Stainless Steel Yacht ?

[s/v Beth]

If a boat was build with a SS steel hull, three thru hulls (engine intake, depth sounder,poo) and parts that could be lifted out for inspection of the hull/bulkheads (block attachments in the engine room and above water tanks etc)...Seems like it would cut down a lot on the worries of maintenance. With SS we would only worry about where it would get no oxygen- the thru hulls perhaps? and where the fin meets the body?

[CharlieCobra]

Why not go with two thru hulls and use manifolds in a water box, if ya wanna limit hull incursions.

[Sam Plan B]

Some years ago when I was young and had all the time in the world I looked into building a boat from a bare hull. Back then the cost of the bare hull was about 10% of the total cost of the boat. That is even considering free labor (my own) to build it. These days with all the new electronics available I suspect that the cost ratio would be even more favor the fitting out side of the ledger. So if SS cost you 3.6 times the price of common steel, have at it. I suppose you will have to do without some bells and whistles at the other end. Some people sail without mechanical propultion. Some people do without electric light. Of course, when time comes to sell your SS boat, you or your heirs may be treated rather harslly by the market place.

The most likely outcome of investing so much in a SS hull is this. You will not have enough money to finish the project and the half finished SS hull will go to someone else at a common steel price.

[David M]

I think you also want to look at the strength to weight ratio versus glass or aluminum. Maybe even the strength to cost ratio.

[minaret]

Originally Posted by CharlieCobra

Why not go with two thru hulls and use manifolds in a water box, if ya wanna limit hull incursions.

A sea chest is the only way to go. Just installed new ball valves on all the fittings on mine, this allows me to shut off individual systems off the chest so I can work on them without shutting off all intake. Works great!

[Ctrich]

Food for thought.
Prop shafts are SS, when zinked there is no crevice corrosion or electrolysis. They are under tremendous loads and do not "work harden" (???) and when maintained last forever.

For steel the sand blasting and coatings inside and out needed to be added to the costs aswell. On my boat this came out to be more expensive than the steel. By about 2x.
So why are'nt more boats made of SS????
I think your onto something.

[capn_billl]

Originally Posted by cat man do

Corten steel hardly rusts and being high tensile, thinner plate thickness can be used

Weathering steel - Wikipedia, the free encyclopedia

Actually the article you linked to pinted aut several spectaculer failures of cor-ten. Including the complete failure to resist salt water. Stainless steel properly formulated would be a good material though expensive.

[delmarrey]

The problem I see with SS is that paint will not stick to SS.. Paint just strips off over time. I would not put any metal structure in the ocean w/o bottom pain!!!

Here's what an expert has to say.........

A structure built in stainless will weigh approximately the same as one built in mild steel, although on occasion one may be able to make use of somewhat lighter scantlings due to the somewhat higher strength of stainless. There are several major drawbacks to the use of stainless, not the least of which is cost. Stainless of the proper alloy will cost nearly six times the price of mild steel!

Even if it were not so costly, stainless has numerous other problems:

Stainless is quite difficult to cut, except by plasma arc.
Stainless work hardens when being formed and can become locally tempered such as when being drilled.
Stainless deforms rather extremely when heated either for cutting or for welding.
Stainless, even in the low carbon types, is subject to carbide precipitation in the heat affected zone adjacent to the weld, which creates an area that is much more susceptible to corrosion as well as to cracking.
Stainless is subject to crevice corrosion when starved of oxygen. This can be prevented only by sandblasting and painting the surfaces, just as it would be done for aluminum, wherever an object is to be mounted onto the stainless surface. The same applies to the back side of any stainless fittings which are applied to hull surfaces.
If the above issues with stainless can be properly accounted for in the design of the vessel and in the building of it, then stainless can be a viable hull construction media.

Type 316-L stainless is generally the preferred alloy. Type 316-L is a low carbon alloy, and is used in welded structures to help prevent carbide precipitation in the heat affected zone. When available, the use of type 321 or 347 stainless will be of considerable benefit in preventing carbide precipitation, since there are other alloying elements (tantalum, columbium, or titanium) which help keep the carbides in solution during welding.

In my view, as a builder the main battle one will face is the rather extreme distortion levels when fabricating with stainless. Stainless conducts heat very slowly and has a high expansion rate. Both of these characteristics conspire against maintaining fairness during weld-up. Short arc MIG welding will be an imperative. In fact Pulsed MIG will probably be desired in order to sustain the right arc characteristics while lowering the overall heat input.

Metal Boats For Blue Water - Kasten Marine Design, Inc.

