So, what can go wrong with aluminum?

[Snowpetrel]

^^@stumble.
Ha, you got me there Greg, but Its interesting that titanium also has a fatigue limit like steel, I hadnt seen that before. An amazing material!

But I do think fatgue might become a bit more of a problem as the modern boats get older particularly when combined with more lightly built high performance hulls. I guess most of them will give plenty of warning just start to go soft, but cheeky rafiki, Polina star and the rudder failures show what could go wrong.

It used to be a big problem on the ships. Not so much with the hull plates (though we did split one once) but all the internal tanks and deck structure often started to crack up as they aged. The old Breman built ships survived into the 20 year old mark before it was a big issue, but the newer lighter built ships where cracking tanks at 10 years.

Ive even seen a steel yacht with fatigue cracks around the keel, and heard of a few skegs in steel boats being lost like that. And I've actually go a few small deck cracks on my boat that need to be welded up and reinforced due to using 3mm plate and not enough frames to support a heavy crew bouncing up halyards and jumping into the cockpit.

[a64pilot]

I believe the first Soviet Alpha was retired almost immediately due to fatigue cracking, at the welds.
Rumor mill had it that an Alpha was dove to beyond 1300 meters I think and many of the interior fittings were broken, but hull was OK.
I think Ti is normally welded with submerged arc? But the Soviets licked the Ti welding issue in the 60's cause I think that sub was made from welded sheets.

I know there was a special CIA program for years to buy Titanium whenever and wherever they could get it for uses like the SR-71.
I thought that was because the only source was the Soviet Union. I know after the collapse of the Soviet Union the price for Ti collapsed, I don't know if it is still low.


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[bdbcat]

Folks...
I've owned and cruised a large aluminum power-cat for 16 years.

FAQs About the Boat

Two points to make:

1. The number one corrosion issue is caused by small particles of of stainless/steel/copper accidentally dropped into a wet bilge. Especially copper, as from shards of stripped wire which inevitably result from electrical projects.
The corrosion is known as "exfolitiate corrosion", and occurs mainly in rolled Al plates. It is as though the foreign metal is "melting" into the Al plate, creating a coin-sized patch that eventually flakes off. The result is locally reduced plating thickness.
So, one must be scrupulous about clean, and preferably dry, bilges.

2. Antifouling: This problem is essentially licked by using an epoxy barrier coat to electrically isolate the hull. Normal high-copper antifouling may then be used over the top. I have seen much more internal corrosion than anything attributable to galvanic action with copper paint.

Cheers
Dave

[pbmaise]

Epoxy is the best way.

Easy to repair.

Minor repairs underwater.

Core thickness adds insulation and strength.

It is far better than GRP using cheaper resin.

No bottom paint required if you clean bottom regularly.

I have a huge trimaran and the epoxy hulls were last bottom painted 6 years ago.

I clean the bottom once a week in seawater. Twice a week if brackish water. It takes me just 2.5 hours.

[Cheechako]

a) aluminum can corrode very rapidly in certain situations. or not!
b) Welds can crack, and often do. So can just the parent metal in higher stress spots.
c) paint can be a real problem, doesn't last long. My friends 48 ft cutter was painted 3 times in about 10 years.




Titanium is actually one of the most prevalent ores there is. The problem is it's not easy to make into metal, and few suppliers do it.
Ti welding requires the weld area to be shielded with inert gas on BOTH sides of the weld.... otherwise the metal goes bad. Timet used to be the big US supplier of Ti products. Not sure anymore. I have toured their plant.

[captain58sailin]

With aluminum, you have to be very careful about the galvanic corrosion and it has a limit to the number of times it can be bent back and forth, as stated previously. Having said that, I had an aluminum commercial fishing boat that was built in 1962, and there were some spots that corroded through that had to be welded, no big deal, I also developed some stress cracks under the stringers where the engine was mounted, again take a skill saw and cut it out and weld back stronger pieces. If you can do your own welding it isn't too much trouble to keep up. I would have to vote with epoxy encapsulated wood for long term, ease of maintenance and longevity. I also like old FRP boats.

[Stumble]

Snow,

The marine industry needs to design boats to fail after some period of time. Boats really are lasting too long. Think about it, the first fiberglass boats built are still out floating around now 50 and 60 years after being built. It cripples the ability of the industry to innovate, restricts new income, and prevents new designs from coming to the fore.

Think of it this way, how healthy would the car industry be if 90% of the cars ever built were still on the road in reasonable condition. Ya sure there would be a lot more really beautiful classics but there would also be hundreds of thousands of yugo's clunking along, with poor safety records and spitting oil everywhere.

