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BOATING
Mini-Articles
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Last updated: 08/05/25
These are short pieces that don't rate full "Article"
status.
- Coast Guard Horsepower Rating System
The formula for determining maximum allowable horsepower for outboard
powered boats under 20 feet in length and with
at least a 20" transom height is: (Lft x Wft
x 2) - 90. Don't ask "Why multiply by 2 and subtract 90?" because
I don't know! It is permitted to round UP to the nearest 5 horsepower.
The manufacturer may also rate his hull at LESS than the maximum allowable.
Tiller or stick steering applications have lower ratings as well. All hulls
produced after mid 1978 must also meet the "positive, upright floatation
(paraphrase: when filled with water at rated load, the boat will not go
down by the stern, nor will it flip and go keel up)" standard.
For the full text (heavy reading) of both the Hp and the floatation regs,
you may visit the USCG website and view the following: Code
of Federal Regulations, 33CFR183.
Horsepower examples
17' x 72": (17 x 6 x 2) -90 = 114 Hp
18'10" x 86": (18.83 x 7.17 x 2) -90 = 180 Hp
- Some definitions of the various parts of a hull:
-30-
Copyright © 2001
Ken Cook, all rights reserved