Stability - calculating BM and KB.
I've always know that boats turn over when they are top heavy, but never really understood the science behind it. Having a boat capsize is not my idea of a good day out. So this little corner of the site is Dr. Holt's attempt to understand model boat stability - without getting too scary or geeky.
Calculating BM and KB.
Both BM and KB can be calculated and when added together these will give us the value KM.
-> For box shapes : BM =B²/12d and KB=d/2
-> For triangular prisms : BM=B²/6d and KB=2d/3
-> For intermediate hull forms approximate using : BM=B²/9d and KB=0.6d
For an intermediate hull form where the breadth is 0.2m and the draft is 0.07m:
Value |
Formula |
Result |
|---|---|---|
BM |
(0.2 x 0.2) / (9 x 0.07) |
0.063 |
KB |
0.6 x 0.07 |
0.042 |
BM |
KB + BM |
0.105 |
So in the diagram below we have now calculated BM and KB and KM.
