Are steel boats stronger than GRP ones?

[roaringgirl]

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?

 

[AngusMcDoon]

Where's our old chum Brent Swain when he's needed?

 

[Tim Good]

Largely depends on use. GRP is very strong but it’s a bit like glass. It’s strong until it breaks…. steel is perhaps like… well it’s like steel. It’ll deform and dent. A bit like aluminium. So you’ll see an aluminium boat dented if it struck a rock or ice badly. A GRP boat might have come away unscathed from the same impact or actually get a hole. There’s kind of no middle ground with GRP.
All that said, you see we’ll founded GRP boats pounded on rocks and come away in tact.

But….. if I were to hit a floating container at sea at 7kts… would I want to be in steel or GRP….. hmm probably steel.

I might add that there are many other factors that make a boat strong… does it have a water tight bulkhead in the bow, is the keel bolted in or encapsulated, does it have a skeg, is the mast deck or keel stepped…. All these things are perhaps as or more important than the hull material. And…. A big and… a lot of steel boats are home made or one off designs that perhaps haven’t had the thought that a well founded GRP boat has had when design by a celebrated designer.

 

[Graham376]

Was the proposed purchase for a new or used boat? There are some well-built and strong steel boats around which would survive an impact better than the an awb and there are some old rust buckets which wouldn't survive much of a knock. Many tend to rust from the inside so not always easy to spot at a glance.

 

[AntarcticPilot]

As I understand it, it's 6 of one and half-a-dozen of the other. Both have advantages and disadvantages. Strength isn't really one of them; there's no real difference in the strength of the hull, providing both are built to appropriate standards and scantlings. It's the old thing - if you have a stronger material, you use less of it to achieve the same strength. GRP thicknesses are usually several times the thickness of the steel plate used in boat-building. The materials have different characteristics, so they are both strong but achieve their strength in different ways.

Both are resilient to a blow, but in different ways. Steel will bend and locally deform; GRP will bend and then bounce back, possibly delaminating or cracking. It's very difficult to break either - the Crash test videos showed the difficulty of making a breach in the hull of a GRP boat (they had to resort to a power saw!)! But in absorbing a blow, both will take damage, and, while both are repairable, ultimately, it's probably easier to repair a steel boat in out-of-the-way parts of the world. A steel boat can be repaired by a guy with welding equipment; plenty of those all over the world and steel is pretty universal too. GRP repair will require a supply of resin and other materials and a reasonably controlled environment. The former is available almost anywhere; the latter is rather less likely in remote places.

Steel has the disadvantage that it rusts! Not a problem where you can see it and keep up with the coating system, whatever it is. But there are lots of places on most yachts where you can't see what's going on, and it's there that steel has the potential to rust away out of sight. Maintaining the protective coating is vital on steel boats; it's cosmetic on GRP.

GRP is not subject to long-term deterioration, to the extent that we have a problem with the disposal of old GRP yachts. Even the dreaded osmosis is not usually a terminal problem.

Steel hulls are more resistant to abrasion; this is a plus in areas where there is brash ice, but its hardly an issue for most people!

 

[Blueboatman]

I like the idea that steel can be a monocoque ie chainplates and stantions, cleats , bollards can be welded to the hull and deck, no leaky bolts.. so that is strong
But you can’t weld Genoa tracks and winches and windows so that is weak, encouraging rust as well as drips ..
And condensation would rust any scratched metal internally ?
?
Maybe a lead bolt -on keel on a grp boat is an acceptable compromise ?

 

[geem]

Assuming both a new steel boat and a new GRP boat then the steel boat is stronger. 30 years down the line, the GRP boat is likely just as strong as the day it was built. The steel boat probably not since most steel boats are uneconomic to repair over 25 years old. We have friends who had a steel boat. The thin hull needed repairing due to corrosion from the inside. They had to remove all the interior in the area of the weld since it would burn. Major work. They no have a GRP boat

 

[GHA]

Off we go again...??

 

[oldgit]

Off we go again...??

