Does every oar need a blade?

[ocni]

Maybe not for recreational rowing in a small dinghy. The three oars shown at start of video can be miss-matched as a pair and in my many tries the dinghy rowed straight indicating some parity. Why would such a reduction in blade area not be evident in performance?

https://vimeo.com/1057557722

[Citroen]

Your video doesn't play for me.

I get "This video is not rated" from vimeo.com and an offer to join (which I won't take).

[ocni]

Electrons always way ahead of me, will try to fix this.

[ocni]

vimeo link should work now

[Citroen]

vimeo link should work now

No. I'm still gettting the same message.

[ocni]

I'm so sorry! But I tried the link, from the post, and it gave me the video. Maybe refresh the page? Here is the link, again: https://vimeo.com/1057557722 Thanks for trying --

[reuben]

The video works for me, and I don't have a vimeo account. Having said that, the only OTW work I do is in a kayak, and in a recreational fashion (touring or fishing), not competition. Compared to rowing sculls, both the paddles and the technique are different, so I can't offer much of a comment, other than anything, including a tree branch or your arm, will do in a pinch. The narrow wooden blade is similar to a so-called Greenland paddle in the kayak world, for whatever that's worth.

[ocni]

I have tried these thin blades on a kayak. It was slow on startup and turning to a stop, but once boat is in motion all 3 blades pictured have equal performance(+ or - 1 second in a 30 second run). If lift, drag or some combination of the 2 is involved, blade area should count?
The Greenland paddle seems to be on its way back to a tree branch -- any old stick will do? maybe I am just looking for a better stick. My interest was inspired by kayaking next to a fast swimming deer which offered no explanation for its performance. Hope to find one here.

[Tsnor]

I have tried these thin blades on a kayak. It was slow on startup and turning to a stop, but once boat is in motion all 3 blades pictured have equal performance(+ or - 1 second in a 30 second run). If lift, drag or some combination of the 2 is involved, blade area should count?
The Greenland paddle seems to be on its way back to a tree branch -- any old stick will do? maybe I am just looking for a better stick. My interest was inspired by kayaking next to a fast swimming deer which offered no explanation for its performance. Hope to find one here.

For the video: When the oarsman wants the boat to TURN they can load each oar differently and get more force applied to their choice of port or starboard. What you can't see from the video is the force needed on each oar to keep the boat going straight. I'd guess its not the same, that the bladeless oar requires more force applied to get the same net force compared to the bladed oar. The bladeless oar is less effective at staying planted.

In sweeps rowing, once the boat is at speed, the oar does *NOT* move through the water. The oar blade gets planted in the water and stays in place as you lever the boat past the oar blade. This is really clear in a race where the oar blade goes into the water near a buoy -- the blade and the buoy stay the same difference apart during the drive. HIGHER drag is what oar blades want so that they can plant better. The bladeless oar does not plant well, it moves through the water resulting in water movement. This water movement is a rowing efficiency loss compared to a blade that stays planted and moves less water.

In practice, the shape of the blade is huge for other reasons too. The blade can either self-regulate its depth in the water or the rower needs to fight the oar every inch of the way to control pitch and depth. Blade shape matters as the oar handle moves through its arc and the blade angle in the water changes. Weight of oars depends on blade shape as well as material. Concept2 Oars have a ton of technical material on why they are better than old spoon oars. This is also an area of research ... example "..In conclusion, the results of this study indicate that the Macon and Big Blade designs have similar fluid dynamic properties at most of the angles studied. However, the Big Blade generated significantly greater drag coefficients at angles of attack around 90 degrees. It was anticipated that the curved Big Blade would be able to generate significantly greater lift coefficients than the flat plate. The results of the study, however, indicated that this was only true when the angle of attack was greater than 90 degrees, when the leading edge changed from being at the tip to the shaft end of the oar blade. This finding was attributed to the shape of the upper and lower edges of the oar blade, causing it to act in a similar way to a delta wing during the second half of the stroke. The findings of this study would suggest that current oar blade designs are not completely optimized. It should therefore be possible to transfer propulsive force to the water more efficiently throughout the duration of the stroke" http://bionics.seas.ucla.edu/education/ ... orm=MG0AV3

[ocni]

The bladeless oar seems to require less force, maybe due to more slippage, and does its sweep in slightly less time. I understand the subconscious corrections of a long time rower and was expecting an unequal input that never materialized
Lots of good research https://eodg.atm.ox.ac.uk/user/dudhia/r ... rowing.pdf https://www.cambridge.org/core/journals ... C5FAE5B458 in sweeps rowing but blade travel and boat speed are very different in dinghy rowing.

[c2jonw]

https://www.concept2.co.uk/oars/how-mad ... ing%20line.


Info on blade path and development

[ocni]

Clear and concise explanation of rowing, though not entirely applicable to dinghy rowing.
In "Pursuing the not so ideal no blade"

surface area - substantially decreased, should result in large slippage. Intuitively I should be rowing in a circle with these miss-matched oars?
tip shape - if blade encounters apparent flow at a good sweep angle and angle of attack it might generate high lift on its long leading edge with less dependence on area?

[pagomichaelh]

I rowed a series of homebuilt dinghies to work for almost 30 years, generally about 1/2k each direction, so a bit of experience here!

The construction of his dink precludes putting any real power into the blades, so he's using really short oars, with the rowlock about 1/2 down the shaft.

He buries the oars so deep, that it doesn't make all that much of a difference. If you go out to a 8' oar, put in a seat that runs fore-to-aft and foot pegs that you can press on, then the blade shape starts to make a difference, because the effort is in going forward, not up and down.

You'll notice how much of his effort goes into burying the bows of his dink, and how little into going forward.

[Tsnor]

I rowed a series of homebuilt dinghies to work for almost 30 years, generally about 1/2k each direction, so a bit of experience here!

The construction of his dink precludes putting any real power into the blades, so he's using really short oars, with the rowlock about 1/2 down the shaft.

He buries the oars so deep, that it doesn't make all that much of a difference. If you go out to a 8' oar, put in a seat that runs fore-to-aft and foot pegs that you can press on, then the blade shape starts to make a difference, because the effort is in going forward, not up and down.

You'll notice how much of his effort goes into burying the bows of his dink, and how little into going forward.

Would he get more power from the bladed oar if he put it in so that the top of his blade is at most at water level? (Sweeps the top of the blade is at the water line or slightly above. The oar blade floats there naturally, you just need to match that depth while driving.) Or does his boat design and oar choice force the type of rowing he is doing ?

[pagomichaelh]

Would he get more power from the bladed oar if he put it in so that the top of his blade is at most at water level? (Sweeps the top of the blade is at the water line or slightly above. The oar blade floats there naturally, you just need to match that depth while driving.) Or does his boat design and oar choice force the type of rowing he is doing ?

Boat design and oar choice forces the rowing. That boat is almost square (LOA 6', Beam 4') with high gunnels relative to the size of the boat.

The reinforced transom tells me the boat was designed for a 2-5 hp outboard, not as a rowing boat.

Looking at the waterline, if he cleaned the growth off the hull, it'd be a lot easier to row as well!