Bow Thruster vs Stern Thruster

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Beaverlake

Beaverlake

Senior Member
Joined
Jan 2, 2020
Messages
239
Location
US
Vessel Name
Knot Home
Vessel Make
Bayliner 4788 - 1998
Bow thrusters are great but expensive. And not a replacement for basic docking skills. That said, has anyone considered the effectiveness of a bow thruster (only) vs a stern thruster (only)? Bow thrusters are wicked expensive to retrofit but stern thrusters not so much. What difference in control should it make to move the extra pivot power from the bow to the stern?

I’ve thought about this a lot calling up my high school and college physics classes and I’m not seeing the value in what might be twice the cost. My context is docking only, not other circumstances and even more focused, single handed in a pilothouse with no cockpit controls.

Or maybe I’ll just continue improving my docking skills including line handling, fender placement, etc....

Anyway - just noodling on the subject the night before Super Bowl.
 
You should get two types of responses, those who prefer bow thrusters and the rest that prefer stern thrusters.

For me logically the bow thruster provides the most oomph, particularly in a wind assuming the thruster has decent power, some seem quite wimpy. If you already have power at the stern, adding a stern thruster is good, but you are already part way there with the current motor without the thruster. In the bow you have no power, unless a sailboat under sail qualifies.

In tight spaces such as my marina, you can put the motor in neutral and drift a bit and with the use of the bow thruster you don't get the dramatic stern swing you find with a boat under traditional power. So I can go in a straight line, hit the thruster and the bow responds with the stern following.
 
Realistically on your boat I would expect most after market stern thrusters would have very limited ability to impact control in conditions (Wind or current) when you need it most. I would bite the bullet and go for the bow thruster or just keep practicing with the thrust from your twin props. In other words I think it would probably be a waste of money. If electric and not hydraulic you can only run them for short duty cycles which would also limit how much a stern thruster could swing your stern.
 
We have a 41 with twin engines and we put a stern thruster in our boat a couple of years ago. Generally I can put the bow wherever I need to and my wife handles the bow lines. I drive from the flybridge and then get down and handle the stern line. By the time I get down from the flybridge and get ready to handle the stern line, half the time the stern has blown off the dock and I can’t get the line on the dock. With the stern thruster I can leisurely get down from the flybridge and then bump the remote for the thruster and bring the stern back to the dock. I do not have room for a traditional bow thruster or I would loose my main water tank as happens in the 4788 according to owners. The stern thruster is simple to install. We did ours in 2 days with 2 of us.

If you want to do a bow thruster, look at the Exturn bow thrusters. No tunnel needed and just 3 holes in the bottom of the boat. If we decide to add a bow thruster that is the one we will add so we don’t loose the water tank.
 
READY said:
Realistically on your boat I would expect most after market stern thrusters would have very limited ability to impact control in conditions (Wind or current) when you need it most. I would bite the bullet and go for the bow thruster or just keep practicing with the thrust from your twin props. In other words I think it would probably be a waste of money. If electric and not hydraulic you can only run them for short duty cycles which would also limit how much a stern thruster could swing your stern.
Click to expand...

Do you have experience with a stern thruster? Our will spin the boat in a 360 very easily and do it in a fairly heavy wind. As to duty cycle, ours will run for 3 minutes before overheating. We have probably never used it for longer than 10 seconds so that is a moot point.
 
Long ago in a land far away I could “side walk” my single engine 26 Pacemaker into the dock. Same for our 26 Tolly. Our Bayliner 3988 had twins but almost no forefoot (can you say weathervane boys and girls?) but I managed by learning how to use “power”. Our Tolly 44 had both both bow and stern thrusters and wow. Now our BL 4788 is once again “naked” so I was thinking of a “smaller” investment that would make a difference. The comment about a remote is duly noted and probably a very important component to successful short handed docking with a thruster. Thanks for the responses and I hope a few more folks will chime in - especially if they have direct experience.
 