It really is a vicious circle... Thin margins in the marine industry means no advertising to the general public, which means a smaller boating population, which means even thinner margins. Small boat manufacturers used to advertise in mainstream publications, now I can't remember when I saw a boat add anywhere but on a sailing website.

[paulajayne]

Ferro cement is the way to go. Mine get stronger every day.

[Stumble]

Originally Posted by a64pilot

I believe the first Soviet Alpha was retired almost immediately due to fatigue cracking, at the welds.
Rumor mill had it that an Alpha was dove to beyond 1300 meters I think and many of the interior fittings were broken, but hull was OK.
I think Ti is normally welded with submerged arc? But the Soviets licked the Ti welding issue in the 60's cause I think that sub was made from welded sheets.

I know there was a special CIA program for years to buy Titanium whenever and wherever they could get it for uses like the SR-71.
I thought that was because the only source was the Soviet Union. I know after the collapse of the Soviet Union the price for Ti collapsed, I don't know if it is still low.


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Not wrong... Just a little missing.

The Alpha subs failed initial testing because of oxygen embrittlement in the welds. Which is a major problem for large constructions like hulls. It is still the primary reason titanium hulls aren't common. But there is hope, a new process called friction stir welding is at the commercial testing phase, and shows serious promise at reliable deep penetration welding of titanium plate.

Currently ti is generally welded in full argon environment, with gas shielding front and back for large welds. For smaller parts the prefered method is to drop the part into an argon box and weld it there. Think of it like a sand blasting box but a 100% argon environment.

So far no one has really licked the problem. Ti is just to suceptable to oxygen at high temperatures to be a 'solved' problem. Better to say it is a managed one. Almost all the ti parts rejected from ti production fail because of poor weld quality.


Because of its value in the defense industry for decades Ti was on the list of strategically important materials in the US. So the Feds and their subcontractors could only use Ti from US sources. Which led to a small number of US companies holding an effective monopoly on TI supplies in the US. because if you can't sell to the aero space and defense world you couldn't make a profit. Luckily this changed about 10-15 years ago which is why Ti prices have fallen off a cliff since then. With volumetric prices of Ti now running about 1.6 times the price of stainless, where before it was closer to 15 times.

It's this 90% reduction in feed stock that is making it reasonable to introduce to the marine market. Add in some decent engineering and the cost of the materials in a titanium part may actually be less than the cost of stainless in the part.

[sailorchic34]

The answer to what can go wrong with aluminum?

Here's a link for ya. Builder Blames Navy as Brand-New Warship Disintegrates | WIRED

Gee galvanic corrosion, who knew......

[Panope]

Panope's integrated water tanks (hull skin forms part of tank) have had water in them continuously for about 40 years. A few tiny corrosion pits about 1/16" deep have formed. Someday, I will coat the inside of the tanks with a food grade epoxy paint.

The 'tailgate' welder dude that my father hired to build the original engine beds did not use the hull framing for support. Instead, he welded the small engine mount pads directly to the (3/16") hull skin. This lasted about 10 years and several thousand engine hours before a fatigue crack formed in the skin that did produce a small leak (I have since re-built with beds that span 3 hull frames).

A small area of the bilge located directly under the (dripping) stuffing box has had water (sometimes fresh water) in it continuously for 40 years. Some shallow pitting has occurred here but the metal in this area (bottom of keel) is very thick. At the current rate, this will need repair in about 100 years. Every week or two, I use a wet/dry vacuum and suck out any foreign material (copper wire, pennies, etc.) that might have found its way to this area. The other 25 feet of keel/bilge is filled with cement (and lead) so no worries there.

That's what I got so far. Ask me again in another 40 years.

Steve

[a64pilot]

https://www.cia.gov/library/center-f...r-mystery.html
http://www.smithsonianmag.com/smiths...aft-180953402/

Ought to be reliable sources?


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[boatpoker]

The biggest threat to an aluminum vessel is an electrician who uses the term "electrolysis".

[Jim Cate]

The other 25 feet of keel/bilge is filled with cement (and lead) so no worries there.

Steve, how is the lead isolated from the hull? Friends with French alloy boats have had serious issues with such interfaces and corrosion... their internal lead ballast was "potted" in coal tar epoxy mastic and it failed.

Jim

[thomm225]

This guy seems to have gotten quite a bit out of an aluminum homebuilt sailboat.

He builds the thing then sails it through some of the roughest waters on the planet. Nice to see he has tiller steering:

https://www.youtube.com/watch?v=iZxPrZAZeXY