January '07

After the extension bit for the hole saw arrived, and an appropriately sized arbor was attached to it, the set up looked like this:

This is still showing the 15/16" hole saw, which could not be used because of the greater diameter of the new arbor, so a larger saw was fitted. This required reboring the shaft hole, which, luckily, had not advanced very far into the hull. As it now did advance, the length of the guide block was shortened each time the saw was backed out for clearing. In the end, only the guide hole in the hull and the bulkhead D complex was left holding the pilot bit, and once through the hull, the saw was withdrawn to recommence work from inside the boat.

From underneath, inside the driver's compartment, the shaft hole appears and the pilot bit enters
bulkhead D's stern side floor (seen at bottom of picture).

The job of clearing the waste gets harder as the cut progresses, especially after the hole saw blade begins to define the front end of its ellipse, but finally, the last plug of the bulkhead D complex is popped out and a clear view of the intermediate floor appears from the outside of the hull.

The final plug from the bulkhead, and the view from within after its extraction.

The next step is to thread a piece of appropriately sized dowel, which has a nail in the centre of its advancing end, down the hole and up as far as the C to D intermediate floor. The nail should touch the point which has been marked as the landing spot for the laser beam.

That was the theory. In practice, using dowel the same diameter as the hole left no room for discrepancy, and there was a discrepancy. The dummy shaft, after some sanding, fitted tightly into the holes, but made a less acute angle with the hull than it should have.

As well as that, the point where the dummy shaft met the intermediate floor was lower than the laser spot (higher if the boat were upright), so it seems that the hole through the bulkhead D complex has been a little off course. Much of this might be less noticeable when the true size of shaft tube is used, as it is a few mm. less than the hole, but it is probably better to be accurate even at this stage, so the bulkhead hole needs to be enlarged.

Very little enlargement is necessary to correct the alignment. A bit more epoxy removed from the bilge area with a rasp did the trick, and the shaft now sat perfectly in line with the template.

Furthermore, the nail on the advancing end of the shaft was within a millimetre of the laser spot on the floor.

There was not enough room between the intermediate floor and bulkhead D to get a power drill into position, so a hand drill was used to make a pilot hole, and then the floor was bored out from the front side, using the pilot hole to guide the bit for the hole saw. After a little more rasping the shaft now slid up to contact the back side of the bulkhead C complex, and had completed its passage through the driver's compartment.

The hand drill aligned between dummy shaft and marked point on the floor (left), and the shaft abutting the stern side
of bulkhead C complex (right).

A similar procedure is used to bore the bulkhead C complex. The laser marks the spot on the floor, and shaft confirms it, the hand drill pre-drills a pilot hole, and the power drill completes the job. Once through into the engine compartment, the shaft has only one more obstruction to navigate. That is the intermediate floor between bulkheads C and B. But that is not in position yet, and will not be until the boat is upright again. It may not even be necessary at all, as the arrangement of engine beds designed for a diesel engine will not be used for the electric motor. The motor has merely to sit on a baffle, which ideally could find itself located between the foot wells, provided there is going to be enough depth in the bilge to accommodate the shaft sprocket here.

All I now have to do is fit a dummy sprocket to the dummy shaft, to find an appropriate location for the motor, and measure the length of shaft required to achieve it. The shaft tube proper, with shaft, bearings and seal can then all be ordered, and work can commence on the keel to house them.

However, before drilling the hole in the bulkhead C complex, I have to decide whether the shaft tube will pass through it, or whether the tube will stop at about the level of the C to D intermediate floor, and only the shaft itself pass forward from there through the bulkhead. The critical factor is the support to the shaft from the bearings.

To reiterate the situation with bearings: at present the design calls for bearings at the stern end of the keel, the point of emergence of the shaft log (tube in this case) from the hull, the front end of the log (tube) where the stuffing box (PSS seal) is to be located, and the thrust bearing at the engine (motor) coupling. Although it is not mentioned, I presume there must also be one at the back of the keel cut out, where the shaft re-enters the stern quarter of the keel (second red dot from the propeller).

These five points of support should be all about equally positioned, or at least no further apart than the diameter of the shaft allows. Once again I am indebted to Solarboat's Charles Fitzhardinge for putting me onto Ian Nicholson's Boat Data Book which allows a determination of bearing spacing in relation to shaft diameter and engine RPM. In this case the maximum spacing allowable is about 1 metre. Since the entire length of the engine compartment is less than 1 metre it is clear that the shaft tube will not need to enter this compartment. It can comfortably stop just forward of the intermediate floor in the driver's compartment, couple with the PSS seal, and allow the bare shaft itself to pass through the C bulkhead. In other words, a hole of just over 20 mm. diameter is all than is required in this bulkhead.

