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 Sail Mag/Dave Gerr Ultimate Stability		  New Topic  Topic Locked
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Sea Trac
Master Marine Consultant

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Vanuatu
1357 Posts
Initially Posted - 10/15/2004 :  15:34:49  Show Profile
Having some spare time on my hands today, I decided to calculate the Angle of Vanishing Stability and the Capsize Screening Ratio for the C25FK. If you have a different config, a C250 or just want to see my spreadsheet, then send me an email.

C25FK AVS = 97.6 degrees (both seawater and freshwater)
C25FK CSN = 1.19

Desired AVS for offshore cruising should be 120 or higher. AVS is the angle of heel beyond which a boat is not likely to recover, but is likely roll and stay upside down. With an AVS of 97.6 degrees, therefore, you don't ever want to roll your C25FK past horizontal. Aren't you glad I'm here to inform you of that?

Desired CSN is 2 or below. This number indicates a boats initial resistance to capsize. So, the 1.19 indicates what we already knew about the C25FK not being a tender boat. Think Hunters are above 5?
J.B. Manley s/v Sea Trac Allied Seawind II #65
DPO s/v Antares Catalina 25 #4849
Association Treasurer 2002 - 2006
Association Bookkeeper 2002 - 2008
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ClamBeach
Master Marine Consultant

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3072 Posts
Response Posted - 10/15/2004 :  17:40:58  Show Profile
Did you include the bouyancy of the coachroof in your calculations ? It's an important design element in producing self-righting hulls that doesn't factor into the usual beam, mass and CG factors.

With the coachroof flotation considered, I don't think a C25 would stay inverted for long in anything but dead calm conditions. Not that you'd want to be rolling a C25, there's lots of other stuff that would probably break under the stress.
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Sea Trac
Master Marine Consultant

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Vanuatu
1357 Posts
Response Posted - 10/15/2004 :  18:25:06  Show Profile
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by ClamBeach</i>
<br />Did you include the bouyancy of the coachroof in your calculations ?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Way beyond this finance major's capabilities! But you already knew that, didn't you? Of course, my battery brackets are likely to fail when completely inverted and punch a couple of big holes right through the sliding hatch, anyway.
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Oscar
Master Marine Consultant

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USA
2030 Posts
Response Posted - 10/15/2004 :  18:35:28  Show Profile  Visit Oscar's Homepage
At some point I laid on the cabin floor and pictured the thing rolling, it would take a lot of hardware to keep stuff in place......

Oscar
C42 # 76 "Lady Kay" (Formerly C250 WB #618)
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joe keith
1st Mate

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USA
26 Posts
Response Posted - 10/16/2004 :  22:54:39  Show Profile
I tried the same calculation and got:

AVS=106
CSN=1.94
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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.