A question about cruising at "Trawler Speed" MPGs

M

MilesandMiles

New member
Hello Everyone,

I've been wondering, has anyone ever had the patience to cruise at 7 or 8 knots for a long period of time (like a full tank of fuel perhaps) with a 90HP and figure our just how economical our boats can be? I am talking about the 22-cruiser. Every mode of exploration I do involves a level of frugality (if only to keep things interesting) Of course it's nice to know the speed is there if you need it, but I see myself continuing my slow poke ways on water, and just wondering what I might expect for fuel consumption.

As usual, if this topic has been discussed to death already, my apologies, and please direct this newbie to the link :)

Brenton (sleeping comfortably in the back of his truck in Port Townsend, leeching wifi from the marina) :)
 
Brenton

The majority of our 1565 mile cruise during a six week period in Southeast Alaska last summer was at displacement speed on one of the two 40 hp motors. The 22 foot CD was loaded very heavy with when topped off 100 gallons of fuel and was towing our motorized Mokai kayak. On one run of 405 miles between fuel stops we averaged 5.3 mpg and 5.0 mpg over the entire 1565 miles. If interested this thread in the Grand Adventure Forum describes the cruise with photos.
http://www.c-brats.com/viewtopic.php?t= ... sc&start=0

Though our boat has twin 40's and not the 90 you requested the 90 hp I think with similar weight should do as well or better. I'm sure others will chime in if not.

Jay
 
We have cruised at 7 knots or less for about 100 miles. Our average fuel consumption was 10 miles per gallon over that distance. The boat has a 90 hp Honda carburetted engine, two on board with all of our cruising gear including the dingy on top. This was in Puget Sound, Edmonds, LaConner,Anacaortes,Coronet Bay etc, two years ago. we were impressed, but it does take determination to avoid pushing that throttle forward!

For a comparison, we usually get about 4 mpg at normal cursing speeds.
 
I might add as you probably know it takes many miles under different tide, wind and wave conditions to get an accurate overall average. Have never averaged better then 6 mpg in combined conditions with all miles at displacement speed with boat loaded heavy on extended cruise. On other long cruises where the majority of time boat was on plane averaged 3.5 mpg
 
Brenton,

As Jay and Dennis have already indicated - slowing down to hull speed greatly increases your fuel mileage, but it also greatly increases your time-to-destination. Trade-off's for sure.

My previous CD22 ("Naknek") had a Suzuki 90 (fuel injected), and I experimented with various prop's. Running on plane (about 4200rpm) yielded about 3.5mpg overall. The best I ever got while on-plane was 3.9mph. Interestingly, the 3.9mph was at about 4400rpm using a graphite "Piranah" prop. I think the boat running slightly faster actually yielded a reduced 'wetted surface, hence the better mileage. ...seems counter-intuitive, but that was my experience. Like Jay's experience, Naknek was usually pretty heavy while cruising.

The "displacement" cruise speed increases the mpg significantly. Overall I would get about 6.5-7mpg in the displacement mode. Displacement speed for a CD22 is right around 6.5mph(statute) and approximately 2200rpm. I had a fuel monitor and would experiment with engine trim for the major adjustment, then trim tab's for "fine" adjustment to yield the lowest indicated fuel consumption.

Cruising at hull speed can become pretty boring - but you do get a good opportunity to see the scenery! ...hour after hour, after hour! I found that having autopilot was Really a lifesaver. Not everyone agree's, but I find that AP permits the captain to relieve some of the tedium of constant course corrections. (Don't tell anyone, but the AP held a better course than I did.) I Alway's made a point of remaining at the helm even with the AP; imagine answering Nature's Call, falling overboard, and watching your boat motor (in a perfectly straight line...) away from you! No thank you! ...but I found an AP to be a Very good investment - particularly for the displacement cruiser.

And displacement cruising can Really increase the useful range of your vessel, not just help the pocketbook.

Best,
Casey
 
Miles & Miles,

We run at displacement speed on Lake Powell more than on plane with a CD-25 powered by a 130 Honda. At about 6 mph we do 4 to 5 mpg. At about 5 mph we do 5.5 to 6 mpg. Saves a lot of money and since we're not usually in much of a hurry the slow pace is not a trade-off. It's too beautiful on the water to rush it, no?! When we do need to make time the throttle is right there under your right hand.

This from Dr. Bob: maximum displacement speed is 1.34 X square root of LWL. That puts max displacement speed for a 22 (using 20 for LWL) at 6 mph.

At Powell elevation (3700') we lose about 10-15% horsepower and of course use a little more fuel than would be experienced at sea level.

Dalton
 
Our boat is a 25, but we do plenty of displacement cruising. When fuel prices spiked a few years ago, I decided to try life with the throttle pulled back. If "the journey is the destination," slow cruising is great. If you want to get somewhere in a reasonable time, it is very nice to have that as an option... one of the best aspects of cruising with a C-Dory.

