We may earn a referral commission from some links on this page. It doesn't change your price or our recommendations.
Bow and stern thrusters together: why two beat one big one
You get quoted one thruster, at one end, and the conversation ends there. Nobody mentions the other option: a small unit at each end of the boat. Two units at the ends turn a boat harder than one bigger tunnel at the bow, and they give her moves one unit cannot make.
This guide helps you decide whether you need one or two. It shows what the pair does, what each route to it costs, and how owners fit it one end at a time.
The short answer
- Start with the end that goes wrong. A bow that blows off on the approach is a bow problem. A stern that won’t follow the wheel backing in is a stern problem, and a bow thruster does nothing for it. One unit at the right end may be the whole answer.
- What a pair adds. On a 40 ft boat, two 90 lb units at opposite ends give 3,510 lb·ft of turning moment. A 150 lb tunnel gives 2,100, so the pair turns her about 67% harder. It also spins her in place and walks her sideways.
- What it costs. On a 42 ft trawler fitted by a yard, two DockStar units come to about $9,000–$10,200. A Sideshift pair runs about $15,500–$20,300, and one tunnel typically $12,600–$15,800.
- Where one stops and two start. In a 15 knot breeze, one DockStar unit covers a trawler to about 44 ft. Two, one at each end, cover it to about 50 ft.
- You can fit it one end at a time. Start with the end that is going wrong, usually the stern on a single-screw boat. Add the other end later if you need it.
Start with the end that is going wrong
A thruster is a steering control. It turns the boat at the speeds where 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. has stopped working. Holding her against a dock in a blow is a different job, and nothing on this site is sized for it. Before anybody sells you two of anything, work out which end is the problem.
A bow that blows off as you slow on the approach is a bow problem. A stern that will not follow the wheel backing into the slip is a stern problem, and a bow thruster does nothing for it.
A 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. boat with the rudder behind the propeller loses nearly all of its steering astern. What turns her 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. The low-speed steering page takes the mechanism apart.
If it is one end, one unit at that end may be the whole answer. Against a 15 knot breeze, one DockStar unit covers a trawler to about 44 ft. Past that, two units, one at each end, cover what one cannot.
This page is for the boat where it is both ends. It is also for the boat where one unit was enough on the calm days and not on the others. The bow-or-stern page is for you if you are only buying one.
What a pair does that one unit cannot
One unit pushes one end of the boat sideways. That is useful, and for a lot of boats it is enough. Two units, one at the bow and one at the stern, give you four moves instead of one, and the fourth is the one you have been wanting since the first time you backed into a slip. The animation below runs through them.
- Spin in place. Run the bow one way and the stern the other, and she turns about her middle without going anywhere. This move gets a long boat round in a fairway her own length wide. No single unit of any size does it.
- Swing one end. Run either unit alone, which is what one thruster has always done. With one at each end, you correct the end that is going wrong instead of the end you happen to have a thruster on.
- Walk sideways. Run both the same way and she moves bodily across, onto the dock or off it, without the bow leading. On a single-screw boat this is the move you have never had.
- Keep her alongside long enough to get the lines on. In the breeze you normally dock in, the pair keeps her parallel while you step off with the line instead of jumping with it. In a gale it will not.
No thruster pins a boat on a gale day. Wind load rises with the square of wind speed. So 20 knots loads the boat 4× what 10 knots does, and 30 knots loads it 9×. Sizing for that day buys hardware you will use a few times a season.
More push is not on that list, and it was never the point. Each end still gets the same 90 lb. The pair turns better because of where the push is applied, and the arithmetic below puts a number on that.
A thruster at each end, worked on a trawler
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.
The arithmetic: two pushes on one long lever
Almost everything written about thrusters assumes you are buying a thruster: one unit, at one end, sized on how hard it pushes. That is how the tunnel market frames it, and on your boat it may be the wrong question.
The case applies to any boat with a bow and a transom the units can reach. It applies hardest to the boats that turn worst: heavy, single screw, tall in the wind, and backing badly by nature. The trawler and sailboat guides take each hull in turn, and a boat of 40 to 49 ft of either kind is the best case.
A tunnel cannot choose where it sits. It goes where the hull is deep enough and wide enough to take a tube. On a 40 footer that is around 6 feet back from the bow. 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 at the very end of the boat.
