Repairs

The title of this post is a little misleading, since what I’m trying to find is where the soft/rotten wood in the centerplate case ends.

In the above photo you can see where I have cut more of the side of the case away and exposed the diagonal end block. I think I have left just one veneer of the plywood on this block and it was very difficult to remove indicating that the plywood here was in good condition. I removed as much as I did so that the new sides will have a significant overlap and therefore a very good seal when it is installed.

The black arrow points to the top of the keel and the green arrow points to a rounded piece of wood placed next to the case side and on top of the keel.

Contrast that with the same area in Naiad (more or less). Again the black arrow points to the top of the keel and the green arrow to the rounded bit. From the Naiad photo it is obvious that the side of the case goes down to the keel at the least and the rounded bit is there to strengthen the joint and to provide a good area for sealant.

But in Shoal Waters there are two rounded bits.

Here’s what I mean. The black arrow points to the top of the keel, the green arrow points to the first rounded bit, equivalent to the one in Naiad and the red arrow points to the extra one. Now, was this original or put in by Charles Stock or Tony Smith? I don’t know but I need to find out how far down the plywood goes so that I can cut away the plywood but nothing else.

I’ve cut away a section out of the top rounded bit but it isn’t clear if the plywood extends this far or not. I’ll let the wood dry and clean it up with a sharp chisel. Hopefully that will show up the demarcation between the plywood and the Mahogany (?) rounded part.

Once that is done then I can carefully cut away the plywood and leave the rest untouched.

Before I go too much further, I should really measure the position of the pivot bolt hole. I’m doing all the exploratory work on one side only chopping away willy-nilly to find out the extent of the plywood. However, when it comes to the the other side I’ll know where cut and should be able to get the side out in one piece. More or less. That’s the plan anyway. That will allow me to use that side as a pattern for the new sides. However, I’ll still make a pattern as best I can once this side is removed just in case the other side doesn’t come out cleanly.

Time for a cup of tea.

The next part of the centerplate case replacement is a bit technical, apologies for that, but has to be done before I cut away any more of the case itself. The first task is to measure as much of the case as I can and draw it out.

I marked a straight batten and 150mm (6″) intervals and then clamped it to the bridge deck such that the forward end was directly above the forward end of the case using a plumb bob to get that lined up.

Then I hung the bob from each of the marks on the batten in turn and made a mark with a white pen on the top of the case and on the bottom.

The marks on the batten.

The marks on the top of the case.

And the marks at the bottom.

The final part of the measuring was to measure from the batten to the top and bottom marks and note these down. At this point it doesn’t have to be precise, with 5mm is close enough for now. Just as well as it’s really hot in the boat and I’m not really that limber, so it’s a bit awkward.

I then drew out the measured line in QCad, the drawing program I’ve used for years. The white line at the top represents the batten, the blue lines are the distance from the batten to the top of the case and the green line are to the bottom.

Then I added a straight line at the top of the case (in red) as I think this is straight on the boat, I’ll have to check, and fitted a smooth curve to the lines showing the bottom of the case.

Now, my CAD program shows me that this much of the case can be cut out of a piece of plywood that is 1210mm long ad 290mm wide. This is good news since quality marine plywood is sold in sheets that are 2500mm long and 1220 mm wide.

Now for the tricky bit. The original case was made from two 7mm thick pieces of plywood laminated together for a total thickness of 14mm. I can’t buy plywood of that thickness, so I have the the following choices. Three laminates of 5mm for a total of 15mm, two laminates of 8mm for a total of 16mm or a single sheet of 15mm thick. I did consider two 6mm laminates, but this will result in a case that is 2mm thinner than the original and although it would probably be fine, I’m not happy about making it thinner so I discarded that idea in favour of making it thicker, and therefore stronger.

I want to cut the pieces on the CNC router so that I have accurately cut, identical pieces, and since my router table is 1270mm x 1270mm square, I’ll not be able to cut a single side at a time as the entire case will be around 1800mm. The above drawing only goes as far as the start of the cabin whereas the case itself protrudes into the cockpit. But this section is certainly not so tall as the rest, so for the purposes of deciding how much plywood I need I only really need to find the tallest part of the case.

So that eliminates the 15mm thick plywood and I’ll have to cut shorter sections and glue them together. The choice between the three 5mm sheets and the two 8mm sheets comes down to the cost. Two sheets of 8mm ply will cost a total of £265.80 whereas three sheets of 5mm will cost £342.18, a significant difference.

