Keel extension Sun Light 31

[eggsi]

We bought a Sun Light 31 last year and were delighted with her, apart from her tender sailing performance. The 1.1T cast iron keel and 1.45 draft and tall rig meant that she performed brilliantly in light winds (we won the 2013 Sydney Jeanneau Rendezvous!) but leant excessively in anything over 10 knots. I factored into the price an allowance to add a lead keel extension of around 150mm deep and 250kg. However the cost was excessive and so a compromise was reached with the marine architect and the final design was a 140kg 80mm deep extension. Although the 3% antimony lead alloy is expensive, the REAL cost comes in the strengthening of the floor.

The initial profile of the bottom of the keel was scribed on a piece of ply wood done underwater. This enabled the design work to start.

The rest had to wait until she was hauled out and suspended so that I could work under the bottom of the keel. A lot of thought and planning was given to ensure the holes drilled and tapped into the cast iron lined up with the holes in the lead extension. It was tricky but worked out perfectly. The normal fairing process smoothed the gap. Before and after stability tests were done and lined up exactly with calculations. For a 12% increase in weight, I got almost double increase in stability. The sailing performance has increased significantly and whilst the 250kg would have been ideal, I am very happy with the compromise for a recreational boat, with the cost ending up only slightly over budget.








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[MartyB]

I for one would be a bit more interested in how you went about this. I've toyed with adding a bit of lead to the bottom of my Arcadia. But figure as you noted, the cost may be a bit much........

Marty

[eggsi]

What would you like to know Marty?