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Attaching bunks to trailer, what fastener?


Arick

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So my "new" boat needed to have the bunks replaced.  So I removed the old ones and found from the factory they were installed with lag bolts. A few were missing and some were stripped. So i bought some 2x6's that were green treated and then headed to the fastener section.  It was there I was told about carriage bolts (stainless) and I decided that was the way to go. This is where I start to run into problems...

I drilled a hole in the wood just big enough to get the bolt in with a few light taps of a hammer.  Once the head was close to the wood, I gave it a nice hard hit from the hammer.  I put a washer, lock washer and nut on the other side and start tightening.  I get to a point where tightening with one hand, the bolt starts to spin.  :Frustrated:GREAT... After a minute of wondering what the issue is, I determine its the wood.  I believe the wood is too wet.  So I go find a nice dry 2x4 in my garage and repeat the process.  Once again the bolt spins.

What am I doing wrong here?  

Should I go back to lag bolts and just be done with it?  It would be a lot easier.

 

EDIT: "There's two O's in goose"

Edited by Arick
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Stainless steel carriage bolts though the wood.

Drill in this order:
1) Start with a small diameter pilot hole--say 1/8" all the way through the wood. 
2) Drill a countersink from the top using a 3/4" spade bit about 3/8" deep.

3) Finish the hole using a bit the same diameter as the carriage bolts.   Make the hole tight so that the wood would hold the bolt firmly. 
Stainless flat AND locking washers. Stainless steel nuts.

Pressure Treated 2" x 4".  While the wood doesn't stay in the water very long, the very nature of carpet is to hold water so your wood is in constant contact with moisture once your boat is back on the trailer.
 

Good luck

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5 minutes ago, ORMailbuboater said:

Stainless steel carriage bolts though the wood.

Drill in this order:
1) Start with a small diameter pilot hole--say 1/8" all the way through the wood. 
2) Drill a countersink from the top using a 3/4" spade bit about 3/8" deep.

3) Finish the hole using a bit the same diameter as the carriage bolts.   Make the hole tight so that the wood would hold the bolt firmly. 
Stainless flat AND locking washers. Stainless steel nuts.

Pressure Treated 2" x 4".  While the wood doesn't stay in the water very long, the very nature of carpet is to hold water so your wood is in constant contact with moisture once your boat is back on the trailer.
 

Good luck

Even though I didn't mention it in my first post, I did try this on a separate test piece of wood. It still ended up spinning.

 

16 minutes ago, jbower said:

Use a cordless impact instead of turning it by hand. It should sink the carriage head 

Not sure how this would help?  The square part of the carriage bolt is stripping the wood when I do it by hand.

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Some stainless hardware is not threaded well and will bind up.  Make sure the nut is spinning freely all the way up on the carriage bolt.  I bought some stainless bolts from Fleet Farm and 3 out of the 6 you couldn't spin the nut to the top of the bolt and I broke 2 of them trying to use them.   

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For future replacement of bunks again with rusted carriage bolts you could use socket flat head bolts or socket button heads. Google for pics.

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I also sometimes drill the hole 1 size to small and hammer the bolt in without drilling a countersink then impact it until it's sunk

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13 minutes ago, jbower said:

I also sometimes drill the hole 1 size to small and hammer the bolt in without drilling a countersink then impact it until it's sunk

Tried that but tried to tighten by hand and it still spun.  Based on all the "Use an impact" comments, looks like I will be headed to a friends house to try it before I buy it!  

Thanks all!

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Just now, Pnwrider said:

Or just counter sink as previously recommended, that's how I did my bunks...

I tried that with a spade bit. However I can only get the bolts snug and not tight.  The bolt starts to spin when I try to go beyond snug. 

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you can counter sink with a spade bit so it is deep enough to sink the bolt and make sure to use one of these: http://www.mcmaster.com/#97449A103

 

Or just counter sink it far enough and use a hex head bolt so you have something to grab with want to take the bolts out in a few years.

 

Edited by twitchee2
  • Like 3
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Impact should work no problem. I think after you use it you'll buy one. I have a porter cable 1/4 inch that works good. Also a Milwaukee 1/4 and 1/2. The Milwaukee works better than the porter

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Can you get a pair of channel locks on the end of the bolt, once the nut is up beyond that point, to keep it from turning? Possibly wrap some duct or electrical tape around the jaws of the pliers to prevent damaging the bolt threads. Just tighten the nut enough to flatten the lock washer, or as I did, use nylock nuts.

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So am I the only one freaking out that the top of these carriage bolts are rubbing the boat. I know they are round but still :(. Unless they are super counter sunk. Why not just stick with lag bolts. It looks like it is off a 1998 boat so if they were the stock bunks the lags lasted 18 years. Go lags for another 18.

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3 minutes ago, tdelandsheer said:

So am I the only one freaking out that the top of these carriage bolts are rubbing the boat. I know they are round but still :(. Unless they are super counter sunk. Why not just stick with lag bolts. It looks like it is off a 1998 boat so if they were the stock bunks the lags lasted 18 years. Go lags for another 18.

I've done a couple trailers with the countersunk carriage bolts.  I fill the top with silicone and have never had any issues.

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Here's how I did mine a year or two ago....

Cut board to length.

Figure out where the holes need to be.  Drill holes a little smaller.

Hammer in carriage bolts.  Smack well to countersink.

Wrap bunk in carpet.

Attach bunk to trailer.

Use impact for nuts.

Carriage bolt are covered with carpet, no scratching gel coat.  If the bolts spin, use a pry bar for leverage between the bunk and frame.  Or vice grips on the threaded part of the bolt and a gear wrench. 

 

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2 hours ago, tdelandsheer said:

So am I the only one freaking out that the top of these carriage bolts are rubbing the boat. I know they are round but still :(. Unless they are super counter sunk. Why not just stick with lag bolts. It looks like it is off a 1998 boat so if they were the stock bunks the lags lasted 18 years. Go lags for another 18.

Because unlike your results, most lag bolts work loose over the years and many fall out. My 4 year old trailer actually had a  bunk float off when all lag screws took a hike. I used to check them yearly too. I rebunked with Galvanized carriage bolts and did not countersink, just drew them in on top of the carpet till they were well below the surface. Checked occasionally for them backing back out but never did.

Edited by dalt1
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26 minutes ago, dalt1 said:

Because unlike your results, most lag bolts work loose over the years and many fall out. My 4 year old trailer actually had a  bunk float off when all lag screws took a hike. I used to check them yearly too. I rebunked with Galvanized carriage bolts and did not countersink, just drew them in on top of the carpet till they were well below the surface. Checked occasionally for them backing back out but never did.

Nyloc nuts stop them working loose.

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1 hour ago, dalt1 said:

Because unlike your results, most lag bolts work loose over the years and many fall out. My 4 year old trailer actually had a  bunk float off when all lag screws took a hike. I used to check them yearly too. I rebunked with Galvanized carriage bolts and did not countersink, just drew them in on top of the carpet till they were well below the surface. Checked occasionally for them backing back out but never did.

Sounds like whoever installed the lag bolts drilled way too large of a pilot hole.

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I used a dab of marine silicone on the end of the carriage bolt to keep the nut from coming off. Didn't use nylock because I didn't want the carriage bolt to spin in the wood. Snug is all you really need (good n snug) if you have a good countersink bore. 

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