There will be plywood to spare after cutting the case pieces out and these will be used to replace the bulkheads that reinforce the case.

These can be seen in the above photo. Cutting these away will destroy them no matter how careful I am, so these will be replaced. They have to be removed as otherwise I’ll not be able to cut the case away from the keel.

The next part of the decision making is how to laminate the pieces together. I’ll join the parts together lengthways using what is known as a puzzle joint since trying to cut a scarf joint in 8mm ply is far beyond my capabilities and as the sides of the case do not bend, a scarf joint would be an overkill. A simple butt joint would work but the puzzle joint increases the glueing surface greatly and that results in a much stronger joint.

Here is an example of a puzzle joint that I made when trying out cutting the joint on the CNC router.

And here is the joint put together. As you can see, it’s not only a very good fit but is self-locating in that it won’t pull apart even without any glue in the joint.

So, that takes care of joining the pieces together but laminating them is another issue. The join between the two laminates much be perfect. No skipped areas of glue and no voids and there is really only one way to do that for a hobbyist and that is a vacuum bag. You get a piece of plywood around 25mm or an inch thick that is flat and slightly bigger all round than the laminates which are glued together and pinned so that they don’t slide over each other You put the laminates on the thick flat piece, put the whole thing into a plastic bag and suck all the air out. This forces all the pieces together and since one of them is thick and flat and won’t bend whereas the others, which are thinner and will bend, the laminates are pressed against the flat bit and will also be flat once the glue dries.

That’s the hand-waving, brief description. You’ll see how it works when I get to that bit and take photos.

Anyway, for now the technical bit is done and I can proceed with the removal of the rest of the damaged case.

Time for a cup of tea.

I had some work to do on the CNC Laser after work and while that was running I decided to look at some of the pieces I removed from the top of the case yesterday.

This is one of them and exhibits one of the things that Charles Stock did consistently wrong when building and maintaining Shoal Waters. He used brass screws. You can see the result in this piece of wood quite clearly, the discoloured circles of wood around the places that the screws were put originally.

This is the view from the other side and you will see that either the screw is missing completely or the zinc has leached out of the brass leaving just copper. These copper fastenings need to be removed and the wood repaired before it is put back in place. Still, enough of that, it was time to move back to the centerplate case. Armed with a multitool with a sharp, fresh blade I set to.

This is the result, a hole in the starboard side of the case. I had to say that it was either a very sharp blade on the tool or it was distressingly easy to cut through the side of the case.

This is the section that I cut out viewed from the inside face.

Looking down the slot through the opening I could easily see the metal spacer and it was easy to fish out with just my fingers.

It is the spacer through which the pivot bolt passes and its purpose is to prevent the bolt from crushing the case inwards when it is tightened. Too loose and the water will get in as the seal is not good enough, but tight enough to stop the water ingress would also deform the sides of the case. But with this spacer in the way, that deformation is prevented.

Back in the workshop I took a closer look at the section of the case that I had just cut out. It is in very poor shape as you can see. This large flake of wood came off just using my fingers.

And this was cause by scraping the wood with a screwdriver. It’s totally rotten. The inner face of the case seems to have been coated with something, presumably to stop the steel plate from damaging the wood, but under that it is soft and fragile.

Looking at the end of the cut piece you can see the plywood that Tony glued to the outside of the case to reinforce it. This split away from the original casing when I prised the section out. Then there is a fairly intact middle layer of plywood and then the darker part that is the rotted plywood. It looks as though the sides of the case were made from two piece of plywood glued together with something like Aerolite glue and the inner face of the case covered with something, perhaps Aerolite glue again, as protection. Over the years the rot has gotten into the inner layer of plywood but has not been able to cross the glue barrier into the original outer layer of plywood except where close to the pivot bolt hole.

As a final task for today I took a screwdriver to the other side of the case and as you can see form the above photo, it too is severely compromised. The conclusion I draw from examination of the casing is that the rot has spread at least as far as the solid ends and will therefore need to be completely removed and replaced with a new case.

Now that I have the side of the case opened up I can see that this isn’t going to be such a difficult job as I had first thought. I will have to cut away the two side reinforcing bulkheads, which is mildly annoying but has to be done, before cutting the case as close to the keel as possible. The idea being that if I’m careful with the removal I should be able to use the removed case as a pattern for the new one.

