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Can you fit a thruster without cutting a hole in your hull?
Yes. But "no hole" turns out to mean four different things depending on who is selling it, and the difference matters a great deal when it is your boat.
We read the installation manuals rather than the brochures. Of everything marketed as external or no-hole, only a small group genuinely avoids a penetration below your waterline. The rest still drill through your hull. What they avoid is the tunnel and all the fiberglass work that goes with it, which is a real and substantial thing to avoid. It is just not the same as no hole.
The clearest example of the gap. Sideshift's printed product brochure headlines "NO HOLES". Sideshift's own SS-series installation manual tells you to "drill two ½" (13 mm) holes and one ¼" hole through the bow of the boat" for the cables, plus threaded inserts for the clamp strap. Their product pages say the accurate thing: no holes below the waterline. That is a genuinely valuable claim. It is not the same claim as the brochure cover.
What each option actually drills
This is the table we could not find anywhere, so we built it from the manufacturers' own installation documents.
Where it goes through
- Above the waterline. Bracket mounts drill two ½″ and one ¼″ cable hole through the bow. Transom-mounted portables use fasteners only. Neither needs a haul-out.
- Below the waterline. Tunnels, pods, jets, retractables and externally braced units all open the hull under the water. That means a haul-out, and a penetration that has to stay watertight for the life of the boat.
How big the hole is, drawn to scale
- ¼″ Cable hole bracket mount
- ½″ Cable hole bracket mount
- 2″ Pod intake Yacht Thruster, ezDrive
- 3–4″ Jet intake Jet Thruster
- 7.3″ (185 mm) Tunnel tube conventional bow thruster
| Option | True hull penetration | Below waterline? | Haul-out | Install time |
|---|---|---|---|---|
| Sideshift bracket-mount | Two ½" plus one ¼" cable holes through the bow, plus threaded inserts | No | Not required | Claimed 6–8 hrs; owners report 24–36 |
| Deck-mounted portable (DockStar) | Fastener holes only, into transom, rail or a bracket | No | Not required | Self-contained battery, no boat wiring |
| Yacht Thruster / ezDrive pod | One 2" (50 mm) hole through the hull plus two 18 mm bolt holes | Yes | Required | Claimed 1–2 hrs, excluding all wiring |
| Sleipner Side-Power SX pod | "Three small holes" through the hull, no glasswork | Yes | Required | Not published |
| Exturn pod | One large through-hull plus two anti-rotation brace fixings | Yes | Required | Owners report 5 hrs to a weekend |
| Jet Thruster | 3"–4" bottom intake plus two 65 mm thru-hull nozzles | Yes | Required | Not published |
| Conventional tunnel, for contrast | A tunnel-diameter hole through both sides of the bow, typically 6"–9" | Yes | Required | 2–4 days professional; 100+ hrs DIY |
| Retractable | Larger than a tunnel, not smaller | Yes | Required | Generally not a DIY job |
-
Bracket mount
Clamps to the bow, unit hangs alongside
Two ½″ and one ¼″ cable hole, all above the waterline
-
Deck or transom portable
Slides onto a fixed track, lifts off between trips
Fastener holes only, above the waterline
-
External pod
Bolts to the outside of the hull, under the water
One 2″ hole plus two 18 mm bolt holes
Yacht Thruster ezDrive Sleipner SX Exturn
-
Jet
Pump inside, water drawn from below and thrown sideways
3–4″ bottom intake plus two 65 mm nozzles
-
Tunnel
A tube glassed straight through the bow
A 6″–9″ hole through both sides of the hull
-
Retractable
Housed inside the hull, drops down when used
A bigger opening than a tunnel, not a smaller one
Why trolling motors are not on that list
They come up constantly, so it is worth saying plainly: a trolling motor is not a docking thruster, and nobody sells one as one. It is built to move and hold a boat slowly for fishing — sustained low thrust, aimed fore and aft, steered by turning the whole unit. Docking asks for the opposite: a short hard push sideways, on demand, while you are also working the throttle and the wheel. A bow-mount trolling motor has to be deployed, aimed, and given several seconds to swing the bow, which is time you do not have when a beam wind is setting you down onto the boat in the next slip.
That is the answer for the boats this page is mostly about. On something light and high-windage — a pontoon, a tritoon, a small aluminum boat — owners do report modern auto-deploy units working for docking, and we have gone through twenty years of their threads in detail: can you use a trolling motor as a bow thruster? The short version is that it splits by boat weight, and that our own calculator and the forums disagree in an interesting way.
