Ballast University — Installation Guide

Supra & Moomba Gravity 3 Ballast Upgrade

Full 3-pump reversible ballast conversion for 2002–2008 Supra and Moomba boats.

The factory Gravity 3 system on 2002–2008 Supra and Moomba boats worked fine when it was new. But after two decades of use, that manifold setup is tired — slow fills, weak drains, leaking fittings, and bags that don't hold up anymore. This upgrade strips all of that out and replaces it with a modern 3-pump reversible system that fills faster, drains cleaner, and actually works the way you need it to.

If you've been nursing that factory setup along, this is the fix.

What Gets Replaced

This upgrade removes the entire factory Gravity 3 system — manifold, fill pump, drain pumps, bags, wiring, and fill plumbing. Everything comes out. In its place: three dedicated reversible ballast pumps with direct plumbing to each bag, new wiring from battery to switch to pump, and a new intake through-hull.

What stays: Factory rocker switches, factory through-hull drain fittings, and factory drain hose (repurposed as vent lines in the rear lockers).

Estimated install time: 5–9 hours. Intermediate to advanced skill level. Plan for a full day.

Before You Start

Disconnect the battery before beginning any wiring work. Have a drill, silicone sealant, zip ties, and basic hand tools ready. Read all steps before you pull the first hose.

This is a full system replacement — not a repair. Once you start pulling the factory manifold, there's no going halfway. Commit to the full upgrade.

Open each locker and access the factory ballast bags. Release the factory quick-connect fittings and disconnect every hose from each bag. Roll the bags up and pull them out of the boat.

All factory bags need to be out before you move to the manifold. Don't skip ahead — you need the access.

Disconnect all manifold hoses. Remove the mounting bracket. Remove the factory strainer. There are three electrical plugs to disconnect — unplug all of them. Then pull the entire manifold assembly out of the boat.

Leave the factory through-hull drain fittings in place. You'll still use those in the upgraded system.

Locate the factory fill pump. Unscrew it from the ball valve and remove it completely. This pump isn't reused — set it aside or toss it.

Trace the factory fill hose from the manifold, remove the entire run, and discard it. This hose is not reused in the new system.

In each rear locker, locate the factory drain pump. Remove the inlet hose, remove the outlet hose, and pull the pump out of the boat. Do this for both port and starboard rear lockers. Both factory drain pumps are removed completely.

Part Two

Install the New System

You're installing three reversible ballast pumps — one port rear, one starboard rear, and one center near the V-drive.

All factory ballast wiring gets removed. The only thing you're keeping from the electrical side is the factory rocker switches themselves.

You're adding a new dedicated intake through-hull for the upgraded system.

Mark your intake location and confirm placement using alignment magnets. Drill through the hull. Apply marine silicone to the bronze through-hull flange, then install the bronze through-hull fitting, bronze ball valve, and plastic hose barb fitting. Tighten the full assembly.

Slide a hose clamp over the intake hose, push the hose onto the intake barb, and tighten the clamp. Connect the other end to the intake side of your pump. Repeat for each intake feed as required by your routing.

The old factory rear drain hose gets a second life here — it becomes the rear vent overflow hose.

Disconnect the old drain hose fasteners but leave the through-hull side connected. Trim the hose to proper length. Install a 3/4" quick-connect fitting and clamp it securely. Install labeled shrink wrap and heat it down. Connect the hose to the top vent port on the rear bag.

Repeat this for both rear lockers — port and starboard.

Go through the full checklist before you hit the water:

Once everything checks out, the system is ready for operation. You just gave your Supra or Moomba the ballast system it should have had from the factory.

Need bags, pumps, fittings, or hose for this upgrade? We build boat-specific vinyl ballast bags for Supra and Moomba models and ship within 72 hours.