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Old 14-08-2015, 19:37   #106
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Re: Steel Hull?

As an aside and on the subject of whale attacks. I worked for 7 years converting an Ex Norwegian Whale Catcher to a charter yacht.

http://thorfinn.net/

Now based in Chuk Lagoon as a dive hotel.... Before ending up there on my last year we travelled the world doing all kinds of commercial jobs then sports fishing and ironically whale watching and nature tours, before we took her to Micronesia.

During this time, I had collected a lot of books and documents on Whaling . (Mostly written by the British onboard fishery inspectors)

There were a number of incidences where these ships with ice breaking hulls were actually sunk or seriously damaged by whale attacks if struck on midship hull sides rather than bow on.

The Norwegian design of those last 1950's ships actually took that risk into consideration.

Even though Diesel was now in vogue... They stayed with Reciprocating Steam so they could repeatedly go from full ahead to full astern without gear damage.

Used large highly pitched single propeller that would pivot dramatically to port when put hard astern

The way they hunted was to sight a whale family.....if calf was of legal size they would shoot the calf first, then the mother, who would try to comfort the calf, was an easy target.


The danger came while pumping air into both whales to keep them afloat...

Captain had to keep ice breaking hull facing the Bulls, who would make numerous charges at ship. Often more than one Bull would charge and while Gunner tried to harpoon with explosive tips from bow, it was often like a matador fight where they had to pivot quickly.

Most of the Whale Catcher's that were critically damaged happened when a Bull stove in the hull midships right where the twin boiler were.... and if the superheated boiler got damaged they exploded.

Great sea boats, horrible original purpose, but an experience I would never forget commanding such a tough, telegraph controlled steamship.
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Old 14-08-2015, 19:50   #107
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Re: Steel Hull?

Pelagic,

Thanks for adding that interesting info and background to the discussion. I wish that was also posted in the "Sunk by a Whale" thread too as it pertains to boats being sunk by whales. Here is a link if you wish to copy your post to the other thread too.
http://www.cruisersforum.com/forums/...es-150847.html

You brought up several facts I had not heard before, making this an even more interesting forum.
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Old 14-08-2015, 20:18   #108
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Re: Steel Hull?

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Originally Posted by Pelagic View Post
Of course, structural flexing of hull in heavy weather, must be to acceptable levels so that sheer stresses are well below failure.
But do you agree that this "designed flexibility" is part of the structural engineering for heavy weather forces?
Hogging and sagging is inherent for all but perfect, theoretical materials.
It isn't isn't intentionally included, it's minimised in design by adding more structure. You could say it's included by design only in that the amount of hogging and sagging is known and chosen by the designer. (Chose because they don't want to add even more structure to reduce it further)

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Rational discussion, which most of the members of this forum desire, is not possible unless both sides of the discussion make a genuine effort to understand what the other side says. Tensen, I am genuinely not trying to give you a hard time. You come across as argumentative and defensive, at least to me. Objectively, you did not understand and reply to my last post. My post dealt primarily with basic physics of kinetics, which is the starting point for any discussion of impact resistance. You did not respond to this at all.

What you have done is given this forum a great example of an individual who is going to argue their point regardless of any and all evidence to the contrary.

As a working engineer I assume you are familiar with design reviews where your peers critique and criticize your work. In the companies I've worked for an inability/unwillingness to understand others would be very career limiting.
What is your career that you're referring to Pauls? Even the slightest relationship to engineering at all?

Your lack of understanding of material properties makes it fairly pointless attempting to discuss them with you.

I did in fact respond to your comments on collisions when I pointed out that (equal mass) carbon fibre composites have a higher ratio of strength over stiffness than steel does - in other words, by the criteria you are so eager to judge impact resistance with, carbon fibre (and E-glass) composites are superior to steel.

I repeat, FRPs have lower stiffness than steel, until you adjust for density, and even then although their stiffness is proportionately higher, their strength has increased by the same factor - FRPs are superior on this point of yours.
The reason you thought otherwise was because you don't understand the difference between stiffness and ductility/brittleness.

So we come to the point I started on: it isn't possible to judge which of two hulls is more resistant to impacts simply by knowing the materials they're made from.
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Old 14-08-2015, 20:53   #109
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Re: Steel Hull?

