My reasons for going for a "box boat" are outlined in the information I supplied with Boxer. I have used round bilged and hard chine stemmed dinghies and hard chine pram dinghies. I currently own a round bilge stemmed dinghy but plan to build a second version of Boxer. I am heading that way because I think boarding and leaving the round bilged dinghy is the most dangerous part of our sailing trips because of its poor initial stability and the difficulty of access for my wife who has short legs. I think Boxer is the safest design available to me and I would still go that way if not constrained by deck space.

In support of my choice I note that the  first design I copied from Worcester is called "the Junk's sampan." Not "a type of sampan I have seen sometimes!" The other design that influenced me was his "Square-head boat." He says "it stands up well to rough weather."  These comments pushed me to my first version Boxer design and my experience with her encouraged the version I have entered in the JRA Competition.

I have made my choice and sleep soundly with it. 

Arne I would agree with you that for a general purpose 3-plank dinghy, not too wide a bottom, and the right amount of flare in the topsides is good. (The box boats have their place, but more for a specific purpose). I don’t think the topsides of a 5-plank need to be flared, as there is enough flare in the middle plank. Both Halibut and baby SibLim are 5-planks with vertical topsides, and both look to me like handsome little vessels which are going to be seaworthy for their size (and, by the way, very different in other respects. Halibut is a much bigger boat – and was a bit easier to plank up than the SibLim, which is noticeably “cods head and mackerel tail”. I like them both. Very much.)

While on the subject of “ease of build”, the box boats are not easier to build – some people might think they are, but ease of build is not a reason for building a barge-type. A flat panel of plywood is not as easy to get to lay fair, as one with a bit of curve in it. Nor is it as strong and stiff, so a bit of extra framing is needed, and the weight goes up and speed of build goes down a bit, with that.

I think the dory shape is much over-rated. They did the job as fishing boats on the Grand Banks, they were quick and cheap to build, stacked up nicely on the deck – and in the water they got stable once they got a bit of freight. There’s nothing wrong with that – but nothing outstanding either, that warrants copying it out of context. Flaring sides is a necessity on that type. An elegant idea - but an 8’ dory is going to be too unstable to be any good as a tender in my opinion. There is an interesting dory which can be made from a single sheet of ply, which might well have been an entry in the JRA competition. Here. I just think its too small to be any good. Some things just don’t scale down so well. Medium Boy is much better – in fact, just as nice and simple, and very good in most respects, in my opinion.

A fender sausage is something which could be worth while on something otherwise a little  bit tender – perhaps if the kids want to go sailing in it. Medium Boy is good and stable as it is, and doesn't need it. As for Simplicity 8, the sausage fender is a complete waste of time except as a workboat fender, to protect other vessels. That thing is so stable I can’t imagine the gunnel ever getting wet, except from spray when some oaf inevitably decides to put a big outboard motor on the back. If that thing ever got up on its side, a sausage fender wouldn't save it.

A Canada canoe has tumble-home for very good reasons (try paddling one). If the dinghy has sufficient beam and freeboard, tumble-home should not be lethal, though I can’t see much point in it for an 8’ rowing dinghy. Oyster (one of the JRA dinghy entries) has tumble-home in the form of an additional strake, on an already fairly high-sided and stable hull. Its an added complication in the build, but looks very nice – and if anything the tumbled-home extra plank adds to its seaworthiness, by creating additional freeboard to the flaring topsides, without making the topsides look too high and ugly. It also stiffens the topsides a little, structurally. That’s the opinion I formed, anyway. Oyster is unconventional in other ways, I am not convinced it is any better for that – but I now believe it is certainly no worse. My main doubt about that one is a fairly minor objection to the designer specifying angle aluminium to protect the two bottoms. I doubt that he has actually done it, I can’t find a way to bend aluminium angle to the shape that would be needed – a minor objection, because there are probably other easier ways to protect the bottom against abrasion.