When we were on the Erie Canal last year, we found much of that stretch has a 10 mph speed limit. Even in the open areas where the speed limit is 30 mph, we found ourselves just putting along most of the time. The towns are only a few miles apart along most of the canal, so there's no need to speed on to the next place. We generally see 5-6 mpg at displacement speed; it drops to less than 3 mpg when up on plane. Unlike many hull forms, the C-Dory is comfortable at both speeds.

Like Casey, I will often use the autopilot at displacement speed, allowing me to check charts, move around a bit, and take in the sights. If we're just wanting to be out on the water for the day, it doesn't matter how many miles we make. Stop, toss out the anchor for lunch, kick back and enjoy some time in the cockpit... no reason you have to rack up miles to enjoy yourself.

Oh, and a nice chair in the cockpit is even more comfortable than the back of the truck. I've been known to make a post or two with our wireless broadband while at anchor or cruising along slowly.

Good luck with your "hunt."

Best wishes,
Jim B.
 
We came from the trawler world and bought the cd22 as a trawler. We cruise with 1 engine up 95+% of the time going 6 knots. We get around 6 to 7 MPG.
 
We have the cc-23/venture witha f115 Yamaha and we get from 4.2-4.4gph.When we slow down I can get over 5mpg thats no wake zones to 6mph and some cruising at 22-25 mph
When we went up to lake Tellico last summer we were getting 3.5 -3.8 not as good as naples fl (sea level, salt water) vs 900ft and fresh water .By slowing down we can achieve over 5-6mpg so slowing down can get one almost double the mileage
 
Our experience on Daydream, a CD25, is right in line with what other CD25 owners are reporting. Realizing that you are doing well with a loaded CD25 to get 2.0 - 2.5 nmpg on the plane, 4.5 - 5 nmpg at 7 knots is a significant improvement! This is our sea level experience. We do a bit better if we slow down to 6 knots but that becomes almost painful. BTW, you need to say whether you are talking about knots and nmpg or mph and smph! It makes a difference!

We did less at Powell, I think we averaged 3.0 nmpg for the whole trip this year, which we did almost entirely at 7.5 knots (8.6 smph). We could have done better slowing down a bit but but 7.5 knots worked well for us and our cruising companions on Traveler. We ended up only using 57 gallons of gas the whole time we were there, which was quite comforting.
 
Being Canadian, and old enough to remember when we did not use the Metric System of Measurement, I can converse in all official units of measure……..Metric, Imperial and US. We in Canada, of course, buy our fuel in Liters.
I have found that if I plan to burn one liter of fuel per nautical mile then I am really close with a small margin of safety. This is cruising at 15 to 17 NMPH between 4500 and 4800 RPM with a 4 bladed prop on our 75 HP Honda and loaded fairly heavy.
To translate……….this works out to a range of 3.8 Nautical Miles per US Gallon or 4.4 Statute Miles per US Gallon.
There is better economy to be had when the load is light and no dinghy on top…..which is very seldom. We don’t cruise much at hull speed so I have no data on that but from all of your posts I know that there are some real savings to be made by doing so. I, like many of you, get too bored going so slow for long periods……..unless we’re fishing……..then I can go all day.

Cheers :beer
Tom
 
As several have noted, the slower you go, the better the mileage (at least to a certain point--and that would be somewhere about 4 mph on the c dory 22. If you look at the sq root LWL, at 20 or so feet, that is 4.5 knots or 5.2 miles per hour. That is a very easily driven hull speed. The max for effeciency would below 6 knots. So if you are going 7 knots in the C Dory, you are not at peak effeciency--I don't know exactly where that break even speed is (Planing vs displacement--but suspect it is below 9 knots--and above 9, until planing is going to get worse economy) Although the C Dory is a rather effecient planing hull, it is not an effecient displacement speed hull. A narrow canoe type of vessel, with rounded chines would get much better fuel economy at the same length water line. Saiboats will do better, even with their keels. My Cal 46 and the considerably larger boat I took cruised for 41,000 miles, would get 6 miles per gallon at 6 knots.

On the other hand, if you are used to going 5 to 6 knots--and many of on this site, have many thousands of miles at that speed in sailboats--and enjoy the journey, it can be very pleasant. 6 knots gives you about 144 miles a day, or about 15 1/2 days Los Angeles to Honolulu (2,225 nautical miles accepted distance on Transpac race). Plenty of time to read several dozen books and relax.
 
thataway":1dipp5qo said:
...

On the other hand, if you are used to going 5 to 6 knots--and many of on this site, have many thousands of miles at that speed in sailboats--and enjoy the journey, it can be very pleasant. 6 knots gives you about 144 miles a day, or about 15 1/2 days Los Angeles to Honolulu (2,225 nautical miles accepted distance on Transpac race). Plenty of time to read several dozen books and relax.
Click to expand...

