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Reefmagnet · 13-11-2015, 05:40

Quote:

Originally Posted by Muckle Flugga

Yeah well, if that were true mate, then the water would just sit there, sloshing around the deck now, wouldn't it? Funny that dozens of liters of it will just evaporate in 2 to 5 minutes, taking much of the deck heat along with it eh? Where do you think it is all going? And no, I have pretty much never seen a situation where this is not effective, having lived on boats in the tropics for a decade or so, all round the world including along the tropical coasts of your fair country.

If the decks become substantially hotter than the surrounding air then of course the water will evaporate and cool the heated surface. So what you say is correct.

On a hot day or if the deck is retaining excess heat, your system works because it cools the deck which cools the cabin by reducing heat radiation. However, at night, wetting a deck that is at or near ambient temperature in no or light breeze is more likely to have no effect at all, and even possibly have the opposite effect because the increase in water vapour raises the adjacent relative humidity to some degree which is more than likely to permeate to the cabin decreasing the cooling efficiency of the occupants inside with no benefit from a cooling of the deck.

See, I don't disagree with your theory, I'm just saying it's not an efficient method of cooling in the context of sleeping on a boat at night in the presence of high humidity.

There are also quite a large number of boats that have decks that don't substantially heat up under the tropical sun and therefore add little radiated heat to the cabin. On my boat, for instance, the deck is fine but the hatches are the worst offenders when closed as they create their own greenhouse effect. No amount of sloshed water will fix that.

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Dennis.G · 13-11-2015, 05:45

Quote:

Originally Posted by Moonos

... an absolute gun marine trimmer, possibly the best in Sydney....

WTF is a "gun marine trimmer"??

Reefmagnet · 13-11-2015, 05:48

Means he's pretty good at at

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valhalla360 · 15-11-2015, 01:35

Maybe someone has dark colored decks and that's why spraying water on them helps. For your typical white fiberglass decks, it just doesn't do much of anything in a humid tropical environment, that's the reality that physics tells us.

Also back to the bug issue for a minute: If the wind is cranking 15-20kts, bugs aren't an issue. Most of the bitey ones aren't strong fliers. It's when the wind drops below 5kts that they get bad and thats also when screens really kill off the breeze and make the cabin stifling.

Can you survive in the tropics withour air/con? Sure but if you have a choice, why would you?

Muckle Flugga · 15-11-2015, 02:20

Quote:

Originally Posted by valhalla360

Maybe someone has dark colored decks and that's why spraying water on them helps. For your typical white fiberglass decks, it just doesn't do much of anything in a humid tropical environment, that's the reality that physics tells us.

Also back to the bug issue for a minute: If the wind is cranking 15-20kts, bugs aren't an issue. Most of the bitey ones aren't strong fliers. It's when the wind drops below 5kts that they get bad and thats also when screens really kill off the breeze and make the cabin stifling.

Can you survive in the tropics withour air/con? Sure but if you have a choice, why would you?

It works best with teak, but your grasp of physics seems a trifle shaky there, mate. Are you suggesting that painting something white prevents transfer of thermal energy into a liquid???

Have you actually tried what I am suggesting and have done for years in the tropics (including on light coloured nonskid and white gelcoat), or are you just going off a hunch and your ideas about "physics"?

As to the bugs. Screens work fine with me. Have lived for a long time on boats in the tropics mate, and they do not kill the breeze entirely, even in fairly light stuff, and believe me are better than having mosquitoes biting crap out of you all damn night. Or else what is your preferred solution? Bitten to death but marginally cooler?

valhalla360 · 15-11-2015, 04:14

Quote:

Originally Posted by Muckle Flugga

It works best with teak, but your grasp of physics seems a trifle shaky there, mate. Are you suggesting that painting something white prevents transfer of thermal energy into a liquid???

Have you actually tried what I am suggesting and have done for years in the tropics (including on light coloured nonskid and white gelcoat), or are you just going off a hunch and your ideas about "physics"?

As to the bugs. Screens work fine with me. Have lived for a long time on boats in the tropics mate, and they do not kill the breeze entirely, even in fairly light stuff, and believe me are better than having mosquitoes biting crap out of you all damn night. Or else what is your preferred solution? Bitten to death but marginally cooler?

Nope, with a white deck, it simply doesn't get significantly hotter compared to the surrounding air, so it doesn't create evaporative cooling effect and the water isn't significantly cooler than the deck so it doesn't absorb any significant amount of heat. I grasp the physics just fine, thank you.

Now if you have an outdated teak deck, yes, it can get drastically hotter as it absorbs heat but a light spray won't absorb much heat. It may make the surface of the teak cool enough to stand on for a few minutes but I'll bet it has negligible effect on the amount of heat that makes it into the boat.

Even spraying it down periodically will still likely leave a teak boat hotter than an equivilent boat with white fiberglass decks. So if the goal is to keep a boat in the tropics, it makes sense to get one with white decks.

