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Fuel mileage

J

jclays

Regular Contributor
"Separate gas tanks twin 350 c

"Separate gas tanks twin 350 crusaders. Almost 12mile trip, mild, seas, 2400rpm at 18.3 knots per gps chart plotter. Each engine consumed 5gals of gas for aprox 2.23 miles per gallon per engine. Is this my true mileage? or do I combine both engines for 10gals total gas consumed for 1.2 miles per gallon???"
 
"Unless someone puts FREE gas

"Unless someone puts FREE gas in the other tank, you need to combine them both for your total GPH, which is not bad at all. Damn good, in fact.

Congrats!

Jeff"
 
Shouldn't the weight of th

Shouldn't the weight of the boat make a little difference? Is it 10K or 15K lbs.? 2400 RPM is unbelievable. I can barely stay on plane at 2800! My boat is 20K with 454s.
 
"weight will make some differe

"weight will make some difference - bigger factor would be surface area and its condition; how much hull is in the water and how rough is it. another variable that doesn't get much attention is the ratio of the gear. Prop condition would factor in, too.

last big variable i've noted is 'sail area' - how much resistance is above the water line; especially if running into a brisk wind."
 
"Yes. Agree makomark. I alway

"Yes. Agree makomark. I always try to do my GPH tests with flat sea and no wind. Wind (10-15 knots) can add or subtract 0.1 MPG to your gas mileage. Current adds even more (+ or - 0.2 MPG with 4 knot current)!

So I can get 1.1 or 0.5 MPG depending on conditions. (IME) In My Experience.
2_cents.gif
"
 
James.... 1.2 aint bad. I had

James.... 1.2 aint bad. I had a similar setup in a 10k lb boat and burned about 1 to 1.1 at 3400RPMs.
 
"Check this out, Al; my 32 foo

"Check this out, Al; my 32 foot Marinette will hang on plane down to 2,000 rpms (13 to 14 mph) with a full load. I can even make a full lock, 360 degree, turn without it dropping off plane! Gas mileage is optimum at that speed (about 1.5 mpg) but I don't like going that slow.

Jeff"
 
"Interesting, my boat is about

"Interesting, my boat is about 20lbs/HP.

And jeff, those are some rediculous numbers you got there!! I can just keep my boat on plane at 24-2600 RPM...I can't wait for all this snow to melt around the boat so I can run her up to her new cruise raneg from 34-3600 RPM!"
 
"How / who tells you how much

"How / who tells you how much your boat weights?
Where do I go from 13,500 dry weight? + 300 gal fuel, + 30 gal water, +???

I figure that Al's boat is 21,780 if his 454's are putting out 330hp ea. but where did he / you come up with that accurate figure?

Fred 156-M"
 
"MY BOAT Dry Weight = 18,000

"MY BOAT Dry Weight = 18,000
Gas = 300 gals x 6 = 1,800
Water = 100 gals x 8 = 800
People = 2 x 200 = 400
Dinghy = 1000
"Stuff" = Guess = 500

GRAND TOTAL = 22,500

My engines produce 300 HP at each propeller, 350 at the crankshaft.

So 22,500/600 = 37.5 pounds for each horse
sun.gif
to push through water.

http://wiki.answers.com/Q/Which_is_heavier_an_equal_volume_of_water_or_gasoline

So what does it all mean?
lame.gif
It's complicated so just cruise and enjoy. Fun comparing boats efficiency to others. Sailboats and diesels always win but how much fun are they?
wink.gif
"
 
as I always say to my sailing

as I always say to my sailing buddies....

"You're never going to enjoy life with a carbon foot print that small...!!"

Burn on (in the most efficient way possible!)
 
"Per advertised specs the boat

"Per advertised specs the boat weighs 10,500 (right!)--more like 14,000. It's a straight inboard. With twin 360 Chryslers (260 hp) that makes 27 lbs./ hp. The low speed torque of the Chrysler marine engines (achieved by using 273 V-8 heads) is what makes them so good at "lugging".

Jeff"
 
"those HP numbers are for WOT;

"those HP numbers are for WOT; if you use the actual 'HP at cruise' values, the lb/hp number will go way up."
 
Deadrise angle is big factor i

Deadrise angle is big factor in fuel economy on plane. I have 20% deadrise at transom and more in the middle. Minimum planing speed is 18 knots and at less than 20 knots with any kind of seas it is hard to keep on plane. Boat is 21 Searay powered by 350 chevy Mercruiser. 8 foot beam and loaded weight about 4500 pounds. Gets 2 nautical miles per gallon at 24 knots 3200 RPM. Currently rebuilding a vortec 350 with edelbrock 1409. Hope to improve fuel economy.
 
