Water on roof cooling

[captain flint]

Hi

 

I've come across plenty of chat, both on here and the cut, about pumping water onto the cabin top in hot weather to help keep the boat cool in hot weather. 

 

What I'm really hoping for here is input from those with hopefully first hand experience of this. But second or even third might be better than nothing. 

 

I have come across a those saying it helps, and those saying it didn't, but only a little bit. I've come across a lot of reasonable sounding theorising, both in favour and against the idea. Hence why I'm really hoping for reports of the reality. Quite a lot of variables and nothing beats actual real-world experience. 

 

The usual (theoretical) issues I've seen raised are (iirc):

 

Against:

 

- evaporative cooling works badly in humid air, which might mean it's not great for the UK 

 

- canal water temperature is higher than you might think

 

- causing dirty marks

 

For:

 

- it's going to make some difference, even if just a bit, and every little helps

 

- er... Not sure I can recall much more than that! 

 

In terms of what people have reported of actual use of such a system I've read two accounts that said it achieved no noticeable cooling, one of which mentioned that it made the boat more humid. 

 

I've read one account that said it helped. 

 

I've heard chat of those saying they know of someone who tried it and it didn't make much difference. I've also heard of those that say it did. 

 

NB: I'm aware of the just sitting in a cool pub option! 

 

If I were to try it I guess I'd rig a bilge pump to some hose with holes on each side running along the centre line. 

 

One solution which I reckon would almost certainly work quite well would be to have a white sheet/tarp/sail over the boat, with a gap between the metalwork and the cloth, and the ends of the cloth in the water. Maybe if I had a permanent mooring I would consider that, but it sounds tricky and faffy for a whole bunch of pretty obvious reasons, not least being where to find and where to keep a big enough bit of absorbant cloth (my boat is 50'x10'). 

 

Be great to hear from you. Thanks! 

 

 

[Alan de Enfield]

If you are going to use all that 'lectric running a big enough pump to do what you suggest, you may be better opening the front and back doors and investing in a medium / large fan.

[Kudzucraft]

It would largely depend on how much insulation you have on in the ceiling.  If you have a lot I can't see how it would make any difference.

[Pluto]

The main reason for washing down boats historically was to keep the woodwork damp and watertight. I washed down the decks on my wooden short boat regularly in hot weather - though they still leaked afterwards when it had been really hot. It didn't do much to the cabin temperature, and the insulating effect of wood probably reduces and cooling effect. However, it is effective on the sheets of Kennet, and we do try to dampen them when we are open to the public on sunny days as it does reduce the sauna effect in the hold. Basically, it will depend upon the thermal efficiency of the covering you are wetting.

[Machpoint005]

Rather than faffing with suspect science and Heath Robinson devices, I would think it would make more difference to change the roof colour. Having said that, I wouldn't want a light coloured roof because of the glare when steering. 

 

 

[Tony Brooks]

I have seen boats with garden canes tied across the handrails supporting sheets held clear of the roof. I think that would make more difference, but never tried it.

[LadyG]

47 minutes ago, Machpoint005 said:

Rather than faffing with suspect science and Heath Robinson devices, I would think it would make more difference to change the roof colour. Having said that, I wouldn't want a light coloured roof because of the glare when steering. 

 

 

I'm painting my NB roof today, it's white grey "undercoat" from SML paints marine, similar to Dulux Weathercoat and it's Matt, so less glare, it is very bright at first but tones down soon enough, (moor boat under trees and it will soon be lightly covered with debris DAMHIK ).

I have half portholes and the windows have insulating curtains which make a big difference.

My solar panels probably help, they are 4/6 inches above roof

 

Edited May 28, 2023 by LadyG

[Ronaldo47]

Many years ago I was able to give my children an impromptu mid-morning physics lesson on the effect of colour on heat absorbtion at a lock gate on the Southern Oxford.

 

In the morning sunshine, the black part of the obviously  freshly-painted  wooden beam was bone dry and warm to the touch, whereas the white end of the same beam was decidedly cold to the touch and was still covered with drops of water from the previous night's rain.  

Edited May 28, 2023 by Ronaldo47
typo

[captain flint]

3 hours ago, Alan de Enfield said:

If you are going to use all that 'lectric running a big enough pump to do what you suggest, you may be better opening the front and back doors and investing in a medium / large fan.

 

Hi Alan, thanks for replying

You will no doubt be positively staggered to hear I actually do all that already.

When it comes to power, I've noticed it tends to be hottest on sunny days (I'm very observant ) and my fairly chunky panels would, I think, more than cope with a little bilge pump on top of their current workload (you say "big enough pump to do what you suggest" but I don't think it would need to be that big...? I could be wrong,though. I'm good at that.) 

3 hours ago, Kudzucraft said:

It would largely depend on how much insulation you have on in the ceiling.  If you have a lot I can't see how it would make any difference.

