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Trawler thrusters: bow, stern or both, and what owners paid
You come off the throttle for the approach, the wheel goes soft, and the bow starts going wherever the wind is going. On a trawler that is the house at work. The house decides how much thruster you need, more than the length does, and where the unit sits matters as much as how hard it pushes. This guide sizes one for your boat and shows what trawler owners have paid, with every figure dated.
The short answer
Which end. If the bow blows off as you slow down, a bow thruster fixes it. If she won't back where you point her, a bow thruster will not help.
Bow, stern, or both on a trawler
On a trawler you have three choices: a thruster at the bow, a thruster at the stern, or one at each end.
Start with what goes wrong, because that tells you which end needs the help. A trawler is typically One engine driving one propeller. It steers with a rudder, so it loses steering at low speed, and in reverse the propeller kicks the stern one way only. with the The blade behind the propeller that steers the boat, and it only works when water is flowing past it. At docking speed it does almost nothing, and in reverse it does nothing at all if it sits behind the propeller. behind the propeller. Going ahead, a burst of power in gear blows water over the rudder and gives her some steering, even when she is barely moving. Coast in at docking speed with the engine in neutral and that steering is gone.
Astern, it falls apart. The propeller now pulls water from around the hull and pushes it forward, away from the rudder, so the wheel does very little. What turns the boat then is The sideways kick a propeller gives when you put the boat in reverse. A single propeller pushes the stern one way and only that way. That is why a single-screw boat backs predictably in one direction and badly in the other., and prop walk goes one way.
Separate the two problems, and watch where the boat hook goes. A bow that blows off as you slow on the approach is a bow problem. A stern that won't go where you point it while backing into the slip is a stern problem, and a bow thruster does nothing for it. Most of the forum complaints are the second kind.
Our page on why your steering leaves you at docking speed takes the mechanism apart.
Our page on what a stern thruster costs has every stern figure this site holds, each one dated. The bow-or-stern page takes the single-end case further. On a trawler the answer to “which end?” is often both. A unit at each end, further down, covers a version of both that most owners have never been shown.
Where the numbers come from
Makers, dealers and magazines have published almost nothing about thrusters on this hull. The real numbers live on Trawler Forum, in threads that run to nine opinions before anyone names a price. This page cites five of those threads and pulls the figures into one table.
Every figure below sits in a table with its date and what it covers. You can see at a glance which ones are too old to trust. Every sizing figure is worked from inputs the page states, so you can run the same arithmetic for your own boat.
Size for the breeze you dock in
Wind load rises with the square of wind speed. So a unit big enough to hold you alongside in thirty knots needs four times the thrust of one sized for fifteen.
Few owners ever need the thirty-knot unit. It is the most expensive case to design for, and on a thirty-knot day the right answer is to stay tied up. Buying a thruster to hold the boat in a gale is a bad plan in itself, because no crew should count on it. The thruster is there to steer you in, and fifteen knots is the design point on every page of this site.
The house matters more than the length
Every sizing chart in the industry asks for your length. On a trawler that is the wrong place to start, because a trawler is mostly house. A tall saloon, a The open upper helm on top of a motor yacht or trawler. It adds a lot of height for the wind to push on., a hardtop and a dinghy on the boat deck give the wind a big, flat area to push on.
Stand on the dock and look at her beside a low, open boat of the same length. One of them is a wall. A length chart sees none of that The area of the boat the wind can push on: the hull sides, the cabin, the mast and rigging, or the canopy. A tall, boxy boat has a lot of it, and wind force does not care how slowly you are moving.. The wind sees all of it.
