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Results 1 to 26 of 26
  1. #1
    Join Date
    Sep 2009
    Location
    Sedro Woolley, Washington, USA
    Posts
    4

    Default "What rpms should I be running

    "What rpms should I be running to get max fuel economy, what speed should I expect prom 2400 rpms and should I be running at 3200 rpms for any length of time and what kind of speed should I expect at that rpm."

  2. #2
    Join Date
    Jul 2009
    Location
    Bel Air, MD,
    Posts
    96

    Default "Gary, Need more data. What

    "Gary,
    Need more data. What year and size engine(s)? What size boat (LWL, beam, LOA, weight, etc). What type of hull? What size props? Gear reduction at the transmission? Etc..."

  3. #3
    Join Date
    Sep 2009
    Location
    Sedro Woolley, Washington, USA
    Posts
    4

    Default "Ww, you ask a lot. I thought

    "Ww, you ask a lot.
    I thought 270 was the size.
    1994, 30 foot 13 foot beam 34 foot overall wt? heavy
    fiberglass
    Props? no idea, I should but i don't
    Gear reduction, this is greek."

  4. #4
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    5,630

    Default "The simple answer is found wi

    "The simple answer is found with a vacuum gauge. Your fuel economy will follow your vacuum but not linearly. Once your vacuum falls below 7 to 8", you find the fuel economy curve gets real steep.

    Having a large boat (lots of wet area) that is heavy will only exacerbate the situation. reduction Gear ratio is one way to balance things out."

  5. #5
    Join Date
    Sep 2007
    Location
    Egg Harbor, New Jersey, USA
    Posts
    1,572

    Default "[url=""]http://www.secondchan

    "http://www.secondchancegarage.com/public/186.cfm

    Mark,

    You may have posted tis originally but here it is again...Nice article"

  6. #6
    Join Date
    Mar 2009
    Location
    Dresden, Maine, United States
    Posts
    276

    Default "Gary, My 25' alglas with

    "Gary,
    My 25' alglas with 9"beam, 350 chevy and a 1 to 1 velvet drive with a 14x10 left hand prop at 2800 rpm uses about 5 gallons per hour."

  7. #7
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,705

    Default More like 8 to 9 GPH at that r

    More like 8 to 9 GPH at that rpm. Honestly.

    Jeff (Flo Scan user)

  8. #8
    Join Date
    Sep 2009
    Location
    Sedro Woolley, Washington, USA
    Posts
    4

    Default "I am sure you all mean well b

    "I am sure you all mean well but again all greek to me.
    All of it.
    Is there no norm (with some kind of spread) that would give me a hint as to how well my engines, trans, and props are doing?
    I run about 2400 rpms only because if "feels" correct. I am moving about 6 miles an hour. That is terrible.
    If I move to 3200 rpm things jump. I am running about 16 20 miles per hour but I worry that I'm straining the engines and sucking gas like there is no tomorrow."

  9. #9
    Join Date
    Sep 2007
    Location
    Egg Harbor, New Jersey, USA
    Posts
    1,572

    Default "Gary, Unlike an automobile

    "Gary,

    Unlike an automobile, there are SO SO MANY variables that a sticker page listing mileage and fuel consumption is unlikely. There is a fuel burn statistic but that can vary by sea conditions, wind direction, steerage corrections, loading, prop size etc.etc. That figure could vary by over 25% between different days on the same vessel and different operators.

    You might find a target but it just is not the same repeatable result given the "options". I can tell you that my boat used to get.7 nm per gallon and at times runs as low as .4 while burning as much as 48 gph. A fuel computer is a great way to make the first step in saving some $$$. They are not that expensive by comparison

    My friend has the same boat as I do 3 serial digits apart...they were on the assmebly line the same day....he gets about 1.1nm per gallon. IF you can get some figures under your belt and learn more about the props and Wide Open Throttle (WOT) rpm and start to put it all together, you may be able to get a standard for your boat. Then there are things like theoretical hull speed, squatting and all kinds of engineering type s%@t. Check some boating forums and try to get a feel what others may get with the same boat and once armed with enough information, you may get your answer

    Good luck AND DONT GIVE UP !!!!"

  10. #10
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    5,630

    Default "I may have posted it here but

    "I may have posted it here but, truth be known, "found it" on one of the other boards here at MarineEngine.com."

