The Naiad Voyages

Mark Austen

2021.05.22 - Rudder Sink Weight II

I've had one of those days that I don't want to end. Everything I have attempted today has not only succeeded but succeeded really well. I'm glad it's now the end of the day since I don't really want to start anything new that will spoil it.

Today's task was to try and finish the rudder sink weights.

I need a tray in which to put the casting sand that will be used to create the mould for the weights. A 20cm (8") square piece of plywood will to the trick.

Followed in quick succession by four pine sides. These were just nailed into place since structural rigidity is not required. I did drill pile holes for the nails, however, since hammering nails into the edge of thin plywood or pine is pretty much guaranteed to split it.

So far, so good. Now for the sand.

This is casting sand using an oil to keep the sand together. Apparently it's very good for this sort of thing.

I found this pan in amongst our medieval kit and thought it might make a good pattern for the mould.

It does have a flat on the bottom, but in the end it wasn't any use.

So,I got the lead started and then went looking for some scrap wood from which I can make a curved scraper.

I had no difficulty on that score, now to try and make the required shape in the sand.

It didn't turn out too bad. I formed a well in the sand by hand and then used the curved edge the pattern to pound the sand down. The pattern was then used to scrape the sides of the well but twisting it round and round so that it carved out the depression. The excess was carefully scraped out by hand.

Baby powder is used to help the metal release from the mould. The professionals use finely powdered talc, but that's expensive compared to baby powder. The downside is that this stuff stinks. It is probably very good to put on a baby's bottom but otherwise....

I was unable to take photos of the lead pouring process as that took two hands to achieve, but this is the result.

After the lead had solidified it was carefully lifted out of the mould.

Not a bad result. Not perfectly round or smooth, but it is a temporary weight and quite good enough.

Less than 30 minutes later I had two.

I reused the mould with a little fresh baby powder and the double duty did scorch the sand, which is quite usual. You carefully scrape the burnt stuff off and throw it away and then save the rest of the sand for the next job.

The heat from the two weights did scorch the bottom off the wooden tray, but that is also temporary so that matters not at all.

While I was in the lead casting frame of mind, I put the casting ladle I bought years ago on the flame and melted some more lead.I had two moulds to try out. You can see them propped up on the burner to heat up before pouring in the lead. I have just added some wax to the molten metal as a flux to encourage the dross to float the surface. The wax vaporises and then catches fire and hence the flames. Once the flames have gone out, the lead is stirred, the dross carefully moved to the side and lifted out with the stirring stick.

The ladle is much easier to use for pouring. The tin can was just too tall and narrow. 

The result is good and I shall have a casting weekend sometime to melt more lead and make it into more convenient sizes.

I also took the time to weigh the two sink weights. I was aiming for 2kg (4.4 lb) and hit the mark. More by luck than good judgement, I have to say.

When the weights were cooled I screwed them to the rudder. I used screws and not bolts since I can countersink the screw heads for a more streamlined profile. Note that for this weight, the line of the screws is vertical.

The second one went on but with the line of the screws horizontal and at right angles to the first so that they do not touch inside the rudder.

Here is the result from an edge-on angle. Now you can see what I mean by a hydrodynamic profile. I'm very pleased at the result. The next task for the rudder is to sand it down and paint it after which I will install the weights with plenty of butyl tape to seal the water away from the wood.

The rudder is now very heavy and it does make you wonder if I've overdone it, but once the blade is in the water, the buoyancy of the blade will counteract the sink weights. How close that will be remains to be seen.

Still, a great day.