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Fuel flow and economy - Marinaut 215
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C-Nile



Joined: 09 May 2008
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C-Dory Year: 2012
Vessel Name: Betty Ann
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PostPosted: Sat Sep 15, 2012 12:11 am    Post subject: Reply with quote

I did not post detailed information in the C-Dory forum, but rather in the Marinaut forum. When I first looked at C-Dorys several years ago, the wealth of information on this site was instrumental in my selecting a CD 16 Cruiser as my first boat. Everything I needed to know to make a decision: handling, economy, value, quality -- it was all there. And when it was time to sell my CD 16, my contributions along with this chorus of information helped me as it has helped those members on this site whom have sold their boats. You should be proud of the respect you have earned from outside the C-Dory community.

There is a dearth of information, at least relatively speaking, about the Marinaut. I have taken great pains to fill in those gaps to help others make informed decisions, and throughout this process, have given C-Dorys their just due. That's why this information was posted in the Marinaut forum. And when the proud owner of Hull #2, #3 and etc. come along, they too can add information to the Marinaut forum. Some of you may not be interested in such detailed information; that's O.K. There is room on this site for both boats.

Finally, the Marinaut belongs on this website. It's designer is Ben Toland, and many of you have enjoyed the fruits of his labor manifested in C-Dorys. The very capable Dave Thompson's ideas gleaned from year's of experience with C-Dorys and learning about so many creative solutions from its owners was the impetus for developing saddle fuel tanks and an open berth on the Marinaut. And many of you truly appreciate the work that Les and Kathy have done for you, as well as contributions made to this site. We are all one family.

Thanks for listening,

rich

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T.R. Bauer



Joined: 17 Nov 2007
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PostPosted: Sat Sep 15, 2012 12:28 am    Post subject: Reply with quote

I have around 1100 hours on my twin honda 45 set up and with a light load (2-3 people, full gas, full water, and a good assortment of fishing stuff) and it takes 17 gallons to go on my 68 mile trip to my halibut spot. I have made the run for around a decade (weather permitting of course) and this burn rate has been extremely consistent. 4mpg isn't too bad in my book.....And I have gotten it for so long, I think it is reasonable to think that next year, that is what I am going to get again......

With a heavier load (4 people and their catch) I have to swith tanks at the Cape (with some gas left as I don't want to run out on step with all the boat traffic) and the 2nd tank typically takes 6 gallons at the dock. The first tank almost always has 2 gallons left in it before the switch (18 gallon tank). This puts the fuel economy at 3 mpg.

So, I am sure you are wondering what speed that is. Well it is everything from 10 mph all the way to 24 with the most typical speed being 13-18. mph. Most of the cruise time has been from 13-18 mph.

I personally think it is going to pretty hard to find much variation in the economy of the boats with similar power plants and similar loads going a similar speed. The design just isn't that different to warrant a significant difference. Something? Well sure....But I bet it is less than 5%, which certainly isn't enough to get upset about. Or, even sing praises about.
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20dauntless



Joined: 23 Jan 2008
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City/Region: Mercer Island and Decatur Island
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C-Dory Model: 22 Cruiser
Vessel Name: Retriever and Nordic Tug 37
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PostPosted: Sat Sep 15, 2012 12:29 am    Post subject: Reply with quote

A couple more observations on CD22 performance/fuel economy...

I tend to use a lot of trim tab deployment to keep the bow down. Normally 65-75% when the boat is loaded heavily (heavy stuff inevitably ends up in the cockpit). The engine (with SST hydrofoil) is also typically trimmed to aggressively keep the bow down.

The BF90D runs at fairly high RPMs to keep the boat on plane. Loaded heavily and spinning a 13.75 x 13 aluminum prop, 4400 RPM equates to only 13-13.5 knots. 4800 RPM brings the speed up to around 16 knots and at 6200 RPM I can make 24 knots. With lighter loads I run a 13.5 x 15 aluminum prop and see higher speeds for a given RPM, but fuel economy seems pretty similar. Bottom line: the engine on my C-Dory is working much harder than the BF115 on Rich's Marinaut.

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C-Nile



Joined: 09 May 2008
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PostPosted: Sat Sep 15, 2012 12:19 pm    Post subject: Reply with quote

T.R. - 4 mpg with a light load is fantastic, but it looks like there is a 15 percent difference, which is explained in Les' comments. Regardless, there are few boats the size of the C-Dory that can get such great mileage, and to do so safely at that.

