Fuel Efficiency/Range-gctid817513

[alanmoor]

I was considering taking some longer trips and wanted to see what my "best" speed would be. My brother in law had a basic spreadsheet he used so I expanded on that. I have a Floscan that gives me MPG and GPH, so I recorded those results (and speed according to Navionics on my phone). I've attached a screenshot of the results. I can't explain the discrepancies. I forgot that I can see GPS data on my radio when I was taking the readings, so maybe the speed was off on one of the GPSs.

No real question here, but if anyone wants the spreadsheet I can e-mail it.


Attached files

[SomeSailor]

That's about where my 2859 ran best. We've argued MPG versus GPH on here many times, but for me I was getting just under 2 MPG under idea conditions. My best speed seemed to be just less that 30MPH. On my trawler I can get just at 5MPG, but at 8kts.

[alanmoor]

What was surprising for me is that a prop change didn't make much difference. I have a Duoprop and the boat came with B5s. My WOT was under 4000. I wanted a spare set so I ordered a set of B4s. My WOT went up (4400), but the speed and fuel efficiency didn't change much. My speed at WOT is 35mph with 2 people on board and over 1/2 tank of fuel. The "comfortable" cruising speed is still about 3200-3400.

What was disappointing for me in all this was that one of the trips I want to make is to the Dry Tortugas (and not at 6mph). However, that's just outside the limit of my boat (assuming I run at 20+ mph). However, I guess I could carry an extra 20 gallons and still have a decent safety margin.

[mister_larry]

I can't believe you will have any trouble getting 10% or so more range in the boat if you are willing to drive safely. Since you have a FloScan, this will be easy to confirm. You have a baseline fuel consumption chart. Make sure you know where the trim tabs and load variables are set that generate these numbers.

On your WARMED UP engine, (cold starting issues can be addressed later) shut it down and advance the distributor timing by 4 degrees. Take the boat back out, pay particular attention to the trim setting, and read the FloScan numbers through your plane to cruising speed power range. Do NOT go for top speed. By advancing the timing you are changing the redline as it applies to detonation: engine pinging.

Did you get 10% or so? Let it cool down and see if the boat will start. You may need to have perfect ignition components and even a hotter coil to pull this off, but you should be able to make it to the Dry Tortugas safely if you drive the boat to the engine timing.

Happy boating.

[smitty477]

"On your WARMED UP engine, (cold starting issues can be addressed later) shut it down and advance the distributor timing by 4 degrees."

Unwise to do this as there are many ways in which you can cause engine damage and not be aware it is happening.

Best to stick with trim, least amount of weight, hull and running gear condition ,and making sure the prop is both the best fit for efficient cruising as well as in great shape.

[Jim_Gandee]

[quote]but you should be able to make it to the Dry Tortugas safely if you drive the boat to the engine timing.[quote]

While one may realize a slight increase in efficiency with advanced timing I certainly would not rely on that to safely reach my destination! There are way to many ocean and other variables that could erode such a thin margin leaving one bobbing like a cork.

Get a bigger boat, carry more fuel or make additional fuel stops.