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Printer Version HORSEPOWER CALCULATIONS FOR OUTBOARD MOTORBOATS WITH ENGINES GREATER THAN 2HP |
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Reason for Safe Horsepower ratings Start-in-gear protection requirements for outboards. The Rules are in 33 CFR Subpart D 183.51 - 183.53 Outboard horsepower ratings are based on a variety of factors. These include; Centerline length. Maximum Transom width. Transom Height. Type of steering: remote or tiller. Hard Chine Flat Bottom or Other. There is a formula for computing Safe Horsepower based on various combinations of the above factors. See the table below. This only applies to a monohull boat less than 20 feet in length (6.096 meters) Canada uses similar formulas for computing outboard power in kilowats. (1 HP = 0.745 KW) The below formulas do not apply to: sailboats, canoes, kayaks, and inflatable boats, that are designed or intended to use one or more outboard motors for propulsion. It does not apply to boats that are true multihulls. A multihull makes two or more separate footprints in the water. A pontoon boat is a multihull. Taken from Title 33 Code of Federal Regulations Subpart 183.53
Example 1: Bow Rider - Length = 19' 6" Transom width = 84" remote steering and 20" transom height. (Length x Transom Width X 2)-90 = HP = ( 19.5 X 7.0 X 2) - 90 = 273 - 90 = 183 (136 KW) Horsepower = 185 (138 KW) Example 2: Length 12' Transom width = 46" Tiller steering and 15" transom height. ( Length x transom Width) = 45.96 Horsepower from table = 10 (7.5 KW) Horsepower is rounded to the next multiple of five.
Beware of steering changes: If your boat is rated for remote steering, and the buyer wants you to reconfigure the boat from remote steering to tiller steering, the boat can no longer be rated for the higher horsepower allowed with remote steering. You will have to change the labels to the lower horsepower rating. Conversely: if the boat is rated for tiller steering and the buyer wants it to have remote, you will have to put on a label reflecting the higher horsepower rating. See Labels https://newboatbuilders.com/pages/labels.html Special Rules: For boats that meet the following qualification there is an optional test course method for determining horsepower:13 feet or less in length. See https://newboatbuilders.com/pages/hp2_print.html Copyright 2010 newboatbuilders.com All rights reserved. Revised 11/21/2014 |