Cut & Thrust
Small boat bow thrusters
This is the second article on fitting a bow thruster, the previous one is here, this time we are concentrating on small boats. Small is a relative term, lets imagine boats that typically would not have thrusters fitted, that said a lot of newer small boats have the option from the factory to have a thruster installed, if this is the case, it does make life easier as at least you know there was some provision for the installation.
Process considerations
Its the same as any other bow thruster installation, but with some caveats. Before starting, a very careful examination of the boat is required, some of these points can be especially difficult on small boats.
Cabling, the thruster motor must be powered, on a small boat that would usually mean 12 volts, the motors use a lot of amperage for a short time, this entails large battery cables, one negative and one positive, the last one I was involved with had 2 50mm2 squared cables. Is there provision to run these cables? These cables will also need to be run in protecting trunking, which further enlarges them.
Batteries, The thruster motor needs battery power, supplied by the aforementioned battery cables. This power will come from the batteries, before installation, make sure enough battery power is available, as part of the thruster installation, upgrading the batteries might be necessary.
Space, this is the biggest problem on smaller boats, to be more precise, lack of space, if the boat was never made or considered to have a thruster installed, a really careful survey/inspection of where the tunnel will be installed needs to be done. Deck supports and reinforcements in the bow area may have to be redone in order to accommodate the tunnel.
Also remember you will need physical space to install the motor and components, a support might be necessary if the motor is lying down.
Installation problems
Aside from the aforementioned considerations that should be inspected before undertaking the installation, there are some additional issues that are commonly run into.
Off centre, the propeller is meant to be in the middle of the bow, on the centreline, NOT the motor or gearbox. There are a lot of factory fitted thrusters that have this problem, not sure whether by error of installation or by lack of space, the significance of this is the thruster will be more powerful in one direction and weaker in the other, on a small boat with little windage this might not be too much of a problem, but, you really want maximum function after having gone to the expense and effort of installing a thruster.
Solenoids, due to space considerations, the solenoid might cause problems, most often with height. Some solenoids are attached to the motor in a way that allows them to be rotated so the battery cables can be attached in different directions. Some models of thruster are a smaller profile than others and may require no modification.
Servicing, in the future, some form of intervention is inevitable, make sure you can remove the motor, or at least have provision to gain access, especially to remove the cover. A couple of service items are located there, the motor brushes and also the over temperature safety circuit, the newer types of these sensors will automatically connect when they cool down, but there is a finite number of times they will work before requiring replacement.
Price
The actual components (tunnel, motor, propeller etc.) have a market value and you should shop around for the one that will serve you best. The tunnel installation costs might not vary as much as you think from a large to a small boat. The work is broadly similar and in small boats more remedial work may well be necessary to ensure the structural integrity and support of the bow area where the tunnel is installed.
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