Anchor Windlass/Bow Thruster Battery Recommendations

Dec 29, 2008
805
Treworgy 65' LOA Custom Steel Pilothouse Staysail Ketch St. Croix, Virgin Islands
We have a 24 Simpson Lawrence dual windlass, and we need to replace the batteries again after 5 years. This is a 24V bank, and I have never been sure what is the best battery chemistry for this use. Similarly, for the 24V bow thruster. I'd like input from those who actually know, what is the right chemistry to use for these applications. I'm not using lead acid for either application, but I've used both GEL and AGM, with no clear understanding of the best for each application. I will say that keeping them charged up to full SOC has been an issue in the past, but I'm preparing to implement a 24V charging alternative from solar, switching between 12 and 24V from the same 12V array.

Thoughts?
 
May 17, 2004
5,032
Beneteau Oceanis 37 Havre de Grace
Just to clarify - they are all lead acid, just flooded vs gel vs agm.

Is the rest of the house system 24V, or just these two devices? If there are other 24V banks I would match their chemistry to simplify charging. If this is the only 24V bank your options are more open. I’d stay away from AGM since they don’t cope well with a partial state of charge, and you said you may not be able to maintain 100% charge.

Is there a reason you don’t want plain flooded lead acid? For that application (short duration usage) I wouLed think they’d be ok.
 
Dec 29, 2008
805
Treworgy 65' LOA Custom Steel Pilothouse Staysail Ketch St. Croix, Virgin Islands
Is there a reason you don’t want plain flooded lead acid? For that application (short duration usage) I wouLed think they’d be ok.
The house, main engine and generator start batteries are all 12V.

The bow thruster can be very deep discharge due to the fact that when you need it, you NEED it, and running it for only 10 seconds doesn't count as needing it. The anchor windless is usually short demand, as you say, except when we may have 800 pounds of anchor and chain out, but it would be much simpler for me in setting up a 24V charging process if both 24V banks were the same battery chemistry.

Point taken on FLA.
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
NotCook. How much money do you want to spend? FLA batteries tend to be lower cost than AGM or GEL batteries. Did you get satisfactory usage from the bank at 5 years based on the cost you paid? What chemistry were they?

FLA chemistry would more than be adequate for the task you have identified. I am guessing here, but during the time you "Really Need the Thruster or the windlass" you are also running the engine and generating power to support the draws you are making on the batteries.

The idea of solar to help charge your batteries when not being used is sound.

Do you have enough charging capacity from your engine? You may find that not having the right charging system limits the life of any and all batteries you buy.

Using FLA 12V batteries in a 24V bank gives you options when you have a failure. Just remove and swap batteries to maintain your ability to provide power just for shorter duration.
 
Dec 29, 2008
805
Treworgy 65' LOA Custom Steel Pilothouse Staysail Ketch St. Croix, Virgin Islands
The idea of solar to help charge your batteries when not being used is sound.

Do you have enough charging capacity from your engine? You may find that not having the right charging system limits the life of any and all batteries you buy.

Using FLA 12V batteries in a 24V bank gives you options when you have a failure. Just remove and swap batteries to maintain your ability to provide power just for shorter duration.
Hi John,

You raise some interesting things to think about.

Our main engine charging is only 12V. What I have in mind is switching the solar between the 12V house bank to the 12V-24V DC to DC converter to charge the 24V bank.

What I have found with the bow thruster is that even with the generator running and pushing the 30Amp 24V charger, it makes little to no difference in the bow thruster capacity. It is just too much load for a charger to support. I could, of course, add a 120 Amp 24V alternator. To your point, we are ALWAYS using the main engine when we are using the bow thruster, such as docking in extremely tight quarters, and have started the generator also to help out, with little to no benefit.

Not sure how the battery type would impact the ability to swap out the batteries for a temporary fix (though I'm not sure I would use "just" and "remove and swap batteries" in the same sentence. And, buy the time you are losing power to the thruster, you aren't going to be having time to go down below, to opposite ends of the boat, and disconnect, move and reconnect batteries for that last turn into a marina. ;) That wouldn't work any better for us than trying to raise the sails to drive us into the slip if the engine died (not to mention dropping the sails after entering the marina!). We're pushing 40 tonnes around - we have to be WAY ahead of the boat.
 
