Bow Thruster vs Stern Thruster

[rsn48]

My sedan cruiser went into refit, it feels like when Jesus was in diapers and its still in refit. I had everything removed and completely gutted the bilge. No engine, no leg, no fuel tanks, no water tank, no nothing. This was done partly to inspect every inch of the wood hull (fiberglass covered - original build). Then one third up the boat hull was painted with an epoxy paint to reduce any damage from intruded water.

I wanted a bow thruster but because of the wooden keel it has, a tunnel job was out. So I had an exturn installed. This is the model I had installed, now discontinued as a new model has slightly more umph.

https://www.amazon.ca/MarinersWarehouse-Thrusters-External-Thruster-SMEX35S/dp/B07HC8PX5D

The theory is that with boats on a plane, the bow raises and the external thruster is either out of the water or just touching the water. The company argues these thrusters are more efficient as it sits lower in the water so no to very little cavitation. Tunnel models can have a great deal of cavitation. Since the external unit sit further in the water with the motor surrounded by water, they are quieter. And since the motor is, in essences, water cooled you don't have to worry about overheating.

Since my boat is older, wood everything, issues have arisen that you wouldn't experience on a normal hull. I won't even discuss the circus that was called a new motor install and new leg added. And my Exturn install was no different.

My boat has a wooden keel down the center, forget how wide it is. The problem was with the hole for the bolt going through the hull. By the time the hole was drilled, not a great deal of wood was left over on the sides of the keel. So long thick brackets were made to shore up both sides of the keel and epoxied in.

The other problem was the water tank, which occupied the area under the V birth. Because the bolt came up enough to intrude on water tank space, the tank was removed permanently. Further back two smaller tanks were added to take its place. Almost everything down below was 50 years old so I didn't trust what was in the water tank so I was happy to install new tanks to replace it. Ditto my fuel tanks.

I haven't tried out my bow thruster except to run it to ensure it worked before the install, my boat is still on the hard but getting closer to completion, thank god.

When choosing my particular model, I took the following into consideration. The model is suppose to be good for boats 24 - 28 feet (there are more powerful models and a 24 V system as well). My boat is 28 1/2 feet but it is a sedan cruiser with no flybridge, translation, less side windage and less windage on the bow helm structure. If this was an anchor I would have gone one size up, but given my boats smaller windage footprint compared to flybridge boats I felt the model I chose would be okay.

Here are some propaganda videos:

Cavitation in tunnel thruster versus deeper in the water Exturn thruster:

Install instructions:

What surprised me in the install video is they state you must have a seperate battery working the thruster in the instructions with the thruster, but this isn't shown in the video. In a moment of enthusiasm replacing my old battery bank with Fireflies, I bought six of them. Latter I decided really I could easily make due with 4 since I have newly installed Efoy and solar. So two fireflies went in the bow to power the windlass and the thruster. I was feeling a little sheepish with possible over kill until I read a review of a cruiser being reviewed in Pacific Yachting and they had installed two Fireflies in the bow was well for both the thruster and windlass.

 

[Comodave]

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.[/QUOTE


We were at a different dock with a 20 knot plus wind blowing us onto the dock and one of the fenders rolled out between a piling and the boat. I went out to reset the fender and I tried as hard as I could push and could not move the boat even a 1/4” off the piling. I pushed and pushed until I finally got my head out of my butt and told my wife to activate the stern thruster. Immediately the boat moved off the piling and I was able to reset the fender. I just had not thought of using the thruster in that application. Worked great. Absolutely could not have done it without the thruster.

 

[Ski in NC]

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.

On a twin, there is a technique that is really useful: Say you want to slide the boat to stbd to dock. Put the rudders hard to port, then go port fwd and stbd rev. Change it to port rev and stbd fwd. Keep alternating. Each time a prop goes in fwd, it will put wash on the rudder kicking stern to stbd. Props are much more efficient in fwd so whenever you put one in rev, leave it in gear longer than the one in fwd. Sometimes I add a little power to the one in rev. By alternating you keep the boat from turning.

With a little practice, you can make the boat go cleanly sideways.

If the wind or current is fighting you, you will need to bark the engines, but don't mess with that until you get some good practice. There is a big difference screwing up a docking maneuver at dead idle (bumping things, leaning on things) and HITTING them with the power up. Ugggh.

 

[Alaskan Sea-Duction]

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.