The first table sizes one 40 ft hull at 15 knots and changes only how much wind it catches. It treats her as a semi-displacement hull, which is what most trawlers are under the water. Full displacement or semi-displacement explains why.
| How much the wind gets hold of you | In a tunnel | External, at the bow |
|---|---|---|
| Low: open boat, low profile | 68 lb | 53 lb |
| Medium: hardtop or bimini | 85 lb | 63 lb |
| High: flybridge, tall house, tower | 105 lb | 78 lb |
The tall house alone adds about 56% more thruster to the same forty feet. The next table puts length and wind exposure side by side.
| Boat | Wind exposure | In a tunnel | External, at the bow |
|---|---|---|---|
| 40 ft | High: a trawler | 105 lb | 78 lb |
| 45 ft | High: a trawler | 135 lb | 100 lb |
| 50 ft | High: a trawler | 168 lb | 123 lb |
| 40 ft | Low: a low-profile hull | 68 lb | 53 lb |
| 50 ft | Low: a low-profile hull | 108 lb | 80 lb |
A 50 ft low-profile boat and a 40 ft trawler need almost the same thruster: 108 lb against 105 lb. The tall house very nearly cancels 10 feet of length, and a length chart cannot see that.
Run it for your own boat. The calculator lets you change the wind exposure and prints every step of the arithmetic.
Where the unit sits
The external column is the more useful one. You are buying a turn, and a turn is thrust multiplied by the distance from the point the boat pivots on.
A A tube bored straight through the hull below the waterline, with a propeller in the middle of it. It is the conventional thruster. Fitting one is mostly a labor job rather than a hardware one. has to go where the hull is deep enough to take a tube. On a forty-footer that is about 6 feet back from the bow, which gives it a short The distance from the point the boat turns about to the place the push is applied. Double the distance and the same push turns the boat twice as hard.. An external unit can sit right at the bow or on the The flat surface across the very back of the boat., farther out. The next table shows what that is worth.
| Where it sits | Distance from the pivot | Thrust to do the same job |
|---|---|---|
| Tunnel, 6 ft back from the bow | 14 ft | 150 lb |
| External, right at the bow | 19 ft | 111 lb |
| External, on the transom | 20 ft | 105 lb |
Full displacement or semi-displacement?
Most owners call a trawler a A hull that pushes through the water rather than climbing on top of it. Most sailboats and the heaviest trawlers have one, and they carry a lot of weight for their length., and in the way she is driven that is right. With the one modest diesel most of them carry, she never climbs over her The fastest a boat that pushes through the water can go before it starts fighting its own bow wave. The waterline length sets it: about 1.34 times the square root of the waterline length in feet, in knots. however far the throttle goes. The hull under her is often a different shape, though, and the word covers two of them.
True full displacement is the round-bottomed, deep, long-range kind: Nordhavn, Kadey-Krogen, Willard, Selene, Diesel Duck. Owners on Trawler Forum list those as the true displacement builders. They describe them as the less common kind, and the dearer one on the used market.
A true full-displacement hull usually stands a little taller for her length. Our sizing puts that at about 25% more thrust on a 40-footer. So on a Nordhavn or a Krogen, add that to each figure.
Semi-displacement is the hull under a great many of the trawlers people own. The back half of the bottom is flatter. The corner where the side meets the bottom is often sharp rather than curved (a hard The angle where the side of the hull meets the bottom. A hard chine is a sharp corner, and a hull with a rounded bottom has none.). Put big engines in her and the shape would go faster.
The Grand Banks 36, the Taiwan-built Marine Trader 34, the Mainship 34 Trawler and Beneteau’s Swift Trawler are all described that way.
That faster shape goes unused, because almost nobody puts big engines in one. Give a semi-displacement trawler the power most of them carry and she behaves exactly like a full displacement boat.
One forum owner puts it plainly: she “will only travel in full displacement mode”. She never climbs up on top of her own bow wave and goes fast, whichever hull is under her.
For sizing a thruster, the bottom shape hardly matters. The height does. A thruster is sized on the wind, and the wind pushes on the house and the The sides of the hull above the water.. This page, the thruster finder and the calculator all size a trawler as a semi-displacement hull that catches a lot of wind, so all three give one answer.
