Sunday, 29 July 2012

Some arrangements for fitting a storm jib.

I am going to a lot of trouble to give the boat a storm jib, mounted on a removable inner forestay. I think a storm jib is a sail that is often left in the bag on a boat - few people use them. But I have sailed all the way from the Canaries - Madeira - the Azores - UK under storm jib for 95% of the trip. I had wind on the nose varying from F6-8 all the way. I'd gone as far west as the Azores to pick up the south-westerlies to get me back to the UK, and did indeed set off from there with a fair wind, but it only lasted 12 hours. Then I was back to the storm jib and either double or triple-reefed main all the way to Start Point, all of it close-hauled.

I had an inner forestay on that boat (a plywood 32' monohull) which I'd fitted specifically for taking a storm jib but I did experiment with hanging the storm jib from the main forestay, to see how it might work. I could go to windward alright, but at only 2-3 knots. Hanging the storm jib from the inner forestay, so that it just about overlapped the reefed main, I got 6-7 knots. For two weeks crashing through waves all the way from the Azores, I was very glad to have that sail and that rig.

Besides allowing me to continue sailing at a reasonable speed in strong winds, the storm jib also allows me to sail slowly in lighter winds - to await daylight before entering a new harbour, to catch up on some rest, or to go fishing. I have already fitted a catwalk between the front aluminium beam and the front of the saloon, but I need bobstays to counteract the upward pull of the inner forestay.

The bobstay fittings that were previously used for the front beam were no use - they were fitted too high for one thing, making the angle too shallow. And the support inside the hull was inadequate too:

In the bows of the boat, a floor is glassed in about 20 cm above the water line. A block of wood has been glassed onto the wall of the hull at floor level to take the load of the old bobstays. I don't think this is strong enough, or low enough. The yellow area behind the text in the image above is a hole I dug through the floor and through the foam that fills that area to place a new load bearing construction.

I used a grinder to cut through the floor - which was surprisingly substantial - an Airex sandwich. And then a wire brush on a drill to pulverise the foam underneath with a hose from a vacuum sucking away the dust.

It would be crazy to do such work in such a confined space without the benefit of an air-fed mask:

These masks sell for £6-700! I was lucky to find one at the local dump, and acquired it for £3. It had no battery and the exhaust valve was ruined. Replacement parts are also very expensive, so I had to adapt it a little. A 6v battery charger wired in to the motor runs the fan, and a vinyl glove with the ends of the fingers cut off works like the valve. An old filter cut down and glued to a flexible pipe allows me to work with either filters or a tube leading to a supply of fresh air. The fan is a bit noisy, and I feel pretty constricted working in it, but I get fresh air to my face and so don't have to breathe either fibreglass dust or epoxy fumes. Ear defenders and a set of plastic overalls for epoxying add to the discomfort. I'm also working in a space where I can just about sit up... but that's enough wingeing! Back to work!
I glued a pad of plywood to the surface of the inner skin of glass with epoxy and fillers. I then glued in a plywood floor, and plywood to the front and back of the hole. I filleted the joins, and glassed it all together with epoxy and biaxial glass. From the outside, I ground away the outer skin, and the foam underneath, and filled the hollow with many layers of epoxy and glass:

In this way, there is no foam where I will attach the bobstay fittings - just solid glass and epoxy. And the load is spread between the outer skin and the inner skin, and via the plywood construction to the inner skin of the other side of the hull. I will use a stainless steel backing plate to spread the load of the nuts of the fitting evenly.

I think this structure is so strong it would be suitable for attaching my anchor bridle too, which I'll bear in mind when choosing the fitting I'll use here.

Phew - several days work grinding and epoxying to create a thing probably no-one will ever see or appreciate, except you reader! Thanks for your attention!

Thursday, 12 July 2012

Improving the front beam

Here's the front beam of the cat:

There's a bridle from the middle of the beam to close to the water line on each hull. I don't like this set up.

The angle of the bridle seems too small - the forestay is under great tension when the boat is sailing to windward, and the tension in the bridle must be greater still given such a small angle. I suspect the hull fittings must be under great load, and though the moisture meter doesn't suggest any water leaking around these fittings, it just seems a matter of time. The builder of this boat wasn't too clever about keeping water out of other places! Like where the beam passes through the hull for instance:

I've scraped away some gel coat at the top of the join. There's a fillet of resin and glass around the beam, but the resin is polyester, not epoxy, and there are places where the fillet is pure polyester resin with no glass or filler in in - it is just brittle resin, with very little strength.

Water has entered the join on each side. The beam passes right through the hull and is bonded to thick plywood above and below the beam. This is a very strong arrangement - or it was, until water softened the plywood. It had even begun to rot in the starboard hull.

I climbed in the little compartment in the forepeak (really small, as the bottom half is a watertight compartment filled with foam) and loosened the bridle attachment fittings. Both fittings were quite bent:

Those really aren't the best fittings for the job anyway. They aren't designed to withstand such forces from an oblique direction.

Time for a total redesign. Googling Richard Woods and Sagitta, I noticed that on the first of these boats that he built, he had a seagull striker rather than a bridle. This is an arrangement I much prefer - no through hull fittings near the water line, no wires below to cause trouble with mooring buoys, anchor ropes, people in dinghys, or my head, when I am walking around under the boat and forget the wires are there.

