GPH Question

[Capt' Ron]

This is my first entry. Hopefully I'll find someone who is familiar with my boat. I own a 1977 Harbor Master 40 houseboat with twin Merc 233 gas inboard V-drives with 2-bbl carbs. I'm interested in obtaining approximate gallons per hour rates at different RPM's. I can't seem to find any specs like that. Please feel free to ask questions that may help out.

Thanks - Capt' Ron

 

[mr 88]

Fuel flow meter is what you need . Way to many variables to even get into . The odds of someone having your exact setup and being on this forum are astronomical. Sorry but this is probably info that you will have to find on your own.

 

[Scott Danforth]

as indicated, where to read your fuel flow at any given time is a fuel flow meter.

if you are just looking for maximum fuel burn

your motor burns 0.4 # / HP / Hr if in a good state of tune (nearly all spark ignited internal combustion motors have a BSFC of .4)

fuel in the us is 6.82# per gallons

so for your twin 240hp fords over a 1 hour period at full throttle would be

.4 x 480 x 1 or 192# or about 28.2 gallons per hour

you probably also realized your houseboat doesnt move any faster at full throttle than it does at 1/4 throttle.

 

[Capt' Ron]

Fuel flow meter is what you need . Way to many variables to even get into . The odds of someone having your exact setup and being on this forum are astronomical. Sorry but this is probably info that you will have to find on your own.

Thanks Mr. 88. I figured chances of my desired response were slim for my niche boat. I appreciate your feedback. I'm actually looking at the Interactio Fuel Management System. Typically I run the boat @ around 1500 RPM which gives me 7-9 MPH. Most fuel usage tables/formulas are rating usage at WOT which is of no use to me. Happy New Year!

 

[Capt' Ron]

as indicated, where to read your fuel flow at any given time is a fuel flow meter.

if you are just looking for maximum fuel burn

your motor burns 0.4 # / HP / Hr if in a good state of tune (nearly all spark ignited internal combustion motors have a BSFC of .4)

fuel in the us is 6.82# per gallons

so for your twin 240hp fords over a 1 hour period at full throttle would be

.4 x 480 x 1 or 192# or about 28.2 gallons per hour

you probably also realized your houseboat doesnt move any faster at full throttle than it does at 1/4 throttle.

as indicated, where to read your fuel flow at any given time is a fuel flow meter.

if you are just looking for maximum fuel burn

your motor burns 0.4 # / HP / Hr if in a good state of tune (nearly all spark ignited internal combustion motors have a BSFC of .4)

fuel in the us is 6.82# per gallons

so for your twin 240hp fords over a 1 hour period at full throttle would be

.4 x 480 x 1 or 192# or about 28.2 gallons per hour

you probably also realized your houseboat doesnt move any faster at full throttle than it does at 1/4 throttle.

Thanks Scott! I figured chances of my desired response were slim for my niche boat. I appreciate your feedback. I'm actually looking at the Interactio Fuel Management System. Typically I run the boat @ around 1500 RPM which gives me 7-9 MPH. As you know, most fuel usage tables/formulas are rating usage at WOT which is of no use to me. This will be a new touring business for us so this info is important to know being a significant portion of our operating expenses. Happy New Year!
BTW...are you of the anchor lineage??
Regards, Capt. Ron

 

[Scott Danforth]

if you command only 75hp per motor (very rough estimate at 1500 RPM)

your burn rate is 150 x .4 x 1 / 6.82 is 8.8 gph

very distant shirt-tail relation.

 

[dingbat]

I'm actually looking at the Interactio Fuel Management System.

Very expensive for what it is.
Most of the major electronics manufactures (Garmin, Simrad, Lowrance, Raymarine, etc.) make fuel flow monitoring systems that plug into their chart plotter/ combo units for ~$150.

I noticed that the system has a range and distance til empty function. Note that these functions require you to enter the amount of fuel you put in the tank each and every time to be accurate. Forget one time and it's no longer accurate. I gave up keeping on top of it long ago.

