Swedish Steel Yacht SSY builds a boat of Sandviken SuperDuplex SAF 2507 stainless steel “Stronger then CF”
https://sv-se.facebook.com/ssyab
Picture below from their Facebook page.
I have been following this build for a while.
This boat is build in 1,6 mm (16 gauge) high strength super duplex stainless steel.
It is an interesting way of making a strong, light and stiff structure of steel. I guess the long “stringers” are filled with some kind of foam to make a local foam/steel composite for added stiffness. The hull will not be painted below the waterline, but will be polished to a high gloss. Tests have shown that nothing will grow on the hull, and most dirt and stuff will be washed of when making 5 (or more) knots through the water.
I hope I can see this boat in real life this summer, since i really like the idea of a strong and maintenance free steel hull.
I know this is not directly proa-related, but i think it is an interesting and promising way of building light strong and safe boats, with minimum maintenance and a very smooth low drag surface - perfect for a high speed vaka. The inventor (Håkan Rosén) says this hull is stronger and stiffer then CF foamcore structures. I don´t really know if I believe this, but i do believe it will be a very lightweight structure. It is sad they did not build a multihull sailboat as a proof of concept instead.
Cheers,
Johannes
The “stringers” or girders or whatever one should call these structures are made of the same type of steel, rolled to a elastic “springy” shape, that will allow 10 mm flex before becoming much more stiff and thereby resist further flexing.
These create the global stiffness needed in order to use very thin plating.
They will not create the same “hungry horse” look thinly plated steel hulls are known to have. They have a very large area of contact with the plating and they are elastic enough not to dent or stretch the plating when impacted by waves.
They use laser welding and hydraulic water shaping of the plates, so i guess we will not see many homebuild yachts using this method in the near future..
I just need to figure out how to make a low-tech diy-friendly version.
Johannes
Some history and info about the stringers - English
I have not found much information in english yet.
Johannes,
You state that when highly polished, this duplex stainless steel will not need antifouling paint. Really?
I know that duplex stainless steel is the right stuff for corrosion resistance in sea water (much more so than “plain” 316 stainless steel for instance) but I have a hard time to visualize no “natural growth” on bare metal.
I read somewhere a long time ago that a cupro-nickel alloy had this property… but I have never seen a picture of any boat built like this. One of the reasons apparently was the cost of the alloy; it was so expensive that one could not justify the investment, compared to a regular paint job.
Is it the material we are talking about here?
Cheers,
Laurent
I think the idea is that if you have a super smooth polished surface, the organisms can’t adhere to the surface. This is the method used by surface finishes such as Intersleek: http://www.international-marine.com/intersleek900/intersleek-900-home.aspx
I think the idea is that if you have a super smooth polished surface, the organisms can’t adhere to the surface.
This is how i understand it from the article i read.
I am not involved in this project in any way. I just like the idea of a light and strong boat hull with minimal maintenance, made from modern steel alloys.
Cheers,
Johannes
I found his patent. Very interesting.
I have always disliked a thin steel skin on a strong frame, due to the inevitable buckling and resulting “hungry horse” look. If most of the strength is in the skin, or if the internal framing is at least as flexible as the skin, it will not develop the unsightly buckling between the frames or stringers. I think his inwards and outwards flexible, but side to side stiff, stringers is a great invention. The can absorb and distribute enormous impacts throughout the structure without buckling or failure. All within the natural elasticity of the steel.
I do like the use of the elastic properties of modern materials, in a smart way to mimic the Viking longships and the pacific islanders proas. Both are examples of brilliant engineering - not trying to resist loads by brute force and raw strength. Making things work in synergy with the elements, not the usual western practice of trying to force nature into submission. The big difference is that the available materials have a whole new level of strength and life-span. The pacific people would have loved to use steel with a expected usable life of 200 - 300 years.
The easiest way of building something similar but much more low tech and diy-friendly i can imagine at the moment would be to cut thin sections of oval pipe (“springy” high strength steel) and weld them between the stringers (internal 3140 chrome-molly steel pipe framing like a race-car/UL airplane/mountain-bike???) and the plating, in a long series of small local “shock-absorbers”. I believe there is much better way of doing this, but i have to start somewhere… I am starting to see another scale-model somewhere in the not so distant future…..
Johannes
I found some pictures of the cross-section of the stringers in his swedish patent (link)
SE536468 C2 Swedish patent databse
Johannes
I read somewhere a long time ago that a cupro-nickel alloy had this property… but I have never seen a picture of any boat built like this. One of the reasons apparently was the cost of the alloy; it was so expensive that one could not justify the investment, compared to a regular paint job.
Is it the material we are talking about here?
The copper association widely touts a copper-clad steel for boatbuilding. 6mm plate is something like 4.5mm steel and 1.5mm copper alloy. You weld it with ordinary electrodes on the inside—it’s all steel—-and from the outside with special copper electrodes, as I recall. The resulting exterior surface is not only all copper, but can be ground smooth if desired, as you’re grinding the pure copper weld material, not the steel. Repair is similar—gashes and even scratches can be repaired by copper welding. The article says that the lack of need for bottom paint (new and especially re-coating over time) plus drag savings due to fouling easily offset the higher price for the material. The website quoted some ridiculously short payback times.
The boat I saw on the interwebs was mirror-polished for looks, and had no antifouling—also no fouling. 😉
So why aren’t all commercial vessels copper-clad steel? Go here and read about it: http://www.copper.org/applications/marine/cuni/txt_biofouling_resist_cuni.html#cla2
Dave
I would prefer 70+30 CuNi plate instead of copper clad steel. If the copper is scraped off somewhere so the steel is exposed, the steel would corrode very fast. 70+30 CuNi is much more corrosion resistant then pure copper, and will still keep the anti-fouling properties.
Copper nickel alloy has a higher density and less strength then steel/stainless steel, and it is more expensive.
I hope polished super duplex stainless steel is smooth enough to keep barnacles from attaching to the hull.
If that is the case i consider SAF 2507 to be a superior metal for proas or any kind of multihull.
I guess i have to learn to TIG weld stainless steel.
http://www.tibnor.se can deliver Duplex stainless steel, and the cost is not to extreme.
I have already made several drawings and calculations of a 25 foot deep V Vaka made of 1,5 or 2 mm stainless.
Still fighting my chronic fatigue, so nothing will happen until i get better. I try to learn as much as possible, so these years being sick is not totally wasted.
Cheers,
Johannes
I would prefer 70+30 CuNi plate instead of copper clad steel. If the copper is scraped off somewhere so the steel is exposed, the steel would corrode very fast. 70+30 CuNi is much more corrosion resistant then pure copper, and will still keep the anti-fouling properties.
My response was directed at a question regarding cost; 70+30 is very expensive—as is stainless steel. These metals are only appropriate for boatbuilding where the builder has a very large budget or the performance advantages are required by the application.
The article I read suggested considering cladded 90+10 CuNi to steel for cost/performance reasons. Certain gold alloys might have huge structural or maintenance advantages, but it is too expensive for most marine uses. 😉 (No, please don’t ask me how gold is structurally superior—I was using it as a metaphor!)
I’m sorry not to recall the details, but one very common question in the FAQ dealt with scratches and blemishes, just as you do. All I can relate today is that the FAQ answer I read satisfied me that this isn’t a practical problem. You’re welcome to follow the link I provided earlier. You, Johannes in particular, might benefit from this as there is much there regarding construction technique, metallurgy and various alloy pluses and minuses.
Cheers,
Dave