Retriever -- My trim tabs are usually set at 20 or 30 percent in following seas, and 40 to 90 percent when bucking the current so as to keep the bow down. Obviously, the degree of trim is also governed by speed travelled. Engine trim is always down. It does not appear that the degree of trim applied necessarily affects fuel economy appreciably. The Marinaut may be a well balanced boat, but we have a lot of weight in the stern. We have the 500 lbs. Honda Bf115, 120 lbs. kicker and offshore bracket, two batteries, and tucked under the splash well: 24 pounds of water in plastic bottles, and a large porta-potti at approximately 40 pounds. I often wonder how much better she would improve with respect to fuel economy if we did not have that kicker, but I would feel very vulnerable without it. Lastly, when we are bucking a significant tide and wind, we extend the trim tabs down and travel around 15 mph (as stated in a previous post, some times even slower then that, which is dependant on wave height.) We could go much faster, but we find that this is an excellent speed for smooth traveling in those conditions.

Thanks,

Rich
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Sea Wolf



Joined: 01 Nov 2003
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PostPosted: Sat Sep 15, 2012 5:40 pm    Post subject: Reply with quote

Les, Rich, and all-

Sorry to get you so upset!

I've very much enjoyed your, Dave Thompson's, and other's posts about the development of the new Maurinaut!

It's just that the daily hammering over the fuel mileage figures has become a bit much (IMHO), and I'm ready and prefer to read about another feature of the new boat, instead.

Sorry, again, and Good Luck with your project!

Joe. Teeth Thumbs Up

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T.R. Bauer



Joined: 17 Nov 2007
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C-Dory Year: 1993
C-Dory Model: 22 Cruiser
Vessel Name: C-Whisperer
PostPosted: Sun Sep 16, 2012 11:51 am    Post subject: Reply with quote

I actually find it really funny that we are talking MPGs and boats in the same sentence. Heck, even my old, but well maintained, 351 powered ford bronco gets around 14 mpg - way better than either boat. And goes ways faster......Of course, it doesn't go well in the water......LOL.....
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ghone



Joined: 13 Aug 2008
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City/Region: Nanaimo
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C-Dory Model: 22 Cruiser
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PostPosted: Sun Sep 16, 2012 12:04 pm    Post subject: Reply with quote

Me too. I came from sail and when a friend found out I was getting my first outboard boat a C dory 19 he told me to be prepared for 2 1/2 mpg. I thought he was nuts. So I am thrilled to get 3-31/2. Powerboats are always going uphill so I really appreciate the detail in Rich's post. As I sort of close my eyes at the pump , fill and then go cruising. When I get low on gas, I get more. Just like Forrest Gump would do. It costs what it costs and that's ok. So I have no real idea on exact numbers on Kerri On. I do know where she's taken me so far, and it's worth the money. thanks for the posts Rich. George
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C-Nile



Joined: 09 May 2008
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PostPosted: Sun Sep 16, 2012 1:03 pm    Post subject: Reply with quote

Joe, it's quite O.K., I have a thick skin. I agree with you about too much talk about mpg. I just made a simple posting to update people, and then get questioned on the results. So I was forced into a position to defend those figures, and ended up killing a dead horse. Unfortunately, even my response was redundant after Les' response; apparently our posts crossed in the mail.

To the writer with the SUV stating that gas usage is a fact of life for boats, that's true, but I had a choice when buying a boat, and chose the most efficient boat for our needs I could. Any time a person can save money, why not take advantage of it?

As for why I will continue to track precisely fuel usage, it provides a way to plan how much fuel We have remaining in our tank before gassing up, without having to rely on the fuel gauge. For example, if we travel 90 miles, we can assume 20 gallons of fuel had been consumed. Thus far, we have been dead on.

George,
I appreciate your comments. Thank you.

Rich
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T.R. Bauer



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PostPosted: Sun Sep 16, 2012 2:42 pm    Post subject: Reply with quote

Rich,

I don't you need to defend your fuel numbers. They seem realistic enough. Out of the open Gulf of Alaska with currents and the winds, I have to have had a number of trips with incredibly similar fuel burn results to what you have recorded. My best economy has always been in PWS - not in the open gulf where my halibut spots are. My very best economy ever was on a Lake Roosevelt- no currents and nearly no wind. Of course it was.

However, stating that one boat is more efficient than the other, while simple to do, is actually very complex to measure accurately. In fact, I am just not going there as I cannot provide a large enough sample of either boats actual mileage in a number of conditions. The best is ball park. Your boat may indeed attain better economy, and I am certain your new boat is putting up better number than your old one. However, assuming it is better soley because of the design, when every other factor hasn't been analyzed completely, or even duplicated, is just one of a number of possibilities.