For transparency I have twins and no thrusters. Like you I have been looking at thrusters. With twins, like you have stated you poke it right into a parking space. There is a lot of good advice here. A traditional thrusters or surface mounted or instead of a fan/prop type thruster using water jets.

Thrusters would be "nice" but I have the boat funds allocated to other items. Maybe someday.

Here are a few links (there are others):

https://www.hollandmarineparts.nl/

https://sideshift.com/

https://www.yachtcontroller.com/

 

[RedRascal]

Larry at Crown Yacht charters in Anacortes has a 4788 with bow and stern thrusters in his fleet. The boat is called Sleepwalk and I thought I remember Sleepwalk posting on the Bayliner Forum. Maybe the owner could offer an opinion, that would seem like a goldmine of a conversation since it's the same boat in the same cruise grounds. If not you could try calling Larry and see if he could comment on how it handles.

I'm curious if the keel on a 4788 is big enough to limit the effectiveness of a stern thruster. I have no experience with a stern thruster so back to the sidelines for me to watch where this goes

 

[Comodave]

Our keel extends down way below our props and the stern thruster works like a champ. The 4788s keel isn’t nearly as large.

 

[Mako]

Mea culpa - in my original post I forgot to be specific about having twin engines.... 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.

Beaver, from reading your last comments I don't think you need thrusters at all. I get the feeling that you either need to develop your skills through practice, perhaps with a skilled captain, or you could increase the size of your rudders if trawler speeds and docking/maneuvering are your concerns.

For example, my previous 65ft 110,000lb twin engine (no thrusters) was designed for trawler speeds and had good sized rudders. I could literally move it sideways perfectly - but it would take a really judicious use of throttle and constant fine adjustments of one or the other engines to keep it balanced.

However my buddy with his twin engine Mainship, designed for speeds in the teens, I could never get to behave the same. It was a higher speed boat and had smaller little rudders.

Best to chat directly with some of the guys on the TF who own your same model boat.

Once you become extremely proficient and comfortable with handling your boat, then you can better determine if rudder modifications or thrusters are needed. Save those tens of thousands of dollars for now.

 

[Arc]

I have a bow thruster, just added a stern thruster. As I get older I move slower. I’ll take all the help I can get.

 

[Beaverlake]

Beaver, from reading your last comments I don't think you need thrusters at all. I get the feeling that you either need to develop your skills through practice, perhaps with a skilled captain, or you could increase the size of your rudders if trawler speeds and docking/maneuvering are your concerns.

For example, my previous 65ft 110,000lb twin engine (no thrusters) was designed for trawler speeds and had good sized rudders. I could literally move it sideways perfectly - but it would take a really judicious use of throttle and constant fine adjustments of one or the other engines to keep it balanced.

However my buddy with his twin engine Mainship, designed for speeds in the teens, I could never get to behave the same. It was a higher speed boat and had smaller little rudders.

Best to chat directly with some of the guys on the TF who own your same model boat.

Once you become extremely proficient and comfortable with handling your boat, then you can better determine if rudder modifications or thrusters are needed. Save those tens of thousands of dollars for now.

Although pride cometh before the fall, I have, over the years, developed pretty good skills at close quarters boat handling. I logged 400-600 hours on Lake Michigan and over 2000 hours in the PAC NW - all “naked” except for our 44 Tolly (about 14 months in 20117-18) that had both. Not boasting, but I have developed proficiency in this regard including single screw boat handling. Mako, I noted or alluded to this in my original post and a follow up shortly thereafter.

As much as a I appreciate the comments and insights my original post was focused on the difference, if any, of using a bow thruster vs a stern thruster (not both). And again - my question was not meant to stimulate a discussion of thruster vs no thrusters or the value of bow thrusters. I am curious about whether or not a 2x cost for bow vs stern thrusters brings with it a significant additional benefit. Frankly at $20k or so I can’t afford a bow thruster but at half that I could consider a stern thruster.

I can pivot our boat using the twin engines but try as I might (and I’ve tried/practiced often), walking sideways using twin screws and rudders on a 4788 is not that effective. For me. And for additional clarity my context is primarily when single handing or when my wife is unable to lend a hand.

But for example, with a starboard-to docking using a stern thruster I could theoretically approach the dock bow in, do the clockwise spin thing to twist the bow even closer to the dock, and use a stern thruster to counteract the twist thus bringing the stern in to the dock in parallel to the twist pushing the bow toward the dock. Theoretically. Or bring the pilothouse close enough to the dock so I could lasso a cleat when boating singlehanded.

