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.

10. Applying west system and peel ply to fibreglass

Now that the main hull was fully planked up with DuraKore it really was looking like a boat, however I had to remind myself that this was only the core of the hull, the core between the fibre glass laminates on the inside and outside of the hull.
The next job was to remove the many hundreds of those screws that were put in to hold the DuraKore in place until the thickened epoxy resin cured, and every one of those hoes needed to be filled. Prior to laying any fibre glass and resin onto the hull, I sanded off very carefully the excess resin all over the hull taking care not to sand away any of the marine hardwood Gaboon veneers, as you will remember they are only 1.5mm thick.
I hate sanding, and fortunately after approximately 6 Duracore planks were edge glued and screwed to the mould frames, I went over the joints with a scraper removing excess resin before it hardened saving a lot of hot sweaty sanding time and cost of sand paper.
The next job was so welcomed, as I needed something different from edge gluing DuraKore strips to a mould.
The next job was to lay up the first layer of Fibre glass which consisted of only 1 layer of 270gm bi-directional glass fibre.
Fibre glass is supplied in several weave patterns. bi-directional as its name suggests, 50 percent of its fibres running the length of the cloth on the roll, and the other 50 percent across the width of the cloth, and its designed strength is in both directions. There are also some other fibres running across the width of the cloth are only there to hold the glass fibres together as a flat cloth so that we as the boat builder can easily lay the fibre onto the hull, without the fibres parting in every direction as the resin is rolled in. The weight 270gm is its weight per square meter, and reasonably light cloth, as DuraKore contributes so much to the strength of the hull in the fore and aft direction no glass fibre is required in that direction.

The Bidirectional glass was laid up 45 degrees to the planking, other words the fibres ran across the strip planking joints at 45 degrees to the joint. This laminate transfers the loads along the fibres in those directions that the DuraKore Gaboon hardwood fibres are not able to as they run the length of the hull, just as internal diagonal bracing does in the old timber constructed hulls.
I started approximately halfway down the Hull and simply draped a length of the cloth over the hull to the opposite edge at 45 degrees, and cut off the surplus close to the edges of the hull.

I mixed small amounts of Epoxy resin at first, about 5 pumps each of West System Resin and hardener and rolled that on with a standard paint roller used for oil based paints.
The temptation is to mix larger amounts, to save time mixing the stuff all day, but this resin generates heat once the hardener is added and stirred, and with larger volumes of epoxy resin in the container the greater the reaction and shorter the pot life. Before you know what has happened your hand is hot and the epoxy is hardening in the pot, as well as melting the plastic. I kid you not!

It is important not to roll too hard or too much as the glass fibres are reasonably brittle and can break therefore affecting the final strength of the laminate. It does not take too long to work out the best method to wet out the cloth. Some areas I found it easier to lift up the dry glass and wet out the duracore, then carefully lay the dry cloth over the wet hull while rolling a wet roller on top to spread the cloth wetting the glass onto the wet hull ensuring that there was no air trapped under the glass.
It may sound difficult but it certainly is not, it is just technique and practice and does not take too long before you are covering larger area’s fairly fast. You need to work reasonably quickly with the pot life in mind.

I only started to use release fabric once I started fibreglasing the inside of the main hull, up until them I did not know about it. After a couple of cloths had been laid onto the hull I laid a release fabric called Peel Ply, which really just looks and feels like nylon spinnaker cloth. It is not necessary but I recomend using it as it really improves the cured finish texture and helps to remove excess resin from the layup, when it is ripped off once the epoxy has cured. The best benefit for me was that as the release fabric was ripped off it also removed the bi products, waxes etc formed during the curing process that would otherwise need to be removed washing or by light sanding etc, which is extremely important before any other epoxy resin work or bond joints are made over top of cured epoxy surface. Sanding is not really recomended as the wax blocks up the sandpaper ver quickly leaving the sander ineffective.

This process was continued until the main hull was finished. I did all this work without any help, in fact the only help I asked for was when I needed to lift the deck, or out rigger hulls into a new position etc. Apart from that it is possible to build a yacht this size by yourself.

9. West System Epoxy Resin for my Grainger MTB920 Trimaran

The Epoxy resin that I chose to use was 105 West System manufactured by Gougeon Brothers, Inc.
I really like using West system as I learnt to use it for many different jobs on my Trimaran.

