In short
- Bunks usually carry the hull for about 60 to 70% of its length, starting at or just ahead of the transom. That is a dealer and owner rule of thumb, not a code.
- The gap between bunks comes from plain geometry: 2 x (bunk height - keel clearance) / tan(deadrise).
- A steeper V (higher deadrise) sits closer to the keel, so the bunks go closer together. A flatter hull lets them spread.
- Your boat maker and lift maker set the final layout. Cape Coral's permit covers the lift, and we found no city rule on bunk spacing.
On this page
- How bunk length and spacing are worked out in four steps
- Bunk gap by deadrise (10 in bunks, 3 in clearance)
- Bunk length by hull length
- What else to check on the hull and lift
- Questions to ask a marine contractor about bunks
- Next step: get a contractor to set the bunks to your hull
- Sources
- Frequently asked questions
This boat lift bunk spacing calculator is for Cape Coral boat owners who are ordering a lift or resetting its bunks. Enter hull length, deadrise and bunk height. It gives a bunk length range and the gap that keeps the keel off the cross beams. It uses geometry only, with no prices. It pairs with our boat lift capacity calculator and the boat lift permit checklist.
En español: calculadora de soportes de casco del elevador de botes en Cape Coral
| Your numbers | Result |
|---|
Example: a 26 ft boat, 20 degree deadrise, 10 in bunks, 3 in of keel clearance and 7.25 in (2x8) boards.
How bunk length and spacing are worked out in four steps
- Pick the supported length
Bunks usually run from the transom, or just ahead of it, forward for about 60 to 70% of the hull. Longer bunks spread the load on a heavy boat.
- Find the clearance height
Subtract the keel clearance (3 in is a common target) from the bunk height. That is how far the hull may sit above the bunk base.
- Divide by the V angle
The hull rises as tan(deadrise) for every inch out from the keel, so the half-gap equals the height divided by tan(deadrise).
- Double it and check
Double the half-gap for the full gap between inside edges, then confirm clearance with the boat on the lift.
Bunk gap by deadrise (10 in bunks, 3 in clearance)
| Deadrise | Inside gap | Center to center |
|---|---|---|
| 12° | 65.9 in | 73.1 in |
| 15° | 52.2 in | 59.5 in |
| 18° | 43.1 in | 50.3 in |
| 20° | 38.5 in | 45.7 in |
| 22° | 34.7 in | 41.9 in |
| 25° | 30 in | 37.3 in |
Center to center uses 7.25 in (2x8) boards.
Bunk length by hull length
| Hull length | Bunk length | Common length |
|---|---|---|
| 18 ft | 10.8 to 12.6 ft | 12 ft |
| 22 ft | 13.2 to 15.4 ft | 14 ft |
| 26 ft | 15.6 to 18.2 ft | 16 ft |
| 30 ft | 18 to 21 ft | 18 ft |
| 34 ft | 20.4 to 23.8 ft | 22 ft |
| 40 ft | 24 to 28 ft | custom length |
Common lengths are a typical set (12, 14, 16, 18, 20 and 22 ft). Your lift maker may offer others.
The numbers are a start, not a spec. Beam, deadrise, internal structure and weight all vary by boat. Start with the guidance from your boat maker and lift maker, then check the boat on the lift for rocking, uneven pressure marks or a keel that touches. See also the capacity calculator for the lift size and the loads near a seawall guide.
What else to check on the hull and lift
- Propeller and rudder. Commonly 3 to 5 inches of clearance from the lift cross beams is suggested.
- Trailer spacing is not lift spacing. Trailer cross members are often V-shaped and lift beams flat, so a trailer setup can leave the keel too low on a lift.
- Bunk angle. Tilt the boards to match the deadrise so the hull does not rock.
- Transom overhang. Bunks that reach the transom support the stern, where outboard weight sits.
- Lift permit. The City of Cape Coral permits the lift and its engineering. See the permit checklist.
Questions to ask a marine contractor about bunks
- What bunk length and spacing do you set for my hull? Ask for the numbers and how you measured the deadrise.
- Do you set the bunks with the boat on the lift? A test lift shows rocking and keel contact.
- Which hull parts carry the bunks? Stringers, not thin skin, should take the load.
- Can the bunks be reset later? Ask what adjusting costs in labor time, and who does it.
- Does the lift warranty cover hull marks? See the warranty guide for how wall and dock warranties usually read.
Next step: get a contractor to set the bunks to your hull
This result is a planning estimate, not an engineering design. We are a referral service, not a contractor; we connect visitors with independent local providers. Use the form below to ask independent marine and seawall contractors about your lift.
Sources
- Make Wake, Setting Boat Lift Bunks for Proper Hull Support: no one-size spacing; beam, deadrise and internal structure vary, so follow the boat and lift makers.
- Dock Stop, The Perfect Cradle: adjusting bunks under the stringers and matching deadrise.
- The Hull Truth, Boat lift bunk spacing: owner discussion; the deadrise formula and 32 to 36 in examples.
- The Hull Truth, Boat Lift Bunk Length: owner rule of thumb of bunks over about two-thirds of the hull.
The 60 to 70% bunk length is our reading of owner rules of thumb; no code or maker standard sets it. The gap formula is geometry with a flat-V hull, so a real hull with a rounded keel or chines will differ.
Frequently asked questions
How long should boat lift bunks be?
A common rule of thumb is bunks that support about two-thirds of the hull, starting at or just ahead of the transom. Lift makers often stock 12 to 20 ft bunks. Your boat maker and lift maker should confirm the length for your hull.
How far apart should boat lift bunks be?
It depends on the hull. The gap between the inside edges equals twice the bunk height minus keel clearance, divided by the tangent of the deadrise angle. With 10 in bunks, 3 in of clearance and a 20 degree deadrise that is about 38.5 in.
What keel clearance do I need on a boat lift?
Three to five inches between the keel and the lift cross beams is commonly suggested, and the same range for the propeller or rudder. Confirm clearance with the boat on the lift.
Can I use my trailer bunk spacing on a lift?
Not safely without checking. Trailer cross members are often V-shaped and lift beams are straight, so the same spacing can leave less keel clearance on the lift.
Does Cape Coral set bunk rules?
We found no city rule on bunk length or spacing. The city permits the lift and asks for its engineering; the bunk layout comes from the lift and boat makers.