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Old 01-19-2018, 02:25 PM   #21
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Since it looks like you will probably install the Vetus 24V Bow160 thruster or similar, let me offer some thoughts on powering it:

You said that you will install a dedicated thruster battery in the bow that is charged by a dedicated shore power charger.

The Vetus specs show the nominal current draw is 540 amps but a fuse size of 355 amps. Hmmm? 4/0 wire which is what you should use to hook it up has an ampacity of 445 amps and that is the fuse size I would use. Locate it within 7" of the battery to meet ABYC standards.

So, what size battery to use. Well 500 amps is a lot, but many 5-8 liter engines draw that much and start fine with a single Group 31 battery. And 8Ds are horribly heavy. So I would use two Group 31s in series to power your windless. You can use AGM or FLAs the choice being the no maintenance aspect of AGMs vs cost.

Group 31s have an MCA rating of about 1,200 which means it will supply 1,200 amps for 30 seconds at 32F without the voltage dropping below 7.2V. It can probably go ten times that much at 500 amps and normal cruising temps.

With a dedicated 24V charger, you will need to put a fuse near the battery commensurate with the wire size and your charger's output. Say it is a 20 amp charger and you use #10 wire, then put a 30 amp fuse near the battery.

I am not really excited about a shore power based charger being the only way to charge up these batteries. It depends on how you use the boat. If you stay away from the dock for extended periods, then you will be ok if you run your genset for an hour or two each day. But if not and you rely on solar or the propulsion engines to recharge the 12V DC system then look at 12 to 24 V converter/chargers.

David
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Old 01-19-2018, 03:40 PM   #22
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Quote:
Originally Posted by boathealer View Post
I had a side power bow thruster on my last boat.

Over 3 years, I think the maximum continuous run time in any docking situation I had was all of 8-10 seconds. Maximum cumulative run time in any docking situation I had was maybe 30 seconds. All thrusts were very short bursts of "full power".

*I* think, if you need to run a thruster for 5 minutes (!!) or more, then you need to work on your initial positioning skills. JMHO. Based on your "doing without" all this time, I think you would be in good shape (MHO) regarding this.

Therefore, I see(saw, for me) no need for the variable speed versions, especially in view of the additional cost.
I agree that in any kind of fair weather you will not come anywhere close to timing out the thrusters. But in foul weather with a strong cross wind or strong cross currents, it can be a whole other situation.
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Old 01-19-2018, 03:41 PM   #23
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We installed 13 HP Wesmar Thrusters on Blue Sky about three years ago. 24V with batteries and chargers adjacent to the thrusters.

We had been cautioned by another NT42 owner not to go over 10 HP because the thrust could be too violent. In practice that was never the case; rather, short blips were manageable and it is nice to have strong authority when you need it.

We did contemplate variable speed thrusters by SidePower, but the only advantage we could see would be the dock holding feature if single handing, but I'm not sure I'd want to get off the boat with thrusters engaged.

And even when using the thrusters for long periods (like breaking out of ice when only the starboardside is semi free) we never timed out.

The only recommendation I would make is to go 24V and dual prop.
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Old 01-19-2018, 06:17 PM   #24
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Originally Posted by djmarchand View Post
You can use AGM or FLAs the choice being the no maintenance aspect of AGMs vs cost.
FLAs are almost always a "No" in this application. The concern is hydrogen gas from charging in what isn't a ventilated compartment.

Quote:
Originally Posted by djmarchand View Post
I am not really excited about a shore power based charger being the only way to charge up these batteries. It depends on how you use the boat. If you stay away from the dock for extended periods, then you will be ok if you run your genset for an hour or two each day. But if not and you rely on solar or the propulsion engines to recharge the 12V DC system then look at 12 to 24 V converter/chargers.

David
The simple solution here is to use a shore power charger if there is an inverter on the boat. On my boat, the inverter is on whenever the engine is running, and most of the rest of the time. The charger I use worked fine for a year on a modified sine wave inverter until I upgraded to a pure sine wave inverter.

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Old 01-19-2018, 06:56 PM   #25
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Here was my experience..... the make of the bow thruster is not important.
I have a cummins 380 engine.

Events, while docking, I used the bow thruster.... 2 or 3 seconds, the main engine shut down. Released the bow thruster, restarted the engine, engaged the bow thruster, again the main engine shut down.
Turned out to be a bad 4D start battery.... that supported both the bow thruster and the engine electronics.
Results, replaced the engine start 4D battery and after discussion with the builder, reminding him I put in a 3rd 4D house battery, I had the bow thruster rewired to the 3 house 4D batteries that also supports the stern thruster.
In my mind, when docking or maneuvering, it is more important to have the main engine running w/o fear the bow thruster will cause a shutdown of the main engine.
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Old 01-19-2018, 09:15 PM   #26
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Ive only had on/off thrusters and have done fine. I think the big advantage of the variable thruster is able to apply just a small amount of power to keep the boat in one spot (that might be nice) and by using less power it is much quieter. Current boat has sidepower thrusters which I can send the motor back and they will change it to a variable power unit. I’m not knowledgeable on this subject (actually most subjects) but why could you not use a large rheostat to make the power variable?
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Old 01-19-2018, 10:10 PM   #27
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Honestly that sounds more like it wasn't fused or wasn't properly fused. That is really the purpose of the fuse and why best practices have you fuse as close to the battery as possible. Draw passed through a fuse and allowed cables and connectors to melt?

That really sounds like an improperly fused circuit IMHO.


Sorry, but I disagree. He said the cable clamp AT the battery terminal melted. That was strictly due to a loose or dirty clamp or an improper crimp creating resistance at the joint.

A fuse would not have helped in that situation. If an overcurrent [short] occured after the fuse then yes but not in this case. It was not an overcurrent but an installation or mtce. problem.
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Old 01-20-2018, 12:07 PM   #28
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Quote:
Originally Posted by OldDan1943 View Post
Here was my experience..... the make of the bow thruster is not important.

I have a cummins 380 engine.



Events, while docking, I used the bow thruster.... 2 or 3 seconds, the main engine shut down. Released the bow thruster, restarted the engine, engaged the bow thruster, again the main engine shut down.

Turned out to be a bad 4D start battery.... that supported both the bow thruster and the engine electronics.

Results, replaced the engine start 4D battery and after discussion with the builder, reminding him I put in a 3rd 4D house battery, I had the bow thruster rewired to the 3 house 4D batteries that also supports the stern thruster.

In my mind, when docking or maneuvering, it is more important to have the main engine running w/o fear the bow thruster will cause a shutdown of the main engine.

Another example of why Tony Athens recommends keeping the engine battery isolated from anything else.
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Old 01-20-2018, 12:38 PM   #29
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Another example of why Tony Athens recommends keeping the engine battery isolated from anything else.
BUT, there is that famous rotary switch ....
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