Cash prize of 250 GBP - Dinghy Design Competition

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  • 09 Apr 2021 11:56
    Reply # 10290636 on 10211344
    Anonymous member (Administrator)

    Deviding the JRA dinghy project into two steps.

    Now it looks to me that the discussion around the 2.4m JRA dinghy has completed a full circle. I and others started with suggesting rowing-only tenders. I then added a dead simple downwind sail, but with no board or rudder planned for it. Then came the junk rig demand, and the 3-panel sail for Halibut was introduced. At the same time, the lines of Halibut were adjusted for better stability. After many words written around the bow-board, leeboards, fixed keel and, finally, the usefulness of a rig at all, we are now back on the rowing tender.

    Here is what I will do:
    Step One:
    I will present the Halibut design with the cb. slot fitted from Day One. I will then suggest that you build it with the slot in (easier during building than retrofitting it), and then go rowing in it.

    Step Two:
    If the desire arises for sailing Halibut, the rig, rudder and bow-board can be constructed and fitted to complete the project.

    Arne


    Last modified: 09 Apr 2021 23:30 | Anonymous member (Administrator)
  • 09 Apr 2021 09:15
    Reply # 10290141 on 10211344

    No David, I expressed that poorly. Not talking about skin on frame (I've never even seen one) or super light weight. By referring to Annie's dinghy I was more referring to its "niceness" in relation to being dragged on its skegs.

    A JRA dinghy such as Arne's Halibut should be easy to carry that way. 8' is about the limit, unless you are tall. You stand it on its transom, snuggle the small of your back into the thwart, reach up with your hands to the forward thwart - and lean forward/straighten your legs, and you can waddle along no problem. The weight is not much of a problem and its easy to put down. Its more a question of your reach. Easier than trying to get a miniature curragh  onto your back, I should think, although I've never seen one of them either. I'm only average strength - less these days.

    Last modified: 09 Apr 2021 09:41 | Anonymous member
  • 09 Apr 2021 08:45
    Reply # 10290094 on 10211344
    (If it were lightly and nicely built, like Annie’s FanTan, I think I would rather carry it on my back like a turtle, which is easy and often done here.)

    We're straying into "The Ideal Tender" territory here, rather than "JRA tender designed to sail under JR" territory. But yes, a dinghy that weighs the bare minimum is best carried coracle- or curragh-fashion, on the back. When I had a miniature curragh, 2.65m long x 1m beam, I could very easily swing it up onto my back by grasping the thole pins. A skin-on-frame boat makes a very satisfactory lightweight rowing or paddling tender, but perhaps not a sailing tender.


  • 09 Apr 2021 08:29
    Reply # 10290055 on 10211344
    We have to ask why a tender should be sailed at all. In my experience it is mainly for fun, will take place mainly in the sheltered waters of an anchorage, often involving children, and where  I live, almost certainly off a gently shelving beach.

    Indeed we do have to ask. It's not because sailing is the best way of propelling a yacht's tender when it is acting in its main role of conveying crew and stores between mothership and shore. Rowing a dinghy is better for moving a heavy load to windward, and paddling a kayak is better for making a lot of distance to windward. That being so, I tend to agree with the concept of providing a tender with means for sailing to and fro across the wind for fun in the manner of a sailboard, which generally only has skegs. Twin skegs on a tender would seem to answer well enough. 

    Samuel Johnson wasn't a small boat sailor, but if he had been, he might have chosen a different simile here:

    Boswell: I told him I had been that morning at a meeting of the people called Quakers, where I had heard a woman preach.  Johnson: "Sir, a woman's preaching is like a dog's walking on his hind legs. It is not done well; but you are surprised to find it done at all."
  • 08 Apr 2021 20:49
    Reply # 10288512 on 10211344

    I think this is an improvement on the original concept in that it provides for the first time a way of mounting the board which looks mechanically credible, ie could actually be removeable, firm while in place – and with a limited ability to fold back in the event of striking something. As you say, “half way” between a dagger board and a swinging board. (I guess it is held in the vertical position by a “weak link” (breakable dowel peg))?

    A dagger board right at the bow, which is what this essentially is, might perhaps need to be able to break out of the slot in the manner you have drawn. I take it there is some sacrificial component pinning it in place?  (Maybe a bungy would be better than carrying a bag full of replacement dowels). Otherwise the bow transom would need to be good and strong to absorb the impact of the leveraged board hitting the bottom, the dinghy and contents having potentially quite a lot of momentum. I still don't like it much. As David points out, it is an inherently directionally unstable configuration - you won't have time to tie your shoelaces with this one, in fact I'd be inclined to leave my shoes ashore.


    We have to ask why a tender should be sailed at all. In my experience it is mainly for fun, will take place mainly in the sheltered waters of an anchorage, often involving children, and where  I live, almost certainly off a gently shelving beach. A dagger board on such a tiny dinghy perhaps makes more sense than a swinging board – both have their merits - but there is no way I would put it in the bow even if it proved possible to sail with it in that position. I leave that to you, in your beautiful sailing grounds.

