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Dashboard - Adjusting gauges and estimating MPG

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  • Dashboard - Adjusting gauges and estimating MPG

    The Faria analog Tilt/Trim gauge does not start moving until the outboard is 1/4 way down and stops 1/4 way from the end. My guess is there is an adjusting screw on the back that lets the tilt indicator be set to the bottom when the engine is all the way down, correct?

    The Faria analog speed gauge does not work all the time. Sometimes, but not always, it does not register until going 15+ MPH, jumps to current speed and then works fine. My guess is there is an air leak in the vacuum line, most likely at the gauge or manifold ends and clipping off a 1/4" at both ends will fix the problem. Either that or the gauge is dirty internally and needs to be taken apart and cleaned or replaced. Am I on the right track?

    Estimating MPG. I have a trip planning program that includes fuel use. The default value is 6.5 MPH / 2.5 gallons. That's 2.6 MPG, WAY too high fuel use. Any guess as to what an 1800 pound 18 foot aluminium bass boat with a 70 HP 4 stroke Yamaha would get at a nominal speed of 10 MPG?

  • #2
    the speedometer is a pitot tube type, clean the tube and pickup. if that doesn't work, the gauge bourdon tube may be tweaked

    if you want 10mpg in a boat, add a sail or a dozen slaves with oars like the vikings did

    2.6 mpg is not bad. best your going to get is maybe 5 miles per gallon, and that is with the wind and current at your back.

    idling along will get you the most fuel economy, however take a month to get anywhere

    fuel economy and boating are two different things.
    1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - http://forums.iboats.com/forum/owner...988-rogue-2420

    Past Boats
    1970 Wooster Hellion - Merc 9.8
    2002 SeaRay 190BR - 5.0 - A1G2 - "Cheasheads in Paradise"
    1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

    What’s behind you doesn’t matter.Enzo Ferrari

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    • #3
      My answers

      The trim gauge is of little value, I've never used one on an outboard, nor have I ever wanted or needed to.

      ​The pitot tube type speedometer is about in the same category, they don't work well at lower speeds and are marginal and untrustworthy at higher speeds. Get a GPS/FF combo.

      ​If you really want to get the best MGP possible, 10MPH is about the worst speed to find it, you need to be going slow at an idle, or on plane and in the sweet spot. The only way to find the best cruising speed is to use a fuel flow monitoring system, there's few out there, but probably not worth the expense for a boat like this one.

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      • #4
        My trim gauges hasn't worked in years. Wouldn't use it if it did. Trim to right running angle by sound and feel.

        Don't have a speedometer. Use combination of gps and paddle wheel speed sensor (trolling).

        Running computerized fuel flow system. When flat, I get 1.9 mpg @ 27 kits. Throw in some wind, wave and tide that number drops to 1.2 - 1.4 mpg @ 20 kts.

        Have experienced less than 1 mile per gallon performance a couple times under adverse conditions.

        Maybe why I have 149 gallon fuel capacity on a 22' boat....lol
        Last edited by dingbat; August 30th, 2017, 06:49 AM. Reason: Change gpm to mpg
        ....

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        • #5
          Originally posted by dingbat View Post
          My trim gauges hasn't worked in years. Wouldn't use it if it did. Trim to right running angle by sound and feel.

          Don't have a speedometer. Use combination of gps and paddle wheel speed sensor (trolling).

          Running computerized fuel flow system. When flat, I get 1.9 gpm @ 27 kits. Throw in some wind, wave and tide that number drops to 1.2 - 1.4 gpm @ 20 kts.

          Have experienced less than 1 mile per gallon performance a couple times under adverse conditions.

          Maybe why I have 149 gallon fuel capacity on a 22' boat....lol
          1.9 gallons per minute? .
          2012 Malibu VTX 5.7 Monsoon 350
          2009 Ram CC 5.7 Hemi

          www.oldjeep.com

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          • #6
            None of my outboards have trim gauges and I don't need one since I can see the engine. However, my I/O has one and its an invaluable tool. When I go over sandbars or the shallows I know exactly when the prop is above the bottom of the boat. Without the gauge I would undoubtedly have hit the bottom more than once.

            My OEM pitot tube speedometer agrees with my GPS and paddlewheel within 1 mph. When it doesn't I clean and/or replace the pitot, and of course check that the tube is air tight. It's been working fine for 33 seasons now.

            My Mercury 4-stroke's sweet spot is 4000 rpm and gets 8.43 mpg at 19.4 mph. The only spot better than that is at 1500 rpm, which equates to 4.5 mph and 11.25 mpg. My boat is a little lighter than yours, and of course the motor is smaller as well. I would guess you could hope for about 6.5 mpg optimum.

