San Juan sharpies

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Re: San Juan sharpies

Post by RGSP » Wed Mar 15, 2017 1:17 pm

I've been wondering whether to write and post this or not, and eventually decided that people can learn from it, pooh-pooh it, or ignore it as they wish.

In the summer of 1974, I collected a 27' workboat from a shipyard in northern Norway (where it had been "repaired"), took it to Spitzbergen, partly under its own marine deezel power, and ran it to take geological research parties to remote areas, collect their samples, and keep them supplied with food. It was a hard-chine hull, constructed very strongly of welded aluminium to withstand minor collisions with ice floes, and mostly very good, but...

1) The repair was to an A shaped skeg bracket, which vibrated resonantly in sympathy with the prop and broke, and the repair soon fatigued off again. I got the boat slipped again, and re-welded the brackets myself using much heavier aluminium section, which behaved nicely with no excess vibration, and no cracks visible in my not-very-professional welds at the end of the season.
2) The fuel tanks (big ones) were formed partly by the outer skin of the boat, and they leaked - sea water inwards. The amount was perhaps 1 pint per day, and the fuel lines had big water traps in them, so operation was fine as long as you emptied the traps regularly, but fogetting was obviously potentially catastrophic in the remote high-arctic. When the boat was slipped at the end of the season, it was JUST possible to see the very fine cracks which allowed the leaks, but no normal inspection would have revealed them. I think they were a result of the excess vibration from the skeg frame in the previous year, but regardless of the cause, they were not obvious, and in a small vessel I would avoid that design of fuel tank in future.
3) As a result of the very strong welding, the whole boat annealed itself in the first few months of operation, and distorted slightly: not generally enough to matter, but the stern tube and shaft were relatively long, and the tube bent enough to make occasional contact with the shaft: unpleasantly noisy on occasion. OK, I borrowed the engine-room lathe aboard a big arctic trawler, and machined up an off-centre front bearing, which solved the problem, but it was an unexpected one.
4) Condensation onto the inside of the hull in cold water was a major irritation: no lockers could be regarded as dry, and brushing against the hull got ones clothes wet. Not good in the Arctic.
5) Not a problem for most, but operating with small bits of ice in the water was incredibly noisy against the alloy hull, and ear defenders were highly desirable below decks.

Otherwise it was an excellent boat, and problems 4 and 5 could have been solved by an insulating lining, but this was omitted so that the hull skin could be inspected regularly for signs of damage resulting from ice-floe collisions.

This isn't meant to put anyone off aluminium hulls, which are good, but if one is aware of the potential problems they can often be avoided.
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Lopez Mike
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Re: San Juan sharpies

Post by Lopez Mike » Wed Mar 15, 2017 2:30 pm

Thank you so much for that.

I do a lot of work in and around sailboats and every time the designer decided to have the hull be the outer plate of a tank it was a disaster. Not only prone to problems but, obviously, impossible to remove for cleaning or repairs. I cannot imagine why the inspecting or insuring people allow this brain dead nonsense.

I don't know about an open hull like a small steam launch but for any sort of enclosed design a metal hull should always be insulated to limit condensation. I don't know how I would deal with a messy place like an engine room. It would seem as though the leaked fluids would creep behind the insulation.

I love the idea of a monolithic hull without seams or joints. I think the move to plywood produces a far better hull than a conventional carvel or clinker built design. It's just that there is no way to build compound curves which nature loves. I guess I'm back to cold molding in wood. But that seems like a lot of work and, frankly, I am much more interested in the power plant and just going steaming. Ah to be rich.
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Re: San Juan sharpies

Post by RGSP » Wed Mar 15, 2017 3:29 pm

Mike,
I really wouldn't be worried about the effort involved in strip-planking a hull. I built an 18' long, 3' beam canoe last spring, using the strip-plank method, because I was dubious about the method and my ability to use it for a steamboat. I was fully convinced, and the actual planking was a lot less effort than marking-out and cutting the moulds + attaching them accurately to a strongback. I think there were 78 planks, each with 16mm cover, 5.5mm thick, and I found I could manage up to 12 planks a day, including scarf joins to almost every one as the available stock wasn't long enough for the hull. The planking therefore took about three weeks in total, working entirely on my own, and not every day.

