Shelduck

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RGSP
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Shelduck

Post by RGSP » Mon Oct 17, 2016 8:46 am

I hope the great and good on this forum will excuse, or even enjoy, this posting, which is really in response to Wesley Harcourt on the SBA site.

I am in the early stages of building a 22' steam launch, with hull built via the cedar strip plant method. Having built several boats in the past, I was tolerably confident, but had never used the strip-plank method, and so decided to make an 18' canoe first, starting from buying wet, as imported, lumber. If it went horribly wrong, then never mind, it's not that big a deal, and the same philosophy allowed me to experiment with all sorts of things while building - most being successful, but some needing a bit of work to undo.

Anyway, you can see the canoe results below: she takes two largish adults and a labrador-cross dog comfortably. Part of the experimentation was to buy a remarkably cheap 400-Watt electric outboard, to run off 12V 85Ah electric fencing batteries, of which we have several for electrified sheep netting. This turned out well: she does 4 knots at full power, and one battery lasts over half a day - not a steam plant I know, but just as quiet, and certainly not an infernal combustion engine.

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Moulds on a strongback in my 17th Century barn/ workshop

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Planking almost finished. Marine-rated polyurethane glue makes an awful mess where it squeezes out of the joints, but it sands off very easily - on the outside of the hull anyway.


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Hull turned the right way up for the first time, with epoxy glass covering on the outside, and untrimmed, but nothing on the inside yet.

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Splicing (scarfing) gunwales and inwales from ash. Too long to get inside the workshop.


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The completed canoe on trestles.

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Another shot in the same spot.
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Re: Shelduck

Post by wsmcycle » Mon Oct 17, 2016 4:38 pm

the boat a wood are beautiful. What a courageous job and fine result!
LIGHT THE FIRE!!
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Lopez Mike
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Re: Shelduck

Post by Lopez Mike » Tue Oct 18, 2016 4:29 am

How long did you have to wait between strips for the glue to dry? Were the strips fastened to the strong back frames and each other with some sort of fastenings? What were the sizes of the strips?

I had discarded the idea of a strip built launch because I thought I could only do two strips per day and I would die of old age before I had a hull.
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RGSP
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Re: Shelduck

Post by RGSP » Tue Oct 18, 2016 8:13 am

Mike,
in reverse order:
i) The strips were 6mm thick, and I machined them convex on one side and concave on the other, so they interlocked to some extent, and the cover was 19mm per plank.

ii) They were fixed to the frames using staples mostly, with small screws where necessary due to high stress from plank curvature. Between frames there was usually one staple, one leg though the edge of the current plank and the previous one: not a strong method of fixing, but enough. The frames were all covered with masking tape round their edges, to stop them getting glued to the planks. All screws and staples ( well over a thousand) were removed before sanding & epoxy.

iii) I had two sorts of polyurethane glue: one rated at 5-minute set, and the other at 30-minutes. Fitting one plank takes longer than 5 minutes, so the slower glue used most. However, the plank length was 4 metres, whereas the hull length was 5.5 metres, so each one had to be scarfed. In fact using a bench mounted disc sander and a bit of jigging, cutting the scarfs was quick and easy, and the gluing was done after the first section was fixed to the hull. This involved the 5-minute polyurethane and a couple of F-clamps, then carry on fixing the remaining (shorter) length to the previous plank and the frames. If I alternated planking, port and starboard, then the 30-minute glue was sufficiently hard to put another on top by the time the one on the other side of the hull was fixed etc.

My maximum for one day, working entirely on my own, was 12 planks: strictly, the glue doesn't really have to be hard before fixing another plank, because the temporary staples and screws hold it in place fairly well, and with two people working well together I think the planking rate could have been triple or quadruple what I managed.

Many people use epoxy glue for planking. Fine, but it's a fiddle having to keep mixing more every few minutes, whereas the polyurethane just comes straight out of its dispenser bottle. Epoxy is also a bit stronger than polyurethane, but the latter is strong enough that if you glue two scrap bits of plank and then break them apart, the wood breaks, not the joint.
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Re: Shelduck

Post by Lopez Mike » Tue Oct 18, 2016 3:47 pm

Thanks. I'll need to think about this.

I've been limiting myself to plywood designs for my replacement hull. This makes getting a plumb bow a total hassle unless I do sharpie design where the boat is pretty much a flat bottom up front. Strip planking opens up many more possibilities.

Also less expensive wood as good plywood has gone through the roof.

Any thoughts (now that you are the expert!) about plank thickness for a light weight 24 foot launch hull? Would 12mm be good enough if glassed on both sides?
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Re: Shelduck

Post by barts » Tue Oct 18, 2016 4:29 pm

Glass on both sides makes things nice and strong; it's much stiffer than the wood itself. Note that for larger boats, the strip planked hull is then covered w/ wood veneer (2 layers) prior to glassing.

Note that plastic staples can also be used; these can be sanded flush w/o hurting anything and they disappear in the finished product.

- Bart
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Bart Smaalders http://smaalders.net/barts Menlo Park, CA
RGSP
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Re: Shelduck

Post by RGSP » Tue Oct 18, 2016 8:18 pm

Lopez Mike wrote:Thanks. I'll need to think about this.

