Narrow boat flex

[Guest]

Does a steel narrow boat expand and contract in summer, winter.

 

reason I ask is for fit out inside, a fellow boater has said he left space between his interior side panels to allow for stretch. And also gaps  between floor and sides.

 

my body work outside has also has extensive fibre glass put in dips, and body filler on top to smooth out its paint job. Will this be an issue?

 

thanks

Graham

Edited June 12, 2019 by Guest

[nicknorman]

Yes steel definitely expands and contracts noticeably with temperature, whereas wood doesn’t. In hot sun, steel cabin sides/roof will be too hot to touch. Meanwhile the bits underwater will remain at water temperature. So there can be quite a lot of distortion of the shape of the hull/superstructure.

 

It is a bad idea to tie a wooden interior too tightly to the hull. In the battle between steel and wood (and screws) the steel will win!

 

Typically one leaves gaps between sheet material, covered over by trim to hide the unsightly gaps when the steel has expanded but the wood has not.

 

Small areas of filler will be OK as there is some slight flexibility in it, and the expansion of steel over a small distance is not much. But on a big scale it is a problem, which is why boats with steel hulls and grp superstructure are high maintenance!

[zenataomm]

Where did you steal it from?

[WotEver]

9 minutes ago, zenataomm said:

Where did you steal it from?

Norty...

[Guest]

23 minutes ago, zenataomm said:

Where did you steal it from?

Well spotted, poor grammar on my part!

[TheBiscuits]

37 minutes ago, Charles_Graham said:

my body work outside has also has extensive fibre glass put in dips, and body filler on top to smooth out its paint job. Will this be an issue?

Assuming you have used chopped strand bridging compound (the stuff you refer to as fibreglass) you will be fine looking at the areas covered in your picture.  It's when you have a totally fibreglass cabin that you get problems.

[PeterF]

We were moored up for the afternoon a few days ago with the weather alternating between bright sunshine and cool showers, the wood lining was creaking all afternoon at the joints as the steelwork of the cabin continually expanded and contracted. It was the best indication yet that there was such thermal movement.

[Guest]

A boat fitter once told me to use a pound coin to gauge the space between plywood sheets when fitting out.
After a cool night and when the sun starts to shine, our boat makes  creaking sounds for a little while. I had one interior piece of trim split a few years ago, but OK otherwise.

[pearley]

Our bathroom floor was originally tiled with ceramic tiles. In the summer one grout line across the boat would open up. It would close again in the winter. 3 years ago we had a screed put down and Karndean tiles laid. A gap still appears in roughly the same line every summer.

[Jen-in-Wellies]

Often get clicks and pops from the lining in my boat as the sun hits it and the steel heats up and expands. Not been happening for the last few days for some reason? ☔

Steel expands around 10ppm/deg, so a 57' (17m) narrowboat is 0.17mm longer for every 1 degree C temperature rise, so CaRT should be charging us higher license fees in summer than winter.

 

Jen

Edited June 13, 2019 by Jen-in-Wellies

[Chewbacka]

Wood moisture content will be higher in winter (condensation etc) and you will have cold (contracted) steel and 'damp' expanded wood so only a small gap in these conditions is required, which will become a much bigger gap in summer with dry wood and hot steel  opening the gaps.  So time of year when fitting new panels etc. will influence the gap required.

[WotEver]

48 minutes ago, Chewbacka said:

Wood moisture content will be higher in winter (condensation etc) and you will have cold (contracted) steel and 'damp' expanded wood so only a small gap in these conditions is required, which will become a much bigger gap in summer with dry wood and hot steel  opening the gaps.  So time of year when fitting new panels etc. will influence the gap required.

Excellent advice there sir

 

[nicknorman]

49 minutes ago, Chewbacka said:

Wood moisture content will be higher in winter (condensation etc) and you will have cold (contracted) steel and 'damp' expanded wood so only a small gap in these conditions is required, which will become a much bigger gap in summer with dry wood and hot steel  opening the gaps.  So time of year when fitting new panels etc. will influence the gap required.

