Funny you ask, I am in the middle of that job right now. I did not buy a tank from Catalina, although if I had known they were that cheap I probably would have...

I picked up a used V-shaped tank locally. It fits all the way forward under the V-berth, so that the aft end of the tank is even with the forward end of the access cutout in the berth.

I built a small suport to hold the tank 'level' and then a mini-bulkhead to keep the tank in place. I cut two access ports, one in the middle of the berth over the tank's built-in access port (for cleaning or whatever) and one at the pointy end of the V berth for acess up there. (If you are wondering, the plywood and the fiberglass in the V-berth construction were not bonded together at all, which kind of equals lots of weight for not much strength)

Currently the tank is in position and I have glued the bulkhead in place, but still have to go back and tab the bulkhead to the hull properly so that it will be nice and strong when the tank is full of water. Then paint and plumbing.

Downside to my sytem is that the weight of the tank would really be better as far aft as possible, but I didn't want to give up storage space. Where does the factory tank sit? Which end of the factory tank has the fill port? Mine is on the forward end of the tank which is going to be a tight fit. I think I will put the deck plate for filling it inside the anchor locker to avoid drilling more holes in the deck.

Once the physical install is done I have to run a water line back to the water pump under the galley. Somewhere in that line I am putting an isolation valve so I can properly control which tank I am using - I think I will want to run off the bow tank first so that the boat spends more time in proper trim. My boat already sits bow-down at the dock with nothing in the front!

If your normally bow-down, do you really want the tank level? It seems to me this will result in the tank being tilted forward and you'll always end up with water in the tank that wont come near the output drain which is normally aft. This will eventually get stuff growing in it that you don't want.

As far as valves to select tanks to drain, there was an excellent article on the old website with all the instructions on adding the valves in the cutout under the galley (at least in the MK II).

Mike,
I installed a bow tank in Julandra, in a very similar mode to what Jason has described. I wrote it up for Mainsheet a number of years ago, complete with pictures. If you have the Tech Notes CD, it will be in there. Fiberglass some wooden "cleats" to the hull, and then attach the new bulkhead to them, just in case you ever want to get the tank out. As Chuck mentioned, it would be a very good idea to build a manifold to be able to select which of the three tanks you are drawing from. There's plenty of room under the dry bin or under the stove for a manifold.

Chuck P - The aft end of the ank is still 10" below the front end due to the shape of the tank.

Tom, I thought about making the retaining bulkhead removable, but really if I need to remove this tank it will be a serious enough task that I don't mind doing a little cutting. I'll be able to cut around and leave a 2" flange of bulkhead to re-attach something to if it comes to that, and in the meantime a bonded bulkhead stiffens the boat, which can't be a bad thing.

I have installed the Plastimo flexable tanks (West Marine) in both my C310 and C375. They are very easy to install and can give an extra 40 gal in the V on the C375. They come all shapes and sizes from 13 gal to 52 gal.

Rod Tennyson
Lila Jean