Steel Pontoon Rust....

Dave I.

Well-Known Member
Hey all Worders!
I have had several people ask in the past 2 years about lifespan of these steel pontoons on these older houseboats. What I have told most is that routine maintenance is an absolute must, but yes, being steel and in the water, yes there probably is a definite lifespan on the pontoons.

The current boat I an scrapping out is a 1977 Boatel 39'er. Rotten floor and walls, was taking on water and owners did just walk away from it after they removed what they wanted. Long story short, here is what I found inside this 43 year old boat's pontoons. Keep in mind that these pontoons had the "preventative oil" in the toons.

First pontoon (Port) has about 2" of ice in the bottom and as you can see, the inside is almost completely coated in rust. But keep in mind, the rust is not cratered at all. For the most part, it's mainly surface rust. Still should be concerning if your inner toons look like this but definitely not enough to be immediately concerned with. If this toon was dried out, welded properly, pressure tested and sealed up, I would see many more years from this toon before any real dramatic problems would happen. But the key words there are drying out and proper welding.

The second (Starboard) pontoon is nearly spotless inside the pontoon. It would be a safe bet this toon has never seen water in it over the last 43 years. There is some rust on the upper right side but the brown on the bottom is the "preventative oil". There is no rust on the bottom of the pontoon.

But please don't go to any of the businesses near the lake and use these pictures as a reference to their repairs and what can be done. I have seen pontoons that are rusted thru from the inside and you can poke a ball point pen thru the steel.

After I have seen this on a 43 year old boat, it really kind of changes the perspective regarding these old rental boats. If someone is looking at a boat for sale, find someone with a bore scope and look inside the pontoons. I am going to do it with the boat I have up for sale. Even if the inside looks like the Port toon, I would feel confident the boat would see many more years of enjoyment.

As far as the "preventative oil" I do not know what kind of oil it is. It is not self burning, but will burn with flame on it (flame resistant). It is pretty thick in cold weather and coming out of the toons, was a pretty dark brown. Would it be recommended to add it to the steel toons? That would have to be your personal choice after doing your own research. But, take into effect that with oil in the toons, some companies may refuse to weld/repair due to fire risk. The choice is completely up to the boat owners.

If I come across a pontoon that shows what to avoid when you look inside, I will post it. Don't give up on all these steel pontoons. Know what to look for. ;)

Happy Boating everyone!


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Dave I.

Well-Known Member
Dave, Has anyone thought about filling the pontoons with Argon or Co2 for corrosion prevention? I did this with a 24' Sylvan steel pontoon I had 25 years ago. Sq
Ya know Sq, while I was writing this I thought about that very same thing. The thing I came up with is if a controlled vacuum (to remove ALL O2) and argon fill, it very well could prevent rust from getting worse, Rust does live off O2.

So now, I am designing the system to implement (in my mind) this but selling it would be the issue. Maybe not either.

Honestly, I think it would be more effective in rust control than the "preventative oil" because it would protect the entire interior pontoon instead of just the bottom and splash areas.

If anyone wants to try it, let me know. I have a plan and an idea. I will get the stuff to implement and we can go from there.
 

Dave I.

Well-Known Member
One catch would be that the Pontoons would have to be guaranteed leak free which would be a warrantee issue with the welding company and boat owner.

This preventative measure wouldn't be covered by my awesome customer service if the toons leak.
 

Rivergoer

Well-Known Member
Dave, those pictures are incredible for a boat that age, even the worst picture isn’t terrible.

One thing I’ve found is there will always be some moisture inside pontoons. It forms through condensation from the daily hot/cold cycles. So obviously steel pontoons will eventually rust from the inside out even if there are no leaks.

Our 36’ 1980 Kayot had severe rust with holes ranging in size from the ‘swiss cheese’ variety all the way up to one that was 3” wide x 30” long. With the exception of the large hole previously mentioned, all were below the waterline. This was due to condensation (and in one case, gray water) settling on the inside bottom.

A word of caution if you own or are considering a steel pontoon boat...these photos were all taken BEFORE blasting. The swiss cheese holes on the bottom of the toon were much more pervasive than shown here because they were hidden by the old coal tar epoxy coating. So visual inspection may not always show what’s going on underneath the coating.

