Cash prize of 250 GBP - Dinghy Design Competition

  • 24 Mar 2021 07:55
    Reply # 10229805 on 10211344

    Graeme, I know all about the impracticability of a full-on JR on an 11ft 6in dinghy. Have a look at the front cover of JRA NL 31, 1995. My dinghy Dorothy has a mast that is the same length as the boat, so that it can act as a ridge pole for the cover, and it is the work of a moment to step it in a Yorkshire Coble type of tabernacle. The sail was another matter. I used to get into awful tangles with the sheet and lifts. Then I made a mast extender - an alloy tube that slipped onto the top of the mast to ship a taller sail - and the tangles resembled the Gordian Knot. 

    So, yes, the challenge is not to design a dinghy. The challenge is to design a simplified form of JR for a dinghy, be it 8ft, 12ft or 16ft, that would be practical enough to actually get used regularly, without causing undue frustration.

  • 24 Mar 2021 07:32
    Reply # 10229756 on 10228715
    Arne wrote:

    2.4m tender «Halibut»

    • ·         The rig is only an add-on for downwind use  -  only fools row downwind...
    Quick question, Arne: your forefathers in the 10th century used square sails for blowing downwind, putting down their battleaxes and shields to row upwind - had you considered putting a light spar along the head of the sail? Then raise one oar as a mast, steer with the other??
    Last modified: 24 Mar 2021 07:34 | Anonymous member
  • 24 Mar 2021 02:44
    Reply # 10229249 on 10211344

    EDITED

     I do own that I made the statement 8' is too small to be worth putting a junk rig on which was a value judgement I should not have made in such blunt terms. I apologise for that, because I do sincerely support and appreciate the efforts of the committee and did not mean that statement to be as negative as it sounds.

    Of course you can put a junk rig on an 8’ dinghy, as we know it has been done. In fact, I am eagerly looking forward to seeing Annie’s junk-rigged tender when the competition eventually yields a winner – in which case I might be very tempted to have a go at making one too.

    (By the way, evidently the committee has thought about this and is maybe on the right track, because nowhere in the criteria is there any requirement for the JRA sailing tender to be junk rigged – merely that it should be easily reefed. Annie and I both overlooked that small point, and it makes a bit of a difference).


    The sponsored JRA dinghy design really ought to be junk rigged, despite the small size of the boat and the (in my opinion) impracticality of it. Annie is absolutely right in her vision of fun and frivolity arising from a few little junks buzzing around the anchorage at a junket. That, surely, must be the main goal and point of the exercise, and is surely more fun than sitting around at anchor all day, which is what I have observed most people doing at the “tall ships” I have attended in the last three years.

    Therein lies the real challenge. There are plenty of simple-to-build plywood tender designs which are known to be (more or less) suitable. But no-one has yet designed a junk rig especially suitable for an 8’ dinghy. That would be a worthwhile challenge.


    The real challenge is not to design the hull, but to make a variation of the junk rig which can be carried as a bundle in one hand, spar lengths stowable, able to be set up or struck in a jiffy (or at least just a minute or two) and able to deploy while actually on the water. Then we will have a tiny, practical junk-rigged tender which will be reefable and really safe to sail away in, turn envious eyes – and actually get used.

    Can it be done? Yes, I think maybe it can. 

    I’m in support of the JRA Tender competition - but I am still going to pursue the junket boat idea.

    You can’t have too many boats…. can you?


    Edit: I've just seen Arne's latest post which popped up while writing this.

    Well done, I love the 5-plank configuration. Handsome and jaunty Halibut is crying out for a little centreboard and rudder, and a bit better sail plan. Back to the drawing board Arne, for 2-minute-deployable Johanna rig!

    When sailing a little dinghy you have to shift your bum around a bit - sometimes from the bottom of the boat (which is the best place) to a thwart. When you get old like me, low thwarts are the best. Its a little beauty Arne.

    So far, David has produced the simplest-to-build hull shape and best arrangement of buoyancy, moveable thwart, and off-centre board (one's enough I reckon) and the best looking rig, but presumably the judging committee will need to see some more details, ie the running rigging and how quickly it can be deployed.

    Last modified: 25 Mar 2021 22:12 | Anonymous member
  • 23 Mar 2021 23:01
    Reply # 10228715 on 10211344
    Anonymous member (Administrator)

    2.4m tender «Halibut»

    Now, of course I could not keep my cotton-picking fingers away from the keyboard, so here are the first two sheets for a design for a 2.4 x 1.3m(!) plywood tender. My two main design goals are:

    • ·         Easy rowing with one or two persons on board.
    • ·         Safe capacity for three persons.
    • ·         The rig is only an add-on for downwind use  -  only fools row downind...

    Next challenge is to be able to develop the plywood sheets  -  using the 2-D QCAD program. Thanks to the simple design with constant deadrise, it should be doable.