We shall see.

I’m fairly confident, however, that if Tony Smith had not reinforced the case when he did then Shoal Waters would have sunk, either on her mooring or, more likely, when being sailed and the leverage of the water on the centerplate on the case cracked the case apart. Scary to think about.

Still, a new case made from high quality marine plywood from Robbins Timber will put her back into sailing condition for many years to come.

I just have to get on and do it.

Time for a cup of tea.

Time to start work on figuring out why the case is leaking and why the surveyor had concerns about the integrity of the wooden casing. This is what he wrote in his report, a copy of which I have been given:

On examination of the casing, there is no indication of leakage through into the bilge compartments of the vessel, all areas are seen well painted, dry and clean. The casing is found generally well fitted still and without obvious movement. There are no areas of soft timber that can be fully determined without further opening up.

However, soundings of the plywood cladding gave dull returns which are indicative of degraded timber that might exist within the original casing boards; beyond the thickness of the added plywood cladding.

We had already been advised by Tony Smith that there is a leak in the region of the centreboard case, it is just not obvious.

The first place to start is the removal of the two metal plates through which the pivot bolt passes. These are held in place by what turned out to be stainless steel screws which came out easily.

The plate itself had to be prised off and underneath the plate was a white sealant.

The same was found for the other side of the case. The wood under the sealant came off in layers like you would expect of plywood, except it seemed to be solid mahogany or similar. It did not come off easily and had to be removed with a chisel.

And that makes quite a mess !

I decided to take another look at what prevented the centreplate from being removed from under the hull by putting my camera on the case looking down through the slot. This is the result:

So, I had briefly entertained the notion that the issue with the case could be easily located and solved, but now that I’ve seen this obstruction more closely and noted the fact that it seems to have made a gauge on the inside of the case, I have not choice but to remove the starboard side of the case so that I can access this damage, asses and repair it.

If the damage was caused by the centerplate removal then I would not have expected so much damage to be caused unless, as I mention in the video, the wood was already soft i that area or possibly rotten.

I’ll cut away a section of the timber in that area, perhaps a foot wide and from the bottom of the case to the top of the side panel. This will give me a large enough area to see how far down the damage goes and will also allow me to examine the wood on the other side of the slot.

I’ll make the cut as carefully as possible in such a way that the replacement isn’t going to be an odd shape. Or no more odd than is normal for a boat, but that’s a task for another day.

Definitely time for a cup of tea.

From an engineering perspective there’s something about Shoal Waters’ road trailer that bothers me. In fact, I’d go as far as to say that it is at least bad practise if not just plain wrong.

Here’s the trailer put out of the way temporarily whilst I try to find space for it in the hay barn. Can you see what bother’s me?

Here’s a closer look at what I consider to be the problem. The cross beam is welded to the wrong side of the side beams. It’s underneath.

The intermediate beams are the same except that they are not welded but use U-Bolts. But they are underneath the side frame. See how rusted that U-Bolt has become? The weight of the hull is being taken but this and the other U-Bolts, not a good place to be.

The cross beam at the rear is also welded and also underneath.

So why do I consider this to be an issue? Simply put, the entire mass of the boat and the strain of it bouncing up and down as the boat is transported from A to B is on the welds and the U-Bolts. I would have designed this with the cross beams on the top of the side beams. In this case the welds would only serve to increase the rigidity of the frame and the U-Bolts would only be there to stop the beams from moving around on the frame. The weight and stresses would be taken by the beams directly.

Now I can see two reasons why this might have been designed this way. The first is that if the intermediate beams are put on top of the side beams, the the U-Bolts would be the other way up and the nuts and protruding bolts would sticking up, rather than down and that might be considered to be a hazard. Secondly, by placing the cross beams underneath, the height of the boat above the trailer is reduced by 60mm. Is that significant? I don’t really think so.

Still, whatever the reason for the design decision, I’m going to change it so that the beams are where I think they should be. I’ll not removed the welded beams, they are there to make the frame rigid but two new beams will be sourced and mounted close by them, but on the top of the side frames.

