Steel Hull Construction

[Valiente]

I would suggest no, but not for the reasons you might think. Firstly, you're right...it will just get worse on what is now the "inner plate", but secondly, you'll make the hull "bumpy" at the new plate's weld and you may have problems getting the barrier coat to grip well there. Best to burn out a single square foot and have a replacement cambered to fit and then professionally welded and ground as fair as possible. Then grind or abrade to bare metal inside and out to beyond the repair, and then prime on the inside, prime, barrier coat and anti-foul on the outside, and paint on the inside with a nice two-part in a colour that will show blisters or other failures easily. Then inspect it.

I will say this: if the spot is appropriate, you could weld anode studs on the new "square" to be welded in, and that would be easier than doing it on the otherwise intact parts of the hull.

Good luck. Don't cheap out on this: anyone can learn to do the prep work and even the grinding, but you want a strong weld done by a pro.

[mallo]

Kater
Having repaired several boats/ships over a number of years my advice would be to cut the area out. When we replaced some plates on our sailing boat the surveyor suggested cutting a radii instead of 90deg corners, as the corners are a stress point and can cause cracking of the welds, when we cut out the plate we left in a 2.5”-3” radii.
Cut the wasted area out (the coldest way possible, heat causes stresses in the steel, grinder with a cutting disc) cut a replacement piece of steel to fit, (again a grinder and cutting disc is the best way if possible) prep up the plate depending on thickness tack into place with loads of tacks, fill in the gaps and then fully weld up. If its possible tack some flats on the back of the plate to stop distortion as much as possible, also use the back step welding process or one of the other process to control the distortion.
I hope this helps, it’s a very brief description on how to repair the wasted area.
We also had some very localized pitting and we just welded these areas with the MIG.
If you can weld its possible for anyone to replace a plate.

[Kater]

Thanks for all the advise. We'll definetely go for the cut out - weld in, I think.

[popeyewanab]

If any of you remember, I was looking for information about steel boats back in March. I appreciate the great advice, and after traveling 3000 miles round trip could not come to an agreement on price. So, I'm back and looking at a 1977 Peterson aluminum sailboat. it was painted above water, and I'm not sure when the last anodes we replaced. I will be making a trip to take a look at her, but wanted some insight as to what type of corrosion may have occurred if the anodes have not been replaced in for instance, 5 years and was left soaking in southern california water? I understand there are variables about other dissimilar metals, electricity etc. I guess I'm wondering if aluminum corrodes to a point and then stops, or could the entire boat be a lost cause in the above scenario? thanks in advance for any insights.

[sailingdog]

Aluminum is relatively low on the galvanic scale...so it will get eaten if the zincs aren't replaced and there is any electrical current in the marina. In some extreme cases, the hull will erode away to the point it isn't reparable.

[popeyewanab]

Thanks saildog, can you offer me any information on typical new aluminum hull thickness, and maybe the minimum thickness and still have some sailing life? the boat was launched in 77. I have an ultrasound so I can take some readings.

[sailingdog]

Popeye-

Without knowing more, like the length and displacement of the boat, I can't really say much about how thick the hull is supposed to be. If it is an 8' skiff, it might be only 20 gauge or so... if it is 50' long and 30,000 lbs... it might be a good deal thicker.

[popeyewanab]

Thx sailingdog,

Yeah guess that kind of info is helpful. It is 42ft, 18 ton displacement. Ill be going to check it out tomorrow morning.

[Valiente]

18 tons in aluminum? That seems heavy, which from a galvanic point of view is desirable, I suppose: more metal to sacrifice before structural compromises.

Aluminum is great, but seems far less forgiving than steel to electrical issues/anode maintenance. You'll need a haul-out and a thorough going-over by someone qualified to survey aluminum hull thicknesses.

[Diligence]

Originally Posted by sailingdog

One person that you might want to contact via PM here is Valiente, since he owns a steel beastie.

Who is Valiente and how do I contact him? I'm also buying a Steel Hull Sailboat and need a survey