Friday, October 21, 2005

Why the ballast

I've had several people, including Rik, who has an excellent blog over at Garfieldt's blog, ask me why I'm putting more weight into Lady Jane.

On the face of it, adding weight to the boat doesn't make sense. However the driver behind the ballast is to get Lady Jane's trim correct.

Lady JaneIf you look at this fairly recent picture of Lady Jane (click on it for a larger image), you can clearly see the line made by the muddy water in Fareham creek, and the horizontal line of the rubbing strakes which run down the length of Lady Jane. These lines show roughly how Lady Jane sits in the water at the moment, compared to how she should sit.

Lady Jane has had masses of material removed from her. According to the previous owners, they took off roughly thirty five tonnes of steel and concrete when they had her. I must have subsequently removed at least another five tonnes so, although I've got tonnes of ballast to go in, it's nothing compared to the overall weight she has lost.

Almost all of the weight removed was from forward of the engine, which is a huge lump fairly far back down the length of the boat, this has had the effect of bringing the bow up and lowering the centre of gravity.

While lowering the centre of gravity is a good thing, there are problems with having Lady Jane's bow so high:

The first being that everything on the boat is at an angle when Lady Jane is afloat, making things a little uncomfortable - sleeping for example.

The second being it is hard to see over the bow from the bridge, making skippering Lady Jane in confined spaces that much more difficult.

The final reason is that with the stern so low in the water, the propeller will tend to push Lady Jane slightly upwards as well as along, wasting fuel and therefore money.

The ballast right down in the bow of Lady Jane will lower her centre of gravity, making her even more stable in the water, and, along with the anchor and winch to be installed, will fix the trim issue.

In the future, when I build forwards, I also have a several tonnes of water in a bow storage tank which I can use to compensate the trim. If need be, I can also move, or remove, the ballast I've put in as it's all in small, manageable, blocks.

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1 comment:

  1. wow, thanks for the great and very clear explanation. :)