Have watched assorted boats ,mainly small commercial stuff , workboats/tugs etc quietly rust away and would say that the longevity of plastic is a big plus especially for leisure boats , not under constant safety checks.
The ability for various owners to neglect and abuse plastic with its stubborn refusal to lose integral strength, more than compensates for any alleged tendency to fail on accidental impact ?
Any structural weakness due to impact in plastic boats tends to be visually obvious in surrounding structure
Steel stealthily corrodes locally from within and only reveals itself when the damage is well underway.
Going to guess locally, much more chance of finding somebody to do bit of gel or mat repair these days ,than finding somewhere or somebody to let a plate into a steel hull, let alone do a proper survey on hull thickness........ and we are in semi industrial area.
Have yet to observe any plastic boat suddenly be in danger of sinking due to neglect of hull.

 

[Spirit (of Glenans)]

I like the idea that steel can be a monocoque ie chainplates and stantions, cleats , bollards can be welded to the hull and deck, no leaky bolts.. so that is strong
But you can’t weld Genoa tracks and winches and windows so that is weak, encouraging rust as well as drips ..
And condensation would rust any scratched metal internally ?
?
Maybe a lead bolt -on keel on a grp boat is an acceptable compromise ?

You could weld suitable brackets to the deck, on which to mount the hardware you mention, so that it doesn't have to be through-bolted, to produce a supremely drip-free boat.

 

[Rappey]

. 30 years down the line, the GRP boat is likely just as strong as the day it was built

Not according to boatbreakers in Portsmouth. At 30+ years grp becomes brittle. They enjoy breaking older boats as the hulls shatter compared to much thinner yet stronger newer boats which bend and spring back.

 

[AntarcticPilot]

Not according to boatbreakers in Portsmouth. At 30+ years grp becomes brittle. They enjoy breaking older boats as the hulls shatter compared to much thinner yet stronger newer boats which bend and spring back.

That's more likely to be bec ause the resins have changed than aging.

 

[PCUK]

Assuming both a new steel boat and a new GRP boat then the steel boat is stronger. 30 years down the line, the GRP boat is likely just as strong as the day it was built. The steel boat probably not since most steel boats are uneconomic to repair over 25 years old. We have friends who had a steel boat. The thin hull needed repairing due to corrosion from the inside. They had to remove all the interior in the area of the weld since it would burn. Major work. They no have a GRP boat

Sorry, that is nonsense. A modern epoxy coated steel boat that is maintained will be as strong as new after 25 years. My 30 year old steel De-Groot is living proof. Also, a steel boat will survive a pounding on rocks. GRP won't!

 

[RogerJolly]

Once gave the channel marker buoy a hefty glancing blow coming out of Poole Harbour after I left my Dad steering and he got caught out by the weather helm in a big gust. Kingfisher 26.

Horrendous creak throughout the boat. It's a gonner I thought. Unscathed though with barely a scuff in the gelcoat though, no cracks at all.

Fibreglass crash helmet makers would have us believe we need to change them every five years as they degrade. Just drumming up sales maybe?

 

[Blueboatman]

You could weld suitable brackets to the deck, on which to mount the hardware you mention, so that it doesn't have to be through-bolted, to produce a supremely drip-free boat.

I like it
That would save so much grief down the line

 

[ean_p]

and.........

Two yachts collide off the Canary Islands and sink

 

[ChromeDome]

On a different note than material strength, GRP vs steel,- build, insulation, internal fit-out and weight ratio will be different.
As will the maintenance, simply because the materials are completely different.

 

[geem]

Sorry, that is nonsense. A modern epoxy coated steel boat that is maintained will be as strong as new after 25 years. My 30 year old steel De-Groot is living proof. Also, a steel boat will survive a pounding on rocks. GRP won't!

Google it. The info is out there?

 

[dgadee]

There's a steel yacht aground on rocks to the west of Lesvos. Lots of it left, but it is still wrecked so strength didn't help it.

 

[Graham376]

Sorry, that is nonsense. A modern epoxy coated steel boat that is maintained will be as strong as new after 25 years. My 30 year old steel De-Groot is living proof. Also, a steel boat will survive a pounding on rocks. GRP won't!

Not nonsense. There are of course some excellent steel boats but I know two UK based ones (both BR Spray design) which sank a few years apart due to rusted hulls. Quite a regular occurrence over the years to have steel boats in the yard here having sections of hulls and decks cut out and patched. There are some very poorly constructed steel boats and problems often seem to be caused by stringers not being notched for drainage and they rot from the inside.