Muckle Flugga · 15-11-2015, 04:52

Quote:

Originally Posted by valhalla360

Nope, with a white deck, it simply doesn't get significantly hotter compared to the surrounding air, so it doesn't create evaporative cooling effect and the water isn't significantly cooler than the deck so it doesn't absorb any significant amount of heat. I grasp the physics just fine, thank you.

Now if you have an outdated teak deck, yes, it can get drastically hotter as it absorbs heat but a light spray won't absorb much heat. It may make the surface of the teak cool enough to stand on for a few minutes but I'll bet it has negligible effect on the amount of heat that makes it into the boat.

Even spraying it down periodically will still likely leave a teak boat hotter than an equivilent boat with white fiberglass decks. So if the goal is to keep a boat in the tropics, it makes sense to get one with white decks.

Both get plenty hot, and teak does get hotter. Water works with both in exactly the same way it works with your (presumably) white skin. I think you are just arguing for its own sake as it is plain to me you have not actually tried this over any extended period. Why even talk about "betting"? I have done this for a long time (with boats of varying decks including pure white plastic) and yes, it works, and yes, it is obviously aligned with basic physics. Now please answer my two questions if you want to carry this on: do you sail at or near the equator for extended periods; and have you actually tried this? Or are you just arguing to be argumentative and not speaking from experience?

And if you acknowledge that such a practise cools a surface significantly and very noticeably at the same time as RAPIDLY evaporating tens of litres of water, then what kind of magical process do you think is involved, that you consider as no effect on the total amount of heat transferred? And you speak of physics?

valhalla360 · 15-11-2015, 05:08

Quote:

Originally Posted by Muckle Flugga

Both get plenty hot, and teak does get hotter. Water works with both in exactly the same way it works with your (presumably) white skin. I think you are just arguing for its own sake as it is plain to me you have not actually tried this over any extended period. Why even talk about "betting"? I have done this for a long time (with boats of varying decks including pure white plastic) and yes, it works, and yes, it is obviously aligned with basic physics. Now please answer my two questions if you want to carry this on: do you sail at or near the equator for extended periods; and have you actually tried this? Or are you just arguing to be argumentative and not speaking from experience?

And if you acknowledge that such a practise cools a surface significantly and very noticeably at the same time as RAPIDLY evaporating tens of litres of water, then what kind of magical process do you think is involved, that you consider as no effect on the total amount of heat transferred? And you speak of physics?

Betting because we aren't silly enough to buy a boat with teak decks so I don't have one handy to test with. Reality is the vast majority of those 10's of liters just run off the deck taking away little if any heat.

We've tried spraying the white decks and the thermometer in the boat showed no measurable change. As far as heating up outside surface to the point that it's hot to walk on...just not an issue with a white deck.

Now if you are in a desert, low humidity environment, I can buy it. My parents had a swamp cooler in thier arizona place and it worked very nicely. No one uses swamp coolers in florida because they don't work in high humidity.

Muckle Flugga · 15-11-2015, 05:15

Quote:

Originally Posted by valhalla360

Betting because we aren't silly enough to buy a boat with teak decks so I don't have one handy to test with. Reality is the vast majority of those 10's of liters just run off the deck taking away little if any heat.

We've tried spraying the white decks and the thermometer in the boat showed no measurable change. As far as heating up outside surface to the point that it's hot to walk on...just not an issue with a white deck.

Now if you are in a desert, low humidity environment, I can buy it. My parents had a swamp cooler in thier arizona place and it worked very nicely. No one uses swamp coolers in florida because they don't work in high humidity.

You have to measure over a significant period in like conditions, and most importantly measure the underdeck over similiar conditions with and without cooling. Your "thermometer in the boat" is not going to register that in any immediate sense. Do it diligently in the tropics and particularly in the truly torrid zones and it definitely makes a difference. Main reason it isn't done? People can't be bothered. And … ha ha. why try spraying white decks if there was no heat issue whatever? As to the "desert" I refer you to my earlier answer: evaporative cooling DOES work in the tropics, in circumstances where the dew point has not been reached, as it has mostly not and most certainly not on or near a sun exposed deck… (otherwise we would all die as we could not lose heat by exactly the same mechanism!) and no most of it is not just running off because I can actually see what I am doing with the pair of eyes in my head. So your 'reality is' statement is based on nothing. From your post I notice you didn't answer my other question, so I take it you sail in Florida, which is NOT in the tropics.

