David Tyler wrote:

OK, winter holiday time is nearly over for me, and I should be getting back to thinking about fairing and adding the hull panels. Yet here, I think we're getting into an area where there are multiple choice questions to be answered: puzzle joints or scarphs or butt joints? Hull panels applied all in one piece or in single sheets of ply or something in between? Framing on the bulkheads or stitch fillet and tape?  Chine logs and sheer clamps or stitch fillet and tape? I don't think I should be making those choices for a prospective builder, as much will depend on tooling and machinery available, skill levels and manpower available, space available, time available and other such factors. I think that I've demonstrated by getting this far with the model that everything in the internal structure fits; and that the method of building "inside out and upside down" and doing the bulk of the accommodation first, from precut components, is going to speed up the build and improve accuracy and rigidity. From that practical viewpoint I needn't take the model any further. If I do, it will be for my own amusement only, not because it's necessary to facilitate building a full size boat.

As an exercise in thought, I would be inclined to assemble the hull panels ahead of time and apply in one piece as giving the fairest curves unless I was doing two layers in which case the second layer could act as a butt block and I would install piece at a time. Having read the G bros. epoxy guide, I might be inclined to use puzzle joints (also looking at the RM Yachts build) because they should be quicker and I suspect no weaker than scarphs (I think butt blocks may be weaker because the join is only one ply of the plywood) Most of the final strength will come from the epoxy impregnated glass tape on either side anyway.

I feel that chine logs and sheer clamps should be thickened epoxy with tape covering both sides.  Anything else would go anti-purpose to the method of build followed so far as hand shaping would become needed. I think the chine joint should have the plywood panels leave a gap between each other of 6mm or so (I was about to say 1/4 inch :) ). This way the hull panels should just get their shape from the bulkheads and turn out fair without having to fit the edges. I would start with the bottom as you have done, but I am not sure if putting the sheer on next or the bilge would be better. In either case the last one would have to be filleted from inside... perhaps if the bulkheads had tabs that fit through the panels so wedges could hold them on that would help. My other thought is that if the sheer panels are added first, it may be possible to do the turn over before adding the bilge panels. I am probably over thinking all this.

Finally, I agree that you have proven this method of assembly. While speed of build may not matter to some people, others may have partners where speed from first cut to water will mean the difference between still having that partner or not. I do not think this is "cheating". The same materials are used either way (plywood and epoxy) with similar amounts being used in either case.

Having built 1.5 boats in similar manner (the dingy has a hull but needs finishing), I think I am more likely to start with a cheap/free glass hull and change it. I am realizing that the main thing I don't like about most glass boats is the cockpit. After seeing what Roger Taylor has done with his MingMings, I think I could just fix that... Yes, more work that I think even still ;)

If I do build another boat, this is the method I would use. No fine finishes for me, paint covers lap joints no problem

Oooohh, let's hope that the poor fellow has good resistance against getting seasick!...

Arne

This caused me to look up going over Niagara falls in a barrel (not sure why) but I reckon that is even crazier. Best not to google that.

On a slightly more serious note the question of stability has been raised, as well as the question of scaling. 

Firstly I should say that the 7 metre version is not just a scaled down version. Look closely and you will see the proportions are different. The two metrics were that beam was restricted to 2.5 metres (for Oz-trine non-escorted towing or shipping) and that gave rise to a length which would just fit into the garage I am about to build. 

As for stability or rather sea keeping ability its all about compromises but anyone who thinks that the bureaucrats will keep you safe with something like the EU RCD better think again. Statistically the edges of bodies of water are where most vessels are lost and hence an ability to continue to plug to windward in horrid conditions is probably the most important aspect of safety at sea. An ability to run off safely if sufficient sea room exists probably comes second.

Both requirements are amply met IMO by raisable leeboards which when raised give the ability get pushed along by the breaking head of the wave ...... however if you get a "washing machine" type sea state such as around Australia's east coast sea mounts where a 4-5 knot south going current hits a northward going East Coast low then a vessel this small (and some much larger) is highly likely to be rolled.

In that case while self righting is highly desirable - and I believe this vessel will self right fairly easily - you will be not be a whole lot better off than the French man in the barrel if at least a large part of the rig does not survive. In the first instance a rig is necessary to remove oneself from the ocean but primarily its the rig that provides a much higher roll moment of inertia. Sans rig in a nasty sea would not be pleasant at all and that motion is sufficient to make people want to abandon an otherwise sound vessel.

Generally a smaller rig has a much better chance of surviving. I think its a scale thing. But in any event keeping some rig is something you really need to plan for probably just as much as self righting.

Now I do recall a comment from David saying that he might add a bit more deadwood beneath the keel were it he but I don't recall how much he suggested (if indeed he listed any dimension any at all) - clearly you would not want to add too much or one might trip over it, and Selden's online righting moment calculator ( http://www.seldenmast.com/en/services/calculators/rm_calculator.html ) indicates that deepening the keel a small amount does not make a huge amount of difference. Its this piece of the puzzle I am pondering at the moment.

The nutters get nuttier.  Excuse my lack of imagination, but why on earth would anyone want to do such a thing??!!  Especially when building a 7 metre variant of SibLimwould probably been quicker and cheaper!!  And a lot more comfortable.

David T wrote:

David W wrote:

David,

with the buoyant and relatively high topsides and the well rounded deck I would imagine that neither Annie's version or the 7 meter version of SibLim will be inverted stable. Is this correct? If so then I would not question their ability to undertake moderate ocean crossings.

David.

I can't give a numerical answer to this, only to say that we're about as good as we can get with the deck shape, and the range of inverted stability should be small, and much less than boats with a wide, flat deck. Yes, the closer one can approach to "a barrel with a keel on it", the better for extreme sailing, but in reality, we have to be able to walk along the deck. Moderation in all things.

What was I saying about going to sea in a barrel??

I've used 20˚ from the horizontal on the side decks, the same as on the foredeck of Tystie, and I've observed that some people are nervous and uncomfortable with that much, if they're not roofers or hillwalkers/mountaineers. It's not sensible to put anything down without securing it, and loading stores and water containers onto the deck from a pontoon or dinghy is difficult. I proposed to Annie that the area outboard of the bilgeboard cases should be horizontal, for those reasons. She didn't go for it, but I'm going to do it on my model so that Gary can see it and make his own decision.