The same idea, built for the job
The comparison is worth running the other way round, because one product on this page is recognizably the trolling-motor idea done for docking instead of for fishing. A DockStar rides on a track on your transom or bow, lifts off between trips, and runs from its own battery. So far, so trolling motor.
What changes is the direction and the timing. It pushes athwartships — sideways, in either direction, the moment you touch the control — which is the only vector that helps when the wind is setting you down onto the boat in the next slip. Nothing has to be deployed or aimed first. The battery is inside the unit rather than a bank you have to find room for and wire in, which is most of the reason the install is a couple of hours instead of a couple of days, with no hole and no haul-out.
Be clear about what you are not buying: more push. Thrust is not the axis where this wins. Minn Kota publishes trolling motors rated at 112 lb of thrust, and Dockstar publishes 90 lb. Both are small-boat numbers next to the 150 to 250 lbf a 40-footer usually wants, and the owner further down this page who found it was not enough in a breeze was not wrong. What you are buying is push in the right direction, at the moment you need it, for a fraction of the cost and none of the glasswork.
Two things fall out of that table. Retractable thrusters get suggested a lot in this conversation and they are the opposite of what the person asking wants, since they need a bigger opening than a tunnel does. And "hydraulic" describes the drive, not the mounting, so it does not avoid a hole either.
So what are you actually avoiding?
Worth being precise about the thing you are trying to get away from, because it is genuinely daunting and the fear is not irrational.
A tunnel install means cutting a hole through both sides of your bow, usually elliptical rather than round to account for the deadrise, bonding a tube in with biaxial cloth and epoxy inside and out, fairing it, barrier coating it, and repainting. One documented DIY job on a 1985 Bayfield hit an inch of solid laminate and fitted a six inch tube with under an eighth of an inch of tolerance. A professional shop doing 400 of these uses a jig that accounts for the hull form. One magazine's framing of the job was simply that it is work for a professional.
“Am I the only one coming out in a cold sweat reading this?”
Trawler Forum, September 2017, on a tunnel install thread
“man does it take some guts to cut a hole that big in a hull...I guess if you do it enought it becomes no big deal!”
The Hull Truth, January 2010
There is a moment in one of these threads that is more honest than anything in the marketing on either side. A poster called cutting a hull tunnel "Easy peasy," and another owner replied that the one person saying it was easy was a professional doing it for a living. Both things are true at once, and which one applies to you is the actual question.
What an external unit costs you
We are not going to sell you the upside without the downside, so here is the downside, collected from owners who fitted these things and then lived with them.
Thrust per dollar
External units generally make less thrust for the money than a tunnel unit of similar price, and larger boats sometimes need a pair. This is harder to check than it should be, because Sideshift publishes horsepower and amperage but no thrust rating in pounds anywhere we could find. You cannot compare it like for like against a VETUS or a Sleipner on published numbers, and we are not going to convert horsepower into thrust to fill the gap.
Credit where it is due on this point: DockStar does publish a thrust figure. According to Dockstar's published specification table, retrieved August 2026, the unit uses two 42A 12V motors for a combined 84A draw, rated at 1,008 watts and 90 pounds of thrust, running from a 12.8 volt 15Ah lithium iron phosphate pack for a stated 10 minutes per full charge, recharging in five hours from a 110 volt outlet.
We ran the arithmetic on those figures before repeating them, because internally inconsistent spec sheets are common in this category. These are consistent. 84 amps at 12 volts is 1,008 watts. That is 1.35 horsepower, which matches what they quote. A 12.8 volt 15Ah pack holds 192 watt-hours, so 10 minutes at full draw implies about 88 percent of the nameplate energy being usable, which is a plausible figure rather than an optimistic one.
What the thrust figure means in practice is the part worth being straight about. Ninety pounds is small-boat territory, roughly comparable to the smallest tunnel units on the market. It is genuinely useful for rotating a light boat in calm conditions, and owners say so. It will not hold a heavy bow up into a stiff crosswind, and owners say that too.
“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 at each end is a different proposition
That wind limitation is real, and it is the honest ceiling on a single unit. But it is a limitation of running one thruster at one end, and the answer to it is the part of Dockstar's own case that a visitor to their site will almost certainly never find: the page carrying it is not in their navigation and not in their sitemap. So here it is.
The same unit works at either end — what changes is the track it rides on. Buy two, put one on the bow and one on the transom, and the remote that ships with every unit already runs both. Their manual is specific about it: the top four buttons drive the bow thruster, the bottom four drive the stern, and neither affects the other. There is no upgraded remote and no second controller to buy. That is a specification, not a marketing line, and it is the detail that makes the rest of this work.
