Size limits of BIG wooden ships? (global strength issues/why not use metal frames)

Howdy everyone, i've been on and off reading boatdesign.net for years usually when entering random google terms on various things that have always fascinated me about boats, ships, yachts and the rest, and decided to finally get an account and make it more interactive since there seems to be some well educated and intelligent people here.


Alot of my explorations are likely to be more "fun" (mental play due to an interest in boat design, no idea how close to actually applying any knowledge I learn will ever be at this point in my life, even if I have a long term interest in moving to the west coast and living on a houseboat) and far more long term (any serious shipbuilding project is at least years off for funding reasons alone even if I relocate to Duluth up by the Great Lakes where I could use it) although some later-in-life career changes with six figure potential could make even large projects feasible by retirement age.


But enough about me - at the moment I had an itch of a question that's been bugging me for about two decades. Why are "truly large" wooden ships uncommon?

Past reading on the topic from web searches seems to indicate much over 200 foot there is very little out there, I read once about some british ship over 300 feet which had problems with endless leaking though i'm not fully sure why... I understand global strength issues but don't know why a bendy boat should leak at one end if it's too big. But it makes me ask the question, why not have a huge wooden hull over a metal frame? Would that make larger sizes feasible? Or are there other engineering problems that would raise their head?

 

It's been done. Ships of the late 1800's were either framed or reinforced with iron or steel. However, at those sizes it is much more economic and structurally superior to build it completely in welded steel.

 

Did that solve the problems of large size though? The only offhand note I have is of the already mentioned british warship whose name I forget at I think 325-340 foot range which wouldn't stop leaking but I thought it was because it was all wood...


Economics I can understand, but could you enlighten me on the structurally superior aspect? Economics might not work on the 'open market' but if you owned a sawmill it might change the equation is the kind of thoughts in my head right now...

I've just read "too many" comparisons of ship design (wood vs steel vs fiberglass vs aluminum) and although specific sizes weren't mentioned normally I have to admit having the most positive feelings for a wooden hull (not necessarily as is, could be lined/covered with something) due to reasons many prefer - patchability in any port, simple to work with, what I thought was good strength-to-weight ratio in all areas except global strength, etc.

 

There were two, Mersey and Orlando, neither much use. The Great Republic clipper was similar lnegth although smaller displaccement, and perhaps the largest successful ship. There was one huge ship built in Canada which did not complete its only voyage but was still accounted a sucess for peculiar reasons - Baron of Renfrew

 

If you owned a sawmill, it would be cheaper to get the profits from your business and buy steel. The labor of building and wood and maintenance is much higher. Also, the tradesmen are very scarce for that kind of construction. Another problem is to get the boat certified to whatever class you want it to. At the size you mention it will be over 500 tons and have to comply with very strict standards.

 

Take a look at the yield strength of steel vs wood. Oak comes in at around 40-60 MPa, aluminum is 100-500, steel is 280-1600. For smaller boats stiffness is much more important than strength because if a structure is stiff enough it is almost by definition strong enough. As boats get bigger this starts to invert because of the square-cube law.

As a practical matter this is why you don't see many steel hulls below 40' and very few that aren't steel over 150'. Sure there are exceptions, but not many.

 

300' ? Pshaw. How about 450' or maybe 520' 8", depending on who you believe.

http://en.wikipedia.org/wiki/Noah's_Ark

Welcome to the forum.

 

Iron and steel structures have existed in wooden ships for quite a while, much longer then you'd think. Welded steel didn't become reasonable until much later, with early renditions being riveted or bolted. Large wooden ships have been possable for (also) longer than you might think.

The Greek trireme Tessarakonteres was all wood and references suggest it was 410', though reliable documentation limited at best, well within your range of a big wooden ship.

We can skip Noah's ark at 450' it think, but a fair bit of gopherwood I'd say. The Chinese built 400' exploration vessels in the 14th century. The Egyptians used 300' barges to move stone for various building projects, at least as far back as 1,500 BC.

The Scottish built Great Michael was about 250' in the 16th century. Of course, no list would be complete without Caligula's love barge which is about 350', built around the time of Christ.

Then there's the better known HMS Orlando and HMS Mersey, the Great Republic and Wyoming and SS Appomattox, all of which pushed the limits off wooden ships, even though fairly heavily reinforced with steel and iron. Even the USS Constitution (1797) used iron strapping.

So from an nautical archeology point of view, it's not as abstract or as recent a development to not only build big in wood, but to employ metal as support.

 

The three masted barque tenacious (213') was built using the cold molded method and west system. Not really pushing the size limits like some of the others listed here but interesting.

http://www.westsystem.com/ss/tenacious-a-look-back/

 

There are a couple building a 38ft wooden yacht near me, and they re-inforced a lot of the hull near the bow with cast silicon bronze angles.

In talking to them, I was surprised how many bronze cast items they had made up by a local foundry, for relatively low cost.

