Results 1 to 16 of 16

Thread: Change of Props to save gas

  1. #1
    Member
    Join Date
    Oct 2007
    Location
    Anchorage
    Posts
    14

    Question Change of Props to save gas

    There is a wealth of knowledge on this forum and I have always recieved good advice here so I have one quick question if anyone out there knows the subject. I push a 22ft Hewescraft with a 225 yamaha 4 stroke, but even at cruising speed (about 4200 rpm or 30 mph) I am still using a whole lot of gas, over 12 GPH. That is with all the shrimping gear and a boat full of kids and their stuff. I run a 19 pitch S/S prop, but I also have a 17 pitch which gets me great speed but drinks the gas. What are your thoughts on increasing pitch, even though it'd slow us down, to save gas. I know what the Yamaha recommendations are for operating range, but with the price of gas, I don't want to have to quit going out because of the gas prices, thanks

    22ft Hewes HT, call sign "Kaya"

  2. #2
    Member ACBMAN's Avatar
    Join Date
    May 2006
    Location
    Anchorage only because that's where the work is
    Posts
    160

    Default

    I have twin 225 yamaha 4 strokes on my 29' ACB, when loaded up with all gear for shrimping\fishing and 4 guys I use 18 gph at 30 mph. I trim motors for best economy.

  3. #3

    Default Prop Info web Sites

    http://www.caravelleboats.com/propeller%20info.htm

    www.piranha.com , which you can try diff pitchs and return the ones that didn't do the best for you.

  4. #4
    Moderator Paul H's Avatar
    Join Date
    Apr 2006
    Location
    Anchorage
    Posts
    5,594

    Default

    If your prop is properly pitched to allow the engine to hit peak rpm's then going to a larger prop isn't going to save you gas, it'll just make the engine work harder to get you on plane and put more wear and tear on the engine.

    I'd recomend investing in a fuel management system, the Lowrance LMF-400 is a decent unit and if you can get a module to communicate with the engine it'll give you fuel flow directly from the engines computer. You'll be able to see how changing the trim and throttle position affects fuel consumption. It cost about the same as an aluminum prop. You might find that your best mileage is obtained at a slower speed, say 25mph with say 3800 rpm. Dropping the speed a bit can have a dramatic difference on fuel consumption.

    You also might want to look at how your boat is balanced in regards to weight in the boat. If you have too much weight forward and the boat is plowing, you'll be burning more gas. Also if the engine is mounted to deep with the trim plate below the bottom of the hull you'll have extra drag and be burning more gas.

  5. #5
    Sponsor potbuilder's Avatar
    Join Date
    Apr 2006
    Location
    Palmer
    Posts
    4,231

    Default

    Paul's advise is right on. Save the money you'd spend on new props and just let off the gas a bit.

    Alaska Shrimp Pots

    Rigid & Folding Shrimp & Crab Pots
    Electra Dyne Pot Haulers
    Ropes, Buoys, Bait
    alaskashrimppots.com
    akshrimppots@mtaonline.net
    907 775 1692

  6. #6
    Member DMan's Avatar
    Join Date
    Oct 2006
    Location
    Wasilla, AK
    Posts
    1,412

    Default Better than that

    Should get better than that. When I had my Hewes I talked to several people with Yamaha 225s that were getting right about 10GPH at 30MPH and they were in the correct WOT range to.

    Do some searches on the Hewes Forum and ask the questions over there.

    http://hewescraft.30.forumer.com/

    Here is one list of Stats a guy posted:

    Following are the fuel stats for my 22' OP HT
    with a Yamaha 225 .

    RPM MPH GPH MPG
    25 12 3.3 3.64
    30 15 5.3 2.83
    35 25 7.1 3.52
    40 29 8.9 3.26
    45 34 11.4 2.98
    50 38 13.5 2.81
    55 41 16.3 2.52
    60 45 20.1 2.24
    61 46 21.6 2.13
    ... aboard the 'Memory Maker' Making Memories one Wave at a Time!

  7. #7
    Member ocnfish's Avatar
    Join Date
    Oct 2007
    Location
    Alaska
    Posts
    542

    Default Prop efficiency

    Here is my two cents ....

    Having been an airplane guy for the last 30 years and a boat guy for the last eight, listening to all the experts. The most eficient prop depends on the speed you are going at. A fix pitch prop will be a compromise either at high cruise or getting on step. Some airplanes use a variable pitch prop like my C-180. It uses high RPM for take off (flat pitch) or lower RPM for cruise (more of a byte into the air). The right pitch depends on how fast you are going. This option does not exist in the boating world, I think the next best option is the Penta IPS system where counter rotating props are addressing undisturbed water. I have a Penta DPS outdtive on my Osprey and it can move 8,000 lbs + at up to 44 mph on a 280 hp 5.7 GM Marine power. Merc also has a dup prop option. Lastly, I think based upon previous outboard experience that stainless steel is more efficient at high rpm because unlike aluminum the blades do not bend, they keep their pitch better. If you go to stainless steel you probably need to decrease pitch a little from the aluminum or you will notice a drop in rpm at wot.

  8. #8
    Member Dupont Spinner's Avatar
    Join Date
    Jun 2007
    Location
    Chugiak
    Posts
    1,425

    Default

    Quote Originally Posted by DMan View Post

    Here is one list of Stats a guy posted:

    Following are the fuel stats for my 22' OP HT
    with a Yamaha 225 .