Not only was it used on the obvious fibre glassing work, but thickened up with additive powders it was used to bond in the bulkheads and furniture, as well as the final water barrier protection before applying the 2 pot undercoat and top coat paints.
I also fitted all my hardware fittings without having to use nuts and washers, as all that was required was too drill an oversized blind hole, fill it with a thickened epoxy resin mixture, place the fitting such as a winch over the filled holes, and drop the stainless bolts through the mounting holes into the epoxy filled holes. It is a superior methodof attachment to the conventional nut and bolt technology.This proved to be a fantantastic solution to preventing water leaking down through bolts into the hull or inside the hull etc. If used on wooden boats it would also prevent ingression of water rotting timbers etc.

The resin is a clear, light-amber, low viscosity epoxy that can be cured in a wide temperature range to yield high strength, rigid solid bond which has excellent cohesive properties and also is an outstanding moisture barrier.
There are two types of hardeners formulated for use with 105 resin.
205 and 206 hardeners require 5 part resin to 1 part hardener mixing ratio. 207 and 209 hardeners require a 3 to 1 ratio, and solid state 6 to 8 hours.
205 hardener is mostly used for general bonding, barrier coating and fabric application. It was also formulated to cure at lower temperatures and to produce a rapid cure that develops its physical properties at room temperatures. Its pot life is 9 to 12 minutes at 22 degrees C, and cures to solid state 9 to 12 hours.
The 206 hardener is a slower hardener and provides a longer working time especially when working in climates of higher temperatures. I tended to use mostly this hardener as its pot life is 20 to 25 minutes at 22 degrees C.
Special pumps can be purchased to dispense the correct amount of resin per 1 full stroke of the resin pump, and the correct amount of hardener per 1 full stroke of the hardener pump.Mixing containers can be bought, however being a scrooge I preferred to put my money into the boat and not the rubbish bin. I had my wife and our neighbours saving plastic milk bottles and other suitable containers for me. My supply of milk bottles was insane at times. I cut the tops off those to make suitable containers.

8. DuraKore strip planking the Grainger MTB920 Trimaran bilges

Laying the DuraKore onto the temporary hull mould frames progressed fairly quickly. I had both sides done in less than 2 months of spare time around a full time job.
I was racing against the seasons, as I needed to be at the fibre glassing stage during summer, so that the west system resin could cure properly in suitable temperatures. Fibre glassing was to be another first for me, apart from a few small repair jobs on previous yachts.
You can see by the photograph that I had deliberately left the bottom of the hull until both sides were completed.
This was because that area had the most curvature and in my mind it was not going to be easy. So while working on the sides I was mentally working out how I was going to attack the bottom of the hull.
Most of the sides were done with 50mm width strips, and the flatter areas were planked with 75mm strips.
I found that I had to cut various sized strips for the bottom, but predominately they were approximately 25mm strips.
This was a lot more work, as there was more cutting, edge gluing and screws to be screwed in, but too me the best way to produce a nicely curved hull shape.

A tip
In hind sight I should have investigated using a staple gun to hold the strips on. The staples could have been fired in through a piece of plastic placed over the top of the DuraKore strip, which then could be used to pull the staple out after the resin had cured.

All the strips were cut with a skill saw set up to follow a fixed stationary straight edge 10M long.

7. DuraKore strips aligned to the hull mould

As the Durakore strip planking process progresses and you need to plank around tighter curved areas such as the bilges, then some dress making skills are required.
Due to the limitations of how much the strips could take up the shape of the hull, some strips needed to be cut to suit the line alignment of the next plank.
I did this by laying a second strip over the full length of the hull, butting the ends against the temporary screwed plank, allowing the strip to run where it naturally wanted to bend around the shape of the hull.
I then traced with a pencil where the edge of the second strip wanted to sit over top of the temporary screwed plank.
I wished I had a photo of that part of the operation, as it is really easy but difficult to describe simply. However the photo to the right will show how the strips were cut to run into each other. This may help.
Hopefully I do not make this too confusing. Basically I would lay the new strip on the edge of the strip already fixed to the hull mould. I would then draw a pencil line in behind the new strip following the top fixed strip edge, to produce the tapered edge to enable to new strip to fit into the tapered gap that had to be filled. Confused, well please take a good look at the photos.
The most important thing I realised here is to take care in the alignment of the strips, so that the strips appear to lay flat and fit perfectly over the entire hull, without any humps or hollows, or being twisted like a propeller blade to lay over the hull mould frames.
It is best to just cut them in allowing the strips to flow into the hull, without unduly forcing them.
This part of the project took me approximately 2 months of spare time after work and full weekends around the clock. There were no recreational days. At the end of this stage of my Trimaran project I was rewarded with a very fair looking hull, it looked good but I had so much more to do.

