Looking for ideas for holding tank size.

centerline · Dec 13, 2013

4 adults for a week in a 15 gallon tank, I dont think this is do-able... lots of variables here... are you tanking all liquids as well as solids? (im not talking about grey water from the galley)
but if you dont keep some liquid in, it wont pump out....

liquid will fill the holding tank up faster than solids do, and how much "insurance" room do you need.... I mean, what will happen if you fill up before the week is up?... what are you going to do and where is the waste going to go....

the RV industry figures 30 gallon capacity to accommodate 4 adults for a week.... i find this to be pretty accurate but you may squeeze by with a bit less, 20gal minimum, but I personally, wouldnt go thru the trouble of the install with the expectation that it would be an adaquate volume....
I dont even know how to say this, but.... when it comes to pooping, you cant cut corners and scrimp and save, to make or save room for someone else.... you better have the space available for all when its needed, and for the duration, or there is going to be an instant mutiny, and that may be the mild part of it... when someone has to go but its already full to the top, do you think that will stop someone from using it anyway?... you dont need to tell me cuz i already know the answer

and then when the boat heels during a gust....:cry:

the variables include diet, habits, and whether the majority of the liquids go over the side or in the tank...

for this many people and this length of time on a boat of this size, the wagbag system would be so much better with less hassle and no worries about filling the tank early.

centerline · Dec 13, 2013

just an idea... im a normal 6ft, 205lb guy and my wife is 5'2" and 125lbs... i pee over the side a lot. she does not. we have to dump our 5 gallon porta-pottie about every 4 days, when we are cruising without other facilities available for use in between times...

drinking water and staying hydrated with it running thru, and at almost a pint per pee, it will fill the tank up quickly. as for the solids, what goes in has to come out.. so if you have about 2 cups of food on your plate for dinner... well.. you get the point

.

it may not sound like much, but with the volume of flush water it all adds up...

AWalker · Dec 14, 2013

No problem using lake water to flush so long as it goes into a tank, just need to look into your legalities of dumping. Best put in a thru hull for emergencies if your area does not ban having the thru hull.

Steve Dion · Dec 14, 2013

I doubt that you will be on the water for a week without visiting a marina that has a pumpout so why not go with a 15-20 gal tank.

I think you will find that most boaters use seawater (whatever it is, fresh or salt) to flush. I do not think that it is practical to use your on board water to flush. You are probably going to run out of potable water before you fill up your holding tank anyway.

Squidd · Dec 14, 2013

Small boat is going to mean small tanks.. I typically get 4-5 days on a 12 gallon tank with 4 adults

But as mentioned, it's not too difficult to drop into a marina for a quick pump out, more ice and walk the dog..(maybe a shower???)

Also the tank never pumps "compleatly" dry... a bit of fluid stays on the bottom no matter how the fittings are placed... so my 12 is more like a 10 useable...

Joe · Dec 14, 2013

never plumb your fresh water/cooking/drinking water system into your MSD.

Find out what direct discharge regs apply to the area you'll visit. For instance, out here it's 3 miles from shore and marked areas.... so make sure you plumb the boat for a macerator type discharge. Check WM advisor for examples.

30 gallon tank on a 26 foot boat is HUGE... where would you fit it, how do you keep the contents from shifting around...etc.

centerline · Dec 14, 2013

for tank size in gallons, multiply all three dimensions, then divide by 233... (233 cubic inches per gallon)

24x 48x 6" = 29 gallon tank, max volume..

12"x 60x 6 = 18 gallon tank, max volume...

David in Sandusky · Dec 15, 2013

30 gal does 2 for 6 nights

That's what we have experienced with good flush discipline, ("if it's yellow, let it mellow, if it's brown flush it down!") and peeing during the morning swim on a chartered h340 in the North Channel. I think 4 for a week is hard to do.

Flushing is about twice the volume of waste. I've seen a formula to calculate capacity, but don't remember where.

Gudenuph · Dec 15, 2013

David in Sandusky said:
That's what we have experienced with good flush discipline, ("if it's yellow, let it mellow, if it's brown flush it down!") and peeing during the morning swim on a chartered h340 in the North Channel. I think 4 for a week is hard to do.

Flushing is about twice the volume of waste. I've seen a formula to calculate capacity, but don't remember where.

Reduce the flushing volume by pumping dry then erasing the skid marks with a jet of fresh water from a recycled plastic syrup bottle and pump dry again. Very effective after your aim improves.
George

quadrille38 · Dec 15, 2013

finding41 said:
I am going into this with no knowledge of how much waist is produced... I know the galley sink will go over the side. But what ever gets into the toilet... goes in the tank. 30 gal standard... (300lb) If I set it up to flush with lake water I could go with a smaller fresh tank. (Is that legal? To use lake water to flush in the Great Lakes?) That would make the most sense. (I think...) Use the lake to flush and keep the potable for drinking and washing dishes. I'm thinking about weight being a problem for handeling and safety. I do plan to keep the tank as low as possible.

Yes it is legal to use lake water to flush in the Great Lakes. It is not legal to discharge waste into the lakes. In fact it is not even legal to have the ability to discharge. Y valves and the like have to be disabled so that it isn't possible. Very stiff fines and in Canada I've heard reports that they will seize your boat if you are caught having the ability to discharge. One downside of using lake water to flush is that the organisms that grow in water get sucked in, grow in your tank making it get smelly faster. The algae and the like create an interesting biology experiment.

Here is a link to a good summary publication.

http://www.miseagrant.umich.edu/downloads/cmp/11-406-Marine-Sanitation-and-Vessel-Sewage.pdf.