What Dockstar says the pair does that one unit cannot: turn the boat through 180 degrees in place, move it sideways — they call it parallel parking — and hold it firmly against the dock while you get lines on. Those are their claims and we have not tested them, but they are the geometrically sensible ones. Push the bow one way and the stern the other and the boat rotates about its middle; push both the same way and it crabs. A single tunnel thruster at the bow can do neither.
| What you get | Cost | Ends of the boat covered |
|---|---|---|
| One unit, stern, standard hull track | $4,270 | One |
| Two units, bow and stern, standard tracks | $8,650 | Both |
| Professionally installed tunnel thruster | $9,690–$12,265 | One |
Read the middle row against the bottom one, because that is the whole argument. A pair — both ends, full rotational and lateral control, no haul-out, no hole — comes in under what one professionally installed tunnel thruster costs at one end of the boat. Unit price is $3,950 each, plus $430 for a standard bow track and $320 for a standard stern hull track. Add shipping and sales tax, which they do not publish.
What two units do not fix. Each one still publishes 90 lb. Two of them is more torque, not more thrust at either end, and the owner above who ran out of push in a breeze would still run out of push in a breeze — he would just be able to rotate and crab in the conditions where it does work. Dockstar's own comparison claims a pair produces 49% more turning torque than a 150 lb tunnel thruster; we are not repeating that figure as fact, because it is calculated on a hypothetical boat using their older 65 lb unit rather than the 90 lb one they sell now, and without published distances nobody can check it.
There is one turning figure here that needs no assumptions at all. Two equal pushes in opposite directions at opposite ends of the boat make a couple, and a couple's turning effect does not depend on where the boat happens to pivot — it is just the thrust times the distance between the units. On a 40 ft boat with the units 39 ft apart that is 3,510 lb·ft, and it stays that whatever else you assume. Comparing it to a tunnel does reintroduce an assumption, because the tunnel's figure moves with the pivot; the review works that through with every distance printed.
We have gone through Dockstar's published specs, their documentation and every owner report we could find in a full review of the Smart Thruster, including a rebuilt version of Dockstar's own turning-moment comparison with every distance stated, so you can disagree with the numbers rather than take them on trust.
One more case worth knowing, because nobody writes about it: if your boat already has a tunnel bow thruster and what you actually lack is stern control, you do not need a second tunnel. A single unit on the transom at $4,270 gives you the end you are missing, and Dockstar say so themselves. Adding a stern tunnel to an existing installation is most of a second install bill. Their track options are here; which one fits depends on your transom and swim platform, and they size it from photographs and measurements rather than selling it off a shelf.
It hangs in the water where things are
“also no bow on the beach--and if you trailer???. If you rip a hole in the boat during an impact--the cost might be more than $3K.....”
The Hull Truth, June 2007
Debris strikes, dock contact, grounding, beaching and trailering are all real concerns and owners raise them constantly. One owner in the Pacific Northwest had his yard fabricate a fiberglass cradle to protect the unit from log strikes, which is fabrication work beyond what the kit includes. Another cruised the San Juans for years and never had a problem. Sailors raise a more specific version: an underwater protrusion at the bow is something for crab and lobster pot lines to find at night.
Appearance, which people care about more than they admit
“Other than being butt ugly the external bow thrusters seem to work well.”
Trawler Forum, May 2021
The counter, from another owner in the same conversation, is that you only ever see it when the boat is hauled. Both camps are well represented and it comes down to taste. Note that the argument runs the other way too. One owner weighing a Sideshift said he preferred the look of the built-in unit and would rather cut the hole.
Growth, and what it can cost you
An external pod is one more thing to scrub, and jamming it is not cosmetic. Yacht Thruster's own FAQ tells you to antifoul it with an aluminum primer. In one documented case a Nordic Tug owner's stern unit failed after about a year and the manufacturer declined the warranty claim, attributing the failure to a barnacle growing in the tunnel and jamming the prop. That owner was roughly $7,000 out of pocket between the replacement, shipping, haul-out and labor. Two other owners of the same boat model in that thread reported good results, so this is one bad experience rather than a pattern, but the mechanism is worth knowing before you buy.
Reliability, honestly mixed
Owner reports on external units run both ways and we are not going to average them into a verdict. On the good side: one owner eight years in on a 50 foot trawler with no issues, another saying his external stern unit gives him as much control over the stern as his factory tunnel bow thruster does over the bow. On the other side: a motor that failed inside two years, a shaft seal that went at about seven years with a replacement motor around $1,000, and a water-damaged receiver. The manufacturer was described as good to work with in the shaft seal case.