I've been limiting myself to plywood designs for my replacement hull. This makes getting a plumb bow a total hassle unless I do sharpie design where the boat is pretty much a flat bottom up front. Strip planking opens up many more possibilities.

Also less expensive wood as good plywood has gone through the roof.
i
Any thoughts (now that you are the expert!) about plank thickness for a light weight 24 foot launch hull? Would 12mm be good enough if glassed on both sides?
The cost of proper marine ply is getting a bit prohibitive, I agree, good stuff though it is.

I'm certainly not an expert, but I am convinced that strip planking is worth the effort to get a pleasingly shaped hull a bit over 20' long. On thickness of wood, I think 12mm/half inch would be enough, given how strong less than 1/4" is in my test-canoe which is only slightly shorter. Paul Fisher of Selway Fisher recommends 5/8" for some of his hulls of that length, and he should know, but perhaps a slightly over-flexible unfinished hull is not too bad a fault. Epoxy-glass, inside and out, does make a huge difference to the hull stiffness. Add to that, a steamboat is going to need fairly substantial stringers to take the engine and boiler weight, which will stiffen the hull significantly more, and at worst all that would be required to stiffen it further (perhaps even after launching) would be a few extra permanent frames. The only big argument for a thicker hull is insurance against collision damage, and I'm not sure I believe in that.

I'm going for a hull of about that length myself, partly because legal limits on towing weight (with trailer) in the UK come to about 1500kg for a slightly over-average sized car and it seems a reasonable target to aim for in a lightweight hull to take a group of up to 6 steamboat nutters. I might go for 1/2" thickness, but the extra weight of 5/8" cedar is small and I might go that way if Paul Fisher convinces me.

By the way, my friend Phil Webster's 117 year old, 22' launch "Banjo" has nominal 1/2" cedar planking with conventional carvel framing and hog, and she's still a very sound little vessel, give or take a few minor "soft" bits.
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Re: Shelduck

Post by Lopez Mike » Tue Oct 18, 2016 9:39 pm

Well, thank you for the information. Both you and Bart have given me hope that I might someday have a hull to replace the "esthetically challenged" hull I have now.

I found a distributor of 'plastic' staples and brads/nails not far from me down in Eugene Oregon and I will be visiting them on my next trip there.
http://ancofastenersales.com/our-produc ... ic-staples

Did you use a hand stapler/nail gun or an air one?

There is a guy in Vancouver, B.C. who builds nice rowing boats using hot glue, of all the strange things. The work goes really fast. He tacks the strips to the strong back bulkheads and then knocks them loose with a wooden mallet after glassing the outside. he feels that once the inner and outer glass and epoxy are cured that the bond between the strips is not that important. Food for thought.
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RGSP
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Re: Shelduck

Post by RGSP » Wed Oct 19, 2016 8:26 am

I used a perfectly ordinary "Stanley" hand staple gun Mike - it doesn't need a lot of effort to get through 6mm cedar. The staples most often didn't go right home into the frames, but in well enough to make them hold, and having the flat top clear of the wood does make getting them out easier.

I don't think stapling as I did would be much use at all for thicker planks as used in a real steamboat, but good quality "non-split" type screws go in just as easily, and more to the point come out easily too, using a fairly light drill/driver (hurrah for Lithium Ion batteries!). I'm not sure I'd fancy getting out the sort of staples used in packing cases (and put in with an air tacker): cedar is very soft and easily bruised. Light gauge good quality screws go though cedar very well without pre-drilling and give no splitting - I doubt hot glue would be much faster.

Plastic staples might be useful, but not into the moulds, where fixings need removing. The other thing I've heard about them is that they sand more slowly than cedar, and leave raised bumps; I have no experience of this, but would have thought the solution would be to sand again after the first priming coat of epoxy had cured, which some builders do anyway.

Concerning edge-gluing planks, the strength certainly isn't essential once the hull is glassed. However, I would be worried about water tracking along joins having got in via pinholes or other minor cuts etc. I know of one rather nice looking steamboat constructed using exterior grade ply strips (not marine ply) rather than cedar, and I suspect polyester rather than epoxy, and she's an absolute nightmare to maintain. It only needs one very minor bash from an underwater rock or bit of iron, and water seeps in, and then tracks along voids in the ply and doesn't dry out. A year later, and the ply swells and tries to delaminate, and several square feet of hull need replacing. This one boat has put a number of steamboaters over here completely off strip planked hulls - understandably. However I was talking to several owners of hulls, constructed using cedar strips and epoxy glass at the SBA Windermere Week, and they have had no problems at all: the hulls certainly need less maintenance than conventional carvel built ones, and it looks as though their long-term life may be good as well, though few are older than 20 - 30 years yet.
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Lopez Mike
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Re: Shelduck

Post by Lopez Mike » Wed Oct 19, 2016 5:21 pm

How has the life span of your LiO battery packs been. I don't mean the time between charges but how long between replacements.

I got so turned off to rechargeable drills years ago that I have not bought any. The battery packs would die and the manufacturers would have change the design to I had to throw away the drill. Not a happy camper.
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