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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 07-06-2008
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Bow thruster - theoretizing :)

Hypothetically speaking, if I had the money, bow thruster would do wonders for docking my boat

Now, installing it would not be technically much of an issue - there is good access and space right where it needs to go.

Electrical installation is another story. There is no way to run appropriately thick cables from where battery banks are to the bow (I barely had space for windlass cables which are a few sizes smaller). Plus, I don't really want to abuse house bank this way, and my starting battery isn't particularly large.

So, what about the installation where there is another battery - something with high cranking amps, sufficient for a few minutes operation of the thruster at a time, sitting upfront next to it? For wiring I could get away with much smaller wires to go from the main bank to the bow to charge this battery. But how could I regulate the power that goes there so that it limits the amps that are going to this battery to what the wiring can support? Ideally an additional automatic regulator/relay/whatever that would charge it at no more than 5-10 amps per hour, regardless of what other banks are doing? Are there devices that could do that out there?
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Old 07-06-2008
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Brak...remote deep cycle battery near the thruster is a good idea. Lets say 100ah group 30. Two options:
1.Echo charger which will recharge it after house bank is fully charged.
2. Separate small 3 stage charger of 20amps or less that can be run off your inverter. A bit less efficient but makes a lot of sense in terms of ease of wiring.

Now even a 2kw thruster is gonna draw 167 amps...or about 3amphours per minute of use. Thus a 100ah battery will give you about 15 minutes of use before recharging is required...so sizing your bank to the amps required needs to be considered as well...but 15 minutes is a LOT of use on a thruster. If you need a bigger thruster for your boat...then you start getting into a need for a bigger battery capacity.
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Old 07-06-2008
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It's not likely that one would uses ones windlass and bow thruster at the sametime. The cables are already there why not use them for double duty?
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Old 07-06-2008
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Quote:
Originally Posted by ebs001 View Post
It's not likely that one would uses ones windlass and bow thruster at the sametime. The cables are already there why not use them for double duty?
First, cables for windlass are about 4 sizes too small. Windlass cables are rated for 50 amps (and it really only draws 30-35). Thruster is 100 amps at least.

Secondly, it can't really be done because windlass control box is near the batteries so the cables are direct power to it. I'd have to move control box and have power up on it all the time. And then the breakers are rated differently.

These are very different devices.
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Brak,

I've done the bow thruster thing, so this isn't hypothetical, it's real world.

Island Breeze is a 56 footer that weighs 26 tons and needs help in tight spots, so the boss decided to install a thruster.

We went with the biggest DC thruster on the market at the time. It's a 13 inch, 24V Vetus.

Since that's the only thing on the boat that operates on 24 volts, we decided on another bank of batteries dedicated to the thruster. They're mounted right next to the thruster, in the watertight forecastle area. DO NOT USE deep cycle batteries for a thruster! A bow thruster is like a starter motor. Lots of RPM, lots of torque, for a very short time. Deep cycle batteries don't like that at all, just the same as starting batteries don't like little loads for extended times. It has to do with the physical qualities of the lead plates in the batteries.

Anyway, put a battery (Batteries? 24 VDC is better!) forward, but try and find a way to remove an equal amount of weight from up there or the boat will start plunging and porpoising. Remember that when you put the thruster tube in, you're removing some of the designed ability to float from the bow. Now add the weight of the motor, gear head, etc, and you've put a bunch of weight up there. We were lucky. Breeze had a bunch of lead ballast bars to put her on her design water line. We put in the thruster and batteries, then, after the yard dropped her back in the water, we added ballast until she was floating right again.

If you don't have that luxury, you may sit a little bow-down. When going to weather, the boat is going to want to stick her nose in the water because of the lost flotation.

Next, you can remove the wiring from your main house bank to the windlass, and connect them to the thruster battery (batteries), because they're the same as the thruster: lot of RPM, lots of torque for a reasonably short time. You'll be surprised (pleasantly, I might add) at how much better the windlass operates.

As to charging, we have a dedicated charger since we have two 12 volt banks of two batteries each wired in series to give us 24volts. You don't say how big your boat is, but it's obviously not a Cal 24 or something. If you tie to shore power, a second charger is no big deal.

