[Public-List] Incline test on an Alberg 30?

[Kris Coward]

But my shakedown cruise is tomorrow (and I now think that said cruise
will include some testing for Metacentric Height)..

Cheers,
Kris

On Mon, May 17, 2010 at 03:46:48PM -0400, Gordon Laco wrote:
> I can just see A30'S all over North America being sallied tonight.
> 
> In some ports where we are thin on the ground there will be only one...in
> others, whole bunches.  Aboard each will be giggling crew members rushing
> back and forth, the ones who have to get over the boom occasionally
> tripping.  Seen from a distance, the affected ports will exhibit the usual
> forests of stationary rigs... But here and there one mast will be swaying
> like an inverted pendulum.
> 
> To individual observers it may appear a local anomaly; but what if somebody
> talks to somebody and realizes it is happening all over...
> 
> Perhaps we should warn our respective Coasties that the unusual activity is
> about to begin so as not to alarm the authorities...
> 
> Gord #426 SURPRISE
> 
> 
> 
> 
> 
> 
> On 17/05/10 3:31 PM, "Robert Kirk" <isobar at verizon.net> wrote:
> 
> > At 06:39 PM 5/8/2010, JT wrote:
> >> Baraka was a wreck when we found her in '06. After a hiatus, we're back to
> >> putting her to rights (so to speak)! We'll eventually take her offshore
> >> and are working with a rigger to ensure her replacement spars and standing
> >> rigging are properly sized for that job. While he can work from standard
> >> tables, he said the best way was to perform an incline test, as in Brion
> >> Toss's book "The Complete Rigger's Apprentice," p. 136: level the boat in
> >> the water, then line up several of your buddies along the toerail after
> >> noting their weights. Note the heel in degrees. (Hopefully, it's a handy
> >> 10 degrees.) By measuring the distance they are from the CL of the boat,
> >> and multiplying their aggregate weight by that distance, then multiplying
> >> again by 3 (if you got 10 degrees), you get the righting moment (RM) for
> >> the boat at 30 degrees of heel.
> > 
> > 
> > Jeff... I'm not sure about the Righting Moment at 30 degrees, but you can
> > get the related Metacentric Height (GM) pretty easily without weighing your
> > friends, by sallying ship (timing an induced roll by having a couple of
> > people run from one side to the other). The shorter the period, the better
> > the stability. GM is approximately (B/(2T))^2 where is B is beam (8.75' for
> > an Alberg) and T is the full period of a roll (average a couple of rolls).
> > 
> > Perhaps one of our naval architect Albergers (Hint: Mike) can comment on
> > the relationship & usefulness.
> > 
> > Maybe a fun Alberg group project, we could each Sally Ship and report the
> > resulting periods, so we can see how stable we are. They should all be
> > pretty much the same, but you's expect a boat with a radar aloft and a
> > light diesel to have a longer period than a clean topper with a lot of gear
> > in the bilges.
> > 
> > If your period is significantly longer that other Albergs, you might worry.
> > 
> > All it takes is two people to induce a nice roll. I've gotten off sandbars
> > that way. A full period is from one side to the other, and back again. Best
> > done at anchor.
> > 
> > Bob Kirk
> > Isobar #181
> > 
> > 
> > 
> > 
> > 
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> 
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-- 
Kris Coward					http://unripe.melon.org/
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