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Old 20-08-2015, 00:23   #61
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Re: And the safest hull material is...

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Ah but it wasn't welded. It was riveted.

Ironically WW2 Liberty Ships were all welded and they cracked without any help from icebergs. They had to be cut all the way around and have riveted section inserted for flexibility.

In the true story "Survive the Savage Sea."
a family of 4 survived 3 months in an 8' fibreglass dinghy after their wooden yacht was sunk by whales off Galapagos.
This one was welded..

The problem with steel ships is that they rot from the inside out.... many bulk carriers are stuffed by 15 years of age.... the front fell off this one at 18yo.
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Old 20-08-2015, 02:26   #62
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Re: And the safest hull material is...

This thread is a lot of fun..... But all steel is not created equal and a yacht made with mild steel will certainly keep its owner busy. But corten steel is in another league, it is a high tensile product with additional strength. Saying all steel is the same is bit like saying all timber yachts or fiberglass yachts are all the same.

CorTen is a trade name for a steel alloy material originally produced by United States Steel. Corten is a weathering steel. This material is a corrosion resistant steel, that left uncoated develops an outer layer patina. This patina protects the steel from additional corrosion.
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Old 20-08-2015, 04:14   #63
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Re: And the safest hull material is...

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Is it just me who is having a deja vu moment all over again re 'all is lost'?

Captain Smith thought steel was good... the iceberg thought different....
It was poor quality steel with a high sulfur content held together with poor quality wrought iron rivets.

Both the steel and rivets used were very brittle.
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Old 20-08-2015, 19:31   #64
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Re: And the safest hull material is...

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The Liberties had a design fault causing stress concentration, which was fixed
I recall being reading somewhere in an article on ship construction that it was square corners in the hatches which caused the problem which was fixed by radiasing the corners.
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Old 21-08-2015, 05:50   #65
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Re: And the safest hull material is...

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I recall being reading somewhere in an article on ship construction that it was square corners in the hatches which caused the problem which was fixed by radiasing the corners.
Now I'm going to transgress to aluminum alloys in the air. It was square corners on a window in the De Havilland Comet jet airliner that resulted in explosive decompression in 2 planes before they were grounded. Cracks had developed and engineers drilled holes to stop the cracks spreading.
Then they put a Comet in a water tank and simulated pressurisation cycles until it also exploded.
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Old 21-08-2015, 07:51   #66
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Re: And the safest hull material is...

Large steel commercial ships (> 100ft) are about equal to a small typical fiberglass boat when it comes to puncture resistance when encountering a rather immobile object, iceberg or rock. A floating shipping container or one of our boats would most likely never touch the ship, the bow wave would just toss it aside. This type of puncture resistance has to do with the relationship of the skin thickness vs the span between supports. Small steel boats have a much thicker skin in this respect, they are more like battle ships.
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Old 21-08-2015, 08:21   #67
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Re: And the safest hull material is...

What is often missed in these discussions is that most metal boats are built with a strong structure holding the hull plating. This structure helps makes the boats strong, rigid and damage resistant. Most metal boats have bulkheads, hopefully water tight ones, frames and longitudinals that greatly add to the strength of the hull.

The big issue with steel is internal rust but that can be prevented with proper hull preparation, painting and insulation.

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Old 21-08-2015, 21:13   #68
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Re: And the safest hull material is...

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Large steel commercial ships (> 100ft) are about equal to a small typical fiberglass boat when it comes to puncture resistance when encountering a rather immobile object, iceberg or rock. A floating shipping container or one of our boats would most likely never touch the ship, the bow wave would just toss it aside. This type of puncture resistance has to do with the relationship of the skin thickness vs the span between supports. Small steel boats have a much thicker skin in this respect, they are more like battle ships.
Unfortunately an American yacht approaching northern New Zealand several years ago was sunk when a container ship ran into it. A family were on board and the mother was on watch in a 50 knot gale. I remember the family name. The yacht was NOT tossed to one side by the bow wave. The father and children below perished (I can't remember the number of children. Perhaps 2)

The woman on watch somehow escaped in a partly inflated dinghy. She drifted for a considerable time in the gale and eventually washed up on a small remote stoney beach near Cape Brett at the entrance to the Bay of Islands NZ.

( I know that area very well and the ocean swells can be very large hitting shear cliffs with 100 m depths right up to them.

