What evidence exists that lighter shells are faster?

[frankencrank]

I can make an argument that a heavier shell could be faster, especially for longer races. Wondering if any evidence exists in this area?

[Cyclist2]

Purely based on weight, I don't see how a heavier boat would be faster. I have no empirical evidence at my fingertips, but my naval architecture and practical background make me believe a lighter boat (no other variables) will be faster. Gravity works.

If you took a boat optimized hydrodynamically with the exact same crew and just placed an extra X pounds evenly distributed along it, it would sit lower in the water creating more drag, in addition to propelling the extra weight along. Hence slower.

If you took the same crew in a different but heavier boat optimized to sit in the water the most hydrodynamically efficient way, then the difference is only the weight you are pushing down the course. Still slower, but maybe not as much.

There are lots of lighter boats that aren't as fast, but there are a lot more variables than just weight involved.

I am curious about your argument.

[frankencrank]

Purely based on weight, I don't see how a heavier boat would be faster. I have no empirical evidence at my fingertips, but my naval architecture and practical background make me believe a lighter boat (no other variables) will be faster. Gravity works.

If you took a boat optimized hydrodynamically with the exact same crew and just placed an extra X pounds evenly distributed along it, it would sit lower in the water creating more drag, in addition to propelling the extra weight along. Hence slower.

If you took the same crew in a different but heavier boat optimized to sit in the water the most hydrodynamically efficient way, then the difference is only the weight you are pushing down the course. Still slower, but maybe not as much.

There are lots of lighter boats that aren't as fast, but there are a lot more variables than just weight involved.

I am curious about your argument.

Here is the argument. shells are not propelled by propellers but rather by episodic impulses. The boat accelerates and then decelerates. There will be an average speed. For the same impulse power a lighter boat will accelerate faster and decelerate faster from the water resistance. That water resistance varies with the square of the speed. So, while a heavier boat will not accelerate to the same top speed, it will also decelerate slower (assuming it only sits minimally lower in the water). This smaller oscillation would result in a higher average speed for the same power input. As long as the race is long enough for this difference to make up for the slightly slower start then the heavier boat should be faster. It is like fuel economy, the steadier car will have the higher fuel economy.

FISA has rules as to how much a boat must weigh but no rules as to how heavy it can be probably thinking heavier is slower.

[jamesg]

Weight is for the best balance of safety, strength and rigidity. Rigidity is for speed. For years now shells, bikes and F1 cars all use carbon fibre and honeycomb structure; not because it's cheap. The 2112m course in Henley takes about a minute less than it did in my day, in an eight. No doubt C2 carbon blades help a lot too.

[frankencrank]

Weight is for the best balance of safety, strength and rigidity. Rigidity is for speed. For years now shells, bikes and F1 cars all use carbon fibre and honeycomb structure; not because it's cheap. The 2112m course in Henley takes about a minute less than it did in my day, in an eight. No doubt C2 carbon blades help a lot too.

Rigidity is best for transferring power with few losses. The UCI, like FISA, limits how light a bike can be. I understand this is for safety reasons, they don't wan't people cutting it too close and a bike failing. Perhaps FISA has the same inclination here.

Would it be worth it to put a little lead into the keel (would help with set up probably) or to add weight to make the oar locks or shell more rigid? There are lots of reasons to think that a little (or a lot) of extra weight could be your friend. Everything is about trade-offs. Our coach at Navy (Paul Quinn) completely changed our rowing style my senior year after analyzing the losses due to the shell velocity varying with the stroke to minimize that variance. That year Navy swept the IRA's.

Before then he was experimenting with putting non-newtonian fluids in the water to reduce water resistance. (FISA has made that illegal I see). He was not afraid to think outside the bubble.

[jamesg]

more rigid?

More than what? Suggest you talk to boatbuilders such as Filippi, who supply most of the Olympic boats nowadays. But with a crew weighing say 800kg, adding 10 to the shell won't change much. Not forgetting that there's already choice of shells available to crews.

