26M/X distance motoring. What is your range?

[ralphk]

After reading an earlier thread about crossing Lake Michigan, it got me wondering, what Mac owners expect their motoring range is?

If I'm setting out with full cruising weight, I expect to get 20 statute miles on a 25 litre(6.6 US Gal) tank at WOT - no ballast.
My 26X with Honda 50 normally carries 2 of these tanks, so a total of 40 statute miles is expected. There is a point just below WOT where the boat
feels pretty stable on it's quasi-plane and I imagine that I'm saving fuel, but have no measured data to back it up.

Of course there are many factors that affect fuel consumption and could fill the newsgroup with physics calculations. I'd really like to hear, what makes other MacSailors think
"I'd better take an extra 5 gallon can" or "Let's throttle back, back because I'm getting nervous and need to start conserving fuel"


We've crossed Lake Ontario several times. As I recall, It's about 36 miles from Whitby, Ont. to Wilson N.Y. Only one crossing had really
favorable reaching winds and that is still a favorite memory of mine.
Other trips had long calms, bouts of close haul, the odd rain shower, even tried trolling for lake trout .....in other words, real world conditions.

Ralph k
Hakuna Matata '97X

[Divecoz]

I have motored a lot on our vessel and seldom have I had it anywhere near WOT. Most often I motored in the range of 2500 to 4000 RPM.
I was towing a 9'9" inflatable with an outboard hanging on its transom. I accomplished between 4 and 8 knots depending on wind and waves and tides I was pushing against. I almost always ran with a full ballast. I realise NOW ........I didn't need to.
I managed to travel the 25 miles to Pelican Bay on 4 to 5 gallons at those speeds fully loaded . As you see in my profile I have a 50 HP Mercury with the Big Foot / 14 -10 Prop. WOT results in about 5800 RPM with this motor and prop.
I carried 24 gallons of fuel on my trip and never came close to needing more fuel. I would be gone for about a week at a time and I never traveled less than about 75 miles by motor.

[Chinook]

For extended passages involving long distances between fuel docks, we carry 39 gallons of gas. We have a pair of 12 gallon tanks, and we strap a pair of 5 gallon plastic gas cans onto a stern platform. Two 2.5 gallon plastic gas cans slip under the steering seat. When motoring on long passages, I run between 2500 and 3000 rpm, and that generally results in around 6 nautical miles per gallon. With my 39 gallon fuel load, I have a maximum potential range of 234 nm. For trip planning purposes, I reduce that by 1/3, and figure I have a conservative range of 150 nm, plus a reasonable reserve. I hate coming in to the dock with only a couple of gallons sloshing around in the bottom of my last tank, which happened once in Alaska, when a planned fuel stop didn't work out because of bad information and a fuel dock no longer in operation. Of course, we'll set sail on a lengthy passage whenever possible, so as to further stretch our fuel supply and range. I usually decide on a minimum acceptable speed for the trip leg, and sail as long as I can while still maintaining that speed. If we drop below that speed but still have a breeze we'll motor sail.

[NiceAft]

Chinook,

Is that 2500-30000rpm your most efficient speed for best fuel ecconomy? If not, how did you determine that range?

Ray

[Retcoastie]

I usually run 1800 - 2100 RPM with a Honda 50. What ever it takes to make about 6 MPH at the weight I'm carrying. I have run over 10 hours on an over-filled 6 gallon tank several times. Twice that turned out to be over 100 miles but, when I looked at my fuel usage data, I realized that was going down a river and probably got a good boost from the current.

[NiceAft]

From the many post I have read on most efficient fuel consumption, it has been determined that for a 50 hp Honda, 4800 rpm's is best. that is 80% of 6K rpm. I assume that other engines have different rpm's to reach for best fuel mileage, but, isn't that a better idea watching the rpm's.

Ray

[Duane Dunn, Allegro]

You will get your best fuel economy at hull speed which is 6-7 knots (6.9 to 8.05 mph). As soon as you go faster than that you are starting to burn more gas. The moment the bow rises even a little bit you are beyond hull speed. Economy will be at it's worst at WOT, particularly with a smaller 50 hp motor as you never reach true planing speed and are just plowing water out of the way.