Put one at each end and they work as a couple: two pushes in opposite directions, 39 feet apart, turning the whole length of the boat between them.
| Configuration | Lever arm | Turning moment | Against one tunnel |
|---|---|---|---|
| One 150 lb tunnel | 14 ft | 2,100 lb·ft | — |
| One 90 lb unit at the bow | 19 ft | 1,710 lb·ft | 81% |
| One 90 lb unit on the transom | 20 ft | 1,800 lb·ft | 86% |
| One at each end | 39 ft apart | 3,510 lb·ft | 167% |
A unit at each end turns the boat 67% harder than a single tunnel, in both directions, with no hole below your waterline and no haul-out. One unit alone gives 81–86% of a tunnel's turning effort, so it comes close and falls short. Two together pass it. What they add is turning, not holding: a pair will not pin her against a dock in a blow.
One 90 lb unit at the stern comes close to a 150 lb tunnel at the bow. It has little more than half the push, but it sits on a longer lever. Run both together and the pair produces about 67% more turning moment than the tunnel.
The pair figure needs no assumption about where the boat turns. Two equal, opposite pushes at different points make what engineers call a couple, and a couple turns the boat equally hard whatever point you measure from. It is simply 90 lb across the 39 ft between the two units: 3,510 lb·ft, the same figure the bars above reach by adding two lever arms. Move the center of rotation anywhere you like and that number does not move.
A 40 ft boat, stopped, turning about her middle. Bow unit 1 ft back from the bow, stern unit on a transom track. Tunnel 6 ft back from the bow, which is far forward for a tunnel and favors the tunnel here. The tunnel's figure depends on where the boat turns, so the comparison does too. A boat with headway turns about a point further forward, which shortens the tunnel's lever and lengthens the stern unit's, so the stopped boat is the case that favors the tunnel most. The 90 lb is DockStar's published figure. The 150 lb tunnel is the size DockStar's own page compares itself against, a worked example with no maker's model behind it. Neither figure is reduced for losses.
It is also a retrofit most boats can take. Two tunnels means two locations with enough hull, two lots of glasswork or welding, and a haul-out long enough to do both. That is why almost nobody does it.
Two external units need none of that: they bolt on, above the waterline, with the boat in the water. DockStar and Sideshift both sell units that pair this way, and Sideshift bundles a bow-and-stern system as one product. What each route costs is a different question for every hull. The cost tables on this site carry a line for the pair beside the tunnel.
Two practical points. You do not have to buy both at once. Fitting one end and adding the other later is a normal path. On a DockStar, one remote runs both units, including a second added years afterwards.
A boat with authority at both ends is a different boat to handle short-handed. You can hold her parallel, walk her sideways, and correct the end that is actually going wrong. If you are singlehanding, or simply not as quick to the foredeck as you were, that matters more than any number in the table.
The Turning effort, measured in pound-feet. It is the force multiplied by how far that force sits from the point the boat turns about. A small push a long way out beats a big push near the middle. figures use DockStar’s published 90 lb. It is the only thrust rating in the category anyone publishes, and Sideshift publishes none for any model. The argument is about lever arms. The DockStar review works the same arithmetic as a Two equal pushes in opposite directions, one at each end of the boat. A couple spins the boat about her middle without shoving her sideways. The further apart the two pushes sit, the harder the boat spins, which is why moving a thruster further from the middle does more than making it stronger., a form that does not depend on where the boat pivots.
What a pair costs, by route
There are three ways to get a thruster at each end. Each is priced here on a 42 ft trawler.
They are priced the way the cost-by-boat-type table prices everything. That means the hardware at its published price and a yard’s hours at $160–$180. It adds batteries and wiring where the unit needs them, and a Lifting the boat out of the water on a travel lift or a trailer so work can be done below the waterline. It is billed separately from the job itself. where the job does. One tunnel is in the table for scale, because it is what most owners were quoted before they found this page.
