# Oar length formula?



## mania (Oct 21, 2003)

Here is a formula that seems to work out for NRS frames.

(Frame Cross Bar Width in inches + 12) * 3/24 = Oar Length in feet

then of course you have to round up or down depending on your preference. remember oar length is measured as shaft plus blade.

comments? 

d


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## Randaddy (Jun 8, 2007)

I get 7.75 feet for my 9'x5' raft. That's too short for my little boat. I ran the formula for the frame size I'm looking at for my 16 footer though and it's pretty accurate. I think your formula works for boats that need frames 58" or wider. Smaller boats (like my Mini-Me or a 10.5 footer) have bigger tubes in proportion to their length and width so they need longer oars because of the sharp angle required to reach the water with shorter oars. You might not get ideal leverage with the longer oars, but you don't really need it with a little boat.

Revised formula:
((Frame Cross Bar Width in inches + 12) * 3/24)+1/2 of the difference between 58" and the width of the frame IF the frame is smaller than 58" wide. = Oar Length in feet. 

This formula gives me 8.25 feet for the mini-me which accounts for some people's preference for the 8 foot oar and some people's preference for the 8.5 foot oar. It also puts a common frame size for a 14 foot raft at 9.75, which accounts for the preference between 9.5 foot oars and 10 foot oars. A slightly wider boat frame than mine would be right at 8.5', where something like a Puma would have oars between 7 and 8 feet. Perfect!


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## caverdan (Aug 27, 2004)

I think you guys are onto something.  Not only tube diameter, but seat height and tower height are also variables to consider. Sitting higher above the tubes has advantages and disadvantages. I prefer to keep my seat height as low as possible.

Do you have a formula for seat height in relationship with tower height? 

I prefer to have my oar locks an inch or two above my knee height while seated with my feet on the foot brace.


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## Randaddy (Jun 8, 2007)

Dan, you have to make the amendments for those variables yourself and build onto the formula. Eventually we will have the solution to the Unprovable Oar Theorem. Nobel Prize here we come!


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## mania (Oct 21, 2003)

here is another one using simple trig.

Oar Length in feet = 3/12 x square root (h^2 + w^2)

were h is the height of your hands above the oarlock in inches and w is the distance from center of boat to oarlock in inches.

so no matter what your seat height or tube diameter you need to know about how high you want your hands above the oarlock which for me is about 15 inches.

no matter what you come up with you've easily got 6 inches of slop to work with.

summary for a guy 5'8" tall

NRS 48" frame = 7.5 to 8 ft oars
NRS 54" frame = 8.5 ft oars
NRS 60" frame = 9 ft oars
NRS 66" frame = 9.5 to 10 ft oars
NRS 72" frame = 10.5 ft oars

which seems to jive with their chart


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## TakemetotheRiver (Oct 4, 2007)

This is all too complicated for me- I just finally found a frame that allows me to reach the foot bar without sitting on the edge of the seat and stretching. I rowed Westy this weekend without falling into the bottom of the boat once. It's a beautiful thing.


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## Randaddy (Jun 8, 2007)

Raymo, I use3 8 1/2 foot oars for my boat with the wide blades. It sweet. I was just doing the math to see if the formula works for my raft, which I already have oars for.

Mania, the trig (Sarah Palin's baby... what a name) still produces too short of an oar for the smaller than 54" frames. If you incorporate the height of the oarlocks above the water surface I think we'll have it.


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## pinemnky13 (Jun 4, 2007)

How do you figure it out if you took business math because you got tired of taking algebra 3 times in a row?


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## caseybailey (Mar 11, 2008)

TakemetotheRiver said:


> This is all too complicated for me- I just finally found a frame that allows me to reach the foot bar without sitting on the edge of the seat and stretching. I rowed Westy this weekend without falling into the bottom of the boat once. It's a beautiful thing.


Wow...you really need to look into how to adjust a frame. As you discovered, being able to reach the footbar is a wonderful thing. It's a pain, but my girlfriend and I take a few minutes and re-adjust the frame based on who's rowing for the day. Check it out...it will make your life much better.


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## brendodendo (Jul 18, 2004)

Running my super modified frame on my super puma, I get 8.5+. Bus as Randy said, I think height off the water is a factor as I use 9ft. thin and wide blades for various rivers.

The super puma is a relatively large chamber diameter boat. Then add the rainbows (height plus extra width) and the raised seat on the cooler. So I need the extra 6 inches to get to the water comfortably.

No Idea how to add that to the formula.

Why start 3/12. Why not just start .25?


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## raymo (Aug 10, 2008)

Personal preference should play a role in determining oar length also. I had the opportunity to run many different size boats and different length oars over the years, which I know is not always possible for many boaters.As a river guide, sometimes starting a river trip, you showed up and had to take the equipment that was left.( first come first served was the rule) That meant a 14. ft. boat with 8 ft. oars or 12 ft. oars or maybe rowing with one 10 ft. oar and one 12 ft. oar at the same time.(you all know where this is going). Using the a basic formula 10 ft. boat 8 ft.oars to 8.5 ft. oars, 14 ft. boat 8.5 ft. to 10 ft. oars, 16 ft. boat 10 ft. to 12 ft.( 33 ft. rubber bridge span pontoon boat, nothing under 15 ft. hand made tead wood oars., might haved aged myself here). Observing boats on the rivers I think most rivers rafters stay within these limits. I personaly like the shortest length oar for the length of the boat with the widest blade possible. Oar tower heigth should depend on where your knees are when you have your oars blades out of the water and oar handles at lowest point and moving foward, handles should clear your knees in rowing position, that depends on if you use a kick bar (foot bar) or have your feet on rowing frame level with bottom of your seat. Adjustments can also be made to distance from oar towers to front of rowing seat.


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