Oyster by Mike Howard

09 May 2021 09:03 | Anonymous member (Administrator)


‘OYSTER’ has her origins in an article published many years ago in the Practical Boat Owner. John Teale's design was for a ‘square’ pram dinghy to be used as a tender for a larger boat. It was split in two so that one half stowed inside the other. His desire to adopt a reverse vee shape for the bottom panels was that it produced a much more stable dinghy than the conventional vee bottom version.

Please look at this complete document to read the full details of Michael's design.


Comments

  • 19 May 2021 10:16 | Anonymous member
    I have some misgivings about the W shaped section. If water has been shipped, when launching off a beach, it is unlikely to be evenly distributed, and if the dinghy heels so that all the water is one side, might become positively dangerous. It's a pity that the build wasn't completed, as it would have been good to get some practical feedback from regular real-life usage.
    Link  •  Reply
    • 21 May 2021 08:09 | Anonymous member
      In some ways this is the most interesting design of all. There is no repertoire of clever small details – in fact what we see here is fairly basic. Instead, there is a single large radical departure from what we expect to see in a dinghy (a bit like Arne’s Halibut rig – a paradigm shift).

      Radical hull shape aside, a look through the “Oyster structural details” list shows a plain, down-to-earth build – full marks for that (apart from the fixed rudder). For a stem dinghy, the seating layout makes sense, and the T-shaped rowing thwart facing aft seems to give the ability to easily adjust positions between one and two adults aboard. Not sure about three – two amidships with an oar each?

      I am not sure that I agree with David’s primary objection to the W section. If it shipped significant water, it would take on a definite list – easily corrected by a simple shift of the bum. A half-full flat bottom boat, on the other hand, is impossible to trim out. The shipped water is most certainly not evenly distributed, as David will well know. It too will run to one side – whichever side you happen to be on! And whichever way you shift, the free water will run to your side, and it will get there before you do, leaving you worse off than before. Then repeat. It’s called unstable oscillation and can land you in the drink within about 2 iterations. The only cure for that eventuality is for-and-aft bulkheads, which are not a practical idea in a small dinghy. The W shape might in fact be a partial solution to that problem. Also, maybe it gets around the dreaded “dragging an immersed transom” issue which has exercised some of the other designers.

      I would like to build this dinghy – just to see how it performs on the water – I simply have no idea. I would also very much like to see if it really will sail to windward without a centreboard. Once again, an 8’ dinghy is probably too small as a test platform to learn very much from. Does the extra build-effort of gluing up an inverted V tunnel provide sufficient benefit to be justified? It might. How will it tow? It might be very good. Pity the prototype was chopped up. I do hope someone builds one, it might be surprising.

      If I can figure out the plywood nesting drawings I might have a go at making a model.
      Link  •  Reply
      • 05 Jun 2021 14:19 | Mike Howard
        Thank you for your comments. The eight foot length of the plywood sheet is extended by utilising the two internal offcuts, 'A' and 'B'.
        Link  •  Reply
    • 05 Jun 2021 14:20 | Mike Howard
      Thank you for your comments. The twin bilges prevent water from sloshing from side to side.
      Link  •  Reply
  • 20 May 2021 00:21 | Anonymous member
    Comment deleted
    • 20 May 2021 10:03 | Anonymous member
      I agree, Graeme, someone should build this, to see whether my armchair misgivings are justified. Yes, it's something different, not just yet another boring dinghy, so it needs trying. It's no more difficult to build than a conventional 4 plank V bottom, though I wonder whether the tumblehome top strake is justified snd necessary.
      Link  •  Reply
      • 20 May 2021 10:16 | Anonymous member
        PS. Is there a case for Paradox-style chine runners here, if there is to be no leeboard?
        Link  •  Reply
  • 21 May 2021 01:26 | Anonymous member
    I wondered exactly the same thing (small chine runners) - but they can't be Paradox-style as the bottom is not flat. Still, a small appendage mounted on the side strakes, at the chine, would be an interesting thought. If needed. Must try only one thing at a time.

    Contemplating a model - the top strake is going to add a lot of extra work. Its part of the deal though - stiffens the gunnel, increases the range of stability - and tumble-home is easier to paddle over the side from, should the need arise. You kayakers will know that.
    Link  •  Reply
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

                                                              Site contents © the Junk Rig Association and/or individual authors

Powered by Wild Apricot Membership Software