    The thwarts have been set quite low to gain stability ( ..I guess I have seen too many video clips from American funniest Home Videos...), but I might have overdone it, what do you think?
    The waterline beam is only 98cm when light, but 125cm (or even 130) with full load.

    Arne


  • 22 Mar 2021 07:48
    Reply # 10223115 on 10222130
    Graeme wrote:

    I wonder if a more practical set of criteria would be not for a TENDER, but instead for a "JUNKET BOAT" - a general-purpose sailing dinghy which does not want an outboard, and which can be easily transported for those who are unable or for whom it is inconvenient at the time to travel to a junket under sail. Ideally it would be transportable on a car top (just) or with a very light trailer, and able to accommodate an air mattress/sleeping bag/canopy arrangement (just).

    These two almost contradictory criteria intersect at about 12'.

    Swapping boats and rigs at a junket, and letting bystanders have a go, would be rather fun.

    The Welsford design [Golden Bay] (12'9") just sneaks in. All John Welsford has to do is modify the plan to provide an offset centreboard case and removable thwart. (Marcus reckons narrow side buoyancy tanks and short centre thwart which just drops into place for rowing. The ideal for me would be a single off-centreboard case incorporated into a side buoyancy tank, with a long swinging board for sailing in shallow bays, and for variable CLR.

    All John Welsford has to do is modify the plan to provide an offset centreboard case and removeable thwart. (Marcus reckons narrow side buoyancy tanks and short centre thwart which just drops into place for rowing. The ideal for me would be a single off-centreboard case incorporated into a side buoyancy tank, with a long swinging board for sailing in shallow bays, and for variable CLR.

    We don't need a sail plan. I am sure people like David, Arne, Sieve, Paul etc can come up with a suitable variety.

    They row beautifully.

    Here's mine

    I agree absolutely, Graeme. This is what the JRA should be sponsoring and encouraging, a one-design Junket Boat, not a design for a tender. 

    I agree, too, with the idea of having two side tanks with parallel sides that are just far enough apart to fit an air mattress of the Thermarest type in between. The removable thwart that can be slid fore and aft for rowing from different positions with one, two or three aboard, or removed for camping, is perfect. Given that, you have a versatile, easily built boat for Junkets, family pottering and minimalist dinghy cruising. Spot on. Again, there's no need to reinvent the wheel over and over again. The Golden Bay, with changes to the interior, fits the brief very well.

  • 22 Mar 2021 03:52
    Reply # 10222621 on 10211344

    Well, I think it's a fun idea and a little bit of frivolity wouldn't go amiss.  8ft is a great size for a dinghy for many boats (and of course there is no reason why one couldn't put two bulkheads in it and transform it to a nesting dinghy.)

    Sure, a unk rig of this size won't allow for any 'meaningful comparisons', but it will allow people to have a lot of fun at a junket and might encourage timid sailors to get into a dinghy, once they see how easily the sail can be reefed.

    I suspect the 'one sheet of ply' has been clumsily worded.  I don't think the competition is for a one-sheet of ply dinghy: what I suspect was meant was that none of the panels should be scarffed.

    Mr Thatcher, you need to get your darling new boat up to the BOI, where there are not only still many solid tenders in use, but you frequently seem them being rowed.

    Yes, there are heaps of dinghy designs around.  There are also heaps of designs for 26ft boats around.  But that doesn't mean that there wasn't room for another one ;-P

    And full marks to the Committee in trying to engage the membership.  I hope people won't be discouraged from the amount of cold water that is being poured over the idea.

  • 21 Mar 2021 23:40
    Reply # 10222130 on 10211344

    I put up a long-winded post advocating the Welsford "Setnet" or "Golden Bay" (same hull) but took it down again because it does not match the "1 sheet of plywood" criterion and is not really suitable as a tender.

    (The reason I put it up was because Marcus has one, I have just bought one - and there is another for sale on Trademe at the moment and I thought the third one might appeal to another JRA member in NI NZ.)


    I agree with David (and Arne) that 8' is too small to be worth putting a junk rig on, and certainly too small if the purpose is to be able to compare junk rig variants in any meaningful way. 12' would be minimum I think, but this will be too large for a tender for most people.

    I wonder if a more practical set of criteria would be not for a TENDER, but instead for a "JUNKET BOAT" - a general-purpose sailing dinghy which does not want an outboard, and which can be easily transported for those who are unable or for whom it is inconvenient at the time to travel to a junket under sail. Ideally it would be transportable on a car top (just) or with a very light trailer, and able to accommodate an air mattress/sleeping bag/canopy arrangement (just).

    These two almost contradictory criteria intersect at about 12'.

    Swapping boats and rigs at a junket, and letting bystanders have a go, would be rather fun.

    The Welsford design (12'9") just sneaks in. Here is one Marcus built many years ago:

    Here's the one he currently owns, with the old Pungy rig and an improvised leeboard.

