Richardw's Narrow Boat Project- PLATE THICKNESS

My name is Richard Wilkinson, I am a new member but I have been visiting this site the past few months harvesting information because I am embarking on a project of designing a new 62ft Live Aboard Narrow Boat.

Apart from my intended construction start date which is Spring 2015 anything can change. I do have a lot of ideas myself but I am open to suggestions that either confirm or criticise the very best way of doing things based upon what I appreciate for some members is years of experience.

I come from wide and varied background as an award winning Architectural Technician but I once also had a previous life as an Design Engineer having served an apprenticeship in the Formula 1 Motorsport Industry back in the 80s. So you could say I know a bit about materials, both in Engineering and Construction fields, as well as fabrication and of course Computer Aided Design and 3D Solid Modelling.

There will be other threads on other subjects that I will start under the heading of "Richardw's Narrow Boat Project" so they can be easily found but on this thread I want to explore all opinions regarding 'Plate Thickness'

There is a saying that goes "Engineering is doing the same thing that any fool could do for twice the price!". My view is that 'Lean Engineering' will be an important part of this project so to that end what is the ideal plate thickness to use and how does if effect the lifespan of the boat? Can the thickness be too thick as how long should the designed lifespan of the boat be? What impact does Galvanic Corrosion play in lessening a boats life? Given that steel is around the £1 per kilo cost which ever gauge whereas the labour element in building the boat remains almost constant, is it worth spending the extra cost in terms of not necessary getting the cheapest price but obtaining the 'best value'. Perhaps you have a boat that years down the line you now wish you had made thicker.

This is just the start; many other threads will follow covering all aspects of Narrow Boat design. Over time I will upload drawings and sketches so you all can follow the process. I want the final design to be the illusion of perfection or else at least have a proper understanding of compromises I have needed to make and the reasons for doing so.

My intention is that the final hull and superstructure will be kit of parts designed in the virtual world and as I am in the construction industry will be sent out for competitive tender to a structural steel fabricator to assemble. I bet even that prospect will horrify several readers.

I would very much appreciate all of your opinions on all of the above.

 

Hmmm...plate thickness.

The bottom panels are thicker than the side panels

5 mm plate is the thinnest plate you can use on a steel boat and expect longevity.

You should look around at other canal boats to get an idea about structure and plate thickness. Make some guesstimates then consult a pro for scantlings.
Scantling on a canal boat are very basic.

The plate thickness will vary due to the anticipated loads.

Corrosion is kept away by properly sandblasting the steel hull and properly priming the steel. Seek pro advice from International paints as the time comes.

As the boat is being built there are hundreds of details that are used to prevent corrosion...most important....no standing water in bilges and all steel edges radiused.

Steel boats have steel water, waste, fuel tanks...corrosion city...good detailing is critical

Electric systems are important on a steel boat. The boat must be isolated f rom
electricity

Why not check out Kasten marine for reading and The Metal Boat Society.

Kasten is articulate , you will gain insights by reading his articles

http://www.kastenmarine.com/articles.htm

Then start scetching and thinking so that when you go for final engineering approval all goes fast

 

Have you talked to any of the numerous builders of narrow boat hulls? Is there any particular reason not to work with an experienced narrow boat hull builder?

Or is one of the primary objectives of the project for you to design the boat?

 

Sounds like an interesting challenge Richard. I am rather intrigued as to why it has to be steel?. It is not a working boat, are there any left? so is not expected to payback build over 10 years or so. If it is purely a live aboard vessel could it not be a slightly different vision or take on the traditional designs?
I think there is room for something a little more modern with that classic workboat twist, and if you go there, then steel may not be the best material.
In terms of warmth and condensation steel and aluminium are horrible materials for a boat. Even glass with roof lining is worse than timber. A foam or wood core hybrid might be a much cosier option. After all the original workboats would have been timber, as are the Norfolk wherries and most Thames barges.
Stiffness is not an issue unless you intend commercial use with 200+ ton loads!. Simple beam loading can sort that fast enough.
Check out some of our Dutch cousins conversions too, but of course their barges are 1,000 ton beasts these days.

The Dutch also have lot of experience of building in steel so you may well pick up some useful information from their naval architects and building yards.
If the boat is for yourself, you should try a winter weekend sailing/motoring in a steel or aluminium boat. If it is for a client get them to do that, and then in an FRP or timber or hybrid composite. Partly a human thing, partly the extra condensation from our bodies and breath as well as the extra corrossion issues.

I look forward to seeing how your project progresses. A careful modern take on the 'narrow boat' may well be a worthwhile design. The traditionalist might hate it but tough a lot more would like it. Good luck.

 

One factor to keep in mind when discussing plating for narrow boats used on British canals is that the canals are fresh water, and my understanding is that corrosion is less severe for boats which only in fresh water than for those which are in salt water.

