Building A Boat - Page 8 - The Outrigger
By Mike on Saturday, August 18, 2007, 20:18 - Permalink
As detailed on previous pages - the launch was a bit of a farce - the boat is very unstable. Several different solutions were considered, but it looks like an outrigger is going to be the best all-round fix for this boat.
18 August 2007: I had some plywood left from the initial build - enough to cut out a rectangle of maximum size 47 inches long by 24 wide, so I'm going to use the prism design to maximise volume/displacement from this material. Here's my cutting diagram
And here are the cut sections (with a metre stick for scale)
Photographs are going to be poor quality for a while, taken on my phone, as my proper camera got wet and died when we capsized at launch
I need to join the two smaller pieces to make one segment, then round off the shoulders and join the pieces together in pairs. I'll be using chine logs for the construction, for simplicity and speed, because the inside of the outrigger pontoon will not be visible - it will be capped with a flat ply top and filled with polyurethane foam. I'll probably glass tape the outside seams - there are only two of them.
19 August 2007: I glued the two part-panels together along their edges - the next job is to trim the shoulders round, but I can't do that until it stops raining, as it's a dusty, outdoor job.
20 August 2007: I clamped all the panels together then took off the sharp shoulders with the electric planer (then I turned half of them over and clamped together to plane again in case they weren't symmetrical, but it wasn't necessary, because they were.
Then I glued two pairs of panels together end to end
I'll do the other pair later - I'm using polyurethane glue, not epoxy, because the pontoon will be foam-filled and won't be subjected to the same kind of joint stresses that the boat will, with humans bumping around inside it.
21 August 2007: Chine logs are going to be a proper pain to plane to the correct angle, so I cut some 120-degree mini-ribs instead and started joining the panels together. I'll add a few more of these to pull it all into shape, plus a temporary strip of duct tape along the outside of the seams (which will also serve to contain and shape the polyurethane foam filling. Later, the duct tape will be removed and replaced with glass and epoxy.
22 August 2007: A bit more gluing and pulling into shape
Where is the Snow Pea now?
In order to work on the outrigger, I've hoisted the Snow Pea up to the ceiling
23 August 2007: gluing with blocks and tacks was getting fiddly and messy, so I decided to stitch and glue the rest - I drilled holes at approximately 15cm intervals and stitched the panels together with cable ties. Then I taped the outside of the seams and poured a bead of polyurethane glue into the crack from the inside. I'm not using epoxy for this because I only have enough left for one mix and that will be used on the glass tapes on the outside.
Polyurethane glue isn't as strong for tacking the seams as epoxy would be, but it doesn't need to be for the outrigger pontoon, as it won't have people clambering about inside it.
24 August 2007: Removed the tape and smoothed off the outside of some of the seams - the polyurethane glue has foamed up a bit to fill and join the seam cracks.
It's holding OK, but I'm not going to remove the stitches until the last possible moment (right before glass taping or foam filling the interior - whichever comes first).
I'm going to have to buy a bit more ply for the top and the daggerboard - I thought I'd be able to use one of the reclaimed pieces you can just see in the background of the above photo, but they're not suitable - they're all voids and the facing veneers are paper-thin.
29 August 2007: I've not had much of a chance to work on the outrigger - my mother-in-law is visiting and a lot of the stuff that was moved out of the garage into the spare room has now reappeared in the garage to make space for her, also, the spare room is right next to the garage, so I can't really be in there late at night, banging and sawing.
I did manage to cut out the top deck for the pontoon, and some other ply components - tomorrow, I'll assemble them.
08 September 2007: Haha! - you thought I'd given up, eh? (I wondered about this myself). Well, a little more progress has happened. I decided to add another strip of ply along the top of the pontoon, to increase the volume and provide more substance and buoyancy (it also makes it look a better match for the boat itself). I've also trimmed and assembled the top deck, so it looks like this.
Attaching the outrigger
One of the design problems to be faced is the question of how high the outrigger will be placed relative to the boat - too high and the boat will lean toward the outrigger - worse still, if it's placed too low, the boat will lean away from it and this could induce a tip that lifts the the pontoon right out of the water enough to take on water over the opposite gunwale (the buoyancy/upthrust of the outrigger to be greater than the downforce from its weight), so the boat will be more stable against tipping in the direction of the outrigger than away from it.
The solution, I think, is to cut a vertical slot through the pontoon (it's going to be filled with closed-cell foam, so that won't make it sink) - line the slot with a ply sleeve and drop a daggerboard keel through it - the outrigger pylons will be fixed to the top of the daggerboard (which will be exactly equal in height to the boat itself) and the pontoon will fix at variable heights to the dagger board - when there's more load, it can be slid up and attached higher.
The part of the daggerboard that protrudes below the water will help to keep the boat tracking straight.
The other obvious advantage is that adjustment will be possible for when the boat is sitting lower or higher in the water due to the load on board that day (i.e. more than one person, or some baggage)
10 September 2007: I cut out and began assembling the channel through which the daggerboard will fit. I also glued the last of the side seams.
11 September 2007: I cut the pieces of ply for the lining of the slot that will receive the daggerboard, then painted the inside faces and assembled it. I also cut a slot in the bottom of the pontoon hull (this felt SO wrong), into which the lining will be fixed.
