How Important/Useful is a Fuel Flow Meter?

Rob & Karen

We are trying to finalize the rigging of a CD22 cruiser. The boat will be used mainly on US inland waterways - rivers and lakes. It will be powered with a single Mercury 115.

We are wondering if a fuel flow meter is a good investment. If so, we would like to buy it up front and have the dealer install it. If not, we can certainly use the cash for other boat needs.

Thanks for any input.

Rob & Karen

drjohn71a · Posted: Thu Jan 25, 2007 10:12 am Post subject:

Fuel flow meters can help you adjust trim, load balance, and rpm's to most efficient combination. However, if you've had one in your auto/truck, you have probably noticed that the reading can vary from 23mpg to 12 mpg and jump up and down. With varying winds, currents, waves, load amounts and load dispositions, it is tough to know exactly what your true total mpg or gal per hr is going to be.

It is handy , though , to find the most efficient planing/cruising speeds for your individual boat set-up. The feel of how much fuel you're saving can be misleading. For example, my TomCat uses much more fuel at slow, displacement speeds, than it does at 22 knots. All my senses make me feel the slower speed is more gentle and more economical, but the flow gauges tell the real story.

Once you know the approximate best speeds/settings for efficiency, though, you'll have little need for the fuel flow gauges unless you're trying some daring feat of long distance cruising far away from a fuel dock.

Since so many C-Brats have done extensive investigation into the most efficient speeds and set-ups for cruising, you could just listen to them and you'd be pretty darned close to what your own individual fuel flow gauges would tell you - unless you have some kind of exotic set-up of engines, weight, etc..

Also, once you've decided upon the speed you want, you can trim the tabs or weight dispositon (forward, aft, starboard, port, etc.) to the best setup by looking and listening for the maximum rpm at any given throttle setting.

John

Alyssa Jean · Posted: Thu Jan 25, 2007 11:31 am Post subject:

Another useful aspect, at least for me on our trip to Ketchikan and back (2300 miles RT) was the fuel guage and fuel used/remaining readout. On the 25 I have a 107 gal fuel tank, but it is under the cockpit floor. There is a fule gauge, but like most boat fuel gauges, very inaccurate. I found that when taking on fuel on the trip I could look at the fuel used readout and tell the fuel dock operator with in 2 gallons of what I would take. And was always right on, usually closer that 2 gallons.

drjohn71a · Posted: Thu Jan 25, 2007 1:41 pm Post subject:

Rob and Karen,

I ordered fuel flow meters with my new TomCat mainly because the TomCat uses about 3-4 times the fuel of a CD 22. The better your economy, the less you might need one. Of course, all of us would like all the information possible, but the returns on a boat that already gets 4-6 mpg would be less than on a boat that gets 1.6-2 mpg.

John

SEA3PO · Posted: Thu Jan 25, 2007 2:36 pm Post subject:

I can't think of anyone that has a 22' that uses a fuel meter... it is so different with a 25' where you use much more fuel and you can't see the level of the fuel... I marked the side of my tanks in 5 gallon increments.. so I can see how fast I am using it, and how much I have remaining....just more stuff to go wrong.

Joel
SEA3PO

B~C · Posted: Thu Jan 25, 2007 3:11 pm Post subject:

I would think that with the price of fuel, a fuel flow meter could potentially be a cause for serious depression.

drjohn71a · Posted: Thu Jan 25, 2007 3:39 pm Post subject:

I should add that, in Suzuki's "fly by wire" option and Honda's "digital guages" option, fuel flow readout is included.

John

tpbrady · Posted: Thu Jan 25, 2007 3:55 pm Post subject:

I've got a fuel flow meter on my 22 and use it quite a bit for more than just fuel flow. The Navman keeps track of fuel flow plus also logs total and trip hours and miles. It is a great indicator of trim and RPM settings. You would think you would get better fuel economy at 16 rather than 22 mph but 22 is a better speed from an economy standpoint at most weights and load configurations. However, I also noticed that I got significantly better economy with some bow down on the trim tabs and up trim on the motor. It sounds counter intuitive in some respects, but that's what the fuel flow showed. To some extent what I am seeing is unique to my setup, but it sure saves a lot of trial and error. I look at it as money well spent.

thataway · Posted: Thu Jan 25, 2007 10:23 pm Post subject:

The fuel flow meters are very easy to install. Be sure that you put them after the filter, and where the flow is vertical, to avoid bubbles being trapped.

The Navman or Lowrance are not expensive--and both can either be used alone or with the respective chart plotters. Not sure if the Lowrance can be used with the Raymarine--but there is a good possibility--if the plugs are conmpatable. (NMEA 2000). Yahama, Honda and Suzuki all have fuel management systems as part of the guage package--and you will have to determine if those are more cost effecient than the add on units.

We didn't see a need for the fuel meters on the 22, but we have used them on most of our larger boats which use more fuel or where we may have marginal fuel capacity.

flapbreaker · Posted: Fri Jan 26, 2007 12:22 am Post subject:

I bought a fuel flow meter for my 22' primarily so I'd have a better idea of range while off shore. Though I suppose one could go take a look at the tank, in rough water conditions that might not be the best of ideas. I view it as just one more piece of information. Oh, and the navman 2100 is super easy to install but then again I have just a single engine. Not sure how it works with twins.

drj · Posted: Sat Jan 27, 2007 10:15 pm Post subject:

If you have twin engines do you have a fuel flow for each one or do you just put one on and assume the other engine at the same rpm is equal. Any tricks and recommendations to installing one?? Any brands to stay away from??
thanks

dan

thataway · Posted: Sat Jan 27, 2007 10:32 pm Post subject:

You want a transducer for each engine. If you use the Lowrance or Navman with their chart plotters (for example) the flow, amount of fuel etc may be read off the chart plotter, and no extra guages are necessary. The flow meters not only tell you current fuel use, but total use, and most can be set to show fuel remaining. After calibration they are quite accurate--1-2%

Bob Austin

Casey · Posted: Sun Jan 28, 2007 6:30 am Post subject:

I use the Navman meter on the CD22 with a Suzuki 90 more than I thought I would. It is surprisingly accurate. (Once, at the Wrangell fuel dock the lad asked how much gas we'd take. Being a bit of a smart ass I said 26.7 gallons ... we took 26.6 as I recall. He was impressed.)

Initially I got the meter to accurately measure fuel consumption with various rpm/prop/load configurations. It was very useful, but I have never quite reached the 4mpg I was hoping-for. As I recall, you can adjust the sampling interval somewhat so the fuel consumption is slightly averaged (30 seconds, one minute, two minutes, etc.). That permits the meter to present more consistent data, but you must let things stabilize for a bit before taking your reading.

Like Tom, I find that using the flow meter plus a bit of bow down trim on the trim tabs and up trim on the motor you can find the "sweet spot" where fuel consumption is best for a given rpm and load. I also found it interesting that with the Suzuki, the best mileage seems to be at 4200rpm, not 4000 (where I normally cruise). I've come close...but I'm still in search of the prop that will allow 4mpg!

Casey
C-Dory Naknek