Larger Holding Tank for Catalina 34 MK II

[Stu Jackson]

I just looked at the C355 specs.  The holding tank is 27 gallons.  It may be worthwhile to contact CY and find out where they put it, and how.

[tonywright]

Frederik: Actually the conversion is 14.9881, or 15 imperial gallons . The actual capacity is 12 gallons. This is 20% less than advertised. By most standards that is pretty far off.  Why would they include the thickness of the walls? That would make no sense.

Stu: on the 355 they put the holding tank in some of the space where the fuel tank is on the C34, and opened up the whole depth of that area as a cockpit locker.  It is a vertical tank with a narrow vertical transparent section so you can see how full it is with no need for a sensor kit. Made me wonder where they put the fuel tank though.

Tony

[Fred Koehlmann]

So I finally got back up to the boat, with a load of cardboard and built in place a potential custom tank model. It is basically as long as the B212 tank, but wider, taking in the space where the macerator and through hull fitting would be. (I still need to remove the through hull). The depth is less than the B179 but more than the B212. For the moment I can take the tank out without cutting the opening larger, but once the hose fittings are in place I suspect that I will need to cut the overhang at the forward portion of the locker somewhat.

Does anyone know what clearance is needed if I want to have the input hose right-angle into the tank from the top. The 1-1/2" i/s dia. hose has an o/s dia. of 2". Currently I have allowed 3" at the aft section and 2" towards the forward section (for the vent hose - hopefully a 1" i/s dia. hose). The existing input hose entered from the aft side, which means that as the tank filled to the top the hose would as well.

Here's the tank on top and inside the locker space:

[Fred Koehlmann]

Here are the comparisions between the three tanks...
B179 on the left, B212 in the middle, and the custom build on the right.

[Fred Koehlmann]

...and the other two sides:

[Ken Juul]

Pictures are a great help.  I still think if I were to go to the expense of having a custom tank made I would extend it farther forward and fill the entire area under the seat.

[tonywright]

Great pictures.

Have you calculated the capacity of the mock-up?

Tony

[Fred Koehlmann]

No not yet. I've started to disect the geometry to do the math, but my evenings are usually spent coaxing the kids to do their homework ;-). I hope to finish it this week.

Actually I'm really interested in finding out what sort of room (clearance) I need for the right angle fixture for the input hose (1-1/2" i/s dia.) and the vent hose (1" i/s dia.). The existing T-fixture for the pumpout hose was 4", but I'm hoping that was because its a T-fitting. Currently I've only allowed for 3" thinking that it should be enough. So far, I can't find anything online, but i think I must be searching incorrectly.

On the original B212 tank the input was into the aft upper side (towards outboard) of the tank and the outlet was in the aft lower side (towards inboard). The outlet hose will always have the s!*t sitting in it, but the inlet doesn't have to if it comes in from the top. I'm planning on having the vent at the forward end of the top side (towards the inboard edge). I'd vent it forward and out beind the port storage locker. I'm through with leaks in behind the electrical.

[Peggie Hall]

I'm really interested in finding out what sort of room (clearance) I need for the right angle fixture for the input hose (1-1/2" i/s dia.) and the vent hose (1" i/s dia.). The existing T-fixture for the pumpout hose was 4", but I'm hoping that was because its a T-fitting. Currently I've only allowed for 3" thinking that it should be enough.

That's not enough.  A 1.5" 90 degree fitting needs at least 5" clearance above the tank.  3" is barely enough for 1".

I'd eliminate any tee or y-valve in the tank discharge by putting TWO discharge fittings in the tank...one directly to the deck pumpout fitting, one directly to the overboard discharge pump.

If you'd like to discuss your options in more detail, I'll be glad to help you.

[Fred Koehlmann]

Ouch Peggie! 5" clearance! That's an additional two inches or over 6 gallons (US) less volume in the tank. I guess that is why the B212 tank has the inlet on the side near the top. The existing tank had only about 2" - 3" clearance. Of course the 3/4" i/s dia. vent hose was connected to an elbow that was patly recessed into the tank.

