I found myself sitting more and more inside in the raised saloon
area. It seemed cooler even though there was less breeze than outside in the cockpit
under the bimini
, so I set about investigating why. The saloon
has a lot of windows, all open and they are shaded externally.
This is what I measured by pointing the IR thermometer at the same cushion after allowing the temperature to stabilise. I picked a cream coloured cushion as close to skin tone I could find to try to simulate how the body might heat up.
In the saloon with a light breeze: 30 deg C
Under the cockpit
table with a light breeze: 30 deg C
Under the cockpit bimini
with a good breeze: 34 deg C
Under the cockpit bimini, behind the windshield with no breeze: 36 deg C
Under full sun, good breeze: 49 deg C (Who doesn't need a bimini...)
So clearly a lot of radiation is getting through the bimini. The breeze also convects a good bit of heat away. The key results from these measurements is that the breeze in the cockpit compared to no breeze reduces the temperature by 2 deg C and full shade i.e. under the table or inside compared to being under the bimini - reduces temperature by a further 4 deg C or probably 5 deg C as a guess. - I'm guessing the difference in temperature between inside and outside would be a degree lower outside than inside as the breeze is better there, but I couldn't find a way to measure that directly.
How much heat is getting through is surprising to me as the bimini is light in colour - a cream Sunbrella, so should reflect a lot of energy. I would expect a dark one would block more IR, but would also absorb more and radiate the heat out again, some of which would be upwards. I wonder if it would be overall better or worse?
I would like to win that 4 deg C of temperature reduction outside. It should improve comfort quite a bit. One option is a fixed white fiberglass
bimini. Or I could insulate the current
one and use an alu foil.
Anyone have any experience or ideas?