Steel Hull?

[Rustic Charm]

Well, an interesting thread.

I'm no metalurgist. When I purchased my boat I avoided just two. I avoided wood because I took a guess I'd not treat it right and I love wooden boats. The other one I avoided but wanted was ferro cement boats. And the only reason I avoided them was because I couldn't seem to find anyone that would provide insurance for one. At the time I didn't know about Aluminium sail boats and probably couldn't afford it anyway.

So, I ended up looking at just glass and steel. Steel boats were and are cheaper and that became an issue. So I purchased a 30 year old steel boat. I learnt very quickly that surveyors are close to a waste of money

But, I now love my steel boat, now that four years later I've almost got all signs of rust out of her and hopefully this year going to give it a really good paint job (I hope).

As I said I'm no metalurgist. Did some basic metal lessons during my origional trade some 40 years ago. But pure antedotal evidence in this neck of the woods (below 40 degrees) clearly indicates that metal boats take a battering that glass boats don't. We have lots down here breaking moorings, running aground, getting hit by other boats and just about everyone survives. But everytime we have a glass boat run aground, break a mooring, get hit by another boat, we also hear of it sinking or being scuttled.

It's also well known that carbon fibre composite yachts are stronger than steel. BUT, look at what happend to Vestus when she hit the reef? It might be stronger than steel and lighter, but I'm personally not convinced it takes the impacts that steel do. She basically lost her rear end entirely.

So, all the science aside, just looking at the antedotal evidence, Steel is a good tough cheap product that will give most people a really good cruising boat with safety for many many years, as long as you maintain it.

But when it gets down to it, it's a personal preference thing. I'm always on the look out for rust, I admit. The main thing with buying used steel boats is to ensure it's cancer is not beyond repairing for a sensible price and then look after it. Maintenance Steel is a great boat for those of us inexperienced or not as delicate as some. And frankly to answer the OP's question, I'd rather hit a whale in a steel boat than a glass one without any doubt what so ever. But, depsite

[Tensen]

Originally Posted by conachair

Does that make any difference in the real world? Not digging too deep onto the figures, would a FRP boat with hull of equal mass/m2 really still be floating after something like this? It takes an incredible amount of punishment to puncture a steel hull, is it really likely that some FRP would withstand the same treatment and still be watertight?

Of equal mass? For any but the weakest composites, absolutely. I don't think you've wrapped your imagination around just how strong that much composite is.

[Tensen]

Originally Posted by micah719

Certainly, but ultimate strength isn't a factor that trumps everything else. The original post was about a whale impact. Those a pretty rare, compared to other impacts which are much more frequent, such as connecting with docks, dinghies and raft-ups.

Ultimate strength *is* something that can trump everything else in an impact, if it's high enough. Toughness is what you're concerned about for impacts, and toughness increases with strength.

There is also fatigue as the boat flexes. Steel's homogenous structure and indefinite fatigue characteristics at low yet constant strains are in contrast to frp's nature.

Composites' non-homogeneity is something to be taken advantage of - it means parts can be laid up with less strength in directions that don't need it, saving even more weight. With a homogeneous material some of your material properties are always wasted.

For impact strength, local ductility is more important than simply the strength of the whole, as Jack Verschuur pointed out.

Rubbish. Try building a hull out of latex or something similar.
High strength can take the place of ductility in toughness, but ductility can't replace the structural integrity that strength gives.

An eggshell is tremendously strong due to its shape but once that integrity is compromised the system fails. It is locally fragile. Human skin is amazingly difficult to penetrate because it gives, and returns to its original configuration; better than steel, and it is a composite. However, we aren't building coracles.

I hope you aren't suggesting the differences between eggshells and skin are similar to those of FRPs and steel. The results of this comparison don't reflect on the one we're discussing.

If the following technology really takes off, we might have a game-changing material. Note that its prime advantage, complementing its amazing strength, is its elasticity. Current composites aren't locally flexible. My fibreglass bow is flexible over its length, but a low radius bend will locally overstress the fibres in it and it will explode.