I will be eliminating the T-fitting, but will replace it with a single elbow. We will be sailing Dolphina on the Great Lakes (specifically Georgian Bay) and don't have any plans to take her into a salt environment. (If we ever do, we'd probalby rent.) It is the removal of the macerator and other stuff that is giving us the extra tank space.

Sure, I'd love to discuss any options. I'd like to cover all my possible bases before I commit to the final design. I was planning on having HMP (Holland Marine Products) build the tank. They will do the work for about $945.00 CAN. The tank would be made from 1/2" high density poly, weled construction. They say that they've never had a leak, but are will to test it to 3 PSI and test with soapy water for another $90. I've already checked with Ronco and their tests are also to 3 PSI.

[Fred Koehlmann]

It has been some time but I finally got around to look at the dimension more of the three tanks (existing B212, potential but non-fitting B179, and the custom). I thought I had allowed for adequate space for the fixtures/fittings, but Peggy note has rearrange my sense of reality. I've had to consider dimensional changes to allow for the fixtures. I came up with what I figured to be my idea fixture layout, and then the "practical" layout. In the end we opted to not perform any heavy or overtly visual modifications, and keep the tank in the existing storage locker area. I was going to attach the PDF with the info included, but it seems too big for the site... so I have posted it to a public folder on my SkyDrive (https://skydrive.live.com/redir.aspx?cid=03c397d808384593&resid=3C397D808384593!154&parid=3C397D808384593!152).
I am hoping to talk with HMP this weekend at the Boat Show about it getting it made this coming February. I am still curious about construction material however. Cory has been investigating a stainless tank for considerably less cost than the welded poly tank. I also figure that the difference in material thickness could gain you about 3 US gallons in capacity. However I've been told that what makes stainless rust resistant in an oxygen environment, does not in an oxygen deprived environment. Which apparently is why there is corrosion of the stainless lifelines under the white vinyl covers and why the shrouds weaken at points where the stainless wire/rod get embedded into other fixtures. How much a concern this is I do not know. Our marina apparently does produce stainless tanks for clients as well. While we plan to pump out basically after every weekend, there is always something that remains on the bottom, and I do not fancy the idea of having the tank bottom weaken (probably at the welds) to the point that some wavy storm sail causes the slug stress the tank to fail an spill into the bilge. Does any one have any thoughts about this?

Much thanks, Fred.

[Roc]

Fred,
Ken made a good suggestion a few replies earlier.  Have you considered using the storage area forward of the existing area of the holding tank?  There is a bulkhead between the two areas, but that area would be ideal to use as part of your increased tank capacity.  You would need to confirm with Gerry Douglas about any structural issues if you cut part or all of that section between the two compartments away.

[Ken Juul]

I think that plywood is just the front wall to support the holding tank.  But it perhaps does keep the seat from sagging.  Since the tank must be have room at the top for fittings, perhaps leaving the top part of the plywood in place would suffice.

Should be an easy answer for the engineering department.

[Fred Koehlmann]

Yes Ken,

Kathy and I discussed it. We were torn between loosing easily accessible storage, versus a few (maybe 6 US) more gallons. Remember that the storage area starts to get narrower in the forward area and thus the cross-section is much smaller. Had the electrical switches not been at the aft end of the locker, I would have gone all the way aft. That definitely would have given more volume, but I wasn't ready to re-due the electrical at this point. Definitely both options would work for someone else that is looking at it differently.

Heck, in many ways I wish the tank was under the aft section of the head. Then the run would be really short and we'd have tons of storeage in the settee. But that area is not as accessible for a simple tank replacement job (IMO) or maintenance (hose replacement).

[Roger Blake]

OK...Maybe I missed a thread somewhere...but why not move the holding tank to the vast area under the head sink? In my 1998, there is a ton of unused space there. Could put a large holding tank there, shorten the distance the waste has to go from head to tank, etc. Then, you get storage space back under the port settee...one would have to reroute the macerator...at least on my boat. But would get a much larger holding tank and get storage space back. Maybe there would be a "listing" issue...but that would probably be a lot of crap...so to speak.