Expansion gap

[Kalapattar]

Hi! How much of an expansion gap should there be laying down ply boards please? I have a steel hull 

[Chewbacka]

From memory my boat had a gap about 1.5 inches either side - can’t see it as it’s behind the side lining.   Obviously too big for expansion, so probably that big to get the least waste/least joins when cutting and laying the boards, though it probably helps with ventilation and keeping the bilge dry.

[koukouvagia]

It depends on what time of the year you are doing this.  In this hot weather the boards in my back cabin have shrunk leaving a good inch gap.  When they were laid in the winter there was almost no gap.  

 

 

eta: didn't notice you're laying ply.  Ignore the above remarks because in my experience ply doesn't shrink or expand very much.

Edited August 7, 2018 by koukouvagia

[Tony Brooks]

31 minutes ago, koukouvagia said:

It depends on what time of the year you are doing this.  In this hot weather the boards in my back cabin have shrunk leaving a good inch gap.  When they were laid in the winter there was almost no gap.  

 

 

eta: didn't notice you're laying ply.  Ignore the above remarks because in my experience ply doesn't shrink or expand very much.

But the boat may. If the OP laid them with no gap in the heat of the day at them moment (south) with no gap then in winter some may     try to bow as the hull shrinks. The hull may not expand a lot but it can be noticeable with things like doors sticking etc. I would think if ding it in the heat of the day 0.5 to 1 mm would be enough for hull expansion but I had a feeling that timber expand more than steel