The Australian version
of West System 403.
March
'06
6.
The Glue Up
7. The Seating
Calculations
8. Lowering the Boat
9. The Floor Timbers
10. The Sheer Clamps
I have decided to use West System Epoxy on this project. There is a cheaper local alternative here in Australia, but the documentation accompanying West is first rate, and the Gougeon Brothers book on boat building is very helpful, so I'll pay a little more. However, the fillers available here, which come through a third party, are slightly different to the American versions. For instance, our 403 microfibre blend is a premixed pack of mircofibres and colloidal silica. In fact colloidal silica is not sold separately here at all. In the US, it seems that the Microfiber 403 is straight unblended. But for most applications the premixed pack is about right for the job, so I will stay with it.
The
Australian version
of West System 403.
Because of the
complexity of the stem end, with two bulkheads and a girder all
having to meet in the right spots, I decided to start the glue up
at the stern. The transom was attached to the bottom, first, and
then to the sides, leaving enough of the side unglued to allow
for the later cut out to accommodate the sheer clamps.
The
transom being glued under peel ply (left). The epoxy fillet is made
with
microfibre/Cabosil blend, and
is radiused to 22mm. Glass
reinforcement consists of 4" biaxial tape, followed by 6" bixial tape,
then 8" woven
cloth. The finished joint (right). Note the tabs
between
wires on the
hull bottom.
The epoxy tabs were used throughout the boat to allow for removal of the wires prior to filleting and glassing. The 16 gauge galvanised wire proved to be quite brittle, and I felt it would not stand up to the strain of being heated and pulled out of set epoxy. Pulling the wires prior to filleting meant no chance of broken off wires being left in the hull accidentally.
Apart from the transom, which is joined with a 22 mm radius epoxy fillet, the seams in the stern half of the boat are more like 35 mm. in radius. As the angle between the panels changes, so too does the radius of the fillet. As this is my first boat I have decided to follow the advice of Devlin and glass all joints with two layers of biaxial tape, and one of woven roving, so the strength of the joint is more dependent on the glass than it is on the fillet. Devlin says to assess which are high stress joints and to treat them with this formula of glass layers, but I have assumed that all joints are high stress, and have given them all the same fibreglass cover. It costs more in epoxy and glass, but it feels better.
In the picture above you can see bulkheads E and F and the transom. Filleting and glassing has progressed to the point where I have to decide where the floors (sole bearers) are going to be located. The level of the floors is marked on the E, D and C bulkheads, but these marks will be covered by any further filleting and glassing.
Floor
level marked on Bulkhead E.
Because the bilge area has changed from the designed profiles, albeit only slightly in the stern half of the boat, the bulkheads have had to be shaved to fit the actual hull panels. The shaving affected the bottom of the bulkheads more than the sides, so the floor levels have been marked measuring from the top instead of the bottom.
It is a slow process gluing every component, considering that there are nine seams in each compartment, and even more in the ones containing the girder. The plans call for floor timbers to be placed at the stem side of bulkhead E, and both sides of bulkheads D and C, as well as intermediate ones. So, until they are in place those bulkheads cannot be filleted to the hull panels. The chine and hull bottom seams were glued and glassed through to the stern side of bulkhead B, and bulkhead B itself was glued and glassed to the hull, stern side.
Then came the forward compartments, which are bisected by the girder. This makes for deep and narrow areas where filleting is difficult, and the glassing is even more so. With some of the spaces too narrow to accept any sort of filleting tool, I resorted to fingers for shaping some of them. Furthermore, the acute angles involved make the fillet depths quite large, so the heat build-up is rapid and they set rock hard within minutes, even with slow hardener. It is a good thing that these areas are never going to be seen!
The
forward compartment with girder and Jarrah fillets.
Epoxy fillets and glass are progressing.
Rear
seating
showing the rake angles.
In the plan, the rear seat is sitting on top of the sole, which is supported on the floor timbers, starting at E and going forward. The space under the seat can be used for stowage, so why have a sole lining it? Probably only to keep the stored contents dry. If any water gets into the rudder compartment it will track forward through the limber holes in E to underneath the seat. But if it stays dry, as I hope it will, then there is no need for floors under the seat. Instead, the front of the seat, which is supposed to be supported by the sole, could become a mini bulkhead and attach to the hull directly. The sole would then only have to go from the seat front forward to the engine compartment. An additional sole can always be added under the seat if it proves to be too wet in the future.