Of course, you know that and so does everybody else. And, I put the referrence to the old bronco in there as a joke as one of the least efficient vehicles on the road literally kicks both boats' proverbial butts when it comes to MPGs. It wasn't meant to anger you and I am sorry it did.

I know you are really enjoying the new boat - who wouldn't? The new Marinaut is beautiful. If I were in the market for a new boat of this size, it is a very good boat for sure and definately deserves a spot near the top of the list.
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starcrafttom



Joined: 07 Nov 2003
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PostPosted: Sun Sep 16, 2012 2:54 pm    Post subject: Reply with quote

Quote:
The M215 was designed specifically for heavier 4-stroke outboards and the weight of the fuel was moved out of the transom (where it has the most affect on balance) and put forward to each side in saddle tanks. The balance, the waterline, and the shape of the M215 is completely different than a CD22 and for good reason given modern power plants and loads.


Why did you folks not tell me there was a fight on? I all most missed out Wink

I got to test drive the above mentioned boat and it runs great. I did not run any fuel numbers but I have no doubt about the numbers given. I think that the quote above seems to really answer the question as to why. Its a completely different hull. You can tell as soon as you push the power forward. It climbs out of the hole flatter and runs at a flatter angle ( not much) then my 22 did. It turns different, it handles different. Just a great preforming boat. I would not buy one as its too small for me and susan now. I will be looking forward to the 25 or 26 if it gets built.

The same argument was ongoing when the venture 23 was first on the marker, a great hull design. It was a step forward in design then the cdory 22 and by the same guy. The marinaut is a another step beyond that in design. What most people forget or do not know, because they have never SEEN one in person, is that the stern of the newer designs are very different then the cd22. All the cd22 and 25 and even my 27 get narrower at the stern. This is the biggest difference to me and I think the reason the newer designs get better fuel economy. I dont have any line drawings in front of me but I am willing to beat that the total square ft area difference is around 3 to 5 ft. Thats a extra 4 ft of lift area. Combined that to the balance issues that Les detailed and you have a more efficient hull.

Its not rocket science and more importantly its not personal. One boater getting better fuel numbers then you takes nothing away from your boat and your love of using it. Its really silly to argue about. Its like saying that because some one else has more money that my money is less or not enough??? justs nuts. or that just because someone else's idea of who to marry is different then mine that my marriage is effected somehow. Just crazy talk.

I love my boat and I love using it. I have friends that have better fishing boats and friends that have better cruising boats. Guess what? I still love to cruise and fish out of my boat and catch more fish then some of my friends with better boats. wise man said " if you cant be with the one you love, love the one your with" He was not or is no longer married but that's a different story. We really need a emotions symbol for stirring Twisted Evil [/url]

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ghone



Joined: 13 Aug 2008
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PostPosted: Sun Sep 16, 2012 2:54 pm    Post subject: Reply with quote

My 90 yamaha came with a twin gauge system with fuel flow, mpg or nmpg, trip total, total miles etc. I recall thinking "that can't be" first time to wot. Gps said 28 knots. Fuel flow said 9gph! But still about 3.2 plus mpg Here we pay about $6 a gallon. I find using my meters as a guide, real world I get a bit better than it says. The thing I like on my 22 is the visible tank level. I try to carry " mission fuel" with reserve. Just out for the weekend in the gulf islands I don't need 50 gallons. I am amazed also by how long fuel lasts if I keep to lower speeds. If we potter about, we can cruise a good long while I tend to spend more in pubs on lunch overall! Keeping these boats light in the stern helps. CoolSmile Mr Toland draws some nice boats!
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hardee



Joined: 30 Oct 2006
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PostPosted: Sun Sep 16, 2012 11:18 pm    Post subject: Reply with quote

Someplace back up there in this thread somebody mentioned Shocked Rolling Eyes Surprised surprise at mentioning MPG and boats in the same sentence. I think likewise. For many of us, boating on salt water, MPG measurement is lunacy. Speed measured by GPS is inaccurate, even if "your" GPS can put you into a 3 foot circle on planet earth.

Today I left Mystery Bay at 1130 and according to my GPS I covered 22.8 miles. Yup. That is a fact. Because The points on the globe did not change in their relationships to each other. How far did I travel on the water. It is probably possible to figure, but I don't have the math skills or the patience, or precise enough records to figure it out. Lets see, the tide was running out of Kilisut harbor, so I was riding down hill on the tide. Then it changed and then it was running against me on the way around the point (Wilson) and when I got to Sequim Bay, it was pushing in, so I got more free ride. Tide running with me. Free miles, or fewer water miles actually traveled. Running against the tide, GPS says I'm running at 13 knots. Hmmm. Same throttle setting as I had before when I was doing 16.5 knots.

