Metal Boats

[Woody5]

I’m looking at some 70s - 80s steel and aluminum boats. Are they much more difficult to determine seaworthy than fiberglass? What methods are used to tell if the are fit to purpose. Are they easier to repair? More trouble to maintain? Better in fresh or salt water? Would it be best to avoid metal boats? I have admired Chris Craft Roamers for years also the spacious steel houseboats.

 

[fdw]

No affiliation, but this Roamer has been on the market for a while:

https://www.harbortownemarine.com/listings/chris-craft-roamer-36

 

[garbler]

Steel and aluminum hulls in question should be Ultrasonically tested often called audio gauging. It is a pricey inspection for several reasons. First the equipment is expensive ( the good equipment anyway ) and testing should be conducted by a minimum certified Level-I technician that has been trained and passed NANDT ( Nat Assc of Non- Destructive Testing ) qualifications. But here is the rub. If the hull has a heavy layer of antifoulant paint it should be blasted to clean metal. There are exceptions as one of my meters can shoot through 4-8 mils of sound firm paint but almost always I find it necessary to grind areas to bright metal to further confirm suspicious patterns. This is costly but if you factor the costs of the vessel and that most major marine underwriters will want this then it’s not that much.

The job as I was trained requires measuring the hull underbody, marking off stations and setting up a grid so that all sounding locations are identified and included in the report. It’s labor intensive and on larger hulls I usually have a helper. Steel and aluminum hulls generally have a certain amount of plate wastage every year depending on service and location. Depending on a hull’s scantlings or plate thickness the amount of tolerable wastage can vary. But when loss of around 30-35% is encountered it’s probably time for a review of the numbers, the vessel’s price and the buyer’s intentions. It should be understood that a full UT inspection will not touch every inch of a hull so localized areas of pitting can be missed unless the hull is blasted clean then a visual and yellow marker will ID such areas for further inspection. Weather conditions from hard freeze to 100° will not affect a good technician with good equipment. In fact I’ve done several barges from underwater with a diver.

With many of the newer primers and paints I’ve found wastage rates diminishing to as much as half. Years ago we could forecast the rate of wastage with surprising accuracy so that fleet managers could budget repairs or life cycle of a hull. With these better coatings this information has to be adjusted sometimes beyond usefulness. Special alloy plating like the old Corten steels that were so popular with the Dutch sustain only minor wastage for the first ten to fifteen years. Same with some 5000 series & 6061 aluminums however aluminum is much more reactionary to galvanic or stray current. Don’t get me wrong I like steel hulls since metal hulls allow the designer to put fuel and other tankage down low where weight is better used and steel can be repaired almost anywhere in the world. Pound for pound steel and aluminum makes a lot of sense.

Rick

 

[Jmarsh203]

As an owner of an aluminum boat I second everything Rick just said. Steel and aluminum to be maintained to a high Yacht finish over long term can be on the harder side to maintain. If you are willing to go bare aluminum above waterline there can be quite a few advantages when maintaining it.

 

[Hippocampus]

With modern coatings, appropriate anodes and wiring what’s the service life of Al & Fe pleasure boats?
Do people apply a voltage to Al to preserve the hull?
Is ultrasound an effective antifouling?

 

[klee wyck]

With modern coatings, appropriate anodes and wiring what’s the service life of Al & Fe pleasure boats?
Do people apply a voltage to Al to preserve the hull?
Is ultrasound an effective antifouling?

Service life: as of the last Audio gage for Libra, she was around 34 years old. The hull was originally built in 6mm and the keel in 10mm steel. We made around 200 pings in grids over the whole hull. For the 6 mm part of the structure, the lowest we recorded was 5.7mm but mostly 5.9 and 6.0.
For the 10 mm we mostly saw 9.5 and up but there was a bit more wastage on the keel in the area near the prop and we had some as low as 8.9mm there.

Based on this rate of wastage over that time frame, the surveyor estimated she would still be in service at 100 years if she continued to get the same care.
We marked all of the audio gage readings right on the hull with white chalk in the grids and then I photographed each section with the markings on so we could compare to the next survey at ten years later.

Coatings matter.

 

[Jmarsh203]

My boat is from 72 so 51 years old at this point. Other than for select spots where there is pitting from stray electricity there is no degradation apparent whatsoever. Stray electricity tears them up pretty quickly if not taken care of. They do make full time gauges that when installed tell you if there is any chance of electrolysis though so whenever you are in a new marina you just keep your eye on it for a few days.

 

[Bmarler]

I just sold my 1940 vintage steel boat. It still sounded within 10% in almost all areas. The only problem areas were where I had leaks and fresh water pooled inside.
I used tar epoxy on mine. It lasts quite a few years but needs stripped to white metal on a regular schedule and recoated. You need to factor in this type of maintenance when purchasing a steel hull. If an audio sounding needs to be done it will compromise the barrier, so the best thing is to plan that so it’s done at the same time.

 

[Hippocampus]

Thanks gentlemen. Was thinking if a small voltage was applied to the hull making it less prone to give up its electrons hull thickness could be better preserved. Is this done?

 

[garbler]

I just sold my 1940 vintage steel boat. It still sounded within 10% in almost all areas. The only problem areas were where I had leaks and fresh water pooled inside.
I used tar epoxy on mine. It lasts quite a few years but needs stripped to white metal on a regular schedule and recoated. You need to factor in this type of maintenance when purchasing a steel hull. If an audio sounding needs to be done it will compromise the barrier, so the best thing is to plan that so it’s done at the same time.

Now coal tar epoxy is one of the coatings I’m talking about. It’s nasty stuff and won’t leave a nice slick smooth surface but it will stick to an oil slick and is ‘ self healing ‘ if scratched or scraped. In fact I think I still have an old pair of boats with coal tar epoxy on them and you can’t wear em out

Rick