UK yacht Cheeki Rafiki missing in mid-Atlantic

[pbiJim]

Originally Posted by sailorboy1

And just what material do you feel should be used?

I've been wanting to try 17-4PH (aka 630) for a while now, but I haven't had a good opportunity.

I have a lot of experience with 316 in industrial applications. I have seen a lot of failures due to repetitive stress embrittlement in places where neither oxygen starvation nor corrosive materials were present.

Since I have not yet tried the 17-4PH, I do not know if it is actually better over the long run or not, but I would like to find out. It's static specifications are very good.

[Rustic Charm]

Originally Posted by pbiJim

I've been wanting to try 17-4PH (aka 630) for a while now, but I haven't had a good opportunity.

I have a lot of experience with 316 in industrial applications. I have seen a lot of failures due to repetitive stress embrittlement in places where neither oxygen starvation nor corrosive materials were present.

Since I have not yet tried the 17-4PH, I do not know if it is actually better over the long run or not, but I would like to find out. It's static specifications are very good.

17 grade steels, or ph steels we call them are not as corrosion resistant as 316 grade. There more often used in aviation.

[pbiJim]

Originally Posted by tedsherrin

17 grade steels, or ph steels we call them are not as corrosion resistant as 316 grade. There more often used in aviation.

Yes, the corrosion resistance is not as good as 316, but the mechanical properties look a lot better, at least from a static test perspective. I would like to try some & find out how badly it corrodes in a marine environment. If the corrosion is minimal, or even tolerable, the tradeoff may be worthwhile for the possible mechanical benefits.

According to one manufacturer:

http://www.aksteel.com/pdf/markets_p...data_sheet.pdf

"17-4 PH Stainless Steel with-stands corrosive attack better than any
of the standard hardenable stainless
steels and is comparable to Type 304 in
most media"


As I said before, I don't know if it would be better in the long run or not, but I would like to find out.

There seems to be room for improvement over what is currently in use.

[MarkJ]

Originally Posted by tedsherrin

LOL no need for a British inquest, between Sailing Anarchy and CF the mystery will be solved by the armchair sleuths.

Originally Posted by tedsherrin

17 grade steels, or ph steels we call them are not as corrosion resistant as 316 grade. There more often used in aviation.

But its OK for you to be an armchair metallurgist?

[Cavalier]

Originally Posted by pbiJim

Yes, the corrosion resistance is not as good as 316, but the mechanical properties look a lot better, at least from a static test perspective. I would like to try some & find out how badly it corrodes in a marine environment. If the corrosion is minimal, or even tolerable, the tradeoff may be worthwhile for the possible mechanical benefits.

According to one manufacturer:

http://www.aksteel.com/pdf/markets_p...data_sheet.pdf

"17-4 PH Stainless Steel with-stands corrosive attack better than any
of the standard hardenable stainless
steels and is comparable to Type 304 in
most media"

As I said before, I don't know if it would be better in the long run or not, but I would like to find out.

There seems to be room for improvement over what is currently in use.

After working for 20 years in subsea oil&gas on Subsea template design, ROVs, ROTs and pipeline repair robots, I'd say that Oil & Gas operators are a conservative bunch. If you get it wrong, as a small company, you're out of business immediately. I can pretty much summarize that the majority of prefered materials used in the marine environment divided into two classes:

1). Short term protection: I.e. Will not be in the water too long so cathodic protection requirements, low oxygen surface cracking, H2S fatigue cracking and are minimal.

2). Long term protection: I.e. 15-20year service lifetime warranty. Complete cathodic protection system for service life, optimal material use and quality sub-selection (each ingot/stock would be tested), proven qualification for all load factors and environmental requirements for service life.

Remember that service life for (2) means 15-20 year on the seabed operating 100% of the time without lifting back to surface for maintenance!

For type (1) preferred materials would be:

A). Structural: St.52-3 and St-52-3N hollow section or open section. Both types painted with an EN/NS epoxy multi coat protection system. If hollow section then the interior would be sprayed through with "tectil" bitumen wax. This would be protected with Zinc anodes. If Aluminum was to be used (popular with ROVs as it reduces dynamic loading at launch and recovery), then it was preferred to leave it uncoated and protect it with Magnesium anodes.
B) Mechanical : Seawater lubricated items would typically be S165M (stock rods for hydraulic cylinders) a 800-900MPa stainless, coupled with bushings of JM7-15 or JM7-20 (oiled bronze). Sometimes 4140 would be used as a substitute for S165M.
AISI 316 and AISI 316L would be very common, and occasionally Aluminium if it was guaranteed to be electrically isolated from other metallics.
POM (Polymer) was used sometimes but frowned upon as it expands in seawater (is slightly porous) so your tolerances go to hell - PEHD was preferred.
PEEK is expensive but as strong as aluminium and survives most chemical issues, and a favorite with me as a bushing material.

