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Cash prize of 250 GBP - Dinghy Design Competition

  • 30 Mar 2021 12:54
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    Reply # 10252381 on 10211344
    Anonymous member

    An atmosphere of friendly collaboration spurs me on to do better than I can do on my own, and has got me thinking about how to combine the better sailing and rowing qualities of Arne's 5-plank Halibut with the stability and practicality of my 3-plank.

    So I've used the transformation tools in Freeship to make the original SibLim form into a dinghy with a bow resembling the bluff bow of the Northern China junks. The width of the flat bottom is not as great as my 3-plank, but is enough to give a flat area to stand on over the whole of the non-tanked area.

    Here's my Wuban 

    It's 2.335m long with 1.04m beam and a draught of 0.2m when laden to 250kg displacement, which just immerses the bottom of the transom. I can nest the components onto three sheets of 4mm or 5mm plywood. There is enough surplus plywood to make a daggerboard case, when I figure out how and where it goes. The lines drawing shows a pretty stable midship section.

    Stitch, fillet and tape construction, with some locating tabs and slots in appropriate places, would be used. The building sequence would start with laying down the tank top, upside down, onto a flat surface, and assembling onto it the tank sides, stn 1 and stn 4 which would be made to slot together like a # - that would make a stiff structure ready to receive the bottom panel, then the middle panels.

    It will of course be fitted with the Halibut rig in due course.

    6 files
    Last modified: 30 Mar 2021 13:24 | Anonymous member
  • 29 Mar 2021 23:17
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    Reply # 10250367 on 10211344
    Anonymous member

    Arne:

    I like that sail plan. As I happen to have an 8 foot dingy looking for a sail (sorry not my plans and even worse: 4 planks) I am thinking that will work wonderfully.
  • 29 Mar 2021 22:24
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    Reply # 10250170 on 10250128
    Anonymous member (Administrator)
    David Tyler wrote:

    Here’s the 'Halibut' sail on my tender. There are just two changes: 1) as we’re reefing upwards, the normal rule for sheet drift doesn’t apply, and we don’t need the bumkin; 2) I’m convinced that instead of a halyard there can be a little strop with a hook or snapshackle. If the lifts are cleated to the mast, we can brail up and then lift the whole rig out of the step.



    David, you are of course free to reef upwards, using the lazyjacks as a brailing line. I, on the other hand meant to reef the sail conventionally, and also drop it that way. Only with the the sail resting in its lazyjacks did I mean to brail the sail bundle up along the mast. The length of mast and battens were calculated such that the brailed-up sail bundle would be flush with the mast top

    I would only reef upwards when I needed headroom for rowing until the wind picked up.

    Clear as mud, right?
    Arne


    Last modified: 29 Mar 2021 22:26 | Anonymous member (Administrator)
  • 29 Mar 2021 22:15
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    Reply # 10250144 on 10211344
    Anonymous member

    My entry for the dinghy design competition is a version of the two part dinghy I posted to the website a year or so ago. I have sent the drawings to Mark but thought that my version of the rig may be of interest here. I originally designed the boat with a 45 sq ft balanced lugsail. This has performed well and balances nicely with the dinghy. I therefore designed a junk rig based on the lusail profile, of the same area and the same center of effort. It is a four panel sail with two parallel lower panels and two triangular upper panels. The halyard is just a rope through a hole near the top of the mast and attached to the yard by a topsail halyard bend or a spar hitch. The topping lifts are a rope knotted either side of another hole just above the halyard with a barton ring on the lower ends; the lower topping lift is attached to the boom at the aft 1/4 point of the boom and threaded through the Barton rings and down to a small cleat at the forward 1/4 point of the boom. There are fixed parells on the yard, battens and boom that are attached to the forward ends and close behind the mast, in order to hold the sail in the designed position. I use a short length of 3 inch diameter PVC pipe threaded over the mast, that has a short length of cord top and bottom, so that when the sail is lowered all of the parells are tied in place and also the sail bundle, the mast can then be pulled out and tied to the bundle. Then when raising the sail everything is in place to just plug in the mast, untie the bundle, hoist the sail and go!

    I use wood for all of the pieces. The yard and boom are finished at 1-1/2 inch square at the mast crossing and taper to 1 inch at the ends. The battens are finished at one inch square. All edges are rounded over at 3/8" or 9 mm. The boom and yard are laced to the sail. The battens are bolted to the sail at the ends with coach bolts. The head side passes through a grommet in the sail and the nut side is recessed into the batten , I use nylock nuts  and stainless bolts and washers. The batten ends are flush with the edge of the sail.The battens are in pockets attached to the sail.

    The sheet horse is a length of 8 mm line threaded through two holes in the transom and knotted on the inside; a short length of 12 mm Alkathene pipe is threaded over the line to take the wear and is slippery enough that no block is needed. The sheet is tied to the end of the boom, goes around the sheet horse and back up to a Barton ring that slides on a sheetlet that spans between the two parallel battens (it threads through holes just forward of the bolts holding the sail and a stopper  knot on the end). The sheet then goes back through the horse and forward to the helmsman. A thumb cleat on the top of the tiller can be used to temporarily hold it. If a slightly larger sail is required then the two lower panels can be enlarged to two feet, adding 7 square feet, or even more if more area is required. A corresponding increase in the mast length would be required.

