Steel Boat Building Techniques

[CB Haws]

I am looking at a custom (homemade) 40' steel boat. The seams appear to be "welded lap joints". I can see not rust from the inside below the water line. The bilge was completely dry. Are lap joints a big no-no in steel boat hull construction? The bow apperas to be double plated. I guess to break ice? Oh the boat is about 30 years old.
Thanks,
Charlie

[Chapman]

This is an interesting question. I have spent many years around steel vessel construction (none of it on recreational vessels though), and have only seen butt joints used on shell plating. I dug out an old book called "A Guide to Sound Ship Structures" and they talk almost exclusively about butt welding sheel plate with one exception. Apparently many years ago it was thought that lapping joints and using a partially welded/partially riveted join was a good methodology. Does the vessel you are looking at have a fillet weld on either side of the lap? Given the uneven surface that a lap joint produces, how are the longitudinal and transverse structural members connected to the plating? Are the lap joints visible on the exterior of the hull, or is some filler compound used to fair it. If a filler compound was used, I would wonder what the condition of the welds under that was. Sorry to answer your question with more questions, but I've never seen a lap joint used on shell plating with the possible exception of doubler plates being added.

[timgoz]

Let me give you some more questions.

Is the boat somewhat conventional other than the lapwelds?

I cannot remember which book I saw it in, but I once saw a boat built in the lapstrake (clinker) style out of steel. This is a real rarity though.

As Chapman mentioned, the joints would need to be continously welded inside and out. If not, interior wise, there would be moisture intrusion into the seams, bad news.

TGoz

[jehardiman]

Sorry to answer your question with more questions, but I've never seen a lap joint used on shell plating with the possible exception of doubler plates being added.

You know...that was my first thought. What you may be seeing are light weight doubler plates welded over an older pitted hull. As Chapman and Timgoz ask....What is the thickness of the exposed lap? Do the laps show up on the inside? Are the plates joggled (i.e. in-out-in-out) or are the lapped (out-out-out)? And do the laps run fore-&-aft, or up-&-down, or both?

[timgoz]

Have you guys ever seen a lapstrake hulled steel boat?

Like I said above, I saw one once in a steelboatbuilding book. May have been in "Steel Away" or Bruce Robert's "Metal Boats".

Although all those welds & resulting heat would be a negative, the longitudinal strength would be impressive. But other than possibly ice-work, I think a proper steel boats much more than adequate strength wise.

All those laps would also present alot of corrosion possibilities, exterior & especially interior. The same would go for a repair where someone welded plate over a bad section instead of properly cutting the section out and insetting a new piece, a matter of fact, plate over plate would be much worse I would think.

TGoz

TGoz

[MikeJohns]

The overlap method was common for a decade or so after the move from riveting joins to welding. The odd hull is still produced that way

I've surveyed a few welded hulls built to the overlap method. the plates are appied longitudinally similar to trad planking but up to around 1m wide the overlap of around 2 inches is treated in several ways.
Either alternate under over plating, or lapstrake or jogged seam where the overlap is heated with a torch and hammered over the lower plate till it fits snug .
In all types both the inner and the outer plate edge are then fully welded to the plate below.

The boatyard saves a lot of time in fitting since you can have a large tolerance on the edges.

The problem is the internal void along the overlap and if the welds don't seal completely it corrodes. Generally it seems to be ok. When they do rust the rust puffs the seam up quite visibly. Repair is easy if you can get at the inside at the trouble spots.

All the best

[timgoz]

Thanks Mike.

[jehardiman]

Have you guys ever seen a lapstrake hulled steel boat?

Like I said above, I saw one once in a steelboatbuilding book. May have been in "Steel Away" or Bruce Robert's "Metal Boats".


TGoz

TGoz, yes I have heard of them, but why on earth anyone would do it is beyond me. The resulting hull is actually weaker (the corner weld is a hard spot that reduces the FOS of the hull), and the layout and cutting is 4 to 10 times longer (depending on the strake to chine ratio) than conventional forming. I could never see anyone skilled in shipfitting doing it for a reason other than "that's what the customer wanted", and only a neophyte doing it because they thought that a corner joint is eaiser to weld than a butt and/or they wanted the traditional look. It was the age of the hull and the doubling of the bow that lead me to the plated over (a common quick fix in the 2nd life commerical world) conclusion.

[CB Haws]

Thanks guys for the input. The boat was built around 1975. It is lap jointed not joggled or over under under over or what he said. Since the interior is pretty much non-existant visual inspection was easy. All seams are welded inside and out. You can see each lap strake from the inside and no rust is visible below the water line. As you get above the water line the inside looks to have been tarred or something. The bow section is doubbled for no apparent reason. The bow section is rust free on the inside and the outside has paint. None of the seams are faired; just very nice welds. The guy was a welder who built this one up. I just figured lap joints were easier to do; but my concern was water in the lap. I could see no evidence of rust. The bilge had no water at all. The boat was in the water and running. The only rust I could find was was in the butt welded deck plate where one side door has been leaking for some time. This boat was never really finnished and I have not found out why. It may be because the original owner builder lost interest. The last two owners were going to finnish her; but got interested in bigger projects. looks like she just needs a little love. The tops sides are aluminum. The inside trim work is all stainless. The guy who did the trim work was a master fabricator. The engine hatches are stainless not welded together; but bent and rivited. A work of art. Other wise the boat looks real crappy, and needs a total redo.
Thanks again. I will let you know what the surveyor says. Oh by the way what is a 40 foot boat worth in scrap metal? I don't want to get stuck having to be the guy who has to have it cut up!

