Selecting an engine for workboats

Guidelines for selecting an engine for displacement workboats

Unfortunately, it is not possible to create a list based on vessel length for working vessels. Too many factors determine the actual selection of the engine and the entire drivetrain. We are ready to help with the selection in cooperation with the vessel's designer or a company selecting the propellers, so that, drawing on our base of experience, you get the most efficient propulsion setup.

Fishing boats and small fishing trawlers

• Assuming the engine is used solely to propel the vessel (without trawling, hydraulic pumps, or other auxiliary equipment), a figure of 4 hp per tonne of displacement is used. This should be increased to 6 hp where the vessel may need to operate in heavy conditions. A larger power reserve should also be assumed for operation on rivers with strong currents and in tidal waters.
• Engine size is often limited by the power allocation assigned to the vessel or its owner. Because of this, by ordering a larger engine, its power output can be de-rated, allowing us to retain high torque while still meeting the regulatory requirement.
• The amount of power available after engaging the gearbox from idle should be considered, so that additional equipment mounted on the engine does not excessively reduce the vessel's ability to get underway/move. In such a situation, it is better to use a larger, de-rated engine.
• A large propeller combined with a high gear reduction ratio, e.g. 3:1, is always the more advantageous solution, as the vessel will have greater thrust at the propeller. The only limitation here may be the amount of space available for the propeller.
• Most small vessels use hydraulic net winches. Beta Marine can mount a hydraulic pump on a crankshaft extension, on rails integrated with the engine, ensuring the whole assembly is always properly aligned.
• On larger engines (over 30 hp), we can mount a hydraulic pump on a power take-off shaft on the gearbox.
• On larger hydraulic gearboxes (from 30 hp), a trawling valve can be fitted. This is a valve that bleeds off oil pressure from the system up to an engine speed of 1200 rpm, causing controlled slip in the gearbox and thereby reducing drive power. This is a very useful option when you want to hold the vessel in place while trawling, or at sea in strong wind. This option can also be useful in places with strict speed limits, where the vessel cannot go any slower — such a valve reduces its speed.

Our goal is to achieve maximum power transmitted to the largest permissible propeller allowed by the vessel's design, while keeping the shaft's rotational speed as low as possible.

In such cases, we need to work closely with propeller manufacturers, since large propellers with a large D.A.R. (Disc Area Ratio) surface are often required.

The current trend toward shorter, fuller-hulled vessels with high-power engines calls for larger, low-revving engines. This is where Beta Marine is an excellent choice. Thanks to our extensive experience, we can advise on selecting the best engine depending on the vessel and its intended use, and can also equip it with accessories not available from other manufacturers.