Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(15May2012) This issue will finish the review of electric boat propulsion. The 1June issue will do some powerboat testing.
THE BOOK IS OUT!
BOATBUILDING FOR BEGINNERS (AND BEYOND)
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....ON LINE CATALOG OF MY PLANS...
...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.
MESSABOUT NOTICE:
THE REND LAKE MESSABOUT WILL TAKE PLACE ON JUNE 8 and 9 AT THE PINTAIL LOOP OF THE NORTH SANDUSKY CAMP GROUND AT REND LAKE IN SOUTHERN ILLINOIS. USUALLY THE SANDUSKY CAMP GROUNDS MIGHT BE FULL FOR THAT WEEKEND. BUT SOME OF OUR BOATERS HAVE RESERVED SOME OF THE SITES THERE SO YOU (AND I) MIGHT PASS THAT WAY FIRST SINCE SEVERAL TENTERS CAN SHARE A CAMPSITE. IF NOT, THEN I WOULD TRY THE WAYNE FITZGERRELL STATE CAMPGROUND WHICH IS ON THE MAIN CAUSEWAY LEADING TO SANDUSKY. THEIR WEBSITE SAYS IT IS STRICTLY FIRST COME FIRST SERVE, NO RESERVATIONS ALLOWED. IT IS A VERY QUICK DRIVE FROM THERE TO SANDUSKY. HOPE TO SEE YOU THERE!
Electric Boats 2
FIRST A BIT OF REVIEW...
Lead and acid batteries are still the best bet for common electric boats since they are cheaper, more available, and lighter (believe it or not) than other suitable batteries. The battery used to start an auto or boat engine is a poor choice for an electric boat power source since they are designed to give a short big jolt of power, not a long even current like a deep cycle trolling motor battery. Deep cycle batteries are usually rated in "amp-hours" by how many amps of current it can deliver over a 20 hour period. Thus a "100 amp-hour" battery can deliver 5 amps per hour for 20 hours for a total of 100 amp hours. But small trolling motors usually draw about 20 amps per hour (at 12 volts). The higher current draw greatly reduces the total amout of current the battery will deliver. Here is a typical curve for a typical 100 amp-hour battery:
So the 20 amp motor will drain the battery in about 3.2 hours, about 70 amp hours total. Also it is best to not drain a battery below 70% of its total to prevent harming it in a way which will prevent future chargings. So the battery here might be limited to .7 x 3.2 hours = 2.2 hours.
Another recommended limit on the battery operation would be to keep current draw per hour within 20% of the total. So in this case the 20 amp motor is about the max to use with this battery.
Finally, a rough guess at trolling motor horse power is apply the conversion of 1 hp equals 750 watts. A 12 volt motor using 20 amps is using 240 watts, or 240/750 = .32 hp.
In Douglas Little's book ELECTRIC BOATS he presents some power measurements from typical trolling motors. Remember that his "horse power ratings" are based on current measured TO the motor and not the acual measured output of the motor. Here is a chart I made from some of his tests:
Finally, here is a new chart of approximate boat performance, speed vs hp, that is in Little's book. This sort of chart takes no account of "fast" and "slow" hull shapes so is only a very general starting point for figuring performance.
...NEXT, I GOT THIS LETTER...
...after posting the last issue. It was from Clyde Osterhout:
"I know from reading your past articles on the subject that you aren't a really big fan of electric boats. I can't really argue with much that you have said, but my personal experience with the RANGE of electric boats is quite different from your own. For the past 12 years, I have been using several trolling motors with my 17' Grumman Eagle canoe. Most of the time, I have been cruising on mainly flat waters with mild to moderate (1-3 mph) currents. These include the St. Lawrence River, in the 1000 Islands area, the Pocomoke River system in MD, the Susquehanna river, near Three Mile Island, and various lakes and ponds around the Mid-Atlantic region. Maybe 2500 miles or so under power in all. Here are a few observations:
1.With a canoe, at full power, I get about 6-8 miles out of a charge. At 3/4 power, I get about 8-10 miles. I never had enough patience to see how far I could go on anything less. I have discovered that I can go considerably farther with the canoe than the manufacturers estimate I should be able to go. That's because their estimates are based on much heavier boat, with a great deal more resistance to forward motion. I doubt that a converted row boat would be as successful as my canoe. I conclude therefore that an electric boat ought to be narrow, long, and as light as possible. Anything "extra" will reduce range.