Regular spray foam amount, 20mm or something. I struggle to believe think if the cabin top were able to be kept cool it wouldn't make a big difference, insulation or not.

Obviously, insulation slows down heat loss and gain, but it certainly doesn't eliminate heat. I'm no expert but there are some fairly constant thermodynamic principles to consider here, I think, that - I'm guessing here admittedly -  the insulation aspect is not really that relevant, unless you're talking about fairly short periods of time. I might be very wrong, but currently I would need some convincing that insulation isn't largely a red herring here

2 hours ago, Machpoint005 said:

Rather than faffing with suspect science and Heath Robinson devices, I would think it would make more difference to change the roof colour. Having said that, I wouldn't want a light coloured roof because of the glare when steering. 

 

 

I suppose I could change the roof colour. But it is currently white....

2 hours ago, Tony Brooks said:

I have seen boats with garden canes tied across the handrails supporting sheets held clear of the roof. I think that would make more difference, but never tried it.

Yes, I'm pretty sure that would make a significant difference, especially if the sheets could be kept damp (which would probably just be  question of putting them on damp, and having a corner trailing in the water. Evaporation and wicking would, I think, keep the whole thing damp. And evaporation from that, if kept clear of the roof, would work well, like an old camp fridge. But as I said in my post, faff-heavy

[cuthound]

4 hours ago, captain flint said:

Hi

 

I've come across plenty of chat, both on here and the cut, about pumping water onto the cabin top in hot weather to help keep the boat cool in hot weather. 

 

What I'm really hoping for here is input from those with hopefully first hand experience of this. But second or even third might be better than nothing. 

 

I have come across a those saying it helps, and those saying it didn't, but only a little bit. I've come across a lot of reasonable sounding theorising, both in favour and against the idea. Hence why I'm really hoping for reports of the reality. Quite a lot of variables and nothing beats actual real-world experience. 

 

The usual (theoretical) issues I've seen raised are (iirc):

 

Against:

 

- evaporative cooling works badly in humid air, which might mean it's not great for the UK 

 

- canal water temperature is higher than you might think

 

- causing dirty marks

 

For:

 

- it's going to make some difference, even if just a bit, and every little helps

 

- er... Not sure I can recall much more than that! 

 

In terms of what people have reported of actual use of such a system I've read two accounts that said it achieved no noticeable cooling, one of which mentioned that it made the boat more humid. 

 

I've read one account that said it helped. 

 

I've heard chat of those saying they know of someone who tried it and it didn't make much difference. I've also heard of those that say it did. 

 

NB: I'm aware of the just sitting in a cool pub option! 

 

If I were to try it I guess I'd rig a bilge pump to some hose with holes on each side running along the centre line. 

 

One solution which I reckon would almost certainly work quite well would be to have a white sheet/tarp/sail over the boat, with a gap between the metalwork and the cloth, and the ends of the cloth in the water. Maybe if I had a permanent mooring I would consider that, but it sounds tricky and faffy for a whole bunch of pretty obvious reasons, not least being where to find and where to keep a big enough bit of absorbant cloth (my boat is 50'x10'). 

 

Be great to hear from you. Thanks! 

 

 

 

When I worked for BT the technicians used to hose down the condenser coils of the air conditioning units to improve performance in very hot weather. It saved many a telephone exchange from going off the air when the ambient temperature exceeded 35 degrees Celsius.

[GUMPY]

First hand experience here.

On a previous boat that had crap polystyrene insulation it worked reasonably well.

On my last boat with decent spray foam insulation it made not a jot of difference.

 

So to sum up if you have crap insulation it works 😉

[harrybsmith]

3 hours ago, Tony Brooks said:

I have seen boats with garden canes tied across the handrails supporting sheets held clear of the roof. I think that would make more difference, but never tried it.

 

Very similar to a "tropical roof" which was an option on Land Rovers used in hot climates, effectively another roof skin held about 1" above the normal roof 

[Col_T]

1 hour ago, captain flint said:

Regular spray foam amount, 20mm or something. I struggle to believe think if the cabin top were able to be kept cool it wouldn't make a big difference, insulation or not.

Obviously, insulation slows down heat loss and gain, but it certainly doesn't eliminate heat. I'm no expert

I think that insulation is about minimising the transfer of heat from one side of an insulated surface to the other. Therefore, the more efficient the insulation material, the less the reduction in heat transfer, so cooling a well insulated hot steel roof may not have as great an effect as you might hope.

[captain flint]

16 minutes ago, GUMPY said:

First hand experience here.

On a previous boat that had crap polystyrene insulation it worked reasonably well.

On my last boat with decent spray foam insulation it made not a jot of difference.

 

So to sum up if you have crap insulation it works 😉

Ah! First hand experience - thank you very much! And if you've tried both that sounds, if not utterly conclusive (every boat is different), about as damn close as I am likely to get. Much appreciated 

9 minutes ago, Col_T said:

I think that insulation is about minimising the transfer of heat from one side of an insulated surface to the other. Therefore, the more efficient the insulation material, the less the reduction in heat transfer, so cooling a well insulated hot steel roof may not have as great an effect as you might hope.