Two things we cannot tell you, because the evidence does not exist. We searched hard for data on how an external thruster affects US resale value and found nothing but aesthetic opinion running in both directions. We also found no US insurance or survey requirement, exclusion or claim data relating to thruster type or install quality. Anyone telling you confidently that an external unit hurts your resale, or that a survey will flag it, is telling you something they do not know. What is documented is narrower and still worth respecting: a badly bedded below-waterline penetration is a recurring source of water ingress that takes a haul-out to fix.
Who should choose which
Pontoons and tritoons: external or nothing
This one is geometry, not preference. A pontoon has no monohull bow to bore through. There are two or three aluminum tubes and a deck, there is no bow cross section for an athwartships tunnel, and putting a hole in a buoyancy tube is the opposite of what you want. The market confirms it: the pontoon products that exist are deck-mounted retractables that bolt to the underside of the deck, and owners who go the cheap route fabricate a bracket for a trolling motor between the logs. That last one is an improvisation, not an equivalent — see above on why a trolling motor is the wrong tool for a docking maneuver — but on a pontoon there is often nothing else to fit. Watch the bow space, though. On many tritoons there is not enough of it for a conventional bow-mount unit.
Houseboats: external, for practical reasons
A tunnel means hauling a 60 to 70 foot houseboat, which on an inland lake is expensive and sometimes logistically awkward. Flat-bottomed shallow-draft hulls also make it hard to get the tunnel the required depth below the waterline. Sideshift sizes a product specifically for this market at $7,080.
Trawlers and displacement cruisers: the best fit for external
This is where the happiest owner reports cluster. Slow speeds mean drag barely matters, single-screw handling makes a thruster genuinely useful, and the space forward is usually full of tanks already. One owner's advice for this class of boat was that if you can fit a suitably sized external stern thruster, fit that and forget the bow entirely.
Sailboats: it depends on the forefoot
Fine bows often have no volume for a tunnel at all, which pushes you external. On the other hand the line-snag concern is sharpest for sailors, and tunnel drag is more modest than it is usually made out to be when the tunnel is properly faired. One owner 13 years into a tunnel with a faired eyebrow reported outpacing similar boats; an engineering estimate on the same thread put the penalty at roughly a tenth of a knot. A widely repeated figure of half a knot is not attributed to any test we could find.
There is one argument here that only applies to sailors, and it is the strongest case for a removable unit anywhere on this page. A deck-mounted portable comes off the track and goes in a locker. On race day the boat is exactly as it was before you owned a thruster — no tunnel, no fairing, no permanent appendage, nothing in the sail plan or the interior. A tunnel is a decision you cannot take back for a weekend. If you race the boat you cruise, that is not a small distinction.
Center consoles and fast express cruisers: the hard case
This is where external is genuinely questionable. Sleipner recommends external units only for boats running under 20 knots, citing risk of damage from wave impacts on planing hulls. Add the beaching and trailering problem and the aesthetics objection, which this group of owners raises more than any other. For a fast planing boat that trailers, a tunnel is often the right answer despite the hole, and the $9,200 to $14,000 figures on a 35 foot center console are the market rate. The exception is a stern unit on an outboard boat, where a transom or swim platform mount stays clear of the running surface.
What your hull is made of changes the answer
On steel or aluminum a tunnel is easier, not harder, because the tube is welded in and there is no glasswork at all. Both VETUS and Side-Power sell metal tunnels off the shelf. If you have a metal boat and a competent welder, the "don't cut a hole" objection loses much of its force. The risk shifts to galvanic corrosion instead, which matters more when you are hanging an aluminum pod on an aluminum hull with stainless fasteners and running hundreds of amps of DC through it.
Wood is the strongest case for staying out of the hull. One owner fitting an external pod to a wooden-keeled boat had to epoxy aluminum braces internally to reinforce around a single penetration, and that was one hole rather than a tunnel. Cored and sandwich hulls are the hardest case for any penetration at all: every hole needs the core dug back and the void filled solid before the fitting goes in.
How long it really takes
The gap between what the marketing says and what owners report is consistent enough to be worth planning around.
| Source | Time |
|---|---|
| Sideshift marketing | "less than a day, with no previous experience" |
| Sideshift installation page | 6 to 8 hours per thruster |
| Owner, bow unit, working with spouse | About a day and a half |
| Owner, stern unit, with help | One day |
| Owner, stern unit connected to existing AGM bank | One day |
| Owner, below-waterline pod including bottom paint | One weekend |
| Yacht Thruster marketing | 1 to 2 hours "for the thruster itself (without cable connections)" |
That last parenthetical is doing a lot of work, because the wiring is the long part and the part people get wrong.
