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firepiper
RO# 22740
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 Posted - Jun 11 2012 : 20:25:43
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I can't afford floscans this year. Several guys have told me that with my setup I should be cruising at about 3300 rpm. I always run at cruise at 2800. Had a mechanic friend out fishing yesterday, and he convinced me on the return trip to run her at 3000 to see if mpg improves. We refueled upon return to port.....drumroll.....I saved 23 gallons! And that was only changing the rpm on the way home. I do the same trip all the time for my charters, 24 miles at cruising speed, run on single engine idling/trolling for 5-6 hours, then return 24 miles back to port. With decent seas, I average 84-90 gallons. Did identical trip on Friday, 85 gallons. I'm thinking i'm gonna start running a little higher on the tach!
Anyone have similar boat/engines? how do you run and what is performance? Thanks
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1987 35' Luhrs Alura
1986 Twin Crusader 454,FWC,MPI (cutler),VD 1.91, 20,000lbs
1994 Whaler Rage Jet Dink |
Homeport: Plymouth, MA
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cwms
RO# 7357
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Posted - Jun 11 2012 : 21:19:05
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if your speed isn't a good plane, then you are wasting gas. Either run at hull speed or get a decent plane, nothing inbetween. My guess is your mechanic could see you were running in that inbetween speed and that's why he suggested higher speed.
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Homeport: VA
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Radioactive
RO# 3238
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Posted - Jun 11 2012 : 22:46:09
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One quick but rough measure is the height of your wake.
If you are throwing a large wake, you are inefficient. Either get further up onto a plane, or slow to hull speed.
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Bill
"No matter where you go, there you are." -- Buckaroo Bonzai
"There is nothing, absolutely nothing, half so much worth doing as simply messing about in boats." - Kenneth Grahame |
Edited by - Radioactive on Jun 11 2012 22:49:46 |
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Homeport: MS Gulf Coast
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Veg
RO# 20854
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Posted - Jun 11 2012 : 23:34:01
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Sounds like you were not fully on plane, dragging the rear end a bit. I'm always in full displacement mode (sometimes on just one engine which gives me a huge upgrade in fuel efficiency), or fully on plane which for me is usually between 3500 and 3800 rpms depending on conditions.
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| 2001 Tiara 2900 Open - "O Sole Mio" - Stillwater, MN |
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Homeport: Stillwater, MN
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jtybt15
RO# 3300
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Posted - Jun 12 2012 : 00:07:05
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It's the throttle setting(opening) that determines the fuel usage. A vacuum gauge is perfect to run at each engines most efficient throttle setting. The vacuum reading should show the highest vacuum for any particular RPM.
There are many other factors such as the most efficient prop size or pitch for your particular set up.
Back to the vacuum setting. My previous set up had an alpha(1.5:1 gear ratio) with a 16x16 prop. This was a very inefficient prop for the weight of my boat. I was running about 8.5-9 in/hg.
I swapped the drive to a bravo II with an 17 3/4x 23 prop (2:1) gear ratio) which allowed me to run at 10.5-11 in/hg.
To get an idea how the vacuum readings affect efficiency, the higher the readings, the smaller the throttle plate is opening which makes the pull of the air thru the carb opening stronger and showing the suction as the amount of vacuum in the intake manifold. Now if you opened the throttle, allowing more air into the intake, there will be less vacuum.
To test your best throttle opening or sweet spot, Pick an RPM...say 3200. Run up to 3300 RPM. That will bring your boat higher out of the water. Mark your RPM, speed and vacuum readings. Slowly tick the throttle back and you will see the vacuum readings increase and RPM slowly drop but you will maintain the same speed and the boat will still ride higher as if running at the higher RPM. Do this at different RPM's to find where you can maintain the highest vacuum readings. That's your sweet spot. Of course, adjusting trim as you go.
You can do this without a vacuum gauge with practice.
