12v Boat with 24v bow thruster

[Hermia II]

Connect the windlass to the starter battery of your engine (which is normally 12v). The windlass doesn't draw that much and you normally run the engine when you hoist your anchor så charging is on. Get a Victron BMV to keep check of the starter battery, in worst case you need to run it for a little while to get the battery up to 100% after hoisting the anchor.

[Cadence]

jt11791 summed up what I was going to suggest, even with a schematic. It may be your cheapest option.

[goboatingnow]

Originally Posted by BillKny

Why on earth would you EVER want to do that?



There is never a need to run a bow thruster while pulling the anchor (or dropping it for that matter!) and the potential for a disastrous wrap around the thruster props is much too high to justify even thinking about it.



I think the whole idea of the 12/24 system that is being described here is way too complex, and there are lots of reasons not to do it (especially as described), but this is NOT one of them...

Very very bad idea to design a system that precludes using both.

[Hermia II]

I sometimes use the thruster hoisting. Since it is not good practice to pull the boat with your windlass it is sometimes necessary to correct direction of the bow when the chain points to the side. Should be possible in my book.

[DesKeech]

Hi, I've got exactly the same set up on my 34ft trader. I have two 12 volt 130ah batteries abs a series /parallel relay. In the quiescent state they are in parallel across the 12 volt alternator, when I iterate the bow thruster the relay both disconnects them from charger and switches then in series across both batteries in series, I. E. 24 volt. You could hook your winch across either one 12 volt. I've had this set up for about 10 years without any problems

[Dockhead]

Originally Posted by jordanbigel

First, thanks very much for your thoughtful reply Dockhead.

WRT the question of the dedicated alternator, I was always of the opinion that supporting the fwd battery with the dedicated alternator was key to keeping the thruster battery powered up during usage. However, other contributors have stated that at the rate the battery can accept amps, the difference between a 30amp charger and a 150amp charger is negligible, and the battery will be depleted almost as fast and probably before the thermal cutout on the thruster kicks in.

I don't know about this - I believe the AGM batteries can accept (in bulk phase) close to the full 150amps the alternator is capable of putting out - wouldn't this at least keep the voltage high which would provide better thruster performance overall? I have to believe there is a difference between a dedicated high output alternator compared to a pair of 30amp chargers...

Well, the batteries don't accept the power from the alternator when the thruster is working. The batteries are discharging, not charging, and alternator power goes directly to the thruster. The output of the alternator is simply subtracted from the power drawn from the batteries -- that's what helps keep the voltage up. But if alternator output is a small percentage of total power needed by the thruster, then it may not be much to write home about. But it's another good thing that the batteries are being charged during the off cycle in intermittent use of the thruster.


One thing to keep in mind -- paradoxically, a more powerful thruster may end up being used on a heavier duty cycle than a less powerful one. Why? Because at a certain point, the thruster might be able to hold up the bow against the wind, so you will end up using it for that purpose. My 10hp thruster is not powerful enough to hold the bow up, so I use it only in short bursts. So tripling (!) your thruster power may cost you a lot more than 3x the power.


Second, I agree completely, there is no cheap way to do this. There are certainly cheaper and more expensive ways of doing this... no doubt. I am not looking for the cheapest way, I am looking for the best compromise. Sounds trite I guess. Sorry.

Originally Posted by jordanbigel

. . .I am leaning in the direction of #1 - replacing my 12v 150amp Balmar small-case alternator with the same deal in 24v - same belt (serpentine), same form factor, should just bolt on (I hope).

So 75 amps * 24v? That's not going to make much a dent in the power demand of a 15hp thruster. If 150 amps * 24v (haven't seen a small case one of those), then make sure the drive is up to it -- that's twice the power compared to 150 amps * 12v. I need double belts for my 100 amps * 24v school bus alternator.

Originally Posted by jordanbigel

WRT to your comment about sufficient bank size - "voltage will sag too much" - you don't think the 150amp alternator will be enough to keep the voltage up during use? This is definitely an important concern. And, you may be right, I may need more than 200ah in the bank - obviously the question is can I fit 3 of them (300ah) and at this point I am not sure.

Replacing the windlass motor with a 24v model might be possible, but I suspect the ancillary wiring (relays, switches) may make this more complicate, PLUS, I just bought a new 12v motor which I have not installed yet (the idea was to install the new motor and keep the old one as a spare) - the current windlass motor works fine, but it is 21 years old and I feel it will die in the next few years if I don't replace it (a hunch).

You can calculate the voltage sag at a given amperage vs a given battery bank. I would find the formulas and run the numbers. My gut tells me 100 amp hours (2x G27 batts in series are 100 AH, not 200, or maybe 110 depending on the battery) is way too little. You can't get 24v out of 3x G27 batts, so you would be looking at 4x of them, if that's the battery type you've settled on. 4x of G27's in series-parallel will give you 200 (or maybe 220) AH @ 24v. That might be enough. But you'll need to run the numbers. I run my much smaller thruster (10hp) off the full house bank, which is 440AH * 24v and I wouldn't say it's overkill. I get voltage drop down to 21 or 22 volts, which I think is at the edge already.