  11. #11
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,705

    Default "I see people with planning hu

    "I see people with planning hull boats plowing along at 6 to 9 mph all the time--and they think they are saving gas! Unless you're running a trawler, your best gas mileage will be below 6 mph. Getting up on plane--fully on plane, so the bow comes back down--will be the next best gas mileage setting since MPG is what it's all about. (Burn the same amount of gas, but go much faster, means better mpg.)

    No way will you harm your engines by running them on plane at 3,000 rpms. You WILL foul plugs and harm them running all day at low speeds, however.

    Jeff"

  12. #12
    Join Date
    Mar 2009
    Location
    Dresden, Maine, United States
    Posts
    276

    Default "No Jeff, 5 Gph at 2800 seems

    "No Jeff, 5 Gph at 2800 seems to be what she runs at, consider my self lucky. Did not use a flow scan Hooked a outboard tank to the engine and ran for an hour and had about a gal left. Idid this several times and same results. Now of course rougher weather will make a differance like so many other things but my low tech fuel use system worked for me. I will do the same thing when I put her in next year with the refreshed engine."

  13. #13
    Join Date
    Jul 2009
    Location
    Bel Air, MD,
    Posts
    96

    Default "Gary, Sorry I didn't mea

    "Gary,
    Sorry I didn't mean to send you into a tail spin. My apologies.
    Based upon your questions and some of the additional information you provided here goes.
    Wide Open Throttle (WOT) - 4600 rpms +/- 200 rpms
    This means that when you smash the throttles your tachs should be reading somewhere in this range. This lets you know your enignes are running at their full potential and that you have the correct props (size and pitch) on your boat.
    If you have a planning type hull your best fuel economy (doesn't mean least burn rate) will be at planning speeds. This is usually somewhere between 3000-3800 rpms. It is generally recommended that you run your cruising speed at no more than 80% of WOT or about 3800 rpms. Now you may be able to maintain planning speed at fewer rpms so this is where you can save a little on gas. Get on plane and then slow down a little. Usually it takes some time with the boat to see how it reacts at different speeds to determine the best cruising speeds/rpms.
    If you have a displacement type hull (which I doubt based upon some of your info) then your maximum fuel economy will be at displacement speeds, usually around 6-8 knots. This is the type of hull that trawlers have and they are very efficient. That is why they have small single diesel engines in them, plodding along sipping fuel.

    Going slow with a planning or semi-planning hull is not efficient and as Fastjeff said would damage your gas engine since they are made to run at higher rpms.

    Hope this helped some. I suggest reading up a little on some boat basics regarding hulls, engines and props. It will help you in figuring out the optimum way to run your boat."

  14. #14
    Join Date
    Sep 2009
    Location
    Sedro Woolley, Washington, USA
    Posts
    4

    Default "Wow, Thank you guys, this was

    "Wow, Thank you guys, this was helpful. My biggest gripe with life in general is that I got into boating late in life and have not had the time to "Live into" all the aspects of boating. IE a very steep learning curve crushed into a smaller time frame.
    It is great to have people such as yourself reinforce what I feel in my heart. My 30 Carver does love to run at around 3200 rmps and seems to scoot very well at that speed and now I feel even better running that fast.
    We are slowly adding "things" each year to make a better boat and experience, I'm thinking some kind of flow meter is next on my list.

    Thank you bunches"

  15. #15
    Join Date
    Jul 2009
    Location
    Bel Air, MD,
    Posts
    96

    Default Shoot yeah! Your good. Go bo

    Shoot yeah! Your good. Go boating and have fun.

  16. #16
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,705

    Default "Paul: A buddy of mine insi

    "Paul:

    A buddy of mine insisted that his gas-guzzling 454 burned "Only 8 gallons an hour". He then "proved" it to me from his log book. "See," he insisted, "I burnt only 16 gallons of gas after running two hours." Uh-huh. Of course, that included starting and warm up time at idle, time spent leaving his slip and the marina, time spent in the no wake zone, then docking, etc. etc.

    In reality, he burnt at least 12 to 15 gph at CRUISING SPEED, and that's what we're talking about.

    Finally, I know of no small block Chevy, Ford or Chrysler that will run at 2,500 rpms ON PLANE and burn less than 8 GPH.