Really, I think it is insane to be trying to figure MPG here. It might work on a lake, but anywhere else, ocean or river, it is a flawed measurement. (Hey Rich, I am not Harping at you. I think it is cool that you have done all the measurements. the more you do of that the more comfortable you are with range in relation to fuel on board.)

Because of frequent changing conditions, even Gallons per hour (GPH) numbers are hard to justify. (At least for me.) I like my fuel visible tanks, and use the 1/3rd rule (1/3 out, 1/3 back and 1/3 for reserve.) AND I like the slow cruise fuel consumption as well as the availability of the on plane speed if i feel the need.

One thing I would like to do, is figure out how to effectively calibrate the paddle wheel speeds to accurately reflect the speed over the water. That should equal either the minus or plus of the current speed and the GPS speed to show me the real difference.

Still things to learn.

Harvey
SleepyC Moon


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starcrafttom



Joined: 07 Nov 2003
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PostPosted: Sun Sep 16, 2012 11:55 pm    Post subject: Reply with quote

Harvey, the GPS is showing how fast the boat is moving forward. It does not care what the tide is doing. Your true speed is gps speed. The paddle wheel can be higher then true speed if you are going against the current and lower is with the current. I set my screen to show both so I know when I am getting a push or not.

as for mpg. yes it will be lower against a current but its higher in my car up a hill to??? whats the point. You are looking for a day long average.

I only worry about my fuel burn to plan a trip or a run on a trip. I have learned that my boat gets 2.2 to 2.5 mpg as long as I'm on plane. I get these numbers depending on water condition any where above 13 mph. From there to 30mph I get the same milage. After that it starts to really suck down the gas.
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hardee



Joined: 30 Oct 2006
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PostPosted: Mon Sep 17, 2012 12:01 am    Post subject: Reply with quote

Tom,

Right GPS is showing speed over ground. NOT true boat speed on the water. As you say the tidal influence is plus or minus. Agreed.

I agree with you about the design factor. Wider flatter aft section equals more lift and planing surface, more bouyancy.

Oh, and sailers and slow cruisers spend their cruising "day" running downstream or with the tide, not usually by accident, increasing their daytime travel distance, (or milage Very Happy

Harvey
SleepyC Moon
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Les Lampman
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Joined: 30 Oct 2003
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PostPosted: Mon Sep 17, 2012 12:35 am    Post subject: Reply with quote

hardee wrote:
Someplace back up there in this thread somebody mentioned Shocked Rolling Eyes Surprised surprise at mentioning MPG and boats in the same sentence. I think likewise. For many of us, boating on salt water, MPG measurement is lunacy. Speed measured by GPS is inaccurate, even if "your" GPS can put you into a 3 foot circle on planet earth.

Today I left Mystery Bay at 1130 and according to my GPS I covered 22.8 miles. Yup. That is a fact. Because The points on the globe did not change in their relationships to each other. How far did I travel on the water. It is probably possible to figure, but I don't have the math skills or the patience, or precise enough records to figure it out. Lets see, the tide was running out of Kilisut harbor, so I was riding down hill on the tide. Then it changed and then it was running against me on the way around the point (Wilson) and when I got to Sequim Bay, it was pushing in, so I got more free ride. Tide running with me. Free miles, or fewer water miles actually traveled. Running against the tide, GPS says I'm running at 13 knots. Hmmm. Same throttle setting as I had before when I was doing 16.5 knots.

Really, I think it is insane to be trying to figure MPG here. It might work on a lake, but anywhere else, ocean or river, it is a flawed measurement. (Hey Rich, I am not Harping at you. I think it is cool that you have done all the measurements. the more you do of that the more comfortable you are with range in relation to fuel on board.)

Because of frequent changing conditions, even Gallons per hour (GPH) numbers are hard to justify. (At least for me.) I like my fuel visible tanks, and use the 1/3rd rule (1/3 out, 1/3 back and 1/3 for reserve.) AND I like the slow cruise fuel consumption as well as the availability of the on plane speed if i feel the need.

One thing I would like to do, is figure out how to effectively calibrate the paddle wheel speeds to accurately reflect the speed over the water. That should equal either the minus or plus of the current speed and the GPS speed to show me the real difference.

Still things to learn.