[timgoz]

Jehardiman,

I hear you. It was an interesting odity though. I never gave thought to what might have motivated this boat being built.

Take care.

TGoz

[MarkC]

Was it sort of like this (see below) - can be used to good effect.

Dutch steel built - BLAUWE BOEI SLOEP BB750

taken from http://www.botenbank.nl - dutch boat sale web-site

contact for the company can be found on the site - i dont know if they do English.

[MarkC]

or like this steel motorsailor 1978 - 10metersx3.1x1.5 - full keel for sale €49K

[CB Haws]

Thanks for the photos. Yes that is pretty much how she looks. The plates are a little wider; but that is the fabrication method. I am sure it is really strong; but the laps had me worried.
Thanks

[CDBarry]

Actually laps have an advantage for some welding issues - you can use drag rod.

[MikeJohns]

Actually laps have an advantage for some welding issues - you can use drag rod.

Christopher
Have you ever supervised a hull built this way? We had a yard bulding a boat here that was offering a discount to plate this way but local DNV were not happy.
I always think of ways to fill the void.. like grease nipples and pump epoxy in, ...there are some very low viscosity 100% epoxies available now which could work well.

Cheers
Mike

[MarkC]

It seems that this construciton method alleviates the need to roll/form largeish plate steel to shape (for instance in the lower-stem-area) because the 'planks' or laps of steel are easier to attach?

the layout and cutting is 4 to 10 times longer (depending on the strake to chine ratio) than conventional forming

I guess that depends on how skilled a former and what equipment (English Wheels etc) you have?

Asthetically it looks great for me (from the Dutch pictures above).

You have that look - like a wooden boat. Some builders do that in fiberglass as well - but this seems more honest because one is still really 'planking'.

[jehardiman]

It seems that this construciton method alleviates the need to roll/form largeish plate steel to shape (for instance in the lower-stem-area) because the 'planks' or laps of steel are easier to attach?

Quote
the layout and cutting is 4 to 10 times longer (depending on the strake to chine ratio) than conventional forming

I guess that depends on how skilled a former and what equipment (English Wheels etc) you have?

Asthetically it looks great for me (from the Dutch pictures above).


The time to form it is not a skill or tool issue, it is a cutting issue. Every inch of cut plate edge represents time. 4 times the cut plate edge, 4 times the time reguardless of what tool (grinder, gas axe, or CNC plasma jet) is being used to cut it. Of course a $500,000 CNC plasma jet could cut it a lot faster (if they had the file) than 1 guy with a box of $5 grinding wheels, but those are other economies. ;)

[FAST FRED]

Would this method of boatbuilding be more suitable for aluminum?

The internal void would no longer be a hassle and the overlaps might add stiffness , requyiring less framing weight ect?




FAST FRED

[rayk]

A couple of years ago I visited a Dutct built yacht, 38ft mod disp steel lapstrake built in 70's, and recall frames without stringers. Internal laps were not fully welded or sealed either. The issue of corrosion was immediately raised, but confidently dismissed by the owners, who explained how condensation travelled directly to the bilge. The owners pointed out the original hull paint and claimed no problems.
If it wasn't such a pain to build, I wouldn't mind having one.

[Milan]

At least one Dutch builder of extremely strong steel boats, Bronsveen, (http://www.bronsveen.nl ), uses laps. Their laps are a bit rounded and very tightly pressed at each other. They are using this method because of additional strength of the joint, (Each lap becomes a sort of stringer). They say that this method doesn't take them considerably more time, because with more common methods more stringers are needed and even if plates edges just touch each other, double welds are needed anyway.

French builder Meta, (http://www.reducostall.com ), built many Joshua, (Bernard Moitessier), type of the boats with the welded laps.

Milan

[MikeJohns]

..................who explained how condensation travelled directly to the bilge. ....................

Rayk

Capillary action stops this moisture "draining" away and if it was salt water sloshing around from the bilges that would ingress too. Voids need to be fully sealed. I would also want to see two fillet welds ie inner and outer at that plate lap, just one on the outer is poor practice.

I just surveyed another riveted steel boat (Dutch 50 footer) but this was flush riveted with a doubler along each plate seam, the corrosion (since 1935) is bad enough to have to re-plate around 10 feet of 10 inch wide strip close to the waterline, it will be an easy enough repair when the tanks are out after the soles have been cut out............................

[MikeJohns]

Would this method of boatbuilding be more suitable for aluminum?

The internal void would no longer be a hassle and the overlaps might add stiffness , requyiring less framing weight ect?

FAST FRED


Thats a thought. But alloy has some detrimental qualities. My immediate concern would be that you then have stress concentrations at the edges of the overlap which are also weakened weld zones (poor property of Alloy welds) and given a poor fatigue response in the weld zones the plating would need to be stiffer (thicker) so you might end up with no net advantage to a simple butt weld.

Alloy is light and easy to work which makes shaping it to a precision fit a lot easier anyway. The big advantage with overlaps is that it allows very fast plating.

cheers