    Jeff"

  17. #17
    Join Date
    Sep 2007
    Location
    Egg Harbor, New Jersey, USA
    Posts
    1,572

    Default "Gary, Sounds like your con

    "Gary,

    Sounds like your confidence level shot up a few points...! Cool

    Jeff....I think my wifes suburban gets 8GPH"

  18. #18
    Join Date
    Jul 2009
    Location
    Bel Air, MD,
    Posts
    96

    Default "Very funny, Al. My Carver&

    "Very funny, Al.

    My Carver's twin 454s easily burn 28 gph (total) at 3600rpms and a 17 kt cruise. I consider myself lucky at only 28 gph. Some boats can easily get into the the low 30s."

  19. #19
    Join Date
    Sep 2009
    Location
    Stamford, Ct, USA
    Posts
    5

    Default I have a 37 silverton converti

    I have a 37 silverton convertible with 1986 454's

    20-22 GPH (floscan) at 2900 rpms -- 12-14knots

    30 GPH at 3200 rpms --15-16 knots

    38-40 GPH at 3600rpms -- 17/18 knots -- rarely run at this speed (did when fuel was $1.5/gallon)

    For long trips I estimate fuel needs at 1/2 mile to a gallon -- underway using gps and floscan I try to get closer to .65 miles per gallon -- unless I am in a hurry and settle for 1/2 mile per gallon

    I have been told its best to run engine at 75% of top end -- 4200 X 75% is 3150 for me

    Boat comes up on plane at 2600 rpm -- doing 10-11knots

    If I run the boat at 9-10 knots I can almost get 1 mile per gallon -- which we did alot of last year when fuel was over $4/gallon !!

  20. #20
    Join Date
    Sep 2007
    Location
    Egg Harbor, New Jersey, USA
    Posts
    1,572

    Default "Greg, When we first got th

    "Greg,

    When we first got the boat we used in rather indiscriminatly crusing at 3300 3400 and had a blast..Our chartplotter GPS showed a speed upwards of 25knots on a Silverton 34C. Towards the end of the first season we hit 31knots on the last day just to see what it would do. It was fast up in that fly bridge.

    The follwing year I had installed a set of the Garmin GFS 10 fuel sensors and brought them into the network display..

    WE ALMOST had a cow on our first run...28 - 32 gph and at WOT near 50 gph...Of course gas that year was $ 4.19...$200.00 an hour to operate this boat...are we NUTS !

    AND after calculating it out..The Suburban does get about 5-6 GPH !"

  21. #21
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,705

    Default Ah-hah! I too have had a few

    Ah-hah! I too have had a few heart-stopping moments when I leaned on the throttles a bit more than necessary.

    Jeff

    PS: My old RV and it's 8 mpg was not bad at all!

  22. #22
    Join Date
    Mar 2009
    Location
    Dresden, Maine, United States
    Posts
    276

    Default "Jeff, My boat is more of a d

    "Jeff,
    My boat is more of a displacment style hull so on plane is a mute point as to get my old gal on what most would consider on plane takes WOT. I generaly am running at 12 knots at 2800 rpm."

  23. #23
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,705

    Default "That's none too shabby fo

    "That's none too shabby for that type of hull. I'll bet it takes the waves really nice as well.

    My next boat might be one of those--don't need to go fast all the time. That's what the dink is for. I slapped a 50 hp Merc on her and she "Looks like the Space Shuttle taking off!" according to my slip neighbors.

    Wait'll they see it with the 65 horse triple on it! Hee, hee, hee!

    Jeff"

  24. #24
    Join Date
    Mar 2009
    Location
    Dresden, Maine, United States
    Posts
    276

    Default "She does ok for a 42 year old

    "She does ok for a 42 year old boat.I used her as an operational facility with the CGaux up till 2003. She has been out of the water since then as I have been putting in a new house as well as getting the work done on her that I wanted to do. Had hoped to get her in this year but did not pan out."

  25. #25
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    12,705

    Default "Another CG Aux guy, eh? Good

    "Another CG Aux guy, eh? Good lad.

    Jeff
    Flotilla 10-2
    Div 5NR
    FSO-IS"

  26. #26
    Join Date
    Sep 2007
    Location
    Egg Harbor, New Jersey, USA
    Posts
    1,572

    Default "Paul, Looks like your rea

    "Paul,

    Looks like your ready to race...Nice weather too"

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