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Thread: Brazilian small boat + 90hp merc. carb. - Help

  1. #11
    modifiedoutboard OUTBOARDER's Avatar
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    Default How much does your boat weigh

    How much does it weigh with you and bait wells full ?
    ANTHONY McCULLOCH
    modifiedoutboard@hotmail.com

    Some things never change!

    They Want it cheap..............

  2. #12
    Team Member alexdante's Avatar
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    Quote Originally Posted by OUTBOARDER View Post
    How much does it weigh with you and bait wells full ?
    Approximately 1000lb full.

  3. #13
    Team Member zul8tr's Avatar
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    Default prop

    I see that the prop hub has a noticably smaller diameter than the gear case bullet diameter. That is not the most optimum condition as seperated flow will occur aft of the gear case bullet and spoil the water flow to the inner portion of the prop. This will cause a reduction in performance but as to how much is open to debate, I think small but noticable compared to a hub that matches the gear case bullet diameter.

    The prop has rear rake that will help lift the bow and that is good in combination with the trim control to reduce hull drag which is a major force at high speed.

    Do you have the original prop for this engine?
    Was it an exhaust thru the hub design?
    If you tried it how did it perform?

    A 1000 lbs is alot of weight to deal with. At speed this has to be supported by aero lift on the hull including air compression on bottom ( aero is 2nd largest force) + hydrodynamic lift on the hull bottom (largest force from water) + bouyancy (smallest force). The hull is not the greatest design to produce aero lift so alot has to be created by hydrodynamic lift and that is a disadvantage since this lift has water drag associated with it which the engine has to fight aganst (including lower unit and prop drag and aero drag) as speed increases. Note water drag is about 780 times aero drag for an equal area, speed and conditions so reduced water drag is the most important at the speeds you are going.

    As I have stated in previous posts raise the engine and play with the trim and record the results and report them here.

  4. #14
    49ci OMC, Alum flat sabine river killer's Avatar
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    a lower unit from a 115 will have a ratio of 2.07 if you switch to a 115 lower unit the tall gear will give you more speed that works better than going to a propeller with more pitch

  5. #15
    Team Member zul8tr's Avatar
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    Default lower unit change

    As usual $$$$ = speed and that is probably a good change but changing it out could be a more expensive option than playing with setup and props.at first. Let's see what he thinks about that?

  6. #16
    Team Member alexdante's Avatar
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    Quote Originally Posted by zul8tr View Post
    Do you have the original prop for this engine?
    Was it an exhaust thru the hub design?
    If you tried it how did it perform?
    Previous tests:

    black max 12x1/2x23p 50.5 miles 5600rpm - 8" jack plate
    Laser 21p 50 miles 6000rpm - 8" jack plate
    Turbo 13.25x23p 50.3 miles - 5200rpm - 8" jack plate
    Ballistic 13.5x24p 53.1 miles - 5600rpm (blueprint by mark croxton). 10" jack plate

    best regards

  7. #17
    Team Member alexdante's Avatar
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    Quote Originally Posted by sabine river killer View Post
    a lower unit from a 115 will have a ratio of 2.07 if you switch to a 115 lower unit the tall gear will give you more speed that works better than going to a propeller with more pitch
    Quote Originally Posted by zul8tr View Post
    As usual $$$$ = speed and that is probably a good change but changing it out could be a more expensive option than playing with setup and props.at first. Let's see what he thinks about that?
    I had thought of using the ratio 2.07, because I will install a kit big foot bobs nose cone machine.

    That way I can lift more and the engine will have more consequentimente RPM.

    But my only fear is the RPM falls too much and not getting the speed you have now.

    There is a formula to know that I would only turn to change the ratio?

    best regards

  8. #18
    Team Member alexdante's Avatar
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    post the new test only at the beginning of movembro.

    I'll be traveling.

    I thank all

    best regards

  9. #19
    Team Member alexdante's Avatar
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    good day

    performed the first test after a long downtime.

    I made some changes to the boat:

    I added a spacer 2 "up with 12" total spacing.

    I installed a lower unit worked by BOB'S MACHINE.

    Go up the engine 1 / 2 "and arrive at the ultimate resource for height adjustment.

    Result: 5700RPM - 55.2 miles.

    The test time was small but I think I can get the next 56 miles.

    My prop is 13x7/8x36p EAGLE by Ron Hill.

    Thank you all

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