470 est MPG

"Have a 1979 Bayliner Admirilt

"Have a 1979 Bayliner Admirilty 19' cuddy with a 470. Had it for years but have never gone more than a few miles at a time, mostly skiing and tubing, so don't have a good feel for MPG on a cruise. Thinking of going 60 miles for an overnighter. Boat weighs about 3000 lbs with full tank (42 gals) and me.

And would a moderate plane result in max fuel economy? Appreciate yout thoughts, experience. Tnx. JW in Dixie"

"Warren;
If you send me your

"Warren;
If you send me your prop size x pitch and your drive leg ratio, I can run some estimates for you at various speeds.
Le me know your current WOT RPM and top speed also if you can.

Rod"

"Thanks, Rod. I am away from h

"Thanks, Rod. I am away from home for a couple more weeks, but when I get back and can look that info up I will be back to you. JW in Dixie"

"A Rule of Thumb is roughly 1

"A Rule of Thumb is roughly 1 nautical mile /gal.
you can test this by running a 6 gal portable tank in place of your tank feed ,a known milage run down the coast untill you empty the 6 gal tank at your cruise rpm.Slower speeds conserve some fuel so run at cruise for testing.And remember usable fuel vs tank capacity vs how far down your pickup is.
eg. 60gal tank with a 2 inch V bottom,pickup 2 inches off the bottom,50 gal usable.
A true test is to run the main dry and refill
60 gal tank takes 50 gal to full =50 usable"

"Wow! If it uses that much per

"Wow! If it uses that much per nmi, guess I won't be taking a cruise in it, just for one night. 120 miles = 120 gals of 91 oct at min $4/gal = $480! I'll drive the car and overnight in the Presidential Suite! Thanks for your response. JW in Dixie"

"Warren;
I think Bt Doctur&#3

"Warren;
I think Bt Doctur's consumption estimate is somewhat high for a light boat, just my opinion.
I would expect about 10 GPH with the 470 at cruise, and if you are doing 30 mph, that would give you about about 3 MPG.
When cruising you should likely be at about 3500 RPM or less for best economy. You don't want the power valves open in your carb (as at WOT), as that is when the consumption shoots way up.

I assume that you have a 1.98 drive ratio and you are running a 21 or 22" pitch prop, and you can do about 45 mph at WOT. This should give you 30 MPH cruise at about 3200 RPM. If you are running say a 19" pitch, this will give you higher RPM at cruise, and perhaps slightly worse fuel consumption.

BTW, terms like "MPG", "mileage" and "fuel economy" are usually not used in the same sentence with "boats"; so I apologize.
Ha, ha, just kidding of course.

Rod"

"Thanks, Rod. Your thinking is

"Thanks, Rod. Your thinking is more in line with mine. The boat runs/feels good at 3200 rpm. WOT with only me - the one time I tried it, shortly after acquiring it - it ran 46 MPH, speedo indicated. Think the rpm was around 4500 at that speed. Long time ago. Still, at 3 mpg a 120 mile trip is 40 gals, x $4=$160. Man, I think gas cost is gonna limit my Bayliner use this summer. Just shor skiing/tubing for the kids. Shame. The Money-Hole-In-The-Water a boat creates is getting bigger and bigger all the time. Oh well, there's still the 8' Merc 200/KG7 RatMotor runabout. Can have a morning's fun on a gallon. Screw Big Oil! Thanks for your thinking. JW in Dix<center><table border=1><tr><td>http://www.marineengine.com/discus/icons/attachment_icon.gif""" align=left alt=""image/bmp"">JW in the 8-foot Eagle runabout
[url=""][b]JW_Eagleboat_Spring_Creek.bmp[/b][/url] (13.7 k)</td></tr></table></center>"

"I think that there will be a

"I think that there will be a bunch of 6 gal. marine fuel tanks switched out on the lake this summer since the cost of fuel is out of control; better chain them while on the lake and put them in the garage at home. I may put a padlock on my I/O gas cap. "

"You're prob'ly right.

"You're prob'ly right. My Bayliner has a keyed gas cap, and sits on an airlift in a boathouse remote from home. Have a roll-up garage door on the water entrance and dead-bolt on the dockside door. I worry about someone swimming under the door and hi-jacking my outdrive, etc. But I do have a WatchSnake - about 5 feet long, who lives there. Grrrr! JW in Dixie"

I'd say 3 to 5 mpg.

Jef

I'd say 3 to 5 mpg.

Jeff

"My real world findings:

I

"My real world findings:

I have a 19 cuddy with 470MCM/ 1.84 gear ratio and I cruise around 3400-3600 rpms. I average 6-7 GPH. Not too bad. Of course it all depends on the winds, tides, loads, etc."

"Thanks, Jeffy and Puget Sound

"Thanks, Jeffy and Puget Sounder. Appreciate your input. Sounding better all the time. I may just give it a shot. Cheers, JW in Dixie"