Ratio of fuel tankage to water to black water tanks

[bowball]

I was curious how boat builders decided to allocate their tankage space. This is especially important for those cruising in no discharge areas like the San Juan’s, where pumping out is essential. Same with water when no water maker is on board.

What do you think is optimal? Above certain thresholds and given whether the boat is designed to cruise coastal or offshore.

And buyers seem to focus on fuel and range and forget water and black water despite the use of the boat.

Helmsman 38E fuel: 400 g. Water 145 g. BW 45 g

Helmsman 43. 500. 200. 60

Helmsman 36. 800. 300. 100.

Nordhavn 41. 900. 300. 70

Nordhavn.43. 1200 300. 50

Nordhavn 52. 1740. 400. 120

Nordhavn 62. 3270. 500. 150

Fleming 55. 1000. 300. 100

Fleming 65. 1700. 400. 330

If you are on a bigger boat doing blue water almost irrelevant as water maker, overboard discharge. But there are an increasing number of no discharge zones, for example Turkey is now allowing boats without holding tanks in popular areas. And obviously more fuel storage means you can take advantage of better fueling situations.

Are boat builders and buyers making the right trade offs?

 

[O C Diver]

It's probably not realistic to factor fuel into your ratio. Increasing speed a knot or 2 could half the number of cruising days between refuelings. As far as waste water, there are several variables (people on board, water consumption per flush cycle, and capturing gray water) that can have a huge impact on frequency of pumpouts. Normally I can easily go a couple of weeks between pumpouts with my 80 gallon holding tank, traveling solo. When at Isle Royale national park, because I'm required to capture gray water, it's maybe a week. While more holding capacity would be nice, my 300 gallons of fresh water seem to match well with my 80 gallon holding tank, unless I need to capture gray water.

Most of the boats you listed are build to order. Maybe you should contact them and see if the tankage is fixed or can be tailored to the customer.

Ted

 

[FWT]

Time. When I ran numbers on the H38 fresh and blackwater tanks both came in at needing attention at about 10 days, for 2 aboard. I figure they match well. Not choosing to push limits, call it a week.

Of course, if cruising waters where one can dump the blackwater overboard and get a watermaker, the limits are just fuel.

 

[SoWhat]

And then there is the Fountain Pajot 43, Fuel-75, water-150, HD-30. Three cabins, 2 heads (each with 15 gal holding tank) $500,000 coastal boat and holding tanks must be emptied daily.

(There is a very convenient valve in each head allowing gravity drop of HT contents.)

 

[bowball]

Most of the boats you listed are build to order. Maybe you should contact them and see if the tankage is fixed or can be tailored to the customer.

Ted

I already have a boat, which has a relatively large BW tank. I was just curious about this after reading the specs on one above that had a smaller one, such that I felt they would have to pump out quite regularly so what was the point of carrying so much fuel in non discharge areas. Consequently I was curious what different manufactures did across the size range and why.

I think buyers focus on range not the other tanks, providing an incentive for boat builders to skew towards relatively larger fuel tanks.

 

[O C Diver]

I think buyers focus on range not the other tanks, providing an incentive for boat builders to skew towards relatively larger fuel tanks.

Not sure that's true. I think if you took the manufacturer's expected use (inshore or offshore), how the vessel is equipped (water maker or not), expected number on board, and expected cruising speed fuel consumption, which tankage became the limiting factor might be very different. As an example, the Flemings are designed to cruise faster with a significantly higher fuel consumption. Fuel may be their limiting factor, not water or holding.

Ted

 

[mvweebles]

I think buyers focus on range not the other tanks, providing an incentive for boat builders to skew towards relatively larger fuel tanks.

Good points. RVers seem to be more atuned to tankage than boaters. I wonder if that's because illegal dumping on a boat is easier to hide vs an RV in a Walmart parking lot?

We carry 200g of water which lasts about 8 days under normal conditions, easily a couple weeks if needed. I used a LectraSan for a while with uneven results though it sure was handy (not legal in NDZ).

I would think 5-7-days capacity for a cruise capable boat. That's fuel, water, and holding tanks. That would mean weekly stops which sounds fine for most. I guess for NDZ crusing, water would be 5-8 gal/day/person. 2-3 black, 3-5 grey. 38-footer would be 2-3 persons onboard (POB), 42-footer 3-5 POB, 48-footer 4-6. Turn the crank on the numbers. Something like that. I would think a builder could advertise being honest with numbers and gain a small competitive advantage.

Peter.

 

[mvweebles]

Not sure that's true. I think if you took the manufacturer's expected use (inshore or offshore), how the vessel is equipped (water maker or not), expected number on board, and expected cruising speed fuel consumption, which tankage became the limiting factor might be very different. As an example, the Flemings are designed to cruise faster with a significantly higher fuel consumption. Fuel may be their limiting factor, not water or holding.



