Bow thruster

Iggy · 01-25-2023, 09:53 AM

Wonder if this is worth doing? I have a 40' trawler with the 21 year old thruster that produces, as the spec's say 147lbs. of thrust. Now the next model up does 161 or 14lbs more. Cost $1,100 just change the motor out. Bolts right in!

The next model does 212lbs of thrust, but everything needs to be replace but the tunnel. Cost around $3500 if I do it myself. But I will need to add one more battery due to the increased amperage. More$$

This being my first boat with a bow thruster I don't have any experience with one. So my questions, is 14lbs more worth the it?? The spinoff to this, the new motor uses 25A less. From 355 down to 325, a very small plus.

Another way to put it! How many lbs to HP with thrusters?

rslifkin · 01-25-2023, 09:56 AM

I'd use it as-is for a bit first and see if you find the current thrust level adequate. If it is, the small upgrade might be worth it at some point, but that's debatable. If you find it's not effective against enough wind, then you might want a bigger upgrade (which, as you pointed out, will cost some money).

Iggy · 01-25-2023, 09:58 AM

This is going on my 3rd year. I think its underpowered but I have nothing to gauge it on. Maybe a expect it more than I should?

At $1,100 the hit I can take! At $3,500 plus will hurt. But will I gain anything?

rslifkin · 01-25-2023, 10:01 AM

Quote:

Originally Posted by Iggy

This is going on my 3rd year. I think its underpowered but I have nothing to gauge it on. Maybe a expect it more than I should?

Expectations are personal. Plenty of thrusters are undersized in my opinion and won't move the bow upwind in more than 10 - 15 kts of wind. I'd personally want to be able to push the bow upwind in at least 20 kts, preferably more. What you really need depends on how you use the boat.

If you're feeling it's underpowered, the small upgrade likely won't make much difference. You'd be better off spending a bit more and upgrading to a larger size thruster with significantly more thrust.

Jeff F · 01-25-2023, 10:06 AM

Quote:

Originally Posted by Iggy

This being my first boat with a bow thruster I don't have any experience with one.

Go use it for a year. If you're not satisfied check all the electrical carefully. Lots of support here as needed.

Then consider options.

Edit to add: I see you've satisfied the waiting period. Let's go to the next step :-)

Mako · 01-25-2023, 10:50 AM

Iggy, you’ve been using the boat with existing thruster for three years now.

How have your boat handling skills grown, can you get by without it, have you become so reliant that your skills have possibly NOT developed? Some people do become over reliant after all. Or perhaps your home port slip is so challenging that a thruster is make-or-break.

ranger58sb · 01-25-2023, 11:18 AM

Quote:

Originally Posted by Iggy

Wonder if this is worth doing? I have a 40' trawler with the 21 year old thruster that produces, as the spec's say 147lbs. of thrust. Now the next model up does 161 or 14lbs more. Cost $1,100 just change the motor out. Bolts right in!

The next model does 212lbs of thrust, but everything needs to be replace but the tunnel. Cost around $3500 if I do it myself. But I will need to add one more battery due to the increased amperage. More$$

This being my first boat with a bow thruster I don't have any experience with one. So my questions, is 14lbs more worth the it?? The spinoff to this, the new motor uses 25A less. From 355 down to 325, a very small plus.

Another way to put it! How many lbs to HP with thrusters?

A: Can you dock without the thruster?

B: $1100 and not much work sounds like a maybe, depending on your answer to A. $3500 and lots o' work sounds like too much trouble, no matter what your answer to A is.

-Chris

Iggy · 01-25-2023, 12:00 PM

I went from a 30' foot boat to this 40 footer. Big jump for me. In most cases the thruster is ok. But, when the lower my boat onto the water once a year I must make a 180 degree turn in a tight place. They drop me in towards the left side of a U I drop it in reverse and the boats stern goes to port about 8' from the main. Pointing me towards the main. Not good.

So yes my skills are rough for a boat this size with 2 years under my belt. It's backing up is the hard part for me.

Comodave · 01-25-2023, 12:03 PM

Most thruster installs seem to be undersized. I don’t understand putting one in and skimping on size. If you are going to do anything then I would go for the gusto. Spending $1,100 for a minor increase isn’t worth it IMO.

Pete Meisinger · 01-25-2023, 12:13 PM

I.M.H.O. it is not the power of the bow thruster that makes the biggest difference. Of course that does figure into the equation, but the time length of the power bursts is often more important. A three second burst may be helpful but sometimes you really need 30 seconds or more. Try to find one that has longer duration of run time.

