The Steam Tug Part 3.

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The Weigh In.

I found all my lead pucks, so it was time to measure the displacement of the tug hull.

I’ve got the lead out.

So tape off the hole at the end of the prop shaft and fill the bath with water. Put the lead in the boat, but it still wasn’t enough to get her down to the waterline. Well, the hull is keeping water out, so it’ll keep it in, right?

Extra weight going in.
Down to her marks!
Now what?

Well, pull the lead pucks out, and then get the water out with a measuring jug. That’s 3.3 Litres of water you’re looking at inside the boat. Which is 3.3 kg. Right?

Now to the weigh-in.

The Weigh-in.

So the lead weighed 7.262 kg. all together, the water 3.3 kg. and the hull 1.398 kg. Making a total displacement of 12.007 kg, (26.47 lbs). Take off that the weight of the hull (1.398kg.) and the weight of the prop and shaft (0.047kg.) and for the rest of the build I have 10.562 kg to play with (23.25 lbs). The next heaviest components are the batteries and the motor.

A 775 motor weighs 0.4 kg. and a 6 volt 4 ampere hour lead acid battery 0.75 kg. I have used these 6 volt lead acid sealed batteries very happily on a couple of Springers and on my Thames Barge for the last 5 years. In this build I am going to need extra weight low down, and a bank of these will do that job nicely. No need to consider Lithium.

Although I don’t have to try to build light, there is still an advantage to keeping the weight as low as possible. The laws of physics mean that scale model boats are much less stable than the full size versions, and you will quite often see our models leaning over a long way to the outside on a tight, fast, turn. This can cause considerable grief on a sleek, fast, warship model, especially on the conversion of a styrene (Airfix) type model to operate in the water. But that’s a part of the joy of tug models. Their hulls are deep, wide and very stable, and it does make a tug build easier.

Anyway, the last 24 hours have confirmed that I don’t have to cut any corners with this build, so I am going to start fitting the hull with a deck, and checking out coffee stir sticks as a way of making those lovely superstructures.