hi all.
i have a flow hive hybrid and im keen on swapping the crown board for a clear one.
can anybody tell me the dimensions of the crown board and in particular the bee space?
cheers kev
You don’t really need to worry about bee space at the top of a hive. Most of the people I know who use a perspex or polycarbonate sheet for an inner cover/crown board replacement, just cut a flat piece to size.
The length and width are approximately 19 3/4" by 14 5/8" (or 16 1/4" for a 10 frame). However, these can vary by up to 1/4", so your best bet would be to go out and measure your own hive if you want an exact fit. If you really want to leave some bee space above the tops bars of the frames, I would aim for no more than 1/4" or 6mm, to avoid comb building.
cheers for that.
i shall start looking for some perspex sheet
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Amazon has polycarbonate sheets. A bit pricey, but this is the right stuff:
You could do much cheaper and probably just as good with some thinner material from your local hardware store.
And it wouldn’t have to be shipped from the UK… 
But @kev1744 is in the UK, @chau06, so it is more convenient for him. The reason I chose that specific thickness and material, is because that is exactly what a British friend of mine used. She didn’t buy it from Amazon, as far as I know, but she tried several materials and that was the best. If you buy stuff that is too thin, it tends to get a lot of condensation in cold weather. Not good for the bees, and you can’t see through it, which is kind of the whole point… 
Ha. I didn’t look where he was before making my smart-ass comment!!
But the R-value per mm of single wall polycarbonate is very low, I think around .15. So, you’d be better off putting a thin sheet of optically better polycarbonate covered with even a thin blanket of some sort of insulation to decrease condensation.
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