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Some time ago I read an article about an individual who was sailing from the Panama Canal to the UK. Sometime during his crossing he is believed to have hit a whale while under auto-pilot. His boat was sunk and he spent some time on a life raft before being rescued (this was in the time before sat phones, EPIRBS, PLB's etc.).

How big of a concern is this type of incident during a ocean crossing? Second would a steel hull prevent this type of incident from happening, or is it just a risk you accept on a crossing?
So. To the OP's two questions I offer my humble opinion.
First, I do not feel striking or colliding with a whale is of great concern in general to the cruising sailor.
Second, I would say yes, a steel hull colliding with a whale would likely prevent this kind of incident. Now my two answers only apply to the situation put forth by the OP. Can't speak to the posts by the engineers, it's above my pay grade.
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Old 14-08-2015, 21:20   #110
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Re: Steel Hull?

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So we come to the point I started on: it isn't possible to judge which of two hulls is more resistant to impacts simply by knowing the materials they're made from.
Howdy Tensen. That is a friendly way of saying "hello."

I have enjoyed reading the posts by you and others here. Obviously you see things differently.

I always appreciate it when people who have educated opinions join a discussion like this. Not all sailors are professional engineers, and it is nice to have some "book knowledge" shared with us.

But, at the same time, not all professional engineers are experienced sailors.
It is good to have the experienced sailors give us their practical experience POV too.
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Who is right and who is wrong when you disagree?

I cannot decide that.

IF my only criteria was resistance to impact, based on seeing examples of holed GRP boats (due to impact) and examples of dented, dinged, bent, banged up, but NOT holed steel boats, I would choose a typical or average steel boat over a typical or average GRP boat.

The key as I see it is "average" build boats rather than "custom or extreme" boats.

IF you made a GRP boat to the same mass of the steel boat, in order to match or exceed its strength, you would NOT have an average or typical GRP boat.

While I assume one could make a steel boat with topsides of 2mm plate (below average), and a GRP boat with 50mm thick topsides (above average), I don't think those are average or typical specs for an average 40 foot boat.
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Let's see if we can agree on something:

IF we look at average yachts used by average sailors and commonly available or built, I think it is practical to assume that:
the average steel 40 foot boat is more impact resistant than the average 40 foot GRP boat.
Could you agree on that?
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Old 14-08-2015, 21:44   #111
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Re: Steel Hull?

Quote:
Originally Posted by Tensen View Post
Hogging and sagging is inherent for all but perfect, theoretical materials.
It isn't isn't intentionally included, it's minimised in design by adding more structure. You could say it's included by design only in that the amount of hogging and sagging is known and chosen by the designer. (Chose because they don't want to add even more structure to reduce it further)
I am not a structural engineer, but having worked with a few and studied ship construction the concept of including flexibility within ship structure was explained the same way as a tree bending in the wind.

I understand Military ships had problems when built too rigid with armour platting.

Cruiser Bow Ripped Off By Typhoon 1945 Newsreel: http://youtu.be/X95kSfi1oSU


Also many of the early bulk carriers had similar issues if they could not flex in extreme sea conditions.

Stress and effect on a vessel in severe weather c…: http://youtu.be/PmlTk_3NN_g

Note ending caption where it warns of building too stiff.
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Old 14-08-2015, 22:09   #112
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Re: Steel Hull?

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Originally Posted by Steady Hand View Post
IF we look at average yachts used by average sailors and commonly available or built, I think it is practical to assume that:
the average steel 40 foot boat is more impact resistant than the average 40 foot GRP boat.
Could you agree on that?
If I had to guess I'd say that's more likely to be correct than it is to be incorrect, although I have no data to be sure.

It isn't something I've offered an opinion on, I've discussed the engineering aspect of the subject only, and it seems there are people here who'd try to teach their grandmother to suck eggs.

I'll repeat my main point: you can't judge a hull's impact resistance based only on the material it's made of.
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Old 14-08-2015, 22:20   #113
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Re: Steel Hull?

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I am not a structural engineer, but having worked with a few and studied ship construction the concept of including flexibility within ship structure was explained the same way as a tree bending in the wind.
Yes, if you were able to build a perfectly stiff object it would have no ability to absorb energy.

