Bertram 25 fuel burn

[Briancc]

Just wondering what others are getting with their setups. I'm running a 25 flybridge with 3.0 mercruisers and 14.5x17 props. After running the numbers I seem to be getting about 1.3 mpg on a typical trip. I usually run about 3400- 3500 rpms at 22 -24 knots. I dont have flow scans so I'm not sure where my best cruise is.. My last trip out we ran 64 miles total while jumping around a couple times bottom fishing and I seldom shuf off the motors while I'm out. Does that number sound a little low to anyone else or is it about right for those conditions. Also a mechanic friend said I might be able to get a little better mileage with 4 blade props any thoughts on that? Thanks

[farmer]

I get 1.9 mpg , running around 2800 rpm at 22 mph. Single 383 ,1.52 velvet drive, 4 blade ,total inboard. Doesn't change much between 14mph and 24 mph.

[Carl]

I do not have a 25 or 3.0's but your burn does sound high for your setup.

I can say from having had 440 gas motors with carbs AND flowscans there can be a huge difference in burn with only a slight touch of the throttle. I found 2900rpm gave me 18mph burning 22-23gph. I could sometime tap the throttle down to the 2850-2875 area and my burn would come down to 20-21gph with speed the same. I could add a little tab and speed would increase a mph or so with same burn...or I brought throttles back to 2850 and burn dropped to 18-19gph. So you need to find your boats sweet spot.

The flowscans also helped me find out I had a worn throttle shaft bushing. Running out to the shark grounds I noticed one motor burning alot more then the other...usually that meant it was pulling the other motor along. So I brought the throttle down some and motors went out of sync...tapped it back up to where it was...motors sync'ed...but I noticed as I tapped the throttle the burn changed by a few gph. Also helped find out plugs fouled and bad wires...although the smal of my back was able to tell that anyway.

If you have carbs, there is a nice spot usually before the 4 barrels kick in...once the 4 are in I started looking for the closest fuel dock.

On a buds Fuel Injection setup with scans...it was just a sweet spot for the boat.

Without flowscans its best to run, shut motors in between and fill up. Not always easy to do. Motors may only burn a couple gallon or tow at idle, but on short runs that does throw the numbers off. But it can be quite accurate. I ran for years without them and found my numbers mostly by charting my longer runs offshore, or to the beach and keeping track that I trolled 3 or 4 hours or had extra people and gear so I had consistency.
I found my best speed was actually 16mph...just on plane. I hated running so slow, but I had my wifes uncle following me in his bottom fouled, too big of a boat for such a small motor Bayliner. He wanted to go to a dock and dine with his boat. Only good part was when I filled up I burnt soo much less then I expected. I was actually expected us to burn through tons of fuel as I thought I was just pushing water like a barge.

Will a 4 blade help...Maybe, maybe not...depends. Best to borrow one if you can. 4 Blade props tend to lift the stern...does you stern need a lift? Does a little tab help?? if so then maybe. But its also an extra blade to push though the water...

[Joseph Fikentscher]

I have 318 Chryslers with V-Drives. I get about 1 gallon per mile.

[ktm_2000]

my B25 moppie is light weight wise and I had twin 3.0L which were under propped running 15x17 - could rev up to 5400 rpm, I probably should have had 14.5x19 or 14.5x20 props.

I regularly cruised 22-23kts at 3600rpm - I didn't have a flow scan but based upon the runs I made vs fuel burnt I was burning around 10gph at cruise. I never did a nmpg calculation but if I had to guess I was close to 2nmpg.

[Carl]

I have 318 Chryslers with V-Drives. I get about 1 gallon per mile.

1mpg, really?? I was getting .9 with the 31 and 440's. What speed are you cruising at to get that?

[Joseph Fikentscher]

Carl,

I'm cruising at about 18-19 knots.

[Carl]

Joe-

I'd have guessed the boat would have been in the 1.2 to 1.4pmg range. The big word is "guessed" and that's about all I'm doing going from boats I've been around in the 25' range. But most of those were single motors with stern drives on flatter bottoms without bridges and they did not have deep vee's. So a whole other class of boat. It just seems odd you cruise 2 knots faster with the same burn as my 440 31. Then again, if I bumped her up to run 19knts I'd be at the .75gpm or more depending on conditions.

[Joseph Fikentscher]

Carl, I cruise at around 2900 to 3000 RPMs. If I go higher the fuel burn really increases.

[Carl]

Carl, I cruise at around 2900 to 3000 RPMs. If I go higher the fuel burn really increases.

Yeah that burn goes pretty high once you start pushing the throttles up. I'd peg my 20gph flowscan just as the 4 barrels kicked in. I've heard I could run there without killing the motors...but 40gph for the 2 motors would kill my wallet in short time. But I had learned that years earlier when I was checking out the carbs when running. I had someone running the boat for me and had them bring up to WOT...looking down the carb it looked like someone was shooting water from a hose at full force. I just kept thinking, we don;t want to do that too often....or like ever. BUT it is such a nice sound.

I assume you get your rated WOT

[Joseph Fikentscher]

Carl,

I get to 4000 rpm. I believe that is the recommended max.

[Carl]

Carl,

I get to 4000 rpm. I believe that is the recommended max.

If that is the rated and your getting it all is good. I had my boat with a single 318 27 years ago...even if I remembered I'm not sure those numbers would be valid. I do recall burning 12gph at cruise though. What does that mean, nothing I think.

[Stephan]

Might part of the decrease in economy come from Ethanol fuel? I have to remind myself to not blame my engines for diminished performance when I'm putting less energy per gallon in them.
Best,
Stephan

[Carl]

Might part of the decrease in economy come from Ethanol fuel? I have to remind myself to not blame my engines for diminished performance when I'm putting less energy per gallon in them.
Best,
Stephan

That is very true. I forgot about the alcohol giving a bit less bang for the buck. At least it cost more, you need to burn more for the same travel and it causes issues with older motors.

[Briancc]

I did a tune up to the 3.0's this week. Headed out again Sunday and hope to do a little better on fuel. I Might pick up some 4 blades to try out if the tune up doesnt help. Any recommendations on 4 blade props? Are the solas 4 blades any good?

[Simpleg1]

Ok I have twin 165 straight six’s, I was running aluminum 3blade 14.5x17 black diamond getting 1.6mpg at 2850rpm doing 21knots.
I recently put counter rotation lower unit on and now run 15x16 solas 4blade which have been terrible props. I ordered solas stainless 14.25x17 3blade which as recommended by a prop shop, I haven’t picked them up yet. Not sure if this helps.