February ' 07

While I am figuring out the best placement for keel bolts, work progresses on laminating the other lifts for the keel.

Once lift 4 is located and locked in by the stem to keel joint at the front and a support at the back, the template can be removed again and lift 3 can be made up and fitted into the acute angle between the hull and lift 4.

Lift 3 has to fit into this space, and around the cut-out in the hull (arrowed).

The dry run for laminating lift no.3. You get an amazing colour variation with Jarrah.

This is a short lift, requiring only 1.5 metres of timber to reach the keel cut-out and a further half metre or so behind it. Its front part can be made separately from its rear, and then grooves have to be cut into them to house the stern tubes. Theoretically, the depth of the grooves should be 17.5 mm. in order to make a 35 mm. trench, but the critical factor here is the meeting of the groove with the through-hull hole. It is no good having the groove obscuring any of the hole, or exposing any more hull around the hole than is necessary, so, initially, shallow trenches are routed into the lift, and these are gradually deepened until they are the right depth

Here are lifts 3 and 4 in place with the dummy shaft fitted again. It is a tight fit at the moment, but bearing in mind that the dummy shaft is a little larger than the real shaft I don't expect any major problems when that arrives.

Nevertheless, I won't be using any glue until then, so for now I will bide my time laminating the remaining lifts, and drilling holes for the keel bolts.

In the area immediately forward of the shaft tube hole in the hull, where the plan calls for a shaft log inside the boat, there is very little room between the shaft tube and the bilge of the boat, so keel bolt placement here is problematic. And behind the hole there is no place for a keel bolt to go until the aft part of the keel is reached, behind the keel cut-out. However, lift 3 can be secured to lift 4 with at least one fastening sunk forward of the trench for the shaft in lift 3, which will effectively replace the function of the aft clamp in the picture above right.

Other keel bolts can be located at approximately 300 mm. centres, but avoiding bulkheads, floors, etc. To start with I am using temporary screws, and there is little difficulty in the forward part of the boat, because the keel is so shallow here. But as you progress aftwards the depth of the keel becomes greater, and the resistance to screwing in hardwood makes it impossible to use ordinary screws. Allen key headed screws are used instead. Later, when the permanent bolts replace them most of the length of their holes will be reamed out for epoxy bedding, so resistance will not be a factor.

Temporary keel bolts in the driver's compartment, which have to leave clearance for the shaft where it will enter the hull (arrow).

With the aft sectors of lifts 1, 2 and 3 cut and shaped, they were fitted up to the rear end of lift 4, but with a minor gap appearing between 3 and 4.

29. Gluing Sequence

The anchor point for the front end of the keel is the stem to keel joint. So the first step in assembling the structure is to attach the stem. It already has screw holes in it for the lamination process, so it was merely a matter of sanding back the epoxy where the stem would be glued on, and where its fillet would sit. Once it was fixed the rest of the keel could be added, but before it became inaccessible I shaped some filler strips to sit between the tapered front end of the keel and the rear end of the stem.

The sanded area of the bow in preparation for the stem.

The filler strips close the gap between the sides of the stem and keel. I still think a
wider stem would have been better.

The taper at the keel to stem joint.

To assemble the keel in a controlled manner a sequence of gluing needs to be adhered to. But before the trenches and hull holes become inaccessible they are given a coating of unthickened epoxy. Next, the forward section of lift 3 is glued and screwed to lift 4, using the screw which was countersunk forward of the trench in lift 3 to locate the two correctly. Further alignment can be achieved by matching up the holes for the temporary keel bolts which pass through both lifts. Once the keel is laid on the hull the screw is inaccessible, hence this is a first step.The combined complex of these two lifts can now be glued to the hull, and provided the pressure from the temporary keel bolts does not cause a distortion of the proper keel angle, they can be screwed in.

The keel flat under lifts 3 and 4 has been sanded (left), and those two lifts are glued and screwed to the hull (right).

If there is any distortion it is better to leave them out until the epoxy has set. If you do use the temporary bolts it is a good idea to back them out before the epoxy goes off completely, or they might be there forever. What is more, any bolts which are located under the forward shaft tube need to be removed and replaced with permanent ones before the tube is glued in. In my case this means one just behind the driver's compartment intermediate floor. The tube passes through the floor and terminates 100 mm. forward of it (at the level of the yellow cross, left).

