Wednesday, September 25, 2013

Proa plank-making

Big flimsy planks are harder to make that I thought. When one constructs a thing like this in one's head the business of cutting a piece of thin plywood doesn't appear to be any kind of obstacle to progress. When one spreads 1200 x 2400 of plywood out, occupying almost all of the workshop floor and requiring a good deal of hopping round the edges on tiptoes like a pixie, one starts to wonder where the other end of the saw will go.

I had vaguely thought I could cut curves on a bandsaw but now started to wonder how to hold all of that vast area up without it bending and flopping everywhere. So the first planks were cut with a circular saw, the sheet of ply raised up on long bits of two-inch-by-one-inch which is actually 50 x 25 mm because they've gone metric and actuallyer 40.2 x 19.1mm because I just measured it. Where they dredge these measurements up from I don't know. The strips of wood, new-sawn along an unused bookshelf-plank as a straight-edge, which I checked for straightness with a piece of taut string, were not straight, and on further taut string investigation, neither was the sheet of plywood. It had a concave edge. How would you set up a plywood-making machine to produce hour-glass shaped sheets? Must have been phenomenally hard to get that right. Bizarre.

 Anyway further research (Googling) revealed that after everything's sewn together you set about loosening some stitches and wriggling things round to straighten the boat before glueing it together. My neighbour Graeme's confidence about inaccuracy not mattering is not misplaced.

I did cut the curves of the plank ends on the bandsaw, and it was traumatic with eight feet of thin material wafting up and down in the air behind me, and being warned in a dream that I would not manage to cut accurately to the line I allowed 3mm of waste. Then I wondered how to remove the waste. A disc sander was purloined and being warned in another dream that its table was pathetically small I built a wooden stool which, with the additional height of the sander table, allowed the planks of wood to be slid off my huge workbench and run past the sanding disc, and d'you know, this actually worked. Well it nearly did. The workbench isn't flat, and the friction of 48" x 8" of thin ply was more than I imagined. It was a bit jerky to move, until I hit on the idea of pouring quarter-inch ballbearings all over the workbench. Then with the plank sitting on the steel balls, it was dead easy to manipulate, and I was able to sand off the waste right to the very edge of the pencil-line. The varying angle of the curve was dealt with by occasionally moving the wooden stool. I felt very proud of my ingenuity. When one plank was done I used it as a template for the other three, and it took a whole day to make the four planks. Blimey. I can see why Mr. Dierking says you'll spend 160 hours on the thing. With all four planks made I clamped them together and discovered they weren't identical and I didn't feel proud of my ingenuity any longer. So I got out a spokeshave and made slightly better job of it by hand. And a jack plane, and planed the edges by hand as well. And started to wonder whether the Amish have it right - that modern machinery is not quite the miracle we've all been brainwashed into thinking it is.
Nevertheless I set up the bench drill on the wooden stool and drilled 2mm holes all along the edges of the planks for the sewing process. The holes were marked along the pre-existing pencil marks from which the offsets had been taken, and by dint of holding a pencil and using one finger as the guide and doing it quickly, I ran a pencil line 7mm in from the edge of the plank so that - um - the thickness of the sewn bit would be 7mm in both directions. Don't s'pose it'll make much difference. Each hole was drilled through all four planks at once, the planks being clamped together. Kept having to use extra clamps too, and unclamp the ones that were getting in the way of the drill table. It took ages. A couple of hours. However my wife was in the kitchen and I didn't want to be found jobs to do.

'Kay, those were the easy planks. The side planks are of 4mm ply, flimsier and at 17.5 inches, wider. Clamped all four together to use the disc sander, didn't worry so much about getting them exactly to the pencil line, and planed them by hand afterwards. 4mm ply really is thin, so lots of clamping and unclamping had to take place along the edge being planed to make a decent job of it. And when finished I discovered that two of them were 3mm narrower at one end, so my boat is going to be just a tiny bit higher at one end than the other. Tough.

 Here are the side plank measurements, 2400mm long:



Bottom, from front:
178.5   115.5
200      111
250      101.5
300      92
400      75
500      59
600      46
700      34.5
800      25
900      18
1000    12
1100    8
1200    4
1300    1
1344    0
Thereafter parallel, 444mm wide.

Front, from bottom:
115.5   178.5
150      156.5
200      125
250      98
300      71
350      45.5
400      20.5
444      0

Now I have to work out how to sew them all together, and how to hold the bottom bits at the correct angle to one another while doing so.

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Friday, September 20, 2013

Proa commenced

The time hath come, saith the walrus, to talk of many things; principally whether I'm going to pull my finger out and actually build a proa or just talk about it.

To recap. - Last summer I sailed an Optimist, a tiny boat designed for tiny people to learn to sail. I am not tiny, but I am learning to sail. Optimists are safe and stable and easy to launch but marvellous slow, so you need a summer onshore breeze which we get every morning from ten thirty onwards. And since the Tasman Bay is shallow, I need a high tide. High tides and ten o'clock coincide for three days a fortnight. So Optimist sailing is limited. But that isn't why I want a different boat. It's because as an elderly person I feel foolish in an Optimist. I discover myself to be a Fashion Queen.  Shallow, like Tasman Bay.

