# Thread: help on oar lengths - Culler's formula...

1. ## help on oar lengths - Culler's formula...

So, a local sawyer brought me some beautiful air dried ash planks today to become oars for my Pete Culler Concordia Sloop Boat. Incrementally moving towards splashing her for the first time, however late in the season ... amazing how work on the house takes away time for working on the boat. But no matter. Pete published a formula he used to determine the optimal lengths for a boat...

• inboard length is 1/2 the beam where the oarlocks are fitted, plus 2" (we'll call this "x")
• total oar length is x/7 *25.
• balance point should be about 12" below the buttons on the leathers.

In my boat the total beam is 68" where the oarlocks are mounted, but as the locks are inset somewhat the total oarlock-pin-to-oarlock-pin breadth is 62". Applying Culler's formula ... migod, those are bloody long. 10'9" overall if I scale things from the total beam, and 9'10" overall if I use the shorter pin-pin breadth.

First off - should I make the nearly 11 footers, or the merely 10 footers? I've plenty of lovely stock for either, but I don't know how to thread the needle between oars so long that the leverage might kill me, or oars a bit shorter than optimal for a decent stroke. While it would be smart to actually sit in the boat and try each length, there's a not-zero chance that I won't actually get her in the water this Fall to do that, and the oars will be made over the Winter. And even were she in the water, I haven't got an easy way to mock up a comparison.

Second, following Culler's plans (and the horns of my oarlocks) the looms with leathers will finish 2 1/4" in diameter, shifting swiftly to a mildly pointed oval profile fore/aft for the length of the loom, with the long dimension of the oval down to 1 1/4" at the narrowest/weakest part of the neck. The oval morphs into a central ridge down the middle of the blade of his working oars, which is what I'm building.

Culler mentioned that he'd use that same 1 1/4" neck dimension, whatever length best suited the boat ... talking genially about oars of 7 through 9 feet. IIRC he didn't describe any like my 10' or 11' behemoths though. You think I oughta keep more meat on the looms? Maybe an extra 1/4" at the weakest spot at the neck, to resist the extra leverage if ever I momentarily feel heroic?

The Concordia isn't a small or light 17'6" boat, but conversely every extra ounce on a set of oars makes itself known...

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## Re: help on oar lengths - Culler's formula...

Make 'em too long Tom then try them out and figure how much to cut off and where to put the leathers/buttons. Just cut off a little at a time. There's no formula that works for everyone.

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## Re: help on oar lengths - Culler's formula...

I'm no expert but I do row my own boat a lot. Culler's formula misses one dimension - height above the water. If the boat has more freeboard than the typical rowboat it makes the oar angle steeper and pushes for longer oars to keep your hands at a reasonable height. You could make a mockup to sit in and try it, especially if you will be putting some effort into nice oars.
As to neck dimensions, the stresses at the neck are about the same at any length with the same gear ratio and rower strength. Lever force is highest at the lock.
Weight does matter but balance matters more. I have two sets of 9' 6" oars, one set weighs 3 lb per oar and the other weighs 7 lb. Both are balanced and both are fine for long rows.

-Rick

4. ## Re: help on oar lengths - Culler's formula...

Thanks gentlemen - helpful thoughts.

5. ## Re: help on oar lengths - Culler's formula...

Peerie Maa at 60" between the thole pins has 10' oars, do not be afraid of length.

6. ## Re: help on oar lengths - Culler's formula...

Much easier to shorten them than lengthen them

7. ## Re: help on oar lengths - Culler's formula...

Well, sadly I have a limit. The planks are only 14' long.

8. ## Re: help on oar lengths - Culler's formula...

Capt. Pete's formula for balanced oars does not consider height above water but they are also meant for his boats. The formula does generate oars a bit longer than oars suitable for less traditional row boats. I've rowed this model, several of her cousins, other Culler models and others. These oars will fit. Start there and later experiment with longer if you wish.

One place where I disagree: I don't like scooped oars. I much prefer a symetrical blade with a strong spine tapering down the center on each side. That gives a blade almost as powerful as a scooped blade but easier to feather and scull and much safer (with open top rowlocks) in rough conditions.

Depending on the quality of the wood - yours sounds good - I like the plane the loom below the leathers to make the loom ovoid with the long axis normal to the blade. I go down to the point where putting the blade on the floor and one hand on the handle, I can put my other hand about half way down the loom and deflect the unit a couple of inches with a good firm push, maybe 40#. That keeps strength but lets the the oar develop a little spring during the stroke, straightening briskly as you're raising the blade up towards the air and turns towards the feather.

G'luck

9. ## Re: help on oar lengths - Culler's formula...

Don't even bother with leathers on ash oars. You won't end up rowing that design enough to cause any wear!

10. ## Re: help on oar lengths - Culler's formula...

Originally Posted by rbgarr
...You won't end up rowing that design enough to cause any wear!
Won't be how I set out for a light bit of exercise, for sure!

