Auto-venting ballast tank

Published date: May 16, 2012
  • Boat Type: Boat Type

I added an auto-vent system to my Mac26 M to make shifting between sailing and motoring easier.

1. I replaced the plug in the forward vent with a threaded pipe to 3/4" hose adapter. I screwed the adapter into the opening, with steady pressure to ensure that I didn't strip the opening.
2. When it was about half-way in, I liberally coated the rest of the threads with 3M 5200 sealant, then cranked it the rest of the way home.
3. I attached a length of 3/4" I.D. clear vinyl hose to adapter with two hose clamps.
4. Then I lead the hose forward to the next compartment (cutting a 1" hole between to allow the hose to pass.)
5. The foam blocks in the bow compartment were loosely packed enough that I could easily rearrange to make a route all the way to the front edge of the compartment.
6. I removed the carpeted panel over the nose (just two screws), then removed enough of the foam blocks behind route the hose all the way up to the anchor locker.
7. I installed a 3/4" thru-hull fitting in the anchor compartment at the top edge of the starboard wall of the anchor locker. I mounted it as high as I could to help ensure that water in the locker didn't back up and flow down the hose to the ballast tank.
8. Final step is to cut the hose to length, then attach it to the fitting with two more hose clamps.

Now all I have to do before sailing is ensure that the valve is opened for a few minutes sitting still. The tank floods quickly and easily. I close the valve before raising the sails. When I want to go back to motoring, I just open the valve once more, and start motoring. As soon as I hit 3-4 knots it starts dumping the water quickly from the stern valve.

I'm investigating a water level sensor, hopefully with just a full/empty LED status panel that I can mount on the pedestal. Since I'm going to be using a full-cockpit enclosure for some of my trips, I won't be able to easily look over the stern to tell if water is still draining or not.

Visit my blog with a lot more pictures and modification descriptions at

Published by: menkalos

Model Year: 2012
Photo Caption: Auto-vent ballast tank plan diagram


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