6. West system resin to edge glue DuraKore strip planking

Now that I had a stock of 50mm x 13mm x 10m plus planks prepared, I was ready to screw the first plank onto the temporary male mould frames. A power screw driver was real handy for this job, as there were thousands of screws to be screwed in, temporarily holding the plank in position while the west system, brand of slow curing epoxy resin cured.
I need to use slow curing west system epoxy so that I could get several planks edge glued and installed onto the hull mould frames, as well as temporary plywood battens screwed across the planks to support the planks in the unsupported areas between the mould frames. You can also see the battens in the photos.
I did all this by myself with no volunteers; it is possible when you set up correctly.
The first plank placement is the most important, as this positioning will be the difference in how all the other planks lay up around the hull frames. Basically you lay the plank onto the hull into the lowest point in the curve along the entire hull or the highest point along the whole hull, and visualise how the next planks will look and sit before selecting the position to screw the first plank on. Some planks will be expected to lay up with a slight twist like a propeller blade, following the hull shape and they can only take a limited amount of flex.
It is not wise to make them lay across the mould frames unnaturally.
The photo demonstrates where I started with my first plank.
Epoxy resin and west system filler powders are mixed to a peanut butter like consistency and then applied to one edge of the fixed plank.
Then the 2nd plank is lifted up and placed against the glued edge and then screwed in place. This job goes on and on until the entire main hull is fully planked up.
After a few planks are edge glued and fitted, I made sure to scrap off all excess resin to save myself a lot of sanding later on.
Remember that DuraKore is only the core, just as foam or divinycell etc are an alternative core material for hulls.

5. Grainger MTB920 Trimaran built with DuraKore planking

Now that the temporary frames were all set up and secured in place, Paula and I held a long board over several frames at a time to see how a Durakore strip plank would look when screwed to the frames, just as a final check to make sure that there were going to be no humps or hollows in the finished hull due to poor temporary frame measurements or cut out.
The 9.2 Meter hull was now ready for the DuraKore planks, but the Durakore was only 2.4 meters long and too wide at 300mm.
DuraKore is a marine grade composite of Baltek end grain balsa bonded in between 2 veneers of marine Gaboon hardwood, providing strength to weight ratio far superior to any traditional method of one off construction.

My next job was to splice those 2.4M planks together to at least 10 meters or longer, and then cut those planks up into suitable strips so that as they could be edge glued and screwed to the male mould frames to form a round bilge hull, and not an obvious multi chined hull shape.
The spliced joint made (male to female) was a 1 in 12 taper cut across each of the hardwood veneers.
Effectively you end up with a tapered male edge, with the marine hardwood veneers tapered down to the edge of the balsa core.
The female joint is obviously the opposite, as the balsa core is machined out a distance equal to a 1 in 12 taper of the hardwood veneers.
I’ll explain, if the hardwood veneer is 1.5mm thick then a 1 in 12 taper will cause a tapered edge to be 1.5mm x 12 = 18mm long. Therefore the balsa removed from between the hardwood veneers will be 18mm deep.
You can see the female joint in the attached photo.
And you will now see that the matching male edge is tapered out to 18mm to accept the female edge.
This 1 in 12 taper splice produces a joint equal if not stronger than the uncut hardwood. West System sells a scarfing tool that can be attached to any Skill saw to do this machining job very easily.
I made a flat “table” area along side one side of the hull, which I could glue and join the planks together, and that they would be perfectly flat long planks (at least 10M or 11M) once the west system epoxy resin was cured. I did not want to make strips which are bent at the joints. That would also have resulted in a hump or hollow to fix up later.
The reason why I made these strips much longer than the hull, was that it is important to stagger the spliced joints. It would be a potentially weaker core if all the strip joints were aligned together.
Once I had glued up a lot of 9.2 meter x 300mm planks, I then sliced them up into approximately 50mm width strips, with a skill saw.
The photos show a pile of those durakore strips ready to be edge glued and fitted to the hull mould.