Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(1September 2014) This issue will be about rowing. The 15 September issue will continue the topic.
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.
THE SAIL OKLAHOMA BOATING FESTIVAL...
...will take place at Lake Eufala on October 9 - 13. I plan to be there on the 10th and 11th and give a talk about Design Your Own Boat. There is a lot going on and you can read about it at SAIL OKLAHOMA .
THE 23rd annual LAKE MONROE MIDWEST MESSABOUT...
...Check the website https://sites.google.com/site/lakemonroemidwestmessabout/home for maps, directions, and general messabout information. Feel free to email or telephone (812-378-4236) if you have any questions. Tell your small boat friends to join us on Lake Monroe, September 19, 20, and 21 for a great time just messing about in boats. See you soon, John & Susan McDaniel
The lake level returned to normal and all that mud returned to flowers.
118 E Randall,
Lebanon, IL 62254
Send $1 for info on 20 boats.
If you've ever cycled, you've rowed. In a lot of ways the two activities are similar. The gear can be very simple and cheap or very complex and expensive. The effort can be very relaxed and enjoyable, or very high strung and demanding. Also, the weather makes all the difference in the world in either sport as to the what can be accomplished.
This essay will explore mostly the simple, cheap, relaxed and enjoyable side of the sport.
FIXED SEAT ROWING
Figure 1 shows a fixed seat rower. His rear is attached to the boat by friction to the seat. His feet should be braced against solid foot braces. The handles of the oars are usually about chest high, or slightly below, when he pulls. The oar handles may overlap each other during some portions of the pull, although it's more comfortable for the casual rower if they don't.
The oars are held to the boat by common pivoting oarlocks. They are somewhat free to slide in and out of the locks such that the distance from lock to handle can be adjusted.
The blades of the oars are dipped into the water with each power stroke and lifted clear with each return stroke.
That's about it.
Here is what the oars do: In effect they are levers that gear up the speed of the rower's hands.
Most people in a good (but not racing) row boat will pull at 25 to 30 strokes per minute. Let's say it's 30 strokes per minute (2 seconds per stroke) to make the figuring easy. And let's say that stroke consists of 1 second of power and 1 second of recovery. If the rower pulls the oar handles through 3 feet with each pull, as shown in Figure 1, then the oar handles are moving 3 feet per second, which is 2 miles per hour.
(One might argue that hull speed and blade speed aren't the same because there is some slippage of the blade in the water. Certainly this exists when you try to start any boat from rest, especially a large heavy boat. But once up to speed in good conditions good rowing boats don't exhibit much slippage. I've noticed that an oar blade produces a small vortex on the water's surface when the power stroke is first delivered, and another small vortex, twisting the opposite way, when the power stroke is stopped, usually when the blade is lifted for recovery. In calm water the vortices are very clear and stay that way for a while. You can row along and see a string of them on each side of the boat. I base my observation that there is little blade slippage on the fact that the starting and stopping vortices of each paddle dip are usually only inches apart once the boat is up to speed, while the paddle dips themselves are spread well apart. Pete Culler said that a good rowing boat will carry or glide about the length of its hull in between strokes. I agree. So a good 16 footer will glide about 16 feet between strokes while its blade vortices might be within 6" of each other. Blade slippage would be 2 or 3%.)
How fast will the boat go? Here the problem is how to match the power delivered by the rower to the power required to push the hull through the elements. (The elements for the time being will be assumed to be just the drag of calm water. That is to say it is a windless and waveless day.)
What is the power of a typical rower? I don't really know. I'm sure there is a very wide range of abilities. I recall that one might expect a long distance recreational cyclist to put out about 1/10th horsepower for hours at a time. Bike racers apparently can pedal 1/2 horsepower for a good while. And I think I saw in Scientific American a long time ago where a multi-time Tour de France winner pushed a dynamometer at a full horse power for an hour!
It's interesting to guess at the load on the oar handles while pulling them at 3 feet per second. A horsepower is defined as moving 550 pounds through 1 foot in a second, (established back in the old, old days when horses were used to lift seepage water out of mines) so 1/10th horsepower would be 55 pounds through 1 foot in a second, or 18.3 pounds at 3 feet per second. But the rower, unlike the cyclist, is actually pulling only half the time, on the average, since half of his time is spent in a powerless return stroke. So his boat might think he is putting out 1/20 hp on the average.