Big floatation tanks is not compensation for bad design. They have their proper place, depending on the primary use of the dinghy. If I had kids that wanted to go sailing in the bay, I would be glad if the dinghy had good buoyancy tanks. Some of these dinghies are built around the buoyancy tanks, which act as a building jig – stiffening the whole thing and leaving the tanks as a bonus – excellent design. Retro-fitting tanks into a dinghy after it is built is not such a hot idea – I am doing that on a dinghy at present, and probably wouldn’t do it again. For some people (me included) buoyancy tanks are not really necessary in a decently designed tender, and for some purposes might be little bit constricting. But they don’t need to be associated with bad design, far from it.

I’d love to do a “swamp test” – I agree that would be very relevant. In fact, although I have nearly run out of enthusiasm, I might yet be tempted to try it. But I don’t have the equipment to quantify the results properly, Arne is right about that. Comparative testing (as opposed to quantifying) would not be so difficult, but if I do any of that again, it will be for my own interest only. I accept and agree that my crude attempts at compensating for over weight are probably flawed, quantitatively at least, and I won’t be posting any more numbers on the web. 

By the way, David - 

I thought that was brilliant.

You are right Arne, it was way “over the top”.

Originally I was just thinking about stepping into a dinghy and standing off-centre – which upsets some boats more than others, and is a matter to be considered. There are plenty of dinghies which I would consider too sensitive, and I think a tender should be fairly robust against clumsy handing, which is pretty commonly seen. (But I would certainly not expect anyone to jump down onto the gunnel of a dinghy, and of course that should not be a requirement).

However, to make a crude experiment with limited equipment, I wanted a simple a procedure which discriminated between dinghies. It had to be a bit over the top.

It wasn’t just a matter of built-in buoyancy,  You have missed something there. General Purpose Dinghy was a stand-out case of that – but Oyster, with no buoyancy, was robust. David’s box boat, with its full buoyancy tanks, flipped instantly. Simplicity8 didn’t flinch – and its buoyancy tanks never came into play.

I think we can learn something – but I wouldn’t take any of it too seriously, as I have repeatedly stressed.

Arne wrote: “Almost any of the shown models could be winners. It all depends on what one needs.”

Quite right. You summed it up perfectly.

PS I thought Medium Boy's slow-mo struggle to survive against that unreasonable assault was quite heroic, don't you?

One last test, a kind of dynamic stability test: A 800 gram soft weight dropping from a height of about 15cm onto the gunnel of each of the models.

This is an attempt to simulate a 100 kg clumsy person jumping down from a height of about 0.75m onto the gunnel of the dinghy. A rather severe test.

The models which were able to tolerate this assault, were subjected to the test again, this time with a quantity of water in the bilge. Anyone who has jumped into their tender, half full of water from over night rain, might be interested to see what happens with these models.

The tests were recorded on video here.

I am not sure if all this "tersting" is going to help the judging committee very much.

For the judging committee's sake, it would probably be better if more people might chime in with their opinions about what makes a good or not-so-good tender.

This is a very interesting series of tests, Graeme, thanks a lot. I hope the results will be edited into a PDF article afterwards.

The results seem to go along these lines.

• ·         The beam decides the maximum stability.
• ·         The slope of the topsides decides the initial stability.
• ·         Flotation along the sides  -  tanks or foam  -  greatly increases ultimate stability.

Problem is; some of the steadiest designs are also the slowest ones in the towing tests. My ‘Simplicity 8’ would probably be best as a harbour barge of some sort.
If Medium Boy’s two brothers had been built; the Fat Boy and the Skinny Boy, they would have underlined what beam does to stability.

My conclusion is that adding some buoyancy along the sides will make any 8-footer a lot safer. This was why I was thinking of adding a buoyant ‘fender sausage’ around the gunnel. These would both act as buoyancy in the best position, as fenders, and as spray rails, all without taking up space on board.

Arne