boat trailer bunks

So the other day I am climbing under the boat as part of changing props (Lake Powell, again), and I notice that bolts that hold the bunks on are loose, nearly all of them. What has happened is that the boards have shrunk from being dunked in the water many times and then left in the 110 degree sun covered in black carpet. This likely happens to all bunks that are made of simple 2 X 4's. Untreated wood is just not made for that kind of abuse. I even have one bunk that bows down a little and does not make full contact with the boat when on the trailer.

My question is this: Why don't trailer makers use a synthetic board that would be more durable? Something like what you can see at Home Depot that people are using now for decks. Why not?

only one reason..., money. Pressure treated wood costs more. Use it when you replace the bunks. Also, it is better to use a recessed carriage bolt coming thru the top of the board, rather than a lag bolt from underneath. This means you have to put the carpet on after drilling a hole and putting the bolt in.

Talltigeguy,

I've also wondered about that. I should replace my bunks before the next 'towing season'. I've thought about replacing them with the recycled plastic/sawdust boards.

Anybody?

Bruce, the plastic deck boards are not nearly as structural as treated pine. You really can't beat pressure treated (wolmanized) lumber for this application.

Ditto Rich's comment.

The plastic wood used for decks has very poor structural strength. Unless you supported the plastic wood along its length it would crack and fall apart under the weight of the boat.

I just want to encouarge everyone to check your bunks. Have the tools and next time you launch go back to you trailer and look to see all the bolts are tight and none have sheared off. I got in a bit of a sticky situation with my 88 Ski Nautique because I had never checked on the bunks and 4 of the bolts on one side near the front sheared off. Granted my trailer is much older than probably most of yours but it still wouldn't hurt to check.

I am not sure what is on the other end of the bolts I see under the boat, if they are lag bolts or carriage bolts. If I need to replace them, will consider the pressure treated lumber. Thanks for the thoughts everybody.

talltigeguy,

Sorry to hear about your shrinkage problem. I thought we only had such issues with our cold water here in the north.

I believe your trailer is an Extreme and if so they are through-bolted not lag bolted. I would just tighten up the nuts and keep an eye on the bunks next season. As you said the heat in your climate has made them shrink but I doubt that the strength of each bunk is significantly diminished after only a couple of seasons.

just replaced mine. Boat is a 1996 and the carpet was finally wearing. The wood on mine was presure treated. It's a DHM trailer. I did replace the week though with new stuff. If you check the bolts with the boat on the trailer you get a better idea of how tight. The weight of the boat loads the board.

Just out of curiosity, are any of you guys doing something to make sure your carriage bolts stay solid on top, like maybe a metal insert? The reason I ask is that when I redid my bunks, I went from a carriage to a lag bolt specifically because the carriage bolts were stripping the wood away because of the constant soaking, and it made them incredibly hard to get out (had to cut a few) when I redid, so I used lag bolts to make sure future replacements were easier.

What are the disadvantages of lag bolts? Are you worried about shearing them, or the point coming through the top and wrecking the hull?

Oh, btw, I am also planning on using the same pressure-treated bunks next time, but was thinking about the possibility of rhino-lining them prior to carpeting (which also might help with the carriage-stripping problem, if i decide to go that route). Any thoughts on that?

i don't think the hull would slide very well on the rhino stuff. I redid mine earlier this year and lag bolted from the bottom. I bought the 2x4s, carpet and spray glue. Pre-assembled the bunks in the garage. Next time out we launched the boat and spent a few minutes under the trailer with a dewalt and then went riding. If the carriage bolt strips, wouldn't the lag bolt be stripped too? Not sure i see the need for the carriage bolt

heh...sorry, I wasn't completely clear, i was saying to rhino-line, THEN carpet...not just the lining, certainly.

I did it the same way...pre-made everything, put the boat in the water and let some buddies drive it for a half-hour or so while i took the old off and popped the new ones on, took almost no time.

I can see a lag bolt stripping out of the wood easier than a carriage bolt, but not by much...so I think you're right, if you're hitting it that hard, you're gonna be screwed either way.

I have seen some teflon type of material applied to the top of the existing bunks. I think it was 1/2" x 4". No scuffing he said it slides right on and off.

Be careful with the teflon strips.... never back down a ramp without the boat connected to the winch. Your boat will easily slide off and could possibly end up laying on the ramp high and dry. That would be a bad day. A very bad day.