| Route | Fitted by a yard | What is in the price |
|---|---|---|
| Two DockStar units, one at each end | $9,000–$10,200 | Two self-contained units and their tracks, 1–3 hours a unit at yard rates. Nothing is wired into the boat and there is no haul-out. The hardware is $8,650 on standard tracks and $9,070 on the extended ones, at their published prices, captured 23 September 2026. The rest of each figure is the hours. DockStar sells no pair bundle, so the totals are our addition. |
| Sideshift SS350 at the bow, ST350 at the stern | $15,500–$20,300 | Two fixed-mount units, 8–20 yard hours each. Add $980–$1,067 of batteries, cable and charger at the bow and $980–$1,067 at the stern: two 24 V starting batteries each, at Sideshift’s cranking figure. Both go on with the boat in the water, so no haul-out is charged. |
| A tunnel at the bow, an external unit at the stern | $12,800–$39,300 | The least expensive to the most expensive combination of a tunnel sized for this boat at the bow and an external unit at the stern. The tunnel is 32–54 billed hours and the stern unit its own install; batteries and cable at each end, and one haul-out where both units need one. We do not price a second tunnel at the stern: the tanks, generator and hoses usually live there, so it is a rare install, and an external unit goes on without moving any of it. |
| One tunnel, for scale | $12,600–$15,800 | What most jobs cost at one end of a boat this size, from the same table. The cost page has every owner figure behind it, dated. |
Every line is priced as a yard job, so the columns compare. Fit the units yourself and the number is the hardware. On the owner-fitted routes, the saving is the labor. The next section has the one owner who priced it both ways.
The hardware prices come from DockStar’s site and Sideshift’s. The DockStar review and the Sideshift review cover each maker's documents and owner reports.
On a pontoon the standard setup is one unit, at the bow. The outboard already steers the stern, so the bow is the end with no steering. Nobody sells a tunnel for one. Sideshift does sell a bow-and-stern joystick system for pontoons, the PT360, at $7,600–$10,900 on a 24 ft boat fitted. The pontoon guide covers the bow units and the outboard-mount stern units on their own terms.
The price tables on this site carry a Bow and stern pair line where a maker sells a pair. The line shows when one unit alone falls short of what the boat needs to steer in a 15 knot breeze. Where one unit already covers that, the tables show one unit and leave the second out.
Fitting it yourself, one end at a time
The two routes owners take to a pair need no hole below the waterline. On the in-water models there is no haul-out either. That is why the setup suits an owner doing the work, on a Saturday, from the dock.
Doing it yourself keeps the labor in your pocket. The DIY page prices every install at $160–$180 an hour.
| Route | Hours, both ends | Who does the work | Worth at yard rates |
|---|---|---|---|
Two DockStar units, each on its track
 DockStar Smart Thruster, stern
The maker’s own listing, read 23 September 2026. Full page: fit, cost and wiring See it on the maker’s site | 2–6 | You, with hand tools, and nothing wired into the boatDIY 5 of 52 to 6 h yours | $320–$1,080 |
|
Two fixed-mount externals
Sideshift SS350 Bow Thruster
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s siteSideshift ST350 Stern Thruster
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | 16–40 | You, or split with a shop for the electricalDIY 4 of 512 to 16 h yours, then an electrician | $2,560–$7,200 |
|
A tunnel at the bow, an external unit at the stern
Max Power CT45
Marinedeal listing, read 15 September 2026. Full page: fit, cost and wiring See it on Marinedeal | 33–57 | A yard for the tunnel, with the boat on the hardDIY 2 of 55 to 19 h yours, then an electrician, needs a haul-out | $5,280–$10,260 |
DIY levels
- Level 5: Owner install. No yard, no electrician.
- Level 4: You fit it, electrician connects. You mount and wire it; a marine electrician makes the final connections.
- Level 3: Split with the yard. The yard does the below-waterline part; you do the wiring.
- Level 2: Wiring prep only. The yard fits the unit and does the hull work; you do the wiring prep.
- Level 1: Yard job. A qualified professional does all of it.
You Yard Electrician. The bar is labor hours; a haul-out is a note.
How we rate DIYThe DockStar hours are the maker’s own two published figures per unit: one to two hours in the manual, and two to three on their About page.
Sideshift’s installation page says six to eight hours per thruster with no special tools. Our fixed-mount figure sits above that. It is worked back from Sideshift’s published installed price range against its kit prices, which is what a yard bills for the whole job, wiring and control included. The maker’s six to eight hours is the thruster alone.
The tunnel hours are a band by boat length, from one itemized invoice up to the job owners describe as typical. The tunnel-and-external row also carries the haul-out the tunnel needs, $750–$2,030 on this 42 ft boat with the lay days counted.
