Horsepower and size

[Ok J]

My old Fiberform (18 ft OB) is rated for a maximum 150 horse engine. I am rebuilding the boat with better materials and better overall strength. Am I limited to the max at which the boat was originally designed for?
Just another question...what dictates the rating?

-Thanks in advance.
Ok J

[marshmat]

You are most certainly restricted to the original 150hp rating unless you are changing the dimensions of the hull.

Regardless of how strong the hull is, hull strength has little bearing on the legal maximum rating. This is derived from the hull dimensions and volume.

Contact the Canadian Coast Guard ( http://www.ccg-gcc.gc.ca/ ) and request a free copy of "Construction Standards for Small Vessels TP1332", I believe April 1999 is the publication date. Section 4 of this document details how power and load ratings are determined. (A side note- the same equations are used for all boats of a similar shape; however, they are in reality not all that accurate under five metres LOA.) There are many other requirements in this book that most home builders miss, that are critical to the safety of the vessel. It also contains the necessary information for requesting a new capacity plate, which is needed if you are altering the static float plane height or if the original plate is not there.