Jim Michalak's Boat Designs

1024 Merrill St, Lebanon, IL 62254

A page of boat designs and essays.

(1 August 2023) We look at "horse power". The 15 August issue is about sharpie sprit sail rigging.




... 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.

ALSO...In addition to the Duckworks downloads I also now have access to a large format inkjet printer which is making very nice full sized prints on paper. So I can return to what I started 30 years ago, you order direct from me by snail mail using the address above only with cash or check in US funds with the prices shown on this website, and I mail you full sized 2'x 3' paper prints. The price includes first class mail to US and Canada.


Another view of the new Piccup Pram by Geoffrey Adams on the Florida Gulf Coast.



Contact info:


Jim Michalak
1024 Merrill St,
Lebanon, IL 62254

Send $1 for info on 20 boats.



Horse Talk


...that you lived in Olde England. Your name is Wilbur. The Duke is starting up a coal mine and wants to hire you and your horse to lift coal out of the pit. You have a horse named Mr. Edward. He is a totally ordinary work horse except he can talk.

The Duke's operation is quite small at this stage and you rig up Mr. Edward like this with a simple rope with one well greased pulley that offers no drag. The barrel is loaded up my the miners and then lifted up by walking Edward at a fast walking pace of 3.75 mph.

All goes very well until the Duke's miners pick up the pace and start working Edward harder than he can on a day to day basis. Edward calls everyone together for a meeting and tells them," Look, I'm a totally average work horse. When I walk at 3.75 mph (which is 330 feet per minute) I can tell that the most weight I can pull is 100 pounds. Let's multiply that speed by the load I pull. So 330 fpm times 100 pounds is 33,000 pounds times feet per minute. Somebody write that down and call it 'one horsepower'!"

So horsepower is a force being pulled at a speed. One horsepower is what you can expect from an average work horse over an average work day. He can come back the next day and do it again."


I used to do a fair amount of bicycle riding. (I quit because of dogs and motorists.) The books all said at the time that the standard rec rider with medium training would put out about 1/10th horsepower. With that you could ride say 100 miles in say 8 hours. Unlike Mr Edward I would never get up and come back the next day and do it again but there were plenty of riders around who could. There were plenty who could drop you off after your 100 mile loop and go off for another 100 mile loop. Really well trained riders who had the right genes could ride 300 or 400 miles a day more or less everyday!

Old timers may recall Paul MacCready's pedal powered airplane the Gossamer Condor. It was a wispy thing, about 70 pounds of tube and tape and mylar with a wing 100 feet long. They say it took 1/3 hp to make it fly at 10mph. Bicycle racer Bryan Allen once pedaled it across the English Channel in a flight that lasted over 2-1/2 hours.

But Allen wasn't in the same class as riders like Eddy Merx who I recall once sat on a dynamometer (it measures horsepower) and cranked out 6/10 hp for an hour. You would think all the great cyclist are up in that category. Most can ride a 30 mile solo time trial on a real road loop in an hour. I recall the record at the time I was riding for distance in an hour was set by a Russian at 36 miles!

And there is the idea that really big and powerful men won't cut it as bike racers. The great speed skater Eric Heyden found his limit when he went bike racing. I guess power/weight figures into it. Still for pure power you would think a big man would have the edge.

Here's a thought. Let's say you are a weight lifter. You lift a 300lb weight set from the floor to over your head in a two second motion. (I'm guessing at this.) So that might be 6 feet in 2 seconds which is180 feet per minute. That times 300 pounds is 54000 pounds-fpm. That is 1.6 horsepower for that short time.

So one might think that the difference between an ordinary man and a superman is a factor of ten. Then maybe a trained and gifted horse can put out 10hp for a short while.


Remember when Mr. Edward told the group to "write it down"? Trouble is the only guy in town who could write was the professor and he didn't quite get it right to my way of thinking. He wrote down "33000 FOOT-POUNDS PER MINUTE" instead of "33000 POUNDS-FEET PER MINUTE" like Mr. Edward said.

They mean the same thing but where I can understand the idea of pulling a load at a speed, what is "ft-lbs/min"? Sounds like a torque divided by a time and how does that explain the power of the weight lifter? The Professor realized his goof but quickly found he could get paid as a consultant to figure horsepower needs, something the Duke didn't need before.


