Hull Pitting Under Trailer Bunks

[nooklegend]

I recently bought a used boat that spent most of its life in Puget Sound. It looks like there is some pitting on the hull under the bunks. (New to aluminum boats and didn't realize this could be an issue) I plan on getting the boat off the trailer and replacing the wood and carpet on the bunks. Is there anything I should do for the hull pitting? This doesn't seem good, but I'm not sure how to remedy the issue. Any advice would be appreciated!

[Chaps]

Not uncommon unfortunately on 5052 hulls or pressed alloy boats that are launched in salt water frequently and sit on carpeted bunks. The pitting is due to lack of oxygen in areas where the hull is sitting on the wet carpet, copper leaching up through the carpet from the pressure treated boards is also part of the problem.

I've repaired a couple of these. Abrasive blast the pitted areas with fine grit, fill and fair with high quality epoxy paste, coat bottom with chlorinated rubber primer and then apply a hard bottom paint. Put plastic covers on bunks.

Don't try to weld the hull in these areas if you have serious pitting, cut out and replace pitted area in this case. A boat builder can handle this.

What kind of boat?

[SJD]

get a roller trailer and forget about the bunks

[goatram]

For a temp and The permanent after you replace the wood get the plastic segments that screw on to the bunks. See here for one type. http://www.surfixinc.com/surfix_trailer_bunkslides.html
EZ loader has a different one that is screwed in from the side.
http://estore.ezloader.com/subcatmfgpro ... 1=289&2=-1

[JETTYWOLF]

I don't even have pressure treated bunk boards but rather no treated Cypress bunks, (cypress is a non-rotting wood in water, since they grow in water)

And still went to the home store and bought heavy carpet runner in black and covered the carpet with them. JUS IN CASE!
(I'm a micro-manager)

I left the carpet to give "cushion" to the bunk boards. No need to go crazy, jus cover up that wood. And don't do it with just Carpet.

[jeffryg]

Does this only occur when the boat/trailer are used in salt water? I'm looking into a new Pacific and would be using it in fresh water (Lake Erie). I've owned both roller and bunk trailers in the past and would prefer a bunk.
Thanks,
Jeff

[Polywave]

Does this only occur when the boat/trailer are used in salt water? I'm looking into a new Pacific and would be using it in fresh water (Lake Erie). I've owned both roller and bunk trailers in the past and would prefer a bunk.
Thanks,
Jeff

I have pitting on the bottom of mine, as well as a friend that has the same boat as me. We both use ours in salt, but religously rinse them after the day (he uses a pressure washer, I immerse mine in a fresh water river, both trailer & boat).

We both still got the pitting, presumably from the carpeted bunks. My friend repaired his at Chap's place, mine is still pitted. We both went to vinyl bunks about a year ago (could it be 2 years now?...). His boat is bottom painted by Chaps and he hasn't has any issues with his at all. I'm holding out to see if going to vinyl is enough. It took about 5 years before we noticed any pitting. My new vinyl bunks are located in a different place than the carpeted bunks (new trailer), so I'll be able to compare one to the other over time.
Poly

[Chaps]

Does this only occur when the boat/trailer are used in salt water? I'm looking into a new Pacific and would be using it in fresh water (Lake Erie). I've owned both roller and bunk trailers in the past and would prefer a bunk.
Thanks,
Jeff

Based on my observations I think the problem appears mainly with boats and trailers frequently immersed in salt water (which keeps the bunk boards and carpet constantly damp with an electrolyte). The bunk boards being pressure treated with chemicals including copper sets up a situation with the alloy hull in the presence of the salty water and voila', pitted hull. I've also seen slight pitting on hulls sitting on bunks covered in plastic if the screws holding the plastic covers on either come into contact with the hull or if there are depressions in the plastic at the screw heads that can trap water which sets up an oxygen depletion situation. Make sure if you have plastic bunks that these areas can drain and dry out. Finally, I have not seen the issue on boats that I'm sure were built out of 5086 plate alloy.

[ALUMINATOR]

I spent the day yesterday replacing the bunks and noticed that even with a 5086 hull I found a lot of corrosion under my front two short bunks. The only thing I could figure out was the hull sets very tightly there and the carpet helped trap the water. No problems under the main support bunks!! Not sure why??? The main bunks sit almost flat while the front pair are sitting on a 50 degree angle. I think I will re-carpet the new bunks but install plastic on the front supports. Since my boat is heavy I used red oak 2 1/4''X 10'' I will keep an eye on the bottom for a while!

[Katoh]

More than likely your problem is from trapped water sitting up against the hull and causing this problem. There also could be another explanation for this. Every time you put your boat on and off the trailer could cause small scratches, Salt gets in and bubble's your paint. Either way it all points to your your skids.
Depending on how far you have to tow your boat, have you thought about changing your skids to a multi roller system. Before people start jumping up and down saying rollers are no good on alloy boats, my boat is 20 years old and there's no damage from the rollers but there's 46 of them.
The other big advantage with the rollers you can drive on and off, without damage.

[goatram]

I will keep the Bunks and plastic caps. Rollers have a tendency to leave the boat at the launch High and dry. Well designed they work great. The cost of switching to rollers will hurt.

[Katoh]

The cost of switching to rollers will hurt.

Yes bugger its not cheap by a long shot, I cant understand why when you mention marine. boat, part, replacement or any of those words in a sentence regarding a cost of an item, the item increases by 100 million % its actual value. Yes toilet paper is 20c a roll but marine or boat toilet paper is $25.50 a roll dolphin safe, and has pictures of octopus and sea shells on it.
I just wonder if the cutting a diagonal grooves in the the skids would help, allow more air flow better cleaning and drainage.
Only a Thought.

[goatram]

Tie Down Engineering has these covers a kit for around $50.

glide covers1.jpg (28.1 KiB) Viewed 9650 times

glide covers1.jpg (28.1 KiB) Viewed 9650 times

(Quote"Black self centering bunk glide on’s with interlocking modular sections. Fits Two 2" x 6" x 8' Bunk Boards. Kits Can Be Combined For Longer Length Bunk Boards and are ideal for painted, NON ALLOY, or aluminum boats.
Kit includes 4 - 1 ft. End Sections, 4 - 3 ft. Sections & 3/4" Stainless Steel Self Tapping Screws. (enough to cover two 8' bunks")

[Tin Cup]

Also have the pitting from carpeted bunks. I put a synthetic siding 'board' over the carpeted bunks with a deep counter sink on the SS screws. I got this product at Lowes and ripped it to width, total cost was under $20 and it has worked out great. Other have used starboard or similar. You can search for detailed thread on this from a while back.