40.5 Stability Index

[DayDreamer41]

Well apparently there are different values for Stability Index, the race measure sheet I have referenced listed the Hunter 41 DS at 122.6 but that really doesn't make sense does it, so I am not sure what that is, sounds more like a number representing AVS.
At any rate here is an interesting site I did find with an extensive data base
http://sailplan.ie/apps/boat-data-result/Hunter+41DS

And DavidinSandusky thanks for the article was rather enlightening

 

[Franklin]

just about any boat larger than 35 feet made since 1990 will meet those requirements.

 

[Jackdaw]

Well apparently there are different values for Stability Index, the race measure sheet I have referenced listed the Hunter 41 DS at 122.6 but that really doesn't make sense does it, so I am not sure what that is, sounds more like a number representing AVS.
At any rate here is an interesting site I did find with an extensive data base
http://sailplan.ie/apps/boat-data-result/Hunter+41DS

And DavidinSandusky thanks for the article was rather enlightening

Stability Index
Formula: T (Roll Period) / Beam x 0.3048
Note: This value is not related to the RCD STIX value. This is another empirical term relating period and beam to stability. Values less than 1.0 are considered stiff. Values greater than 1.5 are considered tender. This ratio includes the hull form, center of gravity and roll moment of inertia in one package.

 

[Gunni]

Higher freeboard (as on a H-41DS) would contribute to increased AVS. But if you lose one of those picture windows or otherwise down flood all bets are off. All these factory stats factor a lightship with none of the stuff people like to put on them which raises the CG.

 

[DayDreamer41]

Higher freeboard (as on a H-41DS) would contribute to increased AVS. But if you lose one of those picture windows or otherwise down flood all bets are off. All these factory stats factor a lightship with none of the stuff people like to put on them which raises the CG.

If I read the article posted by DavidinSaduski correctly downflooding actually reduces the time for a vessel to right itself, although I would not want to put that theory to the test.

 

[SVPardonMyFrench]

ha! here's the link for the 40.5

http://sailplan.ie/apps/boat-data-result/Hunter+40pnt5+Bulb+Wing+Keel

thanks DayDreamer41 for pointing to the db

 

[Gunni]

If I read the article posted by DavidinSaduski correctly downflooding actually reduces the time for a vessel to right itself,

Yes, Calder did give that odd notion a drive-by, but common sense and basic physics tell you that downflooding simply puts water ballast in the part of the boat that works against the righting moment. The boat wallows. And if you take on enough water ballast your freeboard goes to zero, waves break over you and your boat goes to the bottom.

 

[DayDreamer41]

Your very welcome Frederick, was a real challenge finding that kind of information. While they mention the displacement they have no value for draft which I would think would be a principal factor in determining CG and the ability of the vessel for righting itself.

 

[Franklin]

Two things to note:
1) some numbers on that sight are wrong like for my boat's manual says 16,400 displacement and it says 15,900. Says capsize ratio is 2 but it is 1.79 (152 / ((16400/64.2)1/3).

2) the fòrmula all over the internet for capsize is right but the units of measure are wrong. Width is inches not feet and the calculators are wrong too.

 

[SVPardonMyFrench]

Yeah, saw draft was missing just email them to update

 

[SVPardonMyFrench]

Ok so they corrected the draft after i emailed them. Good responsiveness.

so here's the updated data; can't really remember how it compared to previous w/draft.

http://sailplan.ie/apps/boat-data-result/Hunter+40pnt5+Bulb+Wing+Keel