 

My opinion is that it is very possible that the oxidation is very similar in freshwater and saltwater. Salt water, however, is an electrolyte that accentuates the effect of galvanic corrosion.

 

Corrosion of steel by itself is considerably more severe in salt water than fresh water.

 

Thank you for all your replies. Sorry to Tansel if I offended you in any way; It is the Engineer who is supposed to be able to do the job for half the price of any fool. I made no mention mad men as I'm often described as one of those myself. It is often said there is very fine line between Genius and Madness!

The point of mentioning that I have won awards was not to brag but to put my background in context. I do possess a certain mix of knowledge and skills that I feel are transferrable between construction and engineering, (yes that does sound like a brag but it is not meant to be), and I will over the course of discussions bring in materials and processes that you have never heard of but only for the cause of testing opinions as to whether or not they stand a chance of working.

Responses:

Why Steel? Because it is plentiful, durable, agricultural in technology and a time proven material. Of course I am biased as I have a fair bit of knowledge of it and none at all about composites used in a boat that one of the main strengths needs to be strong and dare I say heavy.

Steel Hulls do need to be Earth Bonded as per the Regulations but I understand there is some dark art that I don't quite fully understand as to why it can cause accelerated hull corrosion. Galvanic Isolation is the tern used and I'm sure there must be some expert who reads this forum who can educate us all about it.

On the subject of Canal Boat Plate thicknesses what I'd like to know is how long a 10mm thick bottom would last and how much longer it would last if it were increased to 12 or even 15mm thick. Lets assume it will be coated in epoxy tar and have sacrificial ingots and general maintenance periods will be no closer than the legal minimum 5 years to obtain a boat safety certificate as I'm all for maintenance free. Will ingots last 5 years?

I am really grateful to read others opinions because I know that I am not always right.

 

Some working narrowboats were wood, some were iron and some were iron sides with a wood bottom.

All the recreational UK narrow canal boats over 30 feet which I've seen were welded steel.

 

You've hit the nail right on the head!

The reason I am designing my own boat is because I have looked around as to what's available as a live aboard and considering the British climate frankly I am very disappointed with how they are constructed in terms of , well, everything! Insulation, Condensation, Ventilation, Windows, Security, Propulsion etc. etc.

As an outsider from what I consider to be the more modern field of construction I believe there are things I can bring to the table that would improve the whole design but will do so in open forum because for all I know I might be wrong. We don't build houses the same way we did 5 years ago, let alone 10, 20 and so on. I think if I designed houses to the same standard a typical narrow boat was built to nobody would want to live in them. I have ideas in my head that I cannot believe have not already been adopted so I will air those ideas and find out why they haven't or may be they might just make it into my final design.

 

Most likely you are right but I wonder: if salt water has the same amount of oxygen than fresh water, why is higher oxidation (no galvanic corrosion) in salt water?
Thanks in advance for your explanation.

 

I'm talking about corrosion of steel in water by itself, not steel as part of a galvanic cell with other metals.

I'm not an expert on corrosion. But I do know that corrosion of steel is considerably more complex than simple oxidation as described in a basic chemistry course, and that the process goes much faster in salt water than in clean fresh water.

 

Richard, perhaps you might contact an experienced surveyor of narrow boats and ask what their experience with corrosion of steel in narrow boat hulls is.

I've wondered why narrow boats seem to all have the same general look and look forward to seeing your ideas.

AS I'm sure you are aware a narrow boat has some basic and significant design limitations including maximum beam, maximum length, draft and height above water. Depending on where you want to travel in the boat there are maximum "air draft" (height above water) limitations. Working from the top down if standing headroom is desired then this implies a minimum draft requirement (also dependent on hull and cabin construction thickness), which for a given hull shape and length implies a minimum displacement. Reducing weight hull or furnishings could mean that ballast would need to be added to get the draft back to what's needed to meet the overhead clearance requirements.

 

15mm. Shiver me timbers...ive never seen 15mm plate on a yacht.

Dont be thinking about corrosion...its not an issue. Modern coating are very durable



A boat must never be overweight. You want the thinnest plate that achieves the desired structural integrity

What will be the proposed displacement of your canal boat ? 25 ton, 45 tons ?

This is the first and most important question.

You cant continue unless you have a number in mind.

And ingots ? You mean anodes ? How long do they last ?

Easy...contact MgDuff and they will propose a package to achieve long life

5 years ? Perhaps...but who cares..anodes can be changed in the water

 

DCockey, although not the subject of this debate, oxidation is the combination of an element with oxygen. Therefore, this phenomenon is called oxidation, and not otherwise. Corrosion is another phenomenon, as you very well say, more complex.
Oxidation in hot water is higher than in cold water but I still do not know why the salt water rusts more than fresh. And, if I'm confused, would be happy to have someone explain to me what is my mistake.
richardw66, sorry, my comments were not relevant and I deleted. Like I said, a well-preserved steel can last for many years, regardless of its thickness