Where people actually get stuck
Not the bracket. Almost never the bracket. It is the electrical side, and the failure mode is sneaky because it looks like the thruster is too weak rather than wired wrong.
- Cable gauge over distance. Sideshift's own limits are a maximum 30 foot run on 1/0 for the 230 series and 50 feet at 2/0 for the 340 series. Exceed that and you lose voltage, which you experience as missing thrust. Their manual warns about it directly.
- Underprovisioned batteries. These units pull 300 to 750 amps. A tired house bank will not supply that. The 350 series wants two 12 volt batteries in series for 24 volts, and owners consistently report about $1,000 for the battery side of the job.
- Not getting the prop deep enough. Sideshift specifies the propeller at least five inches below the shallowest waterline. On some bows that rule ends the project before it starts.
- Pairing and programming. One owner reported working through several versions of the instructions, and a receiver that failed from water ingress.
- Running it too long. Sideshift's guidance is bursts of five to ten seconds and a maximum of 30 with a ten second cooldown, and says outright the units are not designed to hold you against a dock for long periods. That is true of every thruster ever made, of any type.
The argument against all of this
Worth putting the strongest opposing case in full rather than a strawman of it, because it is a reasonable position.
“If you must have a bow thruster, get a built in one, of adequate size. The side shift thruster is basically a large trolling motor. On the other hand, spend some more time working on boat handling...”
The Hull Truth, June 2007 — the same post as the beaching and trailering caution above
The economic version of that argument, which followed immediately in the same thread, is that if the external unit costs most of what a proper installed tunnel costs, you should buy the tunnel. Those particular 2007 prices are long gone but the structure of the argument survives, and it is the right question to ask of any quote you get.
There is also the seamanship objection, which shows up less often in US forums than you might expect and is usually aimed at thrusters generally rather than at external ones. The most articulate version we found, from a sailing magazine, is that a thruster can become a first resort instead of a backup, and that skippers who reach for the button without reading the wind or planning the approach find their situational awareness quietly degrading until the day the equipment does not work. That is a fair warning, and the conclusion those writers reach is a good one: learn prop walk, spring lines and the timing of your own boat's momentum first, then treat the thruster as helpful rather than essential.
The answer from the other side is usually more practical than philosophical. One owner backs 300 yards out of his slip on a single screw diesel and calls the thruster a godsend. Another describes docking going from a stressful evolution to a confident one. Both of those are legitimate reasons to buy a thruster.
Where to go from here
If you have got this far and external still looks like the right answer for your boat, the next question is how much thrust you need, because that is what decides whether a single external unit is enough or whether you are looking at a pair.
- Work out your thrust requirement from your hull type and the wind you want to hold against, rather than from your boat's length.
- Check what the two routes actually cost, including the yard labor rates that make up most of a tunnel quote.
If nothing permanent is the requirement. Deck-mounted portable units are the only category that leaves your hull completely alone, with no below-waterline penetration and no haul-out. On the evidence above that suits a lighter boat in ordinary conditions, and it is not the answer if you regularly dock a heavy boat in a stiff crosswind.
DockStar lists the kit as including:
- Smart Thruster assembly
- Controls and mounting components
- Battery and quick-start materials
- Installation hardware
- Support resources
That is DockStar's own summary of the kit, not ours. Note what it does not settle: the mounting track is a separate part, and which one you need depends on whether the unit goes on the bow or the stern. Confirm the exact contents against your boat before you order.
Price a DockStar for your boat
Reference: — mention this if you call or email
Dock Star.
That is a referral link and we earn a commission if you buy through it. It has not changed a word of what is written above, including the part about running out of push in wind. If your boat is heavier or your slip is exposed, one of the other options on this page is the better buy and we would rather you fitted it.
What we could not verify
- Sideshift publishes no thrust rating in pounds. We will not invent one or derive one from horsepower.
- Jet Thruster has no working US distributor site we could reach and we found no independent US owner reports of one in service, only speculation.
- AccuThrust, the integrated pontoon system, has manufacturer material only. No independent owner reports at all. It is also a factory build option rather than a retrofit.
- Galvanic corrosion on external pods is an inference from documented marine corrosion mechanisms, not from a documented external-thruster case study.
- Two large owner forums block automated access, so some threads on this topic are known to exist but unread by us.
Product requirements taken from manufacturer installation manuals and FAQs published by Sideshift, Yacht Thruster, Sleipner and Jet Thruster. Owner accounts from dated posts on Trawler Forum, The Hull Truth, Sailboat Owners, Great Grady, Meridian Yacht Owners and Tugnuts. Manufacturer performance claims are identified as claims throughout.