Whoever installed your bow thruster, you can be sure they did a lot of research before selecting the one they did. If it was the original manufacturer or a marina mechanic or just the boat owner, there was a considerable expense involved. I would bet they weighed all the options.

Personally, I would go with the one just a little bigger. BIGGER isn't always better. You need to consider the battery power available, the fuses, wires and switches might need to be replaced for a truely large unit.

pete

Comodave · 01-25-2023, 12:18 PM

The Sidepower thruster we put in our last boat was rated for 3 minutes before it would overheat. We never came close to that, usually 10 to 15 seconds was all we needed.

**Bacchus** · 01-25-2023, 12:35 PM

Thrust doesn't convert directly to HP... see below... but that is beside the point.
The point is the current thruster adequate?
What difficulties are you experiencing?
Do you stern in or bow in?
Do you have to run the thruster continuously for extended time to accomplish what you are trying to do?
Do you overheat or activate over current/ thermal protection often?
Can you use rudder more and fine tune w thruster?
Have you asked for any help from someone experienced w your or your type vessel?

I dont think it's practical for others to advise re the decision remote... only you can decide.
I'll also throw a few other points you may need to consider...
You mentioned possibility of adding a batty... does that also imply possible need to replace fuses and/ or cables to handle higher A w/o V drop?
Have you considered adding a stern thruster vs changes to bow? It may be even higher $ but could help even more depending on answers to the initial questions. Generally no fiberglass work ( other than cutting) needed for stern as it usually bolts on.

See. https://newportvessels.com/blogs/blo...%20unit%20time.

"First, pounds of thrust is a static force measurement while horsepower is 550 ft-pounds of work per second, a measurement per unit time.**So you cannot make a direct comparison between thrust and horsepower unless you also know the speed of the vessel when it is absorbing that thrust. So although there is no direct translation, you can estimate the horsepower rating of a given electric motor by multiplying the amp draw times the voltage to find the wattage of the motor. Then wattage divided by 746 will give you an estimate horsepower of the motor. So every 746 watts is roughly equivalent to 1 horsepower.

The HP equivalent of our motors:

36lb Thrust (All Series) = 0.48HP

40lb Thrust (All Series) = 0.55HP

46lb Thrust (All Series) = 0.64HP

55lb Thrust (All Series) = 0.84HP

62lb Thrust (All Series) = 0.93HP

86lb Thrust (All Series) = 1.50HP"

ranger58sb · 01-25-2023, 01:41 PM

Quote:

Originally Posted by Iggy

I went from a 30' foot boat to this 40 footer. Big jump for me. In most cases the thruster is ok. But, when the lower my boat onto the water once a year I must make a 180 degree turn in a tight place. They drop me in towards the left side of a U I drop it in reverse and the boats stern goes to port about 8' from the main. Pointing me towards the main. Not good.

So yes my skills are rough for a boat this size with 2 years under my belt. It's backing up is the hard part for me.

Main? Main what?

Is this a single-screw boat?

-Chris

Iggy · 01-25-2023, 01:59 PM

Quote:

Originally Posted by Pete Meisinger

I.M.H.O. it is not the power of the bow thruster that makes the biggest difference. Of course that does figure into the equation, but the time length of the power bursts is often more important. A three second burst may be helpful but sometimes you really need 30 seconds or more. Try to find one that has longer duration of run time.

Whoever installed your bow thruster, you can be sure they did a lot of research before selecting the one they did. If it was the original manufacturer or a marina mechanic or just the boat owner, there was a considerable expense involved. I would bet they weighed all the options.

Personally, I would go with the one just a little bigger. BIGGER isn't always better. You need to consider the battery power available, the fuses, wires and switches might need to be replaced for a truely large unit.

Good point on D.C. power.

pete

Good point on D.C. power. After pulling 350 Amp for 30 sec will bring the batteries down!

Iggy · 01-25-2023, 02:06 PM

Quote:

Originally Posted by ranger58sb

Main? Main what?

Is this a single-screw boat?

-Chris

Is this a single-screw boat?

Meaning the "main" docks and than you have the fingers that the boats are in-between. Very close as I back out.

And yes a single screw. If it was a twin I would not have this problem!

mvweebles · 01-25-2023, 02:12 PM

Check the cabling to make sure it's not undersized. Voltage lag can really take a bite out of available power. Should likely be 2/0 cable.

