Can You Put a Boat Lift on a Floating Dock?
Quick answer
Yes, but only a lift that carries the boat on its own buoyancy (an air-chamber or floating hydraulic lift) or a lift standing on its own pilings or legs beside the dock. A cable lift hung from the dock frame puts the boat's whole weight on the dock's floats. For a 4,000 lb boat on a typical finger slip, that is more than the floats can carry even fully submerged. Published floating lifts run from 1,200 lb to 32,000 lb, but the largest ratings apply only in U-shaped slips.
On this page
- Which lift types work on a floating dock
- Why a hung lift sinks the dock
- Adding flotation does not rescue a hung lift
- L slip or U slip: what changes
- A fixed lift beside a floating dock
- The reverse case: a floating lift at a fixed dock
- Water depth under a floating lift
- Where this answer stops applying
- Frequently asked questions
- Sources and further reading
Yes, if the lift floats itself. An air-chamber lift or a floating hydraulic lift carries the boat on its own tanks or floats, and the dock only holds it in place. A free-standing or piling lift set in the slip next to a floating dock also works, because the bottom carries the boat. The one arrangement that does not work is the one most people picture: a cable lift bolted to the dock frame. That puts the whole boat on the dock's floats, and a dock built to carry people and deck boards does not have that much buoyancy to spare.
The confusion is understandable. The boat already floats in the slip, so it seems the dock never notices it. But a floating boat is held up by its own hull. Once a lift raises it clear of the water, its weight has to go somewhere. On a hung lift, that somewhere is the dock floats. On a floating lift, it is the lift's own tanks.
- Works: air-chamber floating lifts, floating hydraulic lifts, drive-on floating ports, and free-standing or piling lifts that stand on the bottom beside the dock
- Does not work: a cable or hydraulic lift hung from the floating dock's frame
- Published floating-lift range: 1,200 to 10,000 lb (Hewitt BoatPort), 4,400 to 25,000 lb (HydroHoist HarborHoist), up to 32,000 lb (HydroHoist UltraLift-2, U-shaped slips only)
- Dock float math: each square foot of float footprint carries about 5.2 lb per inch it sinks in freshwater
- Slip shape: one walkway finger (L slip) is enough for some lifts; the largest ratings need a finger on both sides (U slip)
Which lift types work on a floating dock
The question is not really whether the dock floats. It is what holds up the boat once it is raised: the lift's own buoyancy, the lake bottom, or the dock. The table sorts lift types by that answer.
| Lift type | What carries the boat | On a floating dock | Published limits |
|---|---|---|---|
| Air-chamber floating lift (Hewitt BoatPort, HydroHoist) | Its own tanks | Works | BoatPort 1,200 to 10,000 lb with one walkway finger, L or U slip. HarborHoist 4,400 to 25,000 lb in U, double-wide, L or square slips |
| Air-chamber lift, largest ratings (HydroHoist UltraLift-2) | Its own tanks | Needs a U slip | Up to 50 ft and 32,000 lb in U-shaped floating slips; 26 ft and 6,600 lb at extra-wide slips or L-shaped moorings |
| Floating hydraulic lift (Sunstream) | Its own floats | Works; built to mount on floating docks | Model-specific; ask the dealer for the rating and slip shape |
| Drive-on floating port (PWC and small boats) | Its own floats | Works | ShoreMaster ShorePort: up to 1,450 lb with all 300 lb of supplemental flotation added |
| Free-standing or piling lift in the slip | The bottom, through legs or pilings | Works if not attached to the dock floats | Water depth and level range must suit the lift; see below |
| Cable or hydraulic lift hung from the dock frame | The dock's floats | No | The worked example below shows why |
How the two families of floating lift work, and how to size their buoyancy, is covered in floating boat lifts. The brand pages for HydroHoist and Sunstream cover fit and dealer questions.
Why a hung lift sinks the dock
A float sinks until the water it pushes aside weighs as much as the load on it. Freshwater weighs 62.4 lb per cubic foot, so every square foot of float footprint carries 62.4 / 12 = 5.2 lb for each inch the float goes down. That number decides everything. A dock carries a boat on a hung lift only if its floats have enough footprint, and enough height left above the water, to take the boat's weight.
Ordinary dock floats are not built for that. A 24 x 48 x 12 in polyethylene float filled with foam is listed at 434 lb of buoyancy (PermaFloat BD2448-12, which weighs 31 lb) or 450 lb (Taylor Made). That is close to what the float can hold fully submerged: 8 cubic feet of water is 499 lb, less the float's own weight. So the listed figure is the load that pushes the float right under. It is not a working load.
Worked example: a 4,000 lb boat hung from a U slip's floats
Dock: a U slip with two 20 ft fingers, each on five 24 x 48 x 12 in floats (one every 4 ft). That is 10 floats with 8 sq ft of footprint each, so 80 sq ft in total. Assume the floats ride 4 in deep under the dock's own weight, which leaves 8 in of float above the water.