On Breeze, the thruster bank of batteries is completely isolated from everything else. The thruster case is tied to the bonding system, but otherwise has no electrical connection to anything else on the boat.

We've never had to do it, but that means if you run your starter bank and both house banks down, you still have batteries aboard to get your engine/genset going again. It might be a pain, but it will work.

As to the suggestion of using the windlass power, I'd be leery of it. You don't say who put the windlass in, but if you did, and followed the manufacturer's guidelines, your wiring is probably on the wrong side of being heavy enough. If a yard did it, you can bet your last dollar they scrimped and maybe went a size too small.

Rule of thumb: run the device for fifteen seconds. If the wiring is warm or worse, HOT, the wiring is too small.

On Breeze, the longest cable is about four feet long, and I used 3-0 cable. The factory said I could use single 0 cable. Sorry. The thing is fused for 355 amps. I'm not going to run 355 amps through single ought cable.

If you decide on going 24v, but don't know how, ask, and we'll exchange emails or phone numbers and I'll talk you through it. No black magic involved.

Cap'n Gary
S/V Island Breeze
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Quote:
Originally Posted by camaraderie View Post
Brak...remote deep cycle battery near the thruster is a good idea. Lets say 100ah group 30. Two options:
1.Echo charger which will recharge it after house bank is fully charged.
2. Separate small 3 stage charger of 20amps or less that can be run off your inverter. A bit less efficient but makes a lot of sense in terms of ease of wiring.

Now even a 2kw thruster is gonna draw 167 amps...or about 3amphours per minute of use. Thus a 100ah battery will give you about 15 minutes of use before recharging is required...so sizing your bank to the amps required needs to be considered as well...but 15 minutes is a LOT of use on a thruster. If you need a bigger thruster for your boat...then you start getting into a need for a bigger battery capacity.
I like to keep things simple and minimal. I would probably need thruster for a total of 30 seconds per day if using a slip (to get through the turn that my boat's steering capabilities otherwise won't let me do). And my boat is relatively easy to push so essentially smallest size thruster would do the job just fine. Though maxpower recommends their 6.4hp thruster for boats 30-42' (which could easily require 400 amps)


What are these echo chargers, do you have a link to something I can look at? The description sounds very much like what I am looking for.
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I would weigh out costs and ease of installation of various scenarios. How far is it from your start battery to the thruster location? Your windlass and bow thruster should more properly be wired off of the start battery than a house bank. You may need a larger starting battery than you have but no larger than you will need for the thruster alone. Will it be easier to run new #3 cables(or whatever is the proper size for the amperage of the higher amperage device) and move the windlass controller. Since they are both motors, the load type is the same. The breaker is there to protect the wire, not the motors which have internal protection. Weigh this against installing a new battery and charging cables and an echo charger. I personally like to keep battery banks to a minimum. I like to keep things simple and I like to get the best bang for my buck. I would choose the solution that better satisfies these criteria.
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Old 07-06-2008
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well, thanks guys - lots of things to consider and again, this is a theoretical project at this point (I am already in the middle of a "big bucks" project right now, so this one has to wait)

but certainly dedicated battery or bank seems reasonable. as far as weight forward, my boat has lots of buoyancy there and a compartment that is usually empty - adding some weight might actually be beneficial.
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Old 07-06-2008
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brak -

Maybe I missed it ... what kind of boat do you have?

Perhaps some time with a really good instructor would help and you could save the boat bucks for something else.

sail fast, dave
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Quote:
Originally Posted by SVAuspicious View Post
brak -

Maybe I missed it ... what kind of boat do you have?

Perhaps some time with a really good instructor would help and you could save the boat bucks for something else.

sail fast, dave
I have Hallberg-Rassy 35, it is listed in my profile. Without going too far into this discussion (and leaving aside my sailing abilitiy), I can only say that there are certain things that cannot be done with a full keel single screw vessel with hydraulic steering. For example - it is not possible to make a 90 degree turn to starboard when confined in a fairway of less than about 60'. It is also not possible to use reverse to control turning. That is something that drivers of fin keel flat bottom boats (such as Beneteau, for example, of which I was one until this one ) usually do not realize

Now, arguably changing a slip may help - though my marina does not have any other slips (and nothing more convenient anyway). But aside from that larger issue remains - certain maneuvers simply cannot be performed.
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