Bowthruster Wiring Options-Ideas?

[lw395]

Ok, ok. It must be said. If you intend to power the bow thruster directly from a battery bank which is some 12 metres away from it, you will need to use at least 70mm2 cables. This is assuming that the bow thruster has a power output in the 1-1.5kW range, and thus a current draw of about 100A @ 12V. That would give you a 0.6V voltage drop, which is high, but ok-ish. Can the OP say how powerful the thruster is?

Edit: to put things into perspective, 24 metres of (tinned) 70mm2 cable would set you back about £250.

That's nearly $100 worth of metal at exchange prices.
The simple copper solution is expensive.

But so are the complications of trying to save that cost.
Don't forget that a battery will drop some voltage internally, you trade the cable drop against having one battery instead of a bank.

how about a nice little 2hp engine?

 

[Lomax]

That's nearly $100 worth of metal at exchange prices. The simple copper solution is expensive. But so are the complications of trying to save that cost.

Indeed. It's a tricky dilemma, fairly unique to 12V systems. High power devices are easier to deal with on a 24V system. Which reminds me, a third (fourth?) option would be to install a hefty DC/DC converter at the supply end, and install a 24V bow thruster instead of a 12V one. You could then get away with 25mm2 cabling, which is a lot cheaper, though on the whole it's likely to be as expensive as the other options - ballpark £250 - if you can even locate a 1kW monster 12->24V DC/DC converter. Yet another crazy option would be to have an inverter powering the thruster, if you can find a suitable 120/240VAC motor. Then the cabling would only need to be about 1mm2 OR, have a 240V transmission line, with an inverter at the supply end, and a massive 12V power supply at the thruster - a bit like having your own national grid on board

Don't forget that a battery will drop some voltage internally, you trade the cable drop against having one battery instead of a bank.

For sheer cranking ooomph, I would pick the local battery with a battery -> battery charger over any of the other options. In fact I'm just looking at what it would take to assemble such a system, for a windlass, to see if it's something I'll be able to afford this century - hence my interest in the thread. It is the nearest to a "plug and forget" solution you're likely to get, though the battery will eventually need replacing of course.

how about a nice little 2hp engine?

Third law of thermodynamics: there is no free lunch.

Edit: Second law.

 

[lw395]

I hesitate to suggest aluminium bus bars... More conduction per kilo and a lot cheaper. Until you need the terminations done.
Basically 12V is not an elegant approach to the bow thruster question.

 

[<152587>]

Hmmm. All sounds like another fire waiting to happen.

 

[Keith-i]

I'm working towards fitting a battery at the bow for my thruster. I have solved the charging issue by installing a 3 bank mosfet split-charger. The charging cables can be a modest size as only ever a charging current going through and nothing more.

 

[DownWest]

.
Basically 12V is not an elegant approach to the bow thruster question.

Quite, boat I am doing a few bits on has a 65 hp diesel bowthruster. Might be a touche bigger than the OP's, but he did change from a dedicated starter battery for it, to running 50 sq mm cables from tthe main bank, about 10mtrs away.

 

[Lomax]

Quite, boat I am doing a few bits on has a 65 hp diesel bowthruster.

So... you work on... ferries? Nuclear submarines? 65hp bow thruster, jesus christ man. My main engine is 120hp, and it's a frikkin monster if you ask me! 65hp, that's about 50kW - if it was an electric thruster, on a 12V system, you would draw over 4000 amperes, instantly vaporising any cable a normal deadly human being could purchase. The voltage drop over a 10+10M run of 50mm2 cable would be about 30V - almost three times the voltage at the supply end Fossil fuel ftw here.

Edit: I have to ask - why not switch to a 24V starter motor? Any boat large enough to justify a 65hp bow thruster surely must have (multiple) 24V and 240V electrical systems?

 

[DownWest]

Lomax
Nothing so grand It is a Dutch steel barge at around 80ft. 2 x 120hp mains and a Panda genset. 65hp for the bowthruster does sound a bit over the top.... It draws water up and pumps it out through a round vaned nozzle that is flush with the bottom. The joystick allows you to rotate the nozzle and direct the thrust in any direction. Getting round to looking at it next week, so not sure if doesn't already have a 24v starter. The main engines are 24v.

 

[Lomax]

Nothing so grand It is a Dutch steel barge at around 80ft. 2 x 120hp mains and a Panda genset. 65hp for the bowthruster does sound a bit over the top.... It draws water up and pumps it out through a round vaned nozzle that is flush with the bottom. The joystick allows you to rotate the nozzle and direct the thrust in any direction. Getting round to looking at it next week, so not sure if doesn't already have a 24v starter. The main engines are 24v.

Sounds awesome.

 

[crispyone]

A few years ago I installed a 75kgf vetus thruster in a 17m barge and ran 2 x 70mm2 welding cables from the starter battery. The thruster failed after a few uses, and I could hear a distinct chattering when I pressed the control button. It turned out that I had burnt the contacts in the Allbright contactor (relay) fitted to the thruster, because there was too much voltage drop, such that the contactor coil was only seeing about 10v when the load came on (about 400A) and kept dropping the contacts out. Load off, contact re-made .. load on, contact lost.
I rectified this by replacing the silver plated contact strips and installing a small starter-type battery in the bow, and connected the welding cables to the battery. Effectively the bow battery was being charged in parallel with the starter battery. No more problems.