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saving gas

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Joined: 10/19/2007
Posts: 15
 posted 02/22/2008 11:45 PM  

I have a 21 foot center console with a 150 hp yamaha.
How can I tell what is the best cruising speed to get the most gas mileage. Does it have to do with RPM's??
Any help is greatly appreciated.

After all, gas money doesnt grow on trees.

Joined: 08/23/2002
Posts: 4205
Location: Newton, NH
 posted 02/23/2008 02:35 AM  

You need to determine MPG... Divide your speed (MPH) by your gallons per hour (GPH) and you get MPG..

Whatever speed the MPG is best is your best cruising speed.

If you have no idea it's something you can feel out; my experience with 2-stroke outboards (both DFI and carbed) is it's somewhere around 75% of top speed.


"Kids, don't try this at home."

Joined: 07/09/2006
Posts: 5870
Location: In the Geeerage with bocephus
 posted 02/23/2008 06:45 AM  

First find where your boat feels happy. You know,....that sweet spot that she likes to cruise in. Trim her up, trim her down, adjust your Rpm's, until she lays down comfortable and is performing without any laboring. You'll know it when it feels right. The boat will just hum along.

After knowing how she likes to ride, which changes with the conditions, then you can find out what your burning. One way it to top of your tank. Then take a nice long cruise, the longer the better. The longer you cruise for the more accurate your numbers will be. Try to take a run where you don't have to change speed or slow to a no wake zone. That will effect the numbers. Take notes while your under way. Once back at the fuel dock note your mileage traveled, (either from your charts or more accuratly, a GPS). Top off your tank and note the gallons replaced. Now you have two numbers to your equation, Fuel burned, and miles traveled.

Keep in mind that this will change depending many variables. Wind, currents, wave heights, etc... All the more reason to do this test in different conditions.

Or you could just install a floScan..Smile

It's Five O' Clock Somewhere

A shot of tequila,...... beer on tap,.......a good lookin woman,.....sittin on my lap

Joined: 02/04/2007
Posts: 248
 posted 02/23/2008 09:35 AM  

the $$ way

I haven't done it yet, but a few of the people at my marina have installed a flo-scan. its a gauge that hooks up to your engine that electronically determines your nmpg. personally, I just track how my boat burns fuel at its sweet spot ( as mentioned above ) and found that it likes a certain spot, and I'm getting about 0.85 nmpg at that speed. It is what it is....Shades

Joined: 11/30/2000
Posts: 1456
 posted 02/23/2008 11:09 AM  

fuel burn...

You can spend $300 for a flow scan to dial in what is best but it will take a real long time to make that $300 back before you start saving money or you can just figure that outboards (2 and 4 stroke) run best around 4,000 rpm's plus or minus 100 to 200 rpm's, call it good and just do the math as you use the boat to come up with the best rpm for your boat within that range.

Other than that make sure your boat is propped right, many boats are overpropped out there.

A couple other things you can do to save fuel is if you slip the boat, make sure you don't have a moon-cratered bottom from too many gallons of bottom paint being slapped on year after year. These days most people know you only have to paint every other year in most cases. The bottom should be smooth and clean. A 'mooncratered hull' offers more surface area for more friction/drag that requires more fuel/rpm's to go the same speed as a clean hull.

Another is if you do a lot of drift fishing and always jumping on plane to start another drift, a stingray fin to pop up on plane faster does save a lot of fuel. This is one of the cheapest things you can do to a boat to save some real money, depending how you use the boat. If you don't do a lot of short runs all day long, then the fin won't save you as much but save it will because you will hold plane at a lower rpm. These prove good for most boats with a very small fraction of boats not handling well with one, usually under 17 footers from my personal experience using them on various boats.

Local Motion

Joined: 08/11/2000
Posts: 985
 posted 02/23/2008 02:16 PM  

The need for speed, ... uh MPG

I keep an eyeball on the mph I'm doing for a given throttle setting, I trim it for the fastest speed for the amount of throttle I have.

Turn the boat upside down and see what falls out ... put back only what you need. My boat ends up looking like a contractor's van after a few weeks. I should get a dock box. And I know I won't be doing any engine swaps while out at sea. I swear the boat just grow crap in every corner.

I hold 250 gallons. At 6 pounds per gallon, there's no way I need to top off and carry 1,500 pounds of gas just to putz around the hahbah and find a few birds diving. Now this condensation thing... damm.


Joined: 06/27/2006
Posts: 440
Location: ISLIP, N.Y.
 posted 02/27/2008 09:15 AM  

Saving Fuel!!

Saving Fuel is knowing your boats sweet spot(mph,gph and mpg) as explained above. I have an I/O and I run her between 3,200 and 3,500 rpms. Listen to your engine and you'll know when she is working harder then she needs to. I rarely travel with more than a 1/2 tank of gas unless I'm heading to a destination that I'll need it. Keep a miminumal amount of paint on the bottom of you boat and if it's moon cratering spend the time sanding it down it will be very cost efficient. Planing off use your power trim and tabs to put you on plan. Also limit your load for what ever equipment your don't need or not using for the day stow it away and save space and fuel!!

Catch em up!!!

Joined: 07/09/2003
Posts: 307
 posted 02/27/2008 12:48 PM  

fuel mileage data

Try here:

You might find your exact boat/engine combination, or at least something close enough.

It will give you MPH, GPH, and MPG at a bunch of different RPM's.

If you have the same exact setup, the numbers should be really close to how your boat runs, but things like a different prop, bottom paint, etc will affect the #'s.

Even if your setup is a little different, I'd think that the most efficient RPM given on Yamaha's site will still be close to the most efficient RPM for your boat - maybe give or take a bit on the actual MPG #.

Joined: 08/05/2004
Posts: 235
Location: Great South Bay, NY
 posted 02/27/2008 05:54 PM  

Heard that we'll hit $4.00 at the pump (on land) real soon......can't imagine what it's gonna be on the water!

Choose your fishing days well this year, boys!

Joined: 11/06/2007
Posts: 1206
Location: Bay Shore
 posted 02/27/2008 09:56 PM  

I hear alot of guys say that the best nmpg is at your lowest possible planning speed, but I have not conducted any tests so I would need someone to agree with me. personaly, I would agree with finding that sweet spot. On my boat it's right were fishbust said at around 3800 rpm. Also, if you don't have trim tabs I can't say enough good things about the hydrofoil, or shark fin as fishbust called it. He's right about it being helpfull if you do alot of short runs or if you want to lower your planing speed. but I have found it to be most valubale in moderate seas. (I say moderate because boats like ours can't do heavy seas.) The hydrofoil enabled me to keep the boat on a plane while playing with the throttle back and forth so I don't snap my boat in half. before I got it I felt like the boat was constantly strugleing to stay on a plane in bad weather, every time I backed off the throttle I was pushing water again. I could hear the fuel being sucked out of the tank.

A good day of fishing is anyday without Sea//Tow

19' CC Aquasport
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