Not to be undone, Mr. Edward invented an engine powered by explosive burning of his own manure. He brought it out to the Duke's mine and rigged it like this:

So when the engine ran it spun a drum with a 1' radius (2' diameter) which wound up a rope and pulled the coal out of the mine. Let's see..... the weight of the load times that 1' radius would give us "foot-lbs". Now how to figure the time into the equation. Here is how it is done. For the "speed" part of Mr. Edward's method of figuring horsepower you need to calculate the speed of the rope as it is wound up on the drum. The circumference of the drum is 6.28 times its radius. So the surface speed in feet per minute is 6.28 times rpm. So if the motor has a 1' drum radius and spins at rpm and pulls up a weight of T pounds (the torque is also T because of the 1' radius) then the horsepower is rpm times T times 6.28 divided by 33000 which all comes to Torque times RPM/5254.


Your 10 hp motor is turning 4500 rpm. What is the torque? Answer: You can rewrite the hp= T x rpm/5254 as T=5254 x hp/rpm so torque for the 10hp motor turning 4500 rpm is T=5254 x 10/4500 = 11.7 foot-pounds. It doesn't sound like much. On Mr. Edward's drum you could easily stall out the motor by grabbing the rope. But the speed of the rope when you grab it would be 4500x6.28=28260 feet per minute which is 320 mph! Best to gear it down.

Some modern dynamometers work more or less as above except they might use a pump like a water pump or electric device with the engine mount reactions having a scale that will read the torque directly. I think the "load" on the pump is controlled by a valve that regulates how much water is entering the pump. So the dyno operator might rev up the motor with no load and then open the water valve to allow it to start pumping water and load up the motor. The rpms will drop until the motor's effort matches the demand of the pump. The operator takes note of the rpm and the torque (which is the reading on the spring scale times the arm length). He will add a bit more load and the rev's drop a bit more and takes his readings. And so forth. If he plots out the torque vs rpm he might get something like this:

Of course since horsepower is just torque times rpm times a constant you can quickly figure the horsepower and plot it. For example from the chart above we might read at 5000 rpm that the torque is 4.05 ft-lbs. So the hp at 5000 rpm is 4.05 x 5000 / 5254 = 3.9. The hp chart below is from a real old magazine where a West Bend 580 gokart motor was tested. Motors like this were also used in smaller outboards like the Elgins. Here is the horsepower chart for that motor:

Note that peak horsepower does not usually occur at the same rpm as peak torque. If you are gearing your motor or prop for say maximum boat speed you will want to arrange it so the motor is turning at the rpm for peak hp with throttle wide open.

For most of us I think the idea of force times speed is a lot more useful than that of torque divided by time.

POP QUIZ #2!!!

You are fishing quietly by the NO WAKE sign when a cruiser boat goes by 20' away at 30 mph. You see his motor cover says 225 hp. How hard is his big outboard pushing on that transom? Of course power at the motor head is not going to be the same as power delivered at the prop but let's take a look at it for fun. 225 hp is 225x33000=7425000pounds-ft/min. 30 mph is 2640 fpm. So the load figures to be 7425000/2640=2800 pounds at the prop.

POP QUIZ #3!!!

You are building a reproduction of the clipper ship Lightning (David McKay design in Boston) for the movies. The rig will be put in digitally but the hull is supposed to move as the real thing. How much horsepower do you need? My book says, "On march1, 1854, the Old Man wrote in the logbook, "Wind South, strong gales .... 18 to 18.5 knots, lee rail under. ..distance run in 24 hours, 436 miles." The ship had a 226ft waterline and 13000 square YARDS of sail. Her backstays were more than 3-1/2" in diameter of Russian hemp. Well, 18 knots is 1800 ft/min. Not sure what a 'gale' might mean but let's say 40 knot winds. Usually I figure sail pressure as 1 psf in a 14knot wind and the force increases with the square of the speed. So in 40 knots the pressure would be (40/14)^2=8psf. Now, the boat sets 13000 x 9 = 117,000 sqft of sail. So in 40 knots (assuming full sail which is not likely) we have 117,000 x 8 = about 1 million pounds of drive on the hull. So the force times the speed is 1800 million pounds-ft/min. Divide by 33000 gives an equal to 54000 hp! It probably isn't really that much but it has to be a really big number and I've heard 25000 sail hp quoted for the sailing clippers. My book points out the Lightning's fast passage still stands to this day (at least until 1952 when the book was written) and that it took 30 years before a steamship beat the Lightning's record.

(Well, John D. Rockefeller squashed Mr. Edward's hopes for a world full of manure powered combustion engines. Mr. Edward moved to Hollywood and changed his name to Mr. Ed and the rest is history.)




