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

[Gordon Laco]

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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