Oar length - what are the limits?

[Thorne]

I was recently given a pair of 10' carbon fiber oars by a neighbor, and tried them out last weekend on the upper Mokelumne. They worked well on the quiet water, hard to compare them with my 8.5' oars.

Is the quiet water limitation either outboard weight being too high and/or the arc of the oar handles inboard?

In other words, if the weight isn't an issue (and it wasn't), then is the oar length limitation solely the arc that the handles make inside the boat -- possibly also catching crabs or hitting the water on the return stroke?

I'm no performance rower, use a fixed seat, and understand that for rougher water you need shorter oars. Just looking for the basics on what are the technical limiting factors on oar length.

Thanks!

Oars on boat with Douglas locks and fitted plastic sleeves -
http://www.luckhardt.com/mokerow6.jpg

[SaltyD from BC]

The way I see it the limitations are not enough angle on the oar outboard to clear waves and get a clean stroke as length of oar becomes extreme. This angle of course is affected by the amount of beam of the boat. There's lots of old sein skiff oars around here that are around 10 feet long but these were beamy boats - 6 or 8 feet. Don't think these oars would be too practical on 4 foot wide dory or such. ..

[htom]

You want long for the force multiplier and short for handiness. As the wave size picks up, very long oars (nominally held horizontally) are going to be grabbed by nearby waves. Approaching the dock, or another craft, the oars are suddenly keeping you away or catching on things. Let go of the oars, they swing down and trip over the rock six feet below the surface. These are not good things to have happen.

If they're comfy, though, on a quiet lake or river (few idiot wake-makers zooming by), I'd use them. Just keep a paddle for when you're approaching something.

[JimConlin]

The limit is the 'gearing', the ratio of the outboard length to the inboard length. If it's too high, you won't be put enough force into the blade to move the boat. For standard carbon sculls, the distance between your locks should be about five feet at the minimum.

[Thorne]

Beam is just over 4', but I've moved the oar sleeves inboard a bit to compensate.
http://concretecanoe.org/FeatureArtcles/CWFig3.gif

If I HAVE to row with the carbon fiber oars, looks like I need to fab up some outriggers -- but I don't think I'll go there unless the difference between the long and short oars is so significant that I can't ignore it.

[JimConlin]

Here (http://www.concept2.com/us/oars/selection/oarlength.asp)'s some wisdom on oar length from Concept2, a manufacturer of carbon sculls. Most of their indicators suggest shorter oars.

If you're not ready for the complication of outriggers, I'd think about shortening those sculls by a foot or so.

[Thorne]

Thanks, everyone. I have wooden oars in various lengths -- 7' commercial flat-blade, 8' home-built flat-blade, 8' home-built spoon and 8.5' home-built spoon == so no real need for these long oars. But they are fun to play with, even if they should be used with a rowing wing unit and/or outriggers.

[David G]

My Twin,

Keep in mind, too, that familiarity is a factor. An oar, as we all know, is a tool. A fellow such as yourself (and, probably, many of us :o) - who's most familiar with the use of a shorter tool - should probably think twice before attempting to step up a size ;):p:D

Seriously, feel free to bring those giraffes up to Timothy Lake... I'd love to try them out.

[Thorne]

Ah, I see - insulting the size of my oars, eh?

This year I get to be the one photographed pushing YOU out into a howling gale on Timothy Lake - turn about being fair play and all...

[David G]

Ah, I see - insulting the size of my oars, eh?

This year I get to be the one photographed pushing YOU out into a howling gale on Timothy Lake - turn about being fair play and all...

Only fair. But if I'm rowing, I won't need a push, eh?

[Thorne]

Nah -- the photo below is more like what I'm envisioning, only with ME standing on the shore and YOU in your boat. Too rough to row with those long oars of mine anyway...

http://i156.photobucket.com/albums/t4/auroradan/Timothy%20Lake%202008/PICT3149.jpg

[Gold Rock]

I was curious to see what the replies to your question would be. I once read a 'rule of thumb' that suggested oar length for an average rowing craft (presumably excluding specialty circumstances like racing shells, etc..), should be "twice the beam plus six inches". I've made four sets of oars for various rowboats and tenders to this rule and they've all been remarkably successful.

[Thorne]

Right -- standard oars should be about that length. What I was looking for was the upper limits of oar length, smooth water being a given.

When the oars are really long, the extreme limit seems to be a toss-up between:
1. the blades catching the water.
2. the handles catching things in the boat.
3. the 'gearing' being so high that unless the boat is slim and headwind nonexistent, you are in too high of a gear to effectively push the boat along.

Since the Cosine Wherry is a really efficient rower / hull form for a 4' wide 14' pulling boat, it seemed to me that the long oars were pulling her along better than the shorter ones. But I'll need more testing as appearances can certainly deceive.

[David G]

Gold Rock,

To be serious for a moment, there are all sorts of formulaes for determining oar length (see sampling below) They may differ slightly, but put you generally in the same ballpark. S & T's - IIRC - tends to result in the longest oar. Keep in mind also that there are other considerations: do you intend to be primarily in rough or smooth water; how much freeboard at the oarlocks; how strong are you; do you row overlapped or not; how heavy is the boat, nd how much carry will she have; what arrangements will you make for stowing, and what level of inconvenience are you willing to live with to have the perfect length of oar; will you use the oars a lot, or only on rare occasion for emergency propulsion; etc.; etc.

http://www.fancyoars-paddles.com/

http://barkleysoundoar.com/oarinfo.htm#information

http://www.islandoars.com/choosing.html

http://www.grapeviewpointboatworks.com/oars.html#length

http://www.shawandtenney.com/wooden-rowing-oars.htm

[George Roberts]

For a given power output a longer oar reduces your cadence and allows you to maintain a higher speed.