 I cannot get anything bigger than eight feet into the van, and I don't want a trailer with its concomitant cost, registration, Warrant of Fitness, and general garden clutter. I don't want anything so bulky as to require a launch team. A slightly larger dinghy was the concept, until the idea of a proa returned along with Paul Candlish's observation the other year when I bumped into him again at the Mot Marina, that a nesting dinghy is dead easy to make and I should get on with it. Mr. Candlish is a Canadian who sailed here in a sailing boat, and lives on one, and rides a recumbent which is how I know him.

John vetoed a larger dinghy. "We've already got an Optimist. Make something fast." The proa is a sailing outrigger canoe that you don't tack: you move the mast from one end to the other. I promptly bought, read, and studied Mr. Dierking's book, and then the late Mr. Best's book and then Mr. Grill's blog. Mr. Grill observed that all his capsizing was done while shunting, and Mr. Best observed that not all pacific canoes shunt. Mr. Dierking observed that actually shunting and tacking canoes aren't much different in speed. And provided the ends are the same, you can make a tacking canoe into a shunting one afterwards. And it doesn't need an eccentric hull. Mr. Dierking's simplest plywood sailing canoe, easy to build and very functional, was a hideous box. Wandering along the seafront I chanced on another hideous box, only this one was a catamaran tender.


It occurred to me that sliced in half and butted end-to-end, it would make a nice shape, so I applied some paper to it with masking tape and took measurements. Matt at the bike shop gave me some bike boxes, and duly flattened they became rough templates which taped together revealed what one end of the boat would look like.

Bike box templates: sides and bottom

I worried only a little that the shape wouldn't be glorious. A boat is a box that keeps the ocean out. Boats come in all sorts of shapes so logic suggests that fine detail of shapes is less important than I as a layman imagine. My guess is that we are looking at an 80/20 rule, where you get 80% of the benefit with 20% of the worry over shapes, and to get the remaining 20% of benefit from a refined shape, you would need to do 80% more work. We shall see if I'm right.

So, to the four identical bottom panels, to be of 7mm exterior 5-ply which is cheap and, the timber merchant said, glued with marine-ply grade glue. To test the glue I took some scraps and put them in a pan of simmering water and left them for an hour and attended to emails and then, distracted, went for a bike ride, and suddenly realised ten miles from home the pan had been simmering for two and a half hours and you never saw anyone ride home so fast in your life. Boiling water remained in the pan, and no sign of delamination.

To check the displacement I used the floor area of the Optimist, which doesn't sink unduly under my ten-and-a-half stone. The back of the Optimist is 34" wide, the front 20" wide, and the middle, 40" from the back, is also 40" wide. Overall floor length is 70". So I calculate it's about 2380 square inches.

My canoe floor is going to be twice 87.5 inches long, and sixteen inches wide for the middle 110 inches, and at each end it will taper to nothing, so that's probably 2520 square inches. - I bet I've got the maths wrong. -

First I cut out a template for the end curvy part, fairing the curve on a disc sander. Then I cut four eight-inch wide plywood planks and found that they weren't eight inches and they weren't especially straight even though I used a circular saw and a straightedge and took infinite pains. So I called in Graeme, who lives next door and has been sailing these seventy years and made several boats. He was reassuring.
"It's a boat. Not engineering. The Tahiti canoes are made with an adze and a log. You planning on entering the Americas Cup or something?"
"What about the Vee where the two curved planks meet?"
"Filler and glass tape."

 Wooden template, redrawn from corrugated card template, redrawn in turn from template made with stuck-together lengths of newspaper

With a sharp pencil I outlined a plank and this will be the template for the others. From the one straight edge of the original ply sheet, here are the measurements, to the nearest half millimetre. The first measurement is the point, so there's only one of it of course. As the curves flatten out, I did fewer measurements. This may be what they call offsets. I don't really know what offsets are. I'm not a proper boatmaker.

The first column is millimetres from the end; the second column is the centreline of the boat measured in millimetres from the edge of the plank; and the third column is the outer edge of the boat, again in millimetres measured from the same edge of the plank. These are just for the shallow floor-pan-thingy, which they probably call garboard strakes if I've got that right.

0        116
25      97      120
50      82.5   124.5
75      70.5   128.5
100    59.5   132.5
125    51      134.5
150    45      140.5
175    39      144
200    34.5   148
250    27.5   155
300    21.5   162
350    17      168
400     14     173.5
450      6.5   178.5
500     10     183.5
550     8       187
600      7.5   190.5
650     6       193
700     5.5    194.5
750     5       197
800     4       198.5
850     3       200
900     3       201
950     2.5    202
1000   1.5    202.5
1050   1       203
1100   0.5    203.5
1150   0       204
Thereafter the plank is eight inches wide if 204mm is eight inches, which it isn't.