After blasting, what we originally thought would be a small project welding-in a few patches here and there quickly became a complete re-skin after hidden cancers were revealed.

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After sandblasting, both pontoons were ‘re-skinned’ with galvanized steel from waterline down, stem to stern. Plus the large hole on the upper inboard shoulder was patched (it had been caused by a broken sink drain that allowed gray water to run directly on top of the pontoon for what appeared to be MANY years).

Fortunately we had connections through a friend with a machine shop and a computerized brake large enough to bend 5’x10’ sheets of steel. Not sure what that service would cost ‘retail’ but we paid $1,500 to form up 8 sheets to the contour of our pontoons (the profile was taken from the aft end of a pontoon and traced onto plywood to form a template).

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Ends were capped (above) and seams were welded then sealed again with 12” wide doublers.

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Then it was a fresh coat of 3M Coal Tar Epoxy (nasty stuff, be sure to wear respirator and painter‘s coverall or plan on tossing whatever you’re wearing. Do NOT get it on skin, it does NOT come off...it eventually ’wears’ off.

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All told (steel, epoxy, machine work, my labor and a hired welder) I estimate this job ran about $6K (boat is 36’ long x 12’ wide). The toons are airtight...how do I know? On a warm day, I can pull the top vent plugs and pressurized air blows out the vent holes.

Anyway, all this to say I agree with you Dave...with the correct process and care, new life can be breathed into old steel boats. Insurance however (sigh) is another ballgame...
 

Attachments

Dave I.

Well-Known Member
Obvoi
Dave, those pictures are incredible for a boat that age, even the worst picture isn’t terrible.

One thing I’ve found is there will always be some moisture inside pontoons. It forms through condensation from the daily hot/cold cycles. So obviously steel pontoons will eventually rust from the inside out even if there are no leaks.

Our 36’ 1980 Kayot had severe rust with holes ranging in size from the ‘swiss cheese’ variety all the way up to one that was 3” wide x 30” long. With the exception of the large hole previously mentioned, all were below the waterline. This was due to condensation (and in one case, gray water) settling on the inside bottom.

A word of caution if you own or are considering a steel pontoon boat...these photos were all taken BEFORE blasting. The swiss cheese holes on the bottom of the toon were much more pervasive than shown here because they were hidden by the old coal tar epoxy coating. So visual inspection may not always show what’s going on underneath the coating.

After blasting, what we originally thought would be a small project welding-in a few patches here and there quickly became a complete re-skin after hidden cancers were revealed.

View attachment 6782View attachment 6783View attachment 6784View attachment 6785View attachment 6786

After sandblasting, both pontoons were ‘re-skinned’ with galvanized steel from waterline down, stem to stern. Plus the large hole on the upper inboard shoulder was patched (it had been caused by a broken sink drain that allowed gray water to run directly on top of the pontoon for what appeared to be MANY years).

Fortunately we had connections through a friend with a machine shop and a computerized brake large enough to bend 5’x10’ sheets of steel. Not sure what that service would cost ‘retail’ but we paid $1,500 to form up 8 sheets to the contour of our pontoons (the profile was taken from the aft end of a pontoon and traced onto plywood to form a template).

View attachment 6787View attachment 6788View attachment 6789View attachment 6790View attachment 6791

Ends were capped (above) and seams were welded then sealed again with 12” wide doublers.

View attachment 6792

Then it was a fresh coat of 3M Coal Tar Epoxy (nasty stuff, be sure to wear respirator and painter‘s coverall or plan on tossing whatever you’re wearing. Do NOT get it on skin, it does NOT come off...it eventually ’wears’ off.

View attachment 6794View attachment 6795

All told (steel, epoxy, machine work, my labor and a hired welder) I estimate this job ran about $6K (boat is 36’ long x 12’ wide). The toons are airtight...how do I know? On a warm day, I can pull the top vent plugs and pressurized air blows out the vent holes.

Anyway, all this to say I agree with you Dave...with the correct process and care, new life can be breathed into old steel boats. Insurance however (sigh) is another ballgame...
Any kind of report that can say these old steel pontoons ae salvageable is always welcome. Some say Lake Powel is dead. I want to prove that wrong.
 

Dave I.

Well-Known Member

Thinking about this more, the more sense it makes. Having worked in controlled air environments for over 15 years, I know that the air we breath is only 21% oxygen and that is what is in your pontoons.

