Hull speed and fuel consumption Hunter 30

Randy

.
Dec 19, 2008
3
Pearson 31 Lake Guntersville
Planning trip up the Tennessee River to bring 1991 Hunter 30 up to Lake Guntersville from Pickwick. Would be very helpful to know hull speed and gal/hr to calculate time and fuel required? Would be very interested in comments from anyone who has made the trip or any part of?
 
May 24, 2004
7,129
CC 30 South Florida
Since water is a fluid medium the formula of Miles Per Gallon does not work. Fuel consumption in boats is measured in Gallons per Hour (GPH). It all relates to the size of your engine and nothing else. A single cylinder will burn approximately 1/4 GPH, a 2 cylinder approximately 1/2 GPH and a 3 cylinder approximately 3/4 GPH. You may calculate your specific Average Burn Rate by Filling up the tank, running engine for a few hours and refilling marking down how many gallons were consumed in that time frame. An Hour Meter gauge connected to the Key Switch measure the time the engine is ran. Gallons / Hours = Burn Rate. Now the Distance Range is the tricky figure, it can only be calculated on the water at the time of travel. It depends on the conditions, mainly wind and currents direction and speed. A rough calculation can be performed pre-trip based on a speed of 4.5knots to say that every hour you may run 5 Statute Miles but once on the water a calculation should be done every hour to see how reality meets the anticipated calculation. Important is the size of your fuel tank but deduct a 20% for emergency reserve and unusable capacity; thus a 30 Gallon tank becomes a 24 Gallon Usable Capacity Tank which for a 2 cylinder engine will give 120 statute miles range in ideal conditions. It is good to calculate fuel burned every hour on your trip so that you know if you can reach your refueling destination or if you have to divert to a closer one. If refueling destinations are sparse or uncertain you may carry additional fuel in fuel cans attached to your stanchions. Keep a log of your Burn Rate calculations as you may with time narrow down a more exact figure. Currently I can pretty accurately calculate my fuel usage to 1/4 of a Gallon per tank.
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
Randy I see you have been on the forum for awhile, but not often posting inquiries. Welcome back.
Sounds like a fun trip.

If my understanding of geography is still valid, you will be traveling downstream through a couple of reservoirs and locks. The downstream part is in your favor. Lake Guntersville being at an elevation of 595 ft and Pickwick 414 ft. Even though the reservoir is a lake, there will still be a current moving through the lake.

A factor affecting your travel will be wind. Wind with you helps wind against you slows you down.

Benny has provided a great outline as to how to calculate your fuel needs. You are planning a trip of about 125 miles (apron 200km). You will likely get better (less) fuel consumption but figuring 4. 5 miles an hour and 1 gallon an hour the trip could conservatively consume 27 gallons. If you have the wind at your back and a 1 mile per hour current you would use much less fuel. It you have to power into the wind the entire distance you could use 30-40 gallons.

That is why Benny's advice to identify a plan then check your fuel consumption as your go is a really good idea.

Who knows you may have the wind at your back and able to raise your sails consuming little or no fuel for most of the trip.
 
Sep 22, 2018
1,869
Hunter 216 Kingston
It all relates to the size of your engine and nothing else. A single cylinder will burn approximately 1/4 GPH, a 2 cylinder approximately 1/2 GPH and a 3 cylinder approximately 3/4 GPH.
Is this based on WOT or ???
 
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
Is this based on WOT or ???
It is based on average use. Rarely does one run completely at WOT and rarely at idle for any long periods of time. The ONLY fuel consumption number you need to know is the average use. Which is the actual use between refills.

I recvommend you do a search on this forum for "fuel+consumption" and read away, all been discussed in great detail many time.
 
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Jan 22, 2008
68
Hunter 30_88-94 Ipswich, Ma MA
Fuel consumption on our 92 Hunter 30 is 1/2 GPH. The engine is a Yanmar 2 GM 20. At slack tide with no wind we’ll do about 5.5 to 6 knots @ 2500-3000 rpm.
 
Sep 11, 2015
147
Hunter 31 Marina del Rey
I calculated average nmpg for my Hunter 31, 2GM20F engine. This was in calm water in the marina. I usually budget 10 nmpg. If you are going into the wind in big waves, you should expect higher consumption.

NMPG2.jpg
 
Feb 14, 2014
7,400
Hunter 430 Waveland, MS
I calculated average nmpg for my Hunter 31, 2GM20F engine.
:plus::plus:

That is a typical engine fuel consumption curve.
Note the "Sweet Spot" at 4 knots. @Pizzazz would go 13 nm on a gallon of fuel.

The peak of that curve can be assumed horizontal, and you see the consumption is very slight changes for speed of 3.5-5.5 Knots. Thus, find the "Sweet Spot" . I found mine at 70% of WOT.

Since in the Tennessee River, you will not be fighting winds or sea state, when motoring.

Many Captain's use 4-5 knots average speed in planning distances traveled.
Jim...