Ted

Fuel is discussed to the umpteenth decimal point so I wouldn't even bother, though at-anchor would be the same. But the other tankage capacities are a bit more opaque. You certainly have to have a general sense of usage and parameters of self sufficiency- I suggested around 5-7 days which feels about right.

I do agree that intended usage is important. NDZ vs open ocean would be the extreme ends. And certainly watermaker is an important factor. I've seen some older larger yachts with 800+ gal of water. Not needed these days with affordable watermakers.

Where I do agree with the OP is there doesn't always seem to be a correlation between tank capacities. Some have lots of fuel and very small holding tanks.

Peter

 

[O C Diver]

I guess for NDZ crusing, water would be 5-8 gal/day/person. 2-3 black, 3-5 grey. 38-footer would be 2-3 persons onboard (POB), 42-footer 3-5 POB, 48-footer 4-6. Turn the crank on the numbers. .

Man am I glad I don't come from a freshwater poor (sailing) cruising background. Less than 10 GPD were be my conservation mode.

Ted

 

[bkcorwin]

Only comment is your numbers for the n62 are not accurate. Generally about 2500-2600 gallons of fuel and that could be increased on some boats if you use the waste oil tank as fuel by another 200 gallons. Also, the typical holding tank on a N62 is only 70 gallons and is the tank under the main engine. I think ours is the only n62 that has two black water tanks in the bustle so we carry 140 gallons of capacity.

I was curious how boat builders decided to allocate their tankage space. This is especially important for those cruising in no discharge areas like the San Juan’s, where pumping out is essential. Same with water when no water maker is on board.

What do you think is optimal? Above certain thresholds and given whether the boat is designed to cruise coastal or offshore.

And buyers seem to focus on fuel and range and forget water and black water despite the use of the boat.

Helmsman 38E fuel: 400 g. Water 145 g. BW 45 g

Helmsman 43. 500. 200. 60

Helmsman 36. 800. 300. 100.

Nordhavn 41. 900. 300. 70

Nordhavn.43. 1200 300. 50

Nordhavn 52. 1740. 400. 120

Nordhavn 62. 3270. 500. 150

Fleming 55. 1000. 300. 100

Fleming 65. 1700. 400. 330

If you are on a bigger boat doing blue water almost irrelevant as water maker, overboard discharge. But there are an increasing number of no discharge zones, for example Turkey is now allowing boats without holding tanks in popular areas. And obviously more fuel storage means you can take advantage of better fueling situations.

Are boat builders and buyers making the right trade offs?

 

[mvweebles]

Man am I glad I don't come from a freshwater poor (sailing) cruising background. Less than 10 GPD were be my conservation mode.



Ted

All relative. When Eric & Sue Hiscock circumnavigated in the 1950s, they carried 40 gals of water (plus rain water collection). My guess is their 30-foot Giles designed 'Wanderer" averaged less than 100 nms per day, so had several >1-month long passages. They had no engine so no fuel. Self-steering vanes had not been invented yet so they hand-steered (or set lines) the entire cruise.

10 GPD of water would be styling in their world.

Peter

 

[bowball]

Only comment is your numbers for the n62 are not accurate. Generally about 2500-2600 gallons of fuel and that could be increased on some boats if you use the waste oil tank as fuel by another 200 gallons. Also, the typical holding tank on a N62 is only 70 gallons and is the tank under the main engine. I think ours is the only n62 that has two black water tanks in the bustle so we carry 140 gallons of capacity.

Yes. Sorry, I wrote down the specs for the N64.

 

[bowball]

Good points. RVers seem to be more atuned to tankage than boaters. I wonder if that's because illegal dumping on a boat is easier to hide vs an RV in a Walmart parking lot?

Peter.

Or the availability of gas stations is easier as is refueling?

 

[mvweebles]

Or the availability of gas stations is easier as is refueling?

Availability of dump-stations for RVs is a BIG topic - only a select number of truck-stops would have them I suppose, and they charge just like many marine pump-out places do. Lot like boats, except RVs can't really dodge the requirements in a way I suspect many boaters do.

Relatedly, we were at a beach-side 'campground' in San Diego a few weeks ago. Man, Californians do 'camping' a lot differently than this Colorado boy does - a bit more like tailgating at the Indy 500 than camping.

As we were leaving, a septic pump truck rolled-through to pump-out a particularly large RV.

Peter

 

[Fletcher500]

I went through all of the tankage numbers for the various boats out there when we made the decision for a new build. Overall, I think the builders do a good job matching things up for the expected use cycles.

