Steel Hull?

[Pelagic]

Originally Posted by Tensen

The myth is that steel is stronger than FRP. When compared pound for pound, FRPs are far stronger.

The survival issue when your boat is heaving up and down and sideways on a reef is.... whether it will bend or break....as the reef and kinetic forces are usually stronger.

Steel bends, FRP tears

[Pauls]

Tensen, I don't know what your technical background is, but a lot of the statements you make are not true. Ability to absorb impact is a complicated subject and it goes far beyond just tensile strength per pound. I suggest you do some research on the subject.

[micah719]

Ultimate strength isn't the be all and end all you assume.
Aluminum Strength vs Steel Strength

"One advantage of steel is that between the yield point of mild steel (around 36,000 psi) and the ultimate tensile failure point (around 60,000 psi) there is quite a large plastic range (around 24,000 psi or roughly 40% of the ultimate strength), permitting a steel vessel to endure deflection without failure, so permitting considerable ability to absorb energy."

Composites for Boats - Kasten Marine Design, Inc.

"It is not at all difficult to design a fiberglass structure to be as strong as or stronger than an aluminum structure - and to also be as light - however since we ordinarily must work within a given budget there will always be definite limits on what will be possible with either type of structure. We also have to ask, "What do we mean by strength..?" Are we talking about impact strength, or stiffness, or fatigue strength, or tensile strength, or yield strength..? We then should consider questions such as insulation, fire resistance, acoustic performance, corrosion vs. boat-pox, long term maintenance, eventual re-sale...

It is obvious that each of the above limitations, questions or considerations will reveal a different winner in the contest. Thus, the question of whether to favor composite or metal construction can really only be answered on a case by case basis after fully considering the owner's requirements and preferences, the available budget, and the intended use of the boat. "

http://www.kastenmarine.com/framing.htm

It takes over 60,000 psi to tear apart a chunk of mild steel (the usual stuff of steel boats). It takes 30,000 psi to deform the same piece. Thus the extreme benefit of steel as a hull material: The "plastic range" of steel is quite large, and the material is therefore able to take a terrific beating without failure.

Fibreglass' yield & tensile strengths are very close together, it has poor abrasion resistance, and poor fatigue resistance. As a composite, its component materials can delaminate, its structure is much coarser than steel and its components have very different characteristics....resin cracks, glass fibres break. Repair is not as easy as cutting out a portion and easily welding in a commonly found material of known and consistent quality. It is useful for large production runs giving consistent, marketable products the great majority of which are intended for moderate recreational use by people with little time for maintenance. It is a fine material, but for playing dodgems with large objects steel is a better choice, particularly when one is working to a small budget of one's own money, and must rely on self-repair in the areas one intends to sail.

[Jack Verschuur]

FRP's may be far stronger pound for pound, but that in itself means relatively little: The deciding factor is how they behave on impact, and the dissipation of the energy of that impact.
Add to that that FRP hulls are generally lighter than a steel hull of comparable size, and the pound for pound comparison becomes irrelevant and steel (or aluminium) wins.

I am certainly a novice to all this, but it seems critical to me that with a metal hull the construction should be such that all parts of the hull should be accessible for inspection. Bilges get wet, coatings fail. A corroded metal hull offers no prtection.

Aluminium was not included in the OP's question, yet IMO offers the best of both worlds?

Best,

Jack.

[micah719]

Yes, alloy is very tempting, but I decided against it after considering the following points in comparison to steel:

As-welded strength, difficulties in welding, fatigue and abrasion characteristics, galvanic sensitivity.

On the plus side; not having to fear the rust bugs, never having to paint above water, easy to cut, light, strong. But, not enough for me, I'm afraid; those four above were the kickers. I'll gladly use it for spars and internals....

[micah719]

Originally Posted by Steady Hand

Hi Michah.

I appreciate your points and your concerns.

I went back and looked at the original post of this thread and see that the original intent was to discuss whether whales are a risk and whether a steel hull would make a difference (be safer).

Since your points are about the proper insulation of a steel hull, I suggest you start a new thread on that topic alone. That way the forum may take notice of it as a separate subject and the discussion can be focused on that topic. Otherwise, people tend to read the Original Post and if it is NOT on something which they have opinion or experience, they move on without seeing the other "off topic" content of the thread. . So, I suggest we spin off a new thread to discuss the pros and cons of insulation and removable interior construction ideas etc.

G'day Steady,

Good idea, I'm cranking up the threadomatic. The topic has been touched on here and there (what hasn't, in the CF maze?) but there isn't a home port for that, as far as I can tell. My security settings and gadgets make google searches impossible, so if there is already one out there, someone please let me know?

[Reefmagnet]

I love steel as a vessel construction material, and a new or near new boat would be great. The issue with steel is that it is way more susceptible to deterioration through bad building or maintenance and damage can be difficult to detect, especially if covered up pre sale.

I see a similar story has already been posted, and this article is one I always revisit when I start dreaming of older steel boats...

The saving of WhiteBird

[micah719]

Horror of horrors, I'd hoped never to see that site again. This pic says it all:



Original Caption: Go ahead... ask me what I think of surveyors...

Still, it also shows how easy steel is to work on. Ok, heavy, loud, hot dirty work, but at least it isn't The Itchy & Scratchy Show (btdt).

