Bow Thruster Electrical Install

[Gordon Valentine]

Hi , Just purchased a re-con Vetus 12 volt , 55kgf Bow Thruster for my B38. Purchased the 1.5mtr GRP Tunnel from Vetus as I suspect it will have to be installed aft of the fresh water tank as I do not want to loose the tank and moving the tank aft is quite a task .
Anyway my main dilema is what best to install electrically , ie, Running heavy cables (approx 5mtrs) from the 2 off 180ah house batteries , or installing a separate battery adjacent the Thruster Motor.
 By going with the 2nd option of a separate battery , can anyone advise the best option for in house charging for this as we rarely use shore power .
Vetus recommends a max of 12 mtrs for heavy cable and a max battery capacity of 150Ah ?
Our onboard system comprises of 1 off Starter Battery Bank , 2 off House Batteries 180Ah each, Engine Alternator rated at 100amp and 2 off Solar Panels fitted aft end .
Any advise would be much appreciated .

Regards
Gordon

[tiger79]

The cheapest solution is probably to run cables from the domestic bank.

If you decide on a separate battery, an AGM would be a good choice.  You could charge it via a VSR or a low-loss diode.

[SYJetzt]

I think the best solution is a separate battery adjacent to the thruster. Charging via B2B-charger next to thruster battery,  connected to house batteries. The cabling needs only small diameters, sufficient for the current of the B2B-charger.
 I former had a solution with heavy cabling from house batteries, but for the long cabling distances (i have a B46)  the cables with 50mm2 were not sufficient. Especially after long days without running engine the house batteries went weak and could´nt provide sufficient voltage for thruster.  So we fitted another AGM-type battery next to the thruster, galvanic-coupled with the house batteries and simulteanously charged with house batteries. This caused the new thruster battery in 2 years to die, because it was not sufficiently charged due to voltage drop between house and thruster battery and different ages and types of house- and thruster batteries. We replaced died thruster battery with a standard starter battery (wet lead acid, 105Ah) and fitted B2B-charger (12V/12V/20A), since then (3 years ago) everthing is fine. I think, an AGM is wasted money, because discharge characteristic of a thruster seems to be similar to starting an engine (high current over short times). In our case dimensions of battery and thruster are fully sufficient.

Regards Robert

[Yngmar]

SYJetzt has the right solution for the thruster battery setup - you'll need a B2B charger to properly charge a battery in the bow and his choice of a starter battery over an AGM makes perfect sense too (you can get AGM starter batteries too though, optimized for high CCA).

However, I'm not a big fan of putting another battery in the bow in the first place. The weight of the battery most likely exceeds that of the big cable run, and even if it won't, you have all that weight in the already sensitive bow (certainly on boats with a water tank there) instead of distributed over the length of the boat. With a separate thruster battery you can also run out of thruster juice in a critical situation, something that can't happen with a setup where the bowthruster is driven from the main batteries, which are always being fed by the alternator whilst the engine is running. Not to mention, it costs less than the extra battery plus B2B charger and is less work to install (either way you have to run cables to the bow, just different size).

[SYJetzt]

Yngmar, you are right with the weight problem on boats like Gordon Valentine ones and the lower cost.
I can´t follow you with thruster juice.
In our case thruster is drawing about 600Amp (measured with DC Clamp Ampmeter), causing a big voltage drop on house batteries, which was disturbing my electronics. With an extra thruster battery we could isolate the voltage-drop to the thruster section, if any,  without affecting the whole power supply of the boat. 
Maybe we had poor, old house-batteries, as our problem occured (we replaced house batteries too in the meantime!).
But on a 46ft boat this is obviously another thing

[tiger79]

I think, an AGM is wasted money, because discharge characteristic of a thruster seems to be similar to starting an engine (high current over short times).

The advantage of an AGM is that it's sealed and doesn't need ventilation.  It is also very flexible in terms of mounting position.  My Bavaria has a factory-fitted bow thruster, and Bavaria used an AGM battery for it.

[Lyra]

Can't provide any input, since I have no bow thruster but have a question - why not use the engine battery? As mentioned, the power consumption regime is similar to that of the starter, when the thruster is used the engine is running so the starter does not require it at that stage, and obviously the alternator charges/supports it. Maybe only get a larger battery for the engine to better support both tasks. A "jumper" between the house and engine batteries can always serve as a backup.
(I guess the exception would be some boat owners with thrusters that I see in the marina which seem to forget that it is also possible to steer a boat using its rudder).

[Gordon Valentine]

Thanks for some great input on this , I am leaning towards the additional battery next to the thruster with the B2B charger , anyone got any preferences to which type of B2B charger to use .
Also the main reason for installing the Thruster is due to the Marina we are berthed can have nightmare cross winds at times and has caught us out on the odd occasion , but due to its location and costs the price of installing the Thruster well outweighs relocating

Thanks
Gordon

[Kibo]

I have a factory fitted thruster. AGM battery in the bow, (which also has my watermaker connected to it too). This is charged from a Mastervolt charger which runs from my boat inverter system which in turn is powered either by engine, genset and solar panels when my inverter is switch on.

I ensure that the AC inverter is turned on when I have engine running so there is no possibility of running out of juice at the bow.

Probably a more expensive solution but if you already have the inverter system then I prefer it. Ensures the battery is always charged.

I agree about the AGM comments. I would not want a wet cell battery up under my bunk.