Replacing your windlass motor will be far superior and not more expensive than rigging up some rube goldberg parallel series switch and all the extra wiring. If I were you, I would look really hard for that 24v motor, or maybe even have the existing one rewound. Changing out the relays without changing any wiring is trivial. You won't need to change the switches. And you won't need to touch the wiring as you will halve the amps running through the system compared to 12v.

[GreenWave]

Originally Posted by Joli

We always use the bow thruster when paying out chain, it allows us to keep the bow into the wind as we back down. We always use the bow thruster when taking up chain, it allows us to follow the chain although we don't have way on.

THIS!!! And with my thruster being recessed their is no danger of fouling. If it were different then that may change the approach a bit.

[JOHNMARDALL]

Bear in mind that to get much more thrust you'll be going to a bigger thruster with a larger prop in a larger tube and the labor involved in changing the tube may come to more than the cost of the components. Just changing to 24 volts may not give you any more thrust, just cooler running and therefore a longer runtime.
Take a look at the Vetus BOWPRO boosted thrusters which have built in voltage step up and use an AC Induction motor with very little heat build up. These are the latest development of recreational thrusters and as you're going to end up changing just about everything in the thruster system, you may as well consider the best technology available. Battery capacity will be the factor that limits runtime, so a motor that runs cool and efficiently makes a big difference.


Good luck
John Mardall

[jt11791]

Originally Posted by Dockhead

Replacing your windlass motor will be far superior and not more expensive than rigging up some rube goldberg parallel series switch and all the extra wiring.

My boat's system with the series-parallel switch is not rube goldberg. It is a clean, elegant, and inexpensive solution. It's been working perfectly without needing any maintenance since Hylas built it in 2001. If the OP wants to build a 24V charging system and switch over both his windlass and bow thruster to 24V, good for him, but it won't be less expensive or simpler.

[Cadence]

Originally Posted by jt11791

My boat's system with the series-parallel switch is not rube goldberg. It is a clean, elegant, and inexpensive solution. It's been working perfectly without needing any maintenance since Hylas built it in 2001. If the OP wants to build a 24V charging system and switch over both his windlass and bow thruster to 24V, good for him, but it won't be less expensive or simpler.

A "cursory" look at the schematic, I can see using both thruster and anchor winch at the same time. I can see it as the cheapest solution for the OP.

[jordanbigel]

Originally Posted by Dockhead

So 75 amps * 24v? That's not going to make much a dent in the power demand of a 15hp thruster. If 150 amps * 24v (haven't seen a small case one of those), ...

You can calculate the voltage sag at a given amperage vs a given battery bank. I would find the formulas and run the numbers. My gut tells me 100 amp hours (2x G27 batts in series are 100 AH, not 200,...

4x of G27's in series-parallel will give you 200 (or maybe 220) AH @ 24v. That might be enough.

I run my much smaller thruster (10hp) off the full house bank, which is 440AH * 24v and I wouldn't say it's overkill. I get voltage drop down to 21 or 22 volts, which I think is at the edge already.

Thanks again! You are correct on both counts - 2 100ah batteries @ 12v = 100ah @ 24v, I knew that. Sigh. Dumb mistake. AND I misread the specs for the small-case Balmar 140amp, its 70amps at 24v, and there is no 150amp 24v small-case alternator. My mistake. No way I can fit a large case (my primary is a large case 200amp on the stbd side, the port side I have the small-case alternator for the thruster).

I need to consider this a lot more. I may be able to fit enough batteries up there - I am thinking I need a minimum of 200ah @ 24v. A lot of space, and weight up there. Damn. Thanks again!

[jordanbigel]

Originally Posted by JOHNMARDALL

Bear in mind that to get much more thrust you'll be going to a bigger thruster with a larger prop in a larger tube and the labor involved in changing the tube may come to more than the cost of the components. Just changing to 24 volts may not give you any more thrust, just cooler running and therefore a longer runtime.
Take a look at the Vetus BOWPRO boosted thrusters which have built in voltage step up and use an AC Induction motor with very little heat build up. These are the latest development of recreational thrusters and as you're going to end up changing just about everything in the thruster system, you may as well consider the best technology available. Battery capacity will be the factor that limits runtime, so a motor that runs cool and efficiently makes a big difference.
John Mardall

Hey John,

Thanks very much for your reply. WRT this proposed upgrad - really, the only reason I am even considering it is because they (Wesmar) makes a 5hp and a 15hp unit with the same prop size (8") same tunnel size (215mm) - according to the manufacturer the 24v 15hp unit will fit in the same tunnel as the 12v 5hp.

WRT Vetus, I did take a look recently at their offerings - at the time, I recall they did not offer a unit which could utilize the existing tunnel, which is why I stopped considering them. I will take another look though, the last time I checked was about 8 months ago (this has been a back-burner issue for some time now).

Thanks again.

