Recommended boat hull/steel

[BD3Bill]

 

Yes you are.

 

Fairplay

 

But you would agree ( for the OP's benefit ) that the treatment of the hull after manufacture is vital in terms of prep & coatings?

Would you also agree that the design and placement of Anodes on the average NB is far from ideal?

[gazza]

 

If high grade steel isn't needed why do some shells corrode faster than others?

I see newish (less than 5 years) boats with frightening amounts of rust especially on the baseplate - yet I've seen old boats (over 25 years) from Springers to Norton Canes shells with hardly any corrosion at all.

 

I must admit to being nervous about the standard of steel these days especially as I know bot all about grades etc. If I was ordering a new shell I would want the same steel as used on the Norton Canes boat I mentioned, hardly any corrosion on the unpainted baseplate after 29 years. How would I spec that?

As Alan points out the variables that determine the rate of corrosion are difficult to nail down.

 

All steels are an alloy, a narrow boat does not need to be anything better than a bog standard Low Carbon Steel. I was using laymen's terms.

 

A well chosen protective coating (not bitumen blacking) and correctly sized and placed anodes are all that is needed to ensure a long life. Stray currents galvanicly killing a boat are a different matter.

 

If you are massively worried about corrosion go for a Stainless Steel build but keep it away from saltwater.

Alternately, go for an Aluminium Sea Otter and keep away from Tim West.

 

Remember though, that no matter what you do a piece of mild steel always wants to get back to nature

Edited February 12, 2016 by gazza

[gazza]

 

Fairplay

 

But you would agree ( for the OP's benefit ) that the treatment of the hull after manufacture is vital in terms of prep & coatings?

 

Would you also agree that the design and placement of Anodes on the average NB is far from ideal?

This time you have got it right

 

Mill scale is the main cause for blacking to fail prematurely on new boats, the best way to eliminate scale is to use pickled steel, most don't because of the dent on profits.

You can build a shell and leave it unpainted outside to rust, costs time and then effort to get rid of the rust and prep for paint.

You can blast it or grind it but again this costs.

 

Then there's the choice of coating, blacking is crap but cheap and popular for that reason.

 

As for anodes, two at the front, two at the back is considered good enough, its not, but as that's what has always been done most follow the well troden path.

[BD3Bill]

This time you have got it right

 

Mill scale is the main cause for blacking to fail prematurely on new boats, the best way to eliminate scale is to use pickled steel, most don't because of the dent on profits.

You can build a shell and leave it unpainted outside to rust, costs time and then effort to get rid of the rust and prep for paint.

You can blast it or grind it but again this costs.

 

Then there's the choice of coating, blacking is crap but cheap and popular for that reason.

 

As for anodes, two at the front, two at the back is considered good enough, its not, but as that's what has always been done most follow the well troden path.

 

And I cut my hands a couple of times on mill scale that came out of a British Steel plant Chap.

 

I concur utterly, bitumen is for wooden boats.

 

Now if they made anodes that were like a rubbling strake from front to back, that'd work ( if it didn't rub on canal 'furniture'

 

Cheers ( I'm not a total numpty, just a bit of a numpty, sometimes :0) )

[Bee]

Just for arguments sake I would say that 4mm steel is strong enough for a narrowboat. The rest is really there for a safety margin re. corrosion, we are talking pleasure craft, not something that is going to have 20 tons of coal dropped in it from a height. (no I would not really spec 4mm steel, just making a point) I would go for just two things, a good builder making a nice looking boat and a good epoxy paint system following manufacturers instructions. Oh, and paint the inside properly as well.

[BD3Bill]

Just for arguments sake I would say that 4mm steel is strong enough for a narrowboat. The rest is really there for a safety margin re. corrosion, we are talking pleasure craft, not something that is going to have 20 tons of coal dropped in it from a height. (no I would not really spec 4mm steel, just making a point) I would go for just two things, a good builder making a nice looking boat and a good epoxy paint system following manufacturers instructions. Oh, and paint the inside properly as well.

 

We don't have arguments here, just discussions

I think the line/ stiffness of a hull is the factor in going to heavier steel to be fair

[Loafer]

Try the 'ex-Hudson' yard at Glascote. I understand that it has been taken over by Norton Canes staff, so between the two they should come up with an awesome build.

[BD3Bill]

"Awesome", really, on this august forum of all places? Well really! Cheers !

[Loafer]

"Awesome", really, on this august forum of all places? Well really! Cheers !

 

Well it is only February!

[gazza]

Just for arguments sake I would say that 4mm steel is strong enough for a narrowboat. The rest is really there for a safety margin re. corrosion, we are talking pleasure craft, not something that is going to have 20 tons of coal dropped in it from a height. (no I would not really spec 4mm steel, just making a point) I would go for just two things, a good builder making a nice looking boat and a good epoxy paint system following manufacturers instructions. Oh, and paint the inside properly as well.

As you say 4mm is strong enough, its lifespan would be a bit shorter, it would also need a good bit of ballast.

 

A realistic build for me would be 10mm bottom (no reason other than keeping COG low and reducing the amount of ballast that needs adding) 6mm hull sides (will last 40 years with normal maintenance) and 3mm superstructure (no earthly reason to go bigger with adequate framing)

 

Every kg of steel costs money, an overspend in areas that have no tangible benefit makes little sense.

A well chosen coating system and anode set up is where I would spend my money.

Looking at it from a longevity point of view, I'm 37 this year, if I got 40 years from the above I'm likely not to be too worried about the state of it approaching 80!

 

The correct material to make a boat from is GRP, ours is 50 years young and in fine fettle....

