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Old 06-08-2014, 04:27   #31
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Re: Keeping Cool Under the Bimini

Originally Posted by Cotemar View Post
We had a huge difference in how cool our cockpit was after changing from blue Sumbrella canvas to an White Azek hard bimini.
A bit like the solution of brazenarticle. I like its simplicity and I can see it is likely to deal with the heat issue really well. I think the main downside is if you ever want to take it down. I can have the bimini down in 15 minutes, so leaving the boat with it up in hurricane season would have me a bit concerned - sailing in a storm also. Heeled over the thing will catch a lot of wind. In your location, far fewer issues due to shelter from the main structure of the boat.

Originally Posted by socaldmax View Post
If you have a good water maker, I'd suggest a mist system installed in the cockpit area. They can drop the temp. something like 20* F or more. I've used them under fabric awnings when the air temp. was 110* and it felt more like 80*, very refreshing. With a diaphragm water pump driving it, it used about 4 or 5 gph.
I've seen these in Florida restaurants. They are nice. I wonder how they would be used all day.

Originally Posted by Jim Woodall View Post
A cruising couple with more than a decade of experience in the tropics swears by the shade-over-shade method. At anchor one might mistake their 45' monohull for a small circus tent, but it is almost always tolerable, even on the days with no wind, and very comfortable onboard their boat if there is even a wisp of wind. They use a fabric shade that covers virtually the entire deck, cabin top, and bimini. The shade is a couple of feet above boom level and leaves plenty of room to move around on the side decks. The times I've been onboard their boat at anchor, I've been amazed at how cool it feels throughout the boat and cockpit. It's a custom-made shade (maybe ShadeTree?), but they love it and say it was worth the expense.

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I can see the benefit of this. I shade all the windows, where most heat comes in and that made a huge difference inside. An awning will do the same thing. It will also shade the decks and if they are teak get really hot. I reckon the underside of my balsa cored decks get to about 40 deg C. This is actually not really noticeable on the underside of the headlining, but I haven't measured it. Will have some effect of course. A big downside though is you can't sail with it. A double skin bimini with window screening would probably get most of its effect.

Originally Posted by Neptune's Gear View Post
We added flexible solar panels directly on the bimini (Sunbrella Navy blue). It made a surprising difference - way cooler with the panels on top! :-)
An IR blocker that earns its keep. Maybe a good solution too. The take down issue could be solved maybe with lightweight flexible solar on dzus fittings or similar, maybe insulated on the back to reduce radiated heat.

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Old 08-08-2014, 07:40   #32
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Re: Keeping Cool Under the Bimini

Our previous bimini was dark blue. Although it provided plenty of shade, on a hot day you could feel the heat radiating from it -- so even though the underside was in the shade, I would wear a hat to protect my head from the heat.

Someone suggested misting the cockpit with freshwater. We do something similar, but with our sea-water washdown. I find that if I hose down the (teak) decks, the evaporation cools the decks, the cabin and even the cockpit a bit. It takes very little power to run the washdown pump (maybe 5A @ 24V for 5 minutes), but provides welcome relief. (the latent heat of vaporization is significant) Ideally the system would mist itself. I'm laughing at the thought of running a lawn sprinkler on deck

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Old 08-08-2014, 08:03   #33
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Re: Keeping Cool Under the Bimini

It's the radiant heat that provides most of the heat load. Up to 1.2 kW / m^2.

Comfort is dependent on temperature, humidity and air flow.

Taking measurements and experimenting is good.

Simplest tweak is to shade the shade. This will negate the effect of color.

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