How big of a jet could I put on my boat?

Discussion in 'Boating' started by Seth, Jun 24, 2007.

  1. Seth

    Seth Active Member

    Messages:
    1,807
    State:
    Owensville, MO
    I have a 1648 welded aluminum jon boat. How big of a jet unit could I put on this thing? The maximum horsepower stickers are not on the boat, but my buddy has one just like it and it is rated at 60 horsepower (for a prop).

    I was told that I could put a 90/65 on it and still be fine.
     
  2. riddleofsteel

    riddleofsteel New Member

    Messages:
    353
    State:
    NC
    (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".

    In my experience this is based on the older two stroke engines.
    To figure four stoke engines I take the HP rating this formula gives me and
    look up the weight of a two stroke engine of that HP.
    Then find a four stroke in that weight range.
     

  3. Seth

    Seth Active Member

    Messages:
    1,807
    State:
    Owensville, MO
    OK I am a bit confused. Are the length and width measurements in feet form or inches? I did feet and I got (2 x 16 x 4) - 90 = 38. That would come up to 40 then right? But this doesn't make since because my buddies boat is rated for 60 on the sticker and they are built exactly the same pretty much.

    Also, the part about motor weight, I should go by how much a motor weighs and not by how much horsepower it has
     
  4. Katmandeux

    Katmandeux New Member

    Messages:
    1,618
    State:
    Checotah, Oklahoma
    I just checked the Alumacraft catalog...their 1650 welded jon is rated for 40hp, 60 with a console.
     
  5. Seth

    Seth Active Member

    Messages:
    1,807
    State:
    Owensville, MO
    So does that mean that I could put a bigger jet motor on the boat, just as long as the actual horsepower being pushed through the lower unit is 60HP? I took the 30% power loss into account and I guess I could have up to an 80 horse jet on the boat and still be ok right?
     
  6. Katmandeux

    Katmandeux New Member

    Messages:
    1,618
    State:
    Checotah, Oklahoma
    Sounds about right. You really should check with the manufacturer of your boat, however.
     
  7. vfourmax

    vfourmax New Member

    Messages:
    251
    State:
    Va
    One thing to take into consideration is the weight of the motor. Generally the larger the engine the more weight sitting on the transom. Not good if when sitting still if the rear of the boat sits so low it can easily be swamped by a passing boats wake.
     
  8. jtrew

    jtrew New Member

    Messages:
    4,404
    State:
    Little Rock, AR
    All those things mentioned are good, commonsense things. Now for the "ain't got no sense" thing....the guv'mint. If you have a tag on your boat that lists a specific horsepower, say 60, or the formula used to calculate allowable horsepower says 60, and the gummint boys catch you with a bigger horsepower motor hung on your transom, you're gonna get a ticket. Hollerin' "But I'm losing horsepower because it's a jet!" isn't going to do any good. I know of some small bass tournaments held on F&G lakes back when there was a 10hp limit on the lakes. If a bass boat got hung up on a stump, couldn't get off with the trolling motor, and couldn't get another boat to help, they'd have to start up their big motor just long enough to get off the stump, and if an officer saw that, they generally got a ticket.
     
  9. deerhunter4

    deerhunter4 New Member

    Messages:
    817
    State:
    Illinois
    wow that is pretty stiff...Darn Guv'mint any how...

     
  10. vfourmax

    vfourmax New Member

    Messages:
    251
    State:
    Va
    I think the laws as far having an boat powered by a higher horsepower than the boat plate says varies by state. I know it is illegal to operate a boat that is overpowered in the state of Florida and if caught you will be ticketed, here in Va. there is no law forbidding the use of overpowered boats but from a liability standpoint you would be probably screwed if involved in an accident whether actually your fault or not. Insurance coverage would probably get pretty sticky also in the case of a claim.
    I would recommend staying within the suggested range of the hull manufacturer to be on the safe side.
     
  11. Seth

    Seth Active Member

    Messages:
    1,807
    State:
    Owensville, MO
    I see alot of boats around this area that are 17-18 foot aluminum welded jon boats with 200-300 HP jets on the back of them. Isn't that way over motored or am I missing something else? Most welded jons of that size that I see have much lower horse power ratings.
     
  12. RivrLivn

    RivrLivn Member

    Messages:
    194
    State:
    Missouri
    Seth, your correct alot of boats in central and southern MO put motors way over the mfr capacity plate rating. They will reinforce the transom with several braces. The down size is these boats sit a** heavy at rest.
    I don't think going with the 80/60 jet will give you any issues.
    I also don't think the Mo water patrol can give you trouble about the engine size, but I think they can give you trouble for going over the overall capacity of the boat. The total weight capacity includes people, gear, and motor. So you go sticking a 200hp motor on a boat and your at least adding the weight of a person or two.
     
  13. GatorAg03

    GatorAg03 New Member

    Messages:
    11
    State:
    Texas - I move a lot
    I have an 18 ft Xpress Aluminum boat that has a 90/65 jet on it. You should be fine putting an engine that size on your 16 ft boat. If you want to go bigger, I would talk to the manufacturer, because it would be extremely heavy back there.

    Think hard about your weight alignment. You will need a good size gas tank due to the less output 90/65 for the long runs. I usually try to put a some weight towards the front to help offset the weight balance. I love my jet engine and can run in some skinny water, just be careful.
     
  14. Seth

    Seth Active Member

    Messages:
    1,807
    State:
    Owensville, MO
    I usually have three 12 volt batteries up front to power my trolling motor that is on the boat so that should add quite a bit of weight to the front. The only reason that I would probably ever swap motors is if the one that is on there right now shoots craps on me. Hopefully that doesn't happen until I have some money saved up. :big_smile:

    I appreciate every bodies advice and help with answering my questions. Thanks