    Arne wrote: “…and the board itself could be fitted and removed from the safety of the fore thwart”.

    I think I would remove the word “safety”, as an adult kneeling on the forward thwart of a lightly constructed 8’ pram dinghy is going to have an interesting effect on the trim if there are no other occupants. If caught in a squall and a bit of a chop, at the head of a bay, you’d want to be careful doing that. Don't forget the clutter of the mast and sail right up there as well, and all that needs to be negotiated while retrieving the board and bringing it into the dinghy, in the event of needing to revert to rowing.

    I return to my original question “why?” and have now convinced myself that if the dinghy were mine I would simply give it a little bit of fixed draft, by way of a deadwood keel from the forefoot to amidships. Then a pair of matching (depth) skegs aft, as I agree this is best if you are dragging the dinghy down a concrete boat ramp. 

    (If it were lightly and nicely built, like Annie’s FanTan, I think I would rather carry it on my back like a turtle, which is easy and often done here.)

    With the amount of rocker you have, an increase of 50mm in the draft full length would probably be enough to sail to windward, and it would sit nice and flat on a trailer or upright on a roof rack too. And maybe it would row better too? (I am not sure.)


    Anyway - I am sure I am not alone in awaiting with considerable interest (and a certain amount of anticipation) the results of your trials with the bow board. Your willingness to push the boundaries is admirable. I am sure the Wright Brothers were given as much skepticism from the sideline.


    Last modified: 09 Apr 2021 02:42 | Anonymous member
  • 08 Apr 2021 14:38
    Reply # 10287320 on 10211344
    Anonymous member (Administrator)

    Graeme,
    maybe we could meet on the middle?
    Here I have brought the bow-board more or less inboard by fitting it in an open-front cb. trunk. The buoyancy bulkhead (not shown here) will be the aft wall of that trunk, and the buoyancy tank will effectively be cut into two separate ones. This slot for the new cb. cum bow-board will be rock steady, and the board itself could be fitted and removed from the safety of the fore thwart.

    Arne


  • 08 Apr 2021 10:53
    Reply # 10286769 on 10211344
    Anonymous member (Administrator)

    Thanks, David,
    Bic must have beefed up the design since I bought mine for Malena. That makes sense, as mine felt rather 'thin'...
    Arne

    Last modified: 08 Apr 2021 10:54 | Anonymous member (Administrator)
  • 08 Apr 2021 10:47
    Reply # 10286752 on 10211344

    The Sportyak 213 is too heavy for me, at 23Kg. That's more than my larger kayak at 18Kg, and it would be impossible to stow aboard. The 3D tender's bare weight is 8Kg, with only a foam seat and paddle to be added.

  • 08 Apr 2021 10:37
    Reply # 10286715 on 10211344
    Anonymous member (Administrator)

    David,
    and then there is the 7’ (18kg?) Bic Sportyak. I had one for several years, and liked it. It could carry two not too big persons and rowed well enough. I kept it on deck for longer trips, and towed it behind when inshore. It eventually fell apart  -  the bottom was rather thin...

    Arne


  • 08 Apr 2021 10:20
    Reply # 10286690 on 10211344
    PS Also hoping David will progress his thinking, at least to the "proposal" stage. Much as I like the "pre lim" - it would be good to have a "san ban" also for consideration, as I still think "three planks" is good enough for such a small dinghy.

    No, sorry Graeme, I'm not going any further, as I've said. If someone approached me, and said that they need to build a dinghy but that their requirements are not met by any existing design, I'd do what I could to help; otherwise, designing in a vacuum is rather pointless. Arne says he is his own 'client' and is designing halibut for his own needs. Fair enough. If I consider myself as my 'client', then my need is for a lightweight tender that can be rolled up and stowed in Weaverbird's forepeak, or kept on the starboard side deck. Just possibly a hard tender could fit there, but it would have to be something like a cross between a sit-on-top kayak, a punt and a SUP, 3m long and 0.8m wide - and it's very unlikely that anyone else would have the exact same requirement.   

    For information, I've withdrawn my 3D superlight round tail tender from sale, as I am considering all the options that I have for this summer's cruising. I already have a 3.8m inflatable kayak (very good to use, but rather heavy and difficult to get aboard), a 2.4m sit-on-top inflatable kayak (light and manageable, but little carrying capacity), and the 1.8m 3D tender (very light, with enough carrying capacity for stores, but impossible to row). I was looking at the heavy duty PVC packrafts from Neris, and it occurred to me that the 3D tender is almost the same in size and weight as one of those, if I take off the thwart, get rid of the rowlock fittings, and put in the seat and backrest from my larger kayak. The internal length is not much greater than my seated length measured from my back to my feet, so I'm sitting either at the bow or at the stern. The bow does not have enough buoyancy to support me, so sitting at the stern and using a kayak paddle, packraft-fashion, is how it has to be. I say all this just to illustrate to the point that everyone, and every mothership, will have a different set of requirements to meet. Mine are not likely to be the same as anyone else's.

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