Certainly, but if it were the same mass as a steel bow, the force required to bend it would be far beyond what was required to break the steel bow.

If the microstructure was finer and the individual components more elastic, it would be more like....synthetic steel. Cumulative damage wouldn't limit the life of the whole item as long as the use stays within design limits.

You misunderstand material properties.
As soon as steel goes beyond yield strength (i.e. it dents) strain is locally increased - that area of steel moves permanently closer to failure.

Composites on the other hand are fully elastic, with virtually no plastic zone - they never deform permanently, until they break.

Most folks will choose off the rack and be fine with it....many will tweak and tune, and there will be the diehard individualists that insist on a tailored solution because their needs dictate a compromise without the limitations of someone else's compromise. What is wrong with combining the strength of composites and the toughness of steel? One can do this and still come in under budget.

Given equal mass, many composites are tougher than steel (as well as stronger, of course). Go back and read post #56.

[MarinerJo]

For what it's worth, if I were to have a custom boat built today, it would be out of steel with out a doubt. Seems to be the best choice over all for most conditions.

[FamilyVan]

Broken steel. He he. I wasn't driving. That's rebar reinforced concrete from the Redpath dock in Toronto the Provider is holding in her teeth.

Sent from my XP7700 using Cruisers Sailing Forum mobile app

[transmitterdan]

Research the number of owners that first had a steel boat and cruised for a few years then upgraded to another steel boat. Do the same for FRP, ferro, alloy or any other material. As a percentage of repeat buyers FRP is the winner. There are geographical exceptions such as high latitude adrenaline junkies who are willing to put up with the maintenance required by steel and the careful electrolysis controls required of alloy. But warm water cruisers (the vast majority) will repeatedly buy FRP. The cruising world is littered with former ferro, steel and alloy owners that have said "never again".

[YachtOgler]

Regarding FRP damage from collision, here's a link to a racing collision in which the visible damage appears minimal after initial impact. I say appears, very specifically.

Note that I suggest you do not browse any more of the site I am linking to. There's some pretty foul stuff there that has nothing to do with boating and is guaranteed to worsen your day, but I couldn't find the video anywhere else of this quality.

Link below.

Racing Yacht Collision

[Rustic Charm]

Originally Posted by transmitterdan

Research the number of owners that first had a steel boat and cruised for a few years then upgraded to another steel boat. Do the same for FRP, ferro, alloy or any other material. As a percentage of repeat buyers FRP is the winner. There are geographical exceptions such as high latitude adrenaline junkies who are willing to put up with the maintenance required by steel and the careful electrolysis controls required of alloy. But warm water cruisers (the vast majority) will repeatedly buy FRP. The cruising world is littered with former ferro, steel and alloy owners that have said "never again".

Can I ask, how one goes about doing this research? How would I begin?

Where do you get support for your last comment 'the cruising world is littered with former ferro, steel and alloy owners that have said never again' ???

[Panope]

1 inch diameter Amsteel rope has a breaking strength of about 100,000 lbs. and weighs about .2 lbs. per foot.

5/16 inch diameter SS 1x19 wire rope also weighs about .2 pounds per foot but only has a breaking strength of about 12,000 lbs. Thus the SS rope is only about 1/8th as strong (by weight) as the Amsteel rope.

I cut Amsteel rope with a knife. I cannot cut SS rope with my knife. Even a hacksaw has trouble because the strands move around too much. A grinder or a torch is best.

Is this not a perfect example of a material that is far far "stronger" than another while also being far less "tough"?

Steve

[conachair]

Originally Posted by Tensen

Of equal mass? For any but the weakest composites, absolutely. I don't think you've wrapped your imagination around just how strong that much composite is.

Where are they all then?

[builder dan]

im pretty sure if my steel yacht was tboned by a fibreglass yacht it would do a lot less damage to me than them,and Im very sure if I tboned a fibreglass yacht it would be holed,anyone keen for a test?

