Engines for Fishing & Work Boats with Displacement Hulls

It is not possible to make a general list of vessel types, sizes and the required horse power for these commercial applications. Beta Marine are very happy to work with you the vessel owner, a propeller specialist / manufacturer, and our a local dealer or engine installer to arrive at a suitable choice based on past experience and the following general principles.

Fishing (Potting/Long Lining) and ‘Free Speed’ Work Boats

  • For general propulsion work (where no trawling is involved) the rule of 4 bhp per ton can be used. This should be increased to 6 bhp per ton when used in heavier seas and or tides.
  • The size of engine is often restricted by a fisherman’s licence which limits the power that can be installed. Beta Marine can assist by de-rating a larger, higher torque engine, to meet the horse power requirements of the licence, but at a lower rpm.
  • Consideration has to be given to the amount of power required at or near tick over, to drive a hydraulic hauler as well as move the boat. A ‘de-rated’ larger engine is best for this application.
  • A larger propeller with say 3:1 reduction ratio is always going to be more efficient and give more bite than smaller propeller with a lower reduction ratio. For more detailed information please refer to Propeller Guidance.
  • Most small fishing boats require a hydraulic hauler / winch. Beta Marine can mount your hydraulic pump off the forward end of the engine with extended rails and a cross member so that everything moves together.
  • On larger engines (above 30 bhp) we can fit your hydraulic pump on the gearbox PTO.
  • Trolling valves can be fitted to a suitable hydraulic gearbox above 30 hp. This valve controls the gearbox oil pressure from tick-over up to 1,200 rpm and causes slippage in the gearbox so that the output rpm is reduced. A very useful option when hauling and trying to hold the boat on station into the wind and sea.

Trawlers and Tugs

In addition to the items listed above the following should be noted

  • The aim here is to get the maximum allowed horse power transmitted to the largest propeller the boat can accommodate at the lowest shaft rpm.
  • A propeller designer needs to be involved as very often a 4 blade propeller may be required.
  • The trend towards shorter, fatter boats with plenty of horse power calls for a larger engine/s to be installed and this is where Beta Marine and our dealers can advise on the most suitable unit including accessories such as PTO, clutched or un-clutched pumps, trolling valves, reduction ratios, hydraulics etc.