Yes it is, but I think it acheives this by being a substance through which heat moves slowly

 

(As I've noted a few times here, though, I'm good at being wrong...  Plus whatever the theory, GUMPY has kindly shared his practical experience, and it very much sounds like it's a waste of time on a spray-foamed boat. I suppose, then, that we can agree that I am least somewhat wrong here, and leave open the possibility that I'm totally and utterly wrong).

[harleyj]

Moor under a tree, wear a hat and drink plenty of water don't spray it on the roof. You Poms are a bit soft!

[captain flint]

38 minutes ago, harleyj said:

Moor under a tree, wear a hat and drink plenty of water don't spray it on the roof. You Poms are a bit soft!

Shade, you say? 

 

Drinking water, you say? 

 

Mind. Blown.

 

Thank god for expats being able to share their experience with us poor old poms, or we'd still be living in caves, eh

 

Though I'm not sure why I would want to wear a hat in the shade. Pretty sure that would just make my head warmer

 

 

[TheBiscuits]

3 minutes ago, captain flint said:

Drinking water, you say? 

 

Have you ever tried Aussie beer?

 

😁

[GUMPY]

Problem for us was being out at work all day the boat was shut up so very hot when we got home.

After the heatwave of 2003 we fitted a roof mounted Aircon which cured the problem 😉

[captain flint]

4 minutes ago, GUMPY said:

Problem for us was being out at work all day the boat was shut up so very hot when we got home.

After the heatwave of 2003 we fitted a roof mounted Aircon which cured the problem 😉

Presumably quite a drain on the batteries?! Then again, I guess hot weather = more solar power

[GUMPY]

12 minutes ago, captain flint said:

Presumably quite a drain on the batteries?! Then again, I guess hot weather = more solar power

In the days before most had solar me included but the 5kVA genset coped well. 

Aircon was 900watt so not that much 

[LadyG]

On 28/05/2023 at 20:34, GUMPY said:

Problem for us was being out at work all day the boat was shut up so very hot when we got home.

After the heatwave of 2003 we fitted a roof mounted Aircon which cured the problem 😉

You could leave the offside windows open, paint the boat grey white, moor where it is shaded after noon day sun, use insulated curtains.

m

My portholes area on the boat are much cooler than window areas, they are not insulated, I have thought about it, bur I think extra window insulation would be more effective, maybe Celotex on sunny side.

[Ray T]

On 28/05/2023 at 18:16, cuthound said:

 

When I worked for BT the technicians used to hose down the condenser coils of the air conditioning units to improve performance in very hot weather. It saved many a telephone exchange from going off the air when the ambient temperature exceeded 35 degrees Celsius.

 

Was that pre 2000 Strowger telephone exchanges?  😁

A opps B opps C...... cannot remember the rest

Edited June 16, 2023 by Ray T

[Dav and Pen]

The majority of Narrow boats have dark or red painted roofs and are probably covered in solar panels, boxes, bags of coal, logs etc so there won’t be many who have tried watering the roof. We went from a red oxide painted narrow boat roof to a Dutch barge with a much bigger roof which was painted a darkish green. I changed this to a light grey as the temperature was often in the mid 30s in central france and I’m sure the colour helped lessen the heat gain in the accommodation I also painted the decks and gunwales the same as these could get unbearable hot. To try and keep the accommodation as cool as possible we kept all the curtains drawn (as is the custom in hot countries) and a fan running. When it got to hot we tried to moor in the shade and sit outside the boat. Our dog used to like laying on the gunwales on the shady side but on a bendy river or canal the shady side kept changing until he got peed off with moving and went downstairs to lay on the Lino floor in the galley.

[IanD]

1 hour ago, Ray T said:

 

Was that pre 2000 Strowger telephone exchanges?  😁

A opps B opps C...... cannot remember the rest

 

Phwooaaah, proper old technology -- just look at the selectors on that... 🙂

[captain flint]

2 hours ago, LadyG said:

 

My portholes area on the boat are much cooler than window areas, they are not insulated, I have thought about it, bur I think extra window insulation would be more effective, maybe Celotex on sunny side.

 

Hmmm. There are special films for Windows which are designed to keep heat out (I'm going to get them applied to my skylight/dogbox windows). They might be good. But I'm not at you can buy the good ones (Vkool, 3M Solar Prestige) for self installation, and not sure installers will be happy with rounded corners on window panes etc. But I might be wrong on both counts there. 

 

But in my experience other insulation just  makes the boat hotter. Following tips from a thread on here from a few years ago, I fitted magnetically attached acrylic secondary glazing to my windows. It's absolutely brilliant in winter, but if I leave it in place in summer it significantly increases the heat inside the boat.