In real life though modern NAs spend time reducing hogging/sagging, and wishing for more stiffness.
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Old 14-08-2015, 22:33   #114
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Re: Steel Hull?

OK I got it..... Your focus is Theoretical rather than Utilitarian.
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Old 14-08-2015, 22:36   #115
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Re: Steel Hull?

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OK I got it..... Your focus is Theoretical rather than Utilitarian.
On the contrary, I pointed out what actually occurs: NAs desire stiffness.
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Old 14-08-2015, 23:39   #116
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Re: Steel Hull?

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Where are all what?
I answered your question, I made no comment on their popularity or rarity.
Where are all the incredibly strong plastic boats?
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Old 14-08-2015, 23:43   #117
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Re: Steel Hull?

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On the contrary, I pointed out what actually occurs: NAs desire stiffness.
Don't we all
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Old 15-08-2015, 00:23   #118
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Re: Steel Hull?

[QUOTE=FamilyVan;1890946]So, I was right, you've never actually run into anything?

Oh, come on mate! One of the good things about education is that one does not have to have all the bad experiences that history records in order to avoid them yourself.

If you insist on this approach, there are countless steel ships (around your postulated 3000 tons level or more) that have been split wide open by colliding with fixed objects. The recent demise of the Costa Concordia comes to mind, to say nothing of the fabled Titanic... and so many others.

Steel is good stuff to build things out of, especially when budget factors are involved. I think that Tensen is simply trying to refute the myth that steel yachts are by definition stronger, more impact resistant, more unsinkable than any other building medium.

I happen to agree with him... but don't deny that plenty of good steel yachts have been built.

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Old 15-08-2015, 02:43   #119
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Re: Steel Hull?

Tensen, you're probably right in your assessment of a theoretical hull of equal mass and corrected for density, but it is a hull nobody would build.

If the theoretical does not meet practicality, it needs adjustment if to be realized, or it will remain just that, theoretical.

In the real world, GRP boats are built for a purpose which they can fulfil as well as any other comparable boat, and the material offers some specific advantages over others.

In the real world however, GRP boats are not built of an equal mass to comparable steel boats, and that is where the discussions of theory and reality go their separate ways.

Like any other hull a GRP hull is the total sum of a number of compromises, and when it is engineered for lightness, this will detract from its' ability to withstand traumatic events, generally speaking.

Then it becomes a matter of personal priorities, where one will choose to go faster and another will choose to go safer.

Since we are on a cruisers-forum, it seems to me that time is less of a factor than safety, hence the opposition. It is the same discussion as fin vs long keel, and spade vs skeg-hung rudder.

There are no winners, just people with different priorities.

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Old 15-08-2015, 03:48   #120
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Re: Steel Hull?

[QUOTE=Jim Cate;1891101]
Quote:
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So, I was right, you've never actually run into anything?

Oh, come on mate! One of the good things about education is that one does not have to have all the bad experiences that history records in order to avoid them yourself.

If you insist on this approach, there are countless steel ships (around your postulated 3000 tons level or more) that have been split wide open by colliding with fixed objects. The recent demise of the Costa Concordia comes to mind, to say nothing of the fabled Titanic... and so many others.

Steel is good stuff to build things out of, especially when budget factors are involved. I think that Tensen is simply trying to refute the myth that steel yachts are by definition stronger, more impact resistant, more unsinkable than any other building medium.

I happen to agree with him... but don't deny that plenty of good steel yachts have been built.

Jim
We're not talking about strength to weight ratio, we're talking about strength as it relates to surviving a collision.

The survivability, or strength of say a glass boat in heavy weather is different from its strength in relation to collision.

An advantage of glass or cf boat is the fact that it can be built with less material weight, giving it more reserve buoyancy, greater stiffness, greater speed, great resistance to hogging, sagging, racking etc. The above factors make them strong boats, but not necessarily good boats to run into solid immovable objects with. Glass won't crumple like steel.

I'm not against the theoretical at all, unless that theoretical is in no way supported by reality.

I'm happy to listen to and reflect on evidence. Are you saying then the typical glass yacht will resist a collision with a heavy solid object as well as a typical steel yacht?


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