Before the rear stern tube can be glued in, I have to be certain that the propeller shaft is going to be aligned with the rudder, so the rudder has to be placed into position. That means that the next step in construction is to attach the keel runner and run the rudder shaft through it.

The keel runner is specified in the plans as being 25 mm. x 25 mm., and passing from the rear of the keel to the back of the boat, where it is finished off with a simple cove. However, I see no reason why the runner should not be the same width as the keel is thick, especially as it has to be widened to negotiate the opening for the rudder tube anyway. So mine will be 60 mm. wide. It has a simple part of the hull to attach to, almost dead straight along its course, so a 25 mm. thick board can be bent to the required shape instead of having to be cut to shape. The runner's front end slots into the triangular gap under the back of lift 1 with a complex joint which is best cut on the table saw after experimenting with a piece of scrap to establish the blade angle and height.

A trial cut for the keel to runner joint.

It is accompanied by four bilge runners, two each side, which begin somewhere between bulkheads B and C, and terminate at the transom. They, however, will have to be added after the hull is faired.


Because they may take a bit of abuse from trailering I propose to go back to the Spotted Gum for these members as it might be a little tougher than the Jarrah.

 
The keel to runner joint (left) and the runner sitting over the stern end of the hull (right).

The transom end of the runner finishes just short of the hull, and the cove is purely for appearance, even although it is hardly ever seen!

The rough cut runner at the cove end.

Before the runner can be glued down, the hole for the rudder stock has to be continued through it. I chose to do that by marking a longitudinal centre line on the hull side of the runner, fixing it temporarily in position and finding the line in the existing hole from underneath the boat. A pilot hole was drilled through the line at its central point, and a hole saw was used to complete the new cut with the runner removed to the drill press.

 
The path of the runner is sanded, and the new hole is bored into it for the rudder stock.

The alignment of the rudder with the prop shaft can now be checked by dropping the rudder into its tube and bringing the shaft back to touch it. If they meet in the centre of the tube or the rudder itself their position is good.

   

Checking rudder and shaft alignment.

However, all the excitement of getting the rudder alignment right led to me making a possible mistake here. I refer to it more fully in the Problems page under "Rudder Shaft Clearance".

Once this is sorted out screws can be drilled into the runner from within the hull, and the epoxy can be laid, both under the runner and around the rudder tube. Before continuing with the outside of the hull, I should then take the opportunity to fix the rudder tube in its permanent position by attaching its top end hardwood block to the front of bulkhead F, and securing the tube to the block there as well.








The block must be at the right vertical level to be able eventually to support the upper rudder stock bearing at the top end of the tube. While the location of that bearing relative to the rudder itself is not specified, the plan shows it about 70 mm. below the top end of the rudder stock.

It has to be sufficient to allow the tiller and its attachments to clear the squared end of the stock where an emergency tiller can be fitted.

So, before the block can be put onto the bulkhead the vertical level of the rudder must be decided, and this means that the skeg and propeller need some consideration.













Now, I know this is beginning to sound like one of those cook books which constantly refer to other sections for a recipe for an ingredient of the current dish, but trust me...


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32. The Skeg

 
The skeg does not need the same amount of clearance from the propeller as the hull does, but it does need to be perpendicular to the rudder stock, and obviously needs to clear the prop by a small distance. The skeg, which is referred to in the plans as the prop guard, is shown right screwed into the bottom of the keel, into which a flat has been planed at the appropriate angle to meet the rudder at right angles. It is interesting to see that there is no attempt to position the rudder so that it is centred horizontally to the propeller. Presumably the critical factor here is the proximity of the rudder blade to the lower rudder stock bearing, and the minimisation of leverage forces at the hull level (although one might imagine that a well fitted skeg would eliminate leverage). Because my propeller is 20 mm. larger than the 300 mm. specified, it may be necessary to drop the rudder a little, just so that the skeg is clear. In order to establish that I need a dummy propeller to be fitted onto the shaft. A 320 mm. long stick will do the job.

