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Old 02-15-2014, 12:09 PM   #1
Shootin&Reelin's Avatar
Join Date: May 2009
Location: San Diego
Posts: 597
Trailer Modification – Replacing Roller Bunks with Bunk Boards

In my research for this project, could not find a lot if information on this process, so I thought my project could provide some insight for others.

I know that this is probably not the best way to do it, but it worked for me.

Purchased the following:

1)2x - 4 ton bottle Jacks – $19.99 each – Harbor Freight tools
2)12x - cinder blocks - $12.99 – Home Depot
3)2x - 4x4x8 - $20.74 – Stabilizing Bunk Boards – Home Depot
4)2x – 2x6x10 - $20.34 – Keel Bunk Boards – Home Depot
5)8x – 3/8-16 x2-1/2” Carriage Bolts SS - $1.88 each - Home Depot
6)8x – 3/8-16x 4” Carriage Bolts SS - $3.94 each – Home Depot
7)2x – 4 pack of 13” Bolster Brackets - $39.96 each – etrailer.com
8)4x – Bunk Carpeting - $21.95 each – etrailer.com
9)8x – u-bolts SS – 4”long x 3-1/8 x 7/16 diameter - $9.99 each – etrailer.com


1)Jacked the boat up off the trailer and supported with a base of cinder blocks and 20” 2x6’s covered in carpet.

2)Was able to remove the u-bolts supporting the roller bunks on 6 of 8 bolts with a impact driver. Other two bolts had to be removed with a 4” angle grinder. Removed roller bunks.

3)Measured the support bars to find center. Mounted 2 inch pieces of 2x6 & 4x4 to the bolster brackets to see where I wanted to mount the brackets to the support bars on the trailer and to see where the boards would be supporting the hull. The boat is a mid-80’s 18ft Boston Whaler Outrage which like to be supported by the keel.

4)Once I identified the ideal location for the bunks, mounted the bolster brackets to the trailer support bars. Placed the bunk boards on bolster brackets. Marked on bunk boards where the mounts were.

5)Removed the bunk boards and drilled the holes for the carriage bolts. Started with 1/8 inch drill bit and increased in size to 3/8 inch. Counter sunk the carriage bolts 1/8 inch into bunk boards. When I hammered in the carriage bolts, I lined with wood glue at head.

6)Carpeted the bunk boards with marine grade carpet.

7)Adjusted the height of the keel bunks bolster brackets to the ideal height.

8)Raised the boat with the bottle jacks and removed the cinder block supports and lowered boat down onto the trailer.

9)Adjusted the 4x4 keel bolster brackets to the ideal height.

10)Did one final adjustment to all bunk boards and brackets to ensure maximum contact between the bunk boards and the hull. I used the bottle jack on each und of the bunk boards bolster brackets to either lower or raise bunk accordingly.
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Old 02-17-2014, 07:42 PM   #2
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Join Date: Apr 2013
Posts: 79
Re: Trailer Modification – Replacing Roller Bunks with Bunk Boards

Great write-up and easy to follow. Center bunks make it easy to power load a boat on the trailer.
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Old 03-02-2014, 10:11 AM   #3
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Join Date: Dec 2006
Posts: 167
Re: Trailer Modification – Replacing Roller Bunks with Bunk Boards

Useful write up. However, you should know that cinder blocks aren't very safe for supporting weight -- they often crack and/or shatter.

If you want to make some cheap supports, cut up some cheap 2x4s into 12" lengths and stack them up, held together with 3" screws. These supports -- called cribbing -- will hold several tons safely no problem.

mactrac is offline   Reply With Quote


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