Fuel consumption on M35

[Jim Hardesty]

I took my first trip that I had to motor & motor sail any distance.  15 hours 15 gal.  This was doing about 6 kn and 1800 to 2000 rpm.  This is not what I expected for fuel economy.  What are other owners with the M35b getting?
The bottom is clean, the conditions were moderate, and I have a 3 blade Max-prop set at 10 inches per rev.  The engine appears to run good and has 590 hours.  I do have some soot around the exhaust but I don't see much smoke. 
Should I have the injectors checked? 

[c34no1471]

I've kept an eye on fuel consumption since I took possession of Breezing Up (#1471) in 2000.  I have the same engine, the M35B.  I have the standard Catalina fixed two-blade prop, and I use about .6 to .65 gallons per hour at cruising RPM (2300 or so).  That number has held up pretty consistently.  When my hull, prop, and prop shaft are clean I do about 6 to 6.5 knots at that RPM.

I'm impressed that you can do 6 knots at those RPMs you mentioned.  Maybe I should switch props....

I'm not a diesel engineer, but I have two thoughts:  checking the injectors makes sense, and I'm mildly suspicious of your tachometer readings.

Good luck!

George Alberts

[wind dancer]

I have the smaller M25XP, so it's not directly comparable, but for what it's worth I cruise at 2100-2200 rpm and burn a little more than 1/2 gallon per hour at 6 1/4 knots.

[Stu Jackson]

Some earlier input from skippers:  http://c34.org/bbs/index.php/topic,3824.0.html

[Steve Sayian]

Jim,

I burn roughly .8-.9 gal at 2000 RPMs that gives me about 5.8-6.2 knots depending on sea state.  I have a 10 inch Kiwi 3-blade feathering set at 17.5 degrees (which is about 10 inches pitch). 

I just cleanded my injectors this spring along with the tank and installed a new tank sensor.  My tach is accurate as I check it against a digital tach yearly.

Steve

[c34no1471]

In reading the other postings, I'm thinking my fuel efficiency number is a bit off.  I don't consistently run the engine at 2300 rpm--if I can do so and maintain a decent speed over ground, I drop it to 2000-2100.  According to my log, I am indeed using a bit than .6 gallons per hour, but not quite .7 gallons per hour. But  if I ran at 2300 all the time it would probably be in the .8-1.0 gallons per hour, especially in anything but calm or moderate seas.

[Ken Juul]

if you are getting soot it sounds like you might be a bit over pitched.  That will also hurt your fuel ecomomy.  Might try a search on Max prop and see what others are running

[jfssail]

Jim, My M35A with Autoprop burned .85 gph at 2000 rpm on the same trip we both made from Ashtabula to Erie, Pa on Wednesday.  . I was towing a dinghy, which kept my speed down to 6 kts. On flat water I will go 6.4 kts at 2000 rpm without the dinghy.  . At 2200 rpm, I achieve 7 kts and 7.3 kts at 2500 rpm. The sweet spot for me is 1900 rpm at 6+ kts and 0.7 gph.  When I motor sail, my fuel consumption drops tp 0.5-0.56 gph at 1500-1700 rpm.
Jack F Stewart
1993 C36 #1233 "Windancer"
Port Clinton, OH

Now at Wolverine Marina in Erie, Pa.  Leaving for Port Dover, Ca on Sunday

[Ron Hill]

Guys, Susan and D. Gill : Fuel consumption is a tough parameter to zero in on!! The previous responce is from a C36 (differant wetted surface area, differant prop and a M35A 30hp engine)

My original M25XPA when it was new was about .46g/h.  In it's later life went up to .5g/h.  My new M25XPB is .56g/h.  Same prop (3 bladed fixed Sailor) - same RPM.

I'll guess that M35XPB is going to be about .75 - in a C34.   A thought

[Stewartn]

Desiree, C34 Mk II, #1472: M35B engine w/fcty installed 3 Blade Fixed Prop.
In 2008, 300+ miles trip resulted in 0.6 -.66 GPH @ 2000-2100 over a wide variety of sea and current conditions. Hope it helps.

[Jack Hutteball]

Mariah lll C34 Mll # 1555, M35B with factory 3 blade.  Average .75-.8 at 2500 rpm towing my 50# hard dingy.
Jack

[Tom Clay]

Cat 34 MKII Hull 1760, M35B factory 3 blade fixed prop.

2200 RPM.......  .6-.7 gal.    6.6 knots
2400 RPM.......  .7-.8 gal.    6.9 knots
2600 RPM.......  .8-.9 gal.    7.2 knots

Add .1-.2 in chop or waves over 2-3 feet.