"2.1MPG.... @ 1200RPM... @ 7.5

"2.1MPG.... @ 1200RPM... @ 7.5 knots
0.8MPG.... @ 2600RPM... @ 18 knots

30,000 pounds... 2X 330 Cummins
+Fuel
+water
+38 cases of beer
+friends
+scantilly clad, morally casual lady friends
+Mistahays"
 
Get those lady friends to leav

Get those lady friends to leave a bit more if their clothing behind and your mileage would be even better! (And it's pretty darn good now).

Jeff
 
Thats funny. Or if I could get

Thats funny. Or if I could get skinnier woman maybe!

Its a diesel... so its better if you go slow and really lean burn it. But who wants to run 7knts!?
 
"Hey Jeff,
not that you ever

"Hey Jeff,
not that you ever run there, but with your ratio gear boxes & the massive pitch of the props you run (3 or 4 blades?), tell us an honest RPM at WOT.

Fred 156-M"
 
"Boat is supposed to have 16 x

"Boat is supposed to have 16 x 16 three bladers. I got a 17 x 15 four blader cheap, so I bought another for the other side. WOT rpm is about 3,900 (though I never hold it open for more than a few seconds). Top speed (with the stock props) was 32 mph.

Jeff"
 
I was discussing our boats WOT

I was discussing our boats WOT and current prop set up with the local propscan folks and thru a series of some different computer programs I am finding out that I can go 3" more on pitch. I am so hungry for 4 blade props. As I had mentioned our last run we had the boat flying...our WOT can reach 5 grand if we just let it climb so I am looking forward to SOME type of change. Our best fuel economy is 1.1 usually .7 to .8 Max fuel useage 46gph.

Jeff's ideas on over prop sounded so nice ( a few posts 2 months ago) I am just wondering what the ACTUAL change will be on this hull.
 
"Try it, Al; you'll like i

"Try it, Al; you'll like it!

Jeff

PS: In NEUTRAl, my engines consume 3 GPH each at 3,000 rpms. This consumption drops off to below 2 GPH as the rpms are reduced to 2,000. Think about that when propping your boat.

Disclaimer: Never over-prop an overweight boat that struggles to plane off. Mine leaps out of the water at less than half throttle, so I can get away with it."
 
"Do you remember what it turne

"Do you remember what it turned with the 16X16's, Jeff?
I was told (rule of thumb) 1"dia = 100rpm., 1" pitch = 200rpm. But I'm sure that the 4 blades are much more efficient than the 3 blades.

See this is whats screwy to me.

I want to know, why I can't fall into that 2,300 - 2,500 rpm cruise / 4,100rpm WOT /range?

My previous boat (I still have)
'76 SlickCraft 245, 24'x 8' beam. IO, single 318/195hp (900hrs.), 1.5:1, guessing 5,000lb. + 100gal fuel cap. 18"X 9" Bennett trim tabs.
248734.jpg

I have 2 props 16X16, 14X21

16X16 is my power prop, Weekenders ect. Basically if the load is more than 800lbs. or skiing I need this one to get planed off. If load is more than 2,000lb I have to shift 300lb. weight into the cabin to get on plane (full tabs, & there big tabs for a boat this size).

At 800lbs. load
WOT 4,700 rpm (36mph).
With the tabs up, if the rpm falls below 3,400 (21mph.) she falls off of plane. I run it at 3,600rpm (24mph).
I figure getting 3mph out of 200rpm is well worth it.
With full tabs down, I can keep it up on plane down to about 3,000rpm. (17-18mph).

If I put the 14X21 on it, (4 adults, 2 squires, & a big cooler) WOT = 4,400rpm., but its a struggle to get her up on plane.

Fred 156-M"
 
Went out again today. Calm sea

Went out again today. Calm seas 26 nm and some change. 2400rmp 18knots with 19.1 max crusing at 2400rpm (must have hit a flatter spot on the sea)each engine consumed 9gals for an average of 1.44mph.
 
"..."Do you remember what

"..."Do you remember what it turned with the 16X16's, Jeff?"

Close to 4,600 rpms as I recall.

..."Is there such-a-thing as an inexpensive fuel flow meeter? "

No.

Deep Vee hulls tend to do as you described--they're on plane or not by a slim margin, and lots of throttle is needed.

I recall my buddy's 27 foot Sea Ray with a Mercruiser 454. It would not hold plane below 3,000 rpms, and needed full throttle (and a tail wind!) to get on plane. It seemed to be laboring like crazy all the time, though it was not that heavy a boat.

Jeff"
 
I hear ya.... My old SBC power

I hear ya.... My old SBC powered 28' would not even think of holding a plane on one engine even at WOT. I was a little surprised.
 
"Re: "Deep Vee hulls tend

"Re: "Deep Vee hulls tend to do as you described"
I don't think so.

I played around in Photoshop this morning (because its that burning question that I needed answer for myself).
Now, am I doing this right? I come up with between 17 & 18 Deg. deadrise. NOT exactly what I would call a "Deep V" hull.
248809.jpg


Or do I need to double that figure (17 on each side) , I don't think so.

Fred 156-M"
 
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