Make a foam-core tiller
Sick of the fleeting life of exterior varnish? Prefer something a lot more enduring? Perhaps a foam tiller is for you!
In know it’s as heinous as kicking kittens or disparaging your national flag but I detest varnish – particularly of the exterior variety. First it seduces you with its sumptuous warmth; then it rewards you by weathering and falling off. My last boat had a laminated mahogany and ash tiller whose contrasting striations were a joy on the eye, the envy of many, and an absolute nightmare to keep in respectable condition. The Zen-like calm that characterises my relationship with my new boat arises from a complete absence of varnish. Not a scrap. Not just on the tiller but not anywhere on our boat. So please don't expect an article on varnish. I would choke on every word.
So, for those similarly tormented, I took at least one small step towards a more tranquil future. The plan was to build a lightweight tiller that would never need varnishing. The result is shown above. Here’s how I went about it:
1: First, the closed cell PVC foam (10mm thick Herex sheet) was cut into over-width strips, keeping the edges as straight as possible. For this I used a band-saw but a razor knife and straightedge would have sufficed. Using offsets taken from the working drawings, I then plotted the arched shape of my tiller on the work surface and screwed the shelf brackets to it, carefully following the line. The melamine surface was lightly waxed to prevent anything sticking to it.
2: Glued up and clamped. The foam is easily crushed but fortunately there’s no call for much pressure. Polyurethane glues swell as they cure, filling any small gaps. The curing process relies on moisture which, of course, occurs naturally in timber but not in PVC foam. To compensate for this deficiency I spread the glue on one surface and moistened the other with a damp rag. Not much, though. It shouldn’t be visibly wet.
3: After leaving it overnight, the foam blank was removed from the jig, cleaned up, and the sides squared off – the last, again with the bandsaw. Parallel from end to end, it was a brutish looking object desperately in need of some shaping. The first step was to mark the tapers on the top and sides and cut away the excess – the hatched areas shown below. This was yet another job for the bandsaw but a carefully wielded handsaw – preferably a Japanese type pull-stroke handsaw – would also have worked well.
4: The blank’s corners were then rounded off with a router and finished by hand with coarse abrasive paper. To hold it clear of the surface and provide access all round, I impaled my now recognisable tiller on a couple of stiff wires clamped in a Workmate. The foam was then primed with epoxy resin and allowed to cure just enough to become tacky. From here on, the work had to proceed in a continuous operation – there’s no going back! Incidentally, the grey patches at the fat end are cores of epoxy filler passing through 1” diameter holes drilled in the foam. Their purpose is to resist the compression loads where the tiller is attached to the associated hardware that connects it to the rudder stock.
5: Here the first layer of unidirectional glass rovings (previously trimmed to size) is being formed around the blank. The tacky resin effectively grabbed the rovings and prevented them slipping off as I teased out the creases. Once the top was done, I turned the tiller over, spiked it the other way up, and did the same along the bottom.
6: Now the unidirectional rovings are in place top and bottom with the overlaps at each side where the double thickness will be the most structurally efficient. A light binding of polyester thread has been half-hitched along its length to make the whole package more handle-able.
7: Wetting out with epoxy. It’s important that no dry patches remain so I was very generous with the goop. This is a spectacularly messy job so the gloves were essential.
8: With the unidirectional rovings thoroughly wetted out, a ‘bandage’ of glass tape was applied. Here I’m using bi-axial tape, where the fibers cross at 45° to the length axis. The more common woven type would have done just fine but, since it’s typically of much lighter weight, I would have wound on a couple of extra layers. To stop it unwinding I secured the trimmed end with a rubber band.
9: Over the still-wet laminate I next wound on a second bandage of special heat-shrink plastic tape, pulling it as tight as I reasonably could and making generous overlaps between turns to ensure there were no gaps. Again, a rubber band held the end.
10: It was then time to shrink the plastic tape with a hot air gun. This had two immediate effects: it dramatically reduced the viscosity of the resin and drew the tape down tight around the tiller, consolidating the laminate and driving out air bubbles. It also kicked in the curing process, so there were only a few minutes for this part of the job. And, since there were only going to be two outcomes – success or failure – I conducted a few tests first to get the hang of it. In the event, it all went very smoothly.
And that’s about it. Once it had all fully cured– a couple of days later – I peeled off the tape to reveal a good quality laminate which only needed fairing and painting to finish the job. The ends were sealed by carefully hollowing out the foam to a depth of about three-quarters of an inch or so before filling the void with lightweight epoxy filler.
The epoxy lamination part of the work took about forty minutes to complete. This was well within the pot life of the resin and certainly much less time than I had spent every year preparing and varnishing my old tiller. The result is light, strong, and durable and – dare I say it? – extremely elegant, as you can see on the photo that heads this article. More importantly: fifteen years on and it hasn’t hijacked a single minute of my time that I could have spent doing something more pleasurable.
To summarise, you will need:
- A non-stick work surface you can drive screws into. You could use a workbench covered in polyethylene film but I used a sheet of melamine faced particle board.
- A number of shelf brackets to form the jig. The more elaborate the tiller’s shape, the more you will need. I used nine. And as many clamps as you can lay your hands on.
- Closed cell PVC foam sheet. I used 10mm thick Herex H60, but anything similar – Klegecell for example – will work fine. Don’t use polyurethane foams which are friable and will break down in time.
- One-pot moisture cured polyurethane wood glue. I had some Balcotan handy but any will do. Make sure it’s not too fast a grade – you will need plenty of time to assemble the laminate stack
- Epoxy resin – again not too fast a grade. Err on the slow side if in doubt. For your ambient temperature allow a pot life of at least two hours.
- Unidirectional and woven or bi-axial glass rovings. The lighter weights are much easier to work with. Don’t be tempted to use chopped strand mats, which rely on the styrene contained in polyester resins to dissolve the binders that hold the fibers together
- Heat-shrink plastic tape and a hot air gun.
Oh, and you can throw way that varnish brush!