....best investments I made. I have a 7 hp on my Moody 42 ketch.
With a bigger yacht and todays crowded marinas I wouldn´t dare to live without it.
Cannot find any drawbacks
..yacht in Scotland -99 and the thruster (made by Sleipner/Norway) was fitted there by a local yard. So it´s been in use for three years now.
My boat has a 24 V system, which in this case is a benefit, it´s much easier keeping up cable areas for min. voltage drop.
A long run with 12 V means VERY beefy cables.
I cannot see any problems fitting by yourself if you are a decent DIY-man.
Probably the most difficult thing is the placement of the tube and doing the correct measurement. There was an article about this in PBO (might have been YM) some years ago.
I would have done it myself if it haven´t been for the fact I´m living in Stockholm and the yacht was at that time in Scotland.
Bearing in mind the fact my boat displaces 12 tons and has a lot of windage and a lot of sailing is done by myself and my wife only I would say that the thruster is one of the additional goodies I value highest.
The only tip I really can give you is a comment regarding placement of the thruster. In my case, because of location of the forecastle bunks the thruster finally ended up pretty long forward - and thus high relative to the waterline.
The distance from WL to the tube is exactly the minimum distance Sleipner recommends.
This has a drawback if there are some waves when manouvering - the thruster can sometimes suck some air - which affects thrust very much.
So, try to get it as low as possible, the recommended minimum distance (in my case equals one tube diametre) from waterline is REALLY a minimum distance.....
....noisy.
But this noise sounds like music in my ears compared with the noise of a 45 lbs CQR bow anchor sweeping along a neighbouring yachts topsides and ripping off stanchions...
Especially in Sweden, where most of the berthing in marinas is done with a bouy/or aft anchor and bows to a pontoon, a bigger yacht with huge windage combined with strong crosswind can be a little bit too thrilling to berth - without a thruster.
It´s only a matter of yacht size I think. Having a bowthruster on a 30-footer displacing 4 tonnes might be unecessary, even ridicoulous. But on my 42-footer displacing 12 tons I think it´s justified, at least if I intend to go into crowded marinas and harbours often.
Regarding hydrodynamics, of course you are right. But you have to pay something for elegant manouvers!
I have just fitted a Vetus 55. If I was doing it again I would try to get the yard to bond the tube in. working upside down with epoxy resin is a nightmare. The cutting of the holes for the tube (once marked out) was easy, though always measure, measure and measure as you only cut once!
I am now on to fitting switch gear, battery and boxing the whole lot up. Hopefully marinas (& our mooring) will be easier though anchoring for the weekend is cheaper.
I had the yard do the tube and everything else myself on my Vetus130kgf.
Electrics are easy push fit connectors and the battery is simple...the longest part of the job is headlinings of and on again, looming wires rights.
As far as 'is it useful' I now have supreme confidence taking my 46' out with one crew....whereas before I always wanted one person forward and another aft as marina is very crowded.
There was an excellent article in PBO 412 (April 2001) by a chap who had fitted a bow thruster himself. I recently fitted a Vetus 55 and referred to that article while doing so. It IS a nightmare epoxying the underside of the tube. Vetus recommend a minimum depth of one half of the diameter, which I did. I have not yet tried it out as my yacht is still out of the water but, after reading other posts, I now wish that I had fitted it deeper.