Who’s done the calcs for the optimal cruising speed to limit gas consumption? I think ours is right after we get on-plane about 5.6gal/hr each engine and 17-20knots depending on wind, waves and current.
Seems like a non-linear increased curve of consumption as I put the throttles down from there.
Any other opinions or thoughts? Ours are 2013/14 Honda 225s.
It’s a great question, I’m just starting to play with mine. I need to pick a calm day and really test out each rpm. Mine does not seem to match what the uscg published, could be the bottom pain or engines….
Mine still has a sticker next to throttles from USCG that recommends 4500 RPM for cruising speed. At that rate I’m almost at 30-40 gals/hour. Must have been very different outboards or configuration, or they just fueled up all the time?
Though, no one knows how to consume fuel like the US Military!
Did a bit of testing on a run yesterday, seems like 3800rpm and 52 percent trim will get me 30knts and just a hair under 2nm/g, that seems to be the most efficient in calm waters.
Yeah - around 4k seems to be the most efficient for me. Although, I’m in the habit of driving around 4500 as I’m impatient and it just feels better. At $6.80/G I’m starting to rethink that…
Ha, this thread started because I kept seeing you and the white Defender blasting through Obstruction Pass! Was thinking you knew something I didn’t about best mpg.
It’s apparently good for the motors to run WOT now and again. I’m convincing myself that it’s ‘preventative maintenance’ and will be cheaper than getting the motors fixed 
Denial is a powerful tool. Every time I pull a pot full of crab - I say to myself “hey - not bad for $8 of bait” while blissfully ignoring the ~ $300 of fuel to set and pull the pots.
I run mine a lot and while 4100ish and just enough trim to stop the engines splashing water sideways feels better through the water(burning 8-9 gal each and 29 kts) just under 4K seems to save a lot of fuel for the 2kt gain in speed and closer to 6.5 gph each). And then is the tank full and how much chain am I hauling around for servicing moorings has an impact as well… and how clean is the bottom?
And as for the military suggestion of 4500rpm- they definitely don’t pay for the fuel so they do not care. I drove tanks in the Army (just a few years ago) and we got 4 gallons to the mile!!!
Hey, don’t get me wrong, cruising everywhere at 4500 RPMs sounds like fun!
You must be the orange defender on the buoy? Go past on my way to Anacortes often, still playing with best balance of fuel efficiency and speed plus comfort, I find in heavier weather I go 34-36 slightly trimmed down. I get about 1.6 that way but it’s more stable. It’s hard to get true numbers without actual testing due to the heavy currents we get…
Anyone used these fin foils before? Buddy in AK just recommended them to me and says everyone he knows using them claims better mpg and quicker onto plane.
Get your boat on a plane quickly by increasing the lift generated by the engine. They also allow you to go more slowly while still remaining on a plane, so fuel consumption is decreased.
[https://www.westmarine.com/davis-instruments-the-original-doel-fin-hydrofoil-351221.html]
They work well on smaller boats but I haven’t seen them used on anything other than tenders, I actually have a set sitting in my shop for a whaler with twin 90s I use in the summer but never installed them. I thought about putting them on the 225s as they may also help some with trim, will likely test it out next time I have the boat out of the water.
I’ve only ever seen them on smaller (usually dinghy) outboards.
Wanna donate your trailer for 30 minutes? I’d be willing to try them out and see if they offer any improvement, my engines are 10 years old so don’t care about putting a few holes in the lower unit fins but I learned the hard way these are a pita to install in the water 
Hi All,
It might years too late to answer this question, but there is a table in the “Defender Operator’s Handbook” that the USCG used. It gives all the fuel burn rates and speeds for the Defender at different RPM. I took all the figures from this table (5-1 on page 5-7), and put them into excel. I could then enter the length of the planned trip as well as the current fuel cost at the local dock and figure out the least expensive speed. The fuel costs, as I have it in the spreadsheet, are in Canadian $ per litre but you could just change your units.
Of course, if you have a set length of trip planned you have to remember that you are running your engines (burning fuel) for a longer or shorter time depending on your speed and that figures into the ultimate cost too.
In the end I found that 4000 RPM was a sufficiently efficient speed, but that 4500 RPM was not too prohibitively more expensive (like $4.00 CDN) for the 24 NM trip to my cabin on Vancouver Island. 2500 RPM and 3000 RPM were the only speeds that were more efficient, but at some point you just want to get where you’re going, so I chose 4000 RPM and 30 knots.
Incidentally, since I changed to 3-blade props I get 1 or 2 more knots at the same RPM, so better fuel economy.
| INDEPENDENT VARIABLES | ||||||||
|---|---|---|---|---|---|---|---|---|
| Length of Trip | 24 | |||||||
| at Speed (NM) | ||||||||
| Fuel Price ($CDN/litre) | $2.00 | |||||||
| DEPENDANT VARIABLES | ||||||||
| Comment | RPM | Speed* | GPH* | Elapsed Time at Listed Speed | Elapsed Time | US Gallons Burned | Litres Burned | Difference litres |
| (knots) | (hours) | (minutes) | from best cruise | |||||
| 6000 | 46 | 44 | 0.52 | 31.30 | 22.96 | 86.78 | 38.39 | |
| 5500 | 42 | 32 | 0.57 | 34.29 | 18.29 | 69.12 | 20.74 | |
| **5000 | 40 | 28 | 0.60 | 36.00 | 16.80 | 63.50 | 15.12 | |
| 4500 | 36 | 20 | 0.67 | 40.00 | 13.33 | 50.40 | 2.02 | |
| Best Cruise Speed | 4000 | 30 | 16 | 0.80 | 48.00 | 12.80 | 48.38 | 0.00 |
| 3500 | 24 | 14 | 1.00 | 60.00 | 14.00 | 52.92 | 4.54 | |
| 3000 | 22 | 11 | 1.09 | 65.45 | 12.00 | 45.36 | -3.02 | |
| 2500 | 16 | 7 | 1.50 | 90.00 | 10.50 | 39.69 | -8.69 | |
| 2000 | 10 | 6 | 2.40 | 144.00 | 14.40 | 54.43 | 6.05 | |
| 1500 | 8 | 5 | 3.00 | 180.00 | 15.00 | 56.70 | 8.32 | |
| 1000 | 7 | 4 | 3.43 | 205.71 | 13.71 | 51.84 | 3.46 | |
| 700 | 4 | 1 | 6.00 | 360.00 | 6.00 | 22.68 | -25.70 | |
| * = From Defender Operator’s Handbook Table 5-1 on Page 5-7 | ||||||||
| ** = Extrapolated |