In addition, the rear seat in the 20 foot version of the boat is marked to be 475 mm. from front to back, not very generous when you take into account the thickness of the back cushion. In the 21'9" version which I am building, there is a space of 1613 mm from D to E, as opposed to 1308 mm. in the 20' version, so there is room to add depth to the seat. 600 mm. is more luxurious.
Finally, the plans show a rake to the seat back of about 4.5 degrees and a flat seat bottom. It is more comfortable for both back and bottom to incline. This will complicate construction a little, but will add a lot to the ambience of the vessel.
Therefore, the front of E can be filleted in, as no floor need be attached to it, and the front of the seat can be cut as a shortened bulkhead and glued to the hull about 600 mm. forward of E. The sternmost floor timber can be attached to the front of the seat bulkhead prior to fitting, and the sole can rest on that.
Part
of
the plan by Paul Fisher of Selway Fisher Design
(see Links) This seat could be set lower and be deeper.
The original slipper
launches had their rear seats much lower to the sole than this one.
They had to, because their hull were not as deep, and because the rear
seat passengers appear to pop out over the top if the seating is too
high. In converting the specified design to accommodate a sloping seat,
I will also lower it a bit for a better overall appearance.
But, in order to start
work on the interior, it is necessary to get the boat off its bench and
bring it down to ground level.
The availability of two assistants allowed me to lower the boat to a more workable height without any great difficulty. The stern was suspended by block and tackle from the wooden beams which support a loft above the garage.
Not
Atlas... just a helper.
At the bow there was nothing in the ceiling to which to attach a block easily, because it is concrete. So the stem was lifted manually and blocked up, while a ladder was slid under to support it. It was then just a matter of lowering each end bit by bit into the supports which had been removed from the table, and reattached to the now legless table top. Some slight chocking was necessary to bring the boat up to horizontal athwartships. It is now ready to have its sheer clamps and floor timbers installed, along with the half bulkhead which will serve as the front of the rear seat.
The
boat at floor level ready for the sheer clamps to be installed(left),
and the
fillet supporting the rear seat is attached to the top
of the half bulkhead (right).
The plans
call for floor timbers 75 mm. wide, raising the floor level to
180 mm. above baseline. This leaves a centrally located gap of 7 mm.
between the
bottom of the floor timber and the hull at the level of bulkhead E, and
of 102 mm. at bulkhead C. Since the hog in the plans is 36 mm.
thick, the rearmost floor timbers have to be notched around the
hog, while the forwardmost ones clear it easily. In the stitch
and glue version there is no hog, so it would seem reasonable to
take at least some of the timbers right down to the hull level to
reinforce the
hull, as well as support the floor. The first floor timber placed
was the one attached to the rear seat's half bulkhead. Two more lie
between it and the one behind bulkhead D. One is attached to both
sides of bulkhead D, one lies between D and C, and one is
attached to the rear of C. The front of C will only need one if
there has to be a cut-out in C to accommodate the driver's feet, and a
continuation of the sole into the motor compartment.
Timbers attached to bulkheads do not absolutely need to reach the hull bottom in order to reinforce it, because the bulkheads themselves do that, but the intermediate ones would add to hull strength by doing so. The floors attached to bulkheads can be shaped from the bulkheads themselves. The others have to be measured
The first floor permanently fitted was the one on the rear seat half bulkhead. After that all the others have to be at the same horizontal plane as the first floor. The rear of bulkhead D takes the second fitted floor, and the intermediate ones between D and E are elevated up against the plane defined by the first two.
First
floor attached to the half bulkhead.
By drilling through bulkhead D at the exact level of the top of the floor attached to its rear side, the level for the floor attached to its front side can be found. That floor can then be attached and a similar process followed to establish the location of the floors behind C and between D and C.
Determining the right level for the bulkhead D floor.
An intermediate floor between the rear seat and bulkhead D is
first shaped to
fit the hull, and then planed down to meet the sole level which
is marked
on
the side hull.
