Fishing and Workboats
Engine selection guidelines for displacement craft
It is not possible to make a general list of boat sizes and the required horse power for these commercial applications. Beta Marine are very happy to work with you the owner, a propeller manufacturer, and our dealer 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 hp per ton can be used. This should be increased to 6 hp per ton where rough conditions are more usual.
• The size of engine is often restricted by the fisherman’s licence which limits the power that can be installed. Beta Marine can assist you 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 a smaller egg whisk!! See propeller drawing for diameter limitations.
• 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 hp) 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 naturally aspirated engine to be installed and this is where Beta 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.