For type (2) [long term] preferred materials would be:

A). Structural: St.52-3 and St-52-3N open section. Painted with an EN/NS epoxy multi coat protection system. This would be protected with heavy Zinc anodes (I'm talking anodes of many hundred kilos).
GRP would be used on large debris covers on subsea templates. Some of these would be 1/4 size of a football field and be hinged to the subsea structure anchored in the seabed. An ROV would connect a pull-wire to the hatch mechanism and the whole hatch would be opened to expose the subsea template system for maintenance.
B) Mechanical : Seawater lubricated items would typically be AISI 316 (rarely 304), coupled with bushings of JM7-15 or JM7-20 (oiled bronze).
PEHD (High Density Polyethylene) was used more commonly for any bushings etc as it doesn't get affected by seawater. PEEK is expensive but as strong as aluminum and survives most chemical issues.
C) Pipelines, flowlines etc (and some fasteners) would be Super Duplex, very very rarely titanium. Inconel which was coated with silver would be a popular choice for pipeline flange-seals as it's good at withstanding H2S corrosion.

As you can see, there really isn't any "aerospace" materials in use. The Aluminium used would be T-6062 (T6061 in the US), so similar to aerospace - but that was it. You'll also note that the list of materials is limited. Of course there are many more materials used, but typically they are more limited than the "usual suspects".. the key to good cathodic protection is to minimize the number of types of materials such that the whole electrical interaction picture is simplified.

Aerospace is a completely different environment to offshore (saltwater). Compared to marine, aerospace materials go through much larger temperature variations. However, they don't need to be as tolerant to humidity (apart from during storage). Their chemical tolerance doesn't need to be as high and their exposure to complex electrolytes is limited. That said, aerospace structural materials need to withstand much higher dynamic stresses as they are intended to operated at the higher end of their utilization factor: there isn't much material to save weight - so it ALL gets used.

Like I said before, the offshore oil & gas industry is actually very high-end with their subsea/sub-surface technology and material science. Literally $Billions has been poured into materials research, due to their risk-aversion and they tend not to use materials which don't stand the test of time... It would be unwise of the yachting industry to play with materials in critical structural applications without considering the hard-learned lessons from other related [and much larger] industries: there are far fewer subsea well-blowouts than their are yachts losing keels!

p.s. I would agree that well blow-outs tend to have a much greater consequence than broken keels.

[Cavalier]

..off topic: but just for information.

This is a small subsea template (well head cluster), and the ROV hovering over the top is about the size of a Ford Transit Van (for scale):

[pbiJim]

Cavaliar,
many of those materials are off-shore spec's that don't have AISI equivalents. I see that you are in Houston. Are you able to source those materials here in the States? If so, can you list a supplier?

Thanks,
Jim

[DumnMad]

Originally Posted by sailorboy1

And just what material do you feel should be used?

Keel bolts;
316 stainless is great if not immersed in seawater and not oxygen deprived and not subject to significant cyclic loading.

I understand ss2205 is better for these conditions but don't know much about it.

Galv bolts are a bit out of fashion but are really good at sending out rust signals to tell you when they need replacing. I think they would be much safer than ss316.

[Rustic Charm]

Originally Posted by MarkJ

But its OK for you to be an armchair metallurgist?

Well I studied metallurgy fool, whilst doing a metal trade, which means I can like anyone else comment on a 'fact'.

[Greg Shakeshaft]

Originally Posted by socaldmax

I'm surprised that they only searched for 2 days. I would have expected a lot longer than that.

As a US citizen who is pretty ticked off about drones being used inside the US against citizens, I'd really like to see them use drones for offshore search operations instead. Assign 4 or 5 drones to a search grid and have them scour the area with FLIR and high res. video cameras. I think they'd be a lot more effective than people using binoculars looking out the windows of C-130s. Far more fuel efficient and cost effective.

I'm not entirely sure if anyone has already responded to this but, if this is true then I think we should be asking our respective governments to utilise our military intelligence and equipment for civilian purposes far more than we do. Afterall, it's our (taxpayer) money that paid for all this in the first place.

