hp ratings for boat ???

[NSBCraig]

Yesterday I was looking through some posts and read about all these factors used to rate a boat for max hp.

What i don't understand is how the size of the boat applies to a outboard and yet an inboard or jet don't have any limitations except for the factory warranty.

And yet there are boats that are much smaller made today that I see on the water with alot bigger o/b then mine. These are newer boats with newer mototors and I'm talking almost twice the motor they are huge.

Kind of leds down to where it really is just a matter of structural integrity of the transom doesn't it?

Why else can you run a bigger motor on a bracket?

It just confuses me any thoughts?

 

[KCook]

Re: hp ratings for boat ???

Hull design is also a factor. In many cases an oversized motor will make a boat unstable, especially in a hard turn with lots of power. Chines, strakes, and exact hull shape all affect this. It's more than just transom strength.

Kelly Cook

 

[gcboat]

Re: hp ratings for boat ???

Kelly is 101% correct. The boat manufacturers know a whole lot more about their products than either you or I do. A lot has to do with the transom but the majority of "reasoning" is as Kelly mentioned. Can you imagine a 12 foot aluminum jon boat with 250 h.p. 4 stroker on the back? If it would hold the weight there's no way in he11 you'd be able to control it. I tell you what though - sure would be a hoot to give it a whirl - !!!!!!!!!!!!

 

[deejaycee_2000]

Re: hp ratings for boat ???

hull design ........ i've done all the crazy test by doing the overkill outboards on a small boat .... and yep it gets unstable ..... fun though .... especially when you realize you are gonna flip ......

 

[freddyray21]

Re: hp ratings for boat ???

there is a formula used by the Coast Guard for home boat builders. I am sure it has been posted on this site many times. Like others have said it has to do with length, beam, chine ect. A lot of people will put a larger motor on their boat than it is designed or rated for. I always counsel against it. Often times the boat is hard to handle or just unsafe, but even assuming it can handle the extra horsepower if you do have an accident however minor your insurance company now has a way to get out of paying a claim if you have more horsepower on your boat than it is rated for. I too am like you as to why there is no horsepower limitation on an I/O or Inboard.

 

[NSBCraig]

Re: hp ratings for boat ???

yeah so was that a big group I don't know cause again you can put any power you want in it if your not bolting it to the transom.

 

[Sailor77.7]

Re: hp ratings for boat ???

All good points. My question is how does that figure on a tri-hull? I've looked at the formula for that and it is confusing to me. I'm new to the boating as well and am working on my boat. It has problems that I will address first before I go on to fixing the outboard. You can do a search for my name and find some of the posts with pics that I have. You'll see what I mean. In plain laymans terms though...what is the easiest way to figure max engine to size?

Vr,

sailor77.7

 

[NSBCraig]

Re: hp ratings for boat ???

Hey Sailor 77.7 I'm guessing you can't read your plate huh? Do you know who built it?

I'm really just trying to learn more about boats so really the answers I got aren't of any real use to me, but I'm glad people respond this is a cool forum.

As for the points about chines etc. they really make no sense for what my question really is...

I know what my Baja 16ss is rated for 60-120hp. not a problem but I also know I could bolt any motor I want inside the boat to stringers ( that I'd have to put in cause it doesn't use stringers)

My brother has a pair of 496 HO merc's with XR drives and it would be perfectly legal for me to put one of them in there.

Not that I want anymore power then I have cause my hull lacks a pad and is really just a family fun ski boatand doesn't handle well once you get into the 70mph range. It's far to crazy.

I also know my motor is the smallest that's been on the boat in fifteen years.

Look at any jet boat with an Olds big block in it though and my boat is huge so size is NOT really the factor.

 

[tashasdaddy]

Re: hp ratings for boat ???

if you go thru this, i believe you will find ratings for inboards, and jets. they change when you get into the 20'+ range.
http://forums.iboats.com/showthread.php?t=191283

 

[Sailor77.7]

Re: hp ratings for boat ???

NSBCraig & Tashasdaddy,

Your correct that I cant read the plate. It does not list a max hp engine or capacity for passangers. It was mad by LasVegas Boat Company back in 1970. There is no information anywhere on the internet that I have been able to find on it. Wish you luck with yours though & lots of fun. Tashasdaddy, thanks alot again. You have been a great deal of help to be thus far and it is greatly appreciated. I will look at the line you provided. Have a great weekend all...

vr,

sailor77.7

 

[PowerAddict]

Re: hp ratings for boat ???

my cobalt tri-hull has a max engine weight of what I think was around 1050lbs. I guess they figure that a marine 8cyl would weigh more than that so they can still cover all bases.

 

[NSBCraig]

Re: hp ratings for boat ???

that's an interesting pdf this weekend I think I;m gonna do the math on my hull to see what it works out to.