Q As my crew become less strong in handling a boat pole and my manoeuvring skills deteriorate, I am considering retro-fitting bow thrusters to our 52ft boat.
I am intrigued that I have read little about hydraulic powered thrusters, yet electric ones seem beset with problems of charging, shorting and only being useable in limited bursts.
Any advice? What sort of boatyard should be entrusted with the work? JOHN RICH, via email A TONY REPLIES: First ensure it is physically possible to retro-fit a bow thruster, it requires a substantial tube across the full width of the boat. This could obstruct the cabin walkway, cause problems for gas bottle stowage, or mean fitting a smaller water tank.
A hydraulic bow thruster will require hydraulic pipes (not easy to hide and messy if they burst) running the length of the boat. It will also require a means of driving the hydraulic pump which adds complications: a power take-off from the gearbox (if available), belt drive from the engine (with the need for jockey wheels and tensioners), or an electric pump (with the same problems of limited use as an electric thruster, albeit at least the batteries will be close to the alternator).
Hydraulic thrusters are not necessarily a bad idea – for example, if you already have hydraulic power for winches or something similar.
The main problem with electrical ones is adequate charging because of long cable runs. If you keep the bow thruster batteries very well charged, the charging current flowing will be small, but once it starts discharging you get into a vicious circle where the high charging current causes volt-drop, which in turn reduces the charge and leads to even flatter batteries. This can be avoided by installing thick enough charging cables.
Alternatively, if you have mains (eg, you use an inverter 24/7 for a mains fridge, charging from a dedicated mains battery charger at the bows minimises problems.
These motors will wear their brushes: follow recommended service intervals to keep on top of wear, and clean brush dust out of the motor as this can cause shorting. Burned cables or connections can also be caused by using the thruster with discharged batteries: as a motor slows below its design speed, the current draw rises, so things can burn out.
Whichever yard you use, make sure they use very thick wall tube (or thinner tube with a wear insert around the impeller) to protect against cavitation pitting, and that they do not weld a mesh over the tube ends as it needs to be removable to black the inside of the tube.
Retro-fitting a bow thruster can be done