PS: I have motored on Kentucky Lake, many times.:)
PSS: The Tennessee River flows in what general direction at its discharge?:pimp:
 
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Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
Since water is a fluid medium the formula of Miles Per Gallon does not work. Fuel consumption in boats is measured in Gallons per Hour (GPH).
I calculated average nmpg for my Hunter 31,
NMPG is NOT a valid method of use for sailboats because their relatively slow speed is more affected by wind, to say nothing about current, even if you're on a lake with no current.
NMPG is used often by motorboats because their much higher speeds are less affected by current. The relative difference between boat speed and currents are an important factor.
@Benny17441 is right.
 
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Feb 14, 2014
7,400
Hunter 430 Waveland, MS
Of course @Benny17441 is right about Sailboats in general.

But @Randy asked about motoring on the Tennessee River!
A very low current speed, most there use Houseboats, since there were Lakes formed between the Dams.
Jim...

PS: Any fuel consumptions rates are Valid, it is the Distance traveled that is the Key!;)
PSS: The Tennessee River flows North to the Ohio river, one of the few rivers that do that.;)
 
Sep 22, 2018
1,869
Hunter 216 Kingston
:stir:

“Since water is a fluid medium the formula of Miles Per Gallon does not work.”

Water can change state so NOT always fluid

“Fuel consumption in boats is measured in Gallons per Hour (GPH).”

A lot of countries use the metric system so litres/km and/or use Imperial gallons which are NOT USA gallons

“It all relates to the size of your engine and nothing else.”

Fuel consumption ALSO depends on other factors such as throttle setting, combustion efficiency etc.


“A single cylinder will burn approximately 1/4 GPH, a 2 cylinder approximately 1/2 GPH and a 3 cylinder approximately 3/4 GPH”

Not true if the cylinder sizes are different.

:)
 
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Mar 20, 2011
623
Hunter 31_83-87 New Orleans
I made the trip from Guntersville to Mobile in the late 80s. Just did a quick search and from Pickwick to Joe Wheeler marina/state park is 70 miles. From Wheeler to Guntersville dam is about 73 miles. When I did the trip I moved the boat from GD to JW marina in one day and overnighted at JW state park marina. Looks like a 2 day trip for you if you wish to stop overnight. We didn’t travel much at night back then due to the number of locks and the amount of tug traffic. It was a great trip. Very scenic, especially near Pickwick. Locking thru was easy with lockmaster being patient with sailboats/recreational vessels. There’s a guide you can pick up from Alabama Waterway or contact Corp of Engineers for locking thru procedures.

Wilson lock was great. Largest single lift lock east of Rockies at near 100’ elevation change. Back then we used a great waterway publication guide/ chart book But can’t recall the name. Also look at marinas along the way for fueling if you don’t carry addl fuel jugs on deck. Might want to see if Waterway Guide has a guide that covers this area (Waterway Guide | Cruising Guide, Fuel Pricing, Navigation Alerts and News for Boaters and Yacht Enthusiasts)

Also check currents in the TennTom. We transited in April and had about a 3 knot current pushing us down River Also bring a backup vhf. My base died in route and had to use horn signals for the last few locks. Wished I had a hand held with me. Enjoy the trip.

 
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Randy

.
Dec 19, 2008
3
Pearson 31 Lake Guntersville
To everyone who responded, thank you! The adventure went better than I could have hoped for. Hour meter indicates 29 hours over three days and about 15 gal. of diesel. Not sure what current was but we bucked 20+ headwinds first and last days. Water level was unusually low even for winter and it would have been more comfortable if temps were higher but we had no problems. Overnighted at Florence Harbor Marina and the folks there were very accommodating. We carried 10 gallons of diesel on deck but refueled at Florence Harbor. Tied up at River Walk in Decature second night. Ate at the restaurant there, good food! All Lock Masters and Bridge Master at Decature were easy to work with.
Fair winds and following seas to all!
 
May 25, 2012
4,333
john alden caravelle 42 sturgeon bay, wis
I been lookin' for one of dem multi-sized cylinder engines for a long time. :beer::beer::beer:
well stu, i work on a ship that had an engine with 3 different sizes cylinders. yepper.
S.S. Sylvania. built in 1902, had a triple reduction steam engine. pretty standard for the day. 1st cylinder maybe 12",second about 24" and the last was about 48". the exhaust from the first cylinder powered the next one, the exhaust from the 2nd cylinder powered the last one. now maybe, i have the sequence reversed, don't know.
580' long, 1200 HP, wind her up and maybe hit 8knts. going up the rivers was quite slow.
the joke aboard was that if you blew too long of a salute you would slow to 6knts. 180lbs low pressure boilers, hand fired coal.

1613240653074.png


one year we ran 201 loads of coal from toledo to detroit
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
Way to go Randy.
Thanks for doing the after trip report.
 
Feb 14, 2014
7,400
Hunter 430 Waveland, MS
Hour meter indicates 29 hours over three days and about 15 gal. of diesel.
That is about 0.5 GPH.
So if you can report the distance traveled, all of the responders can do the math on ...

Miles per Gallon

Thanks for the trip report.:thumbup:
Jim...
 
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