JRA Dinghy Competition 2021
Background

Back in 2017, the JRA committee discussed the idea of creating a one design JRA dinghy that could be used as a tender, a test bed for JR ideas, or to get several dinghies together with different rigs to compare performance.  A designer offered to create a set of plans that would do the trick and could be shared with members, but then got caught up in different projects.

In 2020, the committee decided to resurrect the idea.  After some discussion, the committee went back to an earlier suggestion and decided to create a competition for members and beyond.  The posts below show the entries and have a place for JRA members to add their comments and thoughts - please use the level of respect and consideration in the forums.

The plan is that the judging committee will be put together and final judging will take place late in May and a winner will be announced in June.  For now, though, please enjoy having a look through the designs.

Edit - two designs submitted through the forums added 16th May


  • 16 May 2021 18:32 | Anonymous member (Administrator)

    The lines plan shows Halibut being symmetric fore and aft of the central main frame (stn. 2), just like a shuttle ferry. I found no reason for not doing it like this, and the design and building will be faster this way. The way the curves along the panels run, also saves time when building. When plank no. 2 (bottom side) has been lofted and cut out, it can be used for scribing the lower edge of the topsides and for the side edges of the bottom plank. Only the sheer line has to be lofted in addition.

    As for the 3-panel “Halibut Special” JR, I am quite confident that this will work. After all, it is mainly a top section of a JR, which I am fairly familiar with. The whole idea with it is that the lowered sail bundle can be brailed up with the topping lifts and stowed flush with the mast. The rig can then be lowered for easy stowing  -  and easy rigging again.

    That sail has been made very small, to bring the mast length down to 2.5m. I would not be afraid of scaling this rig up to 3-4sqm with the same number of panels. If that mast is lengthened from 2.5 to 3.0m (20%) and the sail is also expanded accordingly, the sail area would end at 3.6sqm (the sail of the Optimist dinghy is 3.3sqm).



  • 16 May 2021 12:31 | Anonymous member (Administrator)

    I think of this design in the same terms as the initial design brief for SibLim: given a very particular set of requirements, what design will best fulfil them? So I'm imagining a dinghy for a SibLing, a sistership to FanShi, planned to have davits and a complement of two people of average build who will require a workhorse of a tender that can carry them and a reasonable payload to and fro in anchorages that may not be entirely sheltered; and occasionally, will put a simple sailing rig aboard, just for fun. Alter any of those requirements, and a different dinghy is the result. Take away the davits, for example, and the dinghy must be an inflatable, stored on the foredeck.

    These drawings are for manual marking out and cutting from 3 sheets of 4mm plywood, and conventional framing using 20mm sq softwood. I would have to add dimensions and more details, and write down the building sequence, but the major components are there.

    Alternatively, I could add the detailing necessary for CNC cut, slot together construction.

    The sail is 2.4 sq m, large enough, I think. The battens are three equal lengths of 1.66m cut from a 5m tube. The mast is 2.4m long, to act as a cover ridge pole, and the yard is 1.4m, both from a 5m x 45mm dia tube. A 3-point sheet span with single part sheet, a single part halyard and the simplest possible lifts complete the rigging. Steering by oar permits sculling through the un-sailable bits.


  • 09 May 2021 09:08 | Anonymous member (Administrator)
    She was originally built from a design sketch, that I no longer have, as a tender for Arcadian in her original form as Spirit of the Deep. She was designed as a "maximum" 8 footer to carry charter guests and stores to the boat and handle up to a 5 horsepower outboard motor She served well in that capacity, firstly as a rowing tender when she took two or three people and a lot of stores, and once even five people! I later converted her into a sailing dinghy and that is the version I have drawn up, but with a junk rig rather than the balanced lugsail she originally had. She is still serving the new owner of Arcadian in that respect and he is very happy with her performance both as a tender and as a sailing dinghy. He says he has taught a lot of people how to sail using her.

    I have called her AD (Arcadian's dinghy) to differentiate her from my other submissions.

    I hope that you like her as much as I do.







  • 09 May 2021 09:07 | Anonymous member (Administrator)

    John's very detailed introduction to his design and the thoughts behind it are in this document.  The drawings below are in order as referenced in the document.








  • 09 May 2021 09:06 | Anonymous member (Administrator)

    This is a variant of the dinghy I posted a couple of years ago in my designs on the website. I recently built a proof of concept prototype and have attached some photos of the build, more available if wanted.

    The design as shown on the submitted plans is a one-piece dinghy, but it can be made into a nesting two-part dinghy, which reduces the size for storage onboard. I re-used a 45 sq ft balanced lugsail rig from another dinghy design and have included in the design for that rig or a four-panel junk rig of approximately the same area.

