How Fast Can I Go?

Discussion in 'Diesel Engines' started by Downtown, Jan 6, 2011.

  1. Downtown
    Joined: Dec 2009
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    Downtown Junior Member

    Another newbie question. I have a 1982 44' Marine Trader I'm restoring. 14.4 beam. Displacement is about 33,000 lbs. I pulled the FL 120's as they were toast. Replacing the black iron fuel tanks with aluminum. I am putting in 1992 Volvo TAMD 41Bs, taken from a charter boat with 1200 hours. These engines are turbo charged and are rated at about 200 hp. I plan to use the BW trannies that were on the Lehmans.

    What would you imagine my fuel burn to be at various speeds? Top speed?
     
  2. Carteret
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    Carteret Senior Member

    Boatdiesel.com has excellant calculation software. Membership is @ $25. Well worth the investment. The forums alone are worth the membership.
     
  3. Downtown
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    Downtown Junior Member

    I am am member and went in. The calculator is saying that I can only go 8.5 kts, using 69.4 shp. This is standard speed for trawlers with FL 120s. I thought with the 210 hp of the Volvos, I could get up to 12 kts.
     
  4. Pierre R
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    Pierre R Senior Member

    Oh you will probably get around 14-15 knots or so wide open throttle burning around 22 gallons an hour. At 12 knots you will probably burn around 12-14 gallons an hour. Thats a rough guess. Its not the most efficient hull to push up towards planing. It depends on the props and how you have it loaded. I am not sure how the boat will handle either. It may handle poorly.
     
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  5. Carteret
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    Carteret Senior Member

    Perhaps you might want to consider buying a planing hull vessel.
     
  6. Downtown
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    Downtown Junior Member

    Just want to know with the Volvos if I have to get up to 14-15 to run out a storm or in an emergency, I can.
     
  7. daiquiri
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    daiquiri Engineering and Design

    With 33000 lb of weight I sincerely doubt you'll manage to arrive at 14 kts with just 200 HP.
    The maximum speed you can get, imho, will be 10-10.5 kts. Propeller cavitation will probably be the biggest speed-limiting factor, even if you double the engine power.
    Cheers!
     
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  8. Pierre R
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    Pierre R Senior Member

    daiquiri my answer was for 400 hp. The Marine Trader has fairly flat buttock lines at the stern.
     
  9. FAST FRED
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    FAST FRED Senior Member

    Propeller cavitation will probably be the biggest speed-limiting factor, even if you double the engine power.

    There is also the question of weather the tranny will hold up, and weather the shafts will be too small.

    Remember the boat was planned as a 6 -8 cruiser burning 4 -5 GPH and was built as required.

    FF
     
  10. Downtown
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    Downtown Junior Member

    Fred,

    So, if I put the Volvos in with the current set-up, I should just go slow?
     
  11. El Sea
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    El Sea Junior Member

    Downtown,

    If your main concern is to out run a storm - I would recommend that you build your seamanship skills and adapt to the sea. I have a 44' Thompson with a single DD 4-53 and have never tried to out run a storm. Fourty-four foot trawlers were not made for speed, they were build for cruising. Take the time to build those skills and choose the right weather window.

    El Sea/L.C.

    "Suckin Sludge & Havin a Gas"
     
  12. Downtown
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    Downtown Junior Member

    El Sea, you found me out. Truth be told, I like going a little faster than 8 knots. Just for fun.
     
  13. FAST FRED
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    FAST FRED Senior Member

    So, if I put the Volvos in with the current set-up, I should just go slow?

    You can use many books to check on weather the tranny and shaft size are up to the new HP.

    The problem you may end up with is a boat that needs to be used outside , not suitable for the ICW .

    Diesels are not at all like gasoline engines where reducing the load makes them last longer.

    Diesels are designed to operate at a load , at least a load on a turboed engine where the turbo is actually working.
    Most industrial engines love 80% load at 90% rated RPM.
    Truck engine omarinizations will run at lower power ratings as they seldom climb hills all day long.

    But once you get below a point , say 20% of rated output or less , for very long , the engine efficiency and service life DROPS!

    Your boat was built to run with 2 fairly weak engines at 30-60hp output each , about 2 1/2 to 4 GPH . IF the turbo required the engine output to be above this range , just to show a positive boost , you will be tossing 6-8 ft waves at folks docks.

    Underloading can be a problem with diesels , not with gas.

    Underloading is a slow death . so if you only run say 200 hours a year it will take a decade or more to start the slobbering.And every time you get outside a half hour at high load will be a big help at cleaning out the carbon.

    FF
     

  14. Downtown
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    Downtown Junior Member

    Thanks, Fred.
     
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