What trawler owners paid
Our estimate comes first. It prices a boatyard job on a 42 ft trawler from published prices, with the same numbers behind it as the thruster finder, the tool here that matches a unit to your boat.
| External | Tunnel | Retractable |
|---|---|---|
| External thrusters for a 42 ft trawler Fitted by a boatyard, least expensive first:
The thruster itself, before fitting: $4,400–$9,500. Two of these can be fitted with the boat in the water. One at each end: most jobs cost $15,100–$23,000. Find the right one for your boat | Tunnel thrusters for a 42 ft trawler Most jobs cost $12,600–$15,800. The least expensive, fitted by a boatyard:
And 30 more models, up to $21,500 for the Sleipner Side-Power E100/185T. The thruster itself, before fitting: $1,500–$8,800. The boat has to come out of the water for these. One at each end, a tunnel at the bow and an external unit at the stern: most jobs cost $21,000–$26,000. Find the right one for your boat | Retractable thrusters for a 42 ft trawler Most jobs cost $21,800–$27,000. The least expensive, fitted by a boatyard:
And 7 more models, up to $34,600 for the Sleipner Side-Power ERL100 eVision. The thruster itself, before fitting: $7,400–$18,100. The boat has to come out of the water for these. Find the right one for your boat |
A different length, or a different boat? The thruster finder prices your own, and the comparison by boat type puts this row next to every other kind of boat.
Below that is what owners have paid. Every row is a trawler-class boat from the owner reports this site collects, with the date it was posted and what the figure covers.
Read the dates before the numbers. US yard labor roughly doubled between 2021 and 2025. A Florida yard quoted $70, $80 and $90 an hour for thruster work in January 2021, and owners in the same state were reporting $175 an hour by 2025. Both rates are in the table on our cost page. So a figure from before that rise is a low number today.
| Boat | Job | Figure | Basis | Posted |
|---|---|---|---|---|
| 36 ft Heritage East | Stern thruster, Side-Power, yard fitted The owner names the maker and not the kind of unit. | $10,000 | installed | Jun 2022 |
| 36 ft Grand Banks Classic | External stern: what the owner says the job goes for Not an invoice. Verbatim: "you can have an external stern thruster installed for about $9,000, total cost." | $9,000 | unclear external | Jun 2022 |
| 42 ft Nordic Tug | Stern thruster, Side-Power, yard fitted, Seattle Fitted in early 2018 and posted in 2022. The owner names the maker and not the kind of unit. | $9,000–$10,000 | installed | Jun 2022 |
| 47 ft Bayliner 4788 | Bow tunnel, itemized invoice $8,577.50 labor and parts across 70 hours, plus $4,500 for the Side-Power SE120/215. The total is our addition of his two figures. | $13,077.50 | installed | May 2016 stale |
| 47 ft Bayliner 4788 | Bow tunnel, quoted, a second Bayliner owner He was also quoted $10,163.60 for a stern unit. | $11,564.77 | quoted | May 2016 stale |
| 42 ft Grand Banks 42C | Bow tunnel, Sleipner SE120, with battery and charger Posted Aug 2025, fitted "last year", so 2024 work at 2024 rates. | $19,000 | installed | Aug 2025 |
A yard-installed tunnel on a trawler in the mid-forties is a five-figure job. The recent figures sit a long way above the old ones. The $19,000 Grand Banks figure is 2024 work, including the battery and charger. The $13,077.50 Bayliner invoice is from 2016 and would not buy the same job today.
Our cost page, the full picture by length band, has the rest. It covers what the hardware lists for on its own and the seven things that blow a quote up. If a yard has already handed you one number on one line, take it apart line by line.
A thruster at each end
On a trawler this matters more than on almost any other hull. She is heavy and usually powered by a single screw, the wind gets hold of her tall house, and she backs badly by nature. One unit at one end fixes half of that. Two tunnels would fix all of it. Most owners hear what two tunnels cost and stop looking there.
A tunnel goes where the hull is deep enough to take a tube, around 6 feet back from the bow on a 40 footer. A A thruster that bolts to the outside of the hull, up near the bow or on the back of the boat. Its propeller hangs in the water below it. Nothing is cut through the hull, so there is no tunnel. bolts to the outside of the hull instead, with its propeller hanging in the water, so it can go right at the very end.