 

[Capt' Ron]

Very expensive for what it is.
Most of the major electronics manufactures (Garmin, Simrad, Lowrance, Raymarine, etc.) make fuel flow monitoring systems that plug into their chart plotter/ combo units for ~$150.

I noticed that the system has a range and distance til empty function. Note that these functions require you to enter the amount of fuel you put in the tank each and every time to be accurate. Forget one time and it's no longer accurate. I gave up keeping on top of it long ago.

Thanks for your input. One of the features that this Interactio system has is a fuel reading gear system that actually hooks to the fuel line to measure exactly how much fuel is fed to the engines. Do you know whether these other systems do the same? One issue that I have is that I don't have a fuel gauge on my 44 year old boat. I have to use a dipstick. I'm looking for accuracy as this being a business, I need to know fuel usage as it's a large part of my operating expense. I'll look into other manufacturers to see whether they're lower cost. Again, I appreciate your thoughts.

 

[Scott Danforth]

Thanks for your input. One of the features that this Interactio system has is a fuel reading gear system that actually hooks to the fuel line to measure exactly how much fuel is fed to the engines. Do you know whether these other systems do the same? One issue that I have is that I don't have a fuel gauge on my 44 year old boat. I have to use a dipstick. I'm looking for accuracy as this being a business, I need to know fuel usage as it's a large part of my operating expense. I'll look into other manufacturers to see whether they're lower cost. Again, I appreciate your thoughts.

they all hook between the tank and the fuel pump

they all are NMEA 2000 gateways for you to connect your fuel sender to

they all require a tank sender. since you dont have a tank sender, you will need one. my recommendation is if you have an extra 1-1/4 nipple on the tank is to use a cork-screw sender.

 

[Capt' Ron]

if you command only 75hp per motor (very rough estimate at 1500 RPM)

your burn rate is 150 x .4 x 1 / 6.82 is 8.8 gph

very distant shirt-tail relation.

they all hook between the tank and the fuel pump

they all are NMEA 2000 gateways for you to connect your fuel sender to

they all require a tank sender. since you dont have a tank sender, you will need one. my recommendation is if you have an extra 1-1/4 nipple on the tank is to use a cork-screw sender.

Thanks again Scott. Have you looked at the Interactio system? It doesn't seem to need to work off an existing sender. This system has it's own integrated Bluetooth sending system and as I understand, nothing else is needed. I've reached out to the manufacturer to get their feedback.

 

[dingbat]

Thanks for your input. One of the features that this Interactio system has is a fuel reading gear system that actually hooks to the fuel line to measure exactly how much fuel is fed to the engines. Do you know whether these other systems do the same?

All the units I mentioned are in-line units. Cut the fuel line somewhere between the fuel tank and fuel pump ti install.

One issue that I have is that I don't have a fuel gauge on my 44 year old boat. I have to use a dipstick. I'm looking for accuracy as this being a business, I need to know fuel usage as it's a large part of my operating expense.

Not sure what this buys you in this scenario.
Back in the days we stopped at the fuel dock on the last trip of the day to top off the fuel tanks for the next morning. Wrote the gallons and cost on a small note pad the owner keep at the helm.

While real time feedback of fuel consumption is a good tool, it’s usefulness is short lived. Learned everything I needed to know in a handful of trips. Rarely if ever pay any attention to it anymore.

The take away from using the unit is that consumption can and does vary wildly from trip to trip depending on conditions. I almost double my fuel consumption running in flat calm compared with 2 foot seas.

Knowing what I know after 6+ years of using one of these devices, I could have gotten the same information topping off the tanks each day for a week and done a bit of simple math to come up with an average daily consumption cost.

Bear in mind that these units are just the sensors. They are connected to an existing chart plotter or plotter/fish finder combo unit that supports N2K communications....pretty much everything sold in the past 5 years

What chart plotter do you have?

