Trim on a Tunnel Hull with a Jet

Discussion in 'Boat Tips' started by buckeater, Jul 8, 2009.

  1. buckeater

    buckeater Member

    Messages:
    335
    State:
    Indiana
    ive got a new lowe R1860CJ woth a 80hp at the pump jet on it(optimax). i have never had a tunnel hull before and had a ? for those that do.
    how high do you normally trim up the motor when running at full throttle to get max speed?
    only reason i ask is becuase i was a tourney last weekend and got flat smoked by a 17ft with only a 40hp jet on it. now granted the boat and motor ways a little less. but with two good sized guys and all the gear they had on it had to come close to what mine was. i couldnt even keep up with them, they just kept gettin farther down river.
    i had one guy tell me to trim it up till the water quit splashing up in the back. maybe i have to play/learn with it more.
     
  2. Tuttlecat

    Tuttlecat Active Member

    Messages:
    1,281
    State:
    Wamego, Kansas,
    trim it until your jet stream is horizontal with the water line. Do not expect much bow lift with a pump.
     

  3. Hoopie

    Hoopie New Member

    Messages:
    818
    State:
    Ohio
    you have any pictures of that set up?
     
  4. buckeater

    buckeater Member

    Messages:
    335
    State:
    Indiana
    here are two pics that i have. the fastest ive had it is almost 27mph. maybe it is all it has. i know the jets take alot of power to run but i thought i would atleast stay up with the other boat.
    http://www.catfish1.com/forums/showthread.php?t=107683
    for some reason cant get the pic of the the back view to upload on.
     
  5. BajaCoop

    BajaCoop Well-Known Member

    Messages:
    3,206
    State:
    Poplar Bluff,MO
    with our flatbottom jet I trim up until it starts to porpoise then trim down until it settle out.
     
  6. buckeater

    buckeater Member

    Messages:
    335
    State:
    Indiana
    ill try messing with it tomarrow night. after seeing that some guys get there 65hp at the pump jets running between 35-40mph. i know it has to have more in it. the water splashing over the back of the transom when i do start to trim it up just worrys me, but one guy here said his throws water up like that and when it stops it just right.
     
  7. BajaCoop

    BajaCoop Well-Known Member

    Messages:
    3,206
    State:
    Poplar Bluff,MO
    I just reread your post and an 1860 is a pretty good sized boat for that sized jet.

    Not sure how a tunnel hull compares to a regular jet but most of the guys around me that run an 1860 flatbottom are running 150 to 300 horse jet units.


    With jet units the width of the boat really comes into play. While a wider boat can run shallower it will run slower. So those guys running the 17 footers are probably much narrower than you are.
     
  8. Pip

    Pip New Member

    Messages:
    1,670
    State:
    pa
    lot of things come into play when your comparing his boat to yours.

    ---weight is a speed killer for jets.

    ---Could be your jet isn't set exactly right. even a 1/4 or 1/2" higher or lower will make a difference in speed. 1 guy i know locally had his jet sitting to low in the water, was hard to get on plane. He added a manual jack plate and started cranking it up until he got it tuned in. This added 10mph for him and a lot easier to get up on plane. The jetfoot was acting like a plow not allowing him to get the full performance of his jet.

    ---weight distribution will also play a big part in top speed.

    --- did the other guy have a 2 stroke? 2 strokes run pretty good with a jet.

    ---have you sucked a bunch of rocks and gravel up your intake? If the edge's on your impeller is rough this also affects speed. Dressing the fins up could make a difference Mine has been taking a beating and I've lost about 3 to 4 mph with my impeller getting rough edges on. When I got it new I was running 32-33. I'm down to about 28-29mph now.

    just a couple things to think about.
     
  9. buckeater

    buckeater Member

    Messages:
    335
    State:
    Indiana
    no there are no dings on the edges of the impeller. no the other guy had a four stroke. their weight distribution was all in the back being a side concle. my jet is a two stroke alot of people have tried to tell me that it is a four stroke but all i have to do is take off the hood and show them the oil resivoir. it is 80 hp at the pump wich they said if it had a prop it would be 115 hp.
    i called the dealer where i ordered the boat at this morning and they werent much help since they dont deal with alot of jets.
    ill just play with the trim and get it figured out. like i said it starts throwing up the transom when i start trimming it up, but another guy told me his does that and when it stops its good. so ill try that.
     
  10. drpepper

    drpepper New Member

    Messages:
    6,133
    State:
    Indiana
    Was that bens blazerjet by any chance? oh nevermind his is a 2 stroke....
     
  11. BajaCoop

    BajaCoop Well-Known Member

    Messages:
    3,206
    State:
    Poplar Bluff,MO
    if it was a mercury good chance it was actually a 60/40 so 40 at the jet 60 at the flywheel.

