Steel hull repair

We have our boat on the hard right now. We had the hull below waterline sandblasted (big mistake I think). Had I been there I would’ve stopped the sandblaster and rethought the situation.
Anyway we have a hull below the waterline that’s full of 1/4” to 1/2” diameter holes.
The hull is 1/8” thick. We’re considering a re plate of the bottom. I have not had the job quoted yet but was wondering if someone might have a wild guess to what this might cost.
The hull is 44’ long and 13’ wide and flat as a pancake. The yard said 20 to 30k. The frame is in good shape and everything above the waterline is good.
It’s a good old boat and I hate to scrap it. This is just one area but it’s pretty much the same for the entire bottom.

Oof, Marty, I'm sorry you have to deal with that! No idea how to help, but I wish you the very best of luck!

Sandblasting may have saved your life

I agree with Arc. Sandblasting Might have uncovered some bad defects. It is possible to blast a hole in steel if the operator stays in one spot to long. If your redoing the hull you might want think about using little thicker steel. Just my opinion.

You did the right thing to continue the sandblasting. It’s the best way to identify the problem areas, and also prepares the bottom for new metal.
I totally feel your pain though, I went through this myself. It’s a gut punch when you first realize the scope of the entire project. Luckily for me, I can do all the welding myself, and with some help from my son.
Hopefully you have cheaper yard fees than I did. I paid to have the bottom stripped, but did all the reconstruction myself and it was still eye wateringly expensive. My local boatyard is hugely expensive as there’s no competition. I think just for lay days I paid near 10k. I did mine over the winter of 2020. Covid was in full swing and it was tough scheduling anything. Plus it was our rainy season so I had to build an enclosure over the whole thing so I could keep it dry and warm. I still have ptsd from that winter…
Not many people will take on an expensive project that doesn’t really add much to the overall value of the vessel.
I’d hate to see it scrapped too, and I hope you figure out a way to get it repaired.
I used a surveyor to consult with and document the repairs the whole way through the process. Changed out all the through hull fittings to new marelon ones from forspar, installed a drip less shaft seal too. The goal was to completely eliminate water from standing in the bilge. My issues were mostly from water inside the boat causing problems. Yours look more like the metal eroding from the exterior.
The best way to repair it is to cut out and replace the metal. Another way would be to overplate what you have. Just plating over would probably be cheaper, and the boat will most likely outlive you. You have to use weld primer on all the metal you’re covering up to keep corrosion to a minimum.
I coated the hull with tar epoxy after the repairs. That typically is about a 20 year lifespan for protection on the exterior.
If there’s any commercial yards that do work on tugboats and similar vessels they would be more used to this type of work. Of course you can’t move the boat now that it’s all opened up so you need someone to do it where you’re at.
Good luck to you, whatever you decide.

Oh damn, I’m sorry to see this.

I’m so out of the loop, I didn’t realize you had switched boats. When did you sell William?

If that's typical, you need to replate the bottom. How are the sides, bow, and transom? Certainly doesn't need to be done by a certified welder as the boat doesn't have a COI.

Ted

Sorry to read this. To be fair it would be a rare event for sand blasting not to uncover bad news but the scope would have been a shock. I'd agree that it's much better to find out now than out at sea.

I'd take the opportunity to also investigate what the actual cause was. It's hard to tell from the photos but has the rust eaten it's way from the outside in?

Does your boat have an isolation transformer? The hull looks like it may have been subject to stray current corrosion caused by other boats in the marina.

One way to cut the cost is add plating over the existing bottom. It's commonly done on larger vessels where weight isn't an issue. That way you don't have all the cutting and welding prep. You still have to cut gaps in the new plate to tie it to the existing plating, especially to ribs and stringers. But it saves hours of detail cutting each little space along the bottom. Plus cutting old steel that may have rusted spots and paint on one side is a PIA. A plasma arc makes a nice cut thru old steel. It's faster and easier to cut new plate outside the boat. Where you have the holes now would be welded to the new plate so you don't get water between the layers.

Look up the weight of 1/8" plating and figure how much you need and you'll see how much weight you'd be adding to the boat. And your old 1/8" plate obviously isn't 1/8" currently.

Painful discovery, all right, though best discovered while on the hard.

If your yard would cooperate, it might be worthwhile having a couple of other welding shops price the job. At 44' x 13' with no upperworks, the boat appears to be truckable. As Ted notes, since it is an uninspected vessel, you wouldn't necessarily need a specialty welder. I agree with Lepke, it would be interesting to know how much weight overplating would add. At least it would be low to the center of gravity!

All that said, $20K to $30K doesn't sound crazy to me.

trawler nut said:

I agree with Arc. Sandblasting Might have uncovered some bad defects. It is possible to blast a hole in steel if the operator stays in one spot to long. If your redoing the hull you might want think about using little thicker steel. Just my opinion.

Click to expand...