I apologise if I have offended anybody with his comment.

[pbiJim]

Does anyone know if there are plans to recover the hull & do an autopsy on it?

[mbianka]

Originally Posted by pbiJim

Does anyone know if there are plans to recover the hull & do an autopsy on it?

I keep wondering about that too. Just even to check if there are any remains inside or did all the crew get out. Let alone the keel failure. Seems like everybody is just sailing away from this tragedy without further investigation.

I was amazed that the Navy ship that inspected the hull only had a "surface swimmer" on board. Not one diver on board? WTF!

[Paul L]

Originally Posted by Greg Shakeshaft

I'm not entirely sure if anyone has already responded to this but, if this is true then I think we should be asking our respective governments to utilise our military intelligence and equipment for civilian purposes far more than we do. Afterall, it's our (taxpayer) money that paid for all this in the first place.

I apologise if I have offended anybody with his comment.

US drones are used on occasion for civilian SAR. I listened to a USCG search for a cruising sailboat offshore N Florida. They requested the INS (Immigration and Naturalization Service) to fly a drone over the boat to try and determine if it was manned. The single-hander was not onboard and the boat was latter towed into port empty.

[Muckle Flugga]

Originally Posted by mbianka

I keep wondering about that too. Just even to check if there are any remains inside or did all the crew get out. Let alone the keel failure. Seems like everybody is just sailing away from this tragedy without further investigation.

I was amazed that the Navy ship that inspected the hull only had a "surface swimmer" on board. Not one diver on board? WTF!

I would love to see the vessel recovered. However, strictly speaking, as this is no longer an SAR, but rather a recovery and investigation, then the whole responsibility lies with the UK government, and its Marine Accident Investigation Branch (MAIB). It is well possible that the vessels which were in the area lacked the onboard resources to hoist such a large and complex (and until the water drained out of it, very very heavy) object on board.

It likely is still out there... a hazard to shipping. Sadly, whatever remains there are are very likely still within.

As to getting a diver into the hull... it is not so easy. There would be a mass of wire, lines, and possibly broken spars and tangled sail still attached to the hull. Moreover there may be toxic chemicals such leaking battery acid (which would be quickly buffered by the ocean, but maybe dangerous locally), bleach, paint thinner, diesel, and a host of other possible. This is not to mention any human remains, which may be a biohazard in themselves. Apart from which there will be cans, knives, floorboards and all manner of other such inside the rolling hull, sloshing back and forth... it would be an extremely hazardous environment and regardless of whether they had SCUBA equipment aboard, if I was the US skipper I would NOT allow a diver to enter that mess. The only justification could have been in order to save life. If none remained to be saved, I would not endanger another in such circumstances. The surface swimmer already was in significant hazard for all the above reasons, as they attempted to gain knowledge of the position of the liferaft etc. I have every respect for the USCG mariners in this situation, and really, so should we all.

[poiu]

Originally Posted by Muckle Flugga

I would love to see the vessel recovered. However, strictly speaking, as this is no longer an SAR, but rather a recovery and investigation, then the whole responsibility lies with the UK government, and its Marine Accident Investigation Branch (MAIB). It is well possible that the vessels which were in the area lacked the onboard resources to hoist such a large and complex (and until the water drained out of it, very very heavy) object on board.

It likely is still out there... a hazard to shipping. Sadly, whatever remains there are are very likely still within.

As to getting a diver into the hull... it is not so easy. There would be a mass of wire, lines, and possibly broken spars and tangled sail still attached to the hull. Moreover there may be toxic chemicals such leaking battery acid (which would be quickly buffered by the ocean, but maybe dangerous locally), bleach, paint thinner, diesel, and a host of other possible. This is not to mention any human remains, which may be a biohazard in themselves. Apart from which there will be cans, knives, floorboards and all manner of other such inside the rolling hull, sloshing back and forth... it would be an extremely hazardous environment and regardless of whether they had SCUBA equipment aboard, if I was the US skipper I would NOT allow a diver to enter that mess. The only justification could have been in order to save life. If none remained to be saved, I would not endanger another in such circumstances. The surface swimmer already was in significant hazard for all the above reasons, as they attempted to gain knowledge of the position of the liferaft etc. I have every respect for the USCG mariners in this situation, and really, so should we all.

I'd like to get any keel bolts parts out that remain for analysis by the MAIB and I'd like to get a sample of the fibreglass hull as a minimum. I think someone with a pneumatic cutter could get those key samples safely enough given reasonable weather.