Now, this trailer is never going to be road worthy, it’s too rusted for that, but over the next few years a boat will be put on and taken off the trailer at least four times a year and I need to make that as painless as possible. That means a beam under the hull but over the trailer and wide enough to get the trailer out just be pulling it and not by going through the hassle we did previously. Right now, the boat is so low that this isn’t possible. By placing the offending cross beams on top of the side frame and by raising the rollers as high as they will go, there will be ample room to put the beam in place and thus create the required bridge. The down side is that Shoal Waters will be higher and thus slightly more difficult to get into. I’ll just have to lose some more weight and start stretching to increase my flexibility.

So that’s what I’ll do.

Obviously, photos and posts to follow as this progresses. Shoal Waters needs to be moved into shelter of the hay barn as soon as possible.

Time for a cup of tea.

Continuing on from the tasks of the morning, removing the centerplate was next.

The pivot bolt was removed from the case and the salt-encrusted rope cut off the plate itself and a thinner line attached, one that would go down through the centerplate slot with problems. However, the plate just would not drop out of the hull.

It came out this far and no further. In the end I decided that there was either a stone wedged in the case somewhere or the pivot was not just a bolt but a tube held in place by the bolt. Since the plate sounded as though it were being brought up some something metallic, the latter option seemed most likely. That left us with two options. The first was to lift the boat up another 1.5m or so to allow the plate to be taken out vertically, or it would have to be take out from the inside as is the case with Naiad. With Naiad I can easily remove the mast compression post so getting the plate out is just awkward due to the weight and size.

Lifting the boat any higher was just not practical, in fact, with the equipment I have it would be pretty much impossible. So the inside option was the next to be tried.

This is as far up into the cabin I could get the plate, it’s touching the roof at this point. However, by removing the back two covers of the case I could lean it forward and just move to enough to one side to clear the compression post and it slid out.

Then it was just a case of sliding it out of the cabin using a couple of foam mats so as not to damage the varnish in the cockpit.

Judging by the wear at the top of the slot, I would presume that this is the original centerplate made by Fairey back in 1963. It is in remarkable condition. There’s rust on the leading edge but nothing to cause concern, the only two areas that need attention are the worn slot and the worn hole at the top of the plate used to haul it up and down. Once it has been scrubbed a decision on whether it should be re-galvanised or painted with antifoul will be taken.

Here you can see where the two cover boards were removed. They were going to be take out anyway, so that’s not a problem and the screws holding them in place were stainless steel and came out easily.

Difficult to photograph but you can just see the pivot in the case. It may be held in place by the two metal plates screwed to the outside of the case. I’ll check that out another day.

Shoal Waters has been put back to bed ready for the next step.

The trailer was put into the hay barn as the forecast suggests that it might be wet for a few days and having it in the dry means that I can work on it without any hassle.

Time for a cup of tea.

With the weather a little cooler during the day than of late I decided that I would spend the weekend primarily working on Shoal Waters. This despite my task list being some 41 items long. Fortunately, none of them are urgent so it’s time to move on with Shoal Waters

The main tasks for the weekend, should I choose to accept them or not, are as follows:

• Take the boat off the trailer
• Give the trailer some maintenance.
• Raise all the centerline supports on the trailer up to their maximum height
• Drop the centerplate out of the boat and set it aside for future maintenance.

That’s the list. I know that the rollers on the trailer are damaged so I will get buy new ones and replace them before putting Shoal Waters back on the trailer.

One of the good things about Shoal Waters being out of the water under cover for nearly two years is that she has dried out completely. Any water that had soaked into her timbers over the years will have dried out in that time and being out in the blazing sunshine that we have had since she was brought home will only have ensure that she is totally dry. However, we are forecast to get some rain in the next few days so I’m keen to get her into the hay barn as soon as possible. I will probably cover her with a tarpaulin once the centerplate has been removed to keep her as dry as possible. Then, when the trailer has the new rollers installed, she will be moved back on to the trailer and put into the barn.

So this is how Shoal Waters looks at the start of this morning’s work.

Well shored up at the stern and with the cockpit cover in place to stop any rain from getting inside.

I used a long oar as a ridge pole under the cover otherwise any rain that does fall tends to collect in the cover like a small pond.

Before I started on the lifting process I had to make a quick adjustment to the load-spreading pad that I use with the floor jack as Shoal Waters has a metal keel band running along the part of the keel where I will be lifting and the pad needed a groove to allow for this band.

I laso needed to check the state of the pivot bolt. As you can see, this side is well covered in paint.