We carry 5 tanks that are rated for 27 gallons, four 6 gallon tanks in the locker and one 3 gallon tank under the helm seat that is mainly for the dinghy motor but can be used on the main motor. Filled full, past the marked lines I can get 28 gallons on board. I set them all up with connectors that work on the main motor and have a special line for the dinghy motor with mis-matched connectors.

For planning purposes I use 18 Nautical miles (20.7 Statute miles) per tank in my calculations as that is my worst case number running the 90 hp motor at WOT (3 NMpg). This gives me a minimum range of 84 Nautical miles (96.6 Statute miles).

Reality is in the past 9 years of cruising almost 2,000 Nautical miles (95+% under power with empty ballast) on our X I can't think of more than twice when we have ever used WOT. These were times when the water was very calm and we just had a short ways to go and really wanted to get there fast. We have used WOT on the lake pulling toys, but I don't care about fuel mileage in that case. In most cases, real world cruising conditions will not allow the use of WOT, plus the noise from a motor at WOT isn't tolerable for hours on end in my opinion.

For us we have 3 cruise speeds we routinely use. Slow cruise, going right around 7 knots (8.05 mph) where we get 6 NMpg with the new motor giving us a max range of 168 Nautical miles (193.2 Statute miles). Medium cruise, of 10-11 knots (11.5-12.65 mph) where I get 4.5 NMpg giving me a range of 126 Nautical miles (144.9 statute miles). And Fast cruise of 15 Knots (17.25 mph) where I get 3.5 NMpg giving me a range of 98 Nautical miles (112.7 Statute miles).

If you are really worried about range I would do a test to get some real numbers on your boat. Here is how I would do it. First identify three speeds you are comfortable with to test. One should be hull speed, the other two should be ones where you like the handling of the boat, the noise level in the cockpit, and where the motor seems happy running and vibrations are at a minimum. Experiment with different rpms until you find these sweet spots.

I would then take three tanks that I had run dry (not empty as there is always a bit left when the motor runs out) to the gas station and put in exactly one gallon of gas in each. I'd have my fourth tank full for the beginning and end of the test. Go out in some relatively calm, but still real world conditions and test. I wouldn't worry too much about sea state as long as it wasn't really big, but I would look for as little current and wind as possible.

Hook up the first test tank and immediately take her up to hull speed. Note start time, speed and GPS distance. Stay at that throttle setting until the tank runs dry. Note end time, speed and distance. Repeat for the other two test tanks at the other two test speeds. Now you should have enough data to do real trip planning that reflects the true performance of your boat and your motor as every one will be different. Make sure you have a typical load on board that reflects what you cruise with, have all your other tanks full as well as cooler weight and personal items. Have the typical crew on board. Don't do a light ship test as when you most need it you may come up short.

[opie]

In my three years with the MacX, I have never even tried to go WOT. I just never felt the need to do that. I would feel like I was beating my poor horse to death just for the heck of it, assuming I was a cowboy riding the long dusty trail to Durango....

That being said, on our last trip, 161 NM from Wrightsville Beach to Charleston in the ICW, we ran at 5200 RPM, we had trip segments of 3.62, 4.21, 4.24, and 4.29 nm/gallon. Our speed avg was 9.97, 10.75, 9.2, 9.4, 9.6 and 9.14 nm/hour. (Some segments were done without topping off gas.) My top speed was 14.3 to 13.8 nm/hour, per the gps for each leg. The tides were averaged out over the trip. I had to throttle down when going thru no-wake zones. (My boat could be considered "typically laden" with junk,with the mast and sails and water and food, etc, and two persons aboard.)

I held 12 gallons in regular tanks and had two 5 gallon aux cans lashed fore of the helm.

[bastonjock]

when your gas costs eight bucks a gallon you tend to be a little more economy minded.I preferr to cruise at 6n average and i motor sail a lot,you can go a long way with the sails up and the engine running.I also work the tides,on the east coast where i sail it can hit 3 knots in places during high springs,so i plan the journey so that i run with the tide,ive hit 9 knots just with the sails up and riding the tide.

[David Mellon]

I run at two speeds, wakeless and WOT. I have no idea what my gas usage is at harbor speed, I just use it to get to the big blue where I either bring out the rags or get on my way at WOT. At speed I have a range of about 80 miles with 24 gallons of gas. On flat water I can extend that out to almost 100 miles, on the rough it drops to about 50. RPM on the rough drops to around 5200, on flat is runs around 5800, speed from 16 to 21 mph. I feel that planning only gets you so far, adapting to the situation at hand is the key to safe boating, being prepared for any eventuality is the key to adaptation. So, Bring much more fuel than you expect to need. I like to carry an extra third, if going 60 miles I bring gas for at least 80 miles. That is a minimum.