As to your "silly enough" statement… are you just trying to be offensive and ridiculous? Why are you even arguing this so hard? I have found, through long experience, that this works. It is a bit of a pain in the arse to do, but it works and contrary to what you would like to believe its function is obviously supported by basic physics. So what are you trying to say to me in fact?

valhalla360 · 15-11-2015, 05:57

Quote:

Originally Posted by Muckle Flugga

You have to measure over a significant period in like conditions, and most importantly measure the underdeck over similiar conditions with and without cooling. Your "thermometer in the boat" is not going to register that in any immediate sense. Do it diligently in the tropics and particularly in the truly torrid zones and it definitely makes a difference. Main reason it isn't done? People can't be bothered. And … ha ha. why try spraying white decks if there was no heat issue whatever? As to the "desert" I refer you to my earlier answer: evaporative cooling DOES work in the tropics, in circumstances where the dew point has not been reached, as it has mostly not and most certainly not on or near a sun exposed deck… (otherwise we would all die as we could not lose heat by exactly the same mechanism!) and no most of it is not just running off because I can actually see what I am doing with the pair of eyes in my head. So your 'reality is' statement is based on nothing. From your post I notice you didn't answer my other question, so I take it you sail in Florida, which is NOT in the tropics.

As to your "silly enough" statement… are you just trying to be offensive and ridiculous? Why are you even arguing this so hard? I have found, through long experience, that this works. It is a bit of a pain in the arse to do, but it works and contrary to what you would like to believe its function is obviously supported by basic physics. So what are you trying to say to me in fact?

Sorry but I did it for an entire afternoon, spraying it every 10-15minutes. This was after a month in similar conditions, so I had a good feel for how the cabin temps changed over the course of the day. There was no measurable impact. If the thermometer doesn't drop, it's not making the cabin cooler. It might make you feel better that you are doing something but the numbers don't lie.

A guy with the same boat said it worked, so I figured it was worth a try... It wasn't.

Sorry but 95F and humidity in the 90% range is tropical conditions even if YOU don't consider the area tropical.

Muckle Flugga · 15-11-2015, 06:05

Quote:

Originally Posted by valhalla360

Sorry but I did it for an entire afternoon, spraying it every 10-15minutes. This was after a month in similar conditions, so I had a good feel for how the cabin temps changed over the course of the day. There was no measurable impact. If the thermometer doesn't drop, it's not making the cabin cooler. It might make you feel better that you are doing something but the numbers don't lie.

A guy with the same boat said it worked, so I figured it was worth a try... It wasn't.

Sorry but 95F and humidity in the 90% range is tropical conditions even if YOU don't consider the area tropical.

So you took measurements over the course of an afternoon, and the thermometer didn't drop. Did it rise? 'Cause you know, it sounds like it didn't. Which means…

Physics is physics mate. It isn't really up for debate. But for the record, I have made the same experiment over many days (and done this for years living in the actual tropics) and there is a significant difference particularly later on, when the decks are shedding heat into the boat in the evening. Cooling the decks during the day produces an obvious, noticeable, and measurable difference, as it clearly should, given that physics isn't magic. And no, Fla is not in the tropics. It may be hot, but nowhere near the likes of Indonesia or the equatorial zones wherever. I would never consider "sweating the decks" of a boat way up there. No point. Not worth it. So… given that this entire discussion is about cooling a boat in the tropics (currently speaking to you from 7 Deg N) I don't know why you are on here arguing about a subtropical experiment you performed one afternoon?

valhalla360 · 15-11-2015, 06:11

Quote:

Originally Posted by Muckle Flugga

So you took measurements over the course of an afternoon, and the thermometer didn't drop. Did it rise?

Physics is physics mate. It isn't really up for debate. But for the record, I have made the same experiment over many days (and done this for years living in the actual tropics) and there is a significant difference particularly later on, when the decks are shedding heat into the boat in the evening. Cooling the decks during the day produces an obvious, noticeable, and measurable difference, as it clearly should, given that physics isn't magic. And no, Fla is not in the tropics. It may be hot, but nowhere near the likes of Indonesia or the equatorial zones wherever. I would never consider "sweating the decks" of a boat up there. No point. Not worth it. So… given that this entirel discussion is about cooling a boat in the tropics I don't know why you are on here arguing about a subtropical experiment you performed one afternoon?

Clearly you have it all figured out and air/con manufacturers are about to go out of buisness as swamp coolers take over in humid tropical environments.

I'm done with your magic physics.

Muckle Flugga · 15-11-2015, 06:18

Quote:

Originally Posted by valhalla360

Clearly you have it all figured out and air/con manufacturers are about to go out of buisness as swamp coolers take over in humid tropical environments.

I'm done with your magic physics.

What part of the fact that it was one of 7 steps that I suggested are you now choosing to overlook? It may be less efficient as relative humidity increases, but local relative humidity is pretty low in the presence of extremely heated air.

And… I take it from your silence on the matter that in fact the temperature in your experiment did not rise, over the course of a sunny afternoon. Any thoughts as to why not?

And… I suppose you can just go ahead and stop sweating yourself, as it makes no difference in your version of physics, apparently. Amazing how the millions of people who have no aircon in the actual tropics survive, isn't it? Must be magic.