Converting Holding Tank to Fuel Tank? CD 31

[jen1722terry]

Hello Sailors!

As we've opted to replace our old marine toilet with a composter, we now have a large holding tank unused.

We'd love to get more fuel storage. So, has anyone converted their holding tank to a fuel tank?

The holding tank is in the aft section of the keel, under the engine pan. We 're thinking of using a flexible fuel tank, if allowed.

Can anyone think of reasons to do or not to do this? Any technical advice?

Thoughts very much appreciated,

Jenn & Terry McAdams
Kearsarge, NH
Mahone Bay, Nova Scotia
CD 31 "Glissade". # 33

[Steve Laume]

The biggest deterrent I could think of would be the reduction in re sale value or appeal. Not every buyer would want to deal with the composting toilet. I suppose it would depend upon how long you intended to keep the boat. If you kept the holding tank, the next owner could always switch back to a standard marine head and use the holding tank.

If you are just planning to stuff a flexable tank into the existing holding tank, I would worry about abrasion. I doubt that Cape Dory was very concerned about the finish on the inside of the holding tank. Rough edges could do some damage to the badder over time.

I like the idea of the fuel tank being located so any possible leak would be captured in the engine pan before it could get to the bilge. This gives you the opportunity to catch any fuel before it reaches the bilge where it could be pumped overboard.

If I was going to eliminate the use of my holding tank, I would probably allow that space to become extra bilge capacity. If you added a drain hole in the bottom, it could flood with the rest of the bilge. If you sized it for a deck fill fitting you could always plug it again if you wanted to use it as a holding tank in the future. The pump out line could also be converted for the connection of another bilge pump.

I don't know the regulations or recommendations for fuel stowage but would definitely look into that aspect before making this change, Steve.

[jen1722terry]

Hey, thanks so much for the detailed thoughts, Steve.

Hadn't thought about the abrasion problem with the flexible tank. To get any other tank in there would entail some major glass work.

And we agree about the resale value, though we do intend to remove most of the hoses due to age and plug, but not remove, the seawater seacock for the head. Not a huge project for a new owner to reinstall the hoses. We'll keep the manual holding tank pump and vent line connected and maintained for a flooding emergency.

We've also considered installing an extra fuel tank in the starboard cockpit locker. There's a stout deck already built there for two batteries and the fuel tank for the (soon-to-be-removed) pressurized alcohol stove . The batteries were moved down under the cockpit sole, behind the engine (sealed AGM batteries) by the previous owner. Plenty of room now in the locker and, with plans to cruise down to the Bahamas some winters, the extra 20-25 gallons of fuel will be welcome.

We bought the boat in Annapolis last summer an sailed her up to Portsmouth, NH. Motored, mostly, due to a maddening profusion of northerlies on the nose or no wind at all. Anyhow, more fuel on board would have meant fewer marina stops.

Also, having two separate tanks, we think, has the advantage of being able to isolate a tank that has bad fuel. We're wondering, though, if we'll need two Racor filters and two electric fuel pumps to keep the fuel separate or if we could arrange the fuel lines to go to a manifold with shutoff valves. Maybe not. Much to research/think about.

So, thanks again for the sage advice. Enjoy your winter, and best of luck with your spring launching.

Jenn and Terry McAdams

[distand]

Hello Jenn and Terry

I have a 31 also. I am working on a leaky holding tank. Leaking at bottom of the bulkhead. Anyway I am planning to add a pump to remove contents when offshore. My boat was never fitted with a pump. Can you tell me how yours is setup? Where is the pump, the seacock and does it connect to the clean out line that leads to the deck plate in the cockpit?

Did you decide on an second fuel tank?

Thanks

Don

[jen1722terry]

Hey, Don,

Always nice to hear from a fellow owner of these wonderful CD 31s.