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Charlie
There is much to be said, in a world like ours, for taking the world as you find it and fishing with a worm.-Bliss Perry, 1904
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Edited by - jtybt15 on Jun 12 2012 00:17:21 |
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Homeport: Ca
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PascalG
RO# 12212
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Posted - Jun 12 2012 : 06:57:30
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You left out the most critical element... Speed! What speed do you get at 2800 and 3300?
I m guessing that at 2800 you re not fully on plane, and you re just digging a big hole while putting a higher load in the engines.
You also need full tabs at such speed, to get all the lift you can get. Do they work?
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Pascal
1970 Hatteras 53 MY
26' Starfish sloop
12' Westphal Catboat
16' Hobie Cat
13' Sandbarhopper
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Homeport: Miami, FL
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jtybt15
RO# 3300
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Posted - Jun 12 2012 : 12:22:17
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I have 'speed' in the last paragraph...but you're right. That, and throttle opening, determines the efficiency. The physics is simple. By getting the boat higher out of the water, there is less drag. Less drag requires less energy to maintain a specific speed and the ability to hold your boat out of the water.
What gets me is how they get Aircraft Carriers to run at ~50 knts
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Charlie
There is much to be said, in a world like ours, for taking the world as you find it and fishing with a worm.-Bliss Perry, 1904
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Homeport: Ca
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PascalG
RO# 12212
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Posted - Jun 12 2012 : 12:26:39
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Charlie, i was referring to the OP, not your response...
as to aircraft carriers... it's the PENTAGON ! they can afford the fuel :)
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Pascal
1970 Hatteras 53 MY
26' Starfish sloop
12' Westphal Catboat
16' Hobie Cat
13' Sandbarhopper
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Homeport: Miami, FL
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cwms
RO# 7357
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Posted - Jun 12 2012 : 12:29:36
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quote:
Originally posted by jtybt15
What gets me is how they get Aircraft Carriers to run at ~50 knts
I'm not sure they run 50 but hull speed on an aircraft carrier would be at least 40.
You figure it has a waterline length of at least 900' - sq. root of 900 is 30 times 1.33 is 40 knots.
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Homeport: VA
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Billylll
RO# 24494
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Posted - Jun 12 2012 : 12:46:05
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quote:
Originally posted by PascalG
Charlie, i was referring to the OP, not your response...
as to aircraft carriers... it's the PENTAGON ! they can afford the fuel :)
You mean the fuel rods for the reactors.
Bill
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WirelessOne,
40 Mainship
Sedan Bridge
Little Egg, N.J. |
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Homeport: Tuckerton, N.J.
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firepiper
RO# 22740
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Posted - Jun 12 2012 : 19:35:08
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Hi Guys, lots of good info as always. Yes I full tabs, 30 inch i think, and they work. Speed, 18 mph rb2rb2@gr5tgr5t 2700. 21 rb2rb2@gr5tgr5t 3000. I'll try more this weekend.
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1987 35' Luhrs Alura
1986 Twin Crusader 454,FWC,MPI (cutler),VD 1.91, 20,000lbs
1994 Whaler Rage Jet Dink |
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Homeport: Plymouth, MA
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PascalG
RO# 12212
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Posted - Jun 12 2012 : 20:54:18
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. 16kts... You re just on plane... 18 to 20 should be more efficient
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Pascal
1970 Hatteras 53 MY
26' Starfish sloop
12' Westphal Catboat
16' Hobie Cat
13' Sandbarhopper
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Homeport: Miami, FL
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firepiper
RO# 22740
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Posted - Jun 12 2012 : 20:57:19
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dunno why that posted like that.....speed 18 mph at 2700 rpm, 21 at 3000.
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1987 35' Luhrs Alura
1986 Twin Crusader 454,FWC,MPI (cutler),VD 1.91, 20,000lbs
1994 Whaler Rage Jet Dink |
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Homeport: Plymouth, MA
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cwms
RO# 7357
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Posted - Jun 12 2012 : 20:59:36
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As mentioned earlier, what does your wake look like at 18 mph.
