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Fly Navy

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8 minutes ago, JJPHG said:

I remember when I was researching a case once (a good few years ago) that the temperature difference can be as high as 50C, but that was in a slightly more favourable latitude and was with a very dark matt paint.  That said your point is still very valid and even under these extreme and favourable conditions the expansion is not going to get anywhere close to the 1" quoted

Yup. You’d need about a 120C difference to get close to 1”

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25 minutes ago, Fly Navy said:

60 foot boat, Hot day @ 35 degrees celcius (approx 100 farenheit)

I can’t imagine any day in the UK where you would have a difference in temperature between the two sides of the boat that would be anywhere near 35C. 

 

 

At 35C it’s about 67 thou per foot. 

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It doesnt have to be a delta between sunny side and shadow side, does it. The whole boat will expand equally if the ambient temp rises that 35 degrees.

0.17mm / foot of boat. I'd say that, coupled with the natural flexing of a NB, could and does cause cracks.

Theoretically - IF the sun beats down on one side of a boat and the other side of your boat is in shade, the boat could expand assymetrically and become...................wait for it..................

 

a banana boat ?

  • Haha 1
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Certainly I have seen a lot of movement due to temperature on our boat. It often shows as a gap between the side of a bulkhead-mounted cupboard and the adjacent wall, or as a cupboard door which suddenly won't open or shut properly. Last summer the outside of our boat, which is painted black, reached 65 degrees - definitely not to be touched!

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1 hour ago, Fly Navy said:

The whole boat will expand equally if the ambient temp rises that 35 degrees.

0.17mm / foot of boat.

You’re out by a factor of 10 again (or I am), but this time the other way. 67thou is 1.7mm. 

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2 hours ago, Fly Navy said:

It doesnt have to be a delta between sunny side and shadow side, does it. The whole boat will expand equally if the ambient temp rises that 35 degrees.

0.17mm / foot of boat. I'd say that, coupled with the natural flexing of a NB, could and does cause cracks.

Theoretically - IF the sun beats down on one side of a boat and the other side of your boat is in shade, the boat could expand assymetrically and become...................wait for it..................

 

a banana boat ?

Its not theory.

I said in a post a few pages back that our boat gets to 60-70°C on the roof (painted dark blue) whereas the hull and sides on the shaded side will be 20°C or so.

Never seen it not go through locks.

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20 minutes ago, Fly Navy said:

Use my link in post 29, convert to mm rather than inches.

I make it just shy of 0.2 mm.

Your link (or rather its maths) appears to be broken.

 

I switched to metric, entered a length of 305mm (1ft), and with a temperature of 100 degrees the result is 304.97224.

 

35 degrees gives 304.83347

 

Makes no sense to me. 

Post #11 gives the correct maths. 

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Works fine!

 

Enter:

1, Steel

2.  12 inches

3. 100 degrees farenheit

4. click on "calculate"

 

Answer: 12.00657" (which is the amount of expansion per foot of boat - yes?)

 

0.00657" x 60 feet = 0.4" overall.

 

All of the above however, was @ 100 degrees farenheit.  Dr Bob said he'd experienced 70 degrees celcius temperature change (159 degrees farenheit).

 

This therefore equates to 0.7"!

 

So a 60 foot boat 'crept' a further 3/4".....not far off what the expert said - be fair!

Edited by Fly Navy
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