[Bobby T.-26X #4767]

At speed I have a range of about 80 miles with 24 gallons of gas. On flat water I can extend that out to almost 100 miles, on the rough it drops to about 50.

that's very similar to my MPG...
with the 90hp, i frequently travel at 16-18 knots.

Bob T.
"DāBob"
'02X w/ '04 90-TLDI (14" x 11 pitch)
Dinghy Motor: '06 2.5-Suzuki

[Kelly Hanson East]

Couple of things

As Duane notes it isnt the engine rpm that determines fuel economy, it is the hull speed of the boat. Small changes in loading can affect how the boat sits, with significant changes in the economy at a given rpm, especially right 'near' hull speed.

Dont count on using the standard formula for the hull speed to get exact numbers, this is only an approximation, and Macs have funny hull shapes which dont follow the standard displacement formulae.

JamesV has the Mercury 'smartcraft system' on his Merc BF and has posted realtime data on his in Trips and Venues, I think. I dont recall the results but I am sure you will get the best economy down in the idle -1500 rpm range on our boats - the point being no one will have the patience to actually motor down there.

...and for good seamanship, if you have X miles of total fuel capacity, your cruising range should be 1/3 of this number....1/3 for trip, 1/3 to return, and 1/3 to reserve.

[kmclemore]

Couple of things

As Duane notes it isnt the engine rpm that determines fuel economy, it is the hull speed of the boat.

...and it's also wind speed and direction, as well as sea conditions.

[ralphk]

Thanks for sharing your fuel strategies.
I'm a little surprised at the number of replies that never take the Mac up to WOT.

Under the iron Genny, my Mac has only three sweet spots.
1) No wake or docking speed
2) WOT
3) There is a happy mid-point, 1/2 keel, rudders down, steering is not yet heavy. I'll try measuring it in a couple of weeks, but I'll hazard to guess it's around 7 or 8 knots.

On my hull, anything between 9 - 13 is sloppy, washy and feels downright dangerous.

When making passage, I started motor-sailing last season, like the big keel boats.
With engine at idle-speed, engine noise is virtually undetectable, even in light air.
I'll confess that this is somewhat a departure for me, as I used to be very adament about disconnecting the Honda and tilting out of the water.

I did find motorsailing in the following configuration to be a happy compromise,
- Disconnect engine and mount its steering arm on the stationary post.
- At idle speed, the prop's thrust safely drives straight forward only.
This keeps the rudders light, fuel usage is neglible and if desired, gets you there sooner.

JUST DON'T FORGET TO REATTACH THE STEERING LINK BEFORE ENTERING THE HARBOUR!!

....enough; I'm wandering over to a different thread now....

[tangentair]

....I started motor-sailing last season, like the big keel boats..... even in light air.
.....I'm wandering over to a different thread now....

Perhaps but you started with crossing my big lake where I can seldom run WOT more than 5 miuntes due to the waves and chop and wandered to where I also have found myself when by the time I get on the Lake the morning winds have died to 3-5 knots of puffs and zephrs. It is not a recommended practice to motor sail a MAC
from the Factory Website "NEVER POWER THE BOAT OVER 6 MILES PER HOUR WITH THE SAILS UP. The forward speed of the boat can create enough wind to capsize the boat if the sails are up. The result could be instant capsize. If the ballast tank is empty, the boat will not be self righting.
NEVER POWER THE BOAT OVER 6 MILES PER HOUR WITH THE DAGGERBOARD OR RUDDERS DOWN. If you hit something at high speed with the daggerboard or rudders down, you will stop really fast, and may damage the board or rudders .
At high speed, the daggerboard and rudders create lots of sideways lift and can cause the boat to be unstable. This can roll the boat severely or possibly cause a capsize.
But it implies that under 6 mph or 5 kts that motor sailing is acceptable, I remembered KHE "using the motor" on one occassion to outsail some big keel boats in light air and tried it myself a number of times last season.

Anyone else care to comment on this - should we or shouldn't we motorsail?