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Thread: Porposing jet boat

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    Default Porposing jet boat

    I have a 17.5 Wooldringe Alaskan that porposes at about 3/4 throttle unless you weight the heck out of the bow. It has a 115 Suzuki 4 stoke jet (the maximum HP allowed).

    I have been told a few problems may exist:

    1) The rear "trim tabs" may have bent-up. They are not really tabs, but the bottom of the boat sicking out past the transom.

    2) A rounded or cupped under side of the boat.

    All of these could have happened during one of a few inevitable encounters with dry water.

    Any other thoughts?

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    Member Dirtofak's Avatar
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    The 2 fixes suggested are exactly what I would say. If you believe that the bottom is cupped, take out the floor and inspect.

    Mike

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    Member akshrop's Avatar
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    I had the same problem on a brand new boat. I had to put trim tabs on it. I am now looking to put flotation pods on it instead. I couldn't go faster than trolling speed safely in mine. If you have not heard of flotation pods, take a look. I can't recommend them personally as I have not bought any yet, but I fully plan on doing so come spring. There are a couple of older threads addressing them with links.

    Good luck and good boating.

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    Member akriverrat's Avatar
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    if the bottom isnt cupped get some trim tabs to keep that bow down. my northriver will start to porpise at full throttle but if i feather it and work into full throttle i can get it to lay down and just go. i usually only use full throttle when it gets skinny and the pucker factor starts to take over .

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    Strange - haven't seen that condition before, have run that boat for many years, and know several other owners as well.

    Is the jet tab (the UHMW plate bolted to the trim tabs in the center) in good shape, i.e., not cracked, bent up, twisted, etc? It should also have a slight rise in the trailing edge, probably about 1/2", angled up about 25 degrees or so. This widget is designed to maximize the hard/smooth water entering the foot of the jet. I've had "issues" with mine before, but that's for a different thread - related to some dry land interactions

    Also, have you confirmed that when you're trimmed out to the transom, that it's actually all the way down? Does your motor have the little tab/lever you can flip to keep it from going all the way down, possibly in the way?

    Does your transom bracket have round bolt holes, or perhaps the oval ones where you can loosen the bolts and adjust it up/down? Check to make sure one of your "interactions" didn't drive the motor up vertically on the transom.

    Is this a new condition, or has it always performed like this? Is it a new motor? If so, was it rigged by a reputable shop? Getting the motor mounted at the right height on the transom is very important - off by just a hair can give you fits.

    Let us know what your inspection finds...

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    Member broncoformudv's Avatar
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    All Wooldridges have the hull extend past the transom forming a lip this is for adjusting the way they ride as well as strengthening the transom as rocks are less likely to catch on it and pull a weld apart like some other hull designs. You can bend the tabs slightly downward and this will put more pressure on the bow (like when you add the weight up there). It does not take much so try a little and see what happens. With as much bracing that Woolys have its doubtful you cupped the hull but likely you tweaked the lip on the back of the transom.

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    Member Akgramps's Avatar
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    Quote Originally Posted by Daved View Post
    I have a 17.5 Wooldringe Alaskan that porposes at about 3/4 throttle unless you weight the heck out of the bow. It has a 115 Suzuki 4 stoke jet (the maximum HP allowed).

    I have been told a few problems may exist:

    1) The rear "trim tabs" may have bent-up. They are not really tabs, but the bottom of the boat sicking out past the transom.

    2) A rounded or cupped under side of the boat.

    All of these could have happened during one of a few inevitable encounters with dry water.

    Any other thoughts?
    I had a 17.5 wooly and never had a porposing problem, I did bend up the hull extensions thru some interaction w/ river bottoms, oops. when i bent them back level or slightly down I did not notice much of a change.
    A cupped bottom should be ez enough to identify by taking a look at the hull from underneath, presuming its on a trailer.
    What I would take a close look at is the stop or limit bolt that determines how far the lower unit can travel down or (forward). On my Suzi 140 there are two positions this bolt can be placed in, I suspect the 115 is the same way. My current boat likes it with the travel limited so the foot does not go all the way forward, your motor may be set up the same way and if so I would try placing the bolt in the other posistion. It is ez enuf to identify, its about a 1/2" in diameter and fits thru the casting directly below the power trim. If so when you move the bolt and let the foot travel further forward it will push the bow down. Check it out, hope it helps.

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    Quote Originally Posted by akshrop View Post
    I had the same problem on a brand new boat. I had to put trim tabs on it. I am now looking to put flotation pods on it instead. I couldn't go faster than trolling speed safely in mine. If you have not heard of flotation pods, take a look. I can't recommend them personally as I have not bought any yet, but I fully plan on doing so come spring. There are a couple of older threads addressing them with links.

    Good luck and good boating.
    Do you have much of a tunnel extension on that boat? if so take a close look at it relative to the bottom of the boat, it should be on the same plane as the bottom. If your boat is porposing you can modify the top of the tunnel by bending it down a couple of degrees, yeah I know you will have to cut it to do so and may have to lower the motor slightly to match. What will happen is that tunnel top will act like a big trim tab and push the bow down, it doesnt take much, a couple of degrees will have a tremendous effect, guaranteed.....