 
The dummy propeller is on the shaft and a set square with its T piece parallel to the rudder shaft crosses it. There will be 35 mm. clearance
from the runner (>10% of the diameter of the propeller) which is perfect, and there is enough area on the bottom of the keel to attach the skeg,
but what about prop clearance from the skeg?


As can be seen from this other side, the prop will easily clear the skeg
 because it is only 10 mm. thick, whereas the blade on the set
 square is 20 mm.

In the position shown above, which is enough to provide both clearance and an adequate landing area for the skeg on the keel, the rudder needs to be chocked above the keel runner by a minimum distance of 5 mm. The larger block at the back end is to ensure that the rudder shaft is parallel to bulkhead F.

To mark out the skeg's flat on the keel a template is made to represent the rudder shaft, the skeg itself and a button washer which sits between skeg and shaft. It sits on the blade of the set square and slides along to the side of the keel.

The template for the skeg. Shaft is vertical, blade in front of that, and
the skeg is the heavy black line.

The top and bottom of the skeg are scribed onto the keel, and a waste area is mapped out.




Knowing the eventual position of the skeg also allows me to send a coach screw into the top (soon to be bottom) lift of the keel, and into its partner. As this will need to be counterbored it is good to know how deeply it needs to sit to avoid the skeg. This one needed 30 mm. to house the head of the screw and the washer below the lower line (left) which marks the hull side of the skeg.

Initially, a longer screw is used just to hold the lifts together while they are glued, but after it is removed and replaced a plug will be fitted over the top of the new screw.The height of the rudder above the keel runner is determined once the position of the skeg is finalised, and when that is established, the vertical level of the block supporting the rudder tube can be marked on bulkhead F, and the block and tube can be cut and fixed. Then the rudder bearings can be glued into the tube, the rudder can be introduced into its definitive position, and the skeg can be manufactured to suit.

After the counterbored screws are inserted the waste area is planed off and guides are attached to the sides of the keel to act as supports for the router, which will cut a 10 mm. deep groove into the bottom of the keel for the skeg.

The planed flat for the router, and supports which have to be fixed with double sided tape so that the router fence can run against them.


The trench routed for the skeg.

The plan calls for it to be 50 mm. x 10 mm. galvanized mild steel attached to the keel with coach screws, presumably also galvanised. That will mean that there are four metals in the bath at the end of the keel: the bronze propeller, the 316 stainless steel propeller shaft, the mild steel rudder, and the galvanized skeg. It seems to me that this would be an open invitation for the zinc coating on the skeg to act as a sacrificial zinc for the entire boat, and be corroded away without delay. I think I will seek some further advice about this before committing to the galvanized option.

The consensus of opinion on that point is that a trailered boat will not really come to grief with corrosion anyway, so it does not really matter which metal is used. (But the use of a sacrificial zinc is encouraged all the same.) My view is that the galvanization will be breached as soon as screw holes are drilled into the plate, so why bother with it? You might as well use mild steel, or stainless.

Which ever metal I choose, it is held onto the keel by three coach screws, of the same metal of course, and it is not able to be glued in. (The only way to remove the rudder is to remove the skeg.) Instead, I am using Sikaflex 291, but I am told simple butyl mastic would be as good. Because it will be the lowest part of the boat it is the most likely member to get damaged during the coming turn-over, so I will leave off attaching it until after then; but I can drill for the screws once I have their accurate position, which will have to be taken from the skeg itself.



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33. The Rudder Tube

Its position having been determined, it is time to cut a block for the rudder tube. A piece of offcut keel is almost perfect for the job, as it will support the sides of the tube as well as its back surface.

It will eventually be fixed in with M9 coach screws embedded in epoxy, but for the time being it is simply screwed into position with one screw while the verticality of the tube is checked. Once satisfied on that point the tube can be cut to length to coincide with the top of the block. First it is trimmed level with the bottom of the hull, after being suspended in position with bamboo skewers to centre it in its hole.