    Attached are a photo of the sailplan ( which also shows the balanced lugsail), and a couple of photos of the dinghy as built.

    4 files
    Last modified: 29 Mar 2021 22:19 | Anonymous member
  • 29 Mar 2021 22:11
    Quote
    Reply # 10250128 on 10211344
    Anonymous member

    Here’s the 'Halibut' sail on my tender. There are just two changes: 1) as we’re reefing upwards, the normal rule for sheet drift doesn’t apply, and we don’t need the bumkin; 2) I’m convinced that instead of a halyard there can be a little strop with a hook or snapshackle. If the lifts are cleated to the mast, we can brail up and then lift the whole rig out of the step.


    1 file
  • 29 Mar 2021 19:47
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    Reply # 10249773 on 10211344
    Anonymous member

    Thanks for the drawing, Arne. I'll see if I can put a boat underneath it.

    Yes, I too think that it was a mistake to offer a prize. We do these designs in the hope of helping our fellow sailors, not in the hope of reward. I had already decided that if a design of mine were to be selected, I would donate the prize to charity. 
  • 29 Mar 2021 17:58
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    Reply # 10249285 on 10244832
    Anonymous member
    Anonymous wrote:

    Jan,

    the fourth step of my 60second stowing procedure was to unstep and lower the mast.. I would struggle to de-rig the boat more than that ;-) ...

    Arne

    Arne, congratulations on your senior appointment.

    Yes it may be a struggle to de-rig past step four and hopefully nobody has to go as far as step 5a; throwing the whole bundle overboard as it's getting in the way in a gale force survival situation or 5b; trailing the whole bundle behind on a rope as a drogue in a gale force survival situation! 
  • 29 Mar 2021 15:49
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    Reply # 10248706 on 10211344
    Anonymous member (Administrator)

    About that competition, not to mention the cash prize, I couldn’t agree more with you, David. I have an itching feeling about the competition bit, so now I just sent you the drawing of the Halibut Special rig in  .dxf format. Maybe you can make it fit on your preferred 3-plank tender. If any of the others here would like to have a copy as well, just drop me a line, and I’ll mail it to you.

    As for 3-plank versus 5-plank tender; this shows that we have different needs. I don’t have to haul water, petrol or lots of groceries to the ship with the tender. The tender is mainly meant for either getting ashore on a quiet anchorage, or to do a quiet evening sightseeing along the shores after having dropped the hook. An easily driven tender makes this an extra joy.

    I wish the cash prize competition would go away. I fear that many JRA-members with good ideas let be sending their ideas in here because it suddenly got too serious. I don’t want it to be serious  - I am a pensioner now, don’t forget!

    Arne


    Last modified: 29 Mar 2021 15:58 | Anonymous member (Administrator)
  • 29 Mar 2021 13:12
    Quote
    Reply # 10248176 on 10211344
    Anonymous member

    I must say that I'm uncomfortable with the idea of this being a competition, and think that a better final result is likely to emerge if it's seen as a collaboration, instead. That's the way it seems to be happening on the forum anyway.

    I applaud Arne's vertically brailed rig, and think that with a few tweaks to optimise it, and subject always to sea trials, it's as good a solution to the tiny JR problem as is likely to come forward.

    But the 5-plank Halibut, though it's a good dinghy, is not a perfect yacht's tender in my view. I feel that a 3-plank sampan or whatever does a better job, thinking of all the tasks that a cruising yacht's tender has to perform, whatever strange part of the world it happens to be in. Carrying stores, fuel and water; laying out a kedge in a rising wind; landing on and leaving any kind of shore; knocking about on a crowded dinghy dock, when crews have to step from boat to boat to reach their own; these kinds of things require more stability and less draught than a 5-plank hull provides. Just occasionally, when the crew decides to take a day off and go exploring upriver, a 5-plank will be nicer to row and sail, but otherwise the 3-plank wins on practicality.

    So, what I'd like to see is Arne's rig on a dinghy something like my 3-plank design.
  • 29 Mar 2021 00:27
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    Reply # 10245979 on 10211344
    Anonymous member (Administrator)

    Welcome to the pensioners' club, Arne


    A tender tender vs a stiffer tender...


    I'd go for the sailing version because

    1. The competition calls for a sailing dinghy and I think you might have found the perfect tiny rig.

    2. It will have more initial stability and feel more comfortable to get in and out of, especially for people not used to dinghies.

    3. It will still row just about as well. 8' is too small for a proper rowing boat anyway

    (I suppose 1. and 3. arguments could just as well be reversed. And I suppose the rowing version might actually be the best sailer, if you don't mind sitting right in the bottom of the boat.  However, 2. argument is strong, and clinches it for me - I'd go for the shallow-dish version for an 8-foot tender, every time.)

    Question: The rowing version is only narrower on the WL when light - once loaded down, the sailing version will be better anyway, won't it?

    Congratulations on a proposed sailing dinghy that is starting to look seriously practical - AND not something that already exists.

    Last modified: 29 Mar 2021 04:05 | Anonymous member (Administrator)