Cash prize of 250 GBP - Dinghy Design Competition

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  • 13 Oct 2021 09:25
    Reply # 11437410 on 10211344

    Hi, any feedback from the judging committee, it was originally scheduled for a result in June?  

    David.

    Last modified: 13 Oct 2021 09:25 | Anonymous member
  • 02 Aug 2021 17:01
    Reply # 10789540 on 10788149
    Anonymous wrote:

    This one's for Arne.

    The name's been taken.

    I noticed the other day there is already a dinghy called "Simplicity 8", its a Selway Fisher design, here .


    Speaking of Arne's Simplicity 8 - I just knew this would happen - here is an almost identical design, boasting a 25hp outboard motor.

    3m x 1.5 m and almost identical in design to Arne's.

    Pity you didn't enter it in the design competition Arne, you might have won for the highest top speed - its for sale here on Trademe and the owner claims 41 km/hour. 


    I hope never to see it in any peaceful bay in which I may anchor - at least, not with that motor on the back. Its already had a reinforced transom fitted (no surprise there) and the duck-shooter owner now claims it "will take all and any hp engines thrown at it..." Sigh... horses for courses, I guess.

    Graeme,

    You've reminded me of one of the reasons I like this website so much: the never-enough-engine crazies don't show up here.

    I do realize that an underpowered conveyance of any sort can get you into trouble but not out of it.

    Still, If that duck-shooter thinks that boat is all that wonderful, I wonder why he's selling it? I'll bet he'd never admit to having a close encounter with Darwin.

  • 02 Aug 2021 01:31
    Reply # 10788149 on 10211344

    This one's for Arne.

    The name's been taken.

    I noticed the other day there is already a dinghy called "Simplicity 8", its a Selway Fisher design, here .


    Speaking of Arne's Simplicity 8 - I just knew this would happen - here is an almost identical design, boasting a 25hp outboard motor.

    3m x 1.5 m and almost identical in design to Arne's.

    Pity you didn't enter it in the design competition Arne, you might have won for the highest top speed - its for sale here on Trademe and the owner claims 41 km/hour. 


    I hope never to see it in any peaceful bay in which I may anchor - at least, not with that motor on the back. Its already had a reinforced transom fitted (no surprise there) and the duck-shooter owner now claims it "will take all and any hp engines thrown at it..." Sigh... horses for courses, I guess.

    Last modified: 02 Aug 2021 02:09 | Anonymous member
  • 21 Jul 2021 08:50
    Reply # 10765091 on 10211344
    Anonymous member (Administrator)

    Graeme, here is a photo of that dory at a very early stage.

    I think I remember that the bottom was eighty-some cm wide, and the flare of the topsides was considerable. Relatively, the bottom is very narrow, although it is about the same as that of Medium Boy. If those tall frames had been cut half as high, they would almost have fitted into my dinghy.

    Btw, Curtiss built that 19’ dory from a design in some ‘Dory book’. To scale it up a little, he used a Norwegian yardstick, where one  inch ( Norw: tomme = thumb) is about 2.94% longer than the imperial version. That beefed the volume of that dory up with around 9%.

    Arne


    Last modified: 21 Jul 2021 18:17 | Anonymous member (Administrator)
  • 21 Jul 2021 04:30
    Reply # 10764757 on 10211344

    Here are the two drawings from Worcester which John has just referred to as inspiring Boxer

    Junk’s sampan  (9’ x 3’6” x 1’ draft) “Her duties are to provide communication between ship and shore, and to lay out lines…”


      fāng tóu (square head) (12’ x 4’) up to (18’ x 6’6”) “stands up well to rough weather…”


    Boxer is a bit more shapely than a “box boat”. When I made the model I was pleasantly surprised: its nicely proportioned, with a delicate curve to the sides -  and its stability is such that you could step anywhere into that wide cockpit with safety, without having to reach for (commit to) the middle.


    The information John refers to may be found here.

    John is too modest to mention that an early prototype for Boxer came first equal in the Royal Cruising Club/Yachting Monthly Dinghy Design competition in 2012


    Last modified: 21 Jul 2021 05:03 | Anonymous member
  • 21 Jul 2021 02:21
    Reply # 10764673 on 10211344

    Arne, that’s a nice, decent-size dory (nice little video clip too). Such a simple form, which so elegantly matches the original needs and function of these boats. (I like the midships tiller too). You can see straight away it is slightly “tippy” for the first few degrees, then very quickly becomes stable.

    I am sorry, I didn’t understand what you meant by “the lower part of that dory's mid frame” and then “its topside flare” - as if they are two different things. Could you explain that again please?

    Swamping

    I’ve only ever been swamped once, and that was one night in a commercial fishing boat, while constrained by gear, when a huge freighter (perhaps not keeping watch) went by me so close its steep curling bow wave rose up out of the darkness, clear over the side and filled my cockpit (and my gumboots). It was a very steep wave, which I would hope never to encounter in a dinghy.

    I have been tipped out of a dinghy due to a wave – tipped over – a steep little wave right on the beach - that is probably a more likely scenario than being swamped I think, though you may correct me on that. In that case it was a narrow, light weight, 3-plank dinghy – almost like a dory - and the capsize only happened because I was in it (sitting up on the thwart), side on to the beach, could not react quickly enough and toppled over, the dinghy followed. Rather like the scenario David described some posts back. I don’t think the dinghy would have capsized if I had not been in it.

    I would expect an empty dinghy to just bob like a cork, in all but the most extreme of waves, but maybe I am wrong.

    What all this leads up to is: I think another “over the top” situation would be needed to make any of these model hulls become swamped or capsized – it would need to be an extremely steep wave and I am not sure if even a 5 metre log dropped from 10 metres (close nearby, God help us!) would do it, unless the models carried a passenger. Then they would need to have passenger weights added, and then there is the complication which has muddied all the other testing – trying to get correct weights and correct weight distribution into models that were never correct with respect to weight in the first place. The models should have been made from balsa, but I never thought about that when I started.

    I think all this “model testing" stuff has gone too far now. Originally, I only really wanted to see what the dinghies would look like, and to give appreciation to the people who put forward their designs. And I did hope (and still hope) it might provoke lots more other people to chime in and give their opinions about what sort of tender would suit them best, and perhaps which of the JRA dinghies they like best. It’s still possible for people to do that, I think.

    The link (which should have been displayed more prominently on the website) is here, and I think it is still open for people to give their feedback to the designers – or to make their comments on this thread. Most members probably don’t come on the forums, of course – I do hope lots of people we do not yet know about, have responded directly to the JRA. 

    Nobody can say which of these dinghies is best – only which dinghy would be best for their purpose or situation – but that would still be helpful, I guess.


    Last modified: 21 Jul 2021 04:55 | Anonymous member
  • 21 Jul 2021 01:28
    Reply # 10764623 on 10211344

    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. 

  • 20 Jul 2021 20:16
    Reply # 10764045 on 10211344
    Anonymous member (Administrator)

    Graeme.
    I didn’t mean to say that a scaled-down bank dory would be a fine tender. Its fine ends would not contribute to stability at all, much unlike a pram with ‘dory mid sections’  from end to end.
    Here is a little video clip on Youtube, showing my friend Curtiss in his self-built Bank Dory. Actually the lower part of that dory's mid frame is very similar to that of Medium Boy, but I think its topside flare is around 24° from vertical while the flare of Medium Boy is only 22°. Curtiss’ dory behaves much like the 20’ big sisters of the færings (4 oars); the seksærings (6 oars)

    As for swamping test, what about just making a comparing test:

    A heavy ‘log’, 5 equivalent metres long could be dropped from ten equivalent metres’ height at a  distance of 5-10 equivalent metres. Something like that.
    Some models would then ship water while others would not.
    Just a thought....

    Cheers, Arne


  • 20 Jul 2021 11:26
    Reply # 10763056 on 10211344

    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.

    Last modified: 20 Jul 2021 11:56 | Anonymous member
  • 20 Jul 2021 08:23
    Reply # 10762942 on 10211344
    Anonymous member (Administrator)

    Dynamic stability  -  keeping the chop out.

    There is another shape factor, which is more interesting to me than «oaf resistance», and that is resistance against being swamped by waves, either made by the wind or by motor vessels.

    The height, and even more, the flare of the topsides plays a major role here. This is why a bank dory mid-section is so good, while a Canada-canoe with tumble-home topsides is lethal. The canoe is fine on rivers, but there has been some fatal accidents up here when people use them for crossing fjords or lakes. Flaring topsides and ample freeboard at the stern is in my view essential to keep a dinghy safe. One can of course compensate with big flotation tanks and/or a fender sausage around the gunnel, but that is just a compensation for a bad design (like Simplicity 8). My Medium Boy design, with flaring topsides, was a way of trying to address this and still having an easily-driven boat.

    However, these dynamic properties of a boat are not easy to quantify without a test-tank with a wave-generator.

    Arne


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