But the practical issues given above are very limiting.

[gofish]

I'm with David G but there is one other important consideration.
That is height of the rowing seat off WL and height of the oarlocks above seat. Big consideration will the oar handles comfortably clear the rower's thighs.
When I outfitted my Chester Yawl I called Shaw and Tenney and they set me up quite well. Of course it was not cheap but well worth the $
Ed

[Tom Hunter]

I sit on a cushion on the floorboard so that I can cross the handles of my oars without smaking into my thighs or stomach. Works for me.

I think the gearing ratio is an important concept, you are not going to push your boat much above hulls speed. 10' oars are likely much more than you need to get a 14' waterline to top speed.

But, they give you so much leverage that you will get to top speed with a long, slow, relaxed stroke. With the right seat and in fairly calm conditions they should be a real joy.

I have two sets of oars, 8'6" and 9 or 9'6" (can't remember) I switch oars based on conditions ranging from sea state to how tired I am. I also overlap them or not depending on those same factors. It's like having a bike with lots of gears, you can use the gears that match the conditions.

If you are ever in Salem or Marblehead I would like to borrow them.

[Daniel Noyes]

comparing to gears on a bike is good, consider short oars as a low gear, and rowing a boat with any windage into a strong breeze is like riding a bike up hill, a shorter oar and a quicker cadence will get you to your destination at the same speed and with less muscle strain.
Also flexability can have a effect on lenght, rowing the whale boat or Atlantic Challenge Gig you pull on the oar and the handle comes toward you but the blade just sits there, some energy and stroke length is lost in the flexing of the oar.
Dan

[CapnJ2ds]

I was curious to see what the replies to your question would be. I once read a 'rule of thumb' that suggested oar length for an average rowing craft (presumably excluding specialty circumstances like racing shells, etc..), should be "twice the beam plus six inches". I've made four sets of oars for various rowboats and tenders to this rule and they've all been remarkably successful.
I go along with this too, but note that the beam is measured across the rowlocks for determining oar length. Twice that plus around 15cm - doesn't have to be too precise - will give a fairly handy oar with about the right balance between power and maneuverability. The boat's freeboard, the height of the gunwhale above the rower's thwart, and the height and reach of the rower are factors which can cause minor adjustments to oar length.

The thread of this thread would seem to be that for a solo oarsman, longer and skinnier is better - boats that is!

[john welsford]

Many of the suggestions above dont take into account the differences in potential speed of the boat in question. I have had a lifelong interest in sporting fixed seat rowing boats and wrote the little essay below for Gavin Atkins free boat design resources site (http://home.clara.net/gmatkin/design.htm ) quite a while back. It gives a slightly simplistic be effective approach to the issue of working out the correct oar length for a given boat.

" The calculation of oar length for one of my fixed seat boats is based on a movement at the hands of only 700mm. The theoretical cruising speed of the boat is then worked out by taking the square root of the boat's waterline length in feet (Imperial units of measurement are good for some things) and multiplying the result by a figure between 1 and 1.4... A short fat heavy boat will be close to 1 while a really long light slippery boat will be at the other end of the scale. This jiggery pokery tells me how fast the water will be moving in relation to the boat, and by applying a slippage factor appropriate to the oar type, about ten to twelve per cent for the narrow blades I use, I can work out the shaft length needed to move the blade at the right speed when the handle is stroked through 700mm 28 times per minute. "

John Welsford


I was recently given a pair of 10' carbon fiber oars by a neighbor, and tried them out last weekend on the upper Mokelumne. They worked well on the quiet water, hard to compare them with my 8.5' oars.

Is the quiet water limitation either outboard weight being too high and/or the arc of the oar handles inboard?

In other words, if the weight isn't an issue (and it wasn't), then is the oar length limitation solely the arc that the handles make inside the boat -- possibly also catching crabs or hitting the water on the return stroke?

I'm no performance rower, use a fixed seat, and understand that for rougher water you need shorter oars. Just looking for the basics on what are the technical limiting factors on oar length.

Thanks!

Oars on boat with Douglas locks and fitted plastic sleeves -
http://www.luckhardt.com/mokerow6.jpg

[BobW]

While browsing the internet looking for something else, I came across this photo of a U.S. Life Saving Service boat crew.

http://farm3.static.flickr.com/2499/3869365690_6c106011fa.jpg

My guess is those oars are longer than 10' and are not made of carbon fiber (well, unless wood is considered a carbon fiber...) :)

Bob

[Thorne]

Right, but gigs and lifeboats often had one man per oar, so the whole length thing is quite different for them -- although they still had to deal with the ratio of oar outboard and rough water issues.

[john welsford]

Right, but gigs and lifeboats often had one man per oar, so the whole length thing is quite different for them -- although they still had to deal with the ratio of oar outboard and rough water issues.

Generally a large part of the reason for long oars in bigger boats is that the height of gunwale means that the oars need to be longer to reach the water without being at an uncomfortable angle. The boats have a wider beam and longer waterline, and generally the rower sat across the other side from the rowlock, all of which affects the ergonomics of the rowing station. Same rules as I mentioned above for calculating the length though.

A note, lighter or less strong people will generally prefer a higher stroke rate than I do, perhaps 30 to 32 strokes a minute and this affects the calculation. Same process though.
John Welsford