She was very very fortunate to be discovered by a fisherman who came ashore at that beach for some reason. It was very unusual for anyone to go ashore there.

There were some who did not believe her story. Most boating people of course did believe and were very sympathetic as her whole family were lost. An investigator discovered which container ship, Korean I think, hit her without the crew being aware. Or so was made out. The disbelievers were proven wrong.

Just the same as we get bugs on our windshields, the bow wave doesn't necessarily push boats to one side. Don't test your theory.
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Old 22-08-2015, 08:04   #69
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Re: And the safest hull material is...

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. The yacht was NOT tossed to one side by the bow wave. The father and children below perished (I can't remember the number of children. Perhaps 2)
When I said tossed aside, it would be a violent toss, roll, etc. Much like a 50 foot breaking wave. The sailboat would not survive, a container probably would, what I was saying is that there would be no damage to the container ship, the relatively fragile skin of the hull would remain unscathed. The sailboat or container would never touch the steel hull of the ship.
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Old 22-08-2015, 15:34   #70
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Re: And the safest hull material is...

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When I said tossed aside, it would be a violent toss, roll, etc. Much like a 50 foot breaking wave. The sailboat would not survive, a container probably would, what I was saying is that there would be no damage to the container ship, the relatively fragile skin of the hull would remain unscathed. The sailboat or container would never touch the steel hull of the ship.
The container ship had a bulb bow as most do. It was a fatal toss and yacht paint was found on the bulb when inspected in Korea.

Bulbs are similar to the rams Roman Galleys used to sink their enemies. I'm not going to split hairs or hulls about the nature of the toss.

On another tack it occurs to me that vessels using GPS could be unintentionally programing themselves to collide with others
coming or going to the same destination. They each plot the same shortest reciprocal or overtaking route. When there used to be an error they were more spread out. Just a theory.
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Old 22-08-2015, 16:05   #71
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Re: And the safest hull material is...

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No question, steel. Small steel boats (less than 100 ft) are much stronger in impact resistance than anything of reasonable cost and normal construction. Take a piece of steel 1/4 inch plate, 3/8 inch fiberglass, 3/8 inch aluminum plate, 1 inch thick wood and attack them with an axe or sledge. The steel will be bent to heck, but still one piece, and it will last much longer than you will swinging the axe or sledge. The aluminum will easily cut with the axe and fatigue with the sledge and break. The fiberglass might survive one blow of either but not much more than one. A small steel boat is the only thing that might survive a collision with a semi submerged container or an iceberg. Small steel boats are typically much thicker than they have to be for strength, they have to be able to have some extra material for corrosion resistance. The bottom of my keel is 1 inch thick plate, the sides 3/8, it could pound on a reef or rocky shore much longer than any other construction. A container collision a full speed in fiberglass, aluminum, or wood boat, if it didn't have sealed compartments, I don't think you would even have time to get your ditch bag out of a locker, there would be a 4 foot hole and the boat would be under in a minute or less. Steel would most likely have a huge dent but probably still be watertight. I did have a 27 foot steel boat for a small time. I think it could probably survive being dashed onto a rocky shore by 50 foot breaking wave.
Since I've a steel boat, it would be difficult to disagree if one is concerned with punctures. Helps to have strong, commercial-boat doors (doggable) and windows too. Weight isn't critical if one need not exceed displacement speed.

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Old 22-08-2015, 18:16   #72
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Re: And the safest hull material is...

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The container ship had a bulb bow as most do. It was a fatal toss and yacht paint was found on the bulb when inspected in Korea.

Bulbs are similar to the rams Roman Galleys used to sink their enemies. I'm not going to split hairs or hulls about the nature of the toss.

On another tack it occurs to me that vessels using GPS could be unintentionally programing themselves to collide with others
coming or going to the same destination. They each plot the same shortest reciprocal or overtaking route. When there used to be an error they were more spread out. Just a theory.
Spellcheck correction correction Roman Galleons
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Old 22-08-2015, 19:51   #73
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Re: And the safest hull material is...

