Are steel boats stronger than GRP ones?

geem said:
Google it. The info is out there?
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It comes down to quality of construction, how the internal hull was rust treated prior to epoxy coating, how the spray foam insulation was applied ( if at all), how the internal fit out was connected to the hull without exposing bare steel to rust in the future.
Most people know not to buy an old steel boat. They cost as much to build as a GRP boat when new. All the same components go in to them but 25 years down the line they are cheap boats. Few people want them as they become very expensive to maintain. This vast reduction in value is market driven. The market decide they are worth less than a similar GRP boat. Few people wants a rusting hull and the huge amount of work that goes with it.
 
Back in my blue-water cruising days, I was very grateful for having a steel yacht. I hit bottom with monotonous regularity, specially in the Pacific Islands, sometimes at speed, and never had any problems beyond scraped paint. It wasn't so much the overall strength of the material, but that the keel was integral with the hull unlike virtually all GRP yachts, so there was little or no risk of damaging the attachment. Moreover, I could get off the grounding using force which might have further damaged the keel of a GRP yacht. (I never needed outside help).

The reason I hit bottom so often was that having a steel yacht enabled me to take risks, try narrow and/or uncharted channels, and as a result visited fascinating places that few GRP yacht skippers would dare enter.
 
roaringgirl said:
I'm on a cruisers group on facebook, where someone asked for advice on buying a steel boat. There have been all sorts of responses about how much stronger steel boats are. Surely it's that the material is stronger for the same thickness, so that a thicker GRP hull can be just as strong as a steel one? Is there something I haven't understood?
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When I studied materials science at Uni this was one of the interesting challenges. Strength is not something you just measure in one way either - tensile strength, compressive strength, sheer strength (torsional strength), ductility, brittleness, resistance to plastic deformation v structural failure. Then you add the fact that steel is not one material, and grp is not all the same and suddenly you end up with a lot to think about, for what the layman calls strong.

having worked out which type(s) of strength you care about you quite rightly say thatthere needs to be some denominator. It might be thickness (or cross sectional area) or it might be weight, or in might be dollars. Sounds like we are making great progress towards selecting the ideal material until you actually consider the structure it has to go into, the production/design processes available and the options for designing in extra material where it is needed. if your moulding approach allows very complex shapes you can do things that might not be possible (ecconomically) with welding to move stress areas or reinforce weak spots for little cost / weight penalty. This is why naval architects get so interested in the lamination schedule for a boat.
 
AngusMcDoon said:
Where's our old chum Brent Swain when he's needed?
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Well around here on the West Coast (of North America) not all of the trees have been decimated by clear cutting.
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Some of the remaining trees lounge around fir / for a very long time and being in the ocean eventually some sink or try to sink.
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Over time those that are partially successful at this remove unwary plastic boats.
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My dock neighbour's 28 foot plastic boat remains on the bottom close to Crome Island a mere 5 nm from the dock.
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It's demise was sudden but slow enough for boat dog and boat person to reach towed inflatable dinghy and row ashore.
 
arcot said:
Well around here on the West Coast (of North America) not all of the trees have been decimated by clear cutting.
.
Some of the remaining trees lounge around fir / for a very long time and being in the ocean eventually some sink or try to sink.
.
Over time those that are partially successful at this remove unwary plastic boats.
.
My dock neighbour's 28 foot plastic boat remains on the bottom close to Crome Island a mere 5 nm from the dock.
.
It's demise was sudden but slow enough for boat dog and boat person to reach towed inflatable dinghy and row ashore.
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I hit a huge submerged log in the Ria Gaudiana years ago in a catamaran. It was a big old thing and not visible. That tree sent the rear of the cat up in the air.
We really thought we had sustained some serious damage such was the impact. All it did was take some bottom pain off. A suspect luck plays its part in these collisions. Your neighbour had some bad luck
 
This remind me of a steel yacht six years ago who arrived in MDR in Sicily I won't go into the full story but it Tbone a large oil tanker crossing from Malta ,
The bow was pushed in and his forestay being welding on the deck stayed up .
I tho at the time if that was a GRP hull it be on the sea bed in the Maltese channel.
 
hit a ships navigation buoy last year pretty hard and it just flexed the hull under the deck, the toerail was mangled so took most of the inpact
 
UK-WOOZY said:
hit a ships navigation buoy last year pretty hard and it just flexed the hull under the deck, the toerail was mangled so took most of the inpact
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With GRP having a fairly limited range of flexibility, I wonder just to what extent such an impact and movement has now delaminated the 'laminations' of the GRP. Invisible to the eye for sure but to what extent has it weakened ( if at all) the structure....?
i was discussing this effect with a very well regarded Insurance surveyor ( now deceased) who commented that the use of boat shifting trailers if not correctly located often has this effect, especially on the flat under surface of power boats between the chines etc.
 
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When I mention the age of our Fairline to people I am constantly reassured that 40+ years old is of no real concern. My father was a tug skipper and some of the vessels he commanded are starting to show serious rust at around 30 years old and that is with strict maintenance schedules as mandated by relevant commercial shipping authorities. I personally have more confidence in old GRP than steel. A commercial surveyor friend who used to work for the MCA has mentioned several times about cracks being discovered in various areas on the high speed Ro-Ro sea cat ferries (aluminium construction).
 
Helidan said:
When I mention the age of our Fairline to people I am constantly reassured that 40+ years old is of no real concern. My father was a tug skipper and some of the vessels he commanded are starting to show serious rust at around 30 years old and that is with strict maintenance schedules as mandated by relevant commercial shipping authorities. I personally have more confidence in old GRP than steel.
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That probably sums it up. If you want to go places where you might end up on reefs or being humped by a whale, or are not sufficiently crewed to avoid being T-boned by a ship occasionally, then steel is stronger. But if you want to keep a boat more than 25 years, then GRP will end up stronger, because however good the interior coatings, eventually rust will happen.
 
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