Of course if more/most transient marina docks in the PAC NW used cleats instead of the devil’s spawn bull rails I probably wouldn’t care as much because I am, in fact, pretty good at stepping out of the pilothouse and lassoing a dock cleat I can use to maneuver around a spring cleat, but then I can’t change Pac NW dock design so there ya go.

I think the feedback here that relates to use of a stern thruster only confirms that there is benefit and that it might be enough to forego the cost of a bow thruster. I hope a few more folks will chime in with experience using only or primarily a stern thruster or who are curious and have done some experiments.

At this juncture I’m wondering if we haven’t been “brainwashed” to spend more $$ to put thrusters at the pointy end of our boats! ;-)

PS, apologies for a bit of a “testy” response, but my question was born of ignorance, not lack of skills or experience. ghl

 

[BruceK]

Beaverlake, as a fellow owner of twins no thrusters,I can already move the stern towards the dock, but the corollary of doing that is the boat pivots on its axis and the bow moves away from the dock. My hope,when I get a bowthruster, is that by combining the effect of thruster and the chosen prop in reverse,all of the boat will move sideways towards said dock. There are other things I hope it will help with, but that`s a simple example.

Put shortly:you can already swing the stern, what you can`t direct is the bow. I don`t think you need a sternthruster. This advice is from someone who has never enjoyed the benefit of thrusters, bow or stern.

 

[Comodave]

Like I said in my previous posts, the stern thruster will be a benefit to you. Some people will argue that a bow thruster is better, maybe so, but a stern thruster will also be a benefit. Are you any wise handy? Installing a stern thruster is not a simple job, but it isn’t that hard. You can save about half of what you are considering spending. Or do part of the work yourself, like running the control wires, that takes time but it isn’t that hard.

It does upset me when people make judgement calls about others abilities and say that you don’t need a thruster. They don’t know your circumstances and can’t make that call for you. If you think that you need them or that you want them, then you do need them. I have been boating for 53 years in all kinds of boats and all kinds of weather, etc. I found myself rushing to get to the stern to make it fast. After almost tripping and falling several times, I decided that I needed a stern thruster so that I wouldn’t fall and get hurt. At my age 1 fall could end my boating career, or I could put a stern thruster in and not fall rushing down the steps and trying to get past my dog. So what is a thruster worth if it saves me from falling and maybe getting hurt? It is worth a lot to me.

 

[Beaverlake]

Thanks Cdave. I think the mods could close the thread. I’ve got what I need. Using twins I can kick either the bow or the stern to either port or starboard. Basic boat handling.

What I can’t do sometimes is push both ends in the desired direction at the same time. A thruster will make that possible. It seems that a stern thruster is just as capable as a bow thruster in this regard (for my 4788 hull design) but at a much lower cost (boatyard or DIY). Adding a remote control increases functionality when short handed.

Thanks everyone. I’m done !

 

[ranger58sb]

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).

Seems about $10K high for the bow thruster. I got a quote for about $10-11K for in installation in ours, including the thruster and controls (etc.), a pair of dedicated batteries, and a charge relay.

-Chris

 

[Portage_Bay]

snip
Of course if more/most transient marina docks in the PAC NW used cleats instead of the devil’s spawn bull rails I probably wouldn’t care as much because I am, in fact, pretty good at stepping out of the pilothouse and lassoing a dock cleat I can use to maneuver around a spring cleat, but then I can’t change Pac NW dock design so there ya go.

There's an old thread here singlehanded docking aid which discusses the use of small grappling hook or this very handy single bend hook shown in post #18. I have one of those, sorry I don't know where it came from I got it with the previous boat. My variation is I have a line attached to the hook, I tape it to the boat hook with two wraps of electrical tape, drop the hook in place, make it off to a cleat and give the boat hook a yank to break it free.

With either the grappling hook or the single bend hook once the rail is hooked the bow won't wander off. But it's not a secure enough attachment to spring against or to leave in place to tie off the bow.

 

[greysailor]

Salty, our DeFever 44 with twin Deeres, had both bow and stern thrusters installed by the PO. When docking/departing I always strive to position the boat only using the gears, just to keep the skills honed. A little nudge from the bow thruster is the more common usage during strong crosswinds or "too small" marinas. About the only time I exercise the stern thruster is if my mate needs the stern kicked toward the dock so she can grab the stern dock line.