2. The motors seem to propel my canoe at about 3.25 mph at the highest setting. That's true of an 18 lbs of thrust motor, as well as a 30 lbs motor. The 30 lbs motor has a great deal more "kick", and works much better in the wind, but the top speed does not seem to be much different. This must be due to the props, as you have already observed. I just obtained an older 30 lbs trolling motor with a small, 3 bladed prop that seems to push my canoe MUCH faster, maybe as much as 5 MPH. I haven't had a chance to do any real testing yet, but it is obvious that prop design is very important for electric powered boats.
3. Electric boats aren't fast. That much is painfully obvious! But the trolling motor powered canoe can maintain a higher average speed than one that is paddled by average paddlers. It works better in windy conditions, and is great for going against a stiff current. It is also quiet, even quieter than paddling. And if one has kids (as I do), it helps to have a free hand or two to deal with them as they squirm around. Finally, many lakes here in PA won't allow anything BUT electric motors, making the choice of what kind of power to use an easy one. So one can find some truly practical reasons for using a motor.
4. DO NOT USE an electric motor in salt water unless it is specifically designed for salt water use. It does ugly things to an electric motor.
What I would love to find would be a "cruising canoe", a long (16-18 foot), narrow (36-40 inches, max), light (less than 120 lbs) boat with a minimal cabin (for changing, napping, or bathroom purposes, not really for camping) kind of thing that would be good for bird watching, swimming, and good clean quiet family fun. Any chance? Hey, a guy can dream, can't he?
Yes, I use 120 amp deep cycle trolling motors. They make a huge difference. Car batteries, as you have pointed out, simply don't work. And not all deep cycle batteries are the same. Sears Die Hards, for instance, consistently put out more "umph" than Walmart batteries of the same amperage. Never could figure out why. They all seem to last about the same length of time, though.
In the end, electric boats aren't about getting anywhere. They are about enjoying the ride itself. Thanks for putting up with my endless observations! Clyde"
THE NEXT EXAMPLE WILL BE...
..."Electron", a new desing presented in the boat feature below.
NEXT TIME...
Will present some more powerboat testing, this time with gas motors.
Electron
ELECTRON, ELECTRIC CUDDY BOAT, 18' X 5', 900 POUNDS EMPTY
Electron was an interesting project done for a man who had done his homework on electric boats. In particular he had studied Doug Little's great book ELECTRIC BOATS. He wanted a cuddy cabin boat capable of some cruising, the ability to go about 30 miles on batteries when desired.
We started with my old Fatcat2 design, stretched it to 18' and narrowed it to 5', which made it visually a lot sleeker. He told me right off the bat that his figures showed he would need six trolling motor batteries to get the desired range while using a 24 volt, 2hp Minnkota trolling motor at half throttle.
To guess at performance you first guess at the total weight. The batteries will weigh about 400 pounds total and the motor about 60 pounds. With wires and such the power system should go about 500 pounds. The hull structure is guessed at 400 pounds, so the total empty weight might be 900 pounds. Let's add 400 pounds for the skipper and guest and some gear. The total comes to 1300 pounds in this set up.
Next we guess at the waterline length. Let's say 17' for this 18' boat with plumb stem and stern.
Now we go up to the performance chart to guess at the speed of the boat. At full throttle we might have a lb/hp ratio of 1300/2 = 650. The chart predicts a speed ratio of about 1.15. The square root of the water line length is about 4.12. So the chart predicts a top speed of 1.15x4.12=4.7 knots which is 5.4 mph. Not bad.
Cruising at 1 hp gives a lb/hp ratio of 1300. The chart predicts a speed ratio of about .97. So cruise speed should be about .97x4.12=4knots which is 4.6 mph. Not bad (and it shows how boats can cut their power a lot and just slow down a little).
