PROPULSION AND SHAFTINGYour propulsion system is an intricatearrangement of machinery that requires muchattention during the design, building, and life ofyour vessel. It is as important, if not more, thanthe design of the actual vessel and other on-board systems.

Many times the propulsion system is chosensimply for the engine size and horse power,without considering the propeller. This can leadto a system that is not specifically tuned to yourvessel, promoting inefficiency.

These are the signs of a malfunctioningpropulsion system:

• An abnormally low steaming speed vs.RPM compared to similar vessels.

• Trouble reaching or maintainingtrawling speeds.

• High levels of vibration not attributedto engine, generators, or other on-board machinery.

• Little or no gain in vessel speed withsignificant RPM increase.

• Engine unable to reach target RPM.• Black smoke expelled through exhaust.• Chronic blade damage not attributable

to striking underwater objects.

All of the above are indicators that yourpropulsion system is either malfunctioning or isnot optimized for your vessel.

OPTIONS

Below are several options to improve theefficiency of your propulsion system. These arelisted in order of the required capital investment.

1) Perform maintenance before, during,and after the season includinginspection and replacement of all filtersand lube oil. The shaftingarrangement, especially the bearings,couplings, and stuffing box, should beinspected at these times as well.

2) Alter or replace your fixed pitchpropeller. Many of the symptoms above

are due to improper propeller selection.Unsuitable propeller characteristics(diameter, pitch, skew, and/or numberof blades) can lead to majorinefficiencies. The greatest gains inefficiency can be achieved byincreasing the diameter, if you havethe clearance.

3) Install a nozzle either ahead or aroundthe propeller. Nozzles capture and

positively alter water flowing towardsthe propeller. They typically increasebollard pull, steaming speed, and/oroverall propulsive efficiency. Someoffer increased ice protection for yourpropeller, although damage sustainedby the nozzle itself is costly to repair.Each nozzle also has its downsides, thegreatest being the increased drag thenozzle introduces being underwater.

Power losses on vessel with highly efficient propeller and a power take-off (PTO) for electric-power generation on gearbox

4) Install a controllable pitch propeller(CPP). A CPP is a propeller that isequipped with complex machinery thatallows the operator to alter the pitch oncommand. This makes it ideal for bothoptimized towing and steamingspeeds. CPP’s also have drawbacks.They require significant upfront capitalinvestment, and, if damaged, can becostly to repair.

5) Alter your engine and transmission.Depending on your operationalsituation, great efficiency gains can befound in changes to your engine and/ortransmission. If your vessel is over- orunder-powered, it means that theengine is most likely not operating atits optimal RPM. This could beremedied by an alteration to thegearbox, but in more severe cases,changes are required to both.

ALTERNATE RUDDERS AND ADDITIONS

Alternate rudders and additions can deliver anincrease of 3% to 6% in fuel efficiency. This isdue to the increased maneuverability and coursekeeping, increased lift and lower drag, and lesscavitation erosion, fewer vibrations and reducednoise.

Discuss the various possible options with aqualified naval architect/engineer. There are anumber of options available.

All of the above are viable options to increase theefficiency of your propulsion system. All requiresome degree of capital investment and shouldonly be considered if your enterprise can supportit.

Before deciding if new propulsion equipment isthe correct choice for your operation, considersuch factors as:

• the suitability of the proposedmodification

• upfront cost• payback period

• the age of the vessel and existingequipment, and

• the sustainability of the fishery inwhich you are currently involved.

You should discuss your options with yourbusiness manager/accountant/book keeper,equipment manufacturers, and a naval architector engineer before making a decision.

Semi-spade rudder

Spade rudder

Diameter of this propeller is significantly undersized for this boat.