Disasters at Sea

[Pluto]

I would suspect that cabin side gunnels were introduced with steam power, where  it would be necessary to get from the stern to the boiler easily, and without upsetting anyone asleep in the cabin, where they were grabbing a little rest when working the long hours possible with steam power.

 

On torsional movement, it could be seen as beneficial with wooden boats as it helped to work the caulking in the seams. A little such movement certainly tended to make my old wooden boat more water-tight, though too much could have the opposite effect.

[IanD]

2 hours ago, Captain Pegg said:

 

But those questions were the premise of the point you queried and the suggestion to go read a book without even bothering to address the actual point I raised I thought was pretty condescending. As it happens I've studied and practiced structural engineering to a high degree so I don't need to be told that box sections are intrinsically good in torsion. I'd far sooner debate from knowledge than from reference material, I want to hear what people really know and understand, warts and all. Save reading up for afterward when you can go and check up on something you realise you maybe didn't know as well as you thought.

 

I still though suspect that if you induced a twist into a narrowboat accidently it wouldn't take that much to cause cabin distortion that could cause internal damage to linings or fittings, and that would be a result of the thin cabin sides and profile. I'd agree it wouldn't get any near failing but as is common in inhabited spaces serviceability criteria take precedence over structural criteria in design. As boxes go they aren't that great.

 

 

So don't just suspect -- you know how big a boat is, how thick the hull is, and how much it weighs, the formulae are simple and out there, so go and work out how much it will twist by if (for example) all the weight is supported on diagonally opposite corners. Don't forget to allow for the bulkheads which act as panel stiffeners at each end and keep the hull "square" at that point. It's a standard undergraduate exam problem.

 

If it turns out that the distortion will be big enough to cause damage -- as you seem to be claiming -- then I'll agree with you, should a boat ever find itself in this unfortunate (and unlikely) situation. Until then, my view is that it won't, backed by exactly the same hand-waving engineering estimate as yours. In other words until the numbers are crunched we're both just expressing opinions, and we all know how valid they are without facts to back them up... 😉

 

P.S. My suggestion to read the book was because your initial post suggested you didn't understood the subject, and also it's a damn good read for anybody with an enquiring mind 🙂

Edited January 17, 2022 by IanD