Jim Michalak's Boat Designs

118 E Randall, Lebanon, IL 62254

A page of boat designs and essays.

(15Sep04) This issue will rerun the old outboard fuel consumption report. The 1Oct04 issue will be about the size of boats.



is out now, written by me and edited by Garth Battista of Breakaway Books. You might find it at your bookstore. If not check it out at the....


...which can now be found at Duckworks Magazine. You order with a shopping cart set up and pay with credit cards or by Paypal. Then Duckworks sends me an email about the order and then I send the plans right from me to you.

THE 13TH ANNUAL LAKE MONROE MESSABOUT will take place September 17, 18, and 19 at the Paynetown State Recreation Area at Lake Monroe sout of Bloomington, Indiana. For more info contact Bob Bringle at rbringle@iupui.edu.


Fishing again, this time in New York in the prototype Vireo14.




Contact info:


Jim Michalak
118 E Randall,
Lebanon, IL 62254

Send $1 for info on 20 boats.



Old Outboard Fuel Consumption


Max Wawrzyniak, the old outboard guru, has written many times about the wonders of older outboards. After about 1950 the modern outboard took form with its easy starting, full gearshift, and noise and vibration isolators. Many used pretty simple and reliable and cheap technology such that an ordinary guy could fix one with a few tools. The automotive world was similar at the time and most fellows with cars of that vintage can still look under the hood, identify everything that is under there, and fix it. But just as those classic cars are gas guzzlers, so it is with the classic outboards. And as with cars that simple fuel hungry technology was used pretty much unchanged into the 1970's.

Although all the motors used were old, all except the Johnson 10 looked to have been used very little before I got them. There was a boating boom in the mid '50's and a lot of motors were made and bought and used a few times before going into storage for decades. The Johnson 10 was an exception in that all if its linkages were well worn and I suspect it has seen a lot of miles.

I made no attempt to lean these engines out to get improved fuel consumption. All were at the tune that gave good overall operation.


To do the tests in what I think is a halfway scientific way I made up a new "fuel system" with a clear plastic bottle. The bottle is a common soda bottle that you find everywhere. The bottle suits because the center 2/3's is a straight cylinder. This one measured 2.70" in diameter in the straight area. A US gallon is 231 cubic inches, so an ounce figures to be 1.80 cubic inches which would be .316" depth in the straight section of this bottle. I put a piece of tape along the length of that section and marked off 12 ounces. A standard fuel hose and primer bulb is inserted through a hole in the cap and a tiny vent hole is drilled there too. So if this tank is held vertical as the motor draws out fuel you can read pretty well the fuel use in ounces. I would say it is accurate to about a quarter ounce in real use. Smooth water is needed for testing since sloshing in the bottle makes for difficult reading.

The fuel use is timed with the common digital wrist watch set to the stop watch mode, very very accurate.

The speed of the boat is measured with a gps. I suppose the speed here is approximate since holding the boat to within 1/10 mph is difficult over the few minutes it takes to do each run although the gps seems to have no trouble measuring to that degree.

The boat used in all the tests was my AF4 at about 800 pounds total weight. In general this boat goes with little wake until about 6 mph which might be considered the "hull speed". I think it needs about 3 hp to go that fast. Then it starts to drag a big wave until it begins to plane fairly cleanly at 10mph. It needs about 7 or 8 hp to plane at 10mph. I think there is little future in trying to operate AF4 between 6 and 10 mph. So if you don't need to plane 5 hp will allow you to run at 6mph at a comfortable part throttle. And if you want to plane I think it takes 12hp to run it at comfortable part throttle at 12 mph. I think the best option for most would be about 15hp which would allow you the same cruise with another adult on board. Once you start to plane, weight counts for a lot. When my AF4 first was launched it was empty and stripped down at less than 500 pounds total, about 650 with me in it, and it went 17 mph with the Johnson 10. Now it is 150 pounds heavier and the same motor maxes out at 14 mph.

Tests were done like this. The motor to be tested was run a while on the regular tank to warm it up and get its fuel system full. The test tank was prepared and full beyond the 12 ounce marking. Once in the test area the motor was switched to the test tank and the primer bulb pumped hard. The primer bulb holds a large amount of fuel and you need to allow for it. The motor was run up to speed and when the fuel level in the tank had dropped to the 12 ounce mark the clock was started. After the motor had run 4 or 8 ounces, enough to get a valid time, the clock was stopped and the consumption for that run figured. I think the results are pretty accurate. The only problems were with occasional rough water that caused sloshing in the tank and oddly enough, difficulty with readings when the bottle was nearly empty. I think what was happening was that the motor begins to draw fuel out of the primer bulb and not out of the tank such that you motor on for a few minutes with no drop in the tank. So I stopped taking data if the tank dropped below 4 ounces.


An aircooled motor made by Clinton about 1970. Always thought it burned 1/2 gallons per hour at all speeds. Here are the results that about confirm that.


Also from about 1970. Made by Eska I'd say with a Tecumseh air cooled power head. Hard to start sometimes but once going has good power and uses little fuel.


From about 1956. A modern motor with noise and vibration stoppers. Good running and good power but always thought it used a lot of fuel. The motor guru keeps telling me there is something wrong with it but won't tell me what it is.


