Re: Bow thruster does not work in one direvtion

Nick Newington

It seams to me, for those of us with lead acid batteries. It is important to minimise the use of the bowthruster. Having owned other boats not fitted with BT’s and manoeuvred perfectly well this is easily achieved. Using maximum 2 second bursts of the BT should be enough.
If a two second burst is not going to be enough and a difficult situation is developing then I recommend having all chargers on and/or changing plans, because if one needs the BT and it has overheated not only have you damaged your battery bank, you have placed the boat in a potentially dangerous or damaging situation.
Amelia AML54-019
Leros (back in cruising mode)

On 17 Jun 2021, at 04:38, Danny and Yvonne SIMMS <simms@...> wrote:

Hi Ken, I guess this was to me since you refer to my Super Wind 350. I pretty well agree with all you said though the only thing I might question is the need for life po batteries but that is a matter of choice.

As I said I have not measured the current draw but when I am tight reaching in 30 Knots and I roll in part of my headsail under load there is a big power draw. However all that is irrelevant. I just provided the information as an observation.

The important information is 12 years, 8 years + life out of my lead acid batteries and never running the gen set for the bow thruster. I agree with you that with a motor at idle or near idle the output of any alternator would be minimal.

Of course it is important to note the fact that, except in an emergency being swept sideways where you do not want to go, I limit my BT use to short multiple bursts. If a user puts in into use and leaves in there for long runs the situation is totally different.

Kind Regards


SM 299

Ocean Pearl

On 17 June 2021 at 11:12 Ken Powers SV Aquarius <ken@...> wrote:

I have done the measurements.  My bow thruster takes 480 Amps.  It seems there are some misunderstandings with most Alternator systems installed on the main engines, and the amount of current you will get out of your GenSet.

1. Your GenSet is usually a 6.5KW Onan, or maybe you have a bigger one, but this has nothing to do with the current supplied to the 24V system.  The current supplied to the 24V system is only a factor of the battery charger/s on board.  If you only have a 60A battery charger, you will only get 60A into your 24V battery system while running your 6.5KW Onan.

2. I don't know about you, but when I am backing into a "Parking Spot",  and I engage the bow thruster, the engine is usually at idle. "Most" alternators, on an engine at idle, don't produce much current.  If you have a 100Amp Alternator, you may get 25Amps at idle, but probably more like 15Amps at Idle.  There might be alternators that provides max current at lower RPM's, but would you want this?  

3.  Rated power output of the Super Wind 350 generator is 350Watts, which is about 12 to 13Amps into a 24V battery system.  

4.  I believe the rated power for the main outhaul and furling motors is less than 1500W.  This is less than a 60A load.  There is no comparison to the amount of current the bow thruster consumes.

So, if you have Lead Acid Batteries, and lets say your capacity is 300AmpHours...  If you use the bow thruster with no alternator, and no battery chargers, it will be over 1C, which is not so good for the batteries.  If you turn on your Genset, and your 100A charger, you are still over 1C.  And if you also have an alternator that is adding 50Amps, you are still over 1C.  

Good reason to get LiFePO4.  These issues go away.

Ken Powers

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