[PUP] Scelenes vs Nordhavns - stability

[Mike Maurice]

> The data for the Nordhavn 40 shows a positive stability to 145 degrees, I 
> don't have the data curve for the 46 or 62 but it is probably a little 
> higher.
> 
Is this with or without a dinghy on the boat deck?


A few comments of clarification.

An inflatable dinghy with engine will modify the stability in a most 
nonlinear fashion. The weight of it initially acts to lower the range of 
positive stability, but once submerged the buoyancy might act to improve it.

In fact I would think that the buoyancy of the dink acting at some 
distance from the center of buoyancy of the larger boat would prevent 
the big boat from staying inverted, period. Assuming that the dink was 
not dislodged during the inversion.

In the case of the big Norhavn's where the dinks are generally mounted 
on the forward deck instead of up on the flybridge, the buoyancy would 
tend to cause the bow to rise inverted, and might not have enough lever 
arm to cause a re-righting to occur.

In other words, if there were 2 dinks on the bow it would be like having 
a large air mattress installed there and it might result in a stable 
inverted condition. Whereas if there were only one boat and especially 
if it were mounted on one side, the buoyancy would be off center and the 
inverted condition would be unstable.

I am not aware that this situation has been adequately researched, but 
it would apply to any similar boats, regardless of it being a Nordhavn.

Mike

_____________________________________
Capt. Mike Maurice
Beaverton Oregon(Near Portland)