Well, we're not out to win the Tour de France. To a certain extent with a rowing boat, the issue of power delivered becomes moot. The nature of hull drag for boats that don't plane assures that they all go about the same speed. Figure 2 shows what I think the power requirements might be for a boat like my Roar2 in normal one man rowing trim. (These power figures are all guesses.) You can see that power required rises sharply at a hull speed of about 4.5 mph. With a steady 1/20 hp of our rec rower she wants to go 3.5 mph. With 1/10 continous hp, say a maximum power for a short burst of arm power, or an easy continuous power for a small electric trolling motor, she wants to go 4.3 mph. The Tour de France winner might go 7 mph if his arms were as strong as his legs. A tenfold increase in power gives only about a twofold increase in speed.
The point is that large increases in power give only small increases in speed once "hull speed" is neared. So for recreational use it's wise to think in terms of easy steady power that you can maintain for hours, if needed. The big power can be held back for use in hard conditions like pushing into a wind, through a current, or past some rough water.
So let's say the skipper is pulling the boat through the water at 4mph. But his hands are only moving 2 mph! The oar makes the difference in speed easily possible.
If the oar were 84" long (7 feet), and 56" of that were outside the lock, and 28" were outside the lock, then a 2 to 1 ratio will be achieved.
Figure of 3 shows the "freebody" diagrams (the balance of forces) of the oar and the rower and the boat. With the configuration shown the 18 pound load as a 9 pound load on each handle is balanced by a 4.5 pound load on each blade. So the process of gearing up the speed by a factor of 2 has also reduced the balance load on the blade of the oar by a factor of 2.
The forces on the rower's body are also shown in Figure 3. His 18 pounds of force in his hands must be reacted to the boat some way. If he has no feet bracing at all, then the force goes out of his body as friction where he sits. It can hurt a bit after a while! The usual solution is to brace the feet solidly. A handy bulkhead or hull frame might do. Custom cleats for the feet to push against attached to the hull are also common.
If the rower now turns downwind he may find his 1/10th half time horse will push the boat at 5 mph. To get that without changing his stroke he can slide the oars out so that he has 24" inboard and 60" outboards. As shown in Figure 4 he will now have 3.6 pounds of force at the blade of the oar. Less force is required there now since the wind is helping to push the boat along.
Now let's imagine the rower encounters a headwind that slows the boat to 3 mph. How does he match his 1/10 th intermitant horsepower to the new speed? If the rower slides the oars in so that 32" is inboard of the locks and 52" is outboard, his 2mph, 9 pound application at each handle will be geared up to 3.2mph at the blades. As shown in Figure 4 the blade will balance now with 5.5 pounds of force at the blade. That's an increase over the first condition and it's that extra blade force that will help push through the headwind.
One can see from the above discussion that rowlocks that are pinned to the oars in one position don't allow this change of gears, so to speak. (They may have other advantages. More on that later.) By moving the oars in and out over an 8" range we have "regeared" the boat speed to vary over 50% without changing the handle force or speed.
And one can see that the total length of the oar might not really enter into the discussion, only the location of the pivot point effects the gearing of the oar. But the length of the oar does have effects. The longer the oar the less of an angle it will sweep through and the more efficient it becomes. Also the oar must be long enough so that the handles fall conveniently at the hands. But an overly long oar can be a problem, too. An overlap of the handles that many might find very awkward will develop. And the long oars may simply be a bother in confined rowing areas.
We'll take a short look at sliding seats and relatives and a look at setting up the rowing gear.
VIREO, LIGHT ROWBOAT, 12' X 45", 60 POUNDS EMPTY
Vireo is a very light and simple boat with lines that make for very surprizing performance. A while back I built a dink called WeeVee which was the usual 7-1/2' long. It had a V bottom full length and had to be quite deep in the V to get enough capacity (displacement) to carry anything. I've always thought is was one of the fastest rowing dinks ever built as it would go 4 mph with medium effort, unheard of for such a short boat. But the deep V made for problems, the worst being that it made beaching a challenge. The bottom of the V was 9" below the waterline in usual trim so as you approached the beach the center of the V would ground first usually well before you made the shore. And there you balanced precariously until you threw a foot over the side and got wet. It was OK when launching from a dock, of course, but I seldom do that. Later I found I could heel the boat over when approaching shore and get in a lot closer but it was always tricky. She was a bit tippy but that was no problem once you were seated.
