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Express cruiser thrusters: bow, stern or both on a planing hull
An express backs into a slip better than almost anything on the dock, because the whole drive turns. Then a breeze comes across the fairway, the bow swings off, and you find out the drive has no opinion about the front of the boat. This guide works out how much push the bow needs and which kinds of unit will fit a planing hull. It closes with the one tunnel quote an express cruiser owner has published.
The short answer
The bow. The sterndrive already covers the stern, as the section bow, stern, or both explains.
A 35 ft express with a hardtop or bimini needs about 50 lb from a tunnel to keep steering in a 15 knot breeze. A full camper enclosure calls for about 55 percent more than the same hull with an open cockpit.
A tunnel, or a retractable where the hull has the depth. An external unit does not suit the bow of a boat that planes, because that is where a hard wave lands first at speed.
A unit built for sterndrive boats bolts to the drive’s cavitation plate, the flat plate above the propeller on the drive leg. Nothing goes through the hull. Sideshift says it can go on afloat; we recommend fitting it with the boat out of the water. Sideshift’s SD kits run $4,495 to $5,495, for boats to 50 ft. They help when the drive is in neutral and the stern still needs to move.
The one tunnel figure on this hull is a quote of $25,000 for tunnels at both ends of a 41 ft Formula 41PC, never bought. This site's own estimate for a 35 ft boat is in the cost table.
Bow, stern, or both on an express cruiser
Start with the bow. A sterndrive swivels, so it steers the stern ahead and astern while the engine is pushing. Nothing on the boat pushes the bow sideways.
At the bow, the choice is a tunnel, or a retractable where the hull has the depth. An external unit is the easy fit on slower boats, but it does not suit a boat that planes. The section will a tunnel fit forward? works out whether your hull has room.
At the stern, a unit for sterndrive boats does exist, and it is the easy one to fit. It bolts to the drive’s cavitation plate, and nothing goes through the hull. Sideshift says it can go on afloat, but we recommend fitting it with the boat out of the water. It fills a narrower gap: the moments when the drive is in neutral and the stern still needs to move. The section the stern already steers covers it.
At both ends, you can move the whole boat with the drive in neutral. Our page on bow and stern thrusters together explains what that adds.
Buying only one? Our page bow or stern first? helps you choose, and our page on what a stern thruster costs has the dated prices for the back of the boat.
A 35 ft express cruiser, stopped, turning about her middle. The arrows point the way each unit pushes to turn her: the bow one way, the stern the other.
The stern already steers
A An engine inside the boat driving a steerable leg out through the back of the boat. It steers like an outboard with the motor inboard. It is common on express cruisers, and it leaves no room for a stern tunnel. swivels the whole leg, so the push goes where you point it, ahead or astern. That is why an express backs into a slip more accurately than an inboard with a 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.. It is also why almost nobody with one complains about the stern.
A sterndrive covers the back of the boat the way an outboard does, as long as the engine is pushing. The thruster finder counts it that way.
The bow is not covered. Nothing on a sterndrive boat pushes the bow sideways. At approach speed the bow is the end the wind takes first, usually while you are still looking over your shoulder at the stern. The engine makers have come to the same conclusion.
Volvo Penta announced a docking joystick for a single diesel sterndrive in September 2022. Its release called the company the first in the industry “to integrate the steering of the diesel sterndrive with the control of the bow thruster on a single engine installation”. The stick works because a bow thruster is on it. Volvo Penta offers it new or as a retrofit on its single DPI drives.
So on this hull the question is about the bow. On a boat that planes, the answer is 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., or a A thruster that lives inside the hull and drops down through a hatch when you press the button, then pulls back up. It leaves no permanent hole in the water flow. where the hull has the depth.
A stern unit is on the market for sterndrive boats, and it is priced below. It fills a narrower gap than a bow unit: the moments when the drive is in neutral and the stern still needs to move.