Harvey
SleepyC Moon



Harvey,

When you're operating in a fluid medium like water or air you can't get the same precision you can when operating, say, a vehicle. Still, you need some way to predict either how many miles you can typically run between fill ups or how many hours you can run between fill ups. Without one or the other it's a guessing game.

Your 1/3 out, 1/3 back, and 1/3 reserve is fine and a nice safe approach. But what happens when you want to go somewhere? I doubt seriously that if I put you aboard a boat with a full tank and you didn't know how many gallons the tank (or tanks) held you'd be a bit concerned if I said the next fuel was 100 miles away. Your 1/3 out and 1/3 back isn't going to help you very much unless you know that the 2/3 you're allowing yourself to burn is sufficient to make the distance. The way you estimate that is to know how many miles (in general) 2/3 of your fuel will take you or you can figure how much time (in general) it will take to make the run and then figure out how long you can run on the allotted fuel (based on GPH). Either way you're figuring miles-per-gallon or gallons-per-hour even if you're not calling it that. The only way that 1/3 out, 1/3 back, and 1/3 reserve works with no knowledge of fuel burn is if you have no set agenda (that is, no destination) and turn around as soon as you're down 1/3, or you've done the run before and know it's do-able.

It is true that MPG may be more variable in boats than in vehicles but it's still a number that an operator should have in mind (and gallons-per-hour is just another way of saying miles-per-gallon so it counts too) so that one has an idea of whether or not a particular run is achievable. Prudence would suggest that one not use optimum fuel economy for planning purposes but nevertheless some number must be factored in to decide whether or not a destination is reachable with the fuel onboard. So figuring MPG (or its close sibling GPH) is not lunacy at all, having no idea how far (or how long) your onboard fuel will take would be the lunatic part.

Rough water always takes more fuel than calm water, if you know your boat well you generally have a feel for how much more. Current, in saltwater or rivers, is also a factor and must be accounted for whether you're figuring in MPG or GPH if you're route planning.

I'd bet dollars to donuts you wouldn't like to be aboard an airplane if the pilot told you s/he had no idea how far the plane could go or how long it could stay aloft, and that s/he would just fly until 1/3 of the fuel was used then turn back. An aircraft has the same fluid medium issue we have with boats and they don't get a specific MPG either. Usually small aircraft use GPH and in route planning they figure winds aloft and compensate accordingly so they know whether or not the planned fuel stops are prudent (the big boys use pounds of fuel per hour but it's the same process). If you know your GPH rate and the distance you're flying it's not hard to figure MPG.

No information with regard to boat operation, safety, and range should be considered idiotic or lunatic. It all adds up to knowing more about what your boat can or can not achieve. You may not think MPG is very accurate (and it really isn't) but if you totally ignore it (and don't use the related GPH) you really have no clue whether or not you can make a particular destination.

Your boat speed through the water has no effect on how many miles you travel from one point to another. As you say those points on earth do not change (or at least not a rate that affects us during a boat trip). If the GPS says you covered "X" miles than you traveled "X" miles regardless of the speed, or what the current did, or what the wind did. If you fill up your boat, travel "X" distance (GPS miles), fill your boat up again, and then divide the distance by fuel used you will get a precise MPG (and GPH if you noted the times) for that trip. That doesn't mean for any other trip it's repeatable but for that trip is was accurate.

You GPS is speed over the ground and not through the water. If you travel "X" miles at a specific GPS speed it will always take the same amount of time and cover the same distance; that's not variable. If you set your throttle at a particular setting your speed through the water will be (relatively) constant but your GPS speed (speed over the ground) will vary. Let's say in calm water you set your throttle for 12 knots of water speed and in this case (since we have no current or wind) the water speed and the ground speed are the same 12 knots. If we introduce a 3 knot current on the bow then your water speed will remain at 12 knots but your ground speed will drop to 9 knots. If we introduce a 3 knot current on the stern then your water speed will remain at 12 knots but your ground speed will increase to 15 knots.

Figuring MPG is not insane here at all; it's simply the miles covered divided by the fuel used, both of which are attainable figures. It is true that MPG is different in each direction (in the example above) but that doesn't make it useless or impossible to figure. My truck mileage varies a lot with what I'm towing and whether or not I'm on the prairies or in the mountains but I still calculate it so I have a better idea of where I need to stop for fuel next. It can vary from 7.5 MPG to 12.5 MPG so the swing is not inconsequential (and probably worse than on most boats).

What kind of system is the paddle wheel on your boat connected to (make, model, etc)? Many have a way to calibrate the paddle wheel.

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