I was just wondering how closley you should follow what amount of hp your boat is rated for, ie. if the boat says max hp is 175 and you drop a 225 on it what will happen. Will the boat just be faster or do you run some kind of risk because of the added hp and weight on the back end.

Other than the fact that it is dangerous to over power a boat, you may run into problems trying to insure it, and if it's a bass boat, forget about fishing any kind of big money tournament out of it, as no overpowered boats is one of the rules common to all major ciruits. The other thing you have to worry about is that it eliminates a large majority of potential buyers if you ever want to sell it.

HP ratings are related to length and width of the boat.

From the coast guard regs concerning HP ratings (assuming remote steering and minimum 20-inch transom height):

Length over all
times width at the transom
times 2
minus 90.
Round the result up to the next multiple of 5.

So an 18.5ft boat with with a 7.1ft transom width would be rated at 175 hp.

Boats can be rated higher that this if the manufacturer proves they can pass certain on-the-water tests involving high-speed turns and what-not. Lot of boats now are rated for "any V-6 outboard".

The risk is that the motor will be able to push the hull beyond its handling capabilities (apart from what kingwood already mentioned).

Weight is not the biggest problem, i think the extra stress on the hull from the speed would be a bigger problem.

Also, some states (i.e. OK) have regs against exceeding the C.G. plate and if you an accident you are screwed.

for safety reasons it's just not a good idea to exceed the rating plate. whatever it's rated for is what should be on it.

Which brings up the argument...

I can drop a 900 hp V-8 in a stinking Vega, and NO problem drive it up and down the road.

Someone please explain the difference.

not safely.

I've seen more people hurt/maimed/killed in 12' johnboats than anything else, speed isn't the issue, it's the idiot pilot.

you can drop a 300hp merc on a 16ft skeeter. no law against it. no difference.

No difference, really. The first time you do a 4 grand neutral drop or dump the clutch in that Vega, you'll split it in two unless you do some serious structural modifications to it.

Like anything, you can exceed the limits of what a particular design calls for, but you are running the risk of pushing it beyond the breaking point.

Weight can be an issue. I don't know if they still do but for a while Allison rated it's 20'+ boat for a maximum outboard weight. It was over the 20' length where it can be rated as "unlimited" but they put a maximum weight for the outboard instead of the horsepower. Not sure if that particular boat that they still make is rated like that.

This may not be tha place ta ask, but got a question 'bout HP ratings and tournament fishin'. Do tha rules go by manufactor's rating or CG rating. Ally being a good example, Recommended Manufactor rating on tha 2002 and 2003 is 150 but being over 20' CG is unlimited. My insurance Co. is happy with tha CG rules. I just figured if ya can make an INSURANCE co. happy ya could make anyone happy.

Most Allison's have no horsepower or weight restrictions, just recommendations. Allison recommends engines no heavier than 400lbs on the 2002 and 2003 and horsepower between 90 and 150 "for warranty and efficiency" but an average horsepower for these boats is probably somewhere above 225.

Their 21 footers used to have the same restrictions but within the last year they changed that to give them a 225 horsepower limit. They will go in the upper 80's when lightly loaded with a 225pro xs.

TLW, the rules as written on BASS and FLW are slightly different.

In FLW tournaments from the way written, no Allison boat could fish one of their tournaments. Their rules require a plate with a maximum horsepower given and since Allison does not give one or even list unlimited horsepower they fail to meet this criteria. I have heard that they have allowed some boats with 150 to fish before but they are not required to.

BASS is a little different in that they say the boat must have the plate only if required so the way Allison's plates are written they would be allowed up to the maximum 250 horsepower. That is for the 2002 and 2003 and XTB. For the new 21 footers they have a 225 horsepower limit.