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## Re: help on oar lengths - Culler's formula...

If you do plan to row a lot it's worth getting the loom flex right. Concept 2 shows how to measure stiffness of racing oars: https://www.concept2.com/oars/oar-op...afts/stiffness

For my old body parts I've found I prefer very soft flex, twice as soft as what C2 calls extra soft. You can trim the loom below Culler's dimensions to soften the catch and save your shoulder sockets.

Just to show this does not mean the oars will break, a flexible shaft is less likely to break:

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## Re: help on oar lengths - Culler's formula...

I don't see how one could easily shorten a set of oars. Which end gets cut off?

Jeff

13. ## Re: help on oar lengths - Culler's formula...

What I'm thinking is that I make the longer set. Worst that would happen is that I make a second shorter pair down the road ...

14. ## Re: help on oar lengths - Culler's formula...

Originally Posted by jpatrick
I don't see how one could easily shorten a set of oars. Which end gets cut off?

Jeff
The thick round end.
There is less length of the flat bit to go at.

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## Re: help on oar lengths - Culler's formula...

Originally Posted by Peerie Maa
The thick round end.
There is less length of the flat bit to go at.
The looms of Culler oars are typically left square above the leathers to the grip. This is to provide mass to counter-balance the blade. If one goes to shortening this end the square section gets chopped. That seems like a real aesthetic shame and a time/material waste to me. Additionally the loom below the leather begins to taper. So moving the leather down really isn't proper. Now I suppose it's not all so bad if one is not making a Culler oar. But the OP says...Culler.

Jeff

16. ## Re: help on oar lengths - Culler's formula...

These boat row great and are not very weatherly. So row upwind and glide down. Exercise first and beer after.

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## Re: help on oar lengths - Culler's formula...

You can leave the square section long then once you've determined the length you want you can shorten it to above the locks.

18. ## Re: help on oar lengths - Culler's formula...

Originally Posted by jpatrick
The looms of Culler oars are typically left square above the leathers to the grip. This is to provide mass to counter-balance the blade. If one goes to shortening this end the square section gets chopped. That seems like a real aesthetic shame and a time/material waste to me. Additionally the loom below the leather begins to taper. So moving the leather down really isn't proper. Now I suppose it's not all so bad if one is not making a Culler oar. But the OP says...Culler.

Jeff
It is not a straight taper on oars, so lopping a foot off the loom will not move you very far into the taper. lopping a foot off the blade really destroys an oar.
Shetland oars are also square in the loom.finished 008.jpg

19. ## Re: help on oar lengths - Culler's formula...

For RANTAN with 60 inches between locks I was hoping to be able to use 9'6" sculls as that is the normal spread on shells. But freeboard wasn't figured in. I tried the 10'2" oars I had on my faering. Much better and ended up with some 10'6" oars. I was using conventionally shaped oars with a reasonably wide blade and found that these were horribly balanced. I laid my Norse oars over them traced the blades and whacked great shoulders off RANTAN's. Much better balanced. The Norse oars have a ridge that starts below the pins and goes to the tips of the blades, with the ovoid becoming almost like double gothic arches. Another thing I learned by looking at Norse oars is that they tend to be symmetrical for sea boats and have a curved blade for fjord boats. Curved oars are set up as port and starboard oars once the leathers are on them. Can't just be grabbed and used.

On a boat like the Concordia sloop boat you will be rowing when you must. You may be standing and pushing. I'd make the handles long enough for two hands as sometimes you may be using only one oar. Flex is a refinement that isn't real important and you will not get much on your ash oars. While the wood is hard leather would be nice. You will want to either use tholes or have locks that are at least 1 1/2"s which are sold by Shaw and Tenny or look at the larger than 1/2" socket size common in the rafting commmunity. These are often round topped. These can be converted to open horns by cutting enough out of them to be able to get the oar into the lock somewhere down the shaft, then sliding the oars down to the leathers giving you the advantage of both round and open horns.

20. ## Re: help on oar lengths - Culler's formula...

Thanks Ben. Happily, the ears on the existing locks open a full 2 1/4". Glad to hear your comments on oar lengths and shapes for Rantan - makes me more comfortable. I'm thinking of very similar profiles for the looms and blades.

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## Re: help on oar lengths - Culler's formula...

Tom, I have a pair of 11' spruce oars which I use on my Caledonia Yawl (75" between locks). My oarlocks open 2 1/4" and with the oars + wraps being 2 5/8" at that point, they must be put in the locks outboard of that and slid into place. You are welcome to borrow them to try them out for length; it appears that we live in the same city.

22. ## Re: help on oar lengths - Culler's formula...

PM sent - thanks Jim!

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## Re: help on oar lengths - Culler's formula...

The oars on our færing are 11 ft 8in and balance 2/3 from the tip of the blade. They are very easy on the arms and give good speed in the water.
Our rule is double the inboard beam + 8 cm, measured at the rowing station.

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