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Homeport: VA
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firepiper
RO# 22740
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Posted - Jun 12 2012 : 21:15:05
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I think okay....i always thought i was well on plane. dunno. Will take some pics this weekend. Thanks
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1987 35' Luhrs Alura
1986 Twin Crusader 454,FWC,MPI (cutler),VD 1.91, 20,000lbs
1994 Whaler Rage Jet Dink |
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Homeport: Plymouth, MA
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mixman
RO# 25362
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Posted - Jun 12 2012 : 21:52:27
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quote:
Originally posted by cwms
As mentioned earlier, what does your wake look like at 18 mph.
Good point. OP - turn around and see how much water you're pushing. Less is better for both your wallet and the boaters around you.
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--Kurt
17 knot cruise at 5mpg (3.5/gph). Two hulls are better than one! |
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Homeport: Chesapeake Bay
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Salvatore356
RO# 32937
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Posted - Jun 13 2012 : 04:23:55
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I think the business your in you should have diesel engines. I know if I was to charter a boat to go fishing I would like It to be diesel for saftey reason.Gas engines are great if your in business diesel all the way.
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Homeport: NJ
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cwms
RO# 7357
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Posted - Jun 13 2012 : 05:10:35
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quote:
Originally posted by firepiper
dunno why that posted like that.....speed 18 mph at 2700 rpm, 21 at 3000.
The "at" symbol is scrambled on this web site.
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Homeport: VA
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firepiper
RO# 22740
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Posted - Jun 13 2012 : 05:50:07
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Sal- I'd love to have diesels! But.....right now it's not an option.
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1987 35' Luhrs Alura
1986 Twin Crusader 454,FWC,MPI (cutler),VD 1.91, 20,000lbs
1994 Whaler Rage Jet Dink |
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Homeport: Plymouth, MA
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PascalG
RO# 12212
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Posted - Jun 13 2012 : 06:55:18
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At that speed you are on plane but still at the wrong angle.. A couple more knots will help
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Pascal
1970 Hatteras 53 MY
26' Starfish sloop
12' Westphal Catboat
16' Hobie Cat
13' Sandbarhopper
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Homeport: Miami, FL
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Salvatore356
RO# 32937
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Posted - Jun 13 2012 : 08:04:18
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Did you replace the engine from the original one and your props is it 3 blade or 4 blade? I seen test done on the same exact boat with the same engine one had 3 blades the other 4 blade props. The one one with the 4 blade prop had a better performance than the 3 blade one. I found out by getting on plane with almost full throttle then bring the trottle back until you can hear the engines running in sync wich I found out about 3400 to 3600 rpm. You can hear the sound because if you go to low your engines will sound like they are struggling.
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Homeport: NJ
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firepiper
RO# 22740
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Posted - Jun 13 2012 : 09:27:13
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Sal, where did you see that test? On an Alura 35? I'd like to see that. Yes, this boat orig. had 270hp smallblocks. I repowered it.
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1987 35' Luhrs Alura
1986 Twin Crusader 454,FWC,MPI (cutler),VD 1.91, 20,000lbs
1994 Whaler Rage Jet Dink |
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Homeport: Plymouth, MA
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Billylll
RO# 24494
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Posted - Jun 13 2012 : 10:30:10
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quote:
Originally posted by PascalG
. 16kts... You re just on plane... 18 to 20 should be more efficient
I have a similar boat a Mainship 40SB she will stay on plane all day long at 13 knots. At 11 knots it is just getting on plane. However my most efficent slow speed is about 6 knots. On the high end 23 knots is the sweet spot.
I have Merc System View 5000 displays to check the burn rate in addition NMEA2000 GFS-10 Garmin fuel sensors, they match. I am a bit over propped. Top end is 31 knots at 4400 RPM my engines are 2007 Merc 8.1L HO's.
90% of our cruising is in no wake zones or crawling along like a snail.
Bill
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WirelessOne,
40 Mainship
Sedan Bridge
Little Egg, N.J. |
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Homeport: Tuckerton, N.J.
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How do you run?