The owner who priced it both ways. The owner of a 41 ft Formula was quoted $25,000 for tunnels at both ends (Trawler Forum, Aug 2025; the quote itself is undated). The tunnels turned out not to fit his hull, so he canceled. He fitted external units at both ends himself for about $11,000 all in, four Absorbed glass mat: a sealed lead-acid battery with the acid held in fiberglass matting. It gives off no gas in normal use and holds its voltage well under a heavy draw. That is why thruster makers name it. batteries included. Both figures are his own, from that one thread.
He put times on it too. The bow took two people a day and a half, and the stern took one day. On the self-contained units the job is shorter still, with no wiring at all.
Which end first. Fit the end that is going wrong, which on a single-screw boat is usually the stern. Add the other when a day comes that one end was not enough.
Sideshift sells the bow and stern units separately. A DockStar unit added later joins the first on the same remote. The second install is the first one again at the other end of the boat. The stern cost page covers what changes when a yard does both in one visit.
Who needs the pair, and who does not
Where the arithmetic draws the line. DockStar's manual gives 20 to 50 feet as the intended use, with no sizing within it. So we size it on the turning effort a boat needs to steer in a 15 knot breeze.
On a trawler, 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. On a sailboat the same lines fall at about 44 ft and 50 ft.
Around those lengths owners run both setups. The answer depends on how tall the boat is and how much wind you dock in, as much as on the length. The calculator will run it for your own boat.
What one unit does on a boat above that line, from my own boat. I run one DockStar at the stern of my 41 ft CHB trawler. It sorted the end that was going wrong. It will not hold the bow when a strong wind gets onto it. That is the case for a second unit rather than a bigger first one.
An owner of a 34 ft CHB with a full The open upper helm on top of a motor yacht or trawler. It adds a lot of height for the wind to push on. said the same thing about a single unit in May 2022:
“We like the dockstar on calmer days, but if you get in any sort of wind it will not be enough.”
Trawler Forum, May 2022
One unit has a ceiling, and that is the reason for the pair. It is also why every figure here is sized for steering rather than for holding the boat off a dock. On a windy day the answer is steering at both ends, or a different plan. A bigger single thruster does not change that day, however much it costs.
You probably do not need two if:
- You have Two engines driving two propellers, set apart from each other. Running one forward and one in reverse turns the boat on the spot without any rudder at all. That is why twins need less help at the stern.. Running one engine ahead and the other astern already steers the stern at zero speed. A twin-screw boat usually wants steering at the bow only.
- One unit covers your boat and the problem is at one end. On a trawler that is up to about 44 ft in a 15 knot breeze. The thruster finder, our free tool that matches a thruster to your boat, prices it in about a minute.
- You object to hardware on the ends of the boat. External units put a leg and a propeller in the water at each end, where debris and crab and lobster pot lines can reach them. On a boat whose looks you care about, that is a fair objection. The no-hole page lists what each product drills, from the installation manuals.
- She already steers at docking speed. Nothing on this page argues for a thruster you do not need.
If your boat is a trawler or a sailboat, its own guide makes this case with that hull’s figures: trawler, sailboat. The sizing calculator works out what your boat needs to steer in a 15 knot breeze. Hold either setup to that number.
What this means when you dock
- If the bow blows off as you slow on the approach, that is a bow problem. One unit at the bow may be all you need.
- If she won’t follow the wheel backing into the slip, that is a stern problem, and a bow thruster does nothing for it. On a single-screw boat the stern is usually the end to fit first.
- If you have to turn a long boat in a fairway her own length wide, that is the spin-in-place move. It takes a unit at each end, run opposite ways.
- If it is blowing hard, no thruster pins her to the dock, a pair included. The pair keeps her parallel in the breeze you normally dock in. On the hard days, plan the approach differently.
Turning moments are this site’s own arithmetic from the makers’ published thrust figures and stated distances, on a 40 ft boat. Prices are the by-boat-type table’s own cells for a 42 ft trawler, hardware captured 23 September 2026 and priced as a yard job. Owner figures are from public forum threads, linked where they appear and dated by when they were posted.
Where one unit stops and two start is this site’s own sizing arithmetic at 15 knots. DockStar’s manual gives 20 to 50 feet as the intended use and no sizing within it.