What the bow needs at 15 knots
A thruster is a steering control, not a holding device. These figures size it to keep the bow answering in an average breeze, not to pin her against a dock in a strong crosswind. They assume the unit sits where a tunnel has to go: on a 40 ft boat, about 6 ft back from the bow.
| Boat length | Thrust from a tunnel |
|---|---|
| 26 ft | 28 lb |
| 30 ft | 38 lb |
| 35 ft | 50 lb |
| 40 ft | 65 lb |
| 45 ft | 83 lb |
Wind exposure varies more on an express than on most hulls. An open cockpit with a bimini is one boat. A hardtop with a full camper enclosure is a much bigger sail on the same hull. Zip the canvas shut and the wind sees a different boat.
| How much wind she catches | Thrust from a tunnel |
|---|---|
| Low: open cockpit, no top | 40 lb |
| Medium: hardtop or bimini (assumed) | 50 lb |
| High: hardtop with a full enclosure | 63 lb |
The full enclosure calls for about 55 percent more thruster than the open cockpit, on the same boat. Run it for your own boat. The calculator assumes the middle row and lets you change it, and it prints every step of the arithmetic.
Will a tunnel fit forward?
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. needs a spot where the tube sits far enough below the waterline to stay fed with water. It also needs hull on either side to bond into.
A planing hull is fine and shallow at the bow, with a sharp The angle of the hull bottom from flat, seen from the front. A deep V has a lot of it and needs more water under the bow before a tunnel will fit. that only fills out further aft. So the tube goes back to where the hull is deep enough, on a shorter 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.. On some boats it does not go in at all.
The one owner this site holds on this hull found that out with a quote in hand. Comodave, on Trawler Forum, was quoted $25,000 for tunnels at both ends of his 41 ft Formula 41PC. He canceled, because the tunnels would not fit the hull.
He then fitted external units at both ends himself for about $11,000, four batteries included. He reports being pleased with the result in the Sideshift review.
That quote is the one tunnel figure on this hull, and it is in the cost section below. So why does this page still list no external bow unit for a boat that planes? The makers' manuals put a speed limit on one. An express cruiser runs past it the moment she comes up on plane. The next section has the details.
The further back the tube sits, the more thrust the same turn needs. Turning force is thrust multiplied by the distance from the point the boat pivots about. The figures above already assume a tunnel's position.
If a yard tells you the tube has to go well aft of that on your hull, ask them to size for it. The calculator prints what each position needs. Our page on what each product drills goes through the installation manuals.
Why not an external unit on 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. bow unit hangs off the hull where a tunnel cannot go. On a slow boat, that is often the answer.
This site does not list one for a boat that planes. At speed the bow is where a hard wave lands first, and a unit hanging off it takes the hit.
Sideshift's installation manual (Rev 3.1, November 2025) recommends a maximum of 15 mph in rough water “to prevent damage to your bow thruster”. An express cruiser on plane is well past that.
Sleipner's external thrusters page (read 16 September 2026) offers its EX pods as “a practical thruster solution for displacement and semi-planing boats up to 60 feet, independently of hull form, hull-material, propulsion and depth”. The no-hole page treats the fast planing boats as the hard case for the whole external style.
No external bow unit is listed for a boat that planes. The cost table below says so in the External column.
That style earns its place on a slow hull with a bow that refuses a tunnel. The trawler guide and the bow-and-stern page cover those boats.
The retractable: the other bow route
A A thruster that lives inside the hull and drops down through a hatch when you press the button, then pulls back up. It leaves no permanent hole in the water flow. lives in a box inside the hull. At the dock it drops out and works like a tunnel unit. Underway it lifts back in, and a hatch closes the opening flush. Nothing is in the water at speed.
That is the bow unit the makers sell for a fast boat. Sleipner lists its SR80 for motor boats and sailboats of 33 to 49 ft.
Max Power's VIP 150 page reads “high performance sailing yachts and super-fast motor yachts 40-60'”.
In VETUS's retractable manual, the sawn-out hull section becomes the hatch that closes the opening underway. None of the three makers puts a speed limit on a retractable.
What it costs you is depth and a bigger hole. The box needs more hull depth than a tube does, so the forefoot question above comes back with a harder answer. On a planing hull, the box goes further aft than a tube would.
It is a haul-out job, with a large opening and moving parts below the waterline. The cost table below prices the retractables that qualify on a 35 ft express, beside the tunnel column. The types page compares the three styles.
