will a severely barnacled hull prevent engine from reving up to full speed?

Discussion in 'Propulsion' started by sdowney717, Oct 7, 2012.

  1. Frosty

    Frosty Previous Member

    Hes posted 144 pictures in the gallery
  2. FMS
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    FMS Senior Member

    You posted a short while back you thought the boat had nothing to do with maximum thrust from its engine.

  3. Frosty

    Frosty Previous Member

    ????? And

    Are you shure your on the right thread?
  4. FMS
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    FMS Senior Member

    Maximum thrust unaffected by hull while RPM is reduced 500 rpm by hull being dirty?

    Edited Thrust
  5. Frosty

    Frosty Previous Member

    I don't know what your trying to say,-- Torque , RPM , gear ratio, pitch,all very different things and are related to produce thrust. Because different props can be fitted measuring an engine by thrust would be not constant.

    A jet engine that is manufactured by RR or GEC is a set machine --IT is sold as pure thrust available. Doe'st matter if the RB 2-11 goes on a 747 or a fighter you get the same thrust and therefore on smaller plane better performance.

    A dirty hull will, affect the performance of the boat.

    A dirty prop will affect the performance of the propeller affecting performance of the boat.

    I feel like im being toyed with?

    A dirty prop is not clean and will cause drag reducing its efficiency therefore reducing RPM and thrust --not torque unless you can not reach max torque RPM.

    Pedal down the road on your bicycle, you reach 40mph and your little legs are going 100RPM.

    Now strap a 8x4 1/4 sheet of ply to the front. Now you can only reach 20 MPH and you little legs can only do 50RPM.

    Why do you think the sheet of ply affects your legs RPM?
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    FAST FRED Senior Member

    Herrishoff used to suggest that you visualize the prop blown up , barnicals and dents,and all, to the size of the boat, to get the idea of how a bad prop would operate.
  7. sdowney717
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    sdowney717 Senior Member

    It is just that I was wondering if the hull was dirty and prop clean if that would slow down how high the engines can rev.

    I can imagine it like this.
    Totally clean prop and hull
    Boat tied to dock.
    then try a WOT on the engines.
    What will be the effect on the maximum engine rpm achievable?

    I do know the barnacle growth has big effect on forward speed and fuel usage.
  8. Frosty

    Frosty Previous Member

    It will be less RPM.
    The flow of water passing the prop would increase as the boat moves forward needing less and less energy to turn it but--the boat will need more and more energy to go faster.

    Hence a sweet spot where the boat uses least fuel.

    If you stop that by keeping the boat tied to the dock then you have static water all the way to max RPM .

    Imagine nudging you car up to a wall and driving it. You would not get full RPM even though the wheels 'may' be turning.
  9. tunnels

    tunnels Previous Member

    If it has a big effect on the forward speed what about in reverse ?? maybe it will go faster in reverse !!!! hehehehehe:eek:

  10. jonr
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    jonr Senior Member

    Centrifugal pumps use less energy/spin faster when you completely close a valve - no flow, 0 liters/min (because spinning water in a circle is less work than moving it somewhere). Does any of this effect ever occur with props - I don't know. Certainly a car spinning it's wheels will achieve higher rpm.
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