fiberglass over steel?

Stainless Hull

"by accounts it was cheaper build the boat in
stainless"

Cost debate aside, is it so that stainless steel has its own set of problems with respect to longevity as a boat hull material?

A person who has always looked at the kitchen sink might think stainless is impervious to corrosion damage, but that is simply not true on many applications. For example, building a steam boiler out of stainless steel is virtually prohibited by the ASME Boiler and Pressure Vessel Code, which is the most used code for boilers throughout most of the world.

 

Yes. If you want a really expensive and effectively corrosion free hull, build out of cupronickel.

PDW

 

Polyurea is quite hydroscopic and absorbs a lot of water when continually immersed ( 2.4% ). Any voids fill with water which passes slowly through the polyurea and further disbonds the coating.

 

boats in inox existe from long time. But are built in small numbers.
The reason is that the inox costs about as aluminum, but it is heavy as steel.

The main advantage of the normal steel is its low cost. If you want to cover with fiberglass, the result, over time, might even be worse than the cure. and the low cost advantage of the normal steel, lost.

 

Nice lightweight special then.....

Mind you Platinum would look nice....

 

No one mentioned that Polyester resin is not waterproof. Putting it over steel would be asking for trouble IMHO

 

Here is an example.

 

Due you mean epoxy paints are a standard coating or fiberglass?

I don't think I have ever seen a steel hull covered in fiberglass. Seems like asking for all kinds of trouble.

 

Ray

Waterproof is a definition that can be misleading, it's defined as less than 0.01% weater absorbtion in 24 hrs immersion. So polyester is classed as waterproof, just not impermeable.

All plastics including epoxy absorb some water, their molecular bonds have enough space for water molecules to slowly permeate the solid, and also to slowly dry out given the opportunity. Epoxy has the lowest absorbtion.

Polyester resin can be quite problematic for continual immersion, and that same water if it cannot pass through leads to hydrolysis of the polyester the breakdown products are acidic which isn't a good combination with steel. Acid blisters in the plastic to steel interface that will also continue to expand since polyester disbonds easily.

Polyester fairing compound is sometimes used over metal boats with very poor results too.

 

In a previous life I did a great deal work coating the insides of very large steel chemical tanks, the exact resin was chosen depending on the chemical being stored in it.

Most were VE's with at least two layers 3 oz. CSM. Electronic equipment was used to detect pinholes or thin areas.

If better adhesion was needed it could be coated with a product like Atprime prior to glassing.

My current aluminum jet boat has a honeycomb floor that was glassed over, the glass goes up the sides about 4" to create a watertight tub, there are no penetrations in the entire floor. The glass to aluminum bond has help up with no issues for 14 years.

I'm not going to say glassing a steel hull is the best thing to do, only that it is possible to do it and have hold up, technique, skill and attention to detail can make or break the job though.

 

A while back I made some deck alterations to a polyester trawler, there was a large steel gantry on the stern that had to be adapted for new net drums. The gantry was polyester/glass covered and looked as if it had been there since the boat was built, at least twenty years. One of my jobs was to strip off the polyester in the weld areas and clean the metal. Since there were quite a few rust bleeds and bubbles where the legs had been knocked by the trawl 'doors' I expected it to be a corroded mess underneath but actually the corrosion was mostly limited to the damaged areas and hadn't spread much. I was impressed with how it had held up in such an aggressive environment.

 

Using Fiberglass over steel is something very common to avoid rust, if you don't do it right you may end up with some very horrible rust blisters!

 

yes, formal definitions and vernacular are often at variance.

In any event, the outcomes we both expect, agree

 

fiberglass and steel

It will work if you prime the metal with a decent primer. If you can heat the steel up to drive of any moisture spray paint will work as a primer. Steel epoxy fiberglass is your best choice. Straight polyester will fall off with the rust stuck too it.

 

It's always interesting when someone says "polyester does this" or "polyester does that". there are so many different formulas, versions and ideas on how to make a polyester resin that the performance in any application can vary so much it's hard to imagine.

There are polyester resins that hold up very well when being submerged, and others that may fail on a humid day. Part of the problem when formulating a polyester is that 98% of the market is governed by the demand for a low cost product, not high quality. What happens is you get bean counters or cheap fabricators that think any product will work in any application, so they buy the cheapest product they can find, this results in what most peoples opinions are based on.

The highest end of the spectrum of polyesters can challenge epoxy in many applications, even exceeding what epoxy can do frequently, but that market is so small that little or none of these resins are sold. VE's can take it to the next level when the same chemistry is used, but again, nobody wants to pay for that performance.

Many (most) putties tend to get the lower end resins which are then loaded with cheap fillers, not much of a chance for success when $$ is all that counts.