You will see that they clearly state that you must disable the ability to discharge. They point you to the applicable regulations

Peggie Hall HeadMistress · Dec 15, 2013

finding41 said:
I'm planning to add a new manual toilet to my MacGregor 26D. Take a look at the link and you can see the layout. Link: http://sailboatdata.com/viewrecord.asp?class_id=4099
I want to be able to go a week with 4 adults on board and am wondering what size tank I should be looking at.

Impossible with any manual or electric marine toilet. Here's the math: the average adult uses the toilet 5x/24 hours...the average flush water volume from today's basic manual or electric toilet is .5 gallons. That translates to 3 gal/person/day. So you'd need an 85 gallon tank to last 4 adults for a week. (Btw, I've prob'ly posted those stats here at least a dozen times over the years...any of you could easily have found them if you'd bothered to look before posting all those wild guesses).

The best solution for a 26' boat is a self contained system...an "MSD" portapotty. "MSD" means it's a model designed to be permanently installed and pumped out...it's not carried off the boat. The 5-6 gallon models hold 50-60 flushes...still not enough to last 4 adults a week, but you'd have to come in after 3 days for water, ice and other provisions anyway, at which time you'd have it pumped out... so it's large enough to meet your needs. Even better, it has no moving parts, so none of the maintenance required for manual toilets and you don't have to give up a major portion of your storage space for a tank and all the related plumbing...although if you're absolutely determined to have a system that'll let you stay out a full week, you COULD install a separate holding tank and redirect the portapotty's pumpout line to dump into it using a macerator pump...but I can't imagine why anyone would want to complicate a wonderfully simpld system by adding the hassle of maintaining the separate tank and plumbing.

There's been quite a bit of discussion of self-contained systems on this forum...easy find if you use the search terms "self contained system" and/or "MSD portapotty"...search 'em out and then check out the Thetford 550 P
http://www.thetford.com/HOME/PRODUCTS/PortableToilets/PortaPotti550PMarine/tabid/884/Default.aspx
This site has some pretty good prices for it too.

Benny17441 · Dec 15, 2013

The sizing problem is mostly because the volume of water used to flush usually exceeds the volume of waste itself. Some rough calculations lead me to believe that you would need approximately a 25 gallon tank to accommodate four persons for seven days. Sailors are usually beer drinkers so that estimate may need to be revised to 30-35 gallons. Here in the States you can Pee overboard which could considerably reduce the tankage needs but I don't know if that is permissible in Canada. It is not practical to have such a large tank for a 26' boat. (My estimates are the bare minimum, probably Peggie's estimate of 85 gallons is closer to reality, I just know is not possible in a practical sense)

Ron20324 · Dec 15, 2013

I do 2 and 3 day weekends frequently ( with usually 4 people aboard ), and I've decided I can do 12 "people-days" with a 13 gallon holding tank.

centerline · Dec 16, 2013

Peggie Hall-HeadMistress said:
Impossible with any manual or electric marine toilet. Here's the math: the average adult uses the toilet 5x/24 hours...the average flush water volume from today's basic manual or electric toilet is .5 gallons. That translates to 3 gal/person/day. So you'd need an 85 gallon tank to last 4 adults for a week. (Btw, I've prob'ly posted those stats here at least a dozen times over the years...any of you could easily have found them if you'd bothered to look before posting all those wild guesses).

The best solution for a 26' boat is a self contained system...an "MSD" portapotty. "MSD" means it's a model designed to be permanently installed and pumped out...it's not carried off the boat. The 5-6 gallon models hold 50-60 flushes...still not enough to last 4 adults a week, but you'd have to come in after 3 days for water, ice and other provisions anyway, at which time you'd have it pumped out... so it's large enough to meet your needs. Even better, it has no moving parts, so none of the maintenance required for manual toilets and you don't have to give up a major portion of your storage space for a tank and all the related plumbing...although if you're absolutely determined to have a system that'll let you stay out a full week, you COULD install a separate holding tank and redirect the portapotty's pumpout line to dump into it using a macerator pump...but I can't imagine why anyone would want to complicate a wonderfully simpld system by adding the hassle of maintaining the separate tank and plumbing.

There's been quite a bit of discussion of self-contained systems on this forum...easy find if you use the search terms "self contained system" and/or "MSD portapotty"...search 'em out and then check out the Thetford 550 P
http://www.thetford.com/HOME/PRODUCTS/PortableToilets/PortaPotti550PMarine/tabid/884/Default.aspx
This site has some pretty good prices for it too.

in all due respect, just so no one gets the wrong idea, there is a couple things here that is not clear....
even so, that a 5-6 gallon porta-potty may have enough fresh water for 50-60 flushes, (depending on how little water you use per flush) the holding tank is only big enough to hold about a quarter of that, with the waste included...

and I have never studied how a marine toilet works in comparison to a plastic rv toilet, but i know the rv toilet is NOT a metered amount of water on every flush.
and I have owned a couple of different rv's for the last 25 years, and I know for a fact that a 30 gallon tank is plenty to cover 4 adults for a week safely, but this is with an UN-METERED flush cycle...

Stan Breaux · Dec 16, 2013

I think the problem will be the weight.

I had a Mac 26S -- liked it a lot and a camping toilet.

In my mind, the issue here is the weight.

30 gallons of waste and a toilet and a large freshwater tank all weigh a lot for the Mac.

I remember loading my boat down, once, to the point where water started flowing out the top of the ballast tank... meaning the boat was sinking because was overflowing the ballast tank.

I sealed the top of the tank with the drain plug, and it was okay, but it is something to consider.

Just one man's opinion.