To be strictly accurate here I should point out that what I am using is a coach screw, rather than a bolt. There will be no washer and nut at the bottom. This causes some raised eyebrows in the boating fraternity, but it is not a ballast keel I am building, and I am assured that coach screws well set in an epoxy jacket will be strong enough. Even so, I am taking the precaution of going up to M10 instead of M6. And I am using 316 Stainless Steel instead of bronze. It is more readily available in a number of different thicknesses and lengths, and is much cheaper. If you were contemplating using true bolts they could be threaded in from the outside, so this step of removing the temporary screw would only be necessary for the removal of the screw, not the placement of the bolt.

Since I am using the epoxy jacket method to anchor the coach screw in the keel, I need to drill a larger hole, more than 10 mm. in diameter, for most of the length of the screw, leaving a distal shorter segment which is the right diameter for the screw thread. The Gougeon Bros. book recommends that the shorter segment be 2/3 to 3/4 the length of the screw, but they are talking about hardware bonding and prefer screws with thread the full length of the shank. Coach screws have thread only partway up the shank. In the case of a 120 mm. coach screw, the thread is 75 mm., the unthreaded shank is 40 mm. and the head is about 15 mm.

Clearly, the thread acts as a vital component in the bond, and its contact with the epoxy needs to be maximised. The short distal segment, on the other hand, acts only to locate the screw in its correct position. Once that is achieved it contributes little to the strength of the fixation. So I propose to give the screw only about four turns to bed itself, and drill the rest of the shank length oversize. The recommended diameter of the oversize portion is about 6 mm. greater than the diameter of the screw, or 16 mm.

The screw is prepared for bonding by first scrubbing it in acetone to remove any grease, then roughing the bare shank with 40 grit sandpaper. Unthickened resin is applied to the shank and thread, and it is again roughed up with sandpaper which the epoxy is still wet, to work it well into the scratches. It should be used now before the resin sets, or sanded again before use later.

It is not easy to find drills of the right dimension for this job. My longest coach screws are 150 mm. so the nearest I could find for boring the tip was a 170 mm. 3/8" bit. It is a bit thicker than I would have liked, but if I exclude the final pointy bit of the screw from the drill hole it will do the job. The widened portion I am having to do with a 150 mm. 9/16" bit, which is a little narrower than I would have liked. (It equates to about 14.3 mm.), but again, it should suffice. There are plenty of augers available of the right size, but as there are already holes for the temporary screws, they are not an option. Similarly, there are plenty of spade bits, but the same exclusion applies. In a piece of virgin wood though, they would be a good alternative.

The oversize hole is first wet out with resin and then filled with thickened epoxy, and the screw set into it. Now, seeing as how the boat is upside down, the epoxy has to be forced up-hill into the hole. This can be achieved with a decent size syringe, a length of plastic hose and some epoxy which has been thickened enough not to pour straight back out immediately. (That happens when the screw is driven home!). The remaining screws can be placed after the boat has been righted if you like, but bearing in mind some of the forces likely to be placed on the hull/keel joint during the righting process, by the willing, if not always highly skilled, helpers, I thought I would put up with the mess and place all the screws as soon as the keel was glued down. After doing it with the first screw I decided against, not because of the mess, but because I could not be certain that there were not voids and bubbles in the epoxy jacket with the hole upside down. I overfilled the one critical hole in the path of the stern tube and drove it home in a flood of goo, but the others can wait.

The one critical keel "bolt" glued in. You might just make
out a slight ooze of epoxy to the right of the washer.

Once the front part of the keel is fixed permanently in position the filler strips can be attached at the stem to keel joint too.

Cross bracing to ensure alignment between lifts (left), and spring clamps hold the filler strips(right).

Now, while work progresses on the rear section of the keel, the back end of lift 4 can be supported on a purpose built brace which can be either free standing or erected on a shortened keel template. The template has to be shortened because it would get in the way of the keel/hull glue line if it were not. The general location of the brace should be as far aft as possible in the area of the keel cut out.