Link to the installation manual for my unit

https://static.garmin.com/pumac/GFS_10_Install_Multi.pdf

 

[Capt' Ron]

if you command only 75hp per motor (very rough estimate at 1500 RPM)

your burn rate is 150 x .4 x 1 / 6.82 is 8.8 gph

very distant shirt-tail relation.

All the units I mentioned are in-line units. Cut the fuel line somewhere between the fuel tank and fuel pump ti install.

Not sure what this buys you in this scenario.
Back in the days we stopped at the fuel dock on the last trip of the day to top off the fuel tanks for the next morning. Wrote the gallons and cost on a small note pad the owner keep at the helm.

While real time feedback of fuel consumption is a good tool, it’s usefulness is short lived. Learned everything I needed to know in a handful of trips. Rarely if ever pay any attention to it anymore.

The take away from using the unit is that consumption can and does vary wildly from trip to trip depending on conditions. I almost double my fuel consumption running in flat calm compared with 2 foot seas.

Knowing what I know after 6+ years of using one of these devices, I could have gotten the same information topping off the tanks each day for a week and done a bit of simple math to come up with an average daily consumption cost.

Bear in mind that these units are just the sensors. They are connected to an existing chart plotter or plotter/fish finder combo unit that supports N2K communications....pretty much everything sold in the past 5 years

What chart plotter do you have?

Link to the installation manual for my unit

https://static.garmin.com/pumac/GFS_10_Install_Multi.pdf

I've got a Standard Horizon CP170C GPS Chart Plotter. Learning how to use it now. (link to instruction manual Welcome to StandardHorizon.com).
I'm a bit confused as to your statement claiming twice the fuel consumption in calm seas vs. 2-foot seas. I'll be puttering @ ~1500 RPM = 6-8 mph typically. The Interactio system that I'm eying connects to a phone app. Not sure if it could connect to my chart plotter. I have a bunch of questions for the manufacturer.

 

[dingbat]

I've got a Standard Horizon CP170C GPS Chart Plotter. Learning how to use it now. (link to instruction manual Welcome to StandardHorizon.com).

That is a very old unit. Does not support NEMA 2000 communications. Looks like your stuck with an alternative solution unless you update the plotter

I'm a bit confused as to your statement claiming twice the fuel consumption in calm seas vs. 2-foot seas. I'll be puttering @ ~1500 RPM = 6-8 mph typically.

Wind, current and waves all play a huge roll in fuel consumption. The more resistance to the boat making headway, the more horsepower required to maintain speed and course.

My fuel consumption will almost double between calm and “bumpy” days, even at trolling speeds of 3-7 kts.

 

[Capt' Ron]

That is a very old unit. Does not support NEMA 2000 communications. Looks like your stuck with an alternative solution unless you update the plotter



Wind, current and waves all play a huge roll in fuel consumption. The more resistance to the boat making headway, the more horsepower required to maintain speed and course.

My fuel consumption will almost double between calm and “bumpy” days, even at trolling speeds of 3-7 kts.

Interesting...Can't wait till I begin the business driving my huge streamlined floating cube!!

 

[dingbat]

Interesting...Can't wait till I begin the business driving my huge streamlined floating cube!!

Good luck with your new endeavor

 

[Sea Rider]

If you prop right that cube to run towards its max wot rpm range factory stated which is ? will need to throttle less to maintain same 3-7 knots while saving some gallons of fuel. The killer scenario is proping right the motor to push small/medium loads, other heavy loads as in pic or when constantly varying loads.

Happy Boating​

 

[Faztbullet]

Being a V-drive it most likely has 15x12 props ,one RH and one LH. If boating on a lake GPH will only change with load. If on rivers you will use more fuel going upstream vs down.

 

[Scott Danforth]

With a giant floating box of a displacement hull...... Wind, current, air temp, humidity, and drive trim all impact fuel consumption

 

[Faztbullet]

That is the river cruiser hull will cutter bow....slips thru water better. The earlier models with the 318 Chizzlers and Dana drive would actually plane and run high 20's MPH...same hull