What that means for what you buy
At the bow
Two things fit. One is a tunnel unit sized to the table above, from any of the makers whose thrust ratings are published. The other is a retractable, where the hull has the depth for the box.
The ratings are easy to compare, and the cost table below prices both jobs. The finder lists every unit that fits your length with what each costs fitted. Whether your forefoot will take the tube or the box is the yard's call, boat by boat. Ask that question before you price anything, and before you get attached to a model.
At the stern
One family is built for this drive. Sideshift's SD series bolts around the sterndrive leg. Its job is the moment the drive is in neutral and the stern still has to move. On this hull that is a smaller gap than the bow.
The same manual covers these kits on a boat that planes. Page 32 says: “When operating the boat at high speed, trim the outboard motor or I/O to ensure the thruster is just above the water surface when the boat is at planing speed. Failure to trim properly at high speed can cause heavy steering and may damage the thruster.”
| Model | Kit price | Thrust published | Boat length |
|---|---|---|---|
| Sideshift SD230 Sterndrive Stern Thruster
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | $4,495 | Not published | Up to 30 ft |
| Sideshift SD230-D Sterndrive Stern Thruster
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | $4,995 | Not published | 30–40 ft |
| Sideshift SD240 Sterndrive Stern Thruster
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | $4,995 | Not published | Up to 35 ft |
| Sideshift SD240-D Sterndrive Stern Thruster
The maker’s own listing, read 28 August 2026. Full page: fit, cost and wiring See it on the maker’s site | $5,495 | Not published | 35–50 ft |
What it costs
Express cruiser owners have published almost nothing about what they paid. Ask on a forum and you get opinions. A receipt is harder to come by. On the tunnel route, this site holds one quote: 41 ft Formula 41PC, Aug 2025, $25,000 for tunnels at both ends, quoted and never bought. He canceled: the tunnels would not fit the hull. The quote itself is undated.
That is one boat and one yard, and the money never changed hands. It says nothing about what a single bow tunnel would have come to.
This site's estimate is below, priced as a boatyard job on a 35 ft express from published prices. The tunnel column assumes your bow has room for one, which is the forefoot question above.
| External | Tunnel | Retractable |
|---|---|---|
| Not listed for a boat that planes | Tunnel thrusters for a 35 ft express cruiser Most jobs cost $9,500–$10,500. The least expensive, fitted by a boatyard:
And 8 more models, up to $13,000 for the VETUS Bow Pro 421. The thruster itself, before fitting: $900–$3,300. The boat has to come out of the water for these. Find the right one for your boat | All bigger than needed Retractable thrusters for a 35 ft express cruiser Every one we list is more thruster than this boat needs. Fitted by a boatyard, least expensive first:
And 6 more models, up to $39,900 for the Lewmar 250VRTT Vertical Retractable. The thruster itself, before fitting: $7,400–$29,400. 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.
What this means when you dock
If the stern goes where you point it and the bow blows off, that is the end nothing on a sterndrive boat covers. Price a bow tunnel, or a retractable where the hull has the depth, sized from the sizing table.
If you run with a full camper enclosure, size from the high row. That is about 55 percent more thruster than the same boat with no top.
If a yard says the tube has to go well aft, ask them to size for that position. The further back it sits, the more thrust the same turn needs.
If the stern still needs to move with the drive in neutral, the stern kit is the easy fit. It bolts to the drive’s cavitation plate, and nothing goes through the hull. See what that means for what you buy.
What we could not find
Any paid tunnel price on an express cruiser, from an owner or a yard. This site holds one quote, from 2025, for two tunnels, canceled.
Any maker naming express cruisers as a target hull for a bow unit. Sideshift names the sterndrive itself for its SD series.
A speed rating for a retractable from Sleipner, Max Power or VETUS. Their pages and the VETUS manual name the boats and say nothing about speed.
Any published rule for how far aft a tunnel has to sit in a planing hull. Yards answer it boat by boat, usually with a flashlight in the anchor locker, and nobody writes the answer down.
Sizing figures are this site's own estimates, checked against the sizing the makers publish. Owner figure from Trawler Forum, August 2025. Sideshift manual, Sleipner pages, VETUS manual, Max Power page and Volvo Penta release read 16 September 2026.