Thread: Helmsman Hacks
View Single Post
Old 11-21-2022, 02:49 PM   #17
Hydraulicjump
Senior Member
 
City: Davis, California
Vessel Name: Off Leash
Vessel Model: Helmsman 38e
Join Date: Apr 2012
Posts: 207
Blackwater Tank: Trust but Verify

Great hacks you all. Here is another poco nada we have done on our boat. When we got the boat, the gauge on the blackwater tank was clearly stuck. Following the advice of Scott we let the tank get pretty full (a guess) and added a cup of Tide then went out and got beat up by a wind-against-tide day to shake things up. Clearly it broke the sending device loose, but we really can't say how full the tank is at any time based on the gauge. And based on a pretty awful experience of a stuck sending device on our Ranger Tug, we are hyper-cautious.

Here is our "calibration" technique. We bought two of these digital counters:
https://a.co/d/793RkXs
and mounted them with double sided tape right next to the flush control panel. Each flush, you add a count.

On our boat we have the Dometic Masterflush and leave it on the lower volume "dry flush" setting in both heads. This puts .45 gallons plus your additions into the 45 gallon waste tank. So conceptually, that is 100 flushes from empty to full, with a subtraction for whatever volume you have added. Conceptually. And testing that would be a disaster. So we just assume .66 gallons per flush and count them up. Then using the classic rule of thirds applied to fuel tanks, when we get to 30 gallons (roughly 45 flushes) combined it is time to pump out with room to spare.

And what we have found so far is the tank gage is non-linear and is not to be fully trusted until you measure it with the counter. And then, keeping track of flushes is useful to see if it is stuck again.

Scott has pointed out that cleaning the sending device is easy if unpleasant, so that is certainly an option. Not ready for that one just yet.

More hacks! Would love to hear rule of thumb relationships on differences between port side and starboard side fuel levels to level the boat (ours has a small list to starboard due to weight on that side of the boat) and how much to trust the fuel gauges.



Jeff
__________________
Time and tides wait for no one. It is just a whole lot easier to deal with both if you are in a boat.
Hydraulicjump is offline   Reply With Quote