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The container ship had a bulb bow as most do. It was a fatal toss and yacht paint was found on the bulb when inspected in Korea.
Bulbs are similar to the rams Roman Galleys used to sink their enemies. I'm not going to split hairs or hulls about the nature of the toss.
The bulb bow is typically underwater if the container ship is loaded, the purpose of the bulb is to act much like a submarine, so it should be submerged, the bulb then shrinks in size right where the bow wave would be building up, this sucks much of the bow wave down so it is not as large, a smaller bow wave means less energy is wasted making it, and the ship uses less fuel. The bulb would be much stronger than the side of the hull due to it's shape. If it was not underwater there would be a different type of wave build up around it, not one to toss a boat or container aside. There would be a large wave but it's shape would not be such that it would just push something aside, the wave comes up and over the top of the bulb. If it was underwater less than the depth of the keel of the boat than it would most likely hit the keel. There would be a bulge of water above the bulb. I'm not saying that it's OK and not to worry about being run over by a container ship, that is one of my biggest fears sailing single handed in certain areas of the world. I'm just commenting on how steel structures have different strengths with different sizes. Small steel yachts are some of the strongest boat structures on the ocean.
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Old 22-08-2015, 20:18   #74
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Re: And the safest hull material is...

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This one was welded..

The problem with steel ships is that they rot from the inside out.... many bulk carriers are stuffed by 15 years of age.... the front fell off this one at 18yo.
Ping,

Thanks for posting the video clip. I really enjoyed it. It was like watching a Monty Python sketch. Hilarious!

About your point about bulk carriers lasting just 15 years:
I recently looked at a list of about 20 commercial freighters and ships (all steel) that were built in 1980s. They were made by a wide range of builders (some in Europe, some in Far East, some in Asia), and they had a variety of types and sizes (all over 200 feet long). They were large ships. They were ALL scrapped after just about 15-20 years (average) use. When I saw that, I was surprised at the short life of the commercial ships.
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Old 22-08-2015, 20:50   #75
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Re: And the safest hull material is...

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The bulb bow is typically underwater if the container ship is loaded, the purpose of the bulb is to act much like a submarine, so it should be submerged, the bulb then shrinks in size right where the bow wave would be building up, this sucks much of the bow wave down so it is not as large, a smaller bow wave means less energy is wasted making it, and the ship uses less fuel. The bulb would be much stronger than the side of the hull due to it's shape. If it was not underwater there would be a different type of wave build up around it, not one to toss a boat or container aside. There would be a large wave but it's shape would not be such that it would just push something aside, the wave comes up and over the top of the bulb. If it was underwater less than the depth of the keel of the boat than it would most likely hit the keel. There would be a bulge of water above the bulb. I'm not saying that it's OK and not to worry about being run over by a container ship, that is one of my biggest fears sailing single handed in certain areas of the world. I'm just commenting on how steel structures have different strengths with different sizes. Small steel yachts are some of the strongest boat structures on the ocean.

Quite so and I do understand that a bulb produces a negative pressure wave to cancel out the positive pressure bow wave at a certain speed.

And probably like you I have seen bulbs operating close up and have seen the surface of the water lifting up unbroken above a bulb.

I don't think you would want to park you're boat in front of a container ship travelling at 18 knots to see whether it is tossed to one side.

I get back to the bugs that get splattered on our cars and windshields. They don't get tossed to one side by the bow wave of our cars.

Aircraft have often been caught in wind shear or down drafts and smashed into hills without following the path of the wind deflecting off the hills.

It's to do with momentum and even bugs have momentum if they are flying and inertia if they are hovering.

I once contemplated building a steel yacht and decided against it because I lacked somewhere that I could make a lot of noise like a factory.

Another reason is that as I'm sure you know steel yachts need to be over about 30' overall or they are too heavy for their length. So steel only comes into its own at around 40'. The hiulls themselves are quite cheap but you still need to outfit a heavy displacement boat.

Don't misunderstand me there are some very fine steel yachts but I decided not for me but I can still admire them.

David Lewis's Icebird was a secondhand steel yacht that he solo circumnavigated Antarctica with. It's a while since I read his account and I think it was he who found a rust hole below the waterline that caused him a great deal of concern.

Navy vessels as I'm sure you know are fully welded to obtain maximum strength. That is all the frames are continuously welded inside. That's why navy vessels sides can look a bit distorted. Whereas the frames of a steel yachts are not welded continuously so as to avoid welding distortion and to look better. Rather there are a series of unjointed welds.

I once owned gas and arc welding equipment and could easily get up to speed again welding up a hull but life is too short and 30 years ago would have been the time for me to build a steel yacht but 30 years ago my work was too demanding.
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