Hull material question

[Ottocat]

Perhaps a silly question....but why isn't stainless steel used as a hull material? surely it would be much more corrosion resistant.

 

Also are alluminium narrow boats a good idea as I believe alliminium doesn't have the same fatigue properties as steel ..being less forgiving to stresses

Edited February 6, 2008 by Ottocat

[Sir Nibble]

Or titanium, how many millions do you want to spend?

[Ottocat]

Or titanium, how many millions do you want to spend?

 

 

surely stainless can't be that more expensive and wouldn't it last so much longer...although I see where you are comeing from

[Chris Pink]

Perhaps a silly question....but why isn't stainless steel used as a hull material? surely it would be much more corrosion resistant.

 

Also are alluminium narrow boats a good idea as I believe alliminiu doesn't have the same fatigue properties as steel ..being less forgiving to stresses

 

i think you might find some clues here;

http://www.bobsbits.tv/General.aspx?resid=2

 

MILD STEEL

 

Over 99% iron alloyed with less than 0.5% carbon and at least small amounts of manganese and silicon. It is widely used for domestic appliances (white goods), car bodies, construction (such as RSJ’s). Rusts easily in contact with moisture, but can be electro-plated, galvanised (dipped in molten zinc), powder coated or painted to prevent rust. Quite easily drilled, machined or welded. Slightly higher carbon content steels can be surface hardened.

 

Raw material August 2005 price £230 ($410) per tonne (£60 per tonne scrap price).

 

STAINLESS STEEL

 

A low carbon steel that contains a minimum of 10.5% chromium, which gives it its stainless, corrosion resisting properties. Adding other elements such as molybdenum, nickel & nitrogen further increases these properties. Stainless steel was only discovered in the early 20th century. Commonly used for cutlery, kitchen sinks, catering & medical equipment, medical instruments.

 

Raw material October 2006 price approximately £1,600 ($2,850) per tonne (£1020 per tonne scrap price).

 

ALUMINIUM (Al)

 

Aluminium is the ideal metal for set dressing & adding detail to props. It is a light ductile & malleable silver-white metal that is easily machined, drilled, glued and can be polished to a mirror finish. It can be anodised in a wide variety of colours, a process that also hardens the surface & prevents corrosion. Aluminium is the 3rd most abundant element in the Earth’s crust (7.3%). Only discovered in 1808 by Sir Humphrey Davy, originally more expensive than gold!

 

About 80% of an aircraft is aluminium & about 90% of the space shuttle. Most drinks cans are made of aluminium.

 

Raw material October 2006 price £1,325 ($2,480) per tonne (£980 per tonne scrap price).

 

and by the time your 8mm mild steel has rusted through so you can see the green water through it the builder will have retired.

[Ottocat]

 

I'll fetch my coat then

[carlt]

Metal is just such an outdated material, for boat building. The 21st century is all about sustainability, you know.

[ChrisPy]

Metal is just such an outdated material, for boat building. The 21st century is all about sustainability, you know.

[Chris Pink]

Metal is just such an outdated material, for boat building. The 21st century is all about sustainability, you know.

 

But once we scrap all the AK47s there will be enough steel around to keep us in narrow boats until the next century, by which time we will have grown enough oak and elm to carry on.

[steelaway]

But once we scrap all the AK47s there will be enough steel around to keep us in narrow boats until the next century, by which time we will have grown enough oak and elm to carry on.

 

Brilliant!

By that time there will be no fuel and it would be light enough for a horse to pull it.

---- Ahhh evolution

[Speedwell]

Also are alluminium narrow boats a good idea as I believe alliminium doesn't have the same fatigue properties as steel ..being less forgiving to stresses

You have had the answer about stainless steel, so here is a bit about fatigue. It is true that aluminium alloys have low fatigue resistance, especially the low strength alloys that have good corrosion resistance, but the hull is unlikely to be subject to serious fatigue loading (ie vibration or reciprocating loading). Might be a problem with the engine bearers though, which would have to be very sturdily built. The aluminium alloys, with good corrosion resistance, also have low yield strength and would dent more easily than the equivalent thickness of steel. Hopefully the designers of aluminium boats will have taken all this into account.

Arthur

[carlt]

But once we scrap all the AK47s there will be enough steel around to keep us in narrow boats until the next century, by which time we will have grown enough oak and elm to carry on.

Scrapping the ak47s won't happen in this century, though.

[dove]

You have had the answer about stainless steel, so here is a bit about fatigue. It is true that aluminium alloys have low fatigue resistance, especially the low strength alloys that have good corrosion resistance, but the hull is unlikely to be subject to serious fatigue loading (ie vibration or reciprocating loading). Might be a problem with the engine bearers though, which would have to be very sturdily built. The aluminium alloys, with good corrosion resistance, also have low yield strength and would dent more easily than the equivalent thickness of steel. Hopefully the designers of aluminium boats will have taken all this into account.

Arthur

 

From my experience working with Aluminium boats, you can only bend rolled plate one way, it has a grain structure and also work hardens.

with the boats flexing in the water and more so in locks this could lead to proplems. A good example was the fast ferry to Ireland, they had full time welders on the car deck welding patches over stress points.

