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Diesel Marine Propulsion Engines & Marine Generating Sets

Engines for Vessels with Displacement Hulls

The basis of the following guide is that the maximum displacement hull speed is to be achieved by a clean and polished hull in calm sea with no windage.

Racing yachts may wish to opt for more limited horse power as the engine is primarily only used to reach or leaving moorings, motor sailors or yachts used in heavier seas and or tides may opt for up to 30% more horse power to ensure an adequate safety factor is available.

Engine power, rpm, gearbox reduction ratio, propeller diameter and pitch are all variables that will affect a displacement hulls performance and as a consequence is a specialist subject that for new builds, the vessels designer should be consulted.

For vessels which require repowering, there are existing guidelines and or parameters that are already in place to help in making the correct replacement engine choice. The existing engine, gearbox reduction ratio and propeller performance compared to theoretical maximum hull speed for the vessel will be a good indicator on whether it can be improved or not.

Additional there may be some set parameters such as the distance between the centre line of the vessels propeller shaft and the hull that may or may not allow a larger more optimised propeller to be used. If the propeller`s diameter is restricted, this can in part be compensated for by changing the propeller pitch, but there are limitations. For more detailed information on propellers visit Propeller Options.

  • A general engine guideline for yachts with a displacement hull is the weight in tonne multiplied by 4 hp.
  • Theoretical maximum displacement hull speed in Knots = 1.3 (or 1.4 for a sleek hull) x √ Water Line length (in feet).

Theoretical Maximum Displacement Hull Speed

Water Line Length in Feet:

Results

Approx. Calculated Boat Speed in Knots:

EngineBHPYacht Displacement Weight in TonnesLWL in Feet (Water Line Length)
Beta 1010 bhp @ 3,000 rpm1 - 222 - 24
Beta 1413.5 bhp @ 3,600 rpm2 - 3.524 - 26
Beta 1616 bhp @ 3,600 rpm3 - 425 - 28
Beta 2020 bhp @ 3,600 rpm4 - 526 - 32
Beta 2525 bhp @ 3,600 rpm5 - 627 - 34
Beta 3030 bhp @ 3,600 rpm6 - 732 - 36
Beta 3535 bhp @ 2,800 rpm8 - 936 - 38
Beta 3838 bhp @ 3,600 rpm9 - 1037 - 39
Beta 4545 bhp @ 3,000 rpm9 - 1138 - 40
Beta 4343 bhp @ 2,800 rpm10 - 1238 - 42
Beta 5050 bhp @ 2,800 rpm12 - 1542 - 45
Beta 6056 bhp @ 2,700 rpm15 - 1743 - 46
Beta 7070 bhp @ 2,800 rpm17 - 2244 - 47
Beta 7575 bhp @ 2,600 rpm17 - 2246 - 50
Beta 8583 bhp @ 2,800 rpm21 - 2348 - 51
Beta 9090 bhp @ 2,600 rpm22 - 2450 - 52
Beta 10599 bhp @ 2,600 rpm24 - 2651 - 53
Beta 115115 bhp @ 2,600 rpm27 - 3352 - 55

Beta Marine Limited will not accept any responsibility or liability for an incorrect engine selection.

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