[Ctrich]

I am surprised by Mr Kasten's views.
-"Extreme distortion levels when fabricating" not when using a quality TIG or MIG, look at a pro built arch or SS railings on any boat and look for "extreme distortion" A good welder who knows stainless does beautiful work.
-"Stainless is difficult to cut, except by plasma arc." What steel shop does not have a plasma cutter now a days? Use plasma. For small stuff water jet company's are now very cheep and do stunning work. I have no problem cutting SS with a zip disk.
-When drilling SS use lots of water or Walters cutting compound to keep the material cool and saves your drill bit. Learn how to resharpen bits on your grinder.
- After welding SS the weld must be pickled with a mild acid to prevent corrosion or rusting. The best marine SS guy I know rubs the whole piece down with acid before it goes out the door, he never has rust issues. Look at any Monotor wind vane after 12 years at sea. A bit of SS cleaner and she's as good as new.
- crevice corrosion is more difficult as I have seen it on a very few SS pieces I've taken off of old boats being destroyed. I have seen a old colin archer wood boat destroyed. The 12T cast iron keel was bolted to the boats keel with 1 1/2 in SS rods, After removing the 14 by 14 wet keel timber and exposing the SS bolts they looked like they came off the shelf yesterday. Yet I have seen SS screws in wet wood 20 yrs old totally eaten away. Most screws are made of 304 SS so I think its a mater of using 316 or better SS to prevent crevice corrosion, (but thats just an opinion.) I still think a SS hull properly zinked like a prop shaft would out last a steel or aluminium boat and over time have better hull strength that an old fibreglass boat.
In a quality building shop Mr Kasten's "issues" are addressed. In his 3rd paragraph last sentence he says that if his issues are accounted for the SS is a viable hull construction media.








TIG TIG TIG

[Reefmagnet]

Originally Posted by Ctrich

<snip>

-"Extreme distortion levels when fabricating" not when using a quality TIG or MIG, look at a pro built arch or SS railings on any boat and look for "extreme distortion" A good welder who knows stainless does beautiful work.

<snip>

There is a MASSIVE difference between welding short sections of tube together and long sections of thin plate with regards to distortion control.

The points the referenced article makes are all valid if one considers it is directed towards amateur builders who will not have the fabrication skills of a pro. In short, mild steel is MUCH easier to fabricate then austenitic stainless varieties like 316. For example, whilst TIG would seem to be the best welding process over MIG, this is not correct for welding a structure the size of a hull. TIG can cause more distortion, promotes more carbide precipitation and is horribly slow in comparison.

[s/v Jedi]

So, did you check out cupro-nickel? The only negative I can come up with is the cost, butno need for anti fouling means the extra cost is made good by later savings!

And welding it seems easy enough...

ciao!
Nick.

[Ctrich]

x2 Reefmagnet on butt welding thin gauge SS sheets together, very difficult and I have not yet mastered this one. My few attempts have been embarrassing. BUT 1/8 and thicker sheet is a breeze to weld using the step method. 1 inch weld, move 3 ft weld and do not return to that spot for 10 mins. In MIG for a hull.
Armature boat builders........... yes, I can see that. Only seeing a snip of his whole artical I though he was voicing his own concerns for SS as a hull material. Missed that, sorry. But then an amateur boat builder in steel who does not get up to speed on welding skills will build a very distorted poor quality boat too. I've seen disasters in fiberglass and wood too. I've seen a few amateurs with no boat experience build better than production boats.
Welding SS or mild steel is the same difficulty, but taht may only be me, maybe a few other amateurs will comment. I will try and get a survey going on this thread.

[nwdiver]

Yeh, Monel is the stuff to work with, pretty soft though.

[delmarrey]

Originally Posted by nwdiver

Yeh, Monel is the stuff to work with, pretty soft though.

Again you can't expect paint to stick to the bottom.

Should read this article >>> BIG YACHT NOW JUNK AFTER 6 WEEKS' USE - Sea Call's Monel Metal-Steel Hull Ruined by Electrolysis, Builders Admit. COSTLY EXPERIMENT FAILS Action of Sea Water Attributed by Metal Makers to Failure to Use Zinc Insulation. - Front Page - NYTimes.com

Then this >> Copper.org: Copper Nickel : Asperida 70-30 boat hull

Some areas of the hull have lost a measurable amount of thickness, as determined by ultrasonic measurements, but overall, the loss has not been excessive.

[Artif]

How about titanium, doesn't corrode or work harden and very lightweight.
Russians have used it in preference to SS for years, even some of their truck chassis are an alloy of steel and titanium.
Cost might be an issue.