May '06

After fairing the first hull bottom skin, the second skin application was straight forward. Toying briefly with the Sam Devlin recommendation to use unthickened epoxy resin for the job, I quickly abandoned it in favour of thickening it slightly, to about ketchup consistency, with microfibres. Perhaps the marine ply I am using is stiffer than he uses, but short of placing staples at every 20 mm. I could not see how there would be a gap-free bond with unthickened epoxy. The other deviation from his recommendation was that I did not drill holes in the ply to see the epoxy ooze out. With 150 mm. wide strips I think it is unnecessary.

However, copious amounts of thickened epoxy are applied to both surfaces, and staple spacing is at about 75 to 100 mm. The staples are inserted over nylon cord to aid in their removal later, and they are 10 mm. deep so as not to penetrate to the inside of the hull bottom.

Moulding started at the stern end, and was fairly time consuming. I had to take care not to allow the nylon cord to come into contact with excess epoxy, and I took the opportunity to fill between the strips with epoxy as I progressed.

The cold moulding progressing from the stern. Strips are laid at 45 degrees to the keel.

One day of gluing and stapling took me as far towards the bow as the area of the fairing. I am letting that fully harden for a few days before continuing so it will give the staples something to bite into. In the meantime the job of staple removal begins at the stern, and it takes a lot longer to get them out than it did to put them in!

I have found that the rapid cord pull for staple removal is not the best way. It tends to rip out half of the staple too violently and bends the remainder so much that it cannot be extracted. It breaks off instead. A slow tension on the cord usually results in a relatively intact staple which can be fully removed. Nevertheless, a few break off and these have to be set below the surface to be embedded in epoxy later. Notice how deeply the staples wound the wood. All of these voids will need filling before the glass layer goes on.

Staple wounds in the ply, and (bottom right) a broken
staple is set beneath the surface.

Some of the strips lift a little on their sides, especially where the hull becomes more rounded. If the space underneath is not filled with epoxy, a hollow sound develops where there is a void, and these can be drilled into after the glue is dry, to reveal the cavity through a number of bore holes. Thickened epoxy can then be pumped down the holes with a syringe until it comes up through the neighbouring one, and the void can be filled in this manner.

A series of bore holes into a void is filled with thickened epoxy. Some of the drilling dust comes up through the
neighbouring hole with the epoxy.

It is a good example of how much epoxy can be absorbed out of the thickened mixture to look at what happens to the filled staple holes after only one application of filler.

After sanding it is quite clear that the holes need a second application. This time, they will at least be sized by the first lot of epoxy, and will not absorb any more. At least that is the theory. In practice it does not hold up completely. Here is the view after a second application of filler, followed by sanding:

So I will go about it a third time. I do not want to get bubbles under the glass, and with epoxy being sucked into the ply so much that seems quite likely to happen unless it is thoroughly sealed.

Meanwhile, I have been looking around for some authentic slipper launch hardware on Ebay. I have purchased a manual brass bilge pump, which is currently being restored by my bilge man, Wee Davie Cochran, and I have previously acquired some navigation lights.

(Above) Bilge pump from an Andrews Slipper Launch of the 1930's. (Right) Bilge man, Wee Davie, takes his instructions
very seriously.

As the bow was approached the stresses on the moulding strips became greater. They now had to cup as well as bow, and staples were not always up to the task of holding them firm. At this point it would have been possible to lay strips at 90 degrees to the ones already on, but that would also have created some strong stresses. The alternative is to cut the strips even narrower than 150 mm. Here two of them cut to 110 mm. have been laid and the next few will be closer to 50 mm.

Because of the sharpness of the curve in this area the adjoining strips will not abut perfectly. Rather they tend to abut where they meet on their inner surface, but leave a V between them on the outside. In this regard the process is a bit like strip planking. As the V's will all be filled with epoxy anyway it does not matter at all.

But the severe curve in this region does make it too much for staples alone. The last few strips had to be screwed down as well as stapled. Once again, I wonder whether the ply I am using, which is meranti marine ply, is significantly stiffer than others, as the books do not tell of this sort of problem. The screw holes will eventually be filled in with thickened epoxy, before the glass is laid.

Port side hull completely moulded now, with the aid of screws at the sharp end.

One thing that has always bothered me about the design of this boat is the problem of unequal panel thickness between the bottom and side of the hull. After moulding, the bottom is 12 mm. thick, while the side is 9 mm. This only presents a problem at the bow, where the two panels meet at an increasingly obtuse angle, finally becoming 180 degrees at the stem. So what do you do with the overhanging 3 mm.? You can't just plane it off in line with the side panel, because that would take half of the bottom panel's outer skin off at the stem. Some of the excess can be planed certainly, but that still leaves a lip of overhanging outer skin at the bow.

I believe that the only solution here is to fill the overhang with thickened epoxy, and smooth it onto the side panel. Hardly an elegant solution I know, and one which would be impossible if a bright finish were contemplated.

Another possibility would have been to have the bottom and side panels overhang on the inside of the hull, and meet flush after moulding on the outside, but that would have required a transition joint, and the dimensions on the plans do not allow for that.

All considered, I think a boat with equal panel thicknesses would have been a lot easier.

Because the surface for filling is near vertical, and because there is no thixotropic agent used in the mix, for ease of sanding, the fill is applied under peel ply, which helps keep it in place a bit better. While that is setting up I go about the laborious task of filling the staple holes and other gaps with more thickened epoxy. It is probably unnecessary, as the hull will be coated in many more layers of epoxy and fibreglass before it is finished, but it does not do any harm.

