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Propeller Pockets- Benefits and Drawbacks

Discussion in 'General Yachting Discussion' started by jemventures, Jun 8, 2010.

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  1. jemventures, Jun 8, 2010
    #1
    jemventures

    jemventures New Member

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    I am in the early dreaming stage (3 years out) of buying a sportfishing boat in the 45 - 52 ft range and would like people's thoughts on propeller pockets. I can see benefits in reduced draft and maybe some protection for the shafts and props if hitting something like a log while running. Any other benefits? What are the drawbacks? Do they impact fuel economy, slow speed maneuvering, vibration/noise level, planing? Thanks for any input.
  2. Pascal, Jun 8, 2010
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    Pascal

    Pascal Senior Member

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    shallower draft is probably the main benefit. on the downside, you loose some low speed maneuvrability.

    i dont' see how they'd bring more protection, most of the prop still sticks out.
  3. NYCAP123, Jun 8, 2010
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    NYCAP123

    NYCAP123 Senior Member

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    As your shafts are not angled as far down you also get better top end speed and manueverability, come on plane faster and get better fuel ecconomy. All the things you'd expect from having less boat in the water. The biggest difference (and most appreciated on NJ's inland warters) though is less draft.
  4. jemventures, Jun 8, 2010
    #4
    jemventures

    jemventures New Member

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    Thank you for your input. NYCAP123 and Pascal, I appreciate you sharing your expertise on this and other threads.
  5. Capt J, Jun 9, 2010
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    Capt J

    Capt J Senior Member

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    I agree totally with the above posters. I have also run the same hulls with pockets (after them being added) and without on production boats. The speed gain is slight but there, adding slight efficiency. You do lose some low speed maneuverability and also on a sportfish you usually tend to get a slightly less clean wash then without the pockets. Personally I feel a sportfish without pockets raises more fish, but it's unproven. Draft reduction from pockets can be a MAJOR consideration on a sportfish and greatly increases places you can go.

    I agree that they don't usually offer much more protection and there is no excuse for running aground with today's modern electronics equipment in 98% of all cases
  6. Liam, Jun 10, 2010
    #6
    Liam

    Liam Senior Member

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    Propeller Pockets where invented by Italian Renato Sonny Levi. A pioneer in hull design and propulsion which his school of thought still bring lessons to the world today.

    Advantages:

    - minimizes shaft angle which increases performance
    - lower draft

    Disadvantages:

    - higher planning speed 18 knots plus
    - many tunnel prop boats also need a well placed engine and balance or else they tend to ride quite bow high and higher to the water meaning more slamming. Many English builds suffer this trend. This also means dirtier water when cruising.
  7. YachtForums, Jun 10, 2010
    #7
    YachtForums

    YachtForums Administrator

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    When properly configured, that 'dirtier' water can be your friend...

    [​IMG]
  8. Patudo, Dec 2, 2014
    #8
    Patudo

    Patudo New Member

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    Speaking of which, how effectively do prop pockets focus propellor thrust, which would in theory increase manoeuverability?
  9. Capt J, Dec 2, 2014
    #9
    Capt J

    Capt J Senior Member

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    The same as non pockets. The advantages are shallower draft. The disadvantages are that they can slow the boat down on a really fast SF or express because it's hard to get the pockets to fill properly and you lose a little bouyancy in the stern.
  10. NEO56, Dec 2, 2014
    #10
    NEO56

    NEO56 Member

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    What Capt J said...but if the pockets don't fill properly...you can "burn" the tips of the props especially if the clearance between the tips and the tunnel aren't precise...it's a tight rope at best. The pockets really don't provide more thrust in this situation. At displacement speeds, Kort nozzles will channel thrust. I'm telling you this jemventures because everyone else here knows this. Props in reverse lose 60-70% efficiency, than in forward gear (that's the way they were designed...to go forward) and a pocket reduces that efficiency, because the pocket narrows to the forward end, thereby restricting thrust.