What size engine?

[HAS]

What determines the maximum size outboard engine a boat should have?.....HAS

 

[Mi duckdown]

Re: What size engine?

The transom plate ID

 

[cyclops2]

Re: What size engine?

Marine insurance companies & the USCG. With some verified crazy driving tests by the boat design companies.

Those 3 groups are responsible for the MAXIMUM HP rating. Have a accident with more TOTAL horsepower than stated. They could say, we will not pay anything. You are on your own. Has happened.

 

[Johny25]

Re: What size engine?

If the boat can float it then you are good I like to run max HP for my boats and have been known on occasion to run even higher than rated with mods to the max HP motor that are difficult to tell

 

[Frank Acampora]

Re: What size engine?

What determines the maximum outboard horsepower a hull can have attached to it is actually the approximate volume of the hull. US Coast guard has a formula to figure it. My state also has a formula but it seems to be more restrictive (if you go to get a rating on an old hull with no capacity plate) The Coast Guard also figures the maximum weight capacity empirically: They load a test hull with weight.

The formula takes into account the length, widest point, transom width, transom height, and depth of hull. However, it is modified by steering and decking or consoles. For example: A tiller steered model has a lower HP rating than a helm steered model of the same hull.

The same hull with inboard or IO power has all bets off: There is no horsepower limitation. Go figure!

That said, my personal formula is: Too much horsepower is never enough! LOL

 

[Johny25]

Re: What size engine?

My boat is rated 15hp tiller and 25 controls but the boat has no console so I upgraded from my 15hp to a 25hp tiller this winter and just did a mod to make it 30/35hp. The 15 would plane us but not like I wanted after the custom flooring, bass boat seats and casting deck. I am hoping for 30mph but will be happy with 27-28mph

 

[steelespike]

Re: What size engine?

It would be interesting to know what motor and your mods.Also would be nice to know your test results.
What size boat"

 

[NSBCraig]

Re: What size engine?

20' and up have no restriction either.

 

[idonthaveaname]

Re: What size engine?

Here is the formula but there are other things to consider. A 2 cycle weighs less than a 4 cycle. A Mercury weight is different than a Honda, etc. So the question is, if weights are about equal, and the horsepower differs by 10hp, is that a problem? Boat design has a lot to do with it also. Just because the boat is 17 feet doesn't mean it's the same motor. I have seen 17's with 140hp and 17's that would sink with a 140hp. I look for the manufacturer recommendation and stay close to the horsepower...I don't think 10hp will make much difference. For example, my 1986 bass boat (15 feet) is rated for a 60HP. In 1986 a 60HP weighed about 250#...so does a 2001 Johnson 70HP. With that, the Johnson should be fine.

(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

 

[idonthaveaname]

Re: What size engine?

20' and up have no restriction either.

That depends. A 20' open bow, cabin cruiser, canoe, tinnie, race boat, skiff, bass boat ...

just sayin.

 

[Johny25]

Re: What size engine?

Steelespike the motor I modified this time is a 1988 electric start 25hp. I made a thread about the mod with pictures http://forums.iboats.com/showthread.php?t=532265

Not sure if that is the correct link? And my boat is a 2001 Lowe 1467t with all custom flooring and what not. I have pics of the boat mod also but may have to make another thread for that. I didn't run the 25 on the boat yet but I can easily tell after doing the mod that the motor has more HP and runs much better now.

 

[Johny25]

Re: What size engine?

Also last year I took my 1987 Johnson 9.9 and made it into a 15hp by putting a 15hp carb and exhaust on it. The 9.9 would not plane my boat with my son and I in it after I did the custom flooring. But after the mod to the motor we planed out pretty easily. My guess is we were doing 15-18mph since I don't have GPS. But when my wife and other son who is 3 got in the boat it would not plane at all. So this year I bought the 1988 25hp and converted it to a 30/35. I should hit 30mph with just my 6yr old and me and hopefully can do 22-25 with the wife and little guy in it.

 

[HAS]

Re: What size engine?

I bought the boat new in Feb. 1972, no ID tag. The boat is a Orlando Fisherman 16, it is 16ft. weighs 1280lb. with a 50hp. merc.
12 gal. of gas, 12 volt battery, tool box, prop., paddles, boat hook, 4 life preservers, cushions, anchor & line, and everything else
the law requies, plus a box of girl stuff for my wife. The boat will do 30mph. with 2 people with the 50hp. merc. The boat is rated
for 65hp. max..............THANKS A LOT GUYS............HAS