Left:
WALT KAHLHAMER'S ROAR2
Contents:
Contact info:
- Jim Michalak
- 118 E Randall, Lebanon, IL 62254
- Send $1 for info on 20 boats.
Jim Michalak's Boat Designs
118 E Randall, Lebanon, IL 62254
A page of boat designs and essays.
(1DEC98) This issue will start a discussion of rowing. Next issue (about 15Dec) will continue the topic.
HOUSE CLEANING NOTICE....In December I will have to start deleting the links to the past issues so that only the last 25 issues or so are listed. I will try to keep on file the few that I know have been linked to by other sites. The problem is that I have about used up the free storage that Apci gives me. I should be able to keep a year's issues stored for your use. That's enough.
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Left: WALT KAHLHAMER'S ROAR2
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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.
NEXT TIME...
We'll take a short look at sliding seats and relatives and a look at setting up the rowing gear.
ROAR2
LIGHT ROWBOAT, 14' X 45", 75 POUNDS EMPTY
Someday I may get to put my full catalog on the net. For now I'll put one design in each issue.
ROAR2
As I was putting this together it occurred to me that the Roar2 (the above photo shows Stephen Elwell's Roar2) is the same size and weight as the QT skiff of the last issue. But Roar2 is a lot more boat in almost every way. It is probably 20% faster in smooth water and a lot more able in rough water. In fact it might be a good surf boat or rough river boat. I've been tempted to reduce the freeboard of my own Roar2. It has plenty and that freeboard adds a bit of weight and windage. My boat has never taken water over the top. So you would think that it could be slimmed down. I haven't done it because it's comforting in really rough water and I'm the type who will leave well enough alone. I've always thought this boat will pull safely through anything you have the arm strength to handle. It's a bit more involved to build than the flat iron QT.
Roar2 evolved from the plumb bow Roar. (Get the whole story building Roar at Bruce Hollman's great website shown down in the links. ) In fact I stared at my Roar for a while, clamped a batten to the side to visualize a raised bow chine, lean V entry like Toto's, and drew a line. I cut away the bow and added the conversion. .
Here are the Roar2 words from the catalog:
"This is the original Roar with a nose job. The new bow was copied from Toto. It has a deep V entry which carried well aft. About two feet of the sharp bow is immersed and provides a skeg action forward. As a result Roar2 behaves very well in all aspects of wind and waves and is more capable in rough water.
The new shape makes a different sound - a "swish, gurgle" as it cleaves the water, while the original Roar has a "tap tap" sound typical of boats that go over the water instead of through it. I suspect the original shape is slightly faster in smooth water, but the new bow has the edge everywhere else. She'll row at 4-1/2 mph with medium effort using the 7 foot oars detailed in the plans. Adding a passenger to either version will hardly slow her, although acceleration and deceleration are affected.
Water Kahlhamer built a clipper version of Roar2 without the bracing shown across the wales and reports his boat was still rigid. But the stern cross brace is almost mandatory for use as a passenger back rest. Without it the passenger will soon tire and lean to one side or slide aft to rest against the transom, throwing off the trim in a way that will drive the oarsman crazy. (Walter uses a removable passenger seat.)
These are excellent camping boats, light enough to solo cartop, large enough for much gear and with a flat bottom plank long enough to sleep on while the whole rig sits upright. Kevin Garber took my Roar2 on a three day row of the Big Bend region of the Rio Grand, seeing no humans from put-in to take-out. He brought a folding chair, a barbacue, and a tent fly with poles. In camp he set up the fly over the hull and slept in the boat.
There is also a 12' version called Smoar that was prototyped by Bill Wainwright of Somerville, Ma. Smoar might be a better solo boat than Roar2 and may be even easier to cartop.
Plans for either Roar2 or Smoar are two 24" x 36" blueprints with full instructions for taped seam construction for $15. Each needs four sheets of 1/4" plywood. Taped seam construction with no lofting or jigs required.
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. (If you order a catalog from an internet page you might state that in your letter so I can get an idea of how effective this medium is.) 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.
Usually when a design from the Catalog of Prototypes starts getting built I pull it and replace it with another prototype. So that boat goes into limbo until the builder finishes and sends a test report and a photo.
Here are the prototypes abuilding that I know of:
John Bell has launched his Sportdory! I will feature this one in the next issue. Here is a photo he sent. You might see more at John's web site by clicking here.
IMB: Click here to visit Tim Webber's page and see some photos of the Texas IMB under construction. Then poke around Tim's web page a bit. I heard this week from the Texas IMB builder who said,"I want to let you know that IMB is alive and looking good. She is now right side up and sitting on her cradle. Soon this boat and carrier will be mounted on the small trailer I have ready......"
Fatcat2: There is an old timer (80 years +) in Minnesota who has completed the hull of a Fatcat2. Fatcat2 is a simple 15' x 6' catboat, gaff rigged and multichined. I think the sail rig will be done this coming winter. Not only has he finished the Fatcat2 hull but he has started a....
Twister. Go back to the 30dec97 issue in the index to see this one. The Twister hull is pretty well cut and fitted, ready to tape. Walt lives north of Green Bay, working in an unheated shed. He tells me there will be no more building until things warm up again next year in late Spring. If you live up there and would like to contact Walt, let me know.
Jonsboat: A builder in Florida has started a stretched version of Jonsboat (16' stretched to 19'). This boat was featured in the 15 April issue.
Herb builds AF3 (archived copy)
Hullforms Download (archived copy)