Our boat doesn’t want to walk probably due to the large keel, but the keel does protect the props pretty well, but I do like the stern thruster in some docking situations. We bought the boat in Virginia and ran it home to Michigan. We went through 75 locks on the way. Wish we had the stern thruster on that trip. I run the boat from the flybridge and our dog wants to be in front even though he doesn’t always know which way we are going. Particularly after the 2 lock on the TSW when he realized that the lock masters had treats for him. So by the time I could get down the steps from the bridge and past the dog, lots of times the lock cables were our of reach from the stern. That was when I decided on the stern thruster with a wireless remote. In the future we may add a bow thruster depending on what our cruising plans are and the wallet... My feelings are that if thrusters make it able for us to go boating and cruise where we want longer into our senior years then the thrusters are worth the cost. Also they make it safer because we don’t need to rush trying to handle lines before the boat gets blown away from the dock.
 
Also, don’t let people tell you that you just need to learn how to handle your boat. We were in the CG Auxiliary for 30 years. I was a Qualifications Examiner for almost the whole time and taught boat handling so I know how to handle a boat. We also taught boating safety. And that includes docking without putting your crew in danger. So if thrusters make it safer then get them.
 
With twins you can kick the stern in whenever you want, although at times that will move the bow away from where you would like. That's when a bow thruster is useful - without it, you aren't kicking the bow anywhere!

I find a lot of the time I don't use the bow thruster - its the practice and boat handling thing - but I would not be without one. And if you put one in, don't scrimp. I have had times where wind and current overpower the one I have.

In my current marina in a river I need to go cross-current in a fairway past a number of slips and then make a tight 90° turn into my slip. I tend to plan for slack tides, its a lot less stress. Ideally I would add a stern thruster so that I could move along the fairway sideways, always with the boat aligned with the current. Perhaps one day....
 
The twins don’t walk because the props counter rotate. I am not sure of the value of a stern thruster with twin engines. I installed a stern on my Eagle 40 but being the cheapskate I am went with the minimum suggested without considering the how much resistance I have with the rudder and keel depth. Also there is limited depth at the stern so the thruster rides high further reducing its effectiveness. Heading into the wind or current before backing in gives you a better than average shot that the bow will line up as you enter the slip. I vote for the bow thruster.
 
My boat is a single engine with a large keel that draws 4' 6". An 8" propeller isn't going to have the same effect on the stern (because of the keel) that it does in the bow because of it's 2 to 3' draft. The big mistake that so many single engine operators make is not being able to turn there rudder 40 degrees in both directions. With the rudder hard over, it directing 85% of the prop thrust, and the propeller being 28" (not 8"), I can shove the stern sideways with almost no forward motion. Combined with the bow thruster, I can move the boat parallel toward and away from a lock wall.

This is an area where most single engine boats do far better than twins. Most twins have much smaller rudders that can't direct the prop thrust in the same way as a large single rudder.

Ted
 
Insequent said:
With twins you can kick the stern in whenever you want, although at times that will move the bow away from where you would like. That's when a bow thruster is useful - without it, you aren't kicking the bow anywhere. ...
Click to expand...

This!
 
My boat came with a hydraulic stern thruster that the previous owner had installed.
I wasn't trilled at first because I thought a bow thruster would be more effective.
HOWEVER after learning to use it I find I can do anything a single screw boat with a bow thruster can do.
I just have to approach situations differently.
I had zero issues doing hundreds of locks in the Erie, Oswego and Canadian canals. No problems fitting my 40 ft boat into a 42 ft space, etc.
So naysay the stern thruster all you want if you choose to. I'm not saying it's better than a bow thruster, I'm saying it's as effective.
 
I vote for what wets your whistle. Learned on just a bow thruster. Now have both. I very rarely ever use them. If I did have to have one I would offer stern to the dock and keep the thruster in front of me (so yes bow thruster), but also works by offering bow to dock.
 
In my experiences, I believe a properly sized bow thruster with a great rudder gives a slight advantage over just about everything including twins (without a thruster).

But that's the perfect world where perfect solutions are rare.

No matter what, thrusters are often undersized for the owners real need and that is an issue. Comparing improperly sized thrusters shouldn't even be part of the discussion, that's a good one on its own.

So a slight advantage over a stern thruster may exist but really does depend on a few things.

I have neither on my trawler or the towboat I ran for almost 15 years. Can one dock almost anywhere with enough practice? Maybe, maybe not... certainly most recreational boaters never get enough practice, especially in really bad situation. Why? Only a fool would expose their own boat into unsafe or scary docking situations. Too many options usually.

