Time to slow things down?

scross

scross

Well-known member
Joined
Jan 30, 2015
Messages
2,111
Fluid Motion Model
C-28
Hull Identification Number
FMLC2831A717
Vessel Name
R-25 Classic - Sold
MMSI Number
367719470
Just doing some ballpark numbers and pondering.
We typically cruise 900 miles a season and put 75 hours on our C28 diesel engine. That’s an average cruising speed of 12 miles per hour. At 1.2 miles per gallon at that speed (with current diesel prices) we will burn 750 gallons (10 gph) or $5625 in fuel (@$7.5/gallon) for the season. Note that the majority of our cruising time is in BC where fuel is a tad more expensive. We also cruise heavily loaded so our gph burn is a tad higher too.
But, if we slow down to an average cruising speed of 8 mph, we get about 2 mpg. Yes, season total engine hours go from 75 to 112 hrs but total fuel used drops to 450 gallons (4.0 gph) and fuel costs drop to $3375. That’s actually pretty close to our actual fuel cost for the 2025 season.
That’s a fuel savings of $2250 for the season. Hmmm. I think we will be spending more time cruising at 8 mph this year!
Your thoughts?
 
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When I embark on my next loop section cruise, I will slow down for certain. I’m already doing that in my diesel tow vehicle. It is not my daily driver. I drive to our small farm 250 miles southwest of here (my wife’s childhood homeplace) and tow the boat with it. Diesel is 65% higher than this time last year. I keep records. And I know how to figure percentages!
 
We have always cruised at 1500 rpm, 45% power, 6.5 kts, 1.8 gph, 3.6 mpg, about 200 hrs and 1,300 miles per year costing around $2000. Of course there are about 10 minutes of 95% power every few hours to keep the turbo clean. We enjoy the journey as much as the destination. Yes, there are times it gets boring (colvos passage), but most of the time it is just relaxing.
 
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Unless there's a reason to get somewhere by a specific time, we generally putt along at ~7 knots. It's quiet, relaxing, and if you did happen to tap a log (lots of them in the PNW) chances are you won't damage anything.
 
My philosophy is that when I am on the boat I’m already there. So six knots or so is fine with me. I ask every diesel mechanic I meet if I’m harming my engine. The answers are mixed. Some just plain no, slow is ok. Some say slow is ok, but go flank speed five minutes near the end of the trip. I run it up occasionally. I’d be interested in what others think.
 
Our new R29 burns at 1.6 miles per gallon at anything above about 15 MPH...if we pull down to 8-9 MPH, our mileage goes up to 4.5 or so.

Our favorite destination is (rounding) 10 miles away which means the trip either takes 30 minutes and costs us $40 in gas or we take 70 minutes and it costs us $14 in gas.

Time = Money
 
I am confused.
4.5 mpg at 8-9 knots????
I have a 2017 R-29 D4-300.
At 8.5 knots, I get 1.9 mpg.
At $7 per gal, that is $37 not $14
Are new boats that much different?
 
I am confused, you say $7 per gallon for diesel, at our fuel docks it's over $9 /gallon. 🙂
 
I get similar numbers with my 2018 C-30S (~4.5 mpg at slow speeds)

Code: 
+---------+-------------+ --------+---------------+
| Speed    | Burn Rate | NMPG  | Statute MPG |
|-----------|-------------|----------|----------------|
| 6.6 kts    | 1.0 gph     | 6.60      | 7.60              |
| 7.8 kts    | 1.8 gph     | 4.33      | 4.98              |
| 14.5 kts  | 9.1 gph     | 1.59      | 1.83              |
| 19.8 kts  | 17.0 gph   | 1.16      | 1.34              |
+----------+------------+---------+---------------+
 
Mastercraft said:
I am confused.
4.5 mpg at 8-9 knots????
I have a 2017 R-29 D4-300.
At 8.5 knots, I get 1.9 mpg.
At $7 per gal, that is $37 not $14
Are new boats that much different?
Click to expand...
I'll grab a picture at both speeds this weekend and confirm, but yes, we get a massive improvement at 8-9 MPH than we do at high RPM. Maybe we were grabbing some current that improved that efficiency.

One way 10 mile trip at 4 MPG would be 2.5 gallons at $7 per gallon is $17.5...so you're right, did a bit of rounding.

One way 10 mile trip at 1.5 MPG would be 6.7 gallons at $7 per gallon is $47...

I'll play with it this weekend and see what I can figure out.
 
venajeff said:
I am confused, you say $7 per gallon for diesel, at our fuel docks it's over $9 /gallon. 🙂
Click to expand...
Not to rub salt in the would...but we're actually at $6.50 and everyone is super mad about it. ;-)
 
You shop at the wrong dock!
I am in Anacortes at $6.63 per gal.
On "Fuel Dock" app, it varies in Seattle area from $5.70 to $8.50.
 
So is it time to bring back the R-21model?
Or something on the line of the Nordic-26?
 
Fuel snowbirding to FL $3.25 average downbound. $5.50 returning north. Slow down. Stay off the turbo, study tidal currents. Go with the flow. On the Delaware, 7.5ft tidal swing all the way to Trenton, that's a lot of moving water every 6hrs. Did the same timing on the Cape Fear River. Ebb and flow.
 
Mastercraft said:
You shop at the wrong dock!
I am in Anacortes at $6.63 per gal.
On "Fuel Dock" app, it varies in Seattle area from $5.70 to $8.50.
Click to expand...
Diesel is $7.60 USD/US Gallon in Sidney BC area. Maybe I don’t use the boat but I’ve always thought fuel is one of the minor costs.
 
I have always said to my sailor friends that fuel is the least worrisome cost. But at the current prices I think that might be changing. I must say, I am not missing the .50 mpg fuel economy of my previous boat. Not to mention our Ranger Tug is gasoline so that makes a price difference also.
Am I just getting old or does anyone else still feel like diesel is supposed to be cheaper than gasoline?
 
This post is interesting, depending on tides and current on the Columbia at 10 to 12 MPH we get about 2 to 4 per mpg with our 300HP Suzuki Outboard on our R-27- even better if we slow down to 8MPH.
 
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