    RPM MPH GPH MPG
    25 12 3.3 3.64
    30 15 5.3 2.83
    35 25 7.1 3.52
    40 29 8.9 3.26
    45 34 11.4 2.98
    50 38 13.5 2.81
    55 41 16.3 2.52
    60 45 20.1 2.24
    61 46 21.6 2.13
    Here is the answer. I also seen the same in a friend's boat with a Merc and a fuel flow meter. A couple hundred differance in RPM drastically changes the GPH.

    Also going to a larger prop could become a problem in a following sea. The engine would larbor while climbing the backside making it possible for the wave/wake to come over your transom.

    If you could find a few props to test to find the best that would be optimal. Your already have a heavy load prop, your 17 pitch.

  9. #9

    Default

    i use one of these on my 15 foot skeeter bass boat with a 200 mercury outboard.. works great... it gives a 6 inch more pitch at high rpm, better hole shot, less stress, and more speed/fule efficiency at high end. http://www.aerostarmarine.com/

  10. #10
    Member
    Join Date
    Oct 2007
    Location
    Anchorage
    Posts
    14

    Default

    Thanks for the data Dman, after considering the replies and doing a little more research, it seems I will do the following in this order: Get a Fuel management system installed, check my load plan for balance when taking out a lot of gear and cruise at around 25 mph instead of 30 mph. Thanks again all, may you have calm seas and sunny days on the water.

  11. #11
    Member DMan's Avatar
    Join Date
    Oct 2006
    Location
    Wasilla, AK
    Posts
    1,412

    Default

    Quote Originally Posted by Run4yours View Post
    There is a wealth of knowledge on this forum and I have always recieved good advice here so I have one quick question if anyone out there knows the subject. I push a 22ft Hewescraft with a 225 yamaha 4 stroke, but even at cruising speed (about 4200 rpm or 30 mph) I am still using a whole lot of gas, over 12 GPH. That is with all the shrimping gear and a boat full of kids and their stuff. I run a 19 pitch S/S prop, but I also have a 17 pitch which gets me great speed but drinks the gas. What are your thoughts on increasing pitch, even though it'd slow us down, to save gas. I know what the Yamaha recommendations are for operating range, but with the price of gas, I don't want to have to quit going out because of the gas prices, thanks

    22ft Hewes HT, call sign "Kaya"
    Hey man, check this out. Pretty much spot on with what I was thinking and gives you the prop info.

    http://www.yamaha-motor.com/assets/p...ht-f225txr.pdf
    ... aboard the 'Memory Maker' Making Memories one Wave at a Time!

  12. #12
    Member Dupont Spinner's Avatar
    Join Date
    Jun 2007
    Location
    Chugiak
    Posts
    1,425

    Default

    When I was looking at the performance sheet I found it funny at how the motor burned about an extra 2 gallons of fuel for every 500 r increase between 3500 and 5000.

    So here is the bottom line....I will use a 50 mile trip using their data.

    At 3500 r's you will be going 24.5 mph it will take 2.04 hours and you would burn 16.524 gallons of fuel

    At 4000 r's you will be going 30 mph it will take 1.6 hours (saved almost 30 minutes) and you would burn 16.96 gallons (almost a half gallon increase)

    Last at 5000 r's you would be traveling 35.3 the trip would take 1.4 hours and burn 18.06 gallons(no savings in this range).

    All the above is in the perfect world and I thought it would be neat to see the actual numbers for an average PWS round trip.



    Hey I did notice something in your post that gots me to wondering You said you have a 17 pitch which gives you great speed???? The 17 would help carry a heavier load and you would lose a little topend. Your 17 may be your answer over the 19. Trim and a fuel flow will be the best answer.
    Last edited by Dupont Spinner; 06-12-2008 at 23:34. Reason: Last Paragraph

  13. #13
    Member DMan's Avatar
    Join Date
    Oct 2006
    Location
    Wasilla, AK
    Posts
    1,412

    Default

    Speaking of fuel flow, Yamaha makes a real nice fuel flow meter I think everyone with a Yamaha should have. Tie it into GPS and it will give you MPG in addition to GPH.
    ... aboard the 'Memory Maker' Making Memories one Wave at a Time!

  14. #14

    Default

    The general rules for prop selection are that a smaller diameter prop will yield a better hole shot and get a heavy load on step but top speed will be lower, chnaging the pitch of the prop will change the max RPM of the engine (lower pitch = higher RPM.)

  15. #15
    Member Alaska Gray's Avatar
    Join Date
    Apr 2006
    Location
    Anchorage, Alaska, United States
    Posts
    4,925

    Default

    Quote Originally Posted by DMan View Post
    Speaking of fuel flow, Yamaha makes a real nice fuel flow meter I think everyone with a Yamaha should have. Tie it into GPS and it will give you MPG in addition to GPH.
    Do you know where we can pick one up at?
    Living the Alaskan Dream
    Gary Keller
    Anchorage, AK

  16. #16
    Member spoiled one's Avatar
    Join Date
    Apr 2006
    Location
    Anchorage
    Posts
    3,230

    Default

    Quote Originally Posted by Alaska Gray View Post
    Do you know where we can pick one up at?
    You can order on-line or just go to Deweys. They work slick. They show total fuel burn and you can toggle between P or S motors to dial in the correct trim. It will also show the number of gallons burned since the last fill up if you remember to reset the trip.
    Spending my kids' inheritance with them, one adventure at a time.

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •