Cash prize of 250 GBP - Dinghy Design Competition

  • 04 Apr 2022 18:34
    Reply # 12693618 on 10211344
    Anonymous member (Administrator)

    Len,

    did you buy full-size drawings to simplify  lofting the planks and other bits, or did you have to loft the bits from tables of offset?

    I feel that this discussion is running astray.
    The name of the game was originally an amateur design competition for an 8-foot dinghy. Not a professional design project with profitable production of plans or kits in mind. Big difference.

    Arne

  • 04 Apr 2022 17:10
    Reply # 12693510 on 12693194
    Anonymous wrote:https://www.selway-fisher.com/ply_on_frame.htm

    The last link, in particular, as it talks about how the computer-generated "eggbox" "build the interior first" method has revolutionised the ply on frame concept. That's why I used it for my 'tender for SibLing' design. Self-jigging, avoiding the long process of setting up and fairing moulds, has a lot going for it.

    Having built with stitch and glue (stitch and tape or whatever) I would agree that using frames, bulkheads, interior furniture, etc. as the frame would be a step forward. Except in open boats where a temporary spreader may be needed to hold the sheer where it needs to be. Certainly having a full size plank layout is quick and easy to use. Enough easier that I would agree paying to have it printed is worth while (do share it with others when you are done). Considering the cost of even one sheet of plywood anymore....
  • 04 Apr 2022 14:01
    Reply # 12693194 on 10211344

    Arne, might I gently remind you that you said that you haven't actually built a dinghy yet, so all your knowledge is theoretical only? Recently, I needed to learn a new practical skill, and of course I read, studied, watched the videos... but it was only after I got to the hands-on stage that I finally understood what I should be doing.

    Paul Fisher of Selway Fisher is someone who has designed more (and knows a lot more about designing) small plywood boats for amateur construction than most of us. For those thinking of building any of these JRA tender designs, I suggest reading through:

    https://www.selway-fisher.com/boat_building_methods.htm

    https://www.selway-fisher.com/Stitch%20and%20Tape.htm

    https://www.selway-fisher.com/ply_on_frame.htm

    The last link, in particular, as it talks about how the computer-generated "eggbox" "build the interior first" method has revolutionised the ply on frame concept. That's why I used it for my 'tender for SibLing' design. Self-jigging, avoiding the long process of setting up and fairing moulds, has a lot going for it.

    Last modified: 04 Apr 2022 18:15 | Anonymous member
  • 04 Apr 2022 12:18
    Reply # 12693122 on 10211344
    Anonymous member (Administrator)

    David,

    The problem is not the design stage. This may well be all-computer style.

    The problem is to get from the finished design to cutting plywood. I suggest a both-and solution instead of either-or (..which soon ends up at neither-nor...).

    To spell it out; produce a cnc-cutter-friendly file plus a set of offsets so one can loft the thing conventionally ('old-fashioned way').

    Arne

    PS: I think I remember Edward Hooper once recalling the motto of his university: 

    ET NOVA ET VETERA

    Last modified: 15 Apr 2022 10:26 | Anonymous member (Administrator)
  • 04 Apr 2022 08:36
    Reply # 12692930 on 10211344

    I'm guessing that you're agreeing with Jan, Annie, that a table of offsets should be provided. I disagree.

    The first dinghy I built was a dory from a table of offsets in Skene's Elements of Yacht Design. That was the only method available to designers in the first half of the 20th century. They just didn't have large format printers available to them.

    Later, I built a clinker ply dinghy to a design by Iain Oughtred. He draws traditionally with pencil and paper, but instead of, or as well as, a table of offsets, he supplied me with a full size sheet, probably A0 or the imperial 40" x 30", of sections that I had to transfer onto the moulds for building. This was better than lofting from offsets, with less room for error. Todays equivalent is to take a CAD design on a memory stick to a copy shop and ask them to print it full size on A0 paper, or even on a continuous roll of paper or film. Printing at home at A4 size is only really adequate for studying a design, not building it.

    Of course, with boats that are too large for stitch and tape construction, we are stuck with a table of offsets; but with stitch and tape, we need to loft out individual planks. Dimensioning a drawing, whether hand-drawn or computer-drawn, will work - but there is scope for error in both dimensioning and lofting that is not there in transferring a shape at full size from paper to plywood. Remember how we made errors in lofting out station 2 bulkhead on FanShi, which gave you trouble in planking the bow later on?

    I suggest that you're projecting your own likes and dislikes onto today's schoolchildren, Annie! My granddaughter, aged 12, is a budding artist. She draws with pencil and eraser in paper sketchbooks, but is just as happy and more productive on the old computer I've given her, and is now hankering after a state of the art iPad so that she can do even better work. Students today grow up using computer technology from an early age. I wouldn't want to hold them back (but by all means let them be told about yesterday's methods in their history lessons).

  • 03 Apr 2022 23:58
    Reply # 12692546 on 12689237

    I agree - or even a scale would be good.  Some people may want to do everything themselves - I certainly would - and not everyone has easy access to people prepared to cut the plywood for you.

    There are many things I dislike about CAD drawings, but this is high on the list.  Printing things out and sticking them together is also a real nuisance for people who don't have a printer (there are some of us out there!) and doesn't always produce an accurate result.  Not all 'progress' is universally better.

    I remember how my edition of Cruising Under Sail had marks from dividers on drawings  of cruising yachts, which were reproduced between its hallowed covers.  (No longer.  I lent it to someone and it was never returned.)   It was fun figuring out how accommodation had been fitted in to a small boat.

    Edit: I recall that the idea was that the winning dinghy would be built by school children.  To my mind this implies that they should also loft and cut out the panels, to get a full understanding of what building a small boat was all about.  Thus they would need either an accurate scale drawing or stations or offsets.  Although not a stipulation, as such, surely it was certainly an implication!

    Last modified: 04 Apr 2022 00:20 | Anonymous member
  • 03 Apr 2022 12:59
    Reply # 12692117 on 10211344

    If the competition was an exam, I would ask for a remarking of my entry as some of my features were ignored but commended in other designs. In this forum, I only want to say I am confident that Boxer is unlikely to capsize as she has high initial stiffness, and the crew should respond before she goes over. I also gave considerable thought on how I would right her and get back in. Puddle Duck Racers have a similar shape and have no righting problem. I widened the aft thwart for more buoyancy and intend to fit a stirrup to aid boarding and bailing out.

    My reason for writing this is to refer any intending builders to my discussion justifying  Boxer's shape and suggest you consider the punt like dinghies entries as possibly safer alternatives to a more shapely "Western Style" dinghy. The Chinese are unlikely to have chosen it as the standard dinghy shape if it had not been proven to work. When I build Boxer 11, I will sell my shapely Western Style dinghy as it is more likely to drown me.

  • 02 Apr 2022 10:18
    Reply # 12691167 on 12689771
    Anonymous wrote:

    Would have been interesting if there had been a stipulation that the tender had to be built on a beach with only hand tools that were carried on the mothership (I know of one such case). Different designs would have resulted.

    Would have been interesting if [insert theoretical stipulation here]...

    But there were no such stipulations. Only loose guidance.

    How far back would you like to wind the clock, Jan? Is pre-21st century far enough, so as to preclude modern, fast, efficient ply boatbuilding methods? Or must we go back to pre-20th century methods, and fell trees and cut and shape planks with axe, handsaw and adze? 

    Goodness me, such hyperbole! I didn't say anything about exclusively using a table of offsets. Also, I don't see anything retrograde about using tried and trusted simple methods, we don't have to throw the baby out with the bathwater as we rush headlong into the future.

    I dug out an old copy of Percy W. Blandford's Boatbuilding for an example of how little you need to start building yet his lovely pram design doesn't even require offsets, just a few pages of instruction and a couple of drawings. Could easily be made from ply. Also in the book, a 10' rowing boat presented as offsets. Yes, that's going way back to 1953, more recently Reuel Parker's Sharpie Book contains offsets for all the designs in the book, and then rushing on into the 21st Century; Chris Morejohn presented his Hogfish 28 on his blog, provided a table of offsets and more or less said that's all you need, go build. I think this design lead to Frederick's HFY36... pretty contemporary, and certainly an example of modern, fast, efficient ply boatbuilding. 


    2 files
  • 01 Apr 2022 11:58
    Reply # 12689886 on 10211344
    Anonymous member (Administrator)

    Graeme wrote: I still think ply is better than fibreglass for a dingy, Arne.»

    I don’t disagree, for sure. In addition to being lighter, they are also easier (or more inviting) to be modified or customised. It is super easy to increase or reduce the beam of the pram type plywood dinghies, to suit the needed carrying capacity. As shown earlier, I now aim on fitting enough frames (elbows) to secure the shape of the boat without structural thwarts, and thus be free to fit whatever interior one fancies.

    Arne


  • 01 Apr 2022 10:54
    Reply # 12689829 on 10211344

    Perhaps Arne had in mind the rotomoulded and vacuum formed dinghies (eg Sportyak) and sit-on kayaks - that is how to mass produce a robust knockabout boat. But they are all heavier than GRP, which is heavier than plywood.

    CNC cutting is the way for cash-rich but time-poor folks to build a plywood boat. And I suspect that many of the clients of the likes of Jordan Boats, Fyne Boats and other kit boat suppliers are first time builders who are not confident enough that their lofting and cutting abilities are up to the task.

    Last modified: 01 Apr 2022 10:58 | Anonymous member
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