Carpentry in a V hull

[SIBERNUT]

I am totally revamping the excreta management system on Phelps. Major part is installation of the receptacle for said excreta. I have a very nice poly tank that will fit in the fwd bilge area. How should I build a shelf for it in the deep V area? Get it level side to side, fore and aft? Boat is on the hard and not level either way. Measure from existing structure ?

[chilliwackteryx4]

For side to side, you can take gunnel to gunnel measurements under the deck (or any other point across the beam that’s consistent) and find the Center point. Then drop a line to the Center of the bilge and transfer 90 degrees off this vertical line. That will give you level from side to side. For and aft might be a bit trickier, but can you see the waterline on the outside of the hull? If so, an angle finder can be used to find the slope, then use that same angle for the fore and aft slope of the platform.

[Benthic2]

You could use a laser level on any existing flooring, as the floors were level for and aft and side to side.

[Comodave]

You could use a digital angle gauge to measure the deck and see how much it is off level then match the shelf to that angle. Look for the gauge at a woodworking supply store. You just zero the gauge on a level surface then put it on the deck of the cabin to see how far off level it is.

[SIBERNUT]

How about a cheap level glued to a paint stick? Sit it on the cabin floor and shim it to level & glue it there. One for side, one for fore to aft ?

[psneeld]

There isn't necessarily a level, or even major flat spot on a boat even when floating.

That said....just pick the most level, flat spot you think exists and see how many degrees off it is from level in both directions. Then use those same measurements for the tank support. Others before have said the same or similar.

Another way (if possible) would be to build the support structure but only dry fit the final pieces. Then once back in the water, check for level and finish fastening the project after shimming as necessary. This is how I often do things if there is still a way for later on fastening.

Of course it doesn't have to be perfect. the boat tanks have to survive WAYYYY off level for a lot of their lives anyhow.

[SIBERNUT]

Both great suggestions. I just want it as level as I can while the boat isn't moving around so the pump out connection is at a slightly low spot.

[Bacchus]

Originally Posted by SIBERNUT

Both great suggestions. I just want it as level as I can while the boat isn't moving around so the pump out connection is at a slightly low spot.

One suggestion...
On a Carver I owned the holding tank was long and mounted side to side but was not very deep. With 1-1/2" discharge at bottom of side wall pumping out left 1-1/2" in the tank when pump out started sucking air.

The edge of the tank was at the edge of the platform and allowed installation of a PVC trap that allowed emptying the tank. If the trap is on the same side as the pump out fitting standing on that side near the end of pumping pretty much drained the whole contents of the tank.

[SIBERNUT]

Pls explain "PVC trap", like under a sink? Sounds like a great idea, & I have the room.

[Comodave]

Draining from the bottom will get more stuff out of the tank however if the PVC cracks then the tank will drain on its own…. We have a top mounted dip tube on our current boat and it gets almost all of the stuff out.

[SIBERNUT]

Yeah, I would prefer that too. But the fittings already in the tank don't lend themselves to it. Have to remember to put antifreeze in that loop, too after pump out.

[Blues]

My phone has a measurement app with a level function, probably came with the phone.

[Bacchus]

Originally Posted by SIBERNUT

Pls explain "PVC trap", like under a sink? Sounds like a great idea, & I have the room.

Yes... just the U shape let's the discharge hose avoid pulling air until the level is well below the 1-1/2" level than the side discharge.
Dave is correct... a top mounted dip tube cut at a slight angle and at/very near the bottom provides a similar benefit and lowers risk of breakage.
If tank slopes slightly to aft and you place dip tube at the same side as the pump out fitting you can concentrate the last bit of liquid by standing on that side to create a slight list.
If you are ordering a custom tank they will install fittings wherever ever you specify. Even if an existing tank slip fittings are available and easy to install. I've never done it but have read many others that have reported success.

[Comodave]

I have used the Uniseal multiple times and never had any problems.

[Bacchus]

A couple other items to consider...
Vents... the larger the better and short straight runs best. If you can run a vent to both sides better chance that a breeze will create a good flow. Straight thru hulls best to allow back flushing easily with a hose.
If your vent run is longer I'd include a plugged fitting to allow installation of a bubbler if you experience foul tank smells.
IMO the bubbler is the ultimate solution to prevent foul tank odors.
I have details on my Bacchus website in Projects section.

[Comodave]

Yes, a bubbler will kill all the smells coming out of the vent since you will grow aerobic bacteria instead of anaerobic bacteria, the ones that smell. I put in 2 1.5” vents in our current boat. I have done bubblers in 2 previous boats.