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Old 05 May 2015, 11:11   #1
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bilge pump / solar panel solutions?

Hi, newbie here.. i'm just in the process of buying a small rib which i will be fitting out myself. Humber 5m assault with Evinrude 2s 50hp.
as the boat will be kept in a marina all year I'm thinking about fitting a bilge pump with solar charger for the battery top-up. The pump will only be for pumping rain water.
seems like i need to guess how much its going to rain in order to work out what size charger i will need.. Has anyone else been down this route and could you tell me what solution works? i.e. what size solar panel is realistic?
i'm not sure how well a solar charger will work when its raining either!!
Thanks
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Old 05 May 2015, 15:00   #2
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What about spray...?

Anyway 5m x 3m boat = 15sq.m

500mm rain in UK average per year. So 7.5 cu.m or 7500litres. Roughly 2000galons.

That's only 4 hours continuous running on a 500gph pump.
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Old 05 May 2015, 15:04   #3
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Draw is c. 2Amps. So if it was purely rain 8Ah per year. Almost any size panel would do...

I suspect you will ship far more as spray.
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Old 05 May 2015, 15:16   #4
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Originally Posted by ShinyShoe View Post
500mm rain in UK average per year
He's not in the UK. They have a fairly dry summer.

A certain Mod wouldn't have missed that...

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Old 05 May 2015, 15:17   #5
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thanks Shiny, i have been getting to that conclusion - i dont see many solar panels in the marina on small open boats. just worrying about nothing as usual
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Old 05 May 2015, 15:19   #6
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ha Will, good spot
we get our share of flash floods too tho.
but i am looking forward to spinning over to Herm in the summer for an ice cream...
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Old 05 May 2015, 15:42   #7
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Originally Posted by ShinyShoe View Post
Draw is c. 2Amps. So if it was purely rain 8Ah per year. Almost any size panel would do...

I suspect you will ship far more as spray.
You've assumed that the annual rainfall is all in the boat at once, and the pump runs at maximum efficiency. More likely its a stop start process, with a peak draw to "spin up" and then wasted energy pumping air...

Not sure where 500 mm p.a. Comes from CI's can be double that (average is irrelevant it's worst case that matters).

If I was worried about a boat in a marina though I'd look at shore power options rather than solar panel as my first choice. Or fit a cover!
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Old 06 May 2015, 03:55   #8
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Think he's worrying about nothing. If he's at the boat say every two or three weeks it'll never accumulate enough rain water to be an issue, if it's leaking that's another problem and a solar panel's not the solution. However I've seen RIBs moored here that no one has been near for months, full of water, and they seem to survive it ok. Pumped out and off they go
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Old 06 May 2015, 04:51   #9
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or one of these , no power needed Wave powered pump
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Old 06 May 2015, 16:24   #10
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Oh I wasn't necessarily saying its not an issue. I've heard of plenty of people who have found their battery dead... several reasons why that happens:

- Jammed float switch keeps pump on all the time (No solar system will compensate for that!)
- Lots of rain. See below - you need to know if full of water = damage or inconvenience
- Spray / waves. I think is significant
- Frequency of boat use. Can you get by with topping up a bit if not fully

I took a figure from the metoffice website but I can't find the page right now. Re-searching comes up with a different figure on their site! Wiki quotes different data still which is MASSIVELY higher. Climate of the United Kingdom - Wikipedia, the free encyclopedia - some of the regular posters on here will be chaulking up 4,500mm in a year.

So 9 times the figure I quoted and I didn't point out the obvious that Poly did that you don't let the boat fill with a year's water and pump it out. So you don't get the efficiency either. But annually that might mean 36hours of running assuming we are shipping no spray. While thats an average of 3 hours a month not all months are average. Its also not unknown to get "freak" weather events where a months rain falls in a day. You'd need to decide what you want to happen in those situations. Will the boat be damaged by being half full of water?

The Met Office provide monthly data on a map and "helpfully" list a lot of places in winter with >250mm /month, and some with >800mm / quarter. UK climate information - Met Office

I think realistically you might want to assume 500mm per bad month was a possibility - so 8Ah in a bad month from Rain. That will be the same month you don't visit the boat cause the weather is cr@p and the light is poorest so charging is reduced. 8Ah would still be fine. Doubling or even tripping that for inefficiency
would be fine. Doubling that again for spray might be stretching it.

So the other question is what size solar panel were you thinking? If its something permanently attached to A Frame or console then:
- Position not optimal for sun all year round - assume only 50% efficiency (See: Optimum Tilt of Solar Panels) - but may be far worse than this if can't be mounted well even for best winter angle.
- Size is very limiting - 1.5W might be about the right size

In the heaviest rain months (winter) the light will be poorest. Maybe 6-8 hours of decent light and will be some very dull days. The 1.5W is perfect position, with bright sun. Advice I've seen seems to be to assume on a dull day its 50%. So bad position plus bad light takes you to 25% of 1.5W. So 375mW x 6 Hrs = 2.25W/Hr = 187mAh. Over 30 days that would add 5.6Ah of charge to the battery. Over the same period you would be drawing something like 24Ah if its heavy rain, not efficient because of on-off on pump and shipping spray. So you get a net loss of 18Ah from the battery. In a single month thats probably OK - but would question if a loss of 24Ah wasn't also OK. In two months thats 36Ah which is taking a 70Ah battery towards the "discharged" point. Without the solar panel you get there two weeks earlier.

Thats all conjecture. But I doubt 6 weeks vs 8 weeks matters...?

To really know you need to fill your boat to the point the float kicks in and measure the power consumption till the float switches off. Then calculate rain and spray required to activate that and how many times etc, and what power you need to replace that and therefore what solar panel to look at.

Anyway - My message was not so much meant to mean it wont draw that much power rather that rain might not be the biggest issue so calculating for rain rather than spray might not make sense...
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