With the floors, centreboard, breasthooks and inwhale fitted the boat is stable enough to fair – so it is tipped over again and I set to work with a plane. This bit takes a couple of days and is pretty depressing work. The grain in alaskan yellow cedar is tough to fair and bits tear out all the time – most of the time I end up planing at 90 degrees to the grain – not ideal. The general idea when fairing a boat is to plane or sand diagonally across the planks to take all the high spots off and keep the lines.
After a couple of days of this – with only one side done – I get fed up and rush off to Axminster Power Tools (conveniently 10 minutes up the road) a get a Makita ‘Wood Eater’ orbital sander. Most of the other side gets knocked back in a couple of hours and I am ready by the middle of the next day (it’s now Wednesday) to start work with the fairing boards. These boards are, to my knowledge, to only way to really fair a hull. machines all, in various ways, create problems by digging in when wood densities vary across the boat. A long fairing board, matched to the curvature of the hull, bridges the hollow spots and hits the high spots – irrespective of the wood problems and with patience transforms the edgy hull form to something that looks pretty well rounded.
When I start with the fairing boards I’m thinking that fairing and caulking – for which I allowed a week – will take at least a fortnight. However, by Friday morning I have a hull generally judged by all and sundry (Mike B gives it a ‘not bad’) to be pretty fair. I know that it is not – quite fair – but I decide to stop anyway as I don’t want to sand through the planks. At this point the centreboard slot gets routed through from the outside (the only use for a router on this boat so far!) – and I fair the cutwater. (The cutwater is the taper given the the stem(s) to make it (them) non rectangular). Seapod, again, looks quite different after this exercise – much more delicate. By late Friday afternoon I’m ready to coat the hull with sticky stuff (WRA 200) and complete the encapsulation of the planking – which has been a major theme of the Seapod project. The frequent need to remove screws – and re-set deeper – while I was fairing – led to some delays as WRA 200 also needed to be dribbled down each screw hole once it was re-drilled. I have obviously been a bit cautious in setting the depth at which screws were set as at least 50% (i.e. about 500 screws) had to be re-set while I was fairing.
Dust sticks to everything
The screws wait patiently for the ‘Yankee’ to arrive and drive them home.
The hull starts to look quite curvaceous
I get two coats of WRA 200 on the boat by 7pm Friday and leave to join the team in the pub – who I have driven out with the smell of the WRA-200. A few beers and a late curry at Lal Quilla mean that I don’t get started until after 9am Saturday on CAULKING.
Caulking is one of the defining activities of carvel boatbuilding. However well you plank a carvel boat changes in moisture levels mean that planks swell and shrink due the atmospheric conditions as well as swelling when the boat is kept in the water. As I started planking in March – when it was cold wet and miserable – and it is now May and (wet, warm and miserable ) – but normally much warmer and drier – the planks have changed in size – and will continue to change in size for the life of the boat. The fact that I have now encapsulated the planks in epoxy resin will not prevent this – it will just ensure that it takes place much slower than it otherwise would.
There is evidence floating around on the Internet (not published by me of course) that Seapod has gaps between her planks through which light can be seen! This fact, although disconcerting to the casual viewer, is normal.
What keeps a carvel boat waterproof is not good joinery to ensure that planks lie up tight next to each other but consistent joinery and good caulking and paying. The outer seam between each pair of planks is bevelled (see photo above) to leave a gap between the planks. This gap, in the shape of a wedge, is first caulked and then payed. Caulking is done with a fabric, normally cotton or (below the waterline on bigger boats) with oakum. Paying is done, traditionally, using various ‘grandmothers concoctions’ that include putty and linseed oil. I’m caulking traditionally using cotton but paying using a flexible polyurathane, Sikaflex 291. Traditionally, caulking, when wet, swelled up and prevented water ingress. The paying compound had to stay flexible for as long a possible but was mainly there to provide support for the external paint surface. The seam inevitably develops cracks quite quickly (water has to get to the caulking so that it swells up).
In the case of ‘modern caulking’, the primary agent ensuring that the boat is watertight is the paying compound and the caulking has the supporting role – as a backup water seal – assuming that it gets wet and swells, but more importantly, as a base for the paying compound that ensures that the back face of the paying compound is not a wedge. If a flexible polyurathane sealant is forced into a wedge shaped crack (which is what a caulking seam consists of) the back face of the sealant is a feather edge and cannot elongate when the planks move apart. The sealant then separates from the plank – and once it starts to separate from the plank it continues to do so – and the sealed joint fails. So, the traditional cotton caulking has a vital supporting role to play in ensuring that the modern sealed joint works. I think that this is a great way in which old and new technologies work well together. I could, if I routed a rectangular section groove between planks (as is done for teak decking), use a 3m fine tape to get the same effect, but then I would not have the cotton caulking as my backup sealant. Dual insurance against leaks sounds good to me. Of course, I could have chosen to build a cold molded or GRP hull and side-stepped all these issues.
Saturday morning and I start caulking – but not traditionally. I need to prime the seams first – to ensure that the polyurathane sealant will stick well to the epoxy plank encapsulation coating. The recommended primer (for porous substrates note – which epoxy resin is counted as one of!) is Sikaflex 215. This is a particularly nasty sounding methyl ether keratone … with some iso-cyanate thrown in for good measure so it;’s on with the organic vapour mask again. The price of this stuff (about £50 a litre) means that I’ve no intention of using much and I therefore dab it on carefully with a 1/2″ (sorry should that be 12mm) brush.
Once that has dried off – and I have made morning tea for the Saturday crew, I roll out the cotton and get to grips with the caulking wheel. In larger boats several strands of cotton (3, 4, 5 …) would be twisted together and driven into the plank seams using caulking irons and caulking mallets (very strange looking hammers -but quite logical once you understand the issues). Anyway, I don’t need a caulking hammer or irons for Seapod, but just use a wheel (borrowed from Mike B).
It’s hard work, the seams are tight and I only just have room for a single strand of cotton from a rough rolled bale (this is really cotton complete with seeds and all). I caulk alternate seams down and across the boat so that as the boat tightens up with the caulking (and it does) I don’t push all the planks up too much.
The shiny coated hull looks a bit nasty – but it will be painted (soon I hope).
I roll the cotton in so that I am left with a rectangular groove in which the Sikaflex will nest. To give you a sense of scale – the filled seam (illustrated below) is about 2mm wide and about 5mm deep.
It’s a good job that the build primer will fill in those diagonal scratches left from fairing!
Paying the seams with Sikaflex 291 is pretty straightforward. It just uses up loads of masking tape – but this means that I can scoop up the waste and re-use it further down the seam.
The rest should get finished tomorrow so that on Monday (a week after turnover) I can turnover again and get on with second phase fit-out.
Will I be ready for Beale Park Boat Show?
