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Thread: staying within limits of data plate?

  1. #1

    Default staying within limits of data plate?

    So what's your take on the information on a boats data plate. Is it sort of a guideline or set in stone dont ever go over the posted limits sort of thing.

    Specifically I am referring to the max hp rating, my 16 foot high sided aluminum semi v boat has a max rating of 25 hp but would I be ok if I went up to say a 30 of even 40 hp motor with a prop or a jet on it. I understand if it were a jet I would lose 30 percent of the horsepower but my concern is the overall weight of the bigger motor hanging off the transom will this create too much stress. Or is the max hp rating designed for safety of operation while its moving, or is it there so your boat doesnt come apart over time at the higher speeds you would be traveling at with a higher horse power motor.

    Thanks for your input on any questions, feel free to relay any lessons learned the hard way since that's usually the way I learn anyhow!

  2. #2

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    Quote Originally Posted by OIF Vet View Post
    So what's your take on the information on a boats data plate. Is it sort of a guideline or set in stone dont ever go over the posted limits sort of thing.

    Specifically I am referring to the max hp rating, my 16 foot high sided aluminum semi v boat has a max rating of 25 hp but would I be ok if I went up to say a 30 of even 40 hp motor with a prop or a jet on it. I understand if it were a jet I would lose 30 percent of the horsepower but my concern is the overall weight of the bigger motor hanging off the transom will this create too much stress. Or is the max hp rating designed for safety of operation while its moving, or is it there so your boat doesnt come apart over time at the higher speeds you would be traveling at with a higher horse power motor.

    Thanks for your input on any questions, feel free to relay any lessons learned the hard way since that's usually the way I learn anyhow!

    It is for all the reasons you listed. One other is the exra weight will cause the boat to be stern heavy (especially if you go with a 40 hp four stroke)which is really not that great of a thing. I kind of doubt that a 30-40 hp motor would move it fast enough to really have to worry about it coming apart as you probably wouldn't be going that much faster than you would with a 25. And while you probably would get away with overpowering your boat, why risk it? They have those hp recommendations for engineering reasons and I assure you that they didn't just come off the cuff of their sleeve with them.

  3. #3
    Member Akgramps's Avatar
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    Quote Originally Posted by OIF Vet View Post
    So what's your take on the information on a boats data plate. Is it sort of a guideline or set in stone dont ever go over the posted limits sort of thing.

    Specifically I am referring to the max hp rating, my 16 foot high sided aluminum semi v boat has a max rating of 25 hp but would I be ok if I went up to say a 30 of even 40 hp motor with a prop or a jet on it. I understand if it were a jet I would lose 30 percent of the horsepower but my concern is the overall weight of the bigger motor hanging off the transom will this create too much stress. Or is the max hp rating designed for safety of operation while its moving, or is it there so your boat doesnt come apart over time at the higher speeds you would be traveling at with a higher horse power motor.

    Thanks for your input on any questions, feel free to relay any lessons learned the hard way since that's usually the way I learn anyhow!
    Data plate and transom strenght are two seperate things. The data plate is required for boats under 20 feet. as is floatation, and it simply means the manufacturer is guaranteeing there is enough floatation for the capacity on the plate. Thats it. It really does not mean the boat can not safely carry more, it just means there would not be adequate floatation.
    As far as the transom goes, bigger motor typically means more weight, especially with todays heavy 4 strokes. so cannot answer that question, but I do know many boats can exceed the rating safely and suspect a 30/40 hp motor on your boat would be ok. what brand of boat is it? how well is it built?

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    Member Rod in Wasilla's Avatar
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    Quote Originally Posted by T.R. Bauer View Post
    ... They have those hp recommendations for engineering reasons and I assure you that they didn't just come off the cuff of their sleeve with them.
    I think you would be surprised at just how "off the cuff" the horsepower ratings are for small boats. And the "engineering reasons" are more like "liability reasons". You should read the Coast Guard's Boatbuilder's Handbook sometime. If you look at the method used to determine the horsepower rating of a small boat, you'll see that it has little to do with whether or not the boat is safe with a given motor... it is, at it's simplest, a function of the length and width of the hull.