Dec 29, 2008
805
Treworgy 65' LOA Custom Steel Pilothouse Staysail Ketch St. Croix, Virgin Islands
I would be inclined to keep the whole system at 24v and then step down to 12 as needed. 24v devices appear to be more commonly available.
I'd love to have the whole system at 24V. Think how much less resistance there would be in the wiring throughout the boat. However, I'm not about to redesign the entire system at this point. I just need to get these two isolated battery banks recharged after each use underway, preferably without running the generator.
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
What I have found with the bow thruster is that even with the generator running and pushing the 30Amp 24V charger, it makes little to no difference in the bow thruster capacity. It is just too much load for a charger to support.
Have you measured the voltage at the thruster while operating? I'm wondering if you are getting too much line loss from the cable run. Might a larger diameter cable reduce the loss which in effect would increase capacity.
 
May 17, 2004
5,032
Beneteau Oceanis 37 Havre de Grace
Have you measured the voltage at the thruster while operating? I'm wondering if you are getting too much line loss from the cable run. Might a larger diameter cable reduce the loss which in effect would increase capacity.
:plus:
Even 60 seconds at 120 amps of draw is only 2 amp hours, so the battery capacity itself shouldn’t be the issue. If the thruster is bogging down I’d check the wiring before assuming the batteries were dead. Maybe try one of those automotive battery testers, first at the battery posts, then at the thruster. If the readings are very different that suggest wiring resistance.
 
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Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
What we are exploring is the capacities of your batteries, their consumption and how to replace the power used.

To do this we need specifics. How big is are your battery banks? How many amp hours? what types of batteries? what is the recharging capabilities of your current alternators?

At first blush it sounds like you have 2 separate battery banks (maybe 3 if you have a separate starter battery for the engine). Bank 1 is your House which you operate as a 12V system, and Bank 2 powers your windlass and thruster as a 24V system. Are all the batteries in bank 2 - 12V batteries wired in series to give you 24 volts?

It sounds like you have 2 separate ways to charge your system a generator that you produce 24V, and the boat engine which is a 12 V alternator. If the charging units are not producing enough amps to feed your batteries you need bigger alternators. This is why we need the detail. Balmar has large amp (140 AMP 24V & 210 AMP 12V) producing alternators. Note that these are the maximum output limits generally you get a lot less output (some times half) as the alternator does it's thing and heats up.

The concept about the 12V batteries is not about changing or modifying them in the heat of action, but a way to adjust the system after your secure in a remote location, if one craps out. It is a whole lot better to have 4 12V batteries to swap in and out to make say 1 24 volt battery than having one big 24V battery that fails :yikes:.

That is all I was thinking.
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA

senang

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Oct 21, 2009
304
hunter 38 Monaco
I have a 12V system on my boat, but installed a 24V bowthruster because they have more power. I did not want to have 2 12V batteries dedicated to the bowthruster and doing nothing for the 23 hours and 56 minutes a day that I am not using them. I have 2 12V house batteries ( now 3) and I switch the house batteries in series for the thruster when needed. I used a 12/24V switch as used in big trucks for starting their big engines with 24V. Switch to 24V use thruster, switch back. Only downside thing is you need a long big cable from house battery to bow.
 

capta

.
Jun 4, 2009
4,766
Pearson 530 Admiralty Bay, Bequia SVG
Generally, bow thruster and windlass batteries are installed forward so the leads to the equipment are short with little line loss. The charging leads should only need to carry a lot less current and therefore do not need to be battery cable.
It sounds to me as though you just do not have enough amperage in whatever battery(s) you are using for the thruster and windlass by the time it reaches the equipment. You may need much bigger batteries as well as going up in voltage. You should be able to pull up your anchor without the engine or genset in an emergency.
On the other hand the thruster is a nice aid, but should never be considered a necessary tool for maneuvering a vessel. Therefore, I would plan my power consumption around this, making sure that you can get that pick up w/o the engine or genset. As most decent windlasses pull chain at around 60 feet a minute, it's pretty easy to figure out how long you must continuously operate the windlass to get up the scope you usually put out. Then determine the max consumption so this is no more than 20% of the total battery capacity. Then you should never have a discharge problem while using either piece of equipment.
The windlass manufacturers recommend taking the strain off the chain when pulling it up by powering forward. I find I often foul my chain around something on the bottom when we do this so we use the catenary effect of the chain to get the boat moving forward while we pick up.
As I'm sure you know, solar only gives you full output when the sun is unobstructed and mainly right overhead, so a 500 watt rating is only a small percentage of that over a complete day's sunlight. I wouldn't count on it as a reliable charging source, even in the tropics. I'm not certain about the new charge controllers, but generally speaking if you are going to double the voltage, you will halve the amperage, so I'm not sure there is an advantage in going to 24 volts there.