 

Before cutting the tube to length.

 

Checking for verticality.

Dropping the rudder through the enlarged hole in the keel runner, and through the tube, shows that it hangs properly, and that its alignment with the keel has not altered.

 
Rudder located and tube temporarily fixed.

All of this gear can now be removed, and the rudder stock hole can be used to tighten the keel runner down onto the hull while screw holes are bored into it from within. The runner can then be glued down.

The fastened runner.

After the runner glue is dried on the hull the rudder is dropped into the tube again, this time with some mock bearings to keep it centred.

The picture left shows the rudder with its real bearings on the stock, but in order not to damage them while the rudder is being pulled in and out so often, I make up some temporary ones out of wood, just to centre to stock in the tube.

 
Temporary bearing in ply wood.

The propeller shaft is checked once again for alignment with the rudder, and a fine adjustment is made to the lateral displacement of the stern tube in its trench. Epoxy is pumped into the trench and left to set, and the first of many clean-ups of shaft and bearings begins, to keep them free of the epoxy.

 

Checking alignment again. A flood gate of masking tape keeps the epoxy from spilling out of the shaft tube trench.

 

This point marks the end of the keel construction, but the rear bearing housing still has to be shaped, and scallops have to be taken out of the area in front of the propeller to allow water free access. That sort of work can be done sporadically while waiting for glue to dry, or some other delay, in the continuing progress of the boat. The next step is to start sanding for the fillets and eventual fairing of the hull.

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34. Stem and Keel Fillets

It would have been nice to form the fillets immediately when the keel was being glued down, but because that was done in separate stages the fillets had to be laid in afterwards. It wasted a little epoxy, but not enough to justify compromising the job.

Filleting is straight forward, except for the part of the stem where the hull side meets the hull bottom. Here, the side thickness of 9 mm. becomes 12 mm. for the bottom. While there was a 25 mm. wide flat planed onto the bow for the stem, that widened out when the bottom panels were reached because of the extra thickness here. What is more, some of this extra thickness is above the waterline. So, while a fine fillet would do to smooth the stem into the topsides hull, it needs to be thicker at the bottom. A variable radius filleting stick will be the best solution, so that it can be rotated as the fillet is formed and create a smooth but varying radius fillet.

Once onto the keel the fillet is a simple affair. Devlin recommends that the keel should all be epoxied and glassed. I feel that there is inevitably going to be some breaching of the keel from grounding at some time, in which case, epoxy and glass will only serve to prevent any water which has found its way into the timber from getting out again. So I am not going to glass the entire keel; but I am attracted to the idea of glassing the fillet, and spreading the load more evenly onto the hull. Because the keel is only 30 mm. deep in parts, a narrow band of biaxial glass can be used, topped off with a broader tape of woven roving and peel ply.

Before that could be started I had to finish off the outer laminate of the stem. Unfortunately, with all the mucking around with the screw holes the plugs ended up being too loose to close the gaps tightly, so I abandoned that idea in preference for a final unbroken laminate 2 mm. thick. This was glued down over the filled stem and held in place with numerous brads while the epoxy set off.

 
The outer stem laminate being glued down.

It required a little planing to smooth the new stem onto the keel, but fortunately the keel was a bit deeper than the old stem anyway, and was going to have to be reduced, so there was not a big discrepancy.

 
The new stem after sanding.

The keel bottom is still in an unfinished state, covered with epoxy and not precisely squared to the sides. When the retaining screws at the stern were removed they were replaced with the counterbored ones, which were plugged. This area has already been planed for the skeg fitting, but the rest of the keel still needs to be levelled and smoothed with the electric planer. The edges will then be rounded over and the whole structure sanded ready for painting. I propose to paint it the same way as I paint the hull bottom, perhaps, but not necessarily with ultra-expensive anti-fouling, because the boat will spend most of its life sitting on a trailer. The choice of paint is discussed further in the April '07 page. But most of the time until then will be taken up fairing the hull.