13 September 2007: I cut a slot in the deck and fitted the daggerboard slot in place - waiting for glue to set now...
14 September 2007: turns out the slot I cut in the bottom of the pontoon was a bit wide - not sure what happened there, so I had to infill a bit with ply pieces on the inside - attached with the hot melt glue gun - the ployurethane foam filling will make them permanent and I was going to fill any gaps and imperfections on the outside with overpaintable acrylic sealant anyway.
I fitted the top deck tonight - David helped me stick some little pieces of timber to the underside so as to make the joint fall square, and I lashed it all down with a load of Spanish windlasses (String loops twisted tight with sticks)
15 September 2007: That all went very nicely and the deck is now firmly affixed to the top.
I planed up a couple of pieces of unidentified reclaimed hardwood and glued them to the sides of the keel slot on the outside - they're also glued down to the top deck so as to hold the whole thing together.
I cut some holes in the deck and filled the interior with expanding polyurethane foam - it took a fair bit more than I thought it would.
16 September 2007: Funny thing really - I did a number of fairly trivial jobs today, but they add up to a significant leap forward towards the finish.
- trimmed off (flush) all the bits of cable ties showing outside
- planed and sanded the outsides of the joints to make everything smooth
- filled and radiused the joints with acrylic filler
- glued ply circles over the holes through which the foam was added
The result of all this is that I'm now almost ready to put the glass tape on the outside seams - just have to wait for the filler to cure fully.
20 September 2007: I glass taped the bottom two seams the other night - I didn't have enough epoxy left to do the others, so they'll have to do as they are - they're glued with polyurethane glue and held together by the foam fill, plus the acrylic filler in the voids, so they should be OK...
Tonight, I gave it a coat of primer all over. Seems to be going on forever though - I still have to finish the keel, build the pylons for attaching the outrigger, and work out how to fix them to the main boat - it's starting to look horribly probable that this project might not see the water again this year.
24 September 2007: The second coat of gloss is on the underside of the pontoon now - I'm still having some problems with extended drying times on any bits that aren't just bare wood, but I'm going to forge ahead, because the bits on the main boat that were like this did cure hard after a week or more.
This paint is very saggy though - the advice on the tin is 'apply liberally', but I'm finding even an ordinary brushed coat still sags on non-horizontal surfaces - I have to flatten it out again with another brush after it's been there for an hour or two.
Attaching the outrigger to the boat
The outrigger will be attached to the boat by two pylons - these need to be set quite well toward the ends of the boat so as not to interfere with the seating area, or get in the way of paddling - so I intend to make them curved to follow the line of the decks, them they will taper toward each other for attachment to the top of the keel. They'll be something like this.
26 September 2007: I painted the top side of the pontoon - it'll need at least one more coat though
I also trimmed and assembled the dagger board - I had intended to varnish this, but I stupidly left it leaning against the front of my workbench and it has acquired a load of paint drips - so it's going to be green.
30 September 2007: I've finished assembling the keel and have drilled all the bolt holes in it (and the mounting holes on the pontoon).
I've also begun work on the pylons - these need to be curved at one end (see above right), so I ripped a 30mm square piece of spruce into four laminates, but only along part of its length - allowing me to bend it and glue back together in a permanently curved form.
02 October 2007: The glue laminated bends have come out well
There are still some little voids at the ends of the kerfs (they couldn't close up here), but I'll fill these in
20 October 2007: Status update.
I had hoped that today would be the day the boat got wet again, but it just hasn't been possible - due to a combination of short daylight hours, bad weather, other commitments and general apathy, it's still not quite finished. I need to get the boat down off the ceiling, fit the pylons and do a bit of finish work.
But the weather has turned decidedly chilly and wintry here now, so I think it's almost certain that I'll have to put off the relaunch until the spring. I'll finish the remainder of the work over the next week or two, then pack everything up and wait for the daffodils. Disappointing, but there it is.
27 October 2007: Yay! the build is completely finished on the outrigger - just a bit of varnishing left to do - here it is, test-assembled (without the pontoon)
After it's varnished, it's just possible that if we get a nice warm weekend day and there's a high tide, that I'll trundle it down to the river and test it out, but it's more likely that it will end up being put away until spring now.
I was a bit taken aback by the size of the outrigger assembly, but I think that's just because I'm seeing it in a very confined space - the boat itself looks big again now it's indoors, but it certainly didn't when we took it out for the first attempt at a launch.
Hopefully it will just work with the outrigger now, but there are several potential modes of failure that are nagging my mind:
Suppose the outrigger is too far out and causes sufficient drag to make it impossible to keep going straight?
I'm not sure how likely this is - the boat itself is considerably larger than the outrigger pontoon, so as long as power can be applied halfway between boat and outrigger, the boat should drag more and it should still permit a turn away from that side.
What if the pontoon and pylons are just too heavy and this overcomes the buoyancy it's supposed to provide?
I don't think this should happen - the pontoon is heavier than I planned (mainly because of the foam infill, I think), but it's still far lighter than an equal volume of water, so it ought to float very well.
31 October 2007: A plan!
If the weather is really nice and favourable on Saturday 10th November, I plan to test the Snow Pea (with outrigger) for stability, manoeuverability and flotation sometime late in the morning at Botley Quay - when the tide is high.
I'm not going to lay out a grandiose and elaborate voyage plan this time - that was pretty embarrassing last time (and anyway, the tides won't permit a long journey downstream with a daylight return now) - if all goes well, I'll paddle the boat upstream a little bit, then come back to the quay.
Well, that's everything done, time to move on to... the re-launch!