Thermal expansion of a 365

[Dale Tanski]

The extream cold weather we have been experiencing has screwed up my freshly redone teak hull to deck cap.  At the butt joints along the rail I have noticed as of late a "bulging" of the wood.  You can see it as well as feel it.  Apparently the fiberglass hull structure has a much higher thermal expansion coefficient than the teak cap rail does. 

As an engineer this kind of stuff makes me wonder.  Not the same way I wonder about UFO's and time travel, but the "what the heck" kind of wonder.  Unfortunately I could not find any information that would tell me what the actual thermal expansion coefficient of teak was, however I did locate numbers on the fiberglass hull which to me are quite interesting.

The long and the short of it so to speak is that the hull, my hull, your hull any fiberglass hull 36 feet in length shrinks just shy of 3/8" when cooled from 80 degrees F down to 0 degrees F.   I estimate that the actual length of our hull is approximately 38 feet along the rail.  If that were the case, the calculated number is .3648" over 80 degrees.  Now where I live outside of Buffalo, it has been in the single digits almost every morning and down into the negative teens here and there. 

I suspect that the teak shrinks far less than the fiberglass does per degree and that is why at my cap joints I am experiencing compression ridges.  Who would have thought?  I guess this would be a good excuse to heat the boat barn!

Good grief...  About that time travel... Dale

[RayNWanda]

 So with a temperature range of minus teens in N.Y. to 100's in Texas, what is the ideal temperature to install teak toe rails to minimise damage from thermal expansion/contraction? You're gonna have to find a thermal expansion coeffecient for teak to figure this one out.

[graemek]

HI
I had the same problem,I cut the teak rail in to three parts and left a 5mm gap this i filled with sekaflex-221,it is used in the UK to fit windscreens same problem glass expands less than steel.
dont know if we have such a temp problem ,max 40  min -30

[Dale Tanski]

Ray,

Its funny, I could find the Thermal Coefficient for all kinds of other wood, but not teak.  I guess you have thrown the gauntlet down and I will have to endeavor in additional research.  You are correct however, something I did not think about, to do it correctly to minimize the "gap" or the "compression ridge", you would have to install the teak cap at the temperature right in the middle of the anticipated extreams.  This would minimize both phenomenons. In retrospect, we should be glad our hulls are not aluminum! 

Graemek,

Did your joints "compression ridge" when it got colder even with a compressible material in between? Either way I suspect it ruined your varnish over the joint, and... 40 to -30 is a 70 degree F delta.  My example was an 80 degree F delta so you have a very similar problem.  Perhaps if we used degrees C the numbers wouldn't be as bad.

I suppose that in the tropics the temperature would reach say 110 degrees F.  And... if you sailed north or south into Arctic conditions the delta could be as high as 100 degrees F.  I think I am going to apply to the federal government for a grant to study the thermal expansion problems regarding yacht teak and temperature extreams.  Yea...  a little stimulus money for the private sector and something that is meaningful.

Dale

[EdHouston]

Shoot move South

Almost a non-issue!

Ed

[Dale Tanski]

This year Ed, it would have been a problem!

Dale