Put a 90 lb DockStar at each end, 39 feet apart. That pair turns the boat about 67% harder than one 150 lb tunnel, in both directions: 3,510 lb·ft against 2,100. It needs no hole below the waterline and no haul-out. You can fit one end now and the other later.
Two units buy you more turning. They do not buy more push, and a pair will not pin her against a dock in a blow.
DockStar is the figure used here because it is the one external maker that publishes a thrust rating. Sideshift, the other, publishes none for any model in its range, so there is no figure to do the arithmetic on.
The drawing of all three puts one tunnel, one external unit and one at each end on the same boat, with every distance marked. The page it sits on has the whole argument and every route to a pair priced side by side.
Two thrusters let you hold her against the dock, turn her in her own length and slide either end where you need it. Below: how strong a beam wind the cheapest pairs hold her in.
Every knot figure here is wind speed, not boat speed or current.
Why we size on steering, not holding
To hold her against a 15 knot beam wind, the bow alone has to push about 183 lb from the very bow, or 210 lb from a tunnel set further back. To steer her in the same breeze it needs 88 lb. That means a bigger thruster, battery and cable, and usually a tunnel: the cheapest pair from one maker goes from $8,970 to about $15,000 on this boat.
The engines and a dock line do much of the holding, so most owners never need it. It is a good extra, and every pair below shows how much of it you get. To size on it anyway, use the switch above.
Moves her sideways: pin her to the dock, or walk her on and off
Both thrusters push the same way. Against the dock, that holds her while you tie up. Off it, she walks sideways with no way on. The wind's whole push on her side is 275 lb at 15 kt, and the bow carries about two thirds of it, because the wind pushes hardest forward of her middle.
Beam wind, engines in neutral: the hard case.
The pairs that steer her, and how strong a beam wind they hold her in
Solid mark: one maker at both endsOutlined mark: two makers
Matching pairs: one maker at both ends
One remote, simpler wiring and controls, and one maker to call. We list these first, even where a two-maker pair costs less. DockStar is listed only as its own pair: you lower each unit into the water to use it, so both ends work the same way.
- 1 DockStar Smart Thruster, bow and sternSame maker 90 lb each · bolt-on removable from $8,970 Holds her at 11 kt
- 2 Max Power CT45 + CT80 stern pod (24 V)Same maker 99 lb tunnel · 165 lb pod on transom from $14,634 Holds her at 10 kt
- 3 Sleipner SE80/185T + SX80Same maker 212 lb tunnel · 212 lb pod on transom from $21,439 Holds her at 15 kt
Two makers
Two remotes or panels and two sets of controls, so docking means a hand on each. Worth a look where a matching pair is missing, or costs much more. The five cheapest, one per maker pairing.
- 4 Lewmar 185TT GEN 2 Tunnel Thruster Package with Joystick + Max Power CT80 stern pod (24 V)Two makers 128 lb tunnel · 165 lb pod on transom from $15,176 Holds her at 12 kt
- 5 Sleipner SE80/185T + Max Power CT80 stern pod (24 V)Two makers 212 lb tunnel · 165 lb pod on transom from $16,616 Holds her at 15 kt
- 6 VETUS Bow Pro Boosted 57 + Max Power CT80 stern pod (24 V)Two makers 126 lb tunnel · 165 lb pod on transom from $17,465 Holds her at 12 kt
- 7 Max Power CT45 + Sleipner SX80Two makers 99 lb tunnel · 212 lb pod on transom from $19,457 Holds her at 10 kt
- 8 Lewmar 185TT GEN 2 Tunnel Thruster Package with Joystick + Sleipner SX80Two makers 128 lb tunnel · 212 lb pod on transom from $19,999 Holds her at 12 kt
Every pair here steers her at 13 kt or more at both ends, priced as one job. Sideshift's pair (from $15,526) publishes no thrust, so it gets no mark.
What the pair gives her that one thruster cannot
Turns her in her own length
Bow one way, stern the other, and she pivots about her middle. Every pair above steers her at 22 kt or more.
