Grady 336 fuel burn

[beachbum]

just wondering what type of fuel burn people are getting w/twin 350's yamaha's. Loaded with fuel or 1/2 tank fuel, full water tank, at almost any cruise 3500-4100rpm's I get 1.0 mpg at 4200-4500 .9 mpg at WOT i burn 60 gal/hr and 5500rpms at 45 MPH (roughly .8 mpg). I have genset, hardtop, radar, outriggers,etc.

just wondering if people are getting better fuel burn and would props make a difference (4 blade vs 3, different pitch)? I am not complaining, just wondering since GW claims 1.2-1.3...i have never seen that at cruising speeds.

Thx

 

[seasick]

just wondering what type of fuel burn people are getting w/twin 350's yamaha's. Loaded with fuel or 1/2 tank fuel, full water tank, at almost any cruise 3500-4100rpm's I get 1.0 mpg at 4200-4500 .9 mpg at WOT i burn 60 gal/hr and 5500rpms at 45 MPH (roughly .8 mpg). I have genset, hardtop, radar, outriggers,etc.

just wondering if people are getting better fuel burn and would props make a difference (4 blade vs 3, different pitch)? I am not complaining, just wondering since GW claims 1.2-1.3...i have never seen that at cruising speeds.

Thx

Do you have bottom paint? It makes a difference. Most if not all of the factory measurements are done on clean hulls with no bottom paint. Changing to 4 blade props will most likely lower your mpg figures due to added drag.

 

[ElyseM]

you should be getting much closer to the perf bulletin numbers. are you tabbed correctly and trimmed out. my 330 runs at 1.0 to 1.1 mpg with 4 blades (and bottom paint). very close to the perf bulletin numbers. i run north of 8 tons wet, your 336 is a lot lighter. good luck, ron

 

[beachbum]

you are correct, according to GW spec sheet, i am about 1600 lbs lighter than your 330 . but not sure if that adds in the genset, AC, fishbone cooler, etc.Assuming you have those, we are still around 1,000-1600 apart. I have bottom paint. I think i have it tabbed right but will play around.

I assume you are running twin 350's? do you know what props you have.

thx for reply

 

[ElyseM]

the difference is more like 3K plus. i have 350's running xl4 blades. the 4 blades actually nick mpg as seasick noted. i'm heavier than the bulletins since i have everything on the boat (and a bunch of gear). i ran just under the perf numbers with the 3 blade stock props and same with the 4's. the yamaha bulletins are on their website if you want to look at them. tabbing and trim are essential. if you don't have the hull set right, it will significantly affect mpg. good luck, ron

 

[beachbum]

Ron, thx for the info. Not to get into a long debate but our boats start out about 1,000lbs apart,prior to adding options. I don't know how you can assume, not knowing what I have on my boat, that your boat is 3,000 lbs heavier. For example, standard 336 has 4 batteries, I have 5 (AGM 70 lbs) I have full enclosure (additional wind resistance), genset, fuel for genset I fish offshore so I also carry tons if gear. (dredges, down riggers, etc) Do you have an extra fuel tank? 3,000 lbs is a lot

I do agree, that if you are getting better mileage with your additional weight (minimum 1,000 lbs) and stuff you carry, it leads me to get a deeper look. I am going to check my trim (although I have played with it several times) . I am also going to look at my props, engines only turn 5400-5500 rpm when throttles are pinned.

In any case, you are in the highlands, I am in Seaside Park (Barnegat Inlet), hope to see you in the canyons or Shrewsbury Rocks,in the near future!

Hipmotized 65/71

 

[ElyseM]

Thruster, 2 a/c units, refrigerated boxes, 70 lbs radar and mount, about 20 gallons more fuel (around 120lbs.), 4blade props, and 6 years of bottom paint. adds up quick :mrgreen:

just trying to help you out. ron

 

[beachbum]

Got it

I have a thruster, freezer box, AC, radar, flir, sinkers galore! every option grady has...i have 350 gal fuel, sounds like you may have more- @6lbs a gallon, and I don't have the bottom paint build up (thank goodness)!

thx

 

[beachbum]

BTW, you were helpful..will let you know what I find out

thx

 

[ElyseM]

ok, my last post on this. if you look at the published perf bulletin, the tested weight differential is 2.6K. these two hulls don't weigh a smidgen away from each other. you should be doing much better on fuel burn, not similar to a 330. focus on tabs and trim, makes a significant difference in ride and economy. good luck, ron

 

[NOTHING ELSE MATTERS]

Your top speed is a little off, I was doing 49-50 MPH with the same motors and same exact set up and my tank was always 3/4 full. The 1 MPG is just about right. I saw afew times 1.3 but the majority of time was 1.

 

[beachbum]

thx for all the feedback and advice! helpful