[Tensen]

Originally Posted by Pelagic

The survival issue when your boat is heaving up and down and sideways on a reef is.... whether it will bend or break....as the reef and kinetic forces are usually stronger.

Steel bends, FRP tears

Steel bends, and breaks first, FRPs break afterwards (assuming equal mass).

Originally Posted by micah719

Fibreglass' yield & tensile strengths are very close together...

That is neither here nor there. The comparison of it with an equal mass of steel is what's being discussed, and in that comparison it will take more energy, and greater force to break.

...it has poor abrasion resistance, and poor fatigue resistance.

Not a correct statement. Some FRPs have quite reasonable abrasion resistance, and many have truly excellent fatigue resistance.

Originally Posted by Pauls

Tensen, I don't know what your technical background is, but a lot of the statements you make are not true. Ability to absorb impact is a complicated subject and it goes far beyond just tensile strength per pound. I suggest you do some research on the subject.

I'm an engineer Pauls - a naval architect, to be specific. I suggest you don't make assumptions when you don't know someone's technical background.

If you can pick a statement of mine you think isn't true, please do, I'll explain it for you.

[micah719]

Ok, the only way to settle it is a real-world test. All the quotes from actual designers, builders and sailors will never convince you. Are you in the grp business in any way? When I'm finished building and fitting out we can meet somewhere suitable, you with a composite boat of similar dimensions and identical displacement built and kitted out for extended cruising, to the same budget.

Proposed round of tests, preferably with referees of a non law-enforcement nature:

1. Ramming whale at hull speed. Let's choose an already dead whale. Or, we paint the boats red and play recordings of whalesong from the hydrophones, something in Humpbackese for "Hey bignose, I'm the biggest meanest whale around, this ocean aint big enough for both of us, and your mother wears army boots".

2. Collision with vessel. Easy, we just ram another vessel (non-Naval, obviously) bows on and then broadside at hull speed. I dibs port side. If the other boat survives this, he may then be keen to participate in the test, though we may need a pair of identical vessels to make it truly fair.

3. Collision with container. Those things are pretty cheap; if we can't find one already drifting we simply buy and flood one to awash and then charge it. If it's someone else's, let's also look inside for freebees.

4. Ice & Debris test. Simple, we find some suitable bits and run them down: referees to ensure targeted bits to be reasonably equal.

5. The reef test. This one will be the hardest one, so I left it 'til last. Run the boats aground and let them pound for a day on a reef. Nothing too extreme, but no pansy sand or mud, in fact rock is ideal and that way we don't wreck any coral.

After all these tests (or until the first boat blubbs) the loser pays the repairs (to be done in a remote location with only the materials and tools aboard), personally supplies own labour to the winner (under close supervision...), covers all legal fees incurred, and also forfeits his (likely destroyed) boat and contents, all rights to the spectacular videos, tasty whale meat, salvage from other participating vessels, and the 487,263.5 pairs of Adidas sneakers (size 6EEE) from that container. Deal?

[boatman61]

LMAO... anyone know where I can get a 40ft 27000lb GRP boat to replace my steel 40ftr
Its all very well bragging about GRP.. but when one looks at the market one can see (if old enuf) that GRP hulls have been getting thinner and even thinner over the years as manufacturers cut back on materials to increase profit margins.. no longer do we have the 'Tanks' of the 60's and 70's... now if you peel back the liner you can almost see the boat next to you at the dock..
And as for whale attacks.. sailed amongst them in the Biscay, Atlantic and OZ... never been threatened or attacked.. was accompanied by 3 pods down W. Coast Oz all the way to Perth.. at times 5metres from us and swimming alongside..
Much ado about nothing..

[Tensen]

Originally Posted by micah719

Ok, the only way to settle it is a real-world test. All the quotes from actual designers, builders and sailors will never convince you. Are you in the grp business in any way? When I'm finished building and fitting out we can meet somewhere suitable, you with a composite boat of similar dimensions and identical displacement built and kitted out for extended cruising, to the same budget.

....

Deal?

To the same budget? Of course not. Steel is by far the cheapest material.

To the same mass though - any day you like.

(No, I rarely design in FRP, our firm does mainly aluminium designs, occasionally steel.)

[micah719]

Cool!

Btw, I was seriously considering a twin keel Marcon Sabre 27 until I returned to steel. I'd have sought out one of the earlier ones, pre the 1973 oil embargo destruction of massively-built frp production boats.

http://sabre27.org.uk/


Carlotta, for 3550 British pounds (money, not weight).

If they'd made a Westsail 32 with bilge or twin keels I'd stoop to piracy or extortion to get one.

As it is, I'm looking at (mostly) cold molded frames over longitudinal steel stringers to save weight, so it's not as though I'm inherently anti-composite; I'll be using it on yards, booms, battens, dinghy, bulkheads and internal furniture. Bamboo, specifically Tonkin cane, is an eye opener for a natural composite; teamed with epoxy it's looking very tempting, unless someone can persuade a spider to spin a boat.

No hard feelings?

[Jack Verschuur]

https://www.youtube.com/watch?v=6nGNAidhKWc

Doesn't look like fun to me.

Best,

Jack.

[Tensen]

Originally Posted by micah719

No hard feelings?

Of course not!

I don't know why you'd use steel stringers instead of composite top hat stringers - they'd be lighter for the same strength, and none of your attractions to steel are relevant to stringers...