Also worth remembering that wood swells across the grain with moisture, not along it. Relevant for solid timber but not for ply.

[Chewbacka]

9 minutes ago, nicknorman said:

Also worth remembering that wood swells across the grain with moisture, not along it. Relevant for solid timber but not for ply.

When fitting out I looked at some ply spec sheets and from memory an 8ft sheet could have a 2mm difference in length between winter and summer.  So whilst not a lot (and you are correct, less than solid wood), if you fit the panels in hot dry weather so they almost touch you will have winter problems.

[nicknorman]

2 minutes ago, Chewbacka said:

When fitting out I looked at some ply spec sheets and from memory an 8ft sheet could have a 2mm difference in length between winter and summer.  So whilst not a lot (and you are correct, less than solid wood), if you fit the panels in hot dry weather so they almost touch you will have winter problems.

Sorry, what I meant was that solid wood only swells across the grain not along it, whereas ply swells in all directions, but to a lesser extent.

[Chewbacka]

Just now, nicknorman said:

Sorry, what I meant was that solid wood only swells across the grain not along it, whereas ply swells in all directions, but to a lesser extent.

and that we most definitely can agree ? 

[MtB]

2 hours ago, Jen-in-Wellies said:

Often get clicks and pops from the lining in my boat as the sun hits it and the steel heats up and expands. Not been happening for the last few days for some reason? ☔

Steel expands around 10ppm/deg, so a 57' (17m) narrowboat is 0.17mm longer for every 1 degree C temperature rise, so CaRT should be charging us higher license fees in summer than winter.

 

Jen

 

Is that not a volumetric coefficient?

 

The linear coefficient of expansion of steel can be as high as 12.5m x 10 ^-6

 /mK according to Engineering Toolbox.

 

That means a 17m boat expands by 0.00125mm x17 per degree C I reckon, unless I messed up the zeros! 

 

So a 17m long boat is 0.425mm longer at 20 degrees C than at 0 degrees C. A negligible amount practice. 

 

 

 

[MtB]

Nope that cannot be right.

 

12.5m = 12500mm. 

 

12500mm x 10^{-6 = 0.0125mm. I was wrong by a factor of 10 above.} 

 

^{So a 17m long boat is 4.25mm longer at 20 degrees C than at 0 degrees C. Not so negligible!}

Edited June 13, 2019 by Mike the Boilerman
Dammit can't fix the superscript now!!

[TheBiscuits]

2 minutes ago, Mike the Boilerman said:

Nope that cannot be right.

 

12.5m = 12500mm. 

 

12500mm x 10^-6 = 0.0125mm. I was wrong by a factor of 10 above. 

 

So a 17m long boat is 4.25mm longer at 20 degrees C than at 0 degrees C. Not so negligible!

 

[Jen-in-Wellies]

3 minutes ago, Mike the Boilerman said:

 

Is that not a volumetric coefficient?

 

The linear coefficient of expansion of steel can be as high as 12.5m x 10 ^-6

 /mK according to Engineering Toolbox.

  

That means a 17m boat expands by 0.00125mm x17 per degree C I reckon, unless I messed up the zeros! 

 

So a 17m long boat is 0.425mm longer at 20 degrees C than at 0 degrees C. A negligible amount practice. 

 

 

 

Hi Mike,

Nope, linear, not volumetric. It is a dimensionless number for length as it is length change / length per degree, so expressed as degree^-1. ppm/degree is a good way of giving it as most materials come out as nice single, or double digit numbers. Steel varies depending on composition. 10 to 12 or so. I used 10.

The moral being to licence your boat in winter, not summer as it is cheaper!

 

Jen

[WotEver]

35 minutes ago, Jen-in-Wellies said:

The moral being to licence your boat in winter, not summer as it is cheaper!

[trackman]

Think you have problems with boats?

I remember designing bridges, where with long spans lit by sun on one side the whole structure would become significantly curved due to the temperature difference from the hot sunny side to the shady, cool one.

[Guest]

How much body filler can you put on metal?