Trailer Bunk Lag Screws

[rkilpa]

The last time I retrieved my empty EZ Loader trailer, I noticed one of my bunks was lifted from one of the rear brackets due to missing lag screws. I removed all of the rusted galvanized lag screws and replaced 20 screws and washers with $40 worth of stainless steel ones. Where the screws were missing, I moved the bracket slightly to be able to drill new pilot holes and securely tighten the new screws. I'm curious why the original lag screws on a boat trailer would not be stainless steal to begin with. Is there a reason, other than cost, that galvanized screws were used instead of stainless steel?

 

[dingbat]

I'm curious why the original lag screws on a boat trailer would not be stainless steal to begin with. Is there a reason, other than cost, that galvanized screws were used instead of stainless steel?

There are currently over 1,000 different alloys of "stainless steel" in production with varying degrees of suitability for use in the marine environment.

Do you know what grade you installed?
Grades of stainless suitable for marine use are primarily 316 and 316L.
Not readily available at big box stores and expense when you find it.

Two issues with the use of stainless hardware:
1. Zinc hardware is used for cathodic protection. Stainless steel's nobility, or lack thereof, can/will cause less noble metals in the assembly to corrode at accelerated rates.

2. Stainless steel owes it corrosion resistance to a thin layer of chromium oxide that develops on it's surface. Stainless experiances crevise and pitting corrosion when used in an "oxygen free" (wet wood) environments.

 

[rkilpa]

There are currently over 1,000 different alloys of "stainless steel" in production with varying degrees of suitability for use in the marine environment.

Do you know what grade you installed?
Grades of stainless suitable for marine use are primarily 316 and 316L.
Not readily available at big box stores and expense when you find it.

Two issues with the use of stainless hardware:
1. Zinc hardware is used for cathodic protection. Stainless steel's nobility, or lack thereof, can/will cause less noble metals in the assembly to corrode at accelerated rates.

2. Stainless steel owes it corrosion resistance to a thin layer of chromium oxide that develops on it's surface. Stainless experiances crevise and pitting corrosion when used in an "oxygen free" (wet wood) environments.

Wow! Thank you for the info. I didn't realize this. I just thought stainless steel was stainless steel and would be better against rust. Should I have replaced the rusted screws with another set of galvanized screws, or did I remove rusty zinc plated screws?

This is what I purchased from Home Depot, along with SS washers: Stainless Steel Lag Screws

They were pricey, so I hope they are marine grade.

Here is a picture of some of the screws that were removed and what was used as replacements.

 

[Scott Danforth]

95% of stainless is 18-8 or 304

Not 316

Galvanized steel is about 4x the strength, and normally lasts as long as the wood

 

[rkilpa]

Here is the link to the screws: SS Lag Screws

States "grade 2" under specs?

 

[airshot]

Best way to know if it is truly SS is to carry a small magnet with you to test. If the magnet attracts to the SS, then there is not enough nickle in the stainless to stop it from rusting. Nickle is not attracted to a magnet. Cheap SS has small amounts of nickle to slow down the corrosion but not stop it comopletely. I carry a small magnet in my console, whenever I go in to buy SS, I carry the magnet. What I have found on bunks is to use carriage bolts and slightly recess the heads. Nyloc or double nutted on backside makes sure they never fall out. If you carpet your bunks even better.

 

[dingbat]

Best way to know if it is truly SS is to carry a small magnet with you

Stainless steels are classified into four main families: ferritic, martensitic, austenitic, and duplex, with duplex stainless steels being combinations of the first three types, such as martensitic-ferritic or austenitic-martensitic.

Hint…some are magnetic by design. Most “high strength” stainless is magnetic

If the magnet attracts to the SS, then there is not enough nickle in the stainless to stop it from rusting.
Nickle is not attracted to a magnet. Cheap SS has small amounts of nickle to slow down the corrosion but not stop it comopletely.

Stainless steel is by definition an alloy containing a minimum of 10% chromium, which imparts its corrosion-resistant properties. The chromium forms a thin oxide layer on the surface of the metal, shielding it from corrosive elements.

In the case of 316, its molybdenum that provides its superior corrosion resistance.



Nickel is primarily used to enhance the materials mechanical properties

 

[airshot]

I can only say that I have used the magnet trick for over 50 years and in that time have never had a real SS bolt corrode or rust in that time period.

 

[Scott Danforth]

18-8 or 304 hardware is magnetic along with about a thousand other SS alloys

316/316L is not magnetic along with about a thousand other SS alloys

Then there are the duplex alloys

 

[cyclops222]

You can not tell very much with a magnet and S S metals.

 

[airshot]

You can not tell very much with a magnet and S S metals.

I can tell you they won't corrode away....served me well for almost 50 years.

 

[dingbat]

I can only say that I have used the magnet trick for over 50 years and in that time have never had a real SS bolt corrode or rust in that time period.

I will guarantee you 304 and 18-8 will “rust” in the presence of saltwater within weeks of installation.

 

[airshot]

I will guarantee you 304 and 18-8 will “rust” in the presence of saltwater within weeks of installation.

Can't speak for saltwater, as I am in fresh water only area ( great lakes region) ...never had a non magnetic SS bolt corrode in my 50 plus years of boating, but salt water may be a different story.