Re: Cruise range for an Islander? How far can a guy get on a tank of fuel?
I run a 21 Cheiftain, 4 cyl. 140 merc. I/O, I have put 100's of miles on this boat in the past 5 yrs.
Basically if you are proped for pulling tubers, 3500 rpms @ 20 mph gps you will burn about 1/2 gal. per mile.
I just reprop the boat and now run 3000 rpms @ 20 mph, cruise at 3600 rpms @ 24 mph. 4400 wot about 28-30 mph depending on the tide.
I ran about 40 miles halibut fishing one day on approximately 10 gals. In good seas cruise 20 mph you will get about 4 mpg, with the right prop.
I range 2-4 miles per gallon at various cruising speeds and conditions. Rarely get over 4 mpg rarely seem to get less than 2 mpg.
I estimate I just ran the boat 100 plus miles last week with my new prop.
Prop settings and sea conditions have a huge impact. I was running too low of pitch prop for years (tach was wrong) and I would get around 2 mpg. Last week with a different prop I just about doubled my mileage.
Old prop wot pushing 4800 rpms (26 mph), cruised all the time at about 3600-3800 at 20 mph.,
New prop wot about 4400 rpms (30 mph), cruise at 3000-3600 rpms (20-24 mph).
I am going to try my prop so wot is about 4100 rpms see if I can gain some more fuel economy.
I run a pro-pulse adjustable prop, so I just went up a pitch. 17pitch to 18 pitch. Had it at 15 pitch.
I have twin 16 gal tanks, so I have about 28 gallons of usable fuel. 1/3 reserve, 1/3 out, 1/3 in.
18-36 miles from port is my range.
Hope this helps.