Oracle might have been called Roar3. It is a bit longer and lower than Roar2 so it looks sleeker. It is actually closer in shape to my Toto canoe. I'm pretty sure it is a visual improvement over Roar2. Hard to say if it is a practical improvement. Being lower sided it might seem less secure but then again my Roar2 has never taken water over the wale in the ten years I've had it and maybe I've been hauling around excess freeboard. Max Wawrzyniak of St. Louis made the prototype. We rowed our boats side by side on a good day recently. I'd say the Oracle was 1/2 mph faster all around going about 4 mph at cruise and 5+ mph on the gps at full effort. It should float two adults quite nicely.

I'd like to point something about the way I draw the line on many of my boats. I make card models of my designs which help me check the panel expansions and allow me to get a 3D check of the shape. The models are done in the same scale as the blueprint, in this case 1/8 and the model is fairly large. So I knew that Oracle has nice curves all around. But if you look at the end view in the lines drawing you see all straight lines! In a way this is a throwback to the original "instant" boats which had hull panels made from straight saw cuts. It is easy for a designer to make the jump to more flexible shapes, that is hull shapes which can look like about anything you might imagine being made from plywood. Back when I started drawing boats I noticed some of the nicest shapes in 3D had end views made totally of straight line segments. Don't ask me why. Not only does that give a nice shape, the designer's job is simplified. For example, with Oracle I might start by drawing the top view. Then I might sketch in the side view needing nothing more than an idea of what the stem, midsection, and stern will look like. Next I draw the end view which will include those elements connected by straight lines. In normal mechanical drawing it only takes two views to totally define an object. So without even drawing the side view of the boat the shape is defined. It only remains to go back and figure it out and adjust the top view, etc., etc.. Happy is the designer who gets it right the first time through.

Oracle is built with taped seams using four sheets of 1/4" plywood. No jigs, no lofting.

Oracle plans are $20 when ordered direct by mail from me.


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.

We have a Picara finished by Ken Giles, past Mayfly16 master, and into its trials. The hull was built by Vincent Lavender in Massachusetts. There have been other Picaras finished in the past but I never got a sailing report for them...

And the Vole in New York is Garth Battista's of www.breakawaybooks.com, printer of my book and Max's old outboard book and many other fine sports books. Beautiful job! Garth is using a small lug rig for sail, not the sharpie sprit sail shown on the plans, so I will continue to carry the design as a prototype boat. But he has used it extensively on his Bahamas trip towed behind his Cormorant. Sort of like having a compact car towed behind an RV.

And a Deansbox seen in Texas:

Another prototype Twister is well along:

A brave soul has started a Robbsboat. He has a builder's blog at http://tomsrobbsboat.blogspot.com. (OOPS! He found a mistake in the side bevels of bulkhead5, says 20 degrees but should be 10 degrees.) This boat has been sailed and is being tested. He has found the sail area a bit much for his area and is putting in serious reef points.






15aug22, Sharpie Sprit Sails, Cormorant

1sep22, Measuring Prop Thrust, OliveOyl

15sep22, Leeboard Issues, Philsboat

1oct22, Prismatic Coefficient, Larsboat

15oct22, Figuring Displacement, Jonsboat

1nov22, Lugsail Jiffy Reef, Mayfly14

15nov22, Sharpie Reefing, Piccup Pram

1dec22, Making Oars, Batto

15dec22, Taped Seams, Sportdory

1jan23, Rowboat Setup, Normsboat

15jan23, Sail Area Math, Robote

1feb23, Bulkhead Bevels, Toto

15feb23, Trailering Boats, IMB

1mar23, Small Boat Rudders, AF4B

15mar23, Making Sink Weights, Scram Pram

1apr23, Sailrig Spars, RiverRunner

15apr23, Water Ballast, Mayfly16

1may23, AF3 Capsize, Blobster

15may23, Mast Tabernacles, Laguna

1jun23, Underwater Boards, QT Skiff

15jun23, Capsize Lessons, Mixer

1jul23, Rend Lake 2023, Vireo14

15jul23, Rigging Lugsails, Frolic2


Mother of All Boat Links

Cheap Pages

Duckworks Magazine

The Boatbuilding Community

Kilburn's Power Skiff

JB Builds AF4

JB Builds Sportdory

Hullform Download

Puddle Duck Website

Brian builds Roar2

Barry Builds Toto

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