 We shall have to see whether they work when the thing's sewn together.

And if there are any arithmetickal glitches it's because either the pencil line was too thick or I'm stupid, both being likely.

This is what one half will eventually look like. Perhaps.

It will be objected by the proa specialists that my hull is the same on both sides, and not as deep, and doesn't have the dramatic Vee bottom of proper proas. Well, I don't know if the thing will work, so I'm being conservative.

Wednesday, September 18, 2013

Zinc

It is the high school ball on Saturday. John has to Arrive.  There is a tradition that one's arrival is in itself an Event, and the whole town gathers in a huge circle round the school entrance to watch the imaginative forms of transport - mostly American cars from 1957, but the fire service is usually pressed into bringing three teenagers in voluminous dresses and somebody always arrives in a Willys Jeep - and to applaud anything especially striking.  Last year John arrived on a penny farthing. This year it has to be something else.
"You could go on a recumbent."
"I did think about that. But everyone knows I've got one."
"What you really want is a human powered helicopter. The one that just won that prize -"
"How long did he fly?"
"Don't know. But he got three metres up in the air."
"It's a remarkably useless achievement. It's not as if he went anywhere. He was inside a shed. You could just get a ladder."
"All human powered flight is useless. What they really ought to do is get a hydrogen blimp and fit a pedalled propeller. That would actually be useful."
"What for? Where would you go in a pedalled balloon?"
"Well, um, you could go to Adele Island and back."
"Ever heard of a boat?"
"Yes but then you could just wheel it out of the shed and fly there. Actually what you want is a pedalled aeroplane with short thick wings and a thick fuselage all filled with hydrogen. Everyone's using carbon fibre to save weight, and hydrogen is just another sort of stuff, and I can't see why you shouldn't use one sort of stuff to lighten the load when they're already using another sort of stuff to lighten the load."
"How useful would that be? I suppose if you were out on a walk and you suddenly came across a big lake filled with sharks and piranhas you might be able to use it but it'd be a big thing to have to carry around just on the offchance. "
"Actually, what you really want is a hydrogen generator and a big bag. - Actually, what you really want is a stick of zinc and some hydrochloric acid."
"And you could get the hydrochloric acid out of your stomach just by puking."
"You could use a balloon."
"Or condoms."
"So all you want is a stick of zinc. And some condoms."
"You'd want a lot of condoms."
"Yeah but they inflate. And let's face it, any young man out on a walk is going to have pocketsful of condoms, just in case he meets a busload of schoolgirls desperate for sex."
"So all you want, then, is to go on a walk with a stick of zinc. Sorted. - How did we get into this conversation?"


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Wednesday, September 11, 2013

Hack bike

My wife's mother has died.

Every silver lining has a cloud, and she went to England for five weeks. My wife, not her mother. Her mother was already there; all tidied up inside an urn.

She has now returned (wife, not urn), and immediately prior to her return my son and I indulged in some serious kitchen maintenance, including vigorous floor scrubbing. Accordingly I have developed tennis elbow, which is a lot more painful than it sounds. I wander about in agony, unable to hold a pencil, unable to use a hacksaw, scarcely able to roll into a comfortable position in bed. I am typing this with my left index finger.

 My son observed me being a cripple for a while, and then said:

 "Able was I, ere I sore elbow."

 I haven't been riding a recumbent for a while because winter requires a shorter chain, which = less of a nuisance after a rainstorm, and a hack had got itself built some months ago.

Initially it was my wife's friend's racing bike from university thirty years ago, but even replacing his 27 x 1 ΒΌ wheels with 700c did not give me enough room for mudguards. - In passing, 700x32 Specialized All Condition tyres are luxurious to ride on, but much more comfy at 70 psi than at 100, and not much slower either.

It was not a very well cared-for student bike, and my estimate was that it was worth maybe $20 with cables like this.


But it had the merit of being free. Until I broke my $70 Ofmega spanner on the crankset.


I said "Oh bother" or words to that effect.

 In the end I used one of the zillions of old frames that people see fit to give you when they notice that you already have zillions of them cluttering the rafters of your shed.


Lacking an elbow I was not in a mood to ride drop handlebars for my daily exercise quotient. The Duplo bike has been upside down for several months while I fail to work out a neat method of converting the front wheel to a drum brake, which is required because the Vee brake cable interferes with the mudguard. (The mudguard was supposed to be for the winter.)

So I got out one of the trikes, and not having ridden in the recumbent position for months, I can now report that it is perfectly true, you do use different muscles. The big bulgy-out muscle on an upright leg, the one at the side that makes you wear jodhpurs, is no use at all on a recumbent. You need a big bulgy one that goes from your outside hip to your inside knee, a sort of diagonally-muscle-bulgy-thingy, if you see what I mean. - A useful addition to the world's knowledge, esp. if you chance to be an anatomist.

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