Sailing in Shoal Waters

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.

As I mentioned previously, there are two main problems with the trailer as it is right now.

This is the first. One of the side supports is so low that the end almost touches the ground.

This shows the errant support and you can see that it is not vertical but slanted backwards. This is due to it being so low that it dragged on the scaffold boards when we were hauling the boat and trailer on to the car transporter. Still, it needs to be fixed.

This is the second issue. Shoal Waters sites very low on the trailer. I can understand why that should be since this is also her launching trailer and the lower to the ground the hull is, the sooner the boat will float as the tide rises.

However, if you look across the trailer so that the top of the metal beam on this side of the trailer is level with the same beam on the other side, you can see that there is no space here to put a supporting beam on which the boat may rest and be raised such that the trailer can be moved out from under the boat.

There is also another issue but a minor one and that is that the side supports on the left hand side of the trailer are lower than the ones on the right and so Shoal Waters is resting at a tilted angle as you can see here.

When I was replacing the axle and wheels last week I took the opportunity to spray all the nuts and bolts that hold the supports in place with penetrating oil and I was delighted to find that every one turned easily with a spanner despite being fairly rusted. So much so that once I had leveled the boat on the trailer, or close enough for now, I crawled under the boat with the penetrating oil and liberally applied it to the bolts that hold the centre supports since I’ll be needing to raise those up once the trailer is out from under the boat.

Now Shoal Waters is almost level. It isn’t perfect right now but it will suffice since I need to get the changes to the trailer done before I can level the hull properly so that it is level with the trailer.

Now the very low support strut is a lot closer to being vertical and is also a little bit higher off the ground. Silll not high enough but that will be rectified later.

Finally, for today, I blocked up the stern behind the trailer so that there is lateral support once the boat is raised up off the trailer and no longer supported by the side supports.

Time for a cup of tea.

The following day I set too with paint brush and wood preserver to coat all the cut ends of the block in an attempt to slow the cracking of the blocks due to them drying out.

I jacked up the trailer one side at a time and blocked it up such that the tyres were off the ground.

So far so good and the whole thing is really stable allowing me to work on moving the axle without fear of the whole thing collapsing on me as I work.

I decided to move the axle forward 100mm or 4″, an inch or so more than necessary and marked the spot on both sides where the axle should end up. Then it was a case of loosen the nuts on the u-bolts and wriggle the axle forward to the new position. I say wriggle but in practice it was hit it with a mallet as the axle is heavy!

After a dozen or so small moves the axle was in the correct place and I tightened up the nuts again, jacked the trailer up again and took out the blocks. Now for the acid test. I suspended my 350kg scales above the hitch and measured the weight.

Not pretty but it works well.

Not easy to see in the bright sunlight, but the tongue weight of the trailer and empty boat is 37.4kg. That is pretty close to being correct, not that I’ll be towing this trailer anywhere but if I have to do that, then the tongue weight is not far off the correct value.

So, first things first. Off to the local timber merchant to buy six reclaimed railway sleepers. These need to be cut into blocks which will be used to support the trailer and the boat when necessary.

Railway sleepers are heavy so I cut them up by sliding them out of the minibus and cutting the end off, five times per sleeper.

Our super new electric chain saw wasn’t quite wide enough to cut the sleepers so I used the saw that came with the gardening tool thingy and that worked well.

Six blocks on one side of the boat…

… and six blocks on the other

The rest I stacked in the Hay Barn for now.

With the boat now on her trailer with wheels but pretty much empty, now would be a good time to check her weight. We do have a local weighbridge but you need to make two trips, one with the boat on the trailer and one with it off. This is not really practical for fairly obvious reasons. Fortunately, there is an easier option and that is to use a simple method taking advantage of what the physicists would call moments of inertia summing to zero. Fancy name for the fact that the centre of mass of the boat times the distance from the centre of the wheels pressing down must equal the length of the trailer to the jockey wheel pushing up.

But what about the weight of the trailer and the boats centre of mass, to say nothing of the centre of mass of the trailer, I hear you ask, well if you do the measurement twice with the boat moved a bit on the trailer between the measurements, all the unknown bits cancel out (I’ll publish the maths in another post for those that don’t believe me).

So, here is the method.

Move the boat backwards on the trailer about 4″ or 100mm. The more the better but don’t overdo it so that the boat tips the trailer back. Make a pencil mark on the trailer somewhere using a plumb bob from the bow of the boat. Now measure the weight at the jockey wheel, call it M1. You can use bathroom scales if you like but I use a 350 kg scale suspended over the hitch. Now measure the distance from the centre of the wheels to the point at which you made the measurement and call that L. Be as accurate as you can. Now move the boat back to its normal position and make another pencil mark on the trailer using a plumb bob from the same place that you made the first mark. Carefully measure the distance between the two pencil marks and call that D. Measure the weight on the jockey wheel again and call that M2.

Now, the weight of the boat is the (M2 – M1) * L / D

That’s it.

The only hard part about it is moving the boat backwards and forwards, but at least you don’t have to move the boat off the trailer completely and then back on again.

But before I can do any of that, I need to adjust the trailer in two ways. Firstly, the swing arms on the new axle are 3″ shorter that those on the old axle and I now need to move the new axle forward at least 3″ to compensate. Secondly, all the boat supports on the trailer are down very low. Too low to be able to put a beam under the hull but over the trailer that is strong enough to hold the boat up off the trailer, so the trailer has to come out from under the boat so that I can raise the supports as high as they will go.