Incidentally, the compressed length of the PSS seal for this size of shaft is about 6.5". There is a 15" space between bulkhead and floor in which to fit the seal, which leaves plenty of room for easy access to the mechanism from the driver's compartment. It also looks as if it will all fit in neatly beneath the level of the cabin sole, ie. the top of the floors, so will not require a "transmission tunnel" type of hump between passenger and driver.

To allow a bit of leeway I bored a 25 mm. hole through the bulkhead C complex. Then a smaller diameter dummy shaft than I had been using was employed, with a couple of simple sticks running through it, marked at the 50 mm. radius point, to check that there was enough room for the 100 mm. diameter sprocket.

The dark mark on the stick is the 50 mm. diameter point. There is plenty of room here for the sprocket, and easy access
to replace the drive belt.

Well within the 300 mm. mark, measuring from the front of the bulkhead, there was adequate bilge depth to fit the sprocket. That means that the motor will be able to be mounted at the end of the foot wells; ideal!

Incidentally, the laser beam, which was now able to fall on the back of bulkhead B was measured at 140 mm. below the fillet. Back in September, I estimated that it would be 155 mm. from the baseline. That is pretty close, allowing for the thickness of the fillet, and the distance of the baseline from the apex of the bulkhead. So I am happy that all appears to be on course.

Now that the dummy shaft has been inserted, I can measure the length of the shaft tube needed, have it made up and cut to size with the bearings pre-fitted. The tube however, is going to be in two parts, because of the cut out in the keel. Only the actual propeller shaft runs the full length. In order to align the two parts of the tube perfectly I propose to get the shaft made up as well, and have it sitting inside the tubes when they are glued into the keel.

Before I can decide on the lengths required, I have to give some attention to the sternmost bearing. I seems possible that it could be located in the tube within the keel, but many vessels with the traditional bronze tubes have it located within a bearing housing attached to the end of the stern post of the keel. One is illustrated in the Paul Gartside website, from which this picture is taken:

Fibreglass tubes, on the other hand, have only a small amount of extension from the stern post, without a bearing housing, as the bearing is located within the tube itself.

While the plans call for a GRP tube, they also show an external bearing housing. Before I send in any orders I will have to consult on how best to carry this sternmost bearing.

So, once again I have to thank Solarboat for some good advice. It seems that they favour the short tube extension to the bearing housing. That means that the propeller will sit closer to the keel than it would have with the housing, so it will be important to shape the keel surrounding the tube to allow for the least obstruction to water flow, but that was planned anyway. I will also have to be certain that moving the prop closer to the keel does not mean I have to use a smaller prop, because as it gets closer to the keel so does it to the bottom of the hull.

But it occurs to me that the keel could be altered a little so as to get the benefits of both systems: if the central two lifts, the ones actually housing the shaft tube, were to be extended back a short distance from the other two, the propeller would be in the same position it was supposed to be, and the bearing could still be tube mounted. The bearing housing would effectively be part of the keel. That would also move the propeller away from the bulk of the keel, so water flow would not be obstructed, and the fiddly task of fitting the housing to the stern post would be eliminated. The final shape of the keel would be changed only slightly.

In the rear tube the aftmost bearing, which takes a lot of strain is 100 mm. long, and bonded in situ (by the manufacturer) before the tube is fixed into the keel. Although there is no absolute need for another bearing in front of it, as there is a distance of only 507 mm. between the front and back of the tube, a small 25 mm. bearing is fitted here just to limit the amount of rubbish which can enter the tube.

From the beginning of this discussion I should define my terms: keel is the entire apparatus attached to the bottom of the boat, which houses the stern tube. Skeg is the extension abaft of the keel which supports the rudder post. These terms tend to be confused and interchanged at will, but I shall stick to these definitions.

I was lucky enough to locate some Jarrah boards over 4.3 metres, which is what is required to build up the longest of the lifts for the keel. They were 25 mm. thick and 150 mm. wide, and I had them dimensioned to 20 mm. x 100 mm. Three of them are bonded together to make up the lift, but first, one of them has to be shaped to the outline of the relevant part of the keel template.