    The dinghy rows and sails nicely and is good in choppy conditions with its fine bow, deadrise, flare, and rocker.

    Construction of the hull is very simple, the bottom is a single sheet of 1/4" plywood split diagonally from corner to corner and a 3'-10" curve is cut into the panels as shown on the drawings. These two pieces are then joined at the forward and aft end. The parts are not joined along the centerline at this stage. The small transom is constructed as shown on the drawings. The second sheet of 1/4" plywood is cut into three 1'-4" wide pieces, one of which is cut in half. The full-length pieces are then attached to the half-length pieces with an epoxy glass scarf using a 4" wide piece of 12 oz double bias tape overlaid by a 6 inch wide piece of 6 oz glass cloth. The sides are then screwed and glued to the transom, the square end of the side panel being aligned with the start of the taper on the edge of the transom piece. The assembly is then attached to the bottom. The transom sits on top of the bottom piece and the sides lap down over the bottom and are fastened at about 6" centers by cable ties, working from the stern forward. The holes in the side panels need to be drilled 1/4" clear above the bottom to allow the bottom panel to fit inside and be drawn up tight and level when everything is assembled. The holes in the bottom panel should be clear at least 3/8" from the edge and should be drilled to align with the side panel holes as the sides are installed. Once the side panel has been attached up to the bow mark a vertical line on the side panel, then measure 7 1/2" forward from this point, draw a line from there back to the bottom panel, and cut off the excess. The stem post should then be installed to hold the sides together. Leave about 3" above the sides to allow for a purchase to be attached from the transom to get the correct rocker and flare to the hull.

    Clamp a straight timber to the top of the side planks to keep the side straight for the first four and a half feet from the bow, this helps ensure that the hull has the correct flare. Attach a rope in a loop around the extended stem and through the sculling port to a short cross timber on the aft face of the transom. This can then be rotated to tension the rope and hold the hull at the designed flare and rocker. This will create a narrow tapered gap between the two halves of the bottom panel along the centerline. This should be filled by tapered slivers cut from the offcuts of the bottom panel. Once these have been glued in place then the bottom joint can be glassed and epoxied with two layers 12 oz biaxial and one of 6 oz cloth inside and out.

    At this stage the cable ties connecting the sides to the bottom can be finally tightened and aligned. The joint on the inside can then be filled with an epoxy cove and glassed with a layer of 12 oz biaxial and topped with a layer of 6 oz cloth. Once this has set the cable ties can be cut off on the outside, the joint filled, and when set rounded to a radius of at least 1/2". The joint is then glassed with the same layup as the inside.

    At this point, the hull is basically complete and all of the finishing etc can proceed from there as it would for any other dinghy.






     


  • 09 May 2021 09:05 | Anonymous member (Administrator)

    John's design is described in detail along with explanatory drawings in this document.  John also supplied .dxf files of pretty much every component. The introduction and illustration below are both taken from the document.

    The aim is a general purpose boat, a little under 2.4m overall length, that can be used with oars, small outboard motor (2 to 3 h.p. suggested) or under sail.

    This could be used as a yacht tender although it is acknowledged that for many yachts an inflatable tender is more practical being more easily carried on board and less likely to damage the parent yacht or other boats when left at a quayside. Also, these days an inflatable tender is probably cheaper than the materials to build a plywood tender.

    A stowage compartment at the bow is accessed through a lockable hatch having a 450 x 450 clear opening. This compartment should be rain and spray proof but it is not intended to be watertight in the event of capsize. There are good size buoyancy tanks at the sides of the boat so it is not necessary to consider the bow compartment as part of the buoyancy provision.


  • 09 May 2021 09:04 | Anonymous member (Administrator)

    I think the attached design which my grandsons developed years ago answers the design brief quite well.  I am entering my write up of their work on their behalf. I hope this is permissible with the rules. Slieve's write up - and the story of how he and his grandsons came up with the design is in this document.



  • 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.


  • 09 May 2021 09:02 | Anonymous member (Administrator)

    This is a design I did back in 1979 for an 8-foot dinghy. I have built a number of these as well as a version stretched to 10 feet long. It has proved to be a very good dinghy design, rows well and sails extremely well (I used to sail rings around the Sabot fleet in Marina Del Rey with the prototype). I would like to enter this in the dinghy design competition in addition to the one I sent yesterday. The sail on this is virtually the same as the one on my other design, so the junk sail I drew would also fit this, but would need a boomkin for the sheeting.


  • 09 May 2021 09:01 | Anonymous member (Administrator)

    Alex says, "Let me introduce my dinghy design. In French we call this kind of boat a “youyou” and it appears that the name, like the junk rig is originated from China! So we have a link!"

    More information is in the explanatory document and the drawings below.



       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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