    I haven't tried mine out with a junk rig yet, but it sails beautifully with its little western lug rig. Marcus has "cartopped" his, but I am still pondering the practicality of that, for most people. The one currently for sale has a good little trailer. I have trailed mine very easily with a light, domestic, general-purpose trailer.

    All John Welsford has to do is modify the plan to provide an offset centreboard case and removeable thwart. Marcus reckons narrow side buoyancy tanks and short centre thwart which just drops into place for rowing. The ideal for me would be a single off-centreboard case incorporated into a side buoyancy tank, with a long swinging board for sailing in shallow bays, and for variable CLR.

    We don't need a sail plan. I am sure people like David, Arne, Slieve, Paul etc can come up with a suitable variety.

    They row beautifully.

    Here's mine

    Here's the one for sale

    We could have a fleet of three straight off!

    Last modified: 22 Mar 2021 09:27 | Anonymous member
  • 21 Mar 2021 18:57
    Reply # 10220966 on 10211344

    That suitability for being able to be rowed, or sculled is very important. It seems that here in New Zealand almost no one rows their dinghies anymore. Admittedly inflatables now outnumber hard dinghies, and most inflatable don't row well. But I can never understand the people who have a hard dinghy which would row well, yet even at my mooring area I watch people lug the outboard from the car to the dinghy, go through the whole process of clamping it on, trying to get it started, all just to go a distance of a couple of hundred meters to their boat. They seem to go to an awful lot of trouble just to avoid a little exercise. Still, I guess it is the same as all those very good sailing yachts which motor downwind in a perfectly good breeze without even bothering to unroll the furling headsail, which is something I see very often.

    David Tyler's comments about the difficulty of finding a generic design that suits every one are very true. Maybe it should be a design which can be scaled up or down to suit the size of mothership.

    Last modified: 21 Mar 2021 19:01 | Anonymous member
  • 21 Mar 2021 18:42
    Reply # 10220902 on 10211344
    Anonymous member (Administrator)

    Designing a ‘one-size-fit-all’, ideal dinghy is outside my capability, for sure. I have drawn a couple of box-shaped dinghies between 7 and 8’, only meant for towing behind my boat, and then be able to transport two people ashore, safely. No ambitions with respect to sailing or easy rowing.

    However, yesterday Oscar entered my idea generator , with a LOA of 3.00m. This is the biggest dinghy which can be kept freely in my boat club. Now, probably inspired by David’s SibLim design (..plus Phil Bolger’s designs..), I found I would try my hand on a double-chine design. This lets one get away with a narrow waterline and still have a generous beam overall. I have mainly been dealing with the outside dimensions and displacements. Structural stuff must be dealt with later. Priority is on easy rowing with 1-2 people on board, but still with half-safe capacity for four people.

    I even drew up a sailing rig with a big rudder and bowboard providing the lateral resistance. Priority is on fast setting and furling of the rig, including lowering the mast. Since the sail is only 5.2sqm, about the same as one panel on my Ingeborg, I would not bother with using a JR here. The mast is meant to be free to revolve so that one can let the sheet go and even stream the sail straight forward. This adds safety in a strong windgust, and also lets one sail (drift) slowly downwind onto a beech.

    Obviously, there is no use in competing with a design which has not been built and tried yet, so I leave the competition to those of you who already have a few dinghies under your belt.

    Good luck!

    Arne

      

    Last modified: 21 Mar 2021 20:49 | Anonymous member (Administrator)
  • 21 Mar 2021 09:21
    Reply # 10219562 on 10211344

    My initial thought was that this design competition is based on two entirely false premises: 

    1. That there is any such thing as a generic "ideal tender". There might be a tender that is ideal for one particular mothership, with a particular ship's complement and a particular type of cruising in mind; but change just one of those, and that tender would probably be entirely wrong. A boat the size of Weaverbird cannot entertain the thought of a hard dinghy, only an inflatable of some type will serve. FanShi is about the minimum size of boat that can carry a hard dinghy in davits, but the diminutive dinghy that suits Annie wouldn't suit two large people for use in rough exposed waters. A boat of 35ft LOA is of a size that can carry a dinghy on deck, but the size and design of that dinghy will need to be considered very carefully so as to fit the space available. And so on. One size certainly doesn't fit all.
    2. That a dinghy under 8ft LOA can carry a meaningful junk rig. Scaling down JR to that size involves compromises that make it nothing like a cruiser's rig. If the intention is trying out various forms of JR on the same basic dinghy, then the minimum size is a dinghy designed around one and a half sheets of plywood scarphed together, just under 12ft LOA, but better is two sheets of plywood scarphed together, just under 16ft LOA.
    But I don't dismiss the idea entirely. Instead, I think of it 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.

    Not that there is any need to reinvent the wheel: the likes of John Welsford, Paul Fisher, Joel White, Phil Bolger and Iain Oughtred, and a host of other designers both professional and amateur, have already made good designs for plywood dinghies that if laid end to end would stretch from here to infinity. 


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    Last modified: 21 Mar 2021 09:39 | Anonymous member
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
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