Assuming the existing setup is in good working order, I don't think you'll see an appreciable improvement unless you go with a physically larger thruster and corresponding tunnel. $3500 won't do it for you.

Peter

Iggy · 01-25-2023, 02:20 PM

Quote:

Originally Posted by Bacchus

Thrust doesn't convert directly to HP... see below... but that is beside the point.
The point is the current thruster adequate?
What difficulties are you experiencing?
Do you stern in or bow in?
Do you have to run the thruster continuously for extended time to accomplish what you are trying to do?
Do you overheat or activate over current/ thermal protection often?
Can you use rudder more and fine tune w thruster?
Have you asked for any help from someone experienced w your or your type vessel?

I dont think it's practical for others to advise re the decision remote... only you can decide.
I'll also throw a few other points you may need to consider...
You mentioned possibility of adding a batty... does that also imply possible need to replace fuses and/ or cables to handle higher A w/o V drop?
Have you considered adding a stern thruster vs changes to bow? It may be even higher $ but could help even more depending on answers to the initial questions. Generally no fiberglass work ( other than cutting) needed for stern as it usually bolts on.

See. https://newportvessels.com/blogs/blo...%20unit%20time.

"First, pounds of thrust is a static force measurement while horsepower is 550 ft-pounds of work per second, a measurement per unit time.**So you cannot make a direct comparison between thrust and horsepower unless you also know the speed of the vessel when it is absorbing that thrust. So although there is no direct translation, you can estimate the horsepower rating of a given electric motor by multiplying the amp draw times the voltage to find the wattage of the motor. Then wattage divided by 746 will give you an estimate horsepower of the motor. So every 746 watts is roughly equivalent to 1 horsepower.

The HP equivalent of our motors:

36lb Thrust (All Series) = 0.48HP

40lb Thrust (All Series) = 0.55HP

46lb Thrust (All Series) = 0.64HP

55lb Thrust (All Series) = 0.84HP

62lb Thrust (All Series) = 0.93HP

86lb Thrust (All Series) = 1.50HP"

I looked into a aft thruster. But I have a fuel tank there. Is was suggested to put 2 thrusters, one on ether side of the tank. That would lower its self into the water. BIG BUCKS on that one.

Yes I do need to use the thruster a lot to make the 180 deg turn. Another battery may be needed. Upgrading to the next thruster motor would save 30amps.

It never goes into a over current/ thermal protection.

Looking that the chart/specs. that 14lbs more would equal about 1/4 of a HP. Not much at all.

Its sounds like, adding one more battery and the next size up on the thruster. This would do two things.

1. Keep the thruster running longer at full power. How much longer is in question.

2. The new motor pulls about 8% less power with 10% more thrust.

If I did upgrade 2 models up 212lbs thrust. I would have to add another battery anyways.

Thank you all for your input!

**Bacchus** · 01-25-2023, 02:41 PM

I dont understand the layout and manuever from the description, but for once / year (if I understand correctly) is there another way to skin the cat?
Would use of (spring) line enable you to use rudder & fwd to make a turn and avoid backing that puts you in a compromising position?
Or is there a way to tie off from stbd stern that backing would pull the stern to stbd and allow room the use fwd & rudder to turn CCW?

Comodave · 01-25-2023, 02:53 PM

Our Formula has very low bow rails. My wife didn’t want to buy it because she felt unsafe on the bow. I told her that if we bought it I would put bow and stern thrusters in it so she didn’t have to go up on the bow. I had a company that was going to come to Michigan install both for about $25K. But after we bought the boat and I started looking and digging around I figured out that traditional thrusters wouldn’t fit due to the configuration of the boat. I decided on SideShift thrusters. They install externally and are simple to install. My wife and I installed the bow thruster in a day and a half. My neighbor helped with the stern thruster and we got it put in in one day. They work well and the total cost was about $11K. If you have access issues for a stern thruster you might check out SideShift. It takes 4 bolts and 2 holes for the cables all above the waterline. The access at my stern it really tough but we got it done pretty easily.

Portage_Bay · 01-25-2023, 03:15 PM

For a once a year event there are other options to consider. Especially if your thruster is adequate for your other needs. An outboard dingy or skiff can be used. A RIB is it's own fender. Have the RIB driver work under your command. Position the rib to push which ever end you know needs to be pushed. I once turned an 85' single with no thurster in a space with less than 10' to spare. Not something I care to do very often but you are talking about once a year.