[jt11791]

The diagram I posted is not exactly what my boat has, it was just an example of a series-parallel switch that my search engine found. In practice on my boat, for the brief moments when both windlass and thruster are needed simultaneously, the windlass pulls only from one 12V battery.


I should add that I'm not against 24V systems. They have real advantages and if I was building a new cruising boat I would use 24V extensively. But that's not what the OP asked. As the thread title says, he wanted to know how best to run a 24V thruster on a 12V boat.

[Dockhead]

Originally Posted by Cadence

A "cursory" look at the schematic, I can see using both thruster and anchor winch at the same time. I can see it as the cheapest solution for the OP.

That depends on the cost of the switch plus wiring vs. the cost of a 24v windlass motor. The motor for my 24v Lewmar Ocean 3 cost less than €200.


How much does a series-parallel switch rated for say 500 amps continuous cost? A cheap one for starter motors won't do.



The Vetus series-parallel switch costs £886, nearly a thousand euros. https://www.vetus-shop.com/vetus-ser...-vo-p-941.html And this won't do -- it's only 100 amps continuous and the parallel is only for charging the thruster bank.


Even if you find a suitable switch, then you've still got a bunch of extra wiring to do, including extra battery cabling. That alone can cost €200.


All that expense, trouble, and extra complexity just to avoid buying a €200 windlass motor? Really?



And it's another point of failure; probably you'd want a spare on hand.

[jordanbigel]

Originally Posted by Dockhead

That depends on the cost of the switch plus wiring vs. the cost of a 24v windlass motor. The motor for my 24v Lewmar Ocean 3 cost less than €200.

How much does a series-parallel switch rated for say 500 amps continuous cost? A cheap one for starter motors won't do.

The Vetus series-parallel switch costs £886, nearly a thousand euros. https://www.vetus-shop.com/vetus-ser...-vo-p-941.html And this won't do -- it's only 100 amps continuous and the parallel is only for charging the thruster bank.

All good points!

For me (WRT the series/paralell switch) another issue is I try to avoid things I don't understand well and it seems like there are a lot of different switches out there, some of which may allow 12v and 24v simultaneous operation, but I am not qualified to judge and not confident that I can learn enough to make this a sure thing, and I don't like taking risks with electricity, or money. (see below for discussion about finding a local electrical expert).

However, the cost of the motor is a bit higher than what your lewmar windlass motor cost - the 12v windlass motor I bought last year (which I've never installed) cost me US$468 - I just checked, they have a 24v version for the same price (https://www.hodgesmarine.com/maxp120...le-flange.html). I doubt they would take the 12v in exchange since I bought it over a year ago (maybe 18 months) - my plan was to keep using the old one until right before we leave for S. Pac next year. But if they won't take it back, I can surely sell it online (at a loss of course).

I guess if I do this, and it comes down to either pulling 12v from one of the batteries in the bank vs installing a 24v->12v converter for the windlass vs replacing the motor I think the new 24v motor is the obvious choice., though not the cheapest. Pulling 12v from one of the two batteries sounds simplest, but I am still not clear on the ramifications of uneven discharge, so I would prefer to just avoid that issue (either with the 24v motor or the DC-DC converter).

I did find a 24v to 12v converter which can handle up to 150amps (the windlass motor is 1200watts) - but the cost of the converter is appx. $568, so replacing the motor is a no brainer at this point. Of course, then I will want to buy a second motor to keep as a spare (who doesn't love spares when cruising remote areas?).

WRT batteries, my original idea was to replace the single 4D with a pair of 110ah batteries (group 27 or 31) - but I have been convinced that this will not be enough juice, the suggestion was made to use 4 G27 (or G31s) - but if that is the case, it will be far easier for me to just add a second 4D under the forepeak bunk) which would then give me 200ah @ 24v. I definitely have the room for it, I checked last night.

I love the idea of the serial/parellel switch, but as much as I see the appeal, as described by the guy with the Hylas54 said (sorry, cant recall the name) his has worked for 10+ years - but it was wired by Hylas, who presumably know what they are doing! If I knew exactly which switch he was using, and had a diagram of exactly how it was wired, I could copy it easily - I'm good at wiring stuff, just not an expert at designing electrical systems - so I am tending to shy away from that idea due to the complexity, risk involved, etc. If I knew a reliable boat electrician I might try to get some help, but the odds of finding one who knows what he is doing AND has installed one of these switches before (to handle a scenario like this) seems unlikely. San Diego is a great boating town, but unless you own a superyacht, tradesmen like this either won't even talk to boaters like me, or never show up when they say they will (repeatedly).

I like the plan currently in the lead (in my brain its in the lead) because I can understand it and am confident I can do it myself. So, basically, 1) 2nd 4D battery to make 200ah @ 24v bank, 2) 24v alternator to replace my current 12v alternator, 3) 24v windlass motor. Simple. And I believe no new wiring will be required with this plan. Definitely not cheap though.

Plus, if I am not mistaken, the 24v windlass motor will also have the advantage over the 12v windlass motor in terms of longevity (my understanding is that in general 24v motors last longer and run cooler).