I also need to fill the gap between the hull bottom and side once the second skin has been planed back to the level of the side. This area will later be rounded over before the fibreglass is applied, so a mixture of microballoons, microfibres and colloidal silica is used. It won't offer much resistance to sanding right on the corner, and some extra strength on this chine will be useful.

Filling the staple holes and gaps (left) and the chine (right), and yes it is meranti, not purpleheart.

The port half is sanded after filling, while moulding
proceeds on the starboard.

A final morning of activity completed the starboard side moulding. It looks like a drowned woman now until the cords are pulled. Then the same gap filling and planing will have to be done as it was on the port, and the overhang will have to be tapered.

Fill for the starboard overhang prior to sanding, and (right) planing for the stem has begun.

I have been delaying a decision on the transom until now because I have not been sure whether to go with a laminated one or build one out of solid timber. There was certainly something to recommend the old style solid ones when they acted as a landing point for deck beams and chines, but in the stitch and tape boats no such function is required.

Taken during repair of a slipper launch this shows the old solid timber transom.

Another example prior to restoration.

In addition, although I have made allowance for a curvature of 1 metre radius, I have been concerned that a transom which hangs back from the deck that far will get a "bow tie" look. The deck is still sloping down and the hull is still sloping up, so the further back you go the more pinched you get. Hence the aftmost point of the transom will be narrower than its ends.

Now, I don't see that happening in pictures of slipper launches, so it may be that there is still sufficient camber on their decks at the back to compensate for this pinching effect, but my boat's inner transom frame is dead flat. Consider some of the rear ends of these boats:

Of these I find the the transom of Lyre Bird is too truncated, whereas Lisanne is too extended, but definitely benefits from a cambered deck. Perhaps Forever J is about right for me, as it appears to have a flat deck, but its bow tie look as not too pronounced because of its restricted curvature.

The final decision was to laminate, and to go with a radius of 2 metres. The first step was to build a laminating jig, which used up a piece of waste plywood.

Scribing a 2 metre arc onto a piece of ply.

The shaping pegs were glued around the arc as shown, and 3 laminations of 6 mm. marine ply on the inside and one of 6 mm. Fijian mahogany on the outside were stacked up with as many clamps as could fit.

Because the boat is in the upside down position, fitting is a big problem. I could certainly scribe the contour of the hull onto the transom, but not of the deck. So I could not shape the transom's topside. Because it is important that the transom should look as authentic as possible it is going to be vital that the covering board behind the decking, which will join to the outer layer of the transom itself, should do so with an invisible glue line so as to resemble a solid block of timber. Hence the topsides of the transom must be scribed precisely to the deck line.

This made me come up with the idea of building the transom in two halves, with only the bottom half fully laminated now, and the top half laminated later after the decking is on. Initially the ply laminates were glued up, and then the angle of the inner transom frame to the hull bottom was taken with a sliding bevel, and transferred to the table saw blade. The bottom of the transom was sliced at this angle and the structure was fitted onto the inner transom frame.

This is another good reason to use a 2 metre radius: the 250 mm. saw blade only just scribed the inside of this transom at its apex. It was enough to trim it off accurately by hand, but a deeper transom would have made it impossible.

There had been a little spring back with the laminations when they came off the jig, so it was necessary to use a spacer block and screws to get it to sit at the right curvature. That done, it was glued up and left to set.

The overhanging hull bottom was then trimmed flush to the transom, and then the outer laminate of mahogany was added, riding proud of the hull because it had not been bevelled.

Note the dog leg in the hull bottom to accommodate the final mahogany lamination of the transom.

The mahogany is glued on leaving it proud of the hull both over the bottom and over the sides.

The overhang at the sides is designed to give a little room to manoeuvre with a softened curve between side and transom, rather than a sharp corner.

The geometry of the dog leg (left) and the mahogany outer laminate shown glued to the bottom half of the
transom (right).

After the mahogany is trimmed to the level of the hull bottom, and the side overhang is rounded, it makes a neat join with the rest of the boat.

Later, when the top half of the mahogany is added, the join between the two halves will be obscured by the boot top paint over the bottom. The top will be finished bright, and it should look just like a bought one!

Incidentally, the mahogany I am using is not the African type (Khaya spp.). In this part of the world it is easy to get the real thing (Swietenia macrophylla) which is all but logged out in its native Brazil. When the British ruled Fiji they had the foresight to import some Brazilian mahogany plants to the islands, and that was the beginning of an industry of plantation grown trees which are now reaching maturity. It is possible to get good lengths and great widths (up to 300 mm.) for a decent price.

You can get real mahogany (left) from Trend Timbers. Their yard manager, Andrew Hurst (right) is always helpful.

Later, when the covering boards are being made and scarfed for the deck it will be very useful to have 300 mm. of width, so that clinched the deal as far as wood choice went.

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19. The Rudder

Before much longer it will be necessary to cut a hole in the hull for the rudder, and to use it in keel construction. So I have given some thought to the rudder itself. The plan calls for a mild steel one, and that is what I am going to have made, but I will admit to being a bit surprised about the metal. What about rust? It seems that most people think that even a rusty rudder will last longer than a ply boat, so why pay the extra for stainless. But the problem of different metals in a boat cannot be ignored. The potential for damaging galvanic reactions is considerable, and there is certainly going to be some incompatibility between the rudder, stainless steel propeller shaft, bronze keel bolts, etc. An article from the Sea Fish Authority spells out the dangers clearly. There is going to have to be some attention paid later to preventing all these metals from corroding in the great electrolyte bath this boat will be floating in.

Nevertheless, for now I am staying with mild steel, and as I have no metal working skills, I have handed over responsibility for the manufacture of the rudder to my good friend, Lindsay Armstrong.

Rudder man Lindsay, and his project.