Bow Thruster - On/Off or Variable Power

We're planning the installation of a bow thruster this spring and are looking for some input on on/off verses variable power thrusters. The quotes we've received have both recommended a Vetus BOW160 which is an on/off thruster. Our inquiries regarding a variable power thruster have been met with "not really needed and much more expensive +30%". One variable option we've found is a SidePower SEP170 which has a street price of about $1k more than the Vetus BOW160.

So I thought I'd reach out to the forum for opinions on on/off vs variable power thrusters. To me it seems like a variable power unit would be much improved vs and on/off model. However, we've never had a thruster so my opinion is not based on real life experiences.

Thoughts or opinion?

Thanks,
Tim

I think it's nice, but not required. Our ABT hydraulic thrusters are variable speed, and it's nice to not make as much noise as full-on thrusters, And you can use them to hold the boat against the dock while getting tied and untied. So nice to have, but certainly not required. With full-on thrusters, you just operate them in pulses to get whatever control you need. So I think it comes down to how much you are willing to pay for the nicety.

If I were buying electric thrusters, I would be looking at how long each can operate at full power before thermal overload and shut down. That would be my primary feature comparison between brands and models.

My vote is to keep it simple. If you don't need full power thrust, just give it a shorter burst.

I installed a sidepower several years ago and at the time considered the same variable power question and decided not. Since then I have never wished I had it.

how bad was your quote .I got a price of around 10K .from a marina down here .I don't think it was variable speed but it was side power. they said it was 3 for the unit .3 for unit and tube install and about 3 for building battery shelves ,wiring, battery,duel controls ,charger. and possibly a thousand for unforeseen issues.

we have several issues that are way more important so its not going to happen in the next few years. so we will have to pick our spots carefully until I get use to the single engine handling .

Thanks

twistedtree - great point on the max run time. Looks like the Vetus is 4.5 minutes continuous and 4.5 max per hour. The Side Power technical specs don't clearly spell out the max run time, I'll give Imtra a call today.

Ski - thanks for sharing your decision making process for your install. Sounds like you were in the exact place we are right now. While the thought of variable power is attractive maybe not so much needed based on your experience.

We've been running Avalon for 7 seasons without a thruster and while we've always made do there are many times when having the ability to move the bow would have made maneuvering much easier and certainly less stressful.

timb - Our quotes have been mid teens but as Avalon likely requires a much larger thuster we might be in the same ballpark.

On thought on the timeout issue. If you went up one size on the thruster, it would take shorter pulses to control the boat, and probably be able to operate longer before getting too hot. So you would be running it at a lighter duty cycle. It's probably worth an hr of research to see what alternatives there might be.

AvalonGB said:

twistedtree - great point on the max run time. Looks like the Vetus is 4.5 minutes continuous and 4.5 max per hour. The Side Power technical specs don't clearly spell out the max run time, I'll give Imtra a call today.

Ski - thanks for sharing your decision making process for your install. Sounds like you were in the exact place we are right now. While the thought of variable power is attractive maybe not so much needed based on your experience.

We've been running Avalon for 7 seasons without a thruster and while we've always made do there are many times when having the ability to move the bow would have made maneuvering much easier and certainly less stressful.

timb - Our quotes have been mid teens but as Avalon likely requires a much larger thuster we might be in the same ballpark.

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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.

yes you will most likely have a bigger and longer tube, 24v, and thicker hull ect.

Can't imagine using max runtime

boathealer - I can't imaging using anywhere near the max run time either. However, does seem to be a good indicator of the units durability and capability when a unique situation arises that would require extended run time.

Seems like based on the feedback I'm getting that the on/off thruster is likely more than adequate for my application. There is however an attraction to having variable speed control of the thruster - only using whats needed at the time. In the end not sure I'd be willing to pay what's been quoted for the luxury.

twistedtree said:

On thought on the timeout issue. If you went up one size on the thruster, it would take shorter pulses to control the boat, and probably be able to operate longer before getting too hot. So you would be running it at a lighter duty cycle. It's probably worth an hr of research to see what alternatives there might be.

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Excellent point. This is what we did 9 years ago and have had 0 timeouts due to overuse. Also, install the thruster batteries as close to the unit as possible to provide max volts to motor.

IMO, there is no practical benefit to a variable thrust thruster vs a simpler on/off type.

When I hit the thruster, it takes a few seconds for the bow to react and start to move. Say I am leaving a side tie dock and need to swing my bow out to move off. I hit it for about three seconds and then i see the bow begin to move. If I had a variable thruster I would do the same thing at full power.

Most of my thruster use is for short bursts of a few seconds to align the bow with docks, mooring pickup, etc.

Due to the time delay from initiation to seeing the bow move, there isn't any point to a variable thruster. I would use full power whether I had variable thruster or not.

Hydraulic thrusters where variable thrust is inherent with the hydraulics might be a different story and for bigger boats might be worthwhile. But for your size boat go with an on/off electric thruster.

On the topic of maximum time until overheat, no I have never hit that limit, but I have been in situations where if I didn't go around for another shot at the mooring, I could have tripped it by grinding away. This was while positioning for a mooring pickup at Catalina in a heavy wind situation. So as the PP said, proper seamanship will avoid long time thruster use.

