How to Measure Boat Trailer Bunks

Boat width influences trailer bunk placement.

If you've bought a boat from someone, but they aren't including the trailer in the sale, you should ensure that your trailer is big enough to accommodate the boat and that the bunks on your trailer are long enough and wide enough to cradle the new boat while it's being transported. If you're closing the deal at a boat landing (the seller backs the boat off of his trailer into the water and you pull it back up on to your trailer), you want things to go smoothly--including the loading of the boat.

Things You'll Need

• Measuring tape
• Assistant

Instructions

1. Tell your assistant to hold the end of the tape on the forward end of the trailer bunk. Pull the tape to the end of the bunk and read the length from the tape. Set the end of the tape on one side of the bunk and pull the tape across the bunk. Read the width measurement from tape. Record the measurements. Repeat for each bunk.

2. Tell your assistant to hold the end of the tape on the front end of the outside edge of the bunk farthest to the left of the center line of the trailer. Pull the tape to the front end of the outside edge of the bunk farthest to the right of the center line. Read the distance between the bunks from the tape and record the measurement.

3. Tell your assistant to move the tape to the front end outer edge of the next bunk inboard of the bunk you just measured (the next one closer to the center line of the trailer). Pull the tape to the front end of the outside edge of the corresponding bunk on the opposite side. Read the distance between these bunks from the tape and record the measurement.

4. Have your assistant hold the tape at the front of the bed of rollers that support the boat's keel (backbone) on the center line of the trailer and pull the tape to the back of the rollers. Read the distance from the tape and record the measurement.

Tips & Warnings

• Bunks support your boat's hull on the trailer, but your motor needs support as well. Don Casey, boating expert for the Boat Owners Association of the United States (BoatUS), says that, "To protect your transom and outboard from the rigors and stress of road travel, consider a motor support. Adjustable struts hold your engine's lower unit in position, while built-in shock-absorbers prevent damage."

Resources

• BoatUS: Trailering Tips