Little KISS  afloat

I couldn't wait.

Here she is empty. She weighs 427g which (scale factor of 1:5) I take to represent 53kg. Would Arne check my arithmetic please? That's heavier than she should be, but her transoms and centre bulkhead are 5mm ply which scales to 25mm, and her epoxy fillets are giant-size, so I would expect her to be a little over weight. She's a little down by the bow, as she should be, and her stern transom is just kissing the water.

Here she is with a freight of sand, 560 grams including the container.

(That represents 70 kg ? = one trim adult male - (I wish)).

She is trimmed out about right, the stern is immersed about 25mm (12.5cm in real life)? She looks comfortable. (That rowing bench might need to be extended aft a little, otherwise she needs a big bag of groceries in the stern sheets).

Here she is with a freight of 1200 grams (That's 150kg?) The stern is immersed 48mm (that's 240mm in real life)? Her bow transom is just kissing the water. I'd say that's well and truly her limit and about right for a delicate little 7' pram. It means she'd be OK with 2 aboard. I'd be satisfied with that.

So, there we go, JRA Committee. She's not a load carrier - but don't forget to learn from Arne's exercise - you don't have to scale her up much to get quite an increase in carrying capacity.

Personally, I like her just the way she is. Simple, light and easy to build. With two or three buoyancy bags stuffed in the right places, and a little rig, she'd provide plenty of fun for a  couple of kids. Come on Slieve - get those grandkids of yours back to the drawing board, we need that sail plan. What's more, they could build her as a row boat, in a week, with just a hand saw, a battery drill and a roll of sandpaper - as you will no doubt be well aware!

It means "kiss". Its not pronounced like "when" - as it so happens, it sounds auspiciously like "Win".

The sand, by the way (David), is the damp sand I got off the beach a month ago (see thread "Junket Boat 30 April 2021). It doesn't smell a bit. Not even a seaside smell now.

PS as a school build project, I'd get one strip of suitable timber and run it through the circular saw at an angle of 110 degrees to make two chine stringers. Get the kids to figure out the bevels on the stern and bow transoms, they should be able to hand-saw them - and supply them with a couple of drill bits and a packet of screws. Stitch and tape and thickened epoxy is all very well, but epoxy is actually not very nice stuff and perhaps more conventional construction and some other type of glue would be better in a school classroom. Something like that applies to all the entries, and might be a competition requirement that perhaps wasn't thought of, though some of the entrants have already provided for it.

Graeme,  the competition did not ask for a 'School build design'. That was part of the prize, so to speak. If the winner is too easy for the school kids then they can make two, and have much more fun racing them.

Someone suggested making the centre spreader in KISS from ply, but that would probably dig into the back of the rowers legs when rowing from the forward position.

Cheers, Slieve.

I was thinking along the same lines (the ice-cream approach).

But they still have to choose one to build for the school project. Perhaps "suitability for building as a school project" will be the most practical way of deciding in the end - and would possibly  result in the closest to what most people would like to build for themselves anyway. (Entrants were informed at the outset of this intention).

I think Slieve is right, Arne just made a typing error.

To look at it another way:

Scale the dinghy from 7' to 8' - that is a linear scale factor of 8/7 = 1.143 (about 14%)

The surface area (amount of epoxy sealer, sanding and painting required) will be scaled up by the square of 1.143 - that is, an increase of about 30%

The volume displacement will be scaled up by the cube of 1.143 - that is, an increase of about 50% - which I suppose also means the carrying capacity goes up by 50%.

The weight of the dinghy? I am not so sure. Presume we are sticking with the same thickness of plywood, maybe the weight just follows surface area in this case, and goes up only 30%. Anyway, at 8' I think it will still be among the lightest of tenders and still very easy to carry turtle fashion. (By the way, it gets difficult to carry a dinghy this way when greater than about 8'6" - 9' but that's not because of the weight. Just, most people's arms aren't long enough).