 

[Codger2]

My hope,when I get a bowthruster, is that by combining the effect of thruster and the chosen prop in reverse,all of the boat will move sideways towards said dock. There are other things I hope it will help with, but that`s a simple example.
.

Everything you said is true, IMHO. I have a twin engine boat with a bow thruster. It works exactly as you've described but the biggest advantage to me is the thruster's ability to cover up a lot of bad judgement calls when docking. All the photos showing my entrance to my slip are with the rudder centered, the boat in neutral but moving at about 2 knots and all turns are made with the bow thruster.

 

[Shrew]

IMHO you don't really need a bow thruster for a twin engine boat. They are extremely helpful with a single engine boat, however, I made it almost an entire season with no bow thruster on my single engine.

Interestingly, after that season, I ended up using the bow thruster much less frequently once it was repaired.

 

[psneeld]

I've handled a number of twins with one engine inop they are not very maneuverable...a thruster makes life easier in many situations....sure not necessary if you can be towed or assisted...but with one no need to wait.

 

[Beaverlake]

Seems about $10K high for the bow thruster. I got a quote for about $10-11K for in installation in ours, including the thruster and controls (etc.), a pair of dedicated batteries, and a charge relay.

-Chris

I the PAC NW things are spendy. Plus BL4788 requires removing a water tank witch requires disassembly of the vberth etc. when I last investigated a bow thruster for a 4788 it cost more than a hydronic heating system for the whole boat.

 

[Beaverlake]

There's an old thread here singlehanded docking aid which discusses the use of small grappling hook or this very handy single bend hook shown in post #18. I have one of those, sorry I don't know where it came from I got it with the previous boat. My variation is I have a line attached to the hook, I tape it to the boat hook with two wraps of electrical tape, drop the hook in place, make it off to a cleat and give the boat hook a yank to break it free.

With either the grappling hook or the single bend hook once the rail is hooked the bow won't wander off. But it's not a secure enough attachment to spring against or to leave in place to tie off the bow.

Great idea - I was recently thinking about repurposing the tiny folding anchor we have for our RIB for this purpose. I truly hate bull rails unless I’m upwind of them and even then unless they are pipe, you have to contend with slivers.

 

[Beaverlake]

IMHO you don't really need a bow thruster for a twin engine boat. They are extremely helpful with a single engine boat, however, I made it almost an entire season with no bow thruster on my single engine.

Interestingly, after that season, I ended up using the bow thruster much less frequently once it was repaired.

I can’t disagree. No one actually *needs* thrusters. The P6 principal applies (proper planning prevents piss poor performance). Proper fender placement on both sides of the hull, prepositioning dock lines, sufficient close quarter boat handling skills/practice, etc. matter and a thruster is no substitute. In fact for new owners who might not have much if any prior experience I submit that a thruster could interfere with skills development.

But there are times when having that “third hand” makes docking less stressful for the crew, the captain, and perhaps anyone on the dock. And avoiding unnecessary visits from the gel coat guy is always a plus.

In any case, thanks to all. I got the input I needed to make a decision if/when I decide to add a thruster.

 

[MYTraveler]

My last boat had no thrusters, but its slip was next to the seawall with rocks just below the surface within three feet of the seawall. So, if backed into the slip, coming out required that I keep the bow from moving to port (the seawall side) with no ability to move the stern either direction (it was still in the slip with docks on both sides. That is one circumstance where boat handling skills cannot substitute for a thruster (and that boat had none).

My current boat has an adequately sized bow thruster (I can move the boat straight sideways against a 25 knot wind with its help), and I cannot imagine a situation in which I cannot put the boat where I want it without using spring lines, etc. -- at least if the wind isn't too much above 25 knots.

I have never had a stern thruster, but intuitively it could not replace a bow thruster in all circumstances. It would be really interesting to learn from one of the guys who have both whether the bow thruster is necessary in those sorts of circumstances, or whether a stern thruster alone is enough.

Similarly, OP, if you do decide to install a stern thruster, it would be useful to hear from you with an update to this thread.

 

[Codger2]

I have never had a stern thruster, but intuitively it could not replace a bow thruster in all circumstances. .

Ditto! A thorough understanding of "prop walk" & how to use it negates the need for a stern thruster. I do, however, understand why some people like stern thrusters....no need to master the "back & fill" or "prop walk" processes, thus a simpler control of your vessel.

 

[Bacchus]

Ditto! A thorough understanding of "prop walk" & how to use it negates the need for a stern thruster. I do, however, understand why some people like stern thrusters....no need to master the "back & fill" or "prop walk" processes, thus a simpler control of your vessel.

