1998 moomba mobuis ballast

I haven't done a custom system in mine, but if you like it hidden, there is not much choice. I sac in the rear ski locker (assuming the gas tank is under your rear seat) and a sac under each bow seat is a good start. The W704 is a pretty good fit for the rear locker, and a pair of W703s for the bow seats. That will give you about 700-800 pounds (the bow sacs will not fill up all the way). The W704s will also fit pretty well under the bow seats, and are easier to plumb in due to the fitting locations. These are the ones that I would use if I were plumbing in a system. I would probably keep the other W704 in the rear, like I have plumbed in now. (My boat came with the rear system and tanks, so I removed the tanks and put a sac in its place.) This would give you about 1000# of built in hidden ballast, and a pretty good wake. I have found that 60% front and 40% rear is a good proportion for weighting these hulls. It does get the bow very low in the water and it is easy to take rollers over the bow. If you wanted even more weight, a W707 will just barely fit in the rear locker (again, if you don't have the fuel tank under there) but it is hard to plumb in since these boats are not very tall. I had this sac plumbed into my boat, but we were always having to mess with it, and I had to install manual shut off valves to keep it from draining by itself. This is an issue with these boats, since the freeboard is not very high, getting vents and such high enough is tough to do. I hope some of this helps.