Jim Michalak's Boat Designs

118 E Randall, Lebanon, IL 62254

A page of boat designs and essays.

(1Jun03) In this issue we will show fuel consumption tests with old outboards. The 15 June issue wil rerun the all important sail area math topic.



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 14TH ANNUAL MIDWEST HOMEBUILT BOAT MESSABOUT will take place at Rend Lake in Southern Illinois on the weekend of June 7 and 8. Lots of folks come on Friday and leave early Sunday. Take I-57 to exit 77W and then follow the signs to the Gun Creek Recreation Area. Camping at this Corps of Engineers facility is $10/night and that includes the ramp fee. There is no schedule of events except a pot luck dinner in the campground on Saturday evening- we wing it. This year some of us have reserved the campsites on the water of the two middle camping loops so look for us there if we aren't at the boat ramp.


Luke Spreadborough's Campjon down in Queensland.




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.


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.


...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.

NEXT TIME: We practice once again our sail area math.





Campjon is based on my Jonsboat design. I increased the hull depth to 24" from 18" and again to 30" in the region of the 6' long cuddy cabin. The cabin decks slope upward towards the center so the "headroom" in the middle is about 3', usually that is enough to allow sitting up while seated on the floor. There is a slotted walkway on the cabin centerline just like I've used on my AF sharpies, but this one also has a step through to the front deck. The front deck itself is fairly large and easier to use as a boarding platform than with the AF sharpies. But it is very important to NEVER let anyone ride on a front deck like this when the boat is in motion. If they slip off the deck they have no option but to slide under the boat full length and through the prop in an instant.

The prototype Campjon was built by Luke Spreadborough in Queensland Australia. Here he is using a 2.5hp motor.

He now uses an Evinrude18 as shown in this newer photo and like the guru has become something of a collector of old motors and now they show up like orphans on his doorstep.

I doubt if the increased freeboard makes the boat any safer since a flat boat like this is not good in rough water in any case. The higher sides do give a feeling of greater security since this will be a boat you are "in" instead of "on". This would be a better family boat since the kids can be kept cornered in the cuddy while underway. They can stand in the slot, or look out the front or out the windows. I suspect the cuddy will find a lot more use as a spot for the portapotti than as a camping cabin. The cockpit as drawn has no seats and is itself a big playpen. For seating I suggest using common folding chairs like I have used with satisfaction on my AF4. When the boat is not underway the chairs are folded and stowed, or relocated to another part of the boat or the shore.

As for power I would suggest a good 15 hp motor or a 10hp to keep the capability of using the smaller lakes which are wisely limited to 10 hp. With 10hp and with two normal sized adults the boat should plane, and be very lively with one aboard. But I've noticed with my own AF4 that weight gets added as time goes by and I've noticed that folks usually build their boats heavier than I do. I should add that the Coast Guard has suggestions about powering small boats and they come down hard on flat bottomed hard chine boats like jonboats because of handling concerns. I think they would advise a max of 25 hp in a hull like this. (My AF4, which is about the same weight as Campjon, went 22mph with a 40 year old Johnson 18. Greg Rinaca's Jonsboat went 26mph with 18hp.) There is a draining motor well in the stern.

Constuction is nail and glue, with no jigs or lofting. From four sheets of 1/4" plywood, two sheets of 3/8" plywood, and two sheets of 1/2" plywood.

Plans for Campjon are $30.


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.

Here are the prototypes abuilding that I know of:

The Alabama Skat now looks very boatlike:

A Piragua18 is completed in Georgia. I hope to have a writeup in a few weeks.

This Seal Cove Skiff was completed a while back, built within a few weeks of when the plans were released. There was a delay in launch until the Canadian ice melted. Write up soon.





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