So that's how you learn and things evolved quickly into Vireo. Vireo is over 50% longer than WeeVee but is still only 12' long. She has a long lean bow for splitting waves. The V of her bottom is a lot shallower than with WeeVee and although she still needs heeling when beaching, the angle of the heeling is greatly reduced.
I think this shape has great potential, perhaps is the fastest of of any simple plywood shape. Here is why I say that. I try to draw these such that at normal weights the chines will not push through the water, that is to say they are normally above the waterline. Only the two bottom panels flow through the water. Those two panels join only at the centerline and in straight motion no water would cross that joint. So the flow is smoothly down two gently curving panels with no joints or complications. In addition, the shape makes for a boat that cuts chop and likes to go straight. But the V bottom means it won't beach as well or be as easy to move around in as a boat with a flat bottom panel.
The first Vireo was built by Charles McMahan in Ohio. He used lauan underlayment and lumber salvaged from motorcycle crates or from the Ohio River. The Vireo in the photo was a delux version built by Frank Kahr of Providence, RI. Frank wrote me:
"Yesterday I accomplished a long term goat by rowing from Providence to Newport in a Vireo I built from your plans. This was trip of approximately 26 statute miles which took 6 hours, 12 minutes. I had a little help from a fair tide, but this was still a good time for a long trip made without great physical effort."
"I think the Vireo is a good balance of light weight, seaworthiness, and speed. A longer narrower boat would be faster, but would also be less stable and would have less spread at the oarlocks. I built mine from 6mm Okoume plywood with a permanent center rowing thwart. It weighs only 57 pounds and is very easily managed out of the water. I have built several other small boats and this one went together easily in about 30 hous. The plans were very clear."
Vireo plans are $15. Taped seam construction from three sheets of 1/4" plywood. No jigs or lofting required.
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:
Another prototype Twister is well along:
And the first D'arcy Bryn is to the point the builder can sit and relax in it and imagine boating. You can follow the builder's progress at http://moffitt1.wordpress.com/ ....
AN INDEX OF PAST ISSUES
THE WAY BACK ISSUES RETURN!
MANY THANKS TO CANADIAN READER GAETAN JETTE WHO NOT ONLY SAVED THEM FROM THE 1997 BEGINNING BUT ALSO PUT TOGETHER AN EXCELLENT INDEX PAGE TO SORT THEM OUT....
THE WAY BACK ISSUES
1sep13, Lugsail Rigging, Hapscut
15sep13, Sharpie Spritsail Rigging, Philsboat
1oct13, Modifying Boats 1, Larsboat
15oct13, Modifying Boats 2, Jonsboat
1nov13, Modifying Boats 3, Piccup Pram
15nov13, Sail Area Math, Caprice
1dec13, Stretched Stability, Ladybug
15dec13, Trailering, Sportdory
1jan14, Cartopping, OliveOyl
15jan14, Width/Stability, HC Skiff
1feb14, Hiking, Shanteuse
15feb14, Dory Stability, IMB
1mar14, Scram Capsize, Scrampram
15mar14, Bulkhead Bevels, Frolic2
1apr14, Capsize Lessons, RiverRunner
15apr14, AF3 Capsize, Sneakerbox
1may14, Paper Capsize, Blobster
15may14, Prismatic Coefficient, Roar2
1Jun14, Roar2 Repair, Piragua
15jun14, Rend Lake 2014, Toto
1jul14, Mast Tabernacles, Musicbox3
15jul14, Sandell Tabernacle, Mikesboat
1aug14, Taped Seams, Cormorant
15aug14, Plywood Butt Joints, Paulsboat
Mother of All Boat Links
The Boatbuilding Community
Kilburn's Power Skiff
Bruce Builds Roar
Rich builds AF2
JB Builds AF4
JB Builds Sportdory
Puddle Duck Website
Brian builds Roar2
Herb builds AF3
Herb builds RB42
Barry Builds Toto
Table of Contents