Fuel mileage v hp

[Lowlysubaruguy]

Chasing tuna has prompted me to weight options. Its my first year going far out to sea. The cost of bigger power plants seemed not worth it but the amount of fuel I’m consuming may alter that.

First boat specs
2017 Wellcraft CC 26 foot Twin Yamaha 150 outboards dry weight 6000 to 6500 pounds loaded fuel four guys ice gear 10,000 ad another 500 pound of fish on the return

on a good day I can run 30 To 35 mph and get 1.8 to 2.1 mpg However it’s rarely that smooth here.
two trips in ruff water have been about 13 to 15 mph And mileage one trip was .7 mpg that day we stopped 48 miles out because of the time factor we still caught fish but another 20 miles is where they really were. We needed another three hours of daylight and back surgery to go any further than we did.

the question now presents itself if I would gain fuel mileage with larger engines and what engines and size. While a $20,000 engine upgrade is hard to pencil out, if fuel mileage increased enough to offset this by half over the life of the boat I’d be tempted to do so before my outboards have many hours.

I remember when $100 was enough fuel for my entire salmon season but I can burn $500 worth of fuel in a day chasing tuna. Its less horrible with four guys pitching in for fuel and worth every cent on the mental chart. One day was flat we were 92 miles out burned less fuel than my last trip 48 miles out.

in retrospect I was probably better off never catching one Can’t put that geni back in the bottle. It makes scuba diving seem like a cheap hobby.

 

[Scott Danforth]

fuel consumption per HP is a constant.

depending on what you command for HP for the given task will determine your fuel burn.

your outboards are getting a BSFC of about 0.4#/HP/hr.

flat water means steady state loading vs being on/off the throttle. when your in the rough stuff you are constantly throttling up to climb a wave and throttling back at the top of the wave to try to smooth the ride. throttling up means your running richer on the acceleration to pick up load.

under steady state burn with a light load, the larger motors may help the fuel burn reducing your fuel spend for a few instances, however when the ride gets rough, short of a bigger boat to allow you to glide over the waves vs throttling up/down, you may burn more fuel.

 

[mr 88]

Had this ^ discussion with a Bayliners Group and , if not all of them couldn't grasp the concept of fuel consumption per HP is constant . One reply had a sales sheet from Bayliner and showed the fuel usage with different hp. Of course the cruise speeds were never the same for the engines they were comparing and they never took into account a V8s or V6 weights vs a 4 banger. I tried explain how flawed the spec sheet was ,fell on deaf ears.

 

[dingbat]

Scott pretty much hit it on the head.

The only way to increase range is the optimize your props, increase fuel storage, pick your days better or move to Hatteras...pelgics within sight of the beach

 

[Scott Danforth]

spark ignited 4-cycle inboards/I/Os and outboards have a BSFC of about.4#/HP/Hr
spark ignited 2-cycle outboards have a BSFC of about .5#/HP/Hr (the e-tecs are a bit lower)
diesel engines have a BSFC of about 0.33#/HP/Hr

fuel burn is based on commanded power

 

[Lowlysubaruguy]

I’m all for picking the right days but sometimes the fish require alterations.

it was good to see the result of a rough day at sea. We averaged 15 mph fuel consumption was .8 mpg the event was like getting on a single prop airplane flying through really bad turbulence for four hours fishing for three hours then flying back. We did catch a few fish. I had a buddy in from far away the ocean was not rough enough to be Dangerous just very slow going.

I had not ran my boat in this condition long Enough to see the fuel consumption This low but it’s good to know that being caught in something like this would really impact my range. So it was actually a very good day at sea my buddy caught his first tuna we worked the boat out over some rough water and I know for future reference what to expect. There are several places I plan to boat to from the keys which could tax my range if conditions change. Ideally these trips will only be done in good sea conditions but one of our tuna trips the forecast was way off a day and half early. We were out 70 miles when the wind changed and it went from very smooth to moderate quickly. We wrapped up and beat it. But the day was support remain calm. We ran out at 40 mph our trip back we were lucky to break 20.