Boat Lift Bunk Materials Compared: Treated Wood, Carpet, Poly Slicks, Aluminum, and Composites

A bunk has two jobs: it must be a stiff beam spanning between cradle brackets, and it must present a surface that spreads load on the hull without scratching it. Some materials do both (aluminum extrusion with a cover, composite with a bonded face); others combine a structural core (wood) with a separate wear surface (carpet or poly). Choosing well means understanding which job fails first in your water.

Quick decision table

Which bunk material fits which situation

Situation	Good choice	Why
Freshwater lake, budget priority	Treated wood with marine carpet	Cheapest, easy to replace, long life in freshwater
Freshwater, boat often loaded by one person	Treated wood with poly slicks	Boat slides and centers more easily as the cradle rises
Saltwater or brackish, fixed lift	Aluminum extrusion with vinyl or rubber cover, or wood with isolation and 316 hardware	Avoids rot and copper-aluminum corrosion
Floating lift	Lift maker's aluminum or composite bunks	Weight and buoyancy matter; bunks are part of the design
Show-finish gelcoat or painted hull	Clean carpet or poly, with frequent rinsing	Both are gentle if kept free of grit
Heavy boat on long bracket spans	Doubled wood or aluminum extrusion rated for the span	Stiffness, not surface, limits life
Zebra or quagga mussel waters	Poly or smooth aluminum	Smoother surfaces are easier to scrape clean

Treated wood

Dimensional lumber, usually southern yellow pine treated with a copper-based preservative, is the default bunk core on most residential lifts. Common sizes are 2x6 and 2x8 on edge.

Strengths

• Inexpensive and available at any lumber yard.
• Easy to cut, round, drill, and carpet with hand tools.
• Slightly flexible, so it conforms a little to a hull with variable deadrise.

Weaknesses

• Rots from the inside at cut ends and bolt holes, where factory treatment did not fully penetrate, unless cuts are field treated.
• Twists, cups, and checks as it dries, especially if installed wet.
• Copper-based preservatives corrode aluminum and plain or electro-galvanized steel, so brackets need isolation and fasteners need to be stainless or hot-dip galvanized. See corrosion protection.
• Heavy, and it gets heavier when waterlogged, which matters on floating lifts.

Use lumber rated for ground contact at minimum (AWPA Use Category UC4A or higher), and ask about marine use categories for saltwater immersion.

Marine bunk carpet

Carpet is a wear surface, not structure. Bunk carpet is a dense, short-pile marine product (commonly polypropylene or nylon) that drains, resists rot, and cushions the hull.

• Pros: cheap, gentle on gelcoat when clean, grips the hull so a boat settles where it is placed, easy to replace without new wood.
• Cons: traps sand and grit that can haze gelcoat over time; holds water against the wood, encouraging rot; UV degrades it; staples rust if not stainless.
• Typical life: 3 to 8 years depending on sun, use, and how much the boat slides on it.

Poly bunk slicks and caps

These are strips of UHMW polyethylene or HDPE screwed onto the top of a wood bunk, or full poly caps that wrap the top and sides. Some lift and trailer bunks come with a poly face from the factory.

• Pros: very durable, does not hold water or grit the way carpet does, low friction so the boat slides and self-centers between angled bunks or V-sides as the cradle comes up, easy to clean.
• Cons: fasteners must be countersunk and kept below the surface as the poly wears; on a lift the boat can shift slightly on the bunks in wakes while the cradle is partly raised; poly expands and contracts with temperature more than wood, so screw holes need a little slot clearance on long strips.
• Typical life: 10 years or more for the poly itself; the wood underneath still limits the system.

Low friction is a real advantage on trailers, where the boat must slide off. On a lift it is mainly a positioning aid. If you add poly to a lift that has no guide posts or bow stop, add positioning hardware too. See guide posts and V-sides.

Aluminum bunks

Extruded aluminum bunks, typically 6000-series alloys such as 6061-T6 or 6063-T6, are standard on many floating lifts and on higher-end vertical and elevator lifts. They usually carry a vinyl, rubber, or carpet-like cover that snaps or slides into a channel.

• Pros: do not rot, stable shape, light, matched alloy to aluminum cradles (fewer galvanic issues), covers replace without tools on many designs.
• Cons: higher cost; stiff, so less forgiving of variable deadrise; covers degrade in UV and must be replaced; dents or bends from a hard landing are permanent.
• Typical life: 15 to 25+ years for the extrusion with periodic cover replacement.

More on alloys and why 6061-T6 is common in lift structures is in boat lift materials.