Since rust is an oxidization, it takes steel, water and oxygen to make. Perfect example is fire. It takes fuel, oxygen and heat. Take one component away and the fire goes out. Basic thinking would tell you the same about oxidization

But since the air we breath is 78% Nitrogen and only .9% Argon, it would make more sense (and probably cost effective) to go with straight Nitrogen to displace the air in the pontoons instead of Argon.

I am seriously considering adding this to the services I offer as I can see a real benefit to houseboat owners, especially when someone goes thru the expense of re-skinning their pontoons such as Rivergoer has done.

There are a few things to consider if I'm going to move forward with offering this kind of service but would honestly like to know if anyone would consider doing this to their houseboat before the expense of setting up to do it.

Any thoughts are welcome as I will be expanding on this theory.
 

flowerbug

Active Member
my biggest concern with such methods is that by adding weight instead of replacing the pontoons that you are effectively adding to your long term cost of using that boat. a cost analysis should give you a rough idea of where the breaking point is.
 

Squirrel

Well-Known Member
"Dave said" The thing I came up with is if a controlled vacuum (to remove ALL O2) and argon fill, it very well could prevent rust from getting worse, Rust does live off O2.
Dave, I parked the pontoon nose down in my steep driveway and just used gravity. Argon & Co2 being heavier than air i slowly filled (about 2 PSI) the pontoon from the rear drain hole. Sq
 

Dave I.

Well-Known Member
my biggest concern with such methods is that by adding weight instead of replacing the pontoons that you are effectively adding to your long term cost of using that boat. a cost analysis should give you a rough idea of where the breaking point is.
That is a good concern but here is what I have found:

Argon is 1.4x heavier than air (keep in mind that is not just O2) which would add to the total weight of the boat
BUT...
Nitrogen has an atomic weight of 14 while Oxygen has an atomic weight of 16 which means a near pure mixture of Nitrogen should be lighter than atmospheric air which both contain heavier gases such as Oxygen and Argon.

So, in theory, pontoons filled with near pure Nitrogen will actually make your boat lighter and still prevent rust from spreading or getting worse .

But you're right, how much would it cost to replace the air completely inside a pontoon and achieve a pressure of 1-2 psi internally with nitrogen? Also note that this in no way would remove the cost of the exterior maintenance. In fact, it would probably make the boat owner over cautious to insure the Nitrogen investment just doesn't float away.
 
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Dave I.

Well-Known Member
And yet, still a little more research.

Say a pontoon is 2' wide, 3' high and 50' long. That's 300 cubic feet. Of course it would be a little less because of nose cone and transom.

A big bottle compressed Nitrogen @ 2200 p.s.i. will displace approx. 265 cubic feet of space. 3 bottles of Nitrogen should be enough to obtain that 1-2 psi inside the toon.

This is why I think a negative void inside the toon from a vacuum pump would be the best scenario. Instead of trying to push the air out with the Nitrogen, it would be just filling the void.
 
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Cliff

Well-Known Member
I would think you could flush the toon with N2 and get the O2 content so low corrosion would be very much inhibited. You could try with 4 bottles of N2 and have a gas sample pulled to check. I'd also pressurize to 2 PSI and have a pressure gauge on the toon to keep watch on the pressure for leaks.
 

Rivergoer

Well-Known Member
Yes, weight is definitely a factor to consider and something we evaluated carefully before the project.

14 ga steel weighs about 3 lbs/sf and we used a total of 9 sheets (including doublers and end caps). So the total re-skin on a 36 footer added about 1,400 lbs.

1 Cu Ft of air displaces 1 Cu Ft of water or 64 lbs. The calculation on our boat came out to a total displacement of about 24,000 lbs. After the re-skin, we took it to a local quarry and the boat weighed-in around 15,000 lbs (up from 13,500).

So yes, technically there is an approx 10% weight factor to consider. After all said and done this equates to perhaps an inch or two raising of the waterline (hulls sitting slightly lower in the water).

In addition it could be argued the additional weight and drag slows down the boat, given the same power. However at 7-8 mph cruising speed, the difference is not even noticeable.

For those interested, more details and pictures of the build HERE
 

Dave I.