Here, one of the intermediate floors between bulkhead D and the half bulkhead is fitted to the hull. Its shape was defined by running three longitudinal beams between the already attached floors behind and in front, and projecting their under surfaces to the hull sides with a sharpened batten. This locates the top of the floor position at its intersection with the hull, and its remaining dimensions can then be deduced.
Two
intermediate floors are positioned between D and the half
bulkhead, and one between C and D.
With the floors all
fitted they only need to be filleted onto the hull, which is a
repetition of what has already been done with the hull panels.
In the 21'9" version of the slipper launch, the sheer clamps are nearly 7 metres long. As it is impossible to find clear Oregon that length in this part of the world, the timbers have to be scarfed together from two 4 metre pieces. The options for a scarfing jig include: a mitre box, a router bearing jig, an electric plane bearing jig, a hand plane bearing jig, etc. Unfortunately, a table saw is not included, because the mitre fence will not go to the necessary 7 degrees, and the arbor will not tilt to 83 degrees.
If the length of the scarf is to be 8 to 12 times the thickness of the timber, (which is 18 mm.), then a glue surface of 144 mm. to 216 mm. is produced. That requires an angle of about 5 to 7 degrees. Let's settle for 6.
The simplest solution seems to be a hand plane jig, so, the first step is to make one. Cutting the angles on the runners of the jig presents the same problem that cutting them on the sheer did, except that the runners are shorter. They need a taper jig on the saw to hold them at a 6 degree angle. They need to be about 36 mm. wide, before tapering, to allow them to attach to a support block, and to allow a bit of overlap over the top of the sheer timbers. Therefore they need to be 343 mm in length. The feather edges can be chopped off after the tapering.
Long
board scarfing jig.
Scarfing the boards by hand proved to be a bit tedious, but most of the work can be done by power planer. (All of it could have, except that the power planer would have begun to plane one of the tapered supports.) The hand plane can then be used to finish it. Eight scarfs were cut in an hour and the first two full length sheer clamps were glued up immediately.
Meantime, the fitting of the sheer clamps is looking a bit tricky: nail-biting, actually. In order to bend these timbers in two planes at once they have to be subjected to a huge amount of force. Especially in the 21'2" version, whose bow is much more broadly convex that the smaller one. In order to coax the boards to the right shape before gluing them, I attached them to the outside of the hull first to train them for a while.
After that the apertures in the top of the bulkheads had to be opened out to receive the sheer clamps.
After a considerable struggle, the starboard clamp was fitted, while the port one was temporarily attached to equalise the forces. Gluing the starboard clamp went well, but the port one snapped near the A bulkhead. A replacement strake was fitted port side, while the broken one was repaired, and the replacement too snapped at bulkhead A. A third strake was fitted, but this time with boiling water at the forward end to soften it. While that worked and the strake did not snap, it did develop a bend around bulkhead A, and remained relatively straight, forward of that, so the curvature of the top of the hull on the port side is slightly less than that on the starboard. We will see what happens when the second laminates are fitted, but I doubt that there will be much correction occurring.
The
starboard strake is glued in
while the port is attached
temporarily to balance the stresses.
After the gluing of the first laminates was completed, the second laminates, now repaired with further scarf joints, were applied to the outside of the hull to train them. This does not fit them entirely to their final shape, as the inside radius of the first laminate is tighter than the outside radius of the hull, but it does make a big difference to the resistance to final fitting, especially at the bow around bulkhead A, and the stern around bulkhead F. Once the epoxy is applied to the hull and the laminate, it allows for easier gliding of the laminate forward or backwards in the apertures, which makes the laminate bend towards the hull under clamping pressure, rather than making the hull bend towards the laminate.
After training on the outside of the hull for a few days, the second laminates were relatively easy to get into position. The first one was glued in on the starboard while the port was still attached to the hull, to balance stresses, as for the first laminate. The next day the port side second laminate was glued in.
Second
starboard sheerstrake is glued in first, followed by the port.
Sheerstrakes
in and all clamps removed.
With the floor timbers all glued in and the sheer strakes attached, all that remains before the boat is turned over is the fitting of the carlings. These will add considerably to the strength of the long cockpit area, which will help to resist deformation when the boat is resting on its side. Apart from that, any additional woodwork at this stage will only add weight to the boat before its turning, so no major structures are planned.
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'06
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