One thing to watch out for in Eucalyptus is "gum veins". They potentially weaken the boards if they are poorly positioned, but this can be avoided if they are fully embedded in epoxy. So the choice of board and their positioning is important.

The template is detached from the boat and applied to the board, and its outline is scribed onto the board. The waste is cut out with a jigsaw, and fine adjustments are made with a spokeshave, until a fair fit is achieved. The template is now re-attached to the boat, and a support is constructed for the rear end of the long lift, to hold it up at the correct angle with the hull. The front end of the lift is eventually to be locked down by the stem to keel joint, which is a kind of scarf joint.

The pink Jarrah is cut roughly to shape and fitted over the template. At this stage it will not fit properly, because it is longer than the template and the stem has yet
to be removed to allow for the stem to keel joint.

But after removal of the stem it touches the keel flat fairly closely, and even better after some trimming.

At this stage it becomes apparent that the labour saved by finding long boards, and avoiding scarfs, is not without its cost: the bed of the thicknesser in which they were dimensioned to width was evidently not long enough to ensure a flat edge. There is a considerable bow in all of the long boards which will complicate matters when it comes to gluing them together.

The shaping process is repeated with the other two boards which will make up the lift, except that their final shape can be rendered with a router and copying bit. The variable degree of bowing on each of the boards means that they have to be forced into alignment by yet another support block attached to the centre of the keel template.

The central support shows the amount of bow in the board before clamping, and none after.

When clamping pressure is applied to the board against the support it makes the template rise rather than make the board straighten out, so it was necessary to improvise a stable anchor to prevent it. A chain passes from the support, through the hole in the hull for the propeller, and then through a batten where it can become fixed.. Once flat, the board sits nicely against the keel flat as it should.

After the remaining two boards which make up this lift are shaped it is necessary to force them all into alignment with each other on the boat in the position in which they will eventually be glued. This is to check for any combined warps or twists. So the supports on the template have to be enlarged to carry the three boards.

Here you can see the first two boards located on the supports and level with each other, but a warp can be seen about the level of the fifth clamp.
The application of the third board should even that out, but it will have to be checked before gluing.

When all three boards are mounted they seem almost but not quite straight, so I decided to glue them together off the hull, on a work bench, where I can be sure that they will be straight, with the aid of the laser.

There still appears to be a bend in the keel to the left from about midships, even after the third board is added.

With the three glued together a stem to keel joint is cut into both partners and the composite lift is again mounted onto the hull, supported now only at the stern end. Once the lift is in an acceptable position, it can be tapered at its front end to meet the stem. However, before it can be glued to the hull, there has to be some consideration of the keel bolts.

The plan states that bronze M6 bolts should be used at 300 mm. centres. At the very bow end of the keel that will not be possible, because the stem girder sits on the other side of the hull here, between bulkheads A and B. From bulkhead B backwards to bulkhead C, (ie. under the engine compartment) the keel is not very deep, so only short bolts are required. Under the driver's compartment, between C and D, the keel has two lifts and requires longer bolts, but the forward shaft tube begins to get in the way. Under the passenger compartment is the location of the cut out in the keel, where bolts are not practical, but then behind bulkhead E (the rudder compartment) the keel reaches its deepest level, and again needs support.

Furthermore, because there is only about 12 mm. of meat on either side of the propeller shaft tube, it is not really practical to be shoving 6 mm. bolts through on either side of the tube where it is embedded in the keel.

Clearly, some compromise has to be made here, and I have decided that embedding the shaft tube in epoxy in an oversized trench should provide adequate strength without bolts, especially as the cut out in the keel will act to reduce the sideways force it has to withstand. As for the rest of the bolts, I don't fancy the idea of drilling for bolts from within the boat down into the keel in case I am not drilling completely perpendicularly. Instead, I would rather locate the position of the bolts on the outside of the hull, drill through the hull there, and then line up predrilled holes in the keel lifts with the hull holes.

So the next task is to locate the holes in lift 4, the long one, drill there for the bolts, and mark the side of this lift so that the relevant holes can be similarly drilled into the next lot of lifts. These holes will need to be oversize, to allow for slight misalignment, and the bolts then set in an epoxy jacket. The procedure is well described in the Gougeon Brothers' Book on Boat Construction, in the chapter on Hardware Bonding. The Selway-Fisher manual also allows for this method, but also permits threaded rod to be used instead of bolts. These are fixed at both ends with washers and nuts. The keel bottom has to be counterbored for the nuts and washers, and then a metal or hardwood strip glued over to cover them.