The manual pumpout for our holding tank is on the port cockpit sidewall, just below the forward edge of the the port locker lid. It is the standard Whale pump and matches the other manual bilge pump, using the same handle. The outlet hose from the tank goes to a Y valve mounted just below the cabin sole in the upper bilge, port side, near the aft end of the shower sump. It can be accessed via the little cover with the metal dustpan, near the head door. It will clear the tank in 100 pumps or less. The outlet seacock for this pump is also in this locker, aft end, a bit below the water line.

The head intake seacock is under the head sink, behind the engine raw water intake.

As you know, the shore pumpout is located in the forward end of the cabin sole. We have no plans to alter this.

It's looking like the extra fuel tank will go in the starboard cockpit locker, but we're still considering issues raised in our previous posts.

Hope this answers your questions. We're driving down to the boat this week and we can get some detailed photos, if you like, just tell us what you want.

We may now actually keep the holding tank and plumb it directly to the small fluids holding tank on the new Airhead composter. Others have done this. We intend to do some extensive cruising from Nova Scotia to the Great Lakes and down to the Bahamas, so the little 2-gallon fluids tank on the Airhead will be a pain to empty at times. Just using the big holding tank for fluids, without the many gallons or raw seawater used for flushing, should make pump outs very infrequent. We'll add sugar to keep the odors in check as well as a tank level monitor. Keeping the tank does make sense in terms of resale value. We're not looking forward to replacing the old hoses, but it we're going to keep using the tank for fluids from the Airhead, it's a good use of our time.

That's the plan for now, anyway. It could change.

Question for you: have you considered, or completed, adding more insulation to the ice box? We want to do this and are hoping some other 31 owners can offer guidance. We're think that, as we're switching out the old stove for a new Origo 6000, we would drill holes in the side of the stove compartment in front of the ice box to spray in foam, then add flexible sheets to the sides and back from the cockpit locker. We have to study the box configuration more.

Stay in touch, and do enjoy looking forward to the coming season.

Jenn and Terry McAdams
Kearsarge, NH
Mahone Bay, Nova Scotia
CD 31 "Glissade"

[distand]

Thanks very much for the information

Regarding a fuel tank in the starboard locker I would just add that I recently spent some time removing the shaft and coupling. I really needed the room in both lockers to get under the cockpit floor (actually I had a friend do most of the hard work) - good friend.

I carry a Jerry can but I'm sure you've already thought of that.

I have not done any work on the ice box. When I was shopping around for CD31's I visited one in Charleston that had a refrigeration unit installed in the starboard locker. I believe he had 4 batteries and he was in a slip (plugged in).

If you would not mind taking some pictures that would be great. Do you have two separate waste removal lines (Does the Y valve control whether you are using the pump out deckplate in the cockpit or the overboard discharge?). My cleanout line goes directly from the top of the tank up to the deck plate. I would think that a Y valve there would make sense. Then I could run another hose to wherever I decide to put the thru-hull discharge. I was thinking of using one of the cockpit drain hoses so that I don't need to drill another thru hull (probably not a great idea though).

fyi, I did give a lot of consideration to installing an air head. I spoke with the owner of the company and was pretty set to move in that direction. It seems like a very good unit, particularly if you are doing some cruising. I decided, however, to give one try at fixing the holding tank (the boat came with a brand new head). If it doesn't work I am back to the air head. From reading the various posts on holding tanks I think that leaks are somewhat common. After doing some grinding I can see that the way that the forward bulkhead was attached to the bilge bottom may be the culprit (for me).

thanks much

Don

[jen1722terry]

Hello again, Don,

Thanks for sharing the thoughts.

Re: your recent questions (pasted in below)

"If you would not mind taking some pictures that would be great. Do you have two separate waste removal lines (Does the Y valve control whether you are using the pump out deckplate in the cockpit or the overboard discharge?). My cleanout line goes directly from the top of the tank up to the deck plate. I would think that a Y valve there would make sense. Then I could run another hose to wherever I decide to put the thru-hull discharge. I was thinking of using one of the cockpit drain hoses so that I don't need to drill another thru hull (probably not a great idea though)."

