Country Dave
Well-known member
I know this subject has been talked about, discussed and debated probably as long as there have been boats with outboards motors on them.
My intention was and is not to advocate, promote or encourage reckless behavior especially to the degree that it might compromise anyone’s personal safety. Nor was it to intentionally hurt anyone feelings, inevitably that happens after all this is an internet forum and often times things get assumed and or lost in the translation . I just put on my big boy pants and laugh it off when it happens to me.
My intent was to try and get some facts regarding “firstly” how a boat manufacturer goes about determining a max HP rating for their hull and to see if my hunch that most manufactures factor in a “cushion if you will” and untimely put a lower max HP placard on their hulls than what the formula would allow for. My hunch has been substantiated. I’ve learned a lot.
In response to a mandate from Congress contained in the Federal Boating Safety Act of 1971 (FBSA), the United States Coast Guard issued regulations covering small outboard boats and the maximum rated horsepower for them. The regulations bind the manufacturer to provide a capacity plate that shows the maximum rated horsepower for each hull.
My interpretation of those regulations is that the manufacturer must state the horsepower as no more than that computed under the formula, except, if the manufacturer conducts the performance testing procedure, the results of that testing can be used (with some qualifiers). However, the manufacturer is apparently free to state a lower rating if desired, and sometimes does. Note that the regulations only require ratings for monohull boats under 20-feet in length.
The formula provided in the regulations reduces to:
(2 X L X W) -90 = rated horsepower
Where:
L=boat length
W=transom width; if the boat does not have a full transom,
the transom width is the broadest beam in the
aftermost quarter length of the boat.
The rated horsepower may be rounded up to the nearest "5".
Here is an example of how the rating formula works in practice, applied to an older Boston Whaler boat, the V-20 model:
Boston Whaler V-20
Length = 19' 10"
Width = 7' 5"
Thus:
(19.83 x 7.42 x 2) - 90 = 204.15
Rounding up = 205 maximum rated horsepower
In the case of the V-20/Outrage 20, from 1978 through 1985 Whaler chose to give it a maximum rating of 180-HP instead of 205-HP. Affixing rating labels which are lower than the rating permitted under the formula is common and that was my whole point. It’s not unreasonable or unsafe to add a few ponies above the max HP placard, and if you’re over 20 ft it’s not even mandated for the manufacture to affix a hp rating placard all though most do.
It’s interesting and note worthy that this federal mandate is only for monohull boats under 20ft. It’s also note worthy that The United States Coast Guard has an opinion on this frequently asked question, and their answer from their website reproduced below:
Can I use a bigger motor on my boat than what it's rated for?
It is not a violation of Coast Guard regulations to install or use an engine larger than specified on the capacity label, but there may be state regulations prohibiting it, and restrictions from your own insurance company regarding this.
There are no Coast Guard regulations against exceeding the safe loading capacity, however, there may be State regulations or restrictions from your insurance company which prohibit this. There is a Coast Guard regulation that gives Coast Guard Boarding Officers the power to terminate the use of a boat (send it back to shore) if, in the judgment of the Boarding Officer, the boat is overloaded. There is no fine for this, unless the operator refuses the Boarding Officer's order.
NOTE: The Coast Guard Capacity Information label is required only on monohull boats less than 20' in length. The label is not required on multi-hull boats, pontoon boats (catamarans), or on any sailboats, canoes, kayaks, or inflatable boats, regardless of length.
My intention was and is not to advocate, promote or encourage reckless behavior especially to the degree that it might compromise anyone’s personal safety. Nor was it to intentionally hurt anyone feelings, inevitably that happens after all this is an internet forum and often times things get assumed and or lost in the translation . I just put on my big boy pants and laugh it off when it happens to me.
My intent was to try and get some facts regarding “firstly” how a boat manufacturer goes about determining a max HP rating for their hull and to see if my hunch that most manufactures factor in a “cushion if you will” and untimely put a lower max HP placard on their hulls than what the formula would allow for. My hunch has been substantiated. I’ve learned a lot.
In response to a mandate from Congress contained in the Federal Boating Safety Act of 1971 (FBSA), the United States Coast Guard issued regulations covering small outboard boats and the maximum rated horsepower for them. The regulations bind the manufacturer to provide a capacity plate that shows the maximum rated horsepower for each hull.
My interpretation of those regulations is that the manufacturer must state the horsepower as no more than that computed under the formula, except, if the manufacturer conducts the performance testing procedure, the results of that testing can be used (with some qualifiers). However, the manufacturer is apparently free to state a lower rating if desired, and sometimes does. Note that the regulations only require ratings for monohull boats under 20-feet in length.
The formula provided in the regulations reduces to:
(2 X L X W) -90 = rated horsepower
Where:
L=boat length
W=transom width; if the boat does not have a full transom,
the transom width is the broadest beam in the
aftermost quarter length of the boat.
The rated horsepower may be rounded up to the nearest "5".
Here is an example of how the rating formula works in practice, applied to an older Boston Whaler boat, the V-20 model:
Boston Whaler V-20
Length = 19' 10"
Width = 7' 5"
Thus:
(19.83 x 7.42 x 2) - 90 = 204.15
Rounding up = 205 maximum rated horsepower
In the case of the V-20/Outrage 20, from 1978 through 1985 Whaler chose to give it a maximum rating of 180-HP instead of 205-HP. Affixing rating labels which are lower than the rating permitted under the formula is common and that was my whole point. It’s not unreasonable or unsafe to add a few ponies above the max HP placard, and if you’re over 20 ft it’s not even mandated for the manufacture to affix a hp rating placard all though most do.
It’s interesting and note worthy that this federal mandate is only for monohull boats under 20ft. It’s also note worthy that The United States Coast Guard has an opinion on this frequently asked question, and their answer from their website reproduced below:
Can I use a bigger motor on my boat than what it's rated for?
It is not a violation of Coast Guard regulations to install or use an engine larger than specified on the capacity label, but there may be state regulations prohibiting it, and restrictions from your own insurance company regarding this.
There are no Coast Guard regulations against exceeding the safe loading capacity, however, there may be State regulations or restrictions from your insurance company which prohibit this. There is a Coast Guard regulation that gives Coast Guard Boarding Officers the power to terminate the use of a boat (send it back to shore) if, in the judgment of the Boarding Officer, the boat is overloaded. There is no fine for this, unless the operator refuses the Boarding Officer's order.
NOTE: The Coast Guard Capacity Information label is required only on monohull boats less than 20' in length. The label is not required on multi-hull boats, pontoon boats (catamarans), or on any sailboats, canoes, kayaks, or inflatable boats, regardless of length.
Excellent reply Sumdumguy. 