Backs her where you point her
Astern, a single screw walks the stern one way only. A stern thruster swings that end where you need it, and the bow follows under your control.
Slides the stern over when docking
At slow speed you point the bow where you want her to go. With a pair, you slide the stern in or out as needed.
Moves her sideways: pin her to the dock, or walk her on and off
Both thrusters push the same way. Against the dock, that holds her while you tie up. Off it, she walks sideways with no way on. The wind's whole push on her side is 275 lb at 15 kt, and the bow carries about two thirds of it, because the wind pushes hardest forward of her middle.
Beam wind, engines in neutral: the hard case.
The cheapest pairs that hold her at 13 kt or more
- 1 Max Power CT60 (12 V) + CT80 stern pod (24 V) 154 lb tunnel · 165 lb pod on transom from $15,033 Holds her at 13 kt
- 2 Max Power CT80 (12 V) + CT80 stern pod (24 V) 176 lb tunnel · 165 lb pod on transom from $15,094 Holds her at 14 kt
- 3 Max Power CT100 + CT80 stern pod (24 V) 231 lb tunnel · 165 lb pod on transom from $16,665 Holds her at 16 kt
- 4 Max Power CT125 (24 V) + CT80 stern pod (24 V) 254 lb tunnel · 165 lb pod on transom from $17,588 Holds her at 16 kt
Each pair is from one maker: one remote, and simpler wiring and controls. Where both need a haul-out, one covers both.
What the pair gives her that one thruster cannot
Turns her in her own length
Bow one way, stern the other, and she pivots about her middle. Every pair above steers her at 27 kt or more.
Backs her where you point her
Astern, a single screw walks the stern one way only. A stern thruster swings that end where you need it, and the bow follows under your control.
Slides the stern over when docking
At slow speed you point the bow where you want her to go. With a pair, you slide the stern in or out as needed.
Prices are the low end of the fitted total, one row per model. A pair is offered only on the boat lengths its maker names.
What the pair costs
On this hull the money points the same way as the arithmetic. Two 90 lb DockStar units, one at the bow and one on the transom, come to about $8,650 at their published unit and track prices. DockStar publishes no pair price and no bundle, so that total is our addition. The prices come from DockStar's site.
The most recent yard-installed tunnel in the owner reports is the 42 ft Grand Banks 42C at $19,000, for one end of the boat.
Sideshift sells a bow-and-stern system as one product and publishes prices too. On a boat this size it belongs in the same comparison.
Before you compare the two
That is two routes compared, and neither figure is a quote. The pair figure is hardware at list, captured 23 September 2026, with no installation in it. The $19,000 is a finished job including a battery and a charger.
A thruster that bolts to the outside of the hull, up near the bow or on the back of the boat. Its propeller hangs in the water below it. Nothing is cut through the hull, so there is no tunnel. bolt on above the waterline, and several owners have fitted their own. That is why the gap is as wide as it looks. A yard doing it for you is still a bill.
One DockStar or two on a boat this size? DockStar's manual gives 20 to 50 feet as the intended use. We size it on the turning effort a trawler needs to steer in a 15 knot breeze, the same way we size every thruster.
One unit, usually at the stern, steers her in a 15 knot breeze to about 44 ft. Two units, one at each end, do it to about 50 ft, and DockStar’s own 50 ft is as far as this site offers the pair. DockStar's installation page shows units fitted to trawlers at both ends.
On a trawler in the forties, the pair is the setup that covers a 15 knot breeze. The 3,510 lb·ft above is our arithmetic from DockStar's published thrust and stated distances. Ask them about your hull before you order, and read what the manual says first.
Where external units earn their place
A trawler is the strongest case on the water for an external unit, and owners choose them on purpose. Of the 15 stern thruster reports this site collected, 5 name an external unit. Of the 11 bow thruster reports in the same collection, 2 do. That is a much higher share at the stern.