Edited February 12, 2016 by gazza

[peterboat]

i would go for 15mm bottom no ballast, and given our canals are getting shallower it should last a lifetime, without needing edging which can be a problem for high canal miles boats. as for builders its still tyler wilson for me as they keep on winning at crick with their shells

[gazza]

i would go for 15mm bottom no ballast, and given our canals are getting shallower it should last a lifetime, without needing edging which can be a problem for high canal miles boats. as for builders its still tyler wilson for me as they keep on winning at crick with their shells

The trouble with 15mm is it requires a double vee prep to be done correctly - a labour intensive job as it needs welding from both sides of the joint.

It makes little sense to me tbh.

[BD3Bill]

 

The correct material to make a boat from is GRP, ours is 50 years young and in fine fettle....

 

So right, I was so right... sussed!

 

Well it is only February!

Touche !

[peterboat]

The trouble with 15mm is it requires a double vee prep to be done correctly - a labour intensive job as it needs welding from both sides of the joint.

It makes little sense to me tbh.

it does and they do. my old boat by ten years old would have required edging if it had stayed on narrow canals it was quite worn so 15mm will give you a very long life

[bargemast]

Just for arguments sake I would say that 4mm steel is strong enough for a narrowboat. The rest is really there for a safety margin re. corrosion, we are talking pleasure craft, not something that is going to have 20 tons of coal dropped in it from a height. (no I would not really spec 4mm steel, just making a point) I would go for just two things, a good builder making a nice looking boat and a good epoxy paint system following manufacturers instructions. Oh, and paint the inside properly as well.

The idea of what's a safe plate thickness for narrowboats in the Uk is quite far of what the autorities on the other side of the Channel think of being thick enough.

 

For a 38m working barge the bottom plates have to have a minimum of 4.1mm and the sides 3.9mm to keep their commercial trading licence.

 

Peter.

[gazza]

 

So right, I was so right... sussed!

 

Touche !

I work with steel day in day out, I'd never have a boat out if the bloody stuff!

 

I've had the dubious honour of replating a neglected H&L narrow boat, put me off for life!

 

I'm no chippy or sadomasochist so wood is out of the question.

 

Stainless and Ali have there drawbacks, and my pockets are not deep enough for a trick composite such as carbon fibre.

 

GRP ticks all the boxes doesn't it?

[Neil Smith]

If money is no object have it built of stainless steel, it would never need blacking and should last forever.

 

Neil

[WotEver]

If money is no object have it built of stainless steel, it would never need blacking and should last forever.

 

Neil

As long as it never goes near the sea.

 

Edited for tryping

Edited February 12, 2016 by WotEver

[gazza]

As long as it never goes near the sea.

 

Edited for tryping

Two words.

 

 

Crevice Corrosion

[blackrose]

GRP ticks all the boxes doesn't it?

Yes, apart from osmosis and the fact that it can't take a proper knock.

As long as it never goes near the sea.

 

Edited for tryping

Isn't A3 or A4 stainless ok for saltwater, or does it still corrode?

[Alan de Enfield]

Yes, apart from osmosis and the fact that it can't take a proper knock.

 

Isn't A3 or A4 stainless ok for saltwater, or does it still corrode?

 

Type 316 is the marine grade but all will suffer from crevice corrosion.

[gazza]

Yes, apart from osmosis and the fact that it can't take a proper knock.

 

Isn't A3 or A4 stainless ok for saltwater, or does it still corrode?

Osmosis is not as big a problem as those that want to make money out of it would have you believe.

Boats don't sink from osmosis, they do from rotten wood and teabag steel.

 

As for the knock comment, that's bollocks too, if you whack something hard enough to split GRP you shouldn't be boating.

A2 and A4 are grades of bolt.

The most common grade of SS in marine applications is 316, its fine for shafts and fittings, but complex underwater fabrications suffer from crevice corrosion, hence why sterngear is not a good idea in SS on sea going vessels.

 

I had a wrestle when replacing our rudder, I opted for SS as our boat will send nearly all its time in our ownership on freshwater. The odd foray across the wash to Lincolnshire won't hurt it, but strictly speaking 316l is not the preferred material.

 

The original steel rudder stock shaft and rudder had done 49 years with minimal care, I could have stuck with that but preferred SS given our circumstances, had she been on the broads in brackish water I would have used steel.

Edited February 12, 2016 by gazza

[Neil Smith]

Yes I think A4 is marine grade as its used for all the fittings on trawlers and that's a harsh place for steel.

 

Neil

[peterboat]

Osmosis is not as big a problem as those that want to make money out of it would have you believe.

Boats don't sink from osmosis, they do from rotten wood and teabag steel.

 

As for the knock comment, that's bollocks too, if you whack something hard enough to split GRP you shouldn't be boating.

A2 and A4 are grades of bolt.

The most common grade of SS in marine applications is 316, its fine for shafts and fittings, but complex underwater fabrications suffer from crevice corrosion, hence why sterngear is not a good idea in SS on sea going vessels.

 

I had a wrestle when replacing our rudder, I opted for SS as our boat will send nearly all its time in our ownership on freshwater. The odd foray across the wash to Lincolnshire won't hurt it, but strictly speaking 316l is not the preferred material.

 

The original steel rudder stock shaft and rudder had done 49 years with minimal care, I could have stuck with that but preferred SS given our circumstances, had she been on the broads in brackish water I would have used steel.

i agree with you on the grp i have seen some old boats in our yard on the slipway and for the most they have been in very good condition. i was very tempted with one but they upped the price when they realised i was serious about buying

[Loafer]

'Crevice' is a very naughty word where I come from!