For some I think it's a badge of honor to not have thrusters. With a small rudder and single prop in a tunnel I am glad I have thrusters on both ends. I added a remote last year and it has come in handy many times already.

 

[psneeld]

in any of life's pursuits.... there are badges of honor.


Of course boat handling skills, like any other skill well preformed are admired.


Doesn't make one a better person, overall not even a better boater as it is a hobby requiring many skills.


Even the best captains I know use thrusters often as they make life easier....but they also take pride in their boat handling skills.... and they should.


It's not a big deal either way as I see it.... only when either extreme tries to make it so.

 

[Alaskan Sea-Duction]

I the PAC NW things are spendy. Plus BL4788 requires removing a water tank witch requires disassembly of the vberth etc. when I last investigated a bow thruster for a 4788 it cost more than a hydronic heating system for the whole boat.

You could get a bow thruster that is mounted on the bow, with just a few small mounting/wire holes. Thus tearing apart the v-Berth isn't needed.

 

[Baker]

If you notice, the people that are advising against stern thrusters are the ones that do not have stern thrusters. ANd the ones that have them, are surprised at how useful they are!!! I am one of those. I used to be one of those people that always thought a bow thruster was WAY better than a stern thruster. Now I have both...and I will say my mind has changed...just like the others on this post that were surprised at the effectiveness of a stern thruster. I could write a book....but....I'll try to keep it brief.

One thing NO ONE has mentioned that is a basic boat handling characteristic is what end is affected by the wind the most...??? That wold be the bow. So the bow thruster has to fight hard against the wind affect. The stern thruster does not. And therefore can really be effective at moving the stern around.

Another thing. I don't know about you, but I prefer to dock stern in. When the stern is leading the charge into the slip, it is nice to be able to position the stern where you need it on the way in.

Another thing. Let's say you are pinned to a leeward dock with a fresh beam wind. It is easier for a thruster to get the stern off leaving you the ability to back out of the situation versus trying to get the bow off only to have it blow rapidly back into the dock....if it is even able to power against the windage. Yes there are ways to spring off of a dock. But that requires time and startegy and fenders and potentially help on deck. And it also leaves the possibility of damage to the boat as you spring off...bow rails, etc.

Anyway, like I said, I now have both and am surprised at the usefulness of the stern thruster. And I know there are solutions for all of the above scenarios without thrusters. But I am here to tell you a stern thruster is more useful than most people think!!

 

[syjos]

For some I think it's a badge of honor to not have thrusters.

I'm not sure if it's a badge of honor but when I dock Sandpiper, a single, in a tight small marina, I feel pretty good.

We usually back into slips backing and filling using a lot of throttle and that attracts a lot of attention.. Other boaters usually either come running over to help or run back to their boats to fend us off, which is never necessary.

I don't use the thruster because it's undersized and too far from the bow to be really effective. And, I'm pretty busy rapidly shifting the gear lever with one hand and the other goosing the throttle.

I have to admit that when I had my boat handling business, I may have showboated a bit to pick up clients. It was a pretty effective way to get attention and get a conversation started about boat handling and during the conversation mention that I was a boat handling instructor and hand out cards and brochures.

I also have to admit that if the docking was not perfect, I would not mention the instructing business.

 

[Woodland Hills]

If bow and stern thrusters are unnecessary and going without them is a badge of honor, then why does every professional big yacht captain use them constantly? They have lots of skilled crew, the very latest of equipment, lots of dock hands helping them come and go and yet the thrusters are running constantly. As I sit here in Nassau typing this, a 90 footer just came in heralding it’s arrival with the grinding of bow and stern thrusters. Last week a 130 footer used it’s stern thrusters to get off the dock against an adverse current despite having 4 paid crew to spring.

Are you saying these guys take no pride in their skills? That they are unaware of how to use springs and differential thrust to maneuver?

Or perhaps professionals use the appropriate tools at hand for the job they need to do and endeavor to do it as simply and as easily as possible. Maybe having pride in your skills is not showing off and just getting the job done. At a going rate of $1000 to $1500 per foot per year, perhaps they have nothing to prove.....

At 63’ we are the smallest boat in the marina. There are 5 130 to 150 footers here tonight and last week we had a 220 footer. They all came and went to the sound of grinding thrusters. Were their captains all a bunch of low skilled no-priders?

 

[psneeld]

Missed the point completely.