2 years Ive tried to answer this question.

Discussion in 'Surface Drives' started by Frosty, Mar 30, 2007.

  1. tom kane
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    tom kane Senior Member

    2 years ive tried to answer this question

    They are for steering,side rudders,not much steering ability there.
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    RANCHI OTTO Naval Architect

    Thanks Tom for the info....spectacular boat!
  3. Frosty

    Frosty Previous Member

    Really? , that is interesting indeed and this thread is definately going the way I was hoping.

    Its just niggling that when a Surface drive guru like Paul Kamen says some thing and you cant ask why.

    I would really like to know what he meant.

    I am hauling out next week and I am definately going to fit a "vacuum break to the trailing edge of the hulls.

    I need 3000 RPM for 12KTS and 3400 for 17KTS and only 3800 for 24KTS

    (Or there abouts)

    The dryer the props get the more they bite, wierd stuff isnt it?

    I am hoping that the vacuum break will dry them earlier and reduce my cruising speed RPM.
  4. tom kane
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    tom kane Senior Member

    2 years i have tried to answer this question

    Have a look at a new thread in propulsion..A simple jet for a small boat.
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    FAST FRED Senior Member

    Looking at the Sea Sled it would seem the "rudders" are more spoilers than rudders , unless they are mounted further out from the hull than the photo seems to show.

    AS the units seem to be well along side the hull, perhaps the drag when going straight was lessened , compared to standard rudders?

  6. Syed
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    Syed Member

    Thank you, tom kane !
  7. Janamon
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    Janamon Junior Member


    Seafury require a vacuum break because of it's 45 degree transom. If the vacuum beak wasn't there the water would follow up the transom, effectively burying the prop..
  8. Frosty

    Frosty Previous Member

    Janamon, Yes that absalutley correct, but no.

    I recenty hauled out my cat and extended the hulls by 2 inches making a knife sharp edge on the planing section of the hulls transom. I did this because I thought that maybe I did not have the props out high enough, and that the props would be burried.

    It made no difference what so ever.

    I had experimented for hours with models of transoms and a hose pipe and it is easy to sea a big difference in the wake of hulls with the slightest roundness of the transom.

    Handing the helm to my girl freind I left the bridge to go down and look at the props. There was no difference at all. Not even a difference in the rooster tali wich is only say 10 feet and about 4 feet high at 18KTS.

  9. mydauphin
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    mydauphin Senior Member

    Reason is simply

    Surface drives require air in prop. If you put prop too close to transom then prop is going to be fully submerge at anything above idle speed. The heavier the boat the worse the problem. You have to move prop behind wake, after the hump or at least move prop higher. With Arneson you have to trim up to get over hump then trim down when you get to speed. I put surface drive on a shallow draft boat- no problem but when I put it in heavy boat - I couldnt get prop into air. I am looking for ways to ventilate prop like powervent using exhaust. Like I said the draft/weight of boat has a lot to do with it.
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