Anyway, here's my plan for retro-fitting a seagull striker:

I've drawn up plans to hand over to an aluminium fabricator. All the tangs and fittings for rollers are welded to two-part sleeves that can be bolted over the beam. I have anchor rollers on each side as well as the central one - you often need more than one roller, but positioning them here allows me to also use them for a sea-anchor bridle. The sea-anchor lines can be easily led back to the sheet winches.

I'm replacing the plywood around the beams, but will be using epoxy. The plywood will get a couple of coats of epoxy before I glass them in, to ensure they don't become wet.

I'll make a small epoxy/glass strand and filler fillet round the beams where they enter the hull - for strength rather than waterproofing. Over the join, I'll make a thick fillet of Sikaflex to seal it.

That should fix it!

Wednesday, 11 July 2012

Dealing with delamination from the core.

Delamination is the nightmare scenario for the owner of a boat made of composite materials. It means the core is loosened from one or both of the skins, and the strength of the delaminated part is severely compromised. Usually it is caused by a leak of water into the core, and in time the fibreglass and the core become separated.

My moisture meter led me to suspect just one area on the boat may have delamination, although the usual test, tapping on the hull sides to detect a hollow sound wasn't very persuasive. To check, I drilled a hole and water came out, so I drilled some more all around the area that read 30 (full scale) on my moisture meter:

The hole at the top left of the image is a drain pipe from my forward hatch guttering. You can just make out a pencil line around the drilled holes which shows the extent of the delaminated area. It seems the pipe has leaked water into the core and it has delaminated an area of less than 2 square feet.

After draining the water out (maybe 50-100 ml), I left the hull to dry. A week later, the moisture meter still read 30. I paid a visit to a neighbouring catamaran where all the gel coat has been peeled off and the hulls left to dry out since last August - with the wetter areas warmed more recently by heat lamps. His wettest areas also read 30 on the meter, although we couldn't get any water out. Still, this suggested that hoping water trapped between the fibreglass and the core would evaporate out of the little holes was too optimistic.

I inserted some toilet paper wicks:

They helped a lot, and at first, the readings came down a little, and then stopped.

I googled a lot, and found that just removing the water won't be enough. The water contains solvents - either salt, or solvents from parts of the resin that has dissolved. If the solvents aren't removed, the water will never go from the core. Imagine trying to dry out a sweater that has been wet with sea water - it will never be properly dry until it has been rinsed in fresh water. And even if you dried the sweater but left the salt in it, it would absorb moisture from the air.

As it happened, I'd just bought a new vacuum cleaner, a Vax carpet cleaner, and noticed that this model has a little water pump in it, so that it is equipped to pump water through a small pipe. Just the job! I added food colouring to the water so that I could see the water behind the fibreglass. The result was spectacular!

The holes I'd drilled just happened to be the same size as the water pipe. Inserting the water pipe in one hole, and sucking with the vacuum on another, the water was plain to see flooding the delaminated area. What was also plain was the the moisture meter had allowed me to accurately outline the delaminated area - water didn't penetrate beyond my pencil line. Using different holes for the pipes, I was easily able to flush everywhere in the area. I then just sucked as much water out as I could get, and put some new toilet paper wicks in. Out of curiosity, I tested the area again with my meter:

It now reads just 16 units at the bottom of the delaminated area, and read just 5 at the top. This was immediately after flushing, when clearly the area behind the fibreglass was still wet. What was going on?

I guess the meter reads capacitance of the material it is measuring, which must be related to the conductivity. Pure water is a poor conductor, but water containing solvents is much better. I guess removing the solvents was the cause of the lower readings. Anyway, with now just fresh water behind the fibreglass, I left the wicks in place, with the intention of warming the area later with heat lamps to remove the last of the water. I monitored the meter readings every day, and found to my surprise that the readings went down, then up again. I figured the remaining water had dissolved some more solvent and rinsed again. Again, the readings dropped, and then went up a little. In the end, I rinsed the area three or four times, and now the readings are just slowly falling. After a few days with heat lamps, I'm confident that the core will be dry enough to allow me to inject some epoxy resin, and job done.

My progress was monitored by other people in the yard, and they liked what they saw, so we treated the other catamaran in the same way:

With two of us on the job, I was able to take a photograph of the operation this time! The numbers on the hull are the moisture meter readings. It's not so plain to see that water behind the layup in this photo, but we could see it pretty well. This boat also needed several rinses before the readings stayed down. This cat now has heat lamps on the area, and the readings are coming down - as they never did in the last 8-9 months. Clearly, rinsing is an essential part of treating delamination!

Once the area was dry, I tried sucking epoxy into the affected area. I closed all but the highest and lowest holes off with tape, connected a vacuum to the top hole and a tube full of epoxy to the bottom hole and... it didn't work. The epoxy needs a little filler in it to reduce its brittleness, and it was too thick for the vacuum to pull.

Much better was to use a syringe. I added some red chalk powder to the epoxy, so that I could easily see where it went. That worked great! The are now looks like it is bruised, with the red showing through, but I know it is now well sealed from water, and the skin and foam are properly bonded. It'll paint over just fine!