11. Fairing the Grainger Trimaran MTB920 Main Hull

Fairing the Trimaran main hull.
The west system fairing involves applying a light weight epoxy resin fairing compound with a notched plasters float, leaving lots of raised lines spaced about 50mm and about 3-4mm higher than the hull surface to cure hard. If the hull is not very fair then the height of the raised lines will be need to be increased. Once they were cured then I used a 1M long homemade long board with sanding paper attached to it and carefully sanded the tops of the raised lines of fairing down so that the where the overlaps in the glass were, the lines would be about 0.5mm and roughly about half the distance of the long board the raised lines would be deeper depending on how well the hull was made, and then progressively less height the further away from the fibreglass overlap you went. Essentially a fair surface is created across the tops of the railway lines.
With a flat float using the prepared raised lines as guides, I towelled on the fairing, filling in the spaces in-between the raised lines. I learnt not to play with the fairing too much as it only made the finish worse. Once the fairing was applied I let it cure, and then got the long board out again this time with finer grit to carefully sand the filler down to the railway lines, taking care not to take too much of them as that would essentially produce a hollow. After this coat cured, there were a few small local areas that need little more attention, but nothing much.When the fairing was finished the hull could then be turned over up right so that the temporary mould frames could be removed.

4. Hull mould and datum waterline set up

After couple of days later all 14 temporary hull mould frames were cut out, and were ready to be installed onto the strong back.
The photo to the right shows the temporary frames set up on the strong back inside the shed.
The strong back had to be marked out for the position of each of those mould frame stations.
Then to help accurately align each mould frame, a piano wire was set up set up on the centre line of the strong back, and about 25mm clear of and above the strong back.
I used a piece of angle iron bolted to each end of the strong back so that the piano wire could be pulled very tight and tied off once it was level. The point to note here is that you do not want any sag in the piano wire, or your boat hull will have sag in the middle built into it.
I bought a line level that just hooks over the piano wire. It is a simple tool, and does not cost much.
Then all the datum waterline heights marked on the mould frames were then set up the same distance above the piano wire.
A long accurate builder’s level was also used to check that each mould frame was standing up perpendicularly to the piano wire at 90 degrees, using the vertical centre line marked on each station for the level.
A Builders Square (used horizontally against the hull mould frame) was used to check that each mould frame was horizontally 90 degrees to the piano wire.
All this care in setting up is extremely important if the hull is to be perfectly fair (smooth without humps and hollows). It will certainly pay off with a hull fairness that you can really be proud of.
Then after all those set up operations were completed a laser level was hired to do the final check, and then the temporary frames were finally screwed securely in place so that they would not move under the weight of the hull as it was built over this male mould.