Would I like a thruster...you bet. If I got one, I would go with an oversized stern thruster if it was still way cheaper than a bow thruster. I see it as effective enough for a lot less money. If the dollar amount was close...then I would choose a bow thruster.

But because of the cost, and my own personal needs....that day is still down the road if at all.
 
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Stern thruster on a single? Well I'm quite intrigued by the guys who spend less than a hundred bucks to bolt a couple of bent plates to the tail of their rudder, and voila, fish tail.

Fish tail + 40 degrees swing = stern thruster. I say save your money for a bow thruster if your situation requires it.

But it does depend on your situation. I recall when I was in SoCa that horrible Dana Point marina was a nightmare in any winds. No currents there that I recall, but in tight harbors or cross currents then perhaps bow thruster, stern thrusters, ion thrusters and a warp drive couldn't hurt.

But for those who don't lock often, and who spend most time at anchor, then neither.
 
O C Diver said:
My boat is a single engine with a large keel that draws 4' 6". An 8" propeller isn't going to have the same effect on the stern (because of the keel) that it does in the bow because of it's 2 to 3' draft. The big mistake that so many single engine operators make is not being able to turn there rudder 40 degrees in both directions. With the rudder hard over, it directing 85% of the prop thrust, and the propeller being 28" (not 8"), I can shove the stern sideways with almost no forward motion. Combined with the bow thruster, I can move the boat parallel toward and away from a lock wall.

This is an area where most single engine boats do far better than twins. Most twins have much smaller rudders that can't direct the prop thrust in the same way as a large single rudder.

Ted
Click to expand...



I agree 100%
 
Sandpiper, a single, came equipped with an undersized bowthruster mounted too far back from the bow because of the water tank in the bow.

If there is any wind, it's useless.

It comes in handy to hold the bow to the dock until my wife can secure it. It also assists doing a 180 turn in tight waterways and to push the bow off the dock when backing out of a side tie dock.

I would use the bow thruster more if it had more oomph.

As Ted described, I can move the stern anywhere with the large rudder or with prop walk.

I find prop walk to be more effective than using the rudder to move the stern. I usually leave the rudder hard over to starboard and use reverse, neutral, forward and lots of throttle to move the stern to port.

If I had to choose between bow or stern, I would choose bow.

If the boat had no thruster, I probably would not spend the money on installing one.
 
You don't really need either. With a single screw I would go with a bow thruster. Marina dock talk says a stern thruster is very effective but you couldn't prove it by me.

pete
 
As they say....not every handyman should tackle every job....tools are only as effective as the craftsman.....any tool is not the right one for every job and.....in some cases the quality of the tool does count.

Sounds like thrusters too.
 
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I ran my boat for a few years with no bow thruster. I could manage, but once I installed it, it is SOOOOO nice to have. When I built the boat, I left a clear area in the forefoot to make it easier to install, and the install was not too difficult.

In my narrow creek, I have to back out about 100yds before it gets wide enough to spin it around. Thruster makes it easy. Just leave rudder at zero, idle in rev, steer bow with thruster. Before the thruster I had to do lots of "back and fills".

I have never felt the desire for a stern thruster. Just no need. I can kick the stern around well enough by positioning the rudder (and not a huge rudder at that) and bursts of fwd/rev/fwd/rev.
 
Ski in NC said:
In my narrow creek, I have to back out about 100yds before it gets wide enough to spin it around. Thruster makes it easy. Just leave rudder at zero, idle in rev, steer bow with thruster. Before the thruster I had to do lots of "back and fills".
Click to expand...
There is a fuel dock in Cape Haze, FL that requires that same technique for 40'+ boats. As you described, it's so easy, especially from my stern docking station. When the dock attendant sees me backing that way, he just shakes his head, and says,"That's just not fair ".

Ted
 
Mea culpa - in my original post I forgot to be specific about having twin engines. With twins I and “spin” the boat in a fairly tight radius. Using the twins I can effectively push the bow any way I want but the stern will of course go in the other direction which in my proposed use case would beep away from the dock. Using a stern thruster I could “pulse” the twins to push the bow toward the dock and “pulse” a stern thruster to push the steen toward the dock. In asking around, for our boat a properly sized bow thruster would cost about $20k installed and a stern thruster $10-$12k installed (PAC NW). The large cost difference is why I made the post. I can visualize a stern thruster set up working on our hull (not a deep draft) but theory and practice are not always the same.

