dock water softners

They help considerably, however you must backflush them every 500-1000 gallons or they stop producing soft water.

In my experience I have found that trying to soften the water before it goes to the tank does not work very well. The tank is usually already contaminated with trace minerals and by the time it comes out of the vessels faucet, it is hard again (and I tested it with the strips before and after). Best to soften the water right after the vessel's water pump. The deck crew always loved that.

He's talking about using it for washing the boat via a hose directly from the softener and they work well for that.

I would never use a softener for filling the water tank. I'd rather have the chlorine and chemicals to keep the tank from growing algae and such.

It depends on what water your tanks are made of. Chlorine is not good for aluminum tanks. So it's better to filter it out as the water goes in.

And some of the larger filters are good for well over 5000 gallons before you have to recharge them.

http://www.yachtmate.com/watersofteners.html

I have used Wet Spot for years. Here in Mallorca it helps a lot due to the hard water we have here. http://www.softwetspot.com/