Fuel:

We have 500 gals on a Helmsman 43 and I would not want anymore. These are coastal cruising boats so fuel is readily available and I try to run on the lighter side during the Summer anyway to save weight and take on fuel as needed in smaller increments. I have never cruised in AK, so fuel tankage may be more important up there due to accessibility.

The higher fuel tank numbers on the Nordies you quoted make sense. I don't think its needed on the smaller models like the N40 and N41 because 90 plus percent of people with those boats are coastal cruising and have fuel access. But I get it, they market the smaller N’s as go anywhere so they have to include the larger tankage.

Water:

We used our boat for 1 year and found out quickly we needed a water maker. Its not uncommon for us to make 1,500 to 2,000 gals of water in one month when our kids are with us. If tank only, no WM, our 200 gals tank of water would go very rapidly when cruising the offshore islands. By far the largest consumption is the aft shower on the swim step as we are all in and out of the water all day. OTW, 200 gal can go fairly long for 1-2 people with some mindful water conservation and still being comfortable.

Black Tank:

Looks like Helmsman went to a 60 gal tank on the H43 since our build based on your numbers, as we have 45 gals. It has worked fine and I pump it out often. I dont like to discharge in to the ocean unless its needed and do so per local regs, but that is how we get rid of our extra waste when at the Channel Islands.

 

[Delfin]

FWIW....


Some Maine biologists argue that if you want to reduce atmospheric CO2, increase the world's whale population. The reason? Their massive poops are a critical source of nutrients for phytoplankton, which in turn absorb massive amounts of CO2. So, how exactly does pumping black water 3 miles offshore in 600' of water harm the environment?



Dixie Lee Ray, former Governor of Washington, and former head of Atomic Energy Commission, argued in her book 'Environmental Overkill' that the best thing that could be done to improve the marine environment in Puget Sound was for recreational boaters to empty their black water tanks underway. This because Puget Sound was oxygen starved, and black water would feed the phytoplankton who produce oxygen.


Regulators tend to make general rules rather than specific ones. So, a city of 200,000 dumping all sewage out a pipe 50' from shore is highly damaging to the environment, so it is banned, along with prohibitions on boaters whose discharges are arguably beneficial if a little common sense is used.



What is gross to a human is breakfast for thousands of marine species, so methinks that the needed size of BW tanks is a function of where you boat and how interested you are in marine biology.

 

[bowball]

At least Victoria just stopped pumping raw waste into the water.

https://www.cbc.ca/amp/1.5867582

 

[Delfin]

At least Victoria just stopped pumping raw waste into the water.

https://www.cbc.ca/amp/1.5867582

Yep. They were never able to find any contamination as I recall because of the amount of water whizzing by Race Rocks, but they bowed to the popular solution, if not the empirical one.

 

[ronobrien]

I was curious how boat builders decided to allocate their tankage space. This is especially important for those cruising in no discharge areas like the San Juan’s, where pumping out is essential. Same with water when no water maker is on board.

What do you think is optimal? Above certain thresholds and given whether the boat is designed to cruise coastal or offshore.

And buyers seem to focus on fuel and range and forget water and black water despite the use of the boat.

Helmsman 38E fuel: 400 g. Water 145 g. BW 45 g

Helmsman 43. 500. 200. 60

Helmsman 36. 800. 300. 100.

Nordhavn 41. 900. 300. 70

Nordhavn.43. 1200 300. 50

Nordhavn 52. 1740. 400. 120

Nordhavn 62. 3270. 500. 150

Fleming 55. 1000. 300. 100

Fleming 65. 1700. 400. 330

If you are on a bigger boat doing blue water almost irrelevant as water maker, overboard discharge. But there are an increasing number of no discharge zones, for example Turkey is now allowing boats without holding tanks in popular areas. And obviously more fuel storage means you can take advantage of better fueling situations.

Are boat builders and buyers making the right trade offs?

I am refitting my GB36 for retirement cruising/live aboard. I intent to spend some time in the Bahamas where water is expensive and fuel is questionable. I am replacing the water tanks with smaller and I am increasing fuel capacity in a day tank. I also plan to install a water maker, so I have fuel to run the genny and make water more frequently, which is coincidentally better for the W/M membranes. I don't know how the builders come up with their ratios, but my arrangement will be more particular to my intended use.

 

[thataway]

Thoughts on conservation of water:
We have put in bypasses from spigots which were some distance from the water heater, thus would run the fresh water back into the tank until it was warm or hot at the spigot we wanted to use--each use would save up to several gallons of water. All that is necessary is a bypass valve, and a T to put the water back intro the tank via the vent hose.