For example, they designed, and had cast all their cleats, which ended up costing half the price of readymade ones from the chandlers.

 

I have a buddy in Tennessee that has a foundry and he's cast many pieces for me over the years. I've also had a local high school do some casting. These small run shops can offer good pricing and better quality control than a lot of the manufactures, plus the plug they pull the casting from remains "in stock" so if you need more, it's a simple thing. Boat builders have to be inventive, particularly if it's a one off.

 

Longest ships today are tankers, bulk carriers, cruise ships and nuclear-powered aircraft carriers, up to 1600 feet. Cost of wood has climbed dramatically over the last 150 years while availability and quality have fallen. Over the same period of time the cost of steel has fallen and quality has risen due to the introduction of technologies such as the bessemer process, open hearth process and the electric arc furnace.

In industrial countries that can undertake the construction of huge ships, steel is now readily available, has consistent quality control and well-defined characteristics, and there are well-developed handing and processing methods adapted to industrial processes and the manufacturer of very large assemblies together with a large, well-trained and experienced workforce accustomed to working with the material on a large scale. It can be joined rapidly and reliably into virtually unlimited lengths and widths. It can be cut with minimum waste and the waste recycled. Depending on its purpose, a ship built from it can be economically recycled into scrap after a few decades and the scrap reused, while a new and more economical ship is constructed to replace it. Hardly worth re-painting the thing . . .

None of the above applies to wood. Despite its inferior strength, wood would probably be a material of choice for large vessels in some countries even today if the problems of cost, consistency of physical characteristics, quality and availability of large stock sizes were to be solved and availability guaranteed for the foreseeable future and high consumption levels. Biggest problem will always be the recyling time of a century or so compared to a few days for steel, excluding transport of course.

Much the same can be said of aluminum and its alloys, where cost has limited application for many years. Titanium too . . .

 

Also, another benefit of steel, I was watching a documentary of a Danish shipyard building one of those huge containerships last night.

Most of the modules with regular patterns and straight weld runs were done by welder robots. Not easy with wood.

 

Follow the money, and the tech.

In the US, we switched to steel when we could. Iron and steel enabled the propulsion and steering systems needed for such craft, regardless of hull materials.

In the 1840's clipper ships could pay for themselves on the first trip if it was a good one; but by 1850, the smart money, meaning the New England capitalists and their financial apparatus, was doubling up in rail and associated industries. It was a hugely prosperous decade across multiple industries as American production west of the Mississippi came on strong. Very high quality ore deposits were discovered in the midwest in the 1840's. Coal was available, and Carnegie put it all together. In 1857, there was a financial meltdown that ruined many of the New England financiers. It was over fairly quickly, but the slave states saw a weakness and decided this was the best time to settle the slavery issue. That didn't exactly work out as they had hoped. But by the end of the civil war, Carnegie and his Bessemer-process mills were producing more steel than the entire world had only a few decades earlier.

After the railroads in the 50's and the war production in the 60's The industry needed an outlet. Ship building once again attracted investment until Standard oil soaked it all up again in the 1870's. Lots of steam and propeller tow boats were built to tow around the thousands of old schooners which were stripped of their spars (because that made them uninspected vessels under the rules of the day). The towboat industry seems to have been the ones to pioneer the commercial all metal ship in the US. Lots of power density and pretty brutal on the hulls. Steel and iron parts were common by 1885. The screw propeller had arrived in the 1840's, the compound expansion engine in the 1870's. Efficiency had quadrupled compared to early side-wheelers. Finally, there was supply, demand, and the technology to make it attractive to financiers. It wasn't until the propeller arrived that steam ship crewing and maintenance could match that of a sail boat. And prior to the compound engine, steamships were for high end goods. After about 1885, steam and propeller craft were for everything. And at that point, bigger was better.

from here - http://www.mnhs.org/places/nationalregister/shipwrecks/mpdf/mpdf2.html

Another impressive woodie - See the bottom picture of the 1857 ship. http://wnyheritagepress.org/photos_week_2005/city_buffalo_ship/city_buffalo_ship.htm

And the transition to iron - http://query.nytimes.com/mem/archive-free/pdf?res=F50716FE3D541B7A93C1A8178ED85F448884F9

<edit> The first sentence of my second paragraph is dubious at best. Timing varied. After the civil war, the navy struck and auctioned many ships. There was a glut on the east coast after the war. The vast majority of boats were still being built of wood. The navy issued many contracts which kept yards afloat during soft economic times.

 

Phil's quote has it right, the move from wood to iron was based upon increased volume and decreased insurance compared to a wooden hull. An iron (and later steel) hull was lighter and thiner, giving a greater cargo/loadout capacity than a wooden hull, especially when built to large economical size.

From an engineering perspective, there is a real physical limit for wooden ships. It is based upon the outer fiber stress in tension and compression of the primary hull girder (i.e. the old SM problem encountered by the cube law). Realisticly, this limit is ~350' LWL even with steel strapping.