If the OP would not mind, I suggest this illustrates the positive aspects of a steel hull... Namely, a relatively straight forward repair/re-plate. I work with steel and while unfortunately, likely owing to current economics, the repair would be significant in cost, the idea of plating with a heavier gauge makes a great deal of sense should the weight not be excessive.

1/8" steel is about 6 lbs per square foot, and 3/16" almost 9, so he would be adding about 1/2 his original hull weight. It could just be done with the bottom portion, where the majority of the corrosion took place, reducing that significantly...

Arc said:

Sandblasting may have saved your life

Click to expand...

And I second this BIG TIME! The OP did things correctly and did not "half *ss" the inspection...

Are the holes from rusting out? Was the interior of the hull painted?


Thanks,
Dan

No one above has mentioned the interior -- you can't do any welding without removing or isolating the interior. It's even worse if the hull is insulated with foam rather than fiberglass. Removing and replacing interior could cost more than the steelwork.


Jim

Circumnavigator said:

No one above has mentioned the interior -- you can't do any welding without removing or isolating the interior. It's even worse if the hull is insulated with foam rather than fiberglass. Removing and replacing interior could cost more than the steelwork.


Jim

Click to expand...

Good point. One of Kasten's designs caught fire when being built when welding outside of the boat caused a spark to fly into the interior and started a fire. The forward section of the boat had to be replaced as a result. I think the hot bit flew through a port hole. What are the odds?


Later,
Dan

That usually doesn't happen from sparks. It's the heat radiating through the steel, it gets just as hot inside as out and will torch anything in contact, even the paint. It's wise to set a fire watch inside any time welding is done on the outside.

jgwinks said:

That usually doesn't happen from sparks. It's the heat radiating through the steel, it gets just as hot inside as out and will torch anything in contact, even the paint. It's wise to set a fire watch inside any time welding is done on the outside.

Click to expand...

Sound advice. When I have welded on the inside of the hull I was able to
keep from burning off the exterior paint by having a buddy mist the outside
area with a light water stream.

Alternative?

I am by no means a naval or structural engineer but would find one to lend an opinion of a fiberglass and epoxy skin over the existing steel hull.

Thoughts anyone?

I agree with earlier posts that (1) you need to diagnose the source of the problem before sorting a repair and (2) one-eighth is very skimpy, and you should check the rest of the hull above WL by ultrasound. No use spending a lot and then finding more issues later. This is a potential heartbreaker but get a surveyor’s counsel and be very dispassionate when you make your decision. Trying to save a doomed boat has broken many a mariner.

I too have worked with steel my whole life, I was a welder. 1st I would have the rest of the hull blasted to see what kind of shape it is in. May have to replace some plate above the water-line. Go with at least 3/16 steel below the water-line. I would not recommend sheeting over the existing plate. Your inviting moisture and rust to start all over again plus you'll need excellent welds to the boats ribs. Diffently have a fire watch on the inside of your boat. Just my opinion anyone else have anything?

Overplating can be done with good results. You need to paint all the hidden surfaces with weld through primer. Leave small gaps on the edges of the panels for full penetration welds on the panel perimeters. Pre-drill the panels and plug weld at regular spacing, being sure to get good welds at the interior framings. A good coating of tar epoxy will keep any sea water out if there’s any pin holes in the seams.
I caught the interior of mine on fire a couple of times, even with a fire watch. I placed copper sheet over the weld areas and used a water spray to knock down flames when the inevitable fire breaks out.
Remove any soft materials from the interior of the boat or they’ll all smell like smoke. It’s a messy job, but totally doable.
I would use 1/8 again, it’s really very strong in the grand scheme of things. 3/16 at most. Too thick and you’ll have trouble keeping everything tight to the existing structure.

If you plate over the bottom, 1/8" is plenty. It was fine up to this point and you don't want a lot of extra weight. You still have to make the boat go and make it stop. Much more weight will make the boat less responsive.
You should see what the yard wants to plate over the bottom and then take some pictures to local welding shops. Get some prices. You'd have to move the boat but adding plate isn't rocket science. I'd guess a welding shop would be half the cost of a boat yard.

Pack Mule said:

We have our boat on the hard right now. We had the hull below waterline sandblasted (big mistake I think). Had I been there I would’ve stopped the sandblaster and rethought the situation.
Anyway we have a hull below the waterline that’s full of 1/4” to 1/2” diameter holes.
The hull is 1/8” thick. We’re considering a re plate of the bottom. I have not had the job quoted yet but was wondering if someone might have a wild guess to what this might cost.
The hull is 44’ long and 13’ wide and flat as a pancake. The yard said 20 to 30k. The frame is in good shape and everything above the waterline is good.
It’s a good old boat and I hate to scrap it. This is just one area but it’s pretty much the same for the entire bottom.

Click to expand...

Materials wise, 4'x10' 10 ga. (.135) hot rolled plate is $297 each when ordering more than 10 sheets which, you'll need for this bottom job. Find a welder or talk to the local technical school about a project for the students. I've done my share of welding but am comfortably ensconced at 12° north latitude and am retired. Good luck with the project, it'll be worth it in the end.