The back end of the keel. These screws were replaced with counterbored ones set under plugs.

The fillets were done one side at a time, starting with the port. Alongside the keel proper, up to the stem, and forward of the runner, the fillets were reinforced with two layers of tape, and peel ply was used in an attempt to keep down the amount of sanding.

 
Port side fillet area prepared by sanding (left), and after the first layer of tape was applied (right). The other two
layers are standing by.

At the stem there was a fairly sudden gradation from a thin fillet to the thicker one. Some more work will be needed here, above the waterline especially to make it look more feathered.



I have been using fibreglass tape manufactured at 50 mm. wide, so it has a selvedge on both sides. Previously I have cut my own to width. The selvedge causes a little difficulty with the peel ply, in so far as it is easy to starve the edge of epoxy when painting it over the ply. This was quite noticeable near the bow where the steepness of the hull allowed the epoxy to run away a bit. So, instead of having a sanding free fillet, I now have some areas which do need to be sanded or filled. Not too much though, and the peel ply is definitely worth it.

The selvedge here making an escarpment with the hull in places.

Overall, the result on the port side was good, so the same process was repeated on the starboard.

 

 The keel fillets, finished on the port (left) and under construction on the starboard (right). Note the trench for the skeg on the
bottom of the keel.

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One of the disadvantages of a glossy finish is that it shows up every surface defect. What looked to be  a reasonably smooth hull when it was sanded before glassing now looks like a corrugated sand dune. Clearly some work needs to be done fairing it before the final coats of epoxy and the paint go on. Luckily, most of the affected area is under the waterline, where a flat finish will be used, so it does not need to be optically perfect, but the sides of the hull also need some attention, especially around the scarf joints. If I can get a finish as good as that on Blue Swan, I will be delighted (and amazed).

This will not be a job for a sander, so I need to make up a some long file boards. These pictures are from Cliff Ruffner's
website showing his home-made fileboard in use.

Cliff Ruffner at work on his Sam Devlin"Dipper".

He is using a two part polyester filler instead of epoxy, which has the advantage of being easy to sand. He is also applying it to an uncoated hull. I have found that epoxy mixed with West 410 microlight is fairly easy to sand as well, so I will probably stick with it. But my hull already has glass and two layers of epoxy on it. So it is not going to be a simple matter of laying on the filler. Firstly, I will run the file board over the suspect areas to identify any low points. Then, after marking out the deficient area with a Texta-colour I will have to sand the dip so that it will accept the fill. For the file board I can use some softwood or thin ply with handles glued on, and some lengths of sandpaper of various grits.

As most of the problem areas are towards the bow of the boat, I started general sanding from the stern, while the filler which I had applied to the defects in the keel fillets was drying.

It was not all done by hand, but as you sand you find that there are small pits in the surface. You can see two of them (left) in the reflection of the ceiling light on the hull. It is not necessary to sand all the top layer down to the bottom of the pits, but the pits do need to be roughed up. A hand sanding block can get to most of them, and those which are too deep or narrow can be reached with a stiff wire brush.

I did not try to look for minor dips in this part of the hull. Firstly, it is fairly smooth anyway, and it going to get a third coat of epoxy resin before it is painted, and secondly, there is no point aiming for anything more than a hydrodynamically adequate surface here. I will reserve the attempt at optical perfection for the visible hull above the water line.

But at the bow there is a persisting problem from the high riding board edges of the second skin and quite a noticeable ripple.










Preliminary sanding prior to filling and fairing.

I made up a long file board and took to the bow area to show the high and low-lights, and it was immediately obvious where the problem lay. For this preliminary work I used 40 grit Aluminium Oxide paper. Later I will change to 80 grit, and after that it should be ready for the random orbital sander to take over.

The long file board (left) shows up edge highlights towards the bow.