The cost?  - not sure if that follows any mathematical rule, but probably at least to the cube - and in this case might be a quantum jump if an extra sheet of plywood is needed.

We should look at nesting onto a standard sheet of ply, now, to see if an increase in size could be done with offcuts, or to find out what is the maximum length which could be achieved without needing an extra sheet, using butt joins and offcuts. There's another chore for the boys. They will be able to see how Mike utilised this trick with his unconventional Oyster design.  (Or maybe Arne could run it through his CAD software and optimise materials that way).

Turtle fashion. You don't need muscles like this guy (and that looks like a heavy fibreglass dinghy.)

You can carry possibly up to your own weight on your back/shoulders, at least for a short distance, provided the dinghy has a centre thwart and a hand-hold within arm's reach.

I agree partially with David, but not entirely.

“Think along the lines of…” is hardly a definition of what is required, and only emphasises further the deep flaw in this competition, which has already been discussed from the outset.

Performance-wise the 5-planks – and possibly some of the other entries which have not been discussed on forum, could well be the best performers (though not by a large margin). If the intention was for a dinghy to be built on a beach then the organisers should have said so clearly – but I don’t think that was the intention. I don’t think there was any clear intention - except to build the “winner” as a classroom project – in which case Slieve’s design, which was for his grandchildren to build from a cardboard cereal box, might not be challenging enough.

The best boat isn’t necessarily the most suitable boat. But suitable for whom and for what purpose?

(It is also interesting to note that the most popular tenders, by far, are without exception: pigs to row, impossible to sail, prone to theft, don’t last long, you can’t build one yourself, easily damaged and expensive to buy. You know the type. Edit. Not my cup of tea, but my point: they do what their owners want of them.)

I have been very interested in this “competition” but mainly because of what came out from it. The upside of that vague and loosely-worded set of criteria is that it produced a proliferation of very good designs – all of them very good – and with amazing diversity. To be charitable to whoever drafted the terms of the competition, perhaps that was the intention – if so it has been a raging success. We now have a near impossible situation in terms of choosing a “winner” – but a wonderful set of different designs, with something to suit everybody.

If I wanted a lengthy father-and-child winter project and a kid-safe, fully buoyant sailing dinghy for a teenager who had a passion to sail – I might choose John’s design (which he has mis-named) “General  Purpose ‘Pram’ Dinghy.

As rowing boats and casual sailing boats I doubt if there is much to choose between any of them – an 8’ dinghy might as well be just about any shape as its too small to make much difference. As tenders, the differences between the entries will be in matters such as stability, the ability to be overloaded and still do what it has to do, the weight, the ease or otherwise of construction, and the cost.

Whichever dinghy wins it won’t make any difference to which one I would choose. I’m still thinking about it, there are others yet to evaluate - but so far I have to say that much as I love the 5-planks, I am mightily impressed with the ease of construction, the looks, the style, - and what it represents - of KISS.

(Slieve – our posts crossed in the mail. Congratulations to your Grandkids (and their patient supervisor). I made another mistake too – the model is 1:5 not 1:50. Put the decimal point in the wrong place. This is why I loath the metric system. In proper terms, the model came out at 16 ½ inches – so I suppose the dinghy would work out to be about 7’. I wasn’t too fussy with the ruler – no need – that’s another thing I like about it).

(Arne: Crossed post with yours too. I agree with T-thwart. I didn't like that frame, I prefer the low bulkhead supporting the T-thwart and tied in with centreboard case and the mast. Agreed also (strongly) don't alter the beam/length proportions. Thanks for advice. My  model (1:5) is thin plywood and it will get a coat of epoxy, won't need cling wrap. I'll try some weights, as you suggest - although eyeballs and common sense tells me it will carry two adults and a few bags of groceries. That's good enough for me. Too many people drown in dinghy accidents - I don't like to see 3 adults in any small tender).