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    Member akshrop's Avatar
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    Gramps I will have to check that out come spring. I still plan on the pods though. They have some great benefits to them. My real issue is that my engine to too big for the boat, so said the manufacturer that sold them together. They don't offer my combo anymore. I never got whether it was too much HP or too heavy though. The dealer and manufacturer went over it for about 3 weeks before they settled on tabs. The consul was moved, the engine was moved, small tabs installed, then finally 12x12in tabs installed. I trust the shop did everything to fix it. They even discussed remaking the tunnel at one point. I love the design of the boat, and will eventually get it rigged right.

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    Member Akgramps's Avatar
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    Quote Originally Posted by akshrop View Post
    Gramps I will have to check that out come spring. I still plan on the pods though. They have some great benefits to them. My real issue is that my engine to too big for the boat, so said the manufacturer that sold them together. They don't offer my combo anymore. I never got whether it was too much HP or too heavy though. The dealer and manufacturer went over it for about 3 weeks before they settled on tabs. The consul was moved, the engine was moved, small tabs installed, then finally 12x12in tabs installed. I trust the shop did everything to fix it. They even discussed remaking the tunnel at one point. I love the design of the boat, and will eventually get it rigged right.
    I remember when you got your boat last year and some of the issues, the first one was a crestliner? and the welds started breaking?
    And the current one was giving you fits right after you picked it up and you had to go defend our country? Heck I even offered to put some time on it for you ............... LOL.
    I had the opposite problem with the tunnel on my boat, it was angled down about 5 degrees when I got it back from the welder and it pushed the bow down way too much. I of course didnt know any better and used it that way all summer. it made it bow steer, which made the handling really suck. finally in sept. I decided to cut the side of the tunnel and bend it up a couple of degrees, which also allowed me to raise the motor 1 set of holes. Anyway, it was as if I got power steering all of sudden, it picked the bow up, it handled better and it moved the boat back onto the planning surface better. So I am sure you can push the bow down with the tunnel modified. Every boat combo can be a little diffrent getting it set up right.

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    The weight and balance of the load in the boat can lead to porposing. I can make mine porpose with the wrong weight distribution at certain throttle settings, it is normally when carrying a large load distributed improperly.

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    Thanks for the replies. To answer a few questions, I don't know how the boat performed before I encountered the bottom of the river because it was one of my first trips. I was a bit eager and inexperienced (of course).

    I have moved motor up one hole to have the jet more level with the tunnel, I will check to make sure it does not need to be moved up more.

    I will check for a stop bolt on my Suzuki to see if it is not going all the way down/forward. I know when I trim the motor up a bit, the porposing is much worse. This makes sense though. It also makes sense if the motor was able to move down more, it would tim out better. This is also the easiest fix.

    I had never heard of modifying the tunnel. I will reserve that for a last resort I think. I will also look at the angle of the jet boot as it enters the water.

    All in all, I LOVE the boat. It handles like a sports car and will go places I really should not take it. I can't wait to overload it with a moose.

    Thanks for the help.

    Anything else??

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    Member Yukoner's Avatar
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    Any chance you could take a side shot of the transom area? Might help to allow everyone to take a look at the current set up.

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    The boat is tucked away for the winter, so no good pics.

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    Remember, Motor up, Bow up. Motor down, Bow Down. These Four Strokes Are heavy... Move, Stop To last hole closest to transom.Shift your weight up front much as possible, Gas Tanks, Batt. Cooler, Anchor ,Tools, Ect... When Riding on the water Have the biggest people up front.

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    Dave,

    Where are you located? Maybe a local forum follower could take a look if you're interested.

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    Gramps when I get a chance to put it back in the water again, maybe I can talk you into a ride. Let you trouble shoot it for me.

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    I've never driven a boat that I couldn't make porpoise, or one I couldn't prevent from porpoising. It's a combination of engine trim, load distribution, and speed.

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    Quote Originally Posted by akshrop View Post
    Gramps when I get a chance to put it back in the water again, maybe I can talk you into a ride. Let you trouble shoot it for me.
    I would be glad to check it out when things thaw out, I hope I can help in some way.
    The flotation pods may be a good solution, I see G3 offers some that appear to be a bolt on arrangment, are these the ones you are considering?
    The G3 hull is a relatively light hull for the size, they still recomend max power of 90/65. I wouldnt think it would be HP issue, if so then the problem should go away when you back off the throttle, furthermore it would become a speed issue as more hp would theoretically increase the speed. Motor weight should not be a issue either as an older 17.5 wooly w/ a 115/80 has a narrower bottom than your G3..! plus the G3 is longer.
    The big diffrence is the design and the weight of the hull.
    Have you ever had a lot of weight in the boat? say a 1000 pounds or so? Did it still porpoise?
    Just have to wait for the ice to melt..

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    Member Dirtofak's Avatar
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    Do you have a 2006 or new hull or one of the older ones? They widened the hull in 2006 to accomodate the 4 stroke engine weights. I do not believe that the narrower hull would cause problems. It was done to handle the additional weight and should only slow down getting on step.

    I have a 2006 with a 115 Suzuki and do not have any problems with porposing. I would bet that all you need is to set the aft tabs. Maybe you hit them while running? I have hooked them before but have not bent mine.

    Mike

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