Move the water heater to the nearest faucet--for example we recently removed a 6 gallon tank, which about 15 feet of "dead water space, with 1/2" tubing, to a 2.5 gallon Bosch water heater tank which was less than 12" from the galley sink and about 3 feet from the shower, which had a mixing valve. We could set the thermostat on the Bosch up to 140* --vs no thermostat on the typical boat water heater.

Use raw water (Often salt) for washing dishes, cooking, flushing toilets and even showering. Then do a quick rinse with fresh water. The most extreme "low water use" was a TransPac race with 10 man crew and 50 gallons of water over 15 days--and we had a couple of gallons left. We did have some extra bottled water for drinking, as well as other liquid refreshments (only one beer or wine allowed with dinner) but all other functions (bathing, brushing teeth) including most cooking was done with salt water. Let the salt dry and brush it off. We put a parallel water system with its own pump and intake in the boats we used for long distance cruising.

Even with water makers, one should know how to diagnose and repair any malfunction.The Extra membranes, filters, as well as critical pumps should be duplicated. On one boat we had a wobble pump, with ceramic valves rather than the usual high pressure Cat pump. The wobble pump was much quieter, it ran at about 800 RPM instead of the 3000 to 3600 RPM of the Cat pump. We were told by Village Marine execs that this was used more commonly on fishing boats etc which had high demands of water use day in and day out. One set of valve replacements on the Cat pump would equal the difference in costs between the two different types of pumps.

 

[ranger58sb]

Not sure that's true. I think if you took the manufacturer's expected use (inshore or offshore), how the vessel is equipped (water maker or not), expected number on board, and expected cruising speed fuel consumption, which tankage became the limiting factor might be very different.

Where I do agree with the OP is there doesn't always seem to be a correlation between tank capacities. Some have lots of fuel and very small holding tanks.

I think manufacturer's expectation is key. If they target a "marina-hopping" market, probably like ours, they'll likely design the boat around that concept.

Our numbers: 700/175/68.

Big honkin' engines. Generator expected to be running all the time when away from shorepower. If the boat was at full pax capacity, water and holding adequate for short stays at anchor... but the generator would probably drive everyone (me) crazy well before reaching the limits.

Probably different from boats designed from the keel up to be away from the docks for longer periods...

-Chris

 

[ronobrien]

Thoughts on conservation of water:
We have put in bypasses from spigots which were some distance from the water heater, thus would run the fresh water back into the tank until it was warm or hot at the spigot we wanted to use--each use would save up to several gallons of water. All that is necessary is a bypass valve, and a T to put the water back intro the tank via the vent hose.

Move the water heater to the nearest faucet--for example we recently removed a 6 gallon tank, which about 15 feet of "dead water space, with 1/2" tubing, to a 2.5 gallon Bosch water heater tank which was less than 12" from the galley sink and about 3 feet from the shower, which had a mixing valve. We could set the thermostat on the Bosch up to 140* --vs no thermostat on the typical boat water heater.

Use raw water (Often salt) for washing dishes, cooking, flushing toilets and even showering. Then do a quick rinse with fresh water. The most extreme "low water use" was a TransPac race with 10 man crew and 50 gallons of water over 15 days--and we had a couple of gallons left. We did have some extra bottled water for drinking, as well as other liquid refreshments (only one beer or wine allowed with dinner) but all other functions (bathing, brushing teeth) including most cooking was done with salt water. Let the salt dry and brush it off. We put a parallel water system with its own pump and intake in the boats we used for long distance cruising.

Even with water makers, one should know how to diagnose and repair any malfunction.The Extra membranes, filters, as well as critical pumps should be duplicated. On one boat we had a wobble pump, with ceramic valves rather than the usual high pressure Cat pump. The wobble pump was much quieter, it ran at about 800 RPM instead of the 3000 to 3600 RPM of the Cat pump. We were told by Village Marine execs that this was used more commonly on fishing boats etc which had high demands of water use day in and day out. One set of valve replacements on the Cat pump would equal the difference in costs between the two different types of pumps.

Do you have any more info on the desalination wobble pump ?

 

[Mac2]

OP: I am also wondering if tankage is considered for ballast and safety i.e. double bottoms. My 500 gallon bow fuel tank and 500ish blackwater tank (directly behind the fuel tank) is centered in the bilge. Not only does it create a double bottom, the added ballast (if needed), can be controlled.

 

[ronobrien]

OP: I am also wondering if tankage is considered for ballast and safety i.e. double bottoms. My 500 gallon bow fuel tank and 500ish blackwater tank (directly behind the fuel tank) is centered in the bilge. Not only does it create a double bottom, the added ballast (if needed), can be controlled.

I am moving many such components around on my boat during refit and ballast/trim COG & COB are all major considerations for me while doing so.