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	Bow thruster replacement
		Starry Night's bow thruster performance has been deteriorating progressively over the last few years. Last year we replaced the bow thruster contactor with a new one, as the old one looked somewhat corroded. We were able to get a direct replacement from Albright who manufacture their SW102-3 Contactor to order. It was an exact replica of the original version but shiny and new with nice clean contacts! This certainly helped a bit, but then in September the bow thruster failed completely. An electrical check showed plenty of volts on the main connections even under "load", and a diver confirmed that the propeller was free to rotate. The bow thruster on Starry Night is fully submerged, motor and all. The advantage of this arrangement is no gearbox and a lot less noise. The disadvantage is that any remedial attention requires a lift. The motor housing sits in the centre of the prop tube and is held in place by two hollow circular legs which are threaded at one end and are secured to the prop tube with a pair of M32 nuts. Inboard, the electric cables emerge from the tubular legs.  The prop tube itself has protection bars welded across both ends.  These bars theoretically stop debris getting into the prop tube, but in my experience definitely stop debris getting out of the prop tube once in, and stop the bow thruster from being removed! The first step was to track down the bow thruster supplier. After some digging I found out that the make was Cupa, but it took a lot more digging to find out that Cupa bow thrusters were actually made by Alpatek BV in the Netherlands. Once Alpatek's web site was discovered everything fell into place. On their web site I found detailed information that enabled me to identify positively the model fitted to Starry Night,  while she was still in the water. Model CP40. Alpatek were most helpful, and though most of the information on their site is in Dutch, they sent me by e-mail an English language version of the vital removal and installation instructions, and parts list. They do not have any dealers in the UK and you must deal direct with the factory. But this was no problem; the person I have been dealing with speaks fluent English. Boat manufacturer Stevens recommended that we dispensed altogether with the protection bars as these were considered more of a liability than a benefit and they no longer fitted them.  Alpatek were happy to go along with this, so they have been cut off. With Starry Night on dry land, the bow thruster was removed. Once in the workshop it was opened up and about a litre of water drained out of the motor unit! Not ideal and probably explaining everything! I had noticed the ends of the cables inside the boat were weeping and this was probably water seeping up the cable between the conductor strands. There had been a mass of fishing line wrapped very tightly round the shaft between the propeller and the motor housing, and perhaps this had damaged the water seals. The new motor unit was duly ordered as there was no point in trying to repair the old one. It took exactly a week from arranging payment by bank transfer to arrival on my door step - not bad! The new unit was promptly installed and wired up. The latest models all come with an inbuilt thermal cut-out which has to be wired in, and an earth bonding strap to be connected. Otherwise the connections are identical. Once Starry Night was back in the water a quick test showed that everything was wired up the right way round and we were in business again. And what a difference. The bow thruster seems much more powerful. The new performance is so startling that I am convinced that the old unit was not working properly on the day we bought Starry Night back in 1999, and performance just went down hill thereafter. It was obvious that the old unit had never been removed from the boat because the original anti-debris bars were still welded in place - that means 23 years without maintenance for the DC motor. Alpatek say it should be removed for a check every three or four years at least. So all things considered, didn't it do well!		bow thruster tube with the original welded bars preparing to take a look the renovated bow thruster tube - note support fin which gets in the way of easy removal and replacement of the bow thruster itself the armature assembly - seen happier days! the less said!
Updated 12 February 2009 Copyright © 2009 Mike Hawkridge	back to top