From 1956 or 1957. Made by Gale which was part of OMC so it is essentially a Johnson or Evenrude but it doesn't have the modern noise and vibration stoppers. Otherwise a very good running engine. I did not run a test at 8mph but I'll bet the fuel consumption would dip to its lowest there as it did for the Johnson10.


From about 1960, sold by Montgomery Wards but made by Gale which was part of OMC. Very modern with full noise and vibration stoppers. Again, no test at 8mph but I'll bet the fuel consumption would dip to its lowest there.

A new 2004 data point will be for a 1966 20hp Johnson that I picked up at a swap meet for $30. It needed a new spark plug, a good rap on the carb float bowl with a screwdriver, and a prop unit from another junk motor and now it runs great (so far). At 6 mph it got about 5mpg and at 12 mph it got a bit over 6mpg. In general it seems to burn just below 2 gph at about half throttle which is the 12 mph.


We get this:

With the smaller motors the Sears is noticably the better of the two, especially considering it has a lot more power than the Sea King. The Sea King starts easier, an important factor with a motor that is supposed to be a back up. Remember, AF4 won't plane with these motors.

The results with the larger motors are interesting. I did not show it but when I ran these motors at idle in neutral they all burned about 6/10 gallons per hour sitting still. There is no point in slowing down your boat to get better fuel milage with any of these. The faster they go, the better the fuel milage. I did no runs at full throttle but I would expect the miles per gallon would be the best at full throttle! On the other hand the consumption is actually fairly constant and from a fuel planning point of view speed really doesn't matter much (as long as the motor is in gear). As expected the Johnson 10 is the worst although I think that may be just a quirk of this particular motor. The results of the 12 and 15 are pretty consistant. Andso with the 20. Looks like at 12 mph, about 1/2 to 2/3 throttle with these motors, you can expect the motor to burn in gph about one tenth the full hp rating. Thus a 15 will burn about 1.5 gph.


...seem to get about twice the fuel milage as those above. One good data point is John Bell's AF4 "Mr. Moon" which has a new 15hp Mercury four stroke. He carries only 3 gallons of fuel and says it will take him 50 miles, cruising at about the same 12 mph that I prefer with mine.! His top speed is about 20 mph, a shade higher than my AF4 with the SeaKing15. The guru says that newer motors should indeed have a bit more power in reality since a few decades ago motor makers agreed to take the power tests at the prop shaft and not at the power head as with my oldies. Thus my oldies lose, they say, about 10% of their power in getting to the prop due to the gear train and the water pump.

And Asley Cook has a new Tohatsu 30 two stroke on his Dorado which is about the same weight and size as AF4 but modeled more for rough water. He says that motor has run 7 hours on the standard 6 gallon tank. And I think he is cruising a bit faster than we are in our AF4's.

I think new motors in this range cost $2000 to $3000, compared to about $100 for my oldies.


...We'll take a look at the size of boats.



VIREO14, ROWBOAT, 14' X 3.5', 80 POUNDS

Vireo14 is a 14' version of the original 12' Vireo which was quite popular with all of its builders. In this case the extra length comes from a straight "stretch" of the original design. By that I mean that the same cross sections were used but now spaced 14" apart instead of 12". Another way to lengthen a boat is to add a straight "plug" in the center as is sometimes done to even completed boats and full size ships. I doubt if the stretch has any advantages over the plug except maybe in looks. Even there a short plug is hardly noticable, for example in the case of where I put a 30" plug in my Toto canoe to make Larsboat.

The extra length usually gives a bit more speed for the same power in a low powered boat, at least until windage gets to be a big factor. And in the case of Vireo it means about 110 pounds more capacity. The original 12' boat will float 290 pounds before the chines start to enter the water. Beyond that I would expect the boat to slow noticably, although boats with bows shaped like Vireo are superior in this respect. So you see that it is a push to float two large adults in the 12' Vireo. The Vireo14 will float the same way at 400 pounds and will be much better with the two adults. Hull weight will increase by 10 or 15 pounds, of course.

The prototype Vireo14 shown in these photos was built by Steve Fisher in New York in a matter of a few weeks. If you look at his construction photo below you will see that there is not a helluvalot involved. Steve elaborated on some of the details but with these small simple boats often there are between twenty and thirty pieces of wood to make counting everything.

Vireo14 uses taped seam construction needing four sheets of 1/4" plywood.

Vireo14 plans are $20.


Prototype News

Some of you may know that in addition to the one buck catalog which now contains 20 "done" boats, I offer another catalog of 20 unbuilt prototypes. The buck catalog has on its last page a list and brief description of the boats currently in the Catalog of Prototypes. That catalog also contains some articles that I wrote for Messing About In Boats and Boatbuilder magazines. The Catalog of Prototypes costs $3. The both together amount to 50 pages for $4, an offer you may have seen in Woodenboat ads. Payment must be in US funds. The banks here won't accept anything else. (I've got a little stash of foreign currency that I can admire but not spend.) I'm way too small for credit cards.

The AF4G is done and launched. Writeup after testing:

The 30' Cormorant has been flipped! Bottom totally painted so there should be no upside down work to do. Read about the flipping at www.breakawaybooks.com/Flipping_Cormorant.htm

The out West Picara is rightside up now waiting for its roof:

The down South Picara is getting its innards done.





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