1. Sure, we'll get some photos of our head hoses. We were going to go down today to do some work and measurements for the Airhead install, but too darn cold. Probably make it in about 10 days, and we'll be sure to take some photos and PM them to you.

2. Yes, the Y valve switches the system from deck pump out to overboard discharge. We keep an electrical tie on the Y valve, but not sure it that's legal. May need a padlock.

3. For thru-hull discharge, you may need a new thru-hull hole and seacock. Trying to use one of the cockpit drains sounds risky. You'd probably have to close the drain at the cockpit sole to prevent waste backing up into the cockpit. Also, you pretty much always want those drains open when the boat is in the water, unless you have a full cockpit canvas enclosure to keep the sole dry at all times. I'm sure you know that if you install a new overboard discharge hose and seacock, you'll need a vented loop in the line somewhere to prevent siphoning (you may need to consult someone far more experienced that I for that one).

4. Lastly, did you check the old Cape Dory owners manual? I don't have mine with me now, but I recall they have a diagram of the waste system. Might be a nice compliment to my photos. If you're still stumped, maybe contact Dave Perry up at Robin Hood Marine in Maine. You probably know that that company is the remnants of the original Cape Dory Yachts, and they still have a bunch of folks on site with intimate knowledge of all the boats. They may have thoughts on your proposed changes.

Anyhow, best of luck. We'll get those photos up to you in a couple weeks.

Jenn and Terry McAdams
Kearsarge, NH
"Glissade" CD 31

[Maine_Buzzard]

The manufacturer of the holding tanks (Ronco Plastics, love that name) has a big disclaimer in the catalog-

"DO NOT USE WATER TANKS FOR FUEL STORAGE!!" Capitals and excessive exclamation points are theirs...

I'd tend to agree. The holding tanks are not as tough as a molded diesel tank, as other owners with cracked vent fittings can attest.

[MFC]

Hi Guys -
I just stumbled across this thread. Not much to add other than: I have also been considering turning the massive 40gal(?) holding tank on my boat into a fuel tank. I am not sure if I would / will go to an airhead or simply place a 20gal tank in the head compartment on my 330. I have been having never ending problems with my Raritan Phii (blowing unmentionable stuff out the vented loop when it isn't leaking from elsewhere . . . YUUCCKKK). It seems to me that cutting down on the distance between the head and the holding tank can't be other than a good thing. The aluminum fuel tank is nearing 30 years old and needs polishing too. Anyway, I haven't made a decision yet but I have been chewing on the idea of opening up the top of the holding tank and installing a bladder (after appropriate prep of course). Wacky ideas do seem to love company so . . . figured I'd chime in! Keep us posted.

Matt

[jen1722terry]

Hey Matt!

Someone posted earlier that the insides of the holding tanks are unfinished (as in unsanded) glass and could compromise a bladder tank in short order.

Terry

[MFC]

Thanks Terry. I saw that. This is way down the list (and the list is long) -- if it is even "on the list" it certainly comes after resolving the head set-up. Still, if left with an unused holding tank, I'd still consider converting it for use as a fuel tank. I imagine it would be possible to line or coat the interior of the compartment so that it could be used either with or without a bladder.

Best,
Matt

[JAS]

Great thread
My tank discharge is a straight pipe from near bottom of holding tank to pump out connector in cockpit sole. But there is a t just below sole that leads pipe to the hand pump in the starboard locker. There is a sea cock at the forward inboard corner of the locker for discharge. No valve needed (but non used limb of system must be closed during operation.)
Any photos of airhead install? If my attempted fix of holding tank leak (a quart of barrier coat poured in and sloshed around). Does not seal leak, I'm planning to reexplore airhead.
Thanks

[distand]

Jim just noticed your comment. I recently posted some information on my holding tank fix. You can search for"holding tank relocation". I probably should have made a new post rather than tack on to this one as my fix did not involve relocation. I cut a larger hatch in cabin sole to make the repair.