Given that planks for a steamboat hull 20' long and 6' in beam could be perhaps 35 - 40mm wide, it will come out to a comparable number, and the hull will probably take longer to plank than the canoe, maybe double at most, but not grossly longer. Part of the trick was using marine-rated polyurethane glues, in 5-minute and 30 minute varieties in different places. This means no mixing time, and doing planks alternately on port and starboard sides means that any clamps used (and having lots is useful), can be released and re-used on the next plank that side. The excess polyurethane is best cleaned off when fully cured: it's foamy and weak when not confined by the joint, and comes off fairly readily using a sander and/or scraper. I admit the cleaning up is tedious, but not difficult, and not that time consuming.

There is a knack to using epoxy + glass, but not a difficult one to acquire. I would not again try to use the epoxy in cool weather, even inside a heated "tent" within the building shed: it's just enormously easier to use at a steady (say) 22 to 26 Centigrade, plus you use a lot less expensive epoxy.

It's spring here now, and I'm about to start constructing a Selway-Fisher "Indian Runner" hull, with some modifications to pander to my prejudices: that's another feature of the method. As long as you're careful, you can modify the hull shape a bit, and as long as you trim the moulds so that the planks lay over the moulds in "fair curves", then you'll automatically end up with your own unique and lovely looking hull. I've just constructed two 1/10th scale variants on Indian Runner hulls, using scaled moulds, 1/16th" sheet balsa planks 3 -4 mm wide, and 0.6 oz glass cloth + epoxy. It was a most instructive exercise, and if you have doubts about the technique for full-sized craft, the scale models are somewhat quicker to build, and a lot cheaper. You also get an excellent "feel" for the hull shape, and where the trickier bits of planking are likely to be, and the general technique is essentially identical to that for full-size craft. I used cyano-acrylate gel adhesive for edge gluing the balsa planks, which means no pinning or clamping was generally required, and the bits of disposable nitrile glove left glued to the hull sanded off very easily! Not much of my skin is incorporated into the hulls.

Go on! Give it a go! You know you want to....
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Re: San Juan sharpies

Post by DetroiTug » Wed Mar 15, 2017 4:01 pm

"the move to plywood produces a far better hull than a conventional carvel or clinker built design. It's just that there is no way to build compound curves which nature loves."

When I was researching build techniques, I got a copy of "From the old boat shop" by Weston Farmer (Great book). I was reading it one night about half asleep and half-way comprehending the text, and I hit a sentence that said something to the effect that compound curves can be done with flat sheets. I read it back over a couple of times and he explained that if a panel is twisted and then bent, it makes a radius laterally. I took a piece of cardstock and did that, twisted and bent it, and sure enough, it had a belly to it. The designers of steel hulls a long time ago, knew how much twist and bend to get the radius they wanted for soft chines/flowing hull shape keel to gunwale. Sure enough, when welded the bottom hull plates on at the stem, they twist significantly, they have a radius across the panel.

As far is inexpensive Tig welders, there is a place on line that sells welders at good prices, but can't remember the names, I would have a look at Amazon too.

-Ron
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Re: San Juan sharpies

Post by cyberbadger » Thu Mar 16, 2017 1:53 am

RGSP wrote:This isn't meant to put anyone off aluminium hulls, which are good, but if one is aware of the potential problems they can often be avoided.
I'm wondering if any of this is applicable to a tritoon/trimaran like my Nyitra?

The Deck is above and insulated from the pontoons. I can inspect by borscope and drain with a hand powered bilge pump. I think I calculated even if 1 pontoon (out of 3) would flood Nyitra would still float - although probably completely swamped. There are some Dents, but when I bought the first hull both pontoons made a hiss when you unscrewed the caps.

