Length
Koti uses the following table:
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| Oar Length as a Function Oar Lock Spread |
He suggests selecting an oar length between the light blue and red lines if you are strong or rowing in smooth and low wind conditions. If you’re not that strong, or wind/wave conditions are more difficult, then select an oar length between the yellow and black lines. Note that “Beam” is the beam at the oarlocks.
Does this mean you need to have two sets of oars? Not
necessarily… you can adjust the effective length of the oar by using ‘gearing’.
Oar Designs
Following are a sample of oar designs created by small boat designers:
Jim Michalak
Jim, in his book (Boat
Building for Beginners (and Beyond)) diagrams an oar made from a single 8 foot "2 by 6" (1½” by 5½”) (38 mm by 140 mm):
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| Jim Michalak Oar from a "Two by Six" |
If we placed the pivot point (oarlock position) 3 inches
outboard of where the loom changes from square to round, the gear ratio
would be 2.5. If this point were to be the center of 6” (152mm) leathers, we
could adjust gear from a ‘high’ gear of 3.0 to a ‘low’ gear of 2.1.
Gear = outboard length (tip of blade to oarlock) divided by
inboard length (oarlock to end of handle).
See this post for more information on 'gear' for oars.
R.D. Culler, in his book, Boats, Oars, and Rowing, page 44 gives dimensions for 8’ (2,44 m) oars.
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| R.D. Culler's 8' Oar |
And on page 61, he diagrams an 8.5’ (2,6 m) spoon-blade oar. If we place the oarlock 3” from the handle end of the 13” leather, then the gear would be 3.5. If we placed the oarlock 6” from the handle end of the leather, gear would be 3.0.
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| Culler's Design for an 8' 6" Spoon-blade Oar |
Phil Bolger (Small Boats by Phillip C. Bolger, page 30) provides a diagram of a 7’ (2,1m) spoon-blade oar from “Old Town Canoe Company”. According to their site, these are no longer made.
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| Old Town Canoe Spoon-blade Oar Dimensions |
On this oar, placing the lock 3 inches outboard of the button would produce a gear of 2.7, the same as the oar below.
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| Bolger's Suggested Changes to a Mass Produced Oar |
The diagram above shows how Bolger would modify a “mass produced oar” to make it lighter and more efficient.
John DeLapp
John, in the Winter 1990 issue of Ash Breeze (http://www.tsca.net/puget/resources/oars/)published a diagram (below) for how to make a
spoon blade oar. I followed his instructions to make the spoon
blade oars I currently use on my Ross Lillistone Flint. See this post for the process I went through to make these oars.
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| Diagram for Making DeLapp Oars |
Assume lock is 2.5 inches from button, gear is 2.3
Concept2 (www.concept2.com)
“Hatchet” (aka “Cleaver”) bladed oars were first designed in
1991 by Dick and Pete Dreissigacker (https://en.wikipedia.org/wiki/Oar_(sport_rowing)).
The advantages of the hatchet blade are that the blade has more surface area
for a given oar length (thus oars can be shorter) and that the amount of shaft
in the water is reduced compared to a more traditional blade shape.
Pictured below is a Concept2 Fat2 sculling blade:
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| Concept2 "Fat2" Blade |
Blade length is 18.1" (46 cm), width at tip 6.5" (16.5 cm) and width at widest point is 9" (23 cm). Overall oar length is measured from the end of the handle to the point on the blade at the arrow, an extension of the center line of the shaft.
Recreational rowers are beginning to use hatchet bladed oars because of their higher efficiency.
I'm using 9' wooden hatchets on slide seat. 58" oarlock spacing with 28" inboard loom, a little below the chart you show but it works for a big laden cruising boat.
ReplyDeleteTrying to make a new set of light weight sculls, there's a thread on the WBF with the gory details: http://forum.woodenboat.com/showthread.php?201253-Laminated-spoon-blade-wooden-oars
On gearing, you should carry spare oars so make those the low gears.
ReplyDeleteHi Rick...
ReplyDeletePoint well taken in that we need a lower gear for a heavier boat.
Chris Duff, long distance rower, talks about new oars he had made to replace his high tech oars... go to http://www.olypen.com/cduff/Frames.html, click on "Boat Construction" and scroll down to "Oars"
The best pictures I could find were on the same site, click "Photo Albums" >> "Boat Construction", 3rd and 5th photos from the END of the set.
I just read the whole WB forum you referenced... very enlightening and useful... it's made me change my mind about next step on my oars.
I remember Chris' trip from a few years ago, amazing. I see now that his oars are box section using DF and cedar. My current set is DF and redwood 2 part lam, the next are planned as Sitka and redwood 3 part lam. I'm still not sure that birdsmouth or box section looms saves any significant weight over solid lams using light center wood, but they look like much more work to construct.
ReplyDeleteNarrow blades are often preferred in rough water, but I find that wide hatchets are not so bad. A wave hit just knocks them into feather, no big deal.
Reading thru the WB thread last night, I was intrigued by your I-beam suggestion for loom... They'd be really light... I'd be thinking in terms of 1/4" plywood, cut on the bias, scarfed for required length, width out to the full 1.5", with four 1/2" x 1/2" WRC (only decent straight grain wood I can get locally) glued to both sides of the edges (vs. rabbiting the plywood into two 'U' shaped pieces... from handles to 3" past the lock position, make it solid wood for strength at the lock and handle end weight... What do you think?
ReplyDeleteBTW, I agree on the spare set of oars for lower gear...However, I still want the ability to change gears on the fly... I experienced that this last Thursday when bucking a head wind, lowered the gear helped much.
You need to build the I-beams - someone should find out if that works :-]
ReplyDeleteActually thinking about it, they might be more likely to twist than the box section. Probably not a big issue....
As the loom narrows at the blade end, the four 1/2"x1/2" strings would meet into a solid mass... I think that would dampen any tendency to twist, but not prevent... Regardless, it does need to be tested... Any volunteers out there?
ReplyDelete