[Jack Verschuur]

Who builds FRP hulls with an equal mass as a comparable steel hull?

And if we are talking about the strength of GRP, what are we talking about, tensile strength? What about a force perpendicular to the plane of the glass?

The egg-shell above is an excellent example of what happens when an overall immensily strong structure does when impacted locally.

Best,

Jack

[Tensen]

Originally Posted by Panope

1 inch diameter Amsteel rope has a breaking strength of about 100,000 lbs. and weighs about .2 lbs. per foot.

5/16 inch diameter SS 1x19 wire rope also weighs about .2 pounds per foot but only has a breaking strength of about 12,000 lbs. Thus the SS rope is only about 1/8th as strong (by weight) as the Amsteel rope.

I cut Amsteel rope with a knife. I cannot cut SS rope with my knife. Even a hacksaw has trouble because the strands move around too much. A grinder or a torch is best.

Is this not a perfect example of a material that is far far "stronger" than another while also being far less "tough"?

Steve

No, you're talking about hardness, not toughness.

Originally Posted by conachair

Where are they all then?

Where are all what?
I answered your question, I made no comment on their popularity or rarity.

Originally Posted by builder dan

im pretty sure if my steel yacht was tboned by a fibreglass yacht it would do a lot less damage to me than them,and Im very sure if I tboned a fibreglass yacht it would be holed,anyone keen for a test?

An FRP hull of the same mass?
What if you T-boned a steel hull?
What if the FRP hull T-boned you?

Originally Posted by Jack Verschuur

Who builds FRP hulls with an equal mass as a comparable steel hull?

And if we are talking about the strength of GRP, what are we talking about, tensile strength? What about a force perpendicular to the plane of the glass?

The egg-shell above is an excellent example of what happens when an overall immensily strong structure does when impacted locally.

Best,

Jack

A force perpendicular to the plane causes bending, and it's tensile and compression strengths that resist bending - tensile on the outside of the bend, compression on the inside. (When comparing strength with a single figure tensile is typically used in preference to compression)

FRP does not behave or fail like eggshell, that is a strawman argument of no value at all.

[Jack Verschuur]

Originally Posted by Tensen

A force perpendicular to the plane causes bending, and it's tensile and compression strengths that resist bending - tensile on the outside of the bend, compression on the inside. (When comparing strength with a single figure tensile is typically used in preference to compression)

FRP does not behave or fail like eggshell, that is a strawman argument of no value at all.

You fail to address the question about builders of GRP hulls of equal mass to a comparable steel hull, and this is critical.

It also needs to be highlighted that GRP cracks instead of bending (muxh): This may or may not happen at a higher load, but it is still a highly undesirable property where a boat hull is concerned.

I don't reject using GRP as a hull material. In fact, in my search for a vessel I keep an eye out for one specific boat that is made of it. I would, however, vastly prefer the same boat in steel or even better, aluminium.

Best,

Jack.

Best,

Jack.

[Tensen]

Originally Posted by Jack Verschuur

You fail to address the question about builders of GRP hulls of equal mass to a comparable steel hull, and this is critical.

It's no concern of mine, and nothing I've commented on - why address that question at me?
Typically hulls are built to certain strength requirements, regardless of material. FRP hulls meet the same requirements that steel hulls meet, at lower weight.

It also needs to be highlighted that GRP cracks instead of bending (muxh): This may or may not happen at a higher load, but it is still a highly undesirable property where a boat hull is concerned.

Please read the whole thread. This has been discussed and explained.
FRP of equal mass won't crack until long after steel has both bent and broken.

If we consider a hypothetical material with precisely the same toughness, cost, density, hardness, corrosion and fatigue behaviour, and stiffness as steel, but one that had no ductility and achieved it's equal toughness by means of a higher strength instead, it would be considered by boat designers to be by far the superior material compared to real steel.

Ductility itself is not "highly desirable". The toughness it gives is, but toughness can be achieved by strength instead.