Now let's guess at the endurance. The 24 volt motor running at 1 hp should use 750/24 = 31 amps per hour. The six batteries in the plan are like the 12v, 100 amp-hour battery shown in the above chart (power-wise, they are 12x100=1200 watt-hours each for a total of 7200 watt-hours for the six). They must be first wired two in series to produce three 24 volt sources. So in use they will look like three 24 volt batteries, 100 amp-hours each.
If each battery pair pulls its share of the load, about 31/3=10 amps per hour, then the chart estimates an endurance of about 8 hours. keeping the battery draw to 70% maximum would imply an endurance of 8x.7=5.6 hours. At cruise that means 5.6 x 4.6=26 miles.
At full 2hp (1500 watts per hour) the endurance would be about .7 x 3hours = 2.1 hours for a range of 2.1 x 5.4 = 11 miles.
Another check to make is Little's rule of not drawing more than 20% of the power per hour. So a 2 hp motor (1500 watts) needs at least 7500 watt-hours total and the battery bank shown is about minimum.
One might ask about putting a gas motor on Electron. I'm quite sure it will not plane under control in the usual safe sense. So there is little point in using over about 4 hp. A modern 4 cycle engine of that power will run for ever on a little bit of gas, and even a junker 2 cycle that size will burn about a gallon every three hours or so. A tiller extension is mandatory for proper trim, very easily done. For that matter the electric will need a tiller extension or remote steering for proper trim.
I thought this hull would be a good starting point for a sail boat. The lines are right. You will have to rethink the cockpit, trying to make it more watertight. There is a great temptation to use the batteries for ballast but I'm not so sure this boat is a good candidate for a self-righting design because it's side and cabin are low. There might be a compromise where maybe two batteries are used, keeping the battery compartment small and yet with enough endurance for 8 miles or so in calm conditions. The weight of the two batteries might steady the boat but it would not be self righting. Eventually I added the sailrig to the drawings with my usual leeboard and balanced lug.
An Electron was built in California...
...but never had the electric system or sail rig. Shown here it had a 2hp Honda as I recall, which might not be enough in brisk conditions which might also be true with most electrics. Later he went to 10 hp with it which is well beyond the limits of the hull but I suppose you can always throttle back. What happens is that at high power the boat will try to raise its bow and plane but with a sailing type hull the stern is too small to allow doing that under control and your bow points up to the heavens out of control. So my 4hp theory never got a test. The 2 seemed too small and the 10 is too large. Almost any larger sailing boat can make a nice power cruiser provided the power is kept quiet and reasonable and you never intend to go faster than the sailing speed. Just leave the sail rig at home. Your boat will be simple, quiet and smooth and free from the usual restraints of the wind.
Electron is built from eight sheets of 3/8" plywood and three sheets of 1/2" plywood, using taped seams and jigless construction requiring no lofting.
Electron plans including the sail rig are $40.
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.
I think David Hahn's Out West Picara is the winner of the Picara race. Shown here on its first sail except there was no wind. Hopefully more later. (Not sure if a polytarp sail is suitable for a boat this heavy.
Here is a Musicbox2 out West.
This is Ted Arkey's Jukebox2 down in Sydney. Shown with the "ketchooner" rig, featuring his own polytarp sails, that is shown on the plans. Should have a sailing report soon.
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:
The prototype Twister gets a test sail with three grown men, a big dog and and big motor with its lower unit down. Hmmmmm.....
And the first D'arcy Bryn is ready for taping. You can follow the builder's progress at http://moffitt1.wordpress.com/ ....
And the first Brucesboat is in the water for testing. A full report soon.
OK, so he found a major league goof in my plans on fitting the bilge panels. He did some cut and fit and did a great job of salvaging the work, but I have corrected the drawing for the aft end of the bilge panel (I drew it in upside down!!)
The Texas Hapscut awaits testing time. (He has scarfed some material on the stern to finish the boat with a built in motor well like Laguna. Good idea.)
And here is a custom project going together so quickly that I am going to hold releasing prototype plans, just release "done" plans in a few weeks. He also already has a crew. As I write this boat also is complete and awaits testing.
AN INDEX OF PAST ISSUES
Hullforms Download (archived copy)
Brian builds Roar2 (archived copy)
Herb builds AF3 (archived copy)
Herb builds RB42 (archived copy)