The other side has had some of the paint removed, I suspect that this was done by the surveyor when she was surveyed 18 months ago.

Still, painted or not the nut came free quite easily. I didn’t have a 15mm spanner for this so I used adjustable spanners to do the job.

One the nuts had been removed I checked that the bolt was free to move by unscrewing it from the other side a little. This was quite hard but it does have a heavy steel centerplate resting on it so this is not surprising.

With the bolt checked it was time to start the lifting. Here you can see how the groove in the pad works.

The process of removing the trailer is simple if a little tedious. The jack is used to lift the boat off the trailer and the front end is blocked up as close to the forward crossbeam of the trailer.

The boat does not need to be lifted high. just enough for the keel to clear the rollers a little as you can see here.

The hull is then blocked up so that the jack may be let down and moved to another position. The trailer is moved forward as far as it wil go and blocked up again and so on. Here additional blocks have been added behind the trailer and after each move these are shifted forward until they are just aft of the slot in the keel through which the centerplate swings.

Here the trailer is about halfway out but there are still three crossbeams to negotiate before the trailer is free from under the hull. I have to say that it is fairly nerve-wracking and quite tiring as you are up and down the whole time moving the jack and the heavy blocks.

Eventually the trailer could be completely removed and more blocks put under the bilge runners as addition support to stop the boat from tipping sideways.

Time for a cup of tea and a short rest.

We have finally reached the point where the boat can be weighed, so let’s begin.

Firstly the supporting blocks at the stern are moved a little so that they are clear of the hull.

The trailer is leveled using the jockey wheel to raise the tongue.

A suitably sized block of wood put under the hitch to serve as a reference.

The centre beam of the trailer is marked using a plumb bob and a pencil.

The weighing system is installed and the tongue lifted off the reference block.

And the result for the first measurement is 41.8 kg. The distance between the center of the wheels and the point at which the weight was taken was also measured at 3375 mm.

The blocks were put back under the stern and the boat lifted up using a trolley jack so that the trailer could be moved forward a little.

The distance wasn’t that far, just 145 mm but that should be sufficient.

Here is the second line on the trailer, 145 mm away from the first.

The boat was let back down onto the trailer and the tongue weight measured again. this time the weight is 21.9 kg.

The boat was then put back to her original position on the trailer and the tools and wot-not put away.

So, what is her weight? The calculation is 3375 / 145 * (41.8 – 21.9) = 463 kg.

I have to say that this is about 130 kg heavier than I expected since Naiad weighs 305 kg. Still, I’ll re-weigh Naiad the next time she is out for maintenance. Now, let’s talk errors. The scale is +/- 0.1 kg. The distance the trailer was moved has an error of +/- 1 mm and the length from the wheel centres to the lifting point is +/- 5 mm.

So, we have values of:

M1 = 41.7 – 41.9 kg, M2 = 21.8 – 22 kg, delta = 144 – 146 mm and L = 3370 – 3380 mm.

So the calculated weight minimum will be 3370 / 144 * (41.7 – 22) = 461 kg and the maximum will be 465 kg.

So we can say that according to the measurements made today that Shoal Waters weighs 463 +/- 2 kg. Close enough.

Time for a cup of tea.

The next task in the very long list of things to do before Shoal Waters may be relaunched is to make the support beam that will hold her up at the front of the boat so that the trailer may be wheeled out from underneath.

I slid one of the scaffold boards under the trailer and marked off where I needed to cut the board so that about 40 cm protruded past the outside of the tyres.

The board was trimmed to length and then cut into three, more or less, equal pieces.

The three pieces were glued and clamped together and then screwed with timber screws.

I was not stingy with either the glue or the screws since this needs to be very secure.

It is looking quite good but it is not finished yet.

The timber screws are long enough to go through all three pieces and stop just short of the point coming out the other side. I did screw one in slightly too far and the point has penetrated so I’ll have to remember to file the point off before I cut myself on it.

The beam is slightly wider than it is tall deliberately. I’ll probably also build a vee-shaped support in the centre such that Shoal Waters rest nicely on the beam and won’t slip sideways when being raised. This won’t be done until the glue has dried. I’ll weigh the hull, then put the beam in place and then build the vee-section. Once that is all done I’ll coat the while assembly with a preservative as it will be stored in the Hay Barn. Since Shoal Waters is the same hull as Naiad the support beam with be used for both boats as required.

Time for a cup of tea.