David

My boat has the SE100 / 185T 24 volt Side Power single speed thruster. Originally it had the SE80/185 12 volt model. The old unit didn't perform well as a result of voltage drop from long cable runs to the house battery bank. When I reworked the system, I was able to go to the larger motor as they both use the same lower unit. Going to 24 volt batteries next to the thruster eliminated the voltage drop and cut the amps almost in half. Before, the unit was slow to move the boat and would timeout from low voltage line loss. Now, a bump of the switch quickly moves the bow over. There was also a change of propeller design which probably improved performance also.

To answer your question: I'm very happy with single speed short bumps. Since acquiring the new motor, I haven't had a single timeout. Most bow thruster moves are under 5 seconds in duration. Don't think I've used it more than 1 minute in 1 hour, going through 2 back to back Locks.

Ted

Configuration

The Vetus BOW160 is spec'd for a power vessel of 55' - 72' so it may already be a bit over sized for our 46 although I'm sure the keel adds significant resistance over a planning hull.

Regardless of the thruster we select, looking more like on/off at this point, we'll be installing dedicated batteries and charger at the bow with the thruster. Looking to minimize any voltage drop and have a dedicated 24v DC system for the thruster.

There is a possibility that I may install batteries of the appropriate size to also power the windlass and washdown pump. Still working out the details but eliminating the long cable run from the house bank to windlass would be a nice improvement.

Great feedback, thanks everyone.

AvalonGB said:

The Vetus BOW160 is spec'd for a power vessel of 55' - 72' so it may already be a bit over sized for our 46 although I'm sure the keel adds significant resistance over a planning hull.

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I'm not about to tell you what size thruster to get, but , I have a 45' boat with a single engine and big keel. It draws 4.5'. For my boat the 185mm tunnel and SE100 thruster is plenty. Certainly bigger is usually better. The only down side to the larger tunnel is that the top of the tunnel is closer to the surface of the water (unless placement can be moved). The risk from too shallow a tunnel is creating a whirlpool vacuum (sucking surface air) which makes the prop(s) cavatate. Once or twice in small waves, I've had the thruster cavatate, not fun (you don't use it unless you really need it).

If it were me, I would get a second dealer opinion.... a third, and maybe a forth. Might also post on the Grand Banks forum to see what sizes others have.

Ted

2nd Opinion

Thanks Ted - great advice. Our vessels are likely very similar so your experience with size and actual use is invaluable. I'll also post the question on the GB forum so I can get specifics on other 46's with thrusters installed.

I'm in the process of getting a 3rd quote right now. Really it will be the 2nd as I believe the quote I got from the marina is also from FL Bow Thrusters who is the company I got my first quote from.

The following picture is of a GB46 with the Vetus BOW160 installed. Its a little hard to tell from the photo but looks like the tunnel is around 12" below the resting water line. I'm going to confirm with FL BT and discuss tunnel depth etc.

Make sure all cable connections are tight and clean

Short bursts are all you need most of the time. But on occasions more is needed. I lost an engine in a 60' boat and needed to make a turn against wind and current in a marina. No problem I thought I have a thruster. Well, half way through the turn my thruster quit.

Later when I checked the thruster (24V with two 8D batteries in bow), the cable clamp had melted off the battery terminal! At those amps a little resistance is all it takes to generate a lot of heat.

AvalonGB said:

The following picture is of a GB46 with the Vetus BOW160 installed. Its a little hard to tell from the photo but looks like the tunnel is around 12" below the resting water line. I'm going to confirm with FL BT and discuss tunnel depth etc.

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Hard to know exactly, but I'm guessing the top of the tunnel is 12 to 16" below the waterline. Waterline is 3" below the bottom of the tape.



Ted

The guys I and many others would use fr this job are Florida Bow Thrusters, who install all over the country. Superb work, examples of which I have seen first hand, and excellent after the sale service, witnessed by their patiently helping me diagnose an issue with a 20 year old Vetus. They are also the Vetus distrubutor. It wouldn't occur to me to use anyone else.

I liked using my thruster, when I remembered to. The use for a variable speed never occured to me.

I have an "on/off' bow thruster (the conventional kind) and I have never wished I could have less power or adjust the power. I wouldn't spend the extra on variable power unless you have some special need that I can't think of.

gsholz said:

.... I lost an engine in a 60' boat and needed to make a turn against wind and current in a marina. ........
Well, half way through the turn my thruster quit.

Later when I checked the thruster (24V with two 8D batteries in bow), the cable clamp had melted off the battery terminal! At those amps a little resistance is all it takes to generate a lot of heat.

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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.

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

boathealer said:

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.

Click to expand...

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.

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.

djmarchand said:

You can use AGM or FLAs the choice being the no maintenance aspect of AGMs vs cost.

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FLAs are almost always a "No" in this application. The concern is hydrogen gas from charging in what isn't a ventilated compartment.

djmarchand said:

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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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.

Ted

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.

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?

Shrew said:

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.

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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.

OldDan1943 said:

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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Another example of why Tony Athens recommends keeping the engine battery isolated from anything else.

dhays said:

Another example of why Tony Athens recommends keeping the engine battery isolated from anything else.

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BUT, there is that famous rotary switch ....