    Thas being said... yes, I have owned boats that were over powered (still do). And yes, they operated just fine with no adverse effects. And no (due to the inherent liability mentioned earlier), I would not recommend overpowering your boat. It's just like towing beyond your trailer or tow rig's rated capacity. It may be just fine for 99.999% of the time. But, that one isolated incident that goes wrong will have the lawyers frothing at the mouth for someone to blame. And if/when they find out that you had exceeded the rated capacity, they've got you over a barrel.

    My two cents. Spend at your own risk...
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    Member tccak71's Avatar
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    A guy I know had a Hewescraft River Runner and the sticker recommended 80 hp prop and 60 hp jet. He put a 90hp jet on it and it bent/mis-shaped the transom badly, had to pay to get it fixed and reinforced. Quite a few rivets started to come loose too (riveted hull).


    Tim

  6. #6

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    Quote Originally Posted by Rod in Wasilla View Post
    I think you would be surprised at just how "off the cuff" the horsepower ratings are for small boats. And the "engineering reasons" are more like "liability reasons". You should read the Coast Guard's Boatbuilder's Handbook sometime. If you look at the method used to determine the horsepower rating of a small boat, you'll see that it has little to do with whether or not the boat is safe with a given motor... it is, at it's simplest, a function of the length and width of the hull.


    Thas being said... yes, I have owned boats that were over powered (still do). And yes, they operated just fine with no adverse effects. And no (due to the inherent liability mentioned earlier), I would not recommend overpowering your boat. It's just like towing beyond your trailer or tow rig's rated capacity. It may be just fine for 99.999% of the time. But, that one isolated incident that goes wrong will have the lawyers frothing at the mouth for someone to blame. And if/when they find out that you had exceeded the rated capacity, they've got you over a barrel.

    My two cents. Spend at your own risk...
    Rod,

    While I see you point, I don't think a formula is really off the cuff of the sleeve (although I will concede the general boat builders guide for dummies probably is that you posted). Clearly boats are different and different boats made by different manufactures have different ratings. Some boats (like my 16 foot hewescraft I use on the Little Su) are rated for 20 hp. Others like my 16 bayliner ski boat (outboard), is rated for 115 hp. Both boats have a data plate and they while these boats clearly have approximately the same dimensions, they have very different hp rating plates. While I am not here to argue, obviously these two boat builders used a completely different formula in finding max hp. Like you pointed out, these rating are done for liability reasons which are directly tied to safety and risk factors due to the fear (and real risk) of being sued because some catastrophic failure occurred somewhere on the boat. While I am certain there is some wiggle room in hp ratings, I seriously hope that these data plates are done by engineers using mathematical models for their given hull design. If not, I am kind of scared. Overall, I think you and I are speaking in unison; over powering your boat is never really a good idea.

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    Member akshrop's Avatar
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    My boat was rated for more engine (weight is my belief) than it could handle. The boat and motor are both Yamaha and were a manufacturer package. They do not offer it any more. Lucky me being the test bed! My boat was simply not drivable at all. The bow would porpoise 10 feet into the air (read 45-60 degrees). I truly thought it was gonna flip the first time out. Now that being said, if you can afford (dollars and safety) to experiment, so be it. I would be very careful exceeding HP rating without knowing what I was getting into. I do on occasion over weight my boat, but I take safety and speed into consideration and pay a lot more attention to how the boat is handling. I would upgrade to a hull that was rated for the engine I wanted before I would overpower without a controlled test.

  8. #8

    Default Check with manufacturer

    Very interesting thread. I bought a 17 ft flat bottom Alumaweld a few years back. The plate said 90 hp (65 jet), which I started out with. I had dealer put a center console on and a full top. It took for ever to go on plane and had to be run at WOT to stay on step with two men and gear. I talked with dealer and said I wanted to go to 200hp (150 jet), they hesitated, but on my assistance called Alumaweld. Alumaweld said sure! What a difference in performance, I jump up on step and easily cruise at 3/4 throttle. My feeling from working with Alumaweld is that manufactures can give you some good assistance and advice.

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