Well-Known Member
I would think you could flush the toon with N2 and get the O2 content so low corrosion would be very much inhibited. You could try with 4 bottles of N2 and have a gas sample pulled to check. I'd also pressurize to 2 PSI and have a pressure gauge on the toon to keep watch on the pressure for leaks.
That raises a good question then. Since the "air" is only 21% Oxygen, How low would the percentage of oxygen have to be to retard or stop the growth of rust? Also, with just a simple trying to flush, how would there be any certainty that this minimum percentage is met. I personally would hate to spend the money on an inert gas not knowing, without any certainty, that it will be effective in what it's supposed to do.


Considering I am thinking of this in a commercial sense and I am one that stands behind my work, I am looking at the most effective perspective and quickest way to complete the job.

The best comparison I can quickly think of is this. You take a pot of homemade spaghetti (after it's been emptied of course) and which will be the quickest to get it clean?
1. Wipe it clean inside to prep it for washing (equivalent to vacuuming the old air out)
or
2. Putting the pan in the sink and running water into it and waiting for all the sauce to completely flush out (same as trying to flush O2 out of a concealed pontoon) before you wash it?

If someone wanted to try this themselves, yes by all means, do it. I would love to hear the results in a couple years. Since I am considering it a future service thru the business, I am thinking of how to provide a guaranteed O2 free pontoon and a way to monitor it to see that it is O2 free at time of service.
 
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Rivergoer

Well-Known Member
I’d be cautious with any pressurization of pontoons when a boat is stored at dry dock.

Mine are not pressurized but on a hot day, even just an average sunny day in spring, my toons build up a significant amount of pressure inside when sitting on the trailer.

At dry dock it wouldn’t take a lot of PSI to potentially cause a failure at a weak(er) seam, especially on a hot summer afternoon. If you pressurize, definitely keep it relatively low...maybe 2-3 psi to allow for daily temperature fluctuation.

With the boat in the water the pressure differential isn’t an issue as the day/night water temp is pretty constant, naturally regulating pontoon pressure.
 

Dave I.

Well-Known Member
I’d be cautious with any pressurization of pontoons when a boat is stored at dry dock.

Mine are not pressurized but on a hot day, even just an average sunny day in spring, my toons build up a significant amount of pressure inside when sitting on the trailer.

At dry dock it wouldn’t take a lot of PSI to potentially cause a failure at a weak(er) seam, especially on a hot summer afternoon. If you pressurize, definitely keep it relatively low...maybe 2-3 psi to allow for daily temperature fluctuation.

With the boat in the water the pressure differential isn’t an issue as the day/night water temp is pretty constant, naturally regulating pontoon pressure.
Also a good point. More research has been done. lol

Air has an expansion rate of 1% which means for every 10 degree temp change, psi goes up/down by 1 pound. So, say you have your boat welded up in the winter and it's 50 degrees (ambient) when the tighten the plugs up after he toons are sealed. When the temp reaches 105 degrees, that means a rise in pressure of 5.5 psi inside the pontoons. Of course, this is if your boat doesn't hit the water. But even if the lake water is 80 degrees, that is still a rise of 3 psi inside the pontoons because of when the toons were sealed.

But, Nitrogen has an expansion rate of 1.9%. Almost double of air. So, if there was a "rule" that nitrogen couldn't be implemented until ambient temp reaches 70 degrees, then when the ambient temp reaches 105 (with a pre-pressure of 2 psi) that would bring the internal pressure up to a whopping 8.62 psi. That is a little too high for comfort. But, if the boat is in the water that doesn't see any higher than 80 degrees all summer, that would be a max pressure of 3.5 psi. So, comparable to air pressurizing in the toons.

But, with the right equipment, a zero oxygen atmosphere can be created (and tested) in a pontoon without pressurizing it. With that being said. Say 70 degrees ambient temp when Nitrogen is applied, the boat stays in the water all summer so the max pressure it sees is 2 psi. Much lower than the pressure created by air that is sealed up in the toons during the winter months. But, if the boat doesn't hit the water, and with zero psi at 70 degrees, that would still create a pressure of 6.65 psi at 105 degrees ambient.

Maybe a low pressure check valve would be a requirement?

By the way, the houseboats we have here all have the plugs pulled. We got tired of hearing the expanding "thunder" all the time. lol
 
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