I don't want to have to give the hull another full layer of thickened epoxy to make is perfectly smooth here. I figure that I can sand the highlight areas down almost to the glass, and then put a little strip of filler in the centre of the hollows and spread it outwards.

Microlight thickened epoxy fill for the hollows.

You get the impression here that the hollows are huge, but it is not as bad as it looks.

After the filler has dried, a quick swipe with the file board shows where more is needed. The aftmost strip is almost all abraded, the two in front of that are barely touched and the two in front of those are rubbed in their middles. I continue to sand back now, either until there are no low points any more, or, as in this case, until some of the high spots begin to reveal the hull. If you are using Microlight thickened epoxy you have to be careful not to sand too far down, because the colour of the recently sanded hull and of the freshly sanded filler is very close. It is easy to sand right through to the glass without realising it. The high spots have to be inspected closely every minute or so.

Once the stage is reached of adding more filler, it is useful not to have to sand all the previously laid strips for a mechanical tooth. As long as the second application is being made within 24 hours of the previous there should be no need for additional sanding, as the new epoxy will bind with the old. (Some people say that is the case even after 72 hours.)

Some of the glass is beginning to show through. Time to stop sanding.

A re-application of filler to the old sites can be accompanied by a new application to some others, gradually working towards the bow.

The second application of filler tops up old areas and begins new ones.

After sanding the second application there is little left to be done except some minor patching of the surface of the fill.

Minor surface defects remain.

On the starboard bow, where I had taken extra care to screw down the second skin, the problem is not as extensive, except for the large hollow in the area of the old fill which extends across three board widths.

Before and after filling the starboard bow.

It looks like a mess after the filling is done, especially with the various colours of fill, sanded epoxy and bare wood, but it does end up being a very smooth profile, which is what is wanted.

The finished port bow, now completely filled and faired, is being readied for another coat or two of epoxy before the bottom painting.

It occurs to me also that this file board method of fairing the hull is all very well for completely convex hull shapes, but it would not do for a concavity, such as is often found in the traditional boats. Look at this old slipper launch under restoration:

Not that it looks as though it needs it, but there is no place for a file board below the water line in this boat.

Once the bottom of the hull is prepared it is time to tackle the sides. Here, there is much less of a problem, except, as previously pointed out, where the scarf joints of the hull panels are located. They appear to be a little depressed, so I suspect my sanding of the joints, before the panels were stitched together, was too vigorous. It will not take much to correct the depressions, but I am keen to avoid getting filler onto the top 150 mm. or so of the hull sides, where there will be a bright finish, as seen below:

The name bearing strip of hull side is finished bright in slipper launches.

I have already noted the quality of these scarf joints, and the fact that they are not really suitable for a bright finish, but in a narrow strip like this I think it will be possible to disguise any deficiency by the use of a well placed curlicue or other decorative item.

So by keeping this strip as free of the opaque coloured filler as possible, I will make the finishing job a good deal easier. The sides are sanded back to a smooth surface, much as the bottom was, and filler is applied where needed.

 

Sanding back from the bow on the port side, and filling a scarf joint. The bottom 150 mm. of hull surface is kept free of filler.

When that is complete the entire boat needs another coat (or possibly two) of unthickened epoxy resin in preparation for the primer to follow. This time some extra care is taken to ensure a smooth flow of resin and no runs of drips.

Meanwhile work slowly progresses on shaping the back of the keel, which needs to be scooped for the propeller. It means a return to the rasp, and tedious repetitive strokes which seem to achieve little, but eventually yield up a nice shape. I just do a little at a time while waiting for filler to dry.

  

Scooping for water access to the propeller.

Eventually the entire hull is sanded and filled, and the keel is shaped.

Ready for coating with epoxy.

Prior to recoating the entire hull, the keel is brought up to the same state as the rest of the hull (except for the glass sheathing) by a couple of coats of epoxy. The stem and the keel runner are given the same treatment.

With that complete the rest of the hull can be coated, and then the next project will be painting the bottom, which will begin after Easter.

Forward to April '07

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