-CB
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Re: San Juan sharpies

Post by TahoeSteam » Sun Mar 19, 2017 7:24 pm

I really appreciate all of the replies. I think a v-bottomed hull will end up being a little more suitable and allow for greater prop diameter... one could always do a single engine, twin-screw setup! haha
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Re: San Juan sharpies

Post by PeteThePen1 » Mon Mar 27, 2017 5:11 pm

Hi Wes, Mike and friends

An interesting thread this one! I will corrupt it with my thoughts, though you might think them a bit irrelevant.

For Mike, why not build a new hull with plywood, but skip all the epoxy bit? None of the dinghies that I built as a teenager used anything other than waterproof wood glue. From your Forum comments I suspect that you have more than enough skills not to need epoxy and filler to hide crass building errors. If the boat is for using and not intended to be part of your inheritance to the Grandchildren, it should give more than enough years of service as painted/varnished ply. The only rider would be that it should be the best quality of ply as that lasts very well.

I have 'gone off' epoxy after my experiences with Frances Ann. Where the epoxy mix was perfect and applied with perfect conditions it has produced a glass like finish which supports a glass like varnish finish. However, where I have not achieved perfection it has been nothing but trouble and I am currently removing much of it back to the wood. The bare wood, carefully prepared also allows the achievement of a glass like finish with careful varnishing. Given what I know know now about my abilities with epoxy, I would never have put it on any of the bright work on the boat. It was great with filler for attaching the inwales, etc to the glass hull, but I should have quit at that point and saved myself a bucket load of money and days of re-work.

I can see why metal might be good for you Bart, being a mere youngster, and so looking for a boat with a potentially long life.

Strip planking sound interesting, but could you skip the epoxy final stage? I fear not, so that is why I would avoid this method if it were me seeking a hull building approach.

Regards

Pete
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Re: San Juan sharpies

Post by Lopez Mike » Mon Mar 27, 2017 5:39 pm

I don't have any big problems with not glassing the hull. But the stitch and glue system is a separate building method from how one finishes the surfaces.

I almost seem alone in my concern for keeping the hull weight down. If I can get rid of all the chine logs and such, it will go a long way towards that goal.

I would still glass surfaces that undergo abrasion like the keel, stem and such. I deliberately run my boat on the beach to load and unload and except for a bronze or S.S. strap on the stem and part of the keel, I will be depending on a layer of two of glass cloth to help. Also there are some very hard additives to epoxy that are very abrasion resistant.
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Re: San Juan sharpies

Post by DetroiTug » Tue Mar 28, 2017 1:58 pm

"If I can get rid of all the chine logs and such"

Mike, Have a look at "stitch and glue" hull first building technique. It's essentially sewing panels together with tie wires and then grinding the wires away flush and strengthening the butt joint with cloth and epoxy resin. It's very fast and simple to do, it results in a light hull and framing only where it is needed.

Chine logs are really not needed, as far as I can see, their real purpose is something to put screws in. Two panels butted and each with similar radius is very strong on it's own. it would need some framing amidship and some timbers to mount the boiler and engine on, then sort the deck framing if any. If I were going to build a high speed, flat bottom steamer, that is the route I would go.

Pete, I agree with you about the option of forgoing all the epoxy. I remember when all that didn't exist. People built boats from marine ply, good lumber and resorcinol glue and then put good quality paints and varnish on them and with care they lasted many years. It required better jointery as resorcinol had little to no gap filling ability, but it was as strong as epoxy without all the fumes. Epoxy over wood is great until it is breached, then the problems start, water soaks in on the dry wood and it's about impossible to get it dry again.

-Ron
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Re: San Juan sharpies

Post by Lopez Mike » Tue Mar 28, 2017 3:04 pm

Hey Ron. Read my post again. Stitch and Glue is what I was talking about.

Great system. I built the water tanks in my sailboat that way. An old acquaintance of mine, Sam Devlin, was one of the pioneers of that method. In a recent conversation with him he suggested a sharpie shape and, in addition, strongly recommended building test models out of door skins. Including weighting the models with scaled masses to check out any trim issues.

He says that building a model using hot glue allows you to disassemble the model with a hot knife followed by laying the panels on graph paper for scaling up. I see a Winter project of making a mess.
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