Currie wrote:I'll let Leon weigh in (pun intended) on his experience. I know he reported good results in other threads. But maybe this is interesting in the meantime.
A while back I was looking at doing a pumpable water ballast (to either the port side or the starboard side). The ballast would be 150 lbs. of water in glassed-in tanks under the rear berth and salon seats. I ran a bunch of numbers to see how much righting action it would add compared to people in the cockpit. Here's one of my pics...
The whole point was to calculate the center of boyancy, and mass of any added weight...people, water ballast, or a weighted daggerboard. Here's some things I came up with.
(BTW - I did the same test for other parts of the cross-section - not just the cockpit - and combined them )...
1.) The water ballast adds about 3 times as much righting (at 30º heel) as a person in the cockpit (150 lbs water same would be the as a 450 lb man in the cockpit).
2.) If caught on the wrong side (unintentional jibe?), water ballast is neutral (at 30º heel) as far as adding or subtracting more heel. Notice how much a person caught on the wrong side contributes to heeling versus the water-ballast.
3.) A weighted daggerboard exceeds that and is more than 3 times as effective as people in the cockpit. Plus it doesn't need pumping when you tack/jibe. One thing though, lead only weighs about 90% of it's "land weight" when it's in the water, so that probably brings us back to an even 3X factor.
At this point I gave up on the complexity of pumpable water ballast and joined the weighted daggerboard fan-club. The mod is a couple of seasons out though. So if any of this is close to right. Leon's 150 lbs of weight in the bottom 15" of the board (that's what I set the pic to), should right the boat about the same as 450lbs of people in the cockpit when the boat is heeling 30º.
(FWIW - I calculated the center-of-boyancy by filling the under-water area of each station in the factory diagrams with a little checkerboard hatch pattern, then picked the spot in each where there was the same number of hatches on the left side as the right - Oy
)
Cheers
~Bob
Resurrecting an old thread, there's a very simple way to do this:
1) Use freshwater tank bags, so there's no modification necessary and its freshwater storage that will conform to the shape of the storage area. Removable bags is probably ideal. You could also just pack water bottles into the area.
2) Load both sides with 150 lbs. of water.
3) Don't bother transferring anything at all on a tack. The water on the low side is neutral to heel at 30 degrees, and the water on the high side counters heel to 450 lbs. of force.
So according to Currie's calculations, simply storing your fresh water (or anything heavy, such as extra chain, blackwater tanks, whatever) along the sides of the hull and as low as possible will contribute to stability.
The only difference between this and the built-in ballast tanks is that they're optimized to be neutral to heel at 20 degrees, where the hull is at its lowest wetted area and therefore lowest drag.
??? Would be a pretty cool mod if one could get a hold of one of these keels and make it fit. Would probably give the same righting power as the water ballast, allowing a sailor to be about 500 lbs lighter if not using water ballast (empty boat 2550 lbs + 650 lb keel= 3200 lbs vs 3700 lbs ballasted boat w/o keel.) plus having the option of adding the water ballast in heavier air and have a very stiff boat. If a Mac could fly full sail in 25 knots wind, it would really haul 
Think about it. 2100 lbs ballst on a boat weighing 4350 lbs. That's a ratio of 48.3% 
