Recommended Material and Thickness for 40ft, Steel, flatbottom houseboat

I recently purchased a 1976 Somerset Houseboat, steel frame, flat bottom, 40ft in length, 1oft in width. In some places the hull has rusted away from the ribs and I was wondering what is the average depth of material recommended for a metal house boat? I was thinking 10 gauge but was curious to hear and advice on recommended metals and thickness for replacing the flatbottom hull. Photos below. Any videos or links would be great and any recommendations on primer and paint are always appreciated. Thanks so much!

 

Welcome to the Forum JB.

Re the photos you have posted - oh dear, they look ominous.
If you have not yet done so, may I suggest that before you do anything else, you do a thorough hammer test all over the hull bottom.
I just hope that the hammer does not punch through the shell in too many places.
You mention 10 gauge steel plate - the only place this might work would be on the roof of the superstructure.
For the hull bottom and sides it needs to be substantially thicker - I certainly would not go less than 1/4" / 6 mm for the hull bottom, and 8 or even 10 mm (3/8") would be preferable.

 

What is the current thickness, in a non corroded section, now that lasted 45 years (without proper corrosion protection it would appear)

Bottom and sides

Do you have any more pictures of the entire boat?

Are the hull sides impacted with similar corrosion issues?

 

Further to Barry's excellent comment above, if you do not have access to an ultrasound meter for measuring plate thickness, you can drill holes - mark them clearly, so that you can weld them up again afterwards.
Before you even think about installing new plating and frames, you do need to carry out a careful survey of the steel shell - try hammering it first. When you hammer it, ideally with a hammer that has a bit of an edge on it (ie not the type of hammer that you would use for driving nails), thump it hard - do not worry about knocking off paint, that is the least of your concerns at the moment.
If you find that everywhere is very thin, then it would probably be easier to build a new hull from scratch, rather than try to repair this hull.
And then transfer all of the outfit items across to the new hull.

 

A total rebuild of the lower hull was on my mind as well. If cost is an issue there is also a possibility to build the bottom, without sides, remote from the current hull. It is likely that the corrosion may be up the sides say a couple of feet until
the hull is sound. Then cut off the hull bottom and some of the sides with a cut off blade, locate the new hull bottom under the upper part of the hull, then plate the sides.

Certainly you could cut the existing plating off the frames, but with the amount of corrosion that there appears to be there, it is likely that the interface between the frame and the old hull is corroded so badly that good welding
practices could not take place.
Sometimes building from scratch is cheaper and faster than renovating the existing hull.

 

I have surveyed a few of those boats. They had no coating on the inside of the hull. The space between the floor and the bottom is really low, which makes repairs hard. You could cut off the plywood floor and remove some interior cabinetry for access, but will be a fair amount of work. From memory, I am pretty sure the bottoms were 8 gauge. Many of them were repaired by double plating. If the interior and deck are OK, that could be an option.

 

Hey Bajansailor,

Thanks so much

 

Oh dear re an original hull bottom thickness of 8 gauge - that is only 4 mm.. It certainly does not leave much margin for wastage.

I couldn't find a 40' Sumerset houseboat for sale in steel (I did see a later one built in the 80's in aluminium though).
But here is a 46' steel version for reference. She was originally built in 1972.
1972 Sumerset 46 Walkaround, Knoxville Tennessee - boats.com https://www.boats.com/power-boats/1972-sumerset-46-walkaround-7248761/

 

Thanks BajanSailor and thanks Barry,

Those are great suggestions, I have an ultrasound meter and will do a hull check across the entire hull. I was debating between just cutting off sections of the hull and welding in new plate steel, sound like somewhere between 3/8 and 1/4 will do the trick or wet sand blasting the whole thing and trying to repair any smaller sections. Sounds like the later maybe the way to go. Here are some more pixs attached. Thank you for the recommendations, they are much appreciated. With a hull check if I were to drill small holes to test, do you prime them after to keep from rusting or just wait until your ready to weld and brush them clean and weld from there? Thank again for the pointers.

 

Thanks Barry, that's a good call, I'll start by checking the non corroded sections and see where I land with this thing. I'll report back,

 

Thanks Gonzo, it looks like it was painted once upon a time but its long since faded. I was considering opening up some sections of the plywood floor. I was wondering about the double plating, some parts of the hull have pulled away from the original ribs, I thinking about cutting those away and starting with some fresh metal to make sure all the hull is well connected to the ribs before I double plated, do you think that is a good strategy?

 

Thank you for all the extra photos and comments JB.
That is good news re you have an ultrasound meter. I think that I would still be inclined to sound everywhere with a hammer first - if the hammer doesn't go through then that is a positive (of sorts).
How much headroom is there between the steel and the timber beams above? Looks like maybe 3' at the most?
When using your ultrasound meter you do ideally want the probe to land on clean shiny metal - will it be easier to do this from the inside, with limited headroom, or from the outside, working overhead? I wouldn't worry to drill holes once you have a meter.
If you do repairs by double plating, then at best this is a bodge, although it will probably last many years. It will be a much better job if you cut out the old plate, and weld in new plates.
Please do establish some sort of grid reference on the hull and on paper for taking ultrasound readings, including on 'good' steel for comparison, and report back here with your findings.
Have you got any full side profile photos of the boat?

 

There is very little room between the floor and the bottom.
Cutting off the bottom plating is the best route. 1/4" is more than a workboat on that size would have for plating.