Scooping Freshwater

[sailorboy1]

I just read in a "Things I Wished I Knew Before Starting Sailing" book on interest. It was that to extend your fresh water supply you can scoop fresh water off the top of the ocean after a rain because the seawater is denser so the fresh water floats on top.

Guess it is something to consider when you have been in the life raft a few weeks, but overall I now remember why I stopped reading sailing books!

BUT JUST IN CASE - has anyone tried this (just curious really)

[skipmac]

Never even heard of it before, much less tried it. I think it would take a hell of a rain and a very, very calm sea for that to have a chance of working.

I have read that ships used to take on fresh water off the coast of Florida where fresh water springs discharged off shore There are still a number of springs on land that discharge millions of gallons of fresh water per day but since the aquifer has been pumped down I only know a couple that discharge into the ocean.

[Kenomac]

I doesn't seem possible, the rain would agitate the the surface mixing the two solutions. Like you said, I'd have to be pretty thirsty in a life raft and delirious to try it. Sounds like something for "Myth Busters."

While we're on the fresh water topic, do you have plans to add a watermaker before you head out cruising full time?

[sailorboy1]

Originally Posted by skipmac

Never even heard of it before, much less tried it.

But I read it in a book, it must be right!

[newhaul]

Originally Posted by sailorboy1

But I read it in a book, it must be right!

Not necessarily true was it on the internet if so it has to be true they don't lie on there

[colemj]

I think I need a bigger scoop…

Mark

[roverhi]

Unless it was a real downpour can't see there being enough freshwater layer to scoop. Would need 6" or more of rain in a very short period of time and flat seas for a layer to remain stable.

[Cottontop]

Originally Posted by roverhi

Unless it was a real downpour can't see there being enough freshwater layer to scoop. Would need 6" or more of rain in a very short period of time and flat seas for a layer to remain stable.

And a 6" rain event is inconsistent with calm seas, and if you're in a 6" rain event, just open your mouth, don't need a scoop.

Busted, I think.

[sailorboy1]

I'm still reading that book (I read it at the proper place for it's wisdom). Today I came to another item where he once again mentioned the scooping fresh water thing.

So that's twice in a book, must be doubly right

[evm1024]

Originally Posted by Kenomac

I doesn't seem possible, the rain would agitate the the surface mixing the two solutions. Like you said, I'd have to be pretty thirsty in a life raft and delirious to try it. Sounds like something for "Myth Busters."

While we're on the fresh water topic, do you have plans to add a watermaker before you head out cruising full time?

Sounds like something to keep in mind for life raft survival. The mixing could be minimal and with scooping you need only pull off the top fraction of an inch. Also, you do not need pure fresh water in a survival situation, just water with the PSU (salinity) down enough not to kill you or destroy your kidneys. (water intake needs to be less salty than your urine so that you can rid yourself of the excess salt too)

In terms of mixing we do modeling of the Columbia River where I work and see the salt wedge come 20 plus miles up the river with minimal mixing. Of course the fresh water flows out over the ocean for many miles.

Take a look here: Daily Forecasts | Center for Coastal Margin Observation & Prediction

If nothing else you might be able to place a cloth on the surface and soak up some water in a rain.

desperate measures for sure....

Click on the transects to see the salt wedge cross sections along the channel to see the minimal mixing..

Here: http://www.stccmop.org/datamart/virt...&slice=channel

[Canibul]

Interesting. Says here we can survive on a 2:1 mix of fresh to sea water, and live happily on 10:1, if I understand it.

How Much Seawater Can You Safely Drink? - survival | Ask MetaFilter

Could certainly stretch limited supplies, knowing this. Maybe throw one of these in the ditch bag
Amazon.com : Instant Ocean SeaTest Hydrometer : Aquarium Hydrometers : Pet Supplies

Could have a little sundown mixing ceremony.