follow the cone surface around – and in that region, the second skin had to go on, almost on the same angle – the curve was too great to bend around it. In that part of the bow it had to be single diagonal (approximately radial) but doubled up, if you get what I mean - not terribly satisfactory.

On the scow I am currently building I wanted to use plywood, but there was no way it would go round that curve – and I wasn’t confident I could do it in two skins and not get voids. In the end I did it in one skin, full thickness (15mm) by making saw cuts in the outside surface of the ply, approximately along the radial lines of that cone sector. It turned out to be simple and easy. The saw cuts opened up a little. I filled them with thickened epoxy and the result looked good (looked like diagonal planking) – I was sorry to cover it with sheathing.

On the inside the curved surface is smooth and continuous, which is what I wanted. I fitted extra framing to it afterwards, although that part of the hull is very strong.

No mould is necessary, the only difficult part is lofting the panel, which I did not have the drafting ability to do. I made a model, and made the panel with cardboard to begin with, trimming with scissors until it fitted. Then, on the real thing, I fitted a 5mm panel made from cheap plywood, which I then used as a pattern for the 15mm ply. It all proved in the end to be very simple to do, and very strong, I think.

On a dinghy, I would do the bow part the same way (radial saw cuts). with 5mm ply, and leave it frameless. 

I am referring here to just that part of the bow which fans out from the fore foot, to reach that upswept fore part of the chine. The rest of the hull is either flat, or simple roll and easy to do with plywood.

The bottom and bow, well curved and "triangulated", would need no framing for a dinghy, I think. However, the sides would be flat and flimsy and I think your advice regarding stringer is a good idea, and would be simple. As for the gunnel - it also might call for some stiffening - even a narrow side deck perhaps?

 I take your point regarding beam. On that drawing I actually copied the beam (and the run) of Sibling Tender, and maybe it could even be reduced a little.

Arne - thanks too.

I like the pram bow for a small dinghy, better than the "pointy" - and I think I agree with you, except that the NZScow bow doesn't really fit into either category. The first working scows in New Zealand had transom bows, but with the short chop which is so common on our NE Coast, the model very quickly evolved into that bluff, semi-pointed bow which seems to be a compromise between sharp and square. I just thought it might be fun to try it on a dinghy - it does seem to me like a good compromise, retaining a lot of power and buoyancy at the bow, yet maybe handling a chop just a little better than a pram. It still tramples over the waves rather than cutting through them - but maybe does it with a little less fuss. I don't know, I just thought it might be worth to try but I am not interested in something as extreme as a Bolger Brick.

And thanks for suggesting to David about the measuring stick. I don't have good software here and spent a couple of hours this afternoon trial-and-error trying to scale people's drawings up or down so they come out on an A4 sheet as 1:10 scale. If they all had measuring sticks it would be a sight easier! If I make any more models, I want to make them 1:5 and use that super thin plywood I have a stack of - so it still means a trip to the print shop to get everything doubled and onto A3 then paste them onto the plywood. (1:10 cardboard is no good for my clumsy fingers). I made the KISS model that way - but did not need to do any lofting for that, and none of the others will be as easy to assemble as KISS. I wish I had time, it would be rather fun to make more of these models.

PS I can't imagine how to strike diagonals onto a NZScow hull - anyway, I suspect this type of hull follows its own set of rules - I do know that the type can sail quite well, similar to any of the old workboat types.

Edit - a diagonal on the bow section would be interesting. The waterlines are surprisingly hollow. I don't know how to do a diagonal.

Graeme.
I am not convinced that dinghies will row better if fitted with pointy bows. The prams can be made with lower entry angles at the bow (at the wl.) than many pointy bow skiffs and dinghies. In Norway the majority of small traditional everyman’s boats were the double-ended 14-17’ færings. In some areas, mostly sheltered, people preferred prams. Later test-rowing of the prams (Holmsbu type) against færings have shown the prams to be the fastest. The pointy bows are better in a head sea, in my view. I once had a 17.5’ Nordlandsfæring, with vertical stems, very fine entry and generally slim lines. It was a marvellous rower against a nasty chop.

Yacht-designers often operate with diagonals when drawing their yachts. These stand at closer to right angle to the hull sides. The designers aim for the straightest possible diagonals. A round-bottom pram would have the straightest diagonals of all.

Sooo, entry angles are important here. I just found that angle to be 18° on ‘my Boys’. This surely is wide enough, but remember that we are talking about load-carrying 8-footers here.
The entry angles of the topsides are identical to that of the bottom, so this discourage waterflow to be forced to cross the chines and cause turbulence. It will take some rowing to see if this is an important factor or not.

Arne

Arne – sorry, I thought it would have just been a click of the button. Still, when you get time, it would be good to see Medium Boy worked out fully – with the Halibut rig of course!

For resin thickener, I have used the fine wood flour salvaged from the collector bag of a belt sander – but only with epoxy, I’ve never used polyester. (Now I want follow Slieve’s experience and try polyester. I’m not epoxified yet, but I dislike the stuff and its expensive).

David – yes, I couldn’t put my finger on it, but Sibling Tender almost looks “cods head mackerel tail” (whereas KISS is quite the opposite, actually more junk-like). Now I am slowly starting to understand that design. I spent some time this evening thinking about it in terms of making a model – clearly there would be more work in it,

Now I would like some more advice – and blunt criticism. I looked at a video this evening of a Bolger Brick (8’x4’) sailing under a flat junk rig.

https://www.youtube.com/watch?v=zyUg5sOj58o

You want to skip the first 25% of it. Its tootling along, demonstrating reefing etc. It seemed to sail moderately well, which kind of validates what I have tended to believe, that at 8’ just about any shape will do.

This has got me thinking again about the NZScow – not as an entry, its not suitable - but simply as an experiment, or at least a topic for discussion here. I am sure it would sail and row at least as well (if not better) than a Bolger Brick.

For a tiny vessel, I think it has a better bow than either a stem dinghy or a pram dinghy.

Its initial stability would be very high. As for the rest of it, I really don’t know.

The Bolger Brick tells me that it ought to heel a little and sail on its chine as well as any other 3-plank. As for initial stability, and load carrying capacity, it ought to be up there with the best. Lofting and construction can be very simple (I know that much already). Its flat and flabby sections mean it might need to be built a little heavier than a conventional dinghy.

I’ve looked at the run and the sheer line of Sibling Tender, and its proportions – and had another go at trying to cobble together a NZscow dinghy. I’m not looking for anything other than bunt criticism – do you see any particular virtues or vices?

Putting the four drawings side by side is certainly instructive. It makes it clearer how I've put the centre of buoyancy further forward than on the other designs, because that's where the larger, stronger, and therefore heavier rower is going to be sitting, when two-up; and when one-up, that rower needn't move so far aft as to have his legs doubled up against the after thwart.

Arne, if its not too much trouble, could you punch out the developed panels for trimboy and Mediumboy and add them to Arne's Sketches please?