Thanks for the posts - some hit my real question spot on even though I now realize that my original post was slightly but importantly incomplete.
 
My Grand Banks 32 (single engine) came to me with an hydraulic stern thruster made by Dickenson. I was dubious at first but have come to really like it. My home berth is a bit tricky to get in and out of and the stern, rather than a bow thruster, does the job. Despite what some poster above have said, the pivot point of the boat is about the same whether you turn the rudder or use the thruster--near midships. I can easily rotate the boat in her own length. When coming alongside a dock singlehanded, I can come in at an angle, then at the last minute swing the stern in and easy step off the boat carrying the stern line in my hand. Easy peasy. Finally, because it is hydraulic, it can be run all day if necessary. The company even makes one that can rotate 90 degrees, so you can use it as a (slow) get home motor. Bottom line, a stern thruster is just as useful as the more common bow thruster, probably cheaper to buy/install, and sometimes more useful than a bow thruster.
Oldersalt
"Everything on oy boat is broken. You just don't know it yet."
 
O C DIVER/ Ted is correct. I had a GB 36 single no thrusters. If you want the stern to go to port turn the wheel hard starboard and hit power briefly. The stern wil kick to port with little/no forward motion
 
When using prop walk to move the stern on single, I put it into gear, reverse or forward depending on which way I want the stern to move. I give it throttle 800 to 1100 rpm for a short burst, put it into neutral for a moment and repeat going into gear with throttle then back to neutral. Repeat.

By going in and out of gear, prop walk is more effective without allowing the boat to gain momentum.

With the large diameter prop on a single, prop walk is your friend.
 
As usual here, Gordon you have received a plethora of on and off target responses, all likely adding to our understanding of the subject. Your central question seems to accentuate the relative cost of stern versus bow thruster indicating to me that in your own mind you acknowledge the general effectiveness of a bow thruster and are hoping the cheaper stern thruster will somehow make your mooring life easier. Several things come to mind IRT your second post. If you can "pulse" the bow in to the pier using the mains, why can't you pulse the stern in after getting a bow line over? Are we talking singlehanding here? Have you experimented with a spring line, a very powerful and even cheaper tool?

Despite Oldersalt's comments, which BTW is the only direct answer to the maneuverability part of your question about a stern thruster only installation from an experienced hand, I would worry that your 10-12K spent on a ST installation might end up being of marginal use in your considerably larger vessel.

And to cost of a BT install? A friend of mine installed a BT in his single screw boat about four years ago here. He and I cut the holes in the hull using the instructions from the manufacturer. Then he had the tube fiberglassed into place by the yard's expert. From there on it was all his labor, and really not that much, to install the equipment. If you are not a DIYer to that extent, and it sounds like you may not be, well, we are back to the question of effectiveness versus cost.
 
I have both and would not give up either one. I use them occasionally for docking and maneuvering where they are very helpful. But where they really shine is adjusting lines at the dock. Our boat is 100000lbs and has a lot of windage, when it blows up like it did this morning it is great to be able to easily push the boat so that lines can be adjusted. Last night a front rolled in and when I woke up at dawn we were 3 feet off the dock and nearly touching the pilings between the slips. So I just had the Admiral “bump” us in towards the dock while I adjusted the stern and then the bow lines to take out the slack. A 25kt crosswind had stretched our 1” dock lines along with a changing tide enough to allow the boat to move three feet! There was no possible way we could have done this alone and by hand.
Thrusters won’t overcome a decent current, but they will usually overpower a wind and they will certainly help differential thrust when rotating the boat in close quarters.
 
It is really easy to install a stern thruster, we did ours in 2 days. I went oversize on the thruster. Went to the next size larger than Sidepower recommended. The hardest part was running the control wires up to the flybridge. Then we cut an 8” hole in the transom. Did a bit of glass work to flatten the transom in the area it bolts onto. Bolt the tunnel with a lot of 5200. I put in a separate battery and battery charger. I paid about $4300 for the thruster and had maybe another $400 in battery and charger and wiring, etc. was it worth it, yes absolutely. Do we have to have it, absolutely not but it is sure nice to have and makes docking much easier.
 
I have a few photos of the install. I put the photos in order but when I uploaded them they got out of order.
 

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