Too slow!

Discussion in 'Prop Shop' started by qwerty, May 5, 2012.

  1. qwerty

    qwerty Well-Known Member

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    Prop change time. I hit 26mph with a tail wind, lame. Min WOT on the motor is 5500 and I was at around 5300, so I'm under propped for sure, so now I'm wondering if I should go with a 15 or 17 pitch.

    Here are the numbers: Hull is a Hobie Power Skiff, 15ft modified V-hull, Suzy DF-50, 2.27 ratio, 5500-6500 WOT range, currently have a 13 pitch OEM Suzy prop doing 26mph at 5300rpm. Prop calculators have me at .095 slip, is this normal? Hole shot is rediculous, almost no bow-rise. I want balance, not top speed, so I'm leaning towards 15. Let me know if I don't know what I'm talking about. Thanks in advance!
     
  2. cutrunner

    cutrunner Cert. Yamaha technician

    Dont be afraid to turn that motor up! If the max recomended rpm is 6500, then thats where i would prop it to. Just make sure however you decide to prop it that you set it up fr how it is most usually going to be run. 2 people, cooler, livewell, full gas etc.

    Im going to prop mine for a super light load, but i can get away with that a little more than you cuz im gonna have a bit more hp
     

  3. Creek Runner

    Creek Runner Well-Known Member

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    If your running a 13" now and only getting 5300RPM, your not going to be able to turn a 15" or 17" prop. I'm with cut I like to motors to be at the higher rpm range. But it sounds like the 13" is the best prop for the job.

    Every inch in pitch is going to rougly equal 200RPM's so if you move to a 15" your going to lose 400RPM's and be lugging the engine.
     
  4. cutrunner

    cutrunner Cert. Yamaha technician

    ^forgot to mention that part as well lol.
    Im "expexcting" my boat to turn a 17-18pitch 3 blade, so a 17 will definately not work for you. Creek is probably right on the 13 pitch.
    Im guessing that hull design had more to do with why it hopped on plane so well, then the prop.
     
  5. cutrunner

    cutrunner Cert. Yamaha technician

    Also a good 13 pitch mercury prop or other higher name , powertec etc will perform much better than a 13 pitch stock suzi prop.
     
  6. qwerty

    qwerty Well-Known Member

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    Hmm, my brain was working in the other direction with the rpm thing. So you're saying I should adjust my throttle cables so I'm closer to my 6500 rpm?
     
  7. cutrunner

    cutrunner Cert. Yamaha technician

    And another note, the way you have the weight distributed make a big deal a well, and trim, and engine height. Those 3 can severly hurt your mph if incorrect. Get a straight edge and punit along the bottom of the hull and make sure your anti ventilation "cavitation plate" is equal withthe hull bottom or even 1/2 inch above. Also make sure your trimming the boat correctly. I like my boats to run with the bow pretty high up, rides better and gets more boat out of the water, thus reducing friction. So if you had a bunch of heavy stuff in the bow move it back. Alot of weight in the bow could also be why it hopped on plane so good. Does the boat appear to be heavy? I know the glass guy checked but maybe one of the original owners stored the boat with the bow facing down, allowing water to sit in the bow of the boat and soak up the foam in the bow.
    Again all are just assumptions as ive never seen it in person.

    Also, contact Junkin. He gave me some accurate gps speed/rpm stats on his rig. You can compare them to yours as hes running a 50hp four stroke as well
     
  8. cutrunner

    cutrunner Cert. Yamaha technician

    Yoy cables have nothin to do with the rpm "if they are achieving wot" and set up properly. The reason your not gettin 6500rpm is your prop
     
  9. Creek Runner

    Creek Runner Well-Known Member

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    Or simply just not enough power to achieve the RPM's for the speed you want.
     
  10. qwerty

    qwerty Well-Known Member

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    No it doesn't seem heavy, and I just checked the cavitation plate and it's pretty damn right on the money. I'll dig into the foam tomorrow. I was wondering about the bow rise on take-off, it barely comes up at all but all the weight is in the middle of the boat and then there's the motor, which is too heavy, I have my scuppers plugged because of the water that gushes in. I played with the trim a lot last time out to troubleshoot the handling but I didn't focus on the speed/trim relationship, more research to do.
     
  11. cutrunner

    cutrunner Cert. Yamaha technician

    Creek: a 50 horse was basically standard power on these boats, but i have yet to even have mine in the water so i honestly have no clue.

    Ken: looks like you got some tinkering to do ;D