Tender to Sibling by David Tyler

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.


Comments

  • 16 May 2021 13:59 | Anonymous member
    I'm thinking of a deck stepped mast, supported by four shrouds. Why? Because when rowing with 2 up, the rower will have to sit on the forward tank, and a tabernacle or thwart to support an unstayed mast would get in the way. Also, when used as a workhorse, this area will be used to carry stores aboard, clear of the potential wet bottom of the dinghy after a splashy beach launching.
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  • 18 May 2021 22:01 | Anonymous member
    A nice junk-rigged sailing dinghy except for one thing: accepting the need for shrouds is a huge step backwards, in my opinion. There must be a better way to make a tiny free-standing mast stand up - a removeable deck beam (two thumb screws?). Personally, I would offset the mast anyway - it ought to be possible to row with the mast standing. Either that, or put the mast further forward? There's gotta be some way ..
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  • 22 May 2021 14:53 | Anonymous member
    I meant to come back to this one. Its not the prettiest design in the group, and not the prettiest boat David has designed, but it might be the all-round most practical proposition for the committee’s consideration. I think David is right in guessing that if the committee is looking for ease of build and all-round practicality, the 3-plank flat-bottom pram is going to be the obvious choice.

    This one needs three sheets of ply and its good to see how David can use software to nest the components onto a sheet and optimise the materials – I wish I could do that. But the reason for three sheets is: this one has built-in buoyancy – and two off-centre dagger board cases. Initially my thoughts were that built-in buoyancy is a requirement if the dinghy is to be sailed. I have second thoughts now, realising that inflatable buoyancy bags (such as we sometimes see on the ubiquitous Optimist training dinghy) are quicker, cheaper, lighter – and unless the dinghy is furnished with full fore-and-aft bulkheads leaving only a central cockpit (something like John’s so-called “General Purpose Dinghy”) recovery from a capsize is going to be a half-full-of-water proposition anyway.

    I am not sure why it needs two dagger board cases – perhaps because the “dagger” (more like a broad axe) is shallow – it is not clear if there are meant to be two boards, or whether its one foil, swapped from side to side. An interesting quirk is the use of that low aspect ratio board for a rowing seat. Duality of purpose is always nice, and daggerboards otherwise are an annoying encumbrance when not actually sailing. (Its better than Arne’s mock-sour suggestion of using it for a giant bait board!)

    David has brought all his experience to bear, resisted the temptation to create something elaborate or pretty – and produced what he thinks is a sensible, practical tender, which can be climbed in and out of with ease, with some built-in buoyancy and a secondary function (occasional sailing, which I would expect it to do quite adequately) – all round a good compromise. There are some areas in which it could be simplified. (The plywood buoyancy tanks – and the need for two daggerboard cases).

    I think the committee is probably going to look very closely at this design. Above all, it has integrity – I for one would not dare to suggest changes – apart from commenting adversely on that strange reversion to standing rigging!

    (Additional comment: KISS remains my first choice (it was love at first sight) – but some of us still feel more comfortable with the use of light stringers instead of thickened epoxy filets for joining the hull. Especially anyone who might be allergic to epoxy, or trying very hard not to become so. The old-fashion use of stringers allows a choice of glues – and a little training in the use of traditional tools, fairing off, etc. Its not a subject which has been raised in any of the discussions, but I wonder if David has been clever here, in foreseeing a possibility that these matters might be a consideration for the education provider who intends to make the winning design a classroom project).
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  • 24 May 2021 05:25 | Anonymous member
    I've just realised something. This boat does have fore-and aft bulkheads - only up to what would have been thwart height - but possibly high enough to constrain free surface water resulting from a capsize or swamping, to a degree which might be superior to Oyster - not to the degree of "Genera Purpose Dinghy" - but enough - and, of course, superior to buoyancy bags. I can't visualise well enough to guess what she might be like to recover from a capsize, but I suspect David can. This safety aspect - which, because it is restrained to thwart height only, doesn't really compromise too much its use as a tender - and might well be the final deciding factor - might well justify the extra work, extra plywood and extra weight needed.
    There's a lot of good stuff going on here. She's an ugly duckling compared with the usual canard spoon-bowed pram - but maybe she's actually a swan. I really would lie to see this built, and subjected to testing. At the end of the day, capacity, safety and utility as a tender really ought to take priority, and matters such as sailing rig, mast set-up etc can justifiably take second place.
    I really want to see what this thing looks like “in the flesh”.
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