Who sells one. The category is small. DockStar publishes 90 lb from a self-contained external unit at about $3,950 before its track. It carries its own battery, so nothing is wired into the boat and nothing goes below the waterline.
Sideshift builds the other end of the market, including hull-mounted and bow-and-stern systems. It publishes no thrust rating for any model. That is the only reason the arithmetic on this page uses DockStar's figure, and it says nothing about whose unit is better.
Our page on what each product drills goes through both from the installation manuals. The Sideshift review has the trawler owners who fitted one at the stern because nothing else would go in the The storage locker at the very back of the boat, under the aft deck or cockpit. On many boats it is already full of steering gear, tanks and hoses. That is why a stern thruster often has nowhere to go..
There are three reasons this hull suits them. The first is space: there is often nowhere good to put a tunnel far enough forward.
The second is speed. The boat is heavy and slow, so an appendage costs very little in performance.
The third is price. The most recent tunnel figure in the owner table bought one end of the boat, and the pair section above sets it against two external units.
The drawback, in an owner's own words: “other than being butt ugly…” (Trawler Forum, May 2021).
You are hanging a leg and a propeller in the water, where debris and crab and lobster pot lines are, on a boat many owners keep beautifully. That objection stops more people than any thrust figure does. The same page on what each product drills covers it from the installation manuals.
On a trawler the two external makers are DockStar and Sideshift. Their kit prices do not cover the same work.
Compare the whole job. A Sideshift unit runs off the boat’s cranking batteries. Budget $250 to $1,000 for batteries and heavy cable, Sideshift’s own published figure, and about 8 to 20 hours to fit it by our estimate. A DockStar needs none of that wiring, because its battery and charger are inside, and DockStar puts fitting at 1 to 3 hours.
Our fitted estimate counts each Sideshift kit’s own batteries, heavy cable and a charger, at $601 to $2,136. The fitted estimate adds both to every kit, so compare those figures.
My own install: a 41 ft CHB in Port Townsend
My boat is a trawler, a 41 ft CHB I keep in Port Townsend, Washington. I fitted a DockStar stern unit to her myself. It is the one DockStar install on this site with a paid price behind it, and I own the unit, so read it as one owner's account. Here is how it went.
“It's a single screw and our marina can be windy and intimidating. While in another marina, I was chatting with a boat neighbor and he showed me his DockStar thruster mounted on his retired salmon boat. Until then, I thought thrusters were way outside my budget.”
“We installed it in a few hours and I was able to spin the boat around (we had to dock bow-in the last time due to heavy wind) so we were stern-in. I flipped her around single-handed while my daughter recorded it from the dock. I would have been terrified to do that alone before we installed the thruster. She didn’t even have to catch the line for me! Cool, calm, and in control.”
Brian, Aim 2 Try, 41 ft CHB trawler, Port Townsend. More on the About page.
What this means when you dock
If the bow blows off as you slow down, that is a bow problem, and a bow thruster fixes it. With a flybridge or a tall house, size from the high row of the sizing table.
If she won't back into the slip where you point her, that is a stern problem. A bow thruster does nothing for it, so price a stern thruster or a unit at each end.
If a tunnel quote made you stop looking, price the external route. External units bolt on above the waterline, and on the transom one needs about 30% less thrust for the same turn.
If you are comparing against a forum figure, check its date first. US yard labor roughly doubled between 2021 and 2025, and the cost section above has the two rates.
Where this data is thin
A set of 6 owner figures is a handful of boats. Each is real, dated and sourced. The spread shows the outer edges of what yards have charged, but there are too few rows for a price list.
Almost everything is bow tunnels on fiberglass. This site holds very little on steel or aluminum trawlers, where the hull work is welding and a different trade.
Nobody publishes a windage figure for their own boat, so the sizing tables above use our three broad categories. The figures behind those categories are our own estimates, checked against the makers' published sizing. Nobody has measured the wind on a real trawler.
Owner figures collected from public forum threads, each linked at the row or in the cost pages, and dated by when they were posted, which can be later than the work. Sizing figures are this site's own estimates, checked against the sizing the makers publish.