Bow thrusters - sizing & experience of ?

[pragmatist]

About to bite the bow-thruster bullet to save a few grey hairs (ours & others) and give us more scope on/off our pontoon mooring with a Rival 41. (And no, Snow Leopard, it doesn't mean we admit to failure in the parking stakes !)

Does anyone have experience to relate on using a bow thruster with a boat like this (10 tons design weight, long fin, small engine) ? And has anyone got comments on sizing - have read all the Vetus calculations but they're a bit esoteric, especially calculating the lateral wind area.

<hr width=100% size=1>a pragmatist is an optimist with a boat in the UK

 

[jonjo]

Re: No experience

Having the same thoughts as you.

I question how much power is really needed if an owner just wants some extra parking assistance. The smallest Vetus provides 25Kg of thrust which equates to a significant muscle power pulling on a bow line.

I plan to experiment by attaching a line to a stanchion at the probable position of a bow thruster tunnel then let my bow float free in various wind and tide conditions. Using a luggage weighing hook I can then see how useful 25kg is in getting the bow back alongside the pontoon.

Do you know where the tunnel will fit on a Rival 41, I ask because the slender bow of a Nicholson 38 is a problem?

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[pragmatist]

Re: No experience

Measurement method sounds interesting - will be fascinated to hear. Must admit when trying to hold her beam onto a big wind it seems _very_ difficult. Emailed Vetus who recommended a 75 which seems OTT to us. Our biggest problem is our pontoon is an alongside mooring and if we get a westerly we can't get off without a strong ebb and if its an easterly we have trouble getting in !

Neither Sir nor the experienced chap at the boatyard seemed bothered by the fine bow although I raised the issue - whether they'll feel the same way when she's out of the water I'm not sure !

<hr width=100% size=1>a pragmatist is an optimist with a boat in the UK

 

[andyball]

Re: No experience

A sidepower (nearly) 8hp (is that 75kgf?) works wonders on a friend's nauticat 44 with lots of windage.

It's perhaps marginal in F6+ winds, but still helpful of course.

On a boat with rather less windage/length/weight...wd think 8hp good for almost any conditions, though the on/off nature of electric bow-thrusters could be annoying if too oversized? (except with speed control, but as a vetus option that's nearly £1000 !)

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[iangrant]

If you are around Northney then you are welcome to take a look at the one I have installed.
Any more than a force 4 and the bow thruster is really not much help. I have to resort to springings/ramming the jetty going in backwards/forwards etc...

You'll have great fun in marinas where the old soaks rub their chins and say "you'll never get out of there" - wrrrrrrrr.. bye

Ian


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[howardclark]

I've got a 14tonne boat with 12m hull. Fitted a 80kgf Vetus which works fine when 'parking'. Even so in a tight marina above F5 i'd be struggling so it's not a cure-all. The same one should give you a little more power than me if you fit it in the same relative position. I suspect the next one down would be too small.

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[Boathook]

I fitted a Vetus unit the other winter and used their calculations for the size. The wind area is a guessimate along with other measurements but it is a start to see what size is required. The thrust quoted though is in ideal installation conditions so knock off at least 10%. If in doupt fit the bigger unit such as the 55 which has the same size tunnel as the 35. The power coming on and off has not been a problem so far as the boat takes a while to react !

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