 

Andrew

Edited February 6, 2008 by dove

[Speedwell]

From my experience working with Aluminium boats, you can only bend rolled plate one way, it has a grain structure and also work hardens.

with the boats flexing in the water and more so in locks this could lead to proplems. A good example was the fast ferry to Ireland, they had full time welders on the car deck welding patches over stress points.

Andrew

Andrew

I quite agree about grain structure ( as have all metals). You can bend it in any direction but it is more ductile if the heel of the bend is at right angles to the longitudinal grain direction. Also true about work hardening but I can't see why this is a problem.

There is a big difference between the stresses experienced by the hull a high speed sea going ferry and a canal boat. Looks like they have a design problem there.

Can't see why the hull of a canal boat should flex particularly in locks.

Arthur

[Proper Job]

Scrapping the ak47s won't happen in this century, though.

That'll give the trees time to grow.

 

Its all part of life's rich tapestry

[Tony Brooks]

You have had the answer about stainless steel, so here is a bit about fatigue. It is true that aluminium alloys have low fatigue resistance, especially the low strength alloys that have good corrosion resistance, but the hull is unlikely to be subject to serious fatigue loading (ie vibration or reciprocating loading). Might be a problem with the engine bearers though, which would have to be very sturdily built. The aluminium alloys, with good corrosion resistance, also have low yield strength and would dent more easily than the equivalent thickness of steel. Hopefully the designers of aluminium boats will have taken all this into account.

Arthur

 

 

No one has yet mentioned that Vetus push Aluminum anodes - how to solve the GI/transformer thing - don't bother, moor up next to a Seaotter

[Yoda]

That'll give the trees time to grow.

 

Its all part of life's rich tapestry

 

Never heard of Woodstock?

Edited February 6, 2008 by Yoda

[dove]

Andrew

I quite agree about grain structure ( as have all metals). You can bend it in any direction but it is more ductile if the heel of the bend is at right angles to the longitudinal grain direction. Also true about work hardening but I can't see why this is a problem.

There is a big difference between the stresses experienced by the hull a high speed sea going ferry and a canal boat. Looks like they have a design problem there.

Can't see why the hull of a canal boat should flex particularly in locks.

Arthur

 

Work hardening can lead to cracking like with our copper steam pipes, they have to be anealed every so often. every time you have contact with another boat or lock the plate is flexed. If you want to how much a boat flexes in locks, stand on the back of Dove, you'll be supprised

Andrew

[Yoda]

I don't think that there is a better material than mild steel for a long working life of a narrow boat. Other materials are OK but all have their drawbacks. One thing that I would question is the quality of the mild steel used.

[dove]

I don't think that there is a better material than mild steel for a long working life of a narrow boat. Other materials are OK but all have their drawbacks. One thing that I would question is the quality of the mild steel used.

 

 

I agree, if you black it often and moor next to a Sea Otter, it will last for years. And you can DIY repair it

 

Andrew

[carlt]

And you can DIY repair it

I think, if you did a poll of who did diy repairs to their hull you'd find a tiny proportion of steel boat owners were capable (or confident) enough to, a larger percentage of GRP owners would and the vast majority of wooden hull owners do their own repairs.

 

I never did any repairs to my hull when I owned steel boats.

[Chris Pink]

the vast majority of wooden hull owners do their own repairs.

 

That's because no one else would be brave enough to poke at the spongy bits.

[dove]

I think, if you did a poll of who did diy repairs to their hull you'd find a tiny proportion of steel boat owners were capable (or confident) enough to, a larger percentage of GRP owners would and the vast majority of wooden hull owners do their own repairs.

 

I never did any repairs to my hull when I owned steel boats.

 

Eveyone to his own, I afraid I don't do wood, well not very good. GRP.... never had a bash. Prefer Iron personally

 

Andrew

[Machpoint005]

I think, if you did a poll of who did diy repairs to their hull you'd find a tiny proportion of steel boat owners were capable (or confident) enough to, a larger percentage of GRP owners would and the vast majority of wooden hull owners do their own repairs.

 

I never did any repairs to my hull when I owned steel boats.

 

Could that be because a properly built, cared-for and well-maintained mild steel hull probably never needs repairing? Seems to me that good 'ole carbon steel is the right material in the right place, despite the fact that the tinworm likes it so much!

 

Ian

[Speedwell]

Work hardening can lead to cracking like with our copper steam pipes, they have to be anealed every so often. every time you have contact with another boat or lock the plate is flexed. If you want to how much a boat flexes in locks, stand on the back of Dove, you'll be supprised

Andrew

Hello again Andrew

Not too knowledgeable about copper pipes but I would not expect cracking from the amount of cold work, involved in canal boat making, in the type of alloys involved.

I have never noticed either of my boats flexing in locks, although the sides vibrate in and out a bit in sympathy with the engine. Hopefully aluminium would be thicker and vibrate less, although I do not imagine the stresses involved would be very high anyway.

Arthur

[magnetman]

Offtopic but I'm pleased Dove has her real name back and that dodgy steel Britannia top has gone. Nice boat, with a nice thick STEEL bottom. Doesn't stainless steel suffer from weld corrosion and aluminium is advertised as 'free from rust'. I had an ally windlass out of the cut and it was wickedly pitted, not 'rust/iron oxide' but corrosion nonetheless.