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tomvorlostriddle t1_j3lle6z wrote

Reply to comment by RowBull in 2012 Olympic male athletes’ weight [OC] by highcharts

>The heavier you are the more power you need to produce to offset the extra weight (and therefore drag) you bring to the boat

Yes , but it's water and it's flat, not cycling uphill etc., this is easily compensated by how much easier it is to be powerful when you're heavier.

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RowBull t1_j3lopev wrote

I think weight has a bigger impact than you might think. Unlike cycling as rowing is in water. Water will generate a significant amount of drag which constantly effects the boat and the heavier your boat is the more drag you will generate. Secondly unlike cycling rowing does not have constant power application, each stroke will have approx 1s of power application and 1s of recovery as the rower takes the next stroke. This means that while oars out of the water the boat is relying on momentum, so minimising drag is key to reducing the boat slowing in the period. Additionally more force will be required to accelerate the boat at the start of each stroke with more weight. Finally a rowers weight will significantly move within the boat on each stroke against the direction of travel of the boat. This will cause the boat to slow with more weight.

Some coaches will weight adjust everyone’s times off the water for their crew selection because of these factors.

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MeatierShowa t1_j3malqs wrote

>heavier your boat is the more drag you will generate

Not according to this. https://www.rowinginmotion.com/drag-efficiency-rowing/

"the drag force attacking the hull is proportional to the square of boat velocity and a hull-specific drag constant ."

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Fossafossa t1_j3md04j wrote

More weight = sitting lower in the water = more wetted surface.

The more wetted surface of the boat the more drag it creates.

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pitooey123 t1_j3nbn9g wrote

Not necessarily, the boats are rated for certain weight classes so they have different buoyancy

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Coomb t1_j3o1j3f wrote

It is absolutely true that any particular boat will sit lower in the water if it's carrying more weight.

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Deto t1_j3ov4y5 wrote

Yep, if you take a boat and add weight the boat will sink until the additional water it has displaced equals the additional weight.

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oak_pine_maple_ash t1_j3p29qa wrote

in rowing the boats are designed around athlete's weights. So my boat is designed for a 130lb person, and my bf's is designed for a 180lb person. It's both longer and wider. We end up sitting around the same height off the water.

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SomethingMoreToSay t1_j3qa7hh wrote

Yes, but his has more wetted surface because it's longer and wider, hence more drag.

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Korvensuu t1_j3qqt1w wrote

as a simple example, you and your bf now swap boats

the lw boat your bf is in will be deeper in the water than when you were in it >> more drag

his boat that you're in now sits higher in the water >> less drag

the boats are designed for different weights but thats not really what we're looking at here, we want to know how much water is displaced as that determines the amount of water-boat surface contact surface area and hence the drag.

A scull rated to a heavier weight does this by being wider and/or longer, increasing the water-shell contact area [which is the key thing as by spreading your bfs weight over a larger area the boat 'sinks' less and has the right water clearance] and increasing the drag

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Coomb t1_j3sac93 wrote

You sure do, or at least I believe that you do. That doesn't change the fact that in order for the boat not sink, it has to displace slightly more than the weight of water equivalent to the weight of the boat plus all of its occupants. For any given boat, if you put more weight in it, it must displace more water (or be able to provide additional dynamic lift, but that's irrelevant for rowing sculls). Your boat and your boyfriend's boat have approximately the same freeboard, but his boat absolutely must have additional volume displaced below the waterline, and that necessarily induces additional drag.

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KrzysziekZ t1_j3p8hdn wrote

More wetted area or cross section must result in more drag. However, some if not more drag is wave-making drag (which is harder to model) and this is primarily dependent on length of the hull, which doesn't change with displacement.

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MeatierShowa t1_j3r37a4 wrote

The length of the hull doesn't change, but the waterline might, depending on hull shape. I think it's known in sailboats that if you load it down to increase the waterline you might get a little higher hull speed.

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CarpetbaggerForPeace t1_j3lnlqh wrote

I thought strength increases as r^2 and weight increases as r^3 so someone has to gain a lot of weight for harder and harder strength increases.

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tomvorlostriddle t1_j3m54cj wrote

yes, but you are not vertically climbing there, you are not linearly penalized for your weight

and rowing is also about amplitude

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KrzysziekZ t1_j3pbe75 wrote

Force increase as r^2, but energy or power available as r^3. That's why all animals jump (from being still) the same height, be it a flea, a mouse or a human. Cats are better, elephants can't jump at all due to their ankle.

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Adventurous-Text-680 t1_j3n3ro7 wrote

Easily compensated?

https://eodg.atm.ox.ac.uk/user/dudhia/rowing/physics/weight.html

Check section 8.

> So if a 85 kg oarsman pulls a 5 km erg in 19 minutes (=1140s), and a 70 kg oarsman takes 19.5 minutes (=1170s), their equivalent 'boat speeds', normalised for a 75 kg oarsman, would be:

> (8.8) (85kg): TB = 1140 / ( (90/100)0.167 ) = 1160s = 19m 20s > (8.9) (70kg): TB = 1170 / ( (90/85)0.167 ) = 1159s = 19m 19s

> i.e. a bit of a nightmare for the person who has to select between the two. (Using the 0.222 power would give times 1167s and 1155s respectively, so the lighter rower would win).

Now this is using accepted formulas for estimating rower performance on water based on an erg (indoor rower). So it's not perfect, but it's a great example of why not being bigger didn't mean faster. Remember drag is constant for all movement including coasting.

So in this example the 15kg heavier person would be about the same speed as the 70kg person. You can't assume that the extra weight will always be just muscle. Fat, bones, etc count as well. You are unlikely to increase just muscle (at best you will have a body fat percentage of around 5-8% for an elite athlete). So any increase in weight will carry dead weight as well.

Physics dictates that you need to increase displacement in order to float a heavier weight on water. The more water you displace the more water will be in your way when you try to move. Drag is drag and it affects you. People can only gain so much strength improvements with weight.

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