Let's see... 2,225 nautical miles... let's say 5 mpg, just to be safe... um, carry the 2... let me get my calculator... that's 445 gallons of fuel to make that trip. 445 gallons of fuel... let's see, at 7 pounds per gallon... I already have my calculator out... that's 3,115 extra pounds of additional weight. :shock: Oh, and figuring $4 per gallon for fuel... that's $1,780. Yeah, I'm gonna have to trade my C-Dory off and get another sailboat. :wink: Or... check Expedia and catch a flight for $511.90 and save the expense of a divorce lawyer. :mrgreen:

Yeah, I know, Dr. Bob - you were just figuring time. I'm up in the frozen northland right now, staring out at the "white death" as the blizzard (and I ain't talking Dairy Queen) winds down... that trip to Hawaii sounds pretty good to me right now! 8) Want me to book two more seats?

Best wishes,
Jim
 
Jim - I thought you lived in the tropical part of Texas, and with the hurricane season prety well ove would be oiut in the gulf. We are experiencing a Chinook wind right now with temperatures in the mid forties. Slush and water everywhere. Thataway. Good to learn of your successful surgery and hope our wakes cross sometime again.

Milesandmiles, I had a 1996 22' with 90 Honda on it. Shortly after purchase, a Flo-Scan was installed and that along with the GPS was used to determine MPG. I quickly learned that around 900-1000 rpm produced the best MPG, (sometimes as high as 10-12) but many variables kick in: overall weight, current, wind, wave action, elevation, prop, quality of fuel, etc. Seven to eight knots starts working the engine and reduces ultimate efficiency.

But who wants to travel long distances at 4 MPH? The Flo-Scan also showed the Honda's "sweet spot" between 4000 to 4200 RPM and produced 4-5 MPG.

I'm now running a 115 Mercury EFI on my newest 22'. It is not as efficient as the 90 Honda but has that extra boost running with heavy loads. I believe the 90 Honda or any other 90 whatever made today is an ideal power plant for performance and efficiency for 22'. Keep you carbs clean and you will have few problems. John
 
It may have been on this forum, I read somewhere about a guy that overprops with something like a 21 or 23 pitch prop that was producing remarkable mpg at non planing speeds. In that configuration you would want to be cautious operating the motor at higher rpm and planing speeds as that would lug the engine.
 
You might get better mileage by "over propping" an engine, however this will lead to lugging at any speed, and is detrimental to longivity of the engine.

Jim--the trip to Hawaii is what sails were made for!
Now people have made it in low powered vessels, row boats and kayaks--even one guy in an aluminum boat started out going that way....but was stopped by CG. (I think one boat make of Budwiser cans also started thataway...)
Bob
 
Tex,

Here's a challenge for your inventive mind: find a way to incorporate a constant speed (adjustable) prop in marine engines, similar to what is seen in propeller driven aircraft.

For the non-aviation afflicted - "complex/high performance" aircraft have adjustable prop's that can be adjusted to low pitch for high torque requirements (ie. takeoff) and higher pitch for cruise and better economy.

Best,
Casey
 
Casey":2zpxgjed said:
Tex,

Here's a challenge for your inventive mind: find a way to incorporate a constant speed (adjustable) prop in marine engines, similar to what is seen in propeller driven aircraft.

For the non-aviation afflicted - "complex/high performance" aircraft have adjustable prop's that can be adjusted to low pitch for high torque requirements (ie. takeoff) and higher pitch for cruise and better economy.

Best,
Casey
Click to expand...

Casey, it's been done. At one extreme, Pro-pulse makes adjustable pitch props that are manually adjustable in pitch (e.g. multiple fixed pitch positions). At the other extreme are variable pitch props that can be feathered while in operation - see http://www.peluke.com/Propellers/propellers.html for an example.
 
Roger, maybe I'm reading it wrong, but what I get from the information on the Luke feathering propeller is its a two position propeller. When under power it goes into a preset fixed position and when not working automatically goes in the the feathered position which creates the least drag when the boat is under sail. This is not like the helicopters and planes use of a constant speed variable pitch blades or prop whose pitch can be adjusted in extremely small increments of pitch either up or down while under power and load.

I have had the pro pulse propellers on our Honda 40's for the last six years which are like Roger said, "manually adjustable to different prop pitches" and the blades can be changes out separately. Have several times replaced single damaged blades. The blades that fit a 40 hp Honda run $20 per.

What I have never tried and and think I will this summer is increasing the prop pitch before heading out on a day that is planned to be at displacement speed. If necessity arose that called for increase speed don't think it would hurt for short run. It only takes a few minutes to adjust the props to a different pitch and this just may significantly increase the mileage.

I have been very pleased with the Pro-pulse propellers but have heard others comment on the higher hp motors the blades not holding up.

Jay
 
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