Load: a 4,000 lb loaded boat, plus about 420 lb of lift (the listed weight of a 4,000 lb free-standing vertical lift, from how much a boat lift weighs). Total: 4,420 lb.
- Stiffness of the dock: 80 sq ft x 5.2 lb = 416 lb per inch of sinking.
- Sinking needed to carry the load: 4,420 / 416 = 10.6 in.
- Sinking available: 8 in, worth 8 x 416 = 3,328 lb. The load is 1,092 lb more than that.
- Result: the floats go fully under, and the dock keeps sinking until its frame and deck are in the water. All the deck's freeboard is lost, along with any wiring under the deck.
- What it would take: to carry 4,420 lb with only 4 in of extra sinking, the dock needs 4,420 / (5.2 x 4) = 213 sq ft of float footprint. That is about 27 floats of this size against the 10 under the fingers.
Real docks do worse than this. The example assumes the load spreads evenly across every float. A lift puts it on four mounting points, so the floats nearest them sink first and the fingers twist. The dock also rises again each time the boat is lowered, so every lift cycle moves the deck by the better part of a foot, and the gunwale with it.
The same arithmetic shows why a floating lift does not have this problem. Hewitt's 26 ft BoatPort weighs 2,216 lb and is rated for 7,500 lb, and all of that rides on its own polyethylene float tanks. The dock only keeps the lift from drifting. Hewitt describes the dock and lift as moving together, which is the point: the dock follows the lift up and down with the water, not the boat's weight.
Adding flotation does not rescue a hung lift
Dock makers do sell extra flotation, but the increments are sized for people, gangways and PWCs, not boats. ShoreMaster's ShorePort drive-on PWC port takes supplemental flotation in 100 lb increments, up to 300 lb in total, for a capacity of 1,450 lb. Covering the 1,092 lb shortfall in the example would take eleven such increments. Even then the dock would ride on its float tops every time the boat came up, with nothing left for a person stepping aboard.
There is a way to put a hung lift on a floating structure: build a dedicated float under the lift that carries the boat. But a float sized and fixed to a lift frame is a floating lift, and the makers already sell those with tested ratings. Starting from dock floats means doing that engineering again without the testing.
L slip or U slip: what changes
A floating lift sits in the slip and ties to the dock beside it. How many sides it ties to changes how big a boat it can carry.
- U slip (a finger on both sides): the lift is held on both sides and stays square to the dock. HydroHoist's largest published UltraLift-2 ratings, up to 50 ft and 32,000 lb, apply only here. Boarding is possible from either side.
- L slip or extra-wide slip (one finger): the lift is held from one side, so the open side is free to roll and swing. HydroHoist publishes 26 ft and 6,600 lb for the UltraLift-2 at these moorings, about a fifth of the U-slip figure. Hewitt's BoatPort is built for this layout: it needs "just one walkway finger along the side of the lift" and fits L or U docks across its 1,200 to 10,000 lb range.
- Square or double-wide slips: the HarborHoist release lists U, double-wide, L and square spaces across 4,400 to 25,000 lb, and says the lift "can simply be tied to a dock or moored with a conventional mooring system".
The practical rule: if the boat is over 26 ft or 6,600 lb and the slip has only one finger, ask the dealer for the rating at that mooring, not the headline capacity. Slip widths and clearances are in dock and slip layout.
Field tip: the one finger a floating lift ties to has to take wave and wake loads from the lift as well as foot traffic. Check that finger's floats, frame and hinges before ordering. A finger that already rides low or flexes at its hinge to the main dock will get worse.
A fixed lift beside a floating dock
A free-standing lift or a piling lift can sit in the slip next to a floating dock, as long as it does not hang from the dock. The bottom carries the boat, and the dock carries only you. The catch is that the two move differently. The dock rises and falls with the water and the lift does not, so the gap between deck height and the raised gunwale changes all season.
On a lake that moves a foot over the summer, that is a minor nuisance. On a reservoir that drops several feet, or in tidal water, it decides whether boarding is safe, and it can leave the lift in water too deep or too shallow to use. Run the lowest and highest water levels through water depth requirements before choosing this route. Piling costs and sizing are in piling requirements, and the wider trade-off is in floating vs piling boat lifts.
The reverse case: a floating lift at a fixed dock
Floating lifts can also go at stationary docks, with a limit. Hewitt says its BoatPort can be mounted to a stationary dock only where water levels move no more than 16 in in total. A floating lift tied to a fixed dock has to slide up and down past it, and the brackets only allow so much travel. HydroHoist's HarborHoist release lists both fixed and floating docks. If your water moves more than the lift's brackets allow, the floating dock is what makes a floating lift work.
