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Old 09-11-2014, 01:33 PM   #7
Tad Roberts
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City: Flattop Islands
Country: Canada
Vessel Name: Blackfish
Vessel Model: custom
Join Date: Dec 2012
Posts: 711
I'll assume you are asking about the safe number of friends you can take out on the boat? Of course weather plays into this, a quiet harbour cruise for a hour is different than crossing the Hecate Straits.

For existing pleasure boats this size there are no rules on maximum number of passengers. For commercial use there are very strict rules involving a full stability study. One rule of thumb suggests the full crew on one side should not heel the boat enough to immerse more than 1/4 to 1/2 the freeboard. Freeboard is waterline to main deck height (not rail), but that may be complicated if there's a cockpit. All passengers on one side should never heel the boat more than 14 degrees, according to the US Coast Guard.

So lets look at passenger heel.....

We know that a known heeling weight moved a known distance off centerline, divided by the vessel displacement multiplied by the GM, will give us certain heel angle. So we work backwards....

I have to guess at the Sundowner numbers, beam is 11.5' and displacement 11,000 pounds? Lets say 6 people at 185 pounds moving 4.5' off centerline.

Heel angle = sin-1 (1110 * 4.5' / 11,000 * 2.2 )

= 12 degrees heel (that's safe)
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