Arne,

The Freeship program can calculate the Cross Curves, from which it is possible to calculate GZ if the VCG is known (I can't get values of KN for greater heel angles than 40^o as my Freeship model is a bit "leaky" above that, and I don't know how to fix it). VCG can only be a guess, as it depends on what is actually built and how it is loaded up, but it is commonly near the DWL, or somewhat above, for a cruising boat. On that basis, the GZ³⁰ is likely to be somewhere around 0.45

A shoal draught boat simply has to be heavily ballasted. I have put in 1.6 tonnes of keel, for a 40% ballast ratio, and I wouldn't ever want to go for less than that, for any offshore boat.

David,

Looks great. The lines look even better stretched out a bit.

And I like that the rudders are now splayed. Not personally a fan of skegs when you could just as easily have lifting balanced rudders that can be lifted for inspection and work. but thats no biggie.

I noted elsewhere though that you said your preferred draft for a keel was around 2 and a half feet ish. But this drawing seems to show around 840mm. Is there a particular reason for this ? Actually that keel doesn't exactly look attached in the dxf :-)

Cheers

Gary

Thanks for the drawings, David.

I think the 9m SibLim *) looks very promising. With a wll. of 7.7m, her hull speed should rise to 6.7kts, compared to 6.3kts on the 26-footer.

As mentioned earlier, I am looking for two sorts of stability:

1.      The ‘sailing stability’, with witch I mean the stability at max. heeling before reefing, when sailing close-hauled. I guess that is at somewhere between 20 and 30°. At this angle of heel, the vertical position of the centre of gravity is not terribly important, as the hull shape counts more.

2.      The safety- or knockdown stability is the other factor. My guess is that the vertical position and amount of ballast has much more to say here.

What I would want to have is plenty of sailing stability and enough, but not more than enough knockdown stability. In other words, I would try to get away with as little ballast as possible, so I could load the boat with lots of stuff, without ending up sitting low on the waterline.

Would it be possible to export the drawing into a maritime CAD program and find her stability curve, for instance with a constant displacement, but with different amount of outside ballast?

This could ensure a maximum useful boat, without dragging around more than necessary ballast.

Arne

*) sorry if I stuck a wrong name to her...

What's wrong with Siblong? I'm sure we can think up a suitable acronym!

David,

do you by this mean that you have expanded SibLim in 3 planes instead of just stretching it?

Btw. The plans for the schooner Samson that you met in the Rally in Stavanger in 2004, was for a 45-footer. Svein Magnus Ueland stretched it to 49' in a way that the Samson company recommended:

Instead of only increasing the distance between the frames, he combined that method with adding a second main frame at the middle of the ship. The result looks very right.

Arne

PS: That was before the CAD days...