Water depth under a floating lift
A floating dock removes the high-water problem, but not low water. When lowered, an air-chamber lift has to sink far enough for the boat to float off. Hewitt says its BoatPorts can be installed "in water as shallow as 4 to 8 feet to as deep as you want". Measure the depth at the lowest level of the year, at the slip, before ordering. A floating dock that settles onto the bottom in a drought takes the lift with it. The water depth calculator does the check.
Where this answer stops applying
- Barge and concrete floating docks. Large commercial floating docks with deep concrete or steel pontoons have far more footprint and reserve than residential finger floats. Whether one can carry a hung lift is a question for the dock's engineer and its rated live load, not for the example above.
- PWCs. PWC lifts are typically rated around 1,200 lb, under a third of the example load, and drive-on ports exist for exactly this case. They are compared with PWC lifts in PWC lift vs drive-on port.
- Saltwater. Seawater is about 64 lb per cubic foot, so floats carry about 2.5% more than the freshwater figures here. That does not change any conclusion on this page.
- Permits. A floating lift and any new finger usually count as structures in the water. Check before ordering; see boat lift permits.
Safety: never stand or work under a raised boat, and do not board a floating lift that is listing. Blowers and hydraulic pumps on a floating dock need circuits installed by a licensed electrician with GFCI or ELCI protection. Wiring on a dock that moves is exposed to strain and water, and a fault can energize the water and cause electric shock drowning. See boat lift electrical.
Frequently asked questions
Can you put a jet ski lift on a floating dock?
Yes, using a drive-on floating port or a floating PWC lift, both of which float on their own. ShoreMaster's ShorePort takes up to 300 lb of supplemental flotation for a 1,450 lb capacity. A conventional PWC lift bolted to the dock frame would put the PWC's weight on the dock floats. A small dock may carry that, but a port avoids the question entirely.
How much weight can a floating dock hold?
Each square foot of float footprint carries about 5.2 lb per inch it sinks in freshwater. A common 24 x 48 in float is listed at 434 to 450 lb of buoyancy, and that is close to its fully submerged figure, not a working load. Add up the float footprint under your dock and decide how many inches of sinking you will accept. That gives the working load.
Do you need a U-shaped slip for a floating boat lift?
Not always. Hewitt's BoatPort needs one walkway finger and fits L or U docks up to 10,000 lb. HydroHoist's UltraLift-2 needs a U slip for its top ratings of 50 ft and 32,000 lb. At L-shaped or extra-wide slips, HydroHoist gives 26 ft and 6,600 lb. Ask for the rating at your slip shape.
How long does a floating boat lift take to raise a boat?
Hewitt gives about one minute per 1,000 lb of boat weight for its BoatPort, so a 4,000 lb boat takes roughly four minutes. Air-chamber lifts rise as the blower displaces water from the tanks, so heavier boats need more air and more time.
Sources and further reading
- Hewitt, "Boat Port" floating boat lifts: floating dock fit, one walkway finger, L or U docks, 4 to 8 ft water, 1,200 to 10,000 lb, 115 V AC, generator or 24 V battery, 16 in limit on stationary docks (https://www.hewittrad.com/boat-port/)
- Hewitt, 7500 BoatPort 26 ft: 7,500 lb capacity, 2,216 lb, polyethylene float tanks, about one minute per 1,000 lb of boat weight (https://www.hewittrad.com/products/lifts/boatport/7500-boatport-26)
- HydroHoist Boat Lifts, HarborHoist launch release, March 1, 2019, via Great Lakes Scuttlebutt: fixed or floating docks, slip shapes, 4,400 to 25,000 lb, tie or conventional mooring (https://www.greatlakesscuttlebutt.com/news/press-room/hydrohoist-boat-lifts-launches-most-versatile-lift-available-capable-of-raising-25-000-lbs/)
- Jeff Hemmel, "Five Alternative Boat Docks," Boating Magazine, updated July 17, 2013: HydroHoist UltraLift-2 ratings by slip shape (https://www.boatingmag.com/gear/five-alternative-boat-docks/)
- Boat Lift and Dock, ShoreMaster ShorePort drive-on PWC dock: supplemental flotation in 100 lb increments, up to 300 lb, 1,450 lb capacity (https://boatliftanddock.com/p-594-shoremaster-shoreport-drive-on-pwc-dock.aspx)
- Barr Plastics, PermaFloat 24 x 48 x 12 dock float BD2448-12: 434 lb buoyancy, 31 lb (https://www.barrplastics.com/products/24x48x12-dock-float-bd2448-12)
- Fisheries Supply, Taylor Made dock floats: 24 x 48 x 12 in, 450 lb buoyancy (https://www.fisheriessupply.com/taylor-made-products-dock-float)