RHIB Stability

Example RHIB Windage · 46 CFR 170.170 as modified by MTN 01-08 §5.5

Route

Load

Grey: hull, console and seats above the water. Amber: what the hardtop adds. Both count toward A. Magenta dot: the ballast.

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Hardtop length271″

Fixed ballast (or batteries)750 lb

Ballast position, fwd of transom18″

Ballast height, inches above keel6″

Hardtop height above baseline109″

presets

GM required vs. hardtop length

P (tons/ft²) = 0.0025 + (L/14,200)² protected · 0.0033 + (L/14,200)² partially protected · 0.005 + (L/14,200)² exposed · T = lesser of 14° or the heel that immerses 3/8 of the least freeboard, trim held · everything under the hardtop counts as solid area

Wind heel check

Projected lateral area A

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above the waterline, under the top counted solid

Lever H

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center of A to half draft

GM required

–

GM available

–

Margin

–

available − required

Ballast to pass

–

at the ballast position set above

Shorten top to pass

–

at this ballast and height

Lower top to pass

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at this length and ballast