            For your Yami I would consider about 2/3 of the max rpm to give the best economy. 10 mph won't cut it, and it wouldn't meet a no-wake zone either.
            2017 Boston Whaler 150 Montauk & Mercury 60 ELPT Command Thrust & Merc 3.5 Kicker
            2015 Yamaha FX Cruiser HO
            1984 Stingray SVB190SS & Mercruiser 3.0 Liter 140 & Evinrude 9.9 Kicker
            1964 Sea Nymph 14R & 1970 Evinrude Sportwin 9.5
            1960 Mulray 100 Dinghy, equipped with Beaver Oars
            1952 Lyman 15' Mid Steer & Evinrude Big Twin 25
            68 Outboards: 1919-2017, representing 11 manufacturers
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            • #7
              Originally posted by oldjeep View Post

              1.9 gallons per minute? .

              I would love to get 1.9 gal/min at 27 kits, knots, or whatever.
              Rich

              1995 Chris Craft 21 Concept (OMC 50FAPHUE)

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              • #8
                Originally posted by oldjeep View Post

                1.9 gallons per minute? .
                Been close to that in gallons per mile...lol
                ....

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                • #9
                  To get a better idea of what fuel consumption is, go the Yamaha web sit and check the tab that says PERFORMANCE BULLETINS. Select the engine you have, select the boat you have (or one similar to it) and then all the performance and fuel consumption data is shown. I ran a check for you and the sweet spot is about 4.5 MPG. And as is true for most outboards (4-stroke or not) you can use the 10% rule for fuel economy. That's 10% of rated horsepower at wide open throttle. 50 HP = 5 gph, 70 HP = 7 gph (actually 6.4 gph for the combo I looked up which was a couple hundred pounds lighter than your rig).
                  Last edited by Silvertip; August 30th, 2017, 08:15 PM.

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                  • #10
                    Sorry, meant what MPG to expect at 10 MPH, not MPG. Are there boat speedometers with an odometer? I have only seen them with an hour indicator.

                    The pitot pickup opening on the outboard is clean but there may be some obstruction further up the tube. Will try to blow out and cut back the tube at the gauge end. When the speedometer works it agrees with the GPS speedometer on the chartplotter. I am selling the boat and want all the gauges to work if possible.

                    As for trimming an outboard to the right running angle by sound and feel, what am I listening and / or feeling for?

                    Thanks Silvertip, will look up the boat / engine combo. Jumping from 2.6 MPG to 4.5 or better at 6.4 would be great news. Will pay attention and see what the actual MPG is.

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                    • #11
                      The trim gauge on my pontoon boat is going in the trash when I pull the boat out this fall. Useless (or would be even if it worked).
                      Bob, Seneca Lake NY
                      '88 Bayliner 1700 Capri bowrider, 85 HP Force O/B, "Sea Weasel"
                      '94 Grumman Fish'N Fun pontoon, 40 HP Merc
                      Want a vessel safety check? Click here. Want to join the Coast Guard Auxiliary? Click here.
                      Disclaimer: Although I am a member of the USCG Auxiliary, the opinions and advice in my replies are my own and do not necessarily reflect CG or CG Auxiliary policy or regulations unless so specified.

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                      • #12
                        It's a little different if you're trying to sell it.

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                        • #13
                          Thanks Silver Tip,

                          Looked up Yamaha performance.The chart of the 3 speeds I typically run at show much better MPG than 2.6.
                          Will pay attention to boating miles and fuel use to see what actual MPG is.


                          PERFORMANCE DATA
                          Yamaha 70 HP 4 Stroke Polar Kraft Aluminium Bass Boat 1800 Pounds

                          RPM MPH GPH MPG
                          2000 6.4 0.9 7.11
                          2500 8.3 1.4 5.93
                          3000 13.1 1.8 7.28

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                          • #14
                            Not sure on your Yamaha but most trim gauges have a sensor potentiometer on the engine that is adjustable. When they do work it's nice to just trim up to a known good point and tweek it from there. My boat never came with a guage so I trim by feel. You want it down for take off then you trim up until it steers lighter and the rpm come up. Too high and the bow will bounce and or if way too high it will allow the prop to ventilate to air causing an over rev. Bring it up on plane and work your trim up to slow so the trim raises RPM. When it stops raising RPM then stop trimming up. Get to your cruise RPM for best milage ( probably 4300-4800) and just bump the trim until it just stops increasing RPM at that particular throttle setting. That's you best trim and Max efficiency. Your trim guage is worthless to get you to the sweet spot but good at remembering about where that is. Wind and load affect trim so bump it up and down often to keep the RPM's up. I'm also in an 18' aluminum boat and will run 130 miles this weekend so max fuel range will be insured with constant trim tweeks. I'll burn 20 gallons at best but will have 28 on board. Your speedometer is old school junk. Use a phone app, GPS or fish finder with MPH on it instead. You can also fool with trim for max MPH at a given throttle setting. That will be max efficiency as well. Good luck on your trip!
                            Arizona

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                            • #15
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                              Trim gauges are particularly handy if you boat much in skinny water. Nice to know where the drive is...
                              Location: West Central Illinois, USA 1997 Larson 186 SEi Bowrider I/O Mercruiser 350 #0F747565 Mag Alpha One Gen II #1A270120 Transom and Deck Restoration Project on my '97 Larson Bowrider

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