Routing the roundover on the chine.
July
'06
21.
Sheathing the Hull
21. Sheathing the Hull (cont.)
The final step before applying the fibreglass was to round the sharp edges. Fibreglass and epoxy apparently lose a lot of their strength if they have to change direction suddenly, so the hard edges of the chine and keel flat have to be softened. For the chine, in the stern half of the boat this can be accomplished fairly easily with a router. I used a half inch round over bit. But as the hull sides and bottom begin to make a more obtuse angle with each other the router becomes less effective. From amidships forward you have to resort to the old fashioned method.
Routing
the roundover on the chine.
At the keel flat there is no tool which will do the job other than a power sander. You have to be careful not to round over so much that you reduce the width of the flat to less than the width of the keel lifts, but other than that it is not critical.
All these areas where end grain of the ply is exposed will absorb a lot of epoxy. I think it is safer to give them a separate coat or two of resin before the glass is applied, although if the squeegee method is used for glassing there would possibly be so much resin over the areas in question that they would not be starved.
Just before applying the epoxy to the keel flat, I noticed that the planed area seemed to slope a little to one side. Checking it with the spirit level confirmed it, so I checked the level of the boat again with the water tube method.
A hint of
unevenness to the naked eye is a lot more to the spirit level,
The
water tube was slung from one gunwale to the other to check
levelness of the hull.
The boat was perfectly level, so the keel flat needed bevelling a little. After that the edges were rounded again and epoxy was applied to the end grain.
Epoxy
resin is applied to the chine where end grain has been exposed by
rounding...
and to the keel flat.
Glassing is preferably a two man job, not only for lifting the glass onto the boat, but so that one can be mixing new batches of resin while the other applies it. Up to this point I have been using slow hardener for filleting and fairing, but fast hardener will be better for sheathing, not least because it is now Winter, and the temperature in the garage is around 12 deg.C.
The 4 oz. fibreglass is quite fine by comparison with the 6 oz. I have been using for the fillets. It easily curves around the chine and keel flats.
A length of 7 metres is cut from the roll and draped over the hull bottom with 50 mm. overlapping to the other side of the midline. It is held in place with masking tape while the epoxy is applied, and the helper starts mixing up small batches of unthickened resin, which is poured onto the glass near the middle of the work area, so that it can spread in either direction as the epoxy is squeegeed into it.
Unthickened resin has a tendency to run everywhere it can, so I apply it in small batches and spread it quickly to try and avoid too much wastage. Even so, plenty of it spills down the side of the hull.
One reason why you need two people to do this job is to try to
get a straight line on the selvedge of the second piece of glass
where it overlaps the keel. With two pulling the glass tight it
can be dropped into position over the top of the wet resin at the
keel flat. Without that you will have to adjust the position of
the second sheet repeatedly to try to get a straight line, and to
allow for stretching as you apply the epoxy.
Both hull bottoms are glassed first, with the overlap at the keel, bow and transom. I was intending to allow the epoxy to tack up and then cut through the overhanging glass, but even with a scalpel it was too tough, so I had to resort to scissors. That caused the glass on the sides to lift a little, and it had to be squeegeed back again, so it was lucky that I did not wait for the full tack stage. The resin was still wet enough to take the reapplied glass.
The first coat of resin is really only enough to make the glass smooth out and adhere to the ply. The weave pattern should still be visible after the squeegee has done its job. This will be filled in by the subsequent coats.
Fibreglass
weave pattern clearly visible after one coat.
Before the side panels are glassed there is some work to be done on the hull. It may not be obvious, but there is a "bloom" over the first layer of resin. It can just be seen here where two fingers have been drawn across the surface after the resin has cured.
Two
finger marks show the bloom on cured epoxy.
The bloom needs to be washed off before any second coating can be done. But it wipes away easily with water. The second job is to sand back the epoxy spills on the side panels, to smooth sand the selvedge of the first layer of glass, and to sand the area of overlap for the second layer to give it some tooth.
The
frayed edge of the fibreglass is seen, where it was
trimmed to the required width of overlap. This needs to be
smoothed out, and the resin beneath it needs sanding too.
After sanding the edge should be blended into the glass, without cutting into it too much. With a random orbital sander most of the resin and loose fibres can be smoothed out, but it can also cut down to the wood if relied on too much. In some areas hand sanding is necessary, especially on the roundover of the chine.
The
cut
edge is now smooth to the touch and ready for the next layer of
glass. Runs have been cut back.
In preparing the overlap area on the chine, you get the impression that you may have cut through the glass in some places, but it is usually due to a spot of thicker than average resin sitting on top of the glass. If you continue to sand it exposes the glass weave pattern.
An
area
of thickened heavier epoxy coverage is sanded to reveal the
weave.
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