How to Adjust and Replace Trailer Bunks and Rollers So Your Boat Sits Right

With the boat on the trailer on level ground, walk around it. Look along each bunk or roller row: does it touch the hull along its full length? Check the gap between the hull and each fender, and between the keel and the trailer crossmembers and tongue. Look at the transom. Take photos and measurements so you can compare later.

The transom carries the engine's weight, so it should sit on the back of the bunks or rollers. ShoreLand'r's setup guide says the bunk or roller ends should be flush with the transom. If the hull sticks out past the supports, the trailer usually allows the bunks or the rear crossmember to slide back. Check your boat builder's manual for how much overhang, if any, is allowed.

Strakes are the narrow ridges that run fore and aft along the bottom of a fiberglass hull. Bunks and rollers should press on the flat areas between them, not on top of them. ShoreLand'r aims for about half an inch of clearance between a bunk and the nearest strake. Load Rite recommends spacing the main bunks as wide as practical while still clearing strakes and other hull features, which gives more side-to-side support. Not sure your boat sits right? Call the boat builder's customer support: some builders give exact bunk spacing at the transom and toward the bow for each hull, based on where the hull structure is.

Loosen the bunk bracket bolts so the bunks can swivel and slide up or down on their brackets. With the boat on the trailer (or floated on, then pulled out), the bunks should lie flat against the hull for their full length. Adjust the two sides equally so the boat sits level, then tighten. On roller trailers, Load Rite warns that one roller set higher than the rest can damage the bottom, so the load should be shared evenly. The keel should carry a share of the weight on the keel rollers where the trailer maker designed it to.

With the full weight of the boat (and engine) on the trailer, ShoreLand'r recommends at least 3/4 inch between the boat and each fender and between the keel and the front crossmember pad, and at least 2 inches between the keel and the tongue. If the hull touches anything other than the bunks, rollers and keel supports, keep adjusting.

Loosen the winch post bolts and slide it toward the boat until the bow stop sits just above the bow eye. ShoreLand'r then tightens the winch strap to hold that position so the strap runs level with the bow eye, tightens the post bolts, and checks the stop is still just above the eye. The winch should pull straight, not up or down. Leave the boat snug against the bow stop, with the strap tight, for towing.

Where the boat sits fore and aft changes the weight on the hitch. Too little tongue weight can make the trailer sway; too much makes the tow vehicle squat and push. ShoreLand'r suggests about 5 to 7 percent of the total boat, motor and trailer weight, and Load Rite's pages give figures between about 5 and 10 percent. Use your own trailer maker's figure. Measure with a tongue weight scale at towing height. On many trailers the axle position is moved to correct it, which is a bigger job: see "When to call a pro."

Worn-through carpet lets the wood or staples scratch the hull. With the bunk off (or the boat off), pull out the old staples and carpet. Wrap new marine bunk carpet tight around the board, with the seam and staples on the underside, and staple it with stainless or Monel staples so nothing touches the hull. Load Rite recommends bunk slides or covers instead of carpet on aluminum (metal) hulls, because wet carpet holds moisture against the metal.

Probe the boards with a screwdriver: soft, split or cracked wood needs replacing. Unbolt the old board, cut a new one to the same length and profile, and bevel or round the top edges if the old one was shaped. If your hull is aluminum, ask your trailer dealer which board, cover and fasteners suit a metal hull. Carpet the board (step 8), bolt it back on in the same position, and recheck steps 2 through 5.

Spin every roller by hand. Replace rollers that are flat-spotted, cracked, seized or worn down to the shaft, and their pins if they're rusted. Match the size and type, and keep each roller at the same height and angle as its neighbors so the load stays even.

BoatUS describes target bunks as a short pair of bunks near the front of the trailer in a V shape that catch the keel and center the boat as you load, which helps in current and wind. In BoatUS's how-to they mount on the crossmembers just forward of the axle, with the fronts close to the bow and within a few inches of the centerline, widening toward the back. Kits come with brackets and support tubes.

Back the trailer in until the bunks are wet but not floating the boat off, load the boat, and look at how it sits after you pull out on level ground. Adjust in small steps. Before every tow, check that the bow safety chain and transom straps are on: Load Rite stresses that the winch line is not a tie-down.