The keel template has been foreshortened to allow for gluing the keel down at the front, while the support at the
back allows the other keel elements to be set in place in the right order.

The aft section of lift 3 can now be approximated to lift 4 and, while lift 1 and the rear end of lift 2 are screwed and glued to one another, the forward section of lift 2, which is really only a glorified keel runner, can now be slid into position around the forward stern tubing hole. Finally, the lift 1/2 complex is attached to the hull in the correct position, filling the remaining gap.

The forward section of lift 2 being glued down.

Right now there is no glue between the aft ends of lifts 2 and 3. The aft stern tube is slid into place, and the propeller shaft is put through to get the alignment of the tubes correct. Later, thickened epoxy will forced into the housing trenches and the through hull hole, the mating faces of lifts 2 and 3 will be glued and held together.

Dry fitting the shaft tube and shaft.

The back end of lift 2 being glued down to lift 1.

So now, to reiterate this rather confusing sequence, what we have is this: the stem is on, lift 4 is on, but still unglued at the back, lift 3 is on at the front but unglued at the back, lift 2 is on in both forward and aft sections, and it is glued to lift 1 behind. When the time comes to bond in the shaft tubes the remaining unglued joins between lifts 2, 3 and 4 will be done too.

The stem still needs attention. Some of the screw holes in it are no longer centred after it was planed down, so the old holes are filled with thickened epoxy, and new centred ones will be inserted and countersunk, so that there will be a clear space for plugs to fill the outer laminate.

The old screw holes in the stem are filled for reboring.

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30. Shaft Tube Bonding

Although it describes the process of manufacturing a fibreglass tube, rather than the stainless one which I am using, there is a good demonstration of tube bonding to the hull in the Bertram 31 site. The principle remains the same, but extra care must be taken with steel to give it a rough enough surface for the epoxy to get a mechanical tooth. The description of the placement of the tube by means of small wedges is helpful, as the holes are slightly bigger than the tube. This will allow a good amount of epoxy into the area to support the tube, and will dispense with the need for a full size hardwood shaft log. It is not necessary in the Slipper Launch to smooth out the epoxy around the tube on the outside of the hull, because the tube is encased in the keel at that point. So only the inside surface needs attention, where the original shaft log would have gone. Work there can wait until the boat is upright again. However, where the tube emerges from the keel care is needed not to get epoxy into the tube or shaft. Plenty of rags and acetone should be available.

Before the real tubes are placed the dummy shaft is used to make sure that the housings are in approximate alignment, and to test the gluing sequence for practicality. Because the shaft tubing is in two parts it would be easy to get them out of alignment when gluing the keel lifts together. If the two sections of the housing lifts (ie. lifts 2 and 3) are not in a direct straight line with one another the shaft will not sit properly within the tubing. So before the lifts are glued the entire assembly is once again put together dry: tubes, bearings, shaft and lifts. With the shaft placed in the tubes, and with the grooves in lifts 2 and 3 cut slightly oversize there is room to bed the tubes in a straight line and avoid distortion. Only when this has been achieved should the thickened epoxy be run in and the lifts be glued together.

A practice run with the dummy shaft.

The sequence of events then begins by bonding in the front tube. It is fed it into the epoxy primed hole from outside and run forwards to its final position. Then, thickened epoxy is forced into the keel timbers which surround the tube, using a large syringe and a length of fine hose which can be fed down alongside the tube.

In order not to get epoxy into the front end of the tube as it is being fed down its channel, a simple solution presented itself:

As the shaft is only 32 mm. in diameter, make sure to buy the small size.
And don't bother using the ultra-sensitive.

The front tube has been epoxied into its trench with shaft in it to assure alignment.

The forward shaft tube enters the hull and bulkhead D (left) and through the intermediate floor, passing
above the keel bolt already placed. The shaft itself then passes on through bulkhead C into the engine
compartment.

The rear tube will not be bonded until the alignment of the shaft is checked again against the rudder. If it has to move a millimetre or two to achieve a good position it will not make any appreciable difference to the friction on the bearings.