Originally Posted by Marco Esquandolis
Here's a huge problem- lots of people, especially the ones who post on this forum don't know shit about boating. They tell you that you should be using oars as long as flag-poles . . . and other complete nonsense.
Use oars that are . . . nearly balanced in the oarlocks, so like 45% of your oar shaft is inside of the lock. So many . . . boaters are running oars that have like 70%+ of the shaft outside of their locks. They will tell you that it's for the extra leverage- total bs.
Okay, Marco, lets look at what you have said. I'll take your final assertion first, since it is most easily dealt with. Nobody
claims that you get extra leverage with longer oars, because exactly the opposite is true
. Someone using a 70/30 ratio of oar length outside the oarlocks/oar length inside the oarlocks will have far less
leverage than you with your 55/45 ratio.
That said, I'm sure that you've made an error in your arithmetic. What you say is mathematically impossible. Now, I know that you have total contempt for college education, so I won't use college math. In fact, I'll limit this to junior high math, and hope you can follow me.
I'll make some dimensional assumptions about an average 15-foot raft. It will have an overall width of about 7 feet, and the side tubes will be about 20" in diameter. I'm assuming you're using conventional oarlocks, so your oarlock stands need to place the center of the oar no closer than 6 inches above the raft tube, otherwise the bottom end of the oarlock will punch into the raft.
We'll load this raft really heavy
, pushing 25% of the tubes (5") into the water. With 20" tubes, that leaves 15" above the water. Add the 6" minimum oarlock rise, and the center of the oars, at the oarlocks can be no closer than 21" above the waterline. (Loading the raft lighter so that it floats higher will only make everything that follows more extreme, so the heavy raft is your best-case assumption.)
The steeper the angle of the oar, the shorter the distance will be from the oarlock center to the waterline. Since it appears that you want the shortest oars possible, so as not to be rowing with "flag poles," we'll make the oar angle as steep as is practical. Vertical would be the maximum, but I think we can agree that it would not be practical to have your oars enter the water vertically.
In fact, anything steeper than 45° would be at least impractical, if not impossible. But we'll use that as the extreme possibility, because that minimizes the distance from the oarlock to the waterline, and you want short oars.
In 9th grade algebra, you should have learned the Pythagorean theorem, so given the height of the oarlock above the water and the angle of the oar you can calculate that the oar shaft needs to be 31" from oarlock to waterline.
Since the amount of energy you will be able to transmit to the water through the oar is directly proportional to the surface area of the oar blade, we'll assume that you're using a large bladed oar, like the Carlisle Outfitter Blade with a surface area measuring 22" x 8".
Adding the 22" length of the blade to the 31" length of the shaft, you get 53" of oar outside the oarlock. Using your formula of 55% of the total oar length outside the oarlock, the overall length of the oar is 96" (that's 53" divided by 0.55).
So you're going to try to row a 15' raft with 8-foot oars. Here's what's going to happen. You're going to have to space your oarlocks 86" apart (because you have 43" of oar shaft inside the oarlocks) unless you want your handles to overlap each other on your return stroke. Well, that's a foot wider than the raft, and it will make it kind of tough for you to go through some of the narrow passages on the river, but that's the price you have to pay to get your 55/45 ratio. Also, since your oars enter the water so steeply, they go quite deep, meaning that you won't be able to get full purchase on the oars when you're in water shallower than 20" (Pythagoras again), and at that you'll be dragging rock.
If you want the oars to enter the water less steeply, then your oars are going to have to be longer, or you'll have to put only part of the blade in the water, thus sacrificing the amount of energy you'll be able to transmit to the water and correspondingly reducing your ability to control the raft.
Now about your increased leverage that you get from your 55/45 ratio, it will indeed make it easier to pull on the oars. Each pull on the oars would give you a maximum of about 111" of stroke at the tip of the blade, compared with 176" of stroke that you would get from a 10' oar set at 70/30. (Pi times diameter, in case you're wondering.) That means that your pull will be 63% easier, but also 63% less effective, in terms of transmitting energy to water, which is the whole point of rowing.
To compensate for the loss of energy in your stroke, you're going to have to row faster--about 37% faster, to achieve the same control.
At the same time, with your 55/45 ratio on 8' oars, you're going to have to move the oar handles through a 90" arc, compared with 75" for us with our 10' oars at 70/30. But you're going to have to be one huge
dude to reach 90" with each stroke! In fact, 75" is about the maximum for anyone rowing without a movable seat.
So with a 75" pull, you're going to get only 89 inches of stroke at the blade. That means you're getting only 51% of the energy per stroke, so you're going to have to take twice as many strokes. Dude, that's great for aerobics, but you can't do it!
Bottom line here: Let's let everyone figure out for themselves who is full of what and what is complete nonsense.