    Our 1752 with the 60/40 merc 2 stroke will run close to 30.


    You have to watch out for some of those guys running the 40 horse jets though. Since that is the horsepower limit for some parts of a river like the current river they may have a 40 horse sticker but they have had quite a bit of work done to them to "liven" them up a bit.
     
  12. crazy

    crazy New Member

    Messages:
    2,090
    State:
    Kansas CIty, MO
    I don't have a Jet motor but I do have a tunnel hull. By the sound of it this is your first boat. The only way to learn to trim is by doing it. No matter what kind of boat hull/motor combo you have. You can't leave your motor sticking all the way down in the water and expect to get the RPM's you should be getting. Trim it up until the front starts bouncing then bring the motor back down little by little. When it stops then it should be about right. You can also do this by the sound of the motor. Your motor will just hit a sweet spot. There is also another thing to remember you should have a bilge pump so who cares if you have a stream of water coming into the back of the boat from your motor. So things get a little wet. Your console is far enough forward you should stay dry. :big_smile:
     
  13. buckeater

    buckeater Member

    Messages:
    335
    State:
    Indiana
    no not my first boat had a few before this. just my first jet. had it on the river everyweekend since april you think i would have it figured out by now. guess everything is a learning curve on something new ill see if i cant get it improved friday night. it just doesnt look right seeing all the water splash up above the transom. i guess if it had the high transom i wouldnt be so worked up about it because i wouldnt see it.
     
  14. loanwizard

    loanwizard Well-Known Member

    Messages:
    3,297
    State:
    Coshocton,
    I have a SeaArk 2072 with a Yamaha 115/80.

    Fully loaded I get about 30 mph tops.

    Fully loaded means 2 13 gallon tanks of fuel -208 lbs

    2 men and gear 700 lbs

    3 batteries 300 lbs.

    I went out yesterday with 2 girls and me, 3 batteries, 1 tank of fuel, no gear and it was a lot more responsive prolly guessin another 3 mph... enough that I noticed especially now that summer pool makes shallow shallower :wink:

    Trim it up til you hear the rpms pick up pitch. You will feel the boat slow down as the pump stops catching max water. I do not have a tunnel hull and my foots leading edge is just a hair ABOVE the bottom of the boat. If I am not mistaken your leading edge should be a hair above the tunnel and the back of your foot (the lower end) should still be in the tunnel and not below the actual bottom of the boat. That DEFINITELY affects speed. Been there done that lol!

    I will look at the bottom of mine and get back to you. BTW an upgrade to stainless will get you more speed than an aluminum impeller.
     
  15. foghorn

    foghorn New Member

    Messages:
    134
    State:
    Wagoner Ok
    I guess im just old fashion the 48special evinrude will push my 14' fiberglass boat around 35-40 and it jumps up on plane fast.




    Foggy :cool2:
     
  16. gofish98

    gofish98 New Member

    Messages:
    116
    State:
    Lafayette Indiana
  17. great pappy cat

    great pappy cat Active Member

    Messages:
    728
    State:
    P.A
    Chris Gorsuch, the author of that article, came out and looked at my boat for me when I bought it. Probably the most knoledgeable jet boater in PA. I asked him the same thing. I was told to trim the motor the hole way down and leave it. You can damage youre motor buy leaning it out to much plus youre flatter on the water that way. They make spray bars on a lot of newer boats to keep water from comeing over the transome.

    [​IMG]

    [​IMG]

    [​IMG]

    Notice how they built the tunnel out to the foot to prevent spray back

    Like pip, I think you got set up problems ( motor height wrong).

    A tunnel is a performance liability youre boat will go slower than a compareable non tunneled craft. On the good side you can go 2-3 " shallower

    My best freind has a 1654 tracker grizzley(non tunnel) with a 60/40 merc 4- stroke
    I have a 1872 jet tunnel hull with a yamaha 115/80 four stroke

    Our boat go about the same speed approx 30mph give or take.
     
  18. buckeater

    buckeater Member

    Messages:
    335
    State:
    Indiana
    thanks a bunch. played with different trim settings this weekend and figured that all the way down was the best. and yes mine did come with the spray bar already rigged on it. i might get a manual jack plate for it this winter after i have a guy look at it this weekend that is real good with jets. to me it looks like it might be sitting a tick low.
     
  19. blazerjet

    blazerjet New Member

    Messages:
    299
    State:
    indiana
    Jet boats and tunnel hulls dont mix.. Its like cutting half the wing off a airplane then trying to take off. Plus they bit into the water when u turn. Jet boats are supposed to be made out of alumin? My boat runs 38 mph with a 40hr I can smoke them g3 with 90 on them.