How to Modify a Boat Trailer

Modifying a boat trailer will give your boat a stable ride to the ramp.

Modifying a boat trailer that you already own to work with a boat that you just bought is a matter of adjusting the trailer's bunks, rollers and the winch to keep your boat cradled, as if it were a newborn needing support along its back (the keel), around its sides (under the flat bottom surfaces) and under its head (the bow). Look at the way the boat rests on the trailer before you begin modifying things, and make only the modifications necessary to support the boat and make it stable on the trailer.

Things You'll Need

• Adjustable wrench
• 6-foot spirit level

Instructions

1. Take your adjustable wrench and raise the roller on the center line of the trailer if the boat is resting on the bunks, but not on the keel roller. To adjust the roller, loosen the nuts on the bolts that hold the roller in place, lift the center of the roller until it touches the keel of the boat and tighten the nut. Then, move to one end, raise the rollers to the keel and tighten the nut. Move to the other end of the roller and repeat the process.

2. Set a 6-foot spirit level across the stern of the boat, so you can see if it's level from side to side. Use your adjustable wrench to loosen the nuts holding the bunk in place under the port side of your boat and lower the bunk until your boat is sitting firmly on its keel. Re-tighten the nuts.

3. Loosen the nuts holding the bunk under the starboard side of your boat and lower the starboard bunk until the level shows that your boat is level. Re-tighten the nuts.

4. Move the winch on the front of the boat backward or forward to the length of the boat, if necessary. Depending on the trailer, you might unbolt the winch mount or simply pull a pin.

5. Modify the way the boat "rides" by hooking the trailer to your vehicle, "blocking" the trailer wheels with a block of wood or a concrete block and pulling the latch (next to the axles, on the frame) that allows you to move the trailer axles forward or backward under the frame. If the weight on the trailer tongue exceeds 5 to 7 percent of your vehicle's Gross Axle Weight Rating (its "GAWR," usually shown on the placard inside your vehicle's door frame and found in your owner's manual), you need to back the axle car a little, to put more of the boat's weight behind the trailer axles, instead of on its tongue. If it seems "just a bit light" on the forward end--perhaps to the point of trying to lift the tongue off of the vehicle's trailer hitch--then you need to pull the axle car forward a bit, to shift some of the weight to the trailer's tongue and onto your trailer hitch.

Tips & Warnings

• Before you begin shifting bunks, make sure that they are equally spaced on both the left and right side of the trailer; otherwise, the boat will ride off-center and damage may occur. The spacing on the bunks doesn't need to be even from the front of the trailer to the back of the trailer.

• When adjusting the trailer axles, the towing vehicle's rear end shouldn't sag more than an inch when you put the trailer on the vehicle's trailer hitch, if you have good shock absorbers.

• Never put your hands, fingers, head, feet, or any other part of your body between the bottom of a boat and a bunk or roller while you are modifying the trailer.

Resources

• BoatUS: Trailering Tips