Composite and engineered bunks

Fiberglass-reinforced plastic, solid HDPE beams, and wood-plastic composites appear on some lifts and as aftermarket bunks. Quality varies widely. Solid plastic beams are rot proof but can be much less stiff than wood of the same size, so they may sag between brackets under a heavy boat, especially in summer heat. Fiberglass-reinforced profiles are stiffer. If you consider a composite bunk, ask for the supplier's load and span rating and compare it with your bracket spacing and boat weight.

Cost comparison

Typical 2026 material cost per linear foot of bunk (materials only)

Material	Typical range per ft	Notes
Treated 2x6 or 2x8 with marine carpet	$5 to $12	Plus fasteners and isolation
Treated wood with poly slick strips	$8 to $20	Depends on strip width and thickness
Full poly bunk caps on wood	$12 to $30	Wraparound profiles cost more
Aluminum extrusion with cover	$20 to $60	Often sold as manufacturer-specific kits
Replacement vinyl or rubber cover only	$4 to $15	For existing aluminum bunks

These are typical ranges that vary by region, supplier, and lift brand, not quotes. For installed costs of bunk work and other maintenance, see the Boat Lift Lab cost index.

Freshwater, brackish, and saltwater

• Freshwater lakes: carpeted wood is cost-effective and long-lived. Watch for rot at the brackets.
• Brackish canals: the wood itself does fine, but copper-treated wood on aluminum brackets corrodes quickly without isolation. Aluminum bunks avoid the issue.
• Saltwater tidal: aluminum bunks with replaceable covers or well-isolated wood with 316 stainless hardware. Marine borers can attack wood that stays submerged in some warm coastal waters, though treated lumber resists them better than untreated.
• Ice country: any material can be damaged if left in the water through freeze-up. Raise or remove the cradle as part of winterizing.

Lifespan figures by environment for bunks and other components are in the component lifespan reference.

What most guides get wrong

• "Carpet scratches gelcoat." Clean carpet does not; trapped grit does. Rinse it.
• "Poly is always better." On a lift without positioning aids, slick bunks can let the boat settle off center.
• "Plastic bunks never wear out." They do not rot, but some sag under sustained load and heat, and covers break down in UV.
• "Any treated lumber will do." Above-ground rated lumber rots quickly in a wet bunk; use ground-contact rated or better.

Frequently asked questions

Are carpeted or poly bunks better for a boat lift?

Both work. Carpet is cheaper, grips the hull, and is gentle when kept clean, but it holds water and grit. Poly slicks last longer, shed grit, and let the boat self-center as the cradle rises, but the boat can shift on them if there are no guide posts or bow stop. In freshwater with good positioning aids, either is fine; choose for maintenance preference.

Do aluminum bunks last longer than wood?

Usually yes. An aluminum extrusion does not rot and commonly lasts 15 to 25 years or more, with the vinyl or rubber cover replaced every several years. Carpeted treated wood typically lasts 8 to 15 years in freshwater. Aluminum costs more up front and is less forgiving of hulls with variable deadrise, but it is a strong choice in saltwater.

Can bunk carpet damage my boat's gelcoat?

Clean marine carpet is gentle on gelcoat. Damage comes from sand and silt trapped in the pile, which can haze the finish as the hull moves on the bunk, and from staples or bolt heads that work through worn carpet. Rinse bunks with fresh water regularly, replace worn carpet promptly, and keep all fasteners on the underside.

Is treated wood safe to use with an aluminum boat lift?

Yes, if isolated. Copper-based wood preservatives corrode aluminum on contact, especially when wet or salty. Put a rubber, EPDM, or HDPE barrier between the wood and aluminum brackets, and use stainless or hot-dip galvanized fasteners. Many lift makers supply isolation pads for this purpose. Without isolation, expect pitting at the brackets within a few seasons.

What is the best bunk material for saltwater?

Aluminum extrusion bunks with replaceable vinyl or rubber covers are a common saltwater choice because they do not rot and match aluminum cradles. Well-isolated treated wood with 316 stainless hardware also works and costs less. Whatever you choose, rinse the cradle with fresh water periodically and inspect fasteners and brackets every season.

Sources and further reading

• American Wood Protection Association (AWPA) Use Category System (UC4A, UC4B, UC5)
• Aluminum Association, alloy and temper designations including 6061-T6 and 6063-T6
• ASTM A153 (hot-dip zinc coating on hardware)
• Boat lift manufacturer owner's manuals and bunk specifications
• U.S. Coast Guard boating safety resources, uscgboating.org