[hjs]

I can make an argument that a heavier shell could be faster, especially for longer races. Wondering if any evidence exists in this area?

I can make an argument, that a very heavy boat will not move at all, it will sink

The lighter a boat, the faster, the lighter the crew the faster. Everything else being equal.

[c2jonw]

(assuming it only sits minimally lower in the water)

Big assumption there. It's the wetted surface of the boat that creates the majority of the resistance. Does your argument assume the same wetted surface?

[Nomath]

In 2006 Stephen Seiler made a nice powerpoint survey of One Hundred and Fifty Years of Rowing Faster. Pages 31-32 deal with drag forces on the boat. There is a formula at the bottom half of page 32 for the effect of boat weight on speed. In fact, it's the lumped weight of boat, rowers and oars that matters.

[frankencrank]

(assuming it only sits minimally lower in the water)

Big assumption there. It's the wetted surface of the boat that creates the majority of the resistance. Does your argument assume the same wetted surface?

It would assume a minimally increased wetted surface. I haven't done the calculations but, in an 8, 50kg would have small effect on wetted surface. As I said, I can make the argument. I cannot prove although, I know Paul Quinn did that work and showed that reducing boat speed variation would result in higher average speed without changing wetted surface.

[frankencrank]

In 2006 Stephen Seiler made a nice powerpoint survey of One Hundred and Fifty Years of Rowing Faster. Pages 31-32 deal with drag forces on the boat. There is a formula at the bottom half of page 32 for the effect of boat weight on speed. In fact, it's the lumped weight of boat, rowers and oars that matters.

Thank you for that link. Very interesting. On the pages 31-32 he give the physics of rowing as a reference. http://eodg.atm.ox.ac.uk/user/dudhia/ro ... eight.html
Section 7 discusses the effects of dead weight. Here he shows the effects of an extra 10 kg in an 8 would slow it .6 sec in a 6 minute race, or 4 m difference. There is only one problem, he uses constant propulsion in his calculations. So, the question remains unanswered. The slowing effect of weight is small. Is the slowing effect of increased variation of speed smaller or bigger? That still remains unanswered to me.

I emailed this author regarding some issues I had with his assumptions in comparing ergometers to shells. I will mention this to him also.

[Cyclist2]

Is the slowing effect of increased variation of speed smaller or bigger?

This is why crews work so hard on perfecting the stroke - to minimize that speed variation. "Let it run" is heard often and the catch is worked on constantly. I doubt the small difference in weights to even out the speed variation is going to make a bigger difference than the ability and efficiency of the crew to propel the boat on the drive and then minimize the checking during the recovery and catch. Therefore, go with the lighter boat and improve the crew's technique.

[frankencrank]

more rigid?

More than what? Suggest you talk to boatbuilders such as Filippi, who supply most of the Olympic boats nowadays. But with a crew weighing say 800kg, adding 10 to the shell won't change much. Not forgetting that there's already choice of shells available to crews.

More rigid than what is present now. Everything can be made more rigid. There are always design trade-offs. Are shell designers over emphasizing weight reduction over rigidity (power transfer losses)? I don't know. Are they basing their decisions off the "physics of rowing" site that ignored the fact that propulsive force isn't constant when doing its calculations? I don't know. I just threw this out for discussion. If you found out that a 10 kg heavier shell that transferred power more effectively to the water was 0.1 second faster over 2k would you say "isn't worth it"?

[frankencrank]

Is the slowing effect of increased variation of speed smaller or bigger?

This is why crews work so hard on perfecting the stroke - to minimize that speed variation. "Let it run" is heard often and the catch is worked on constantly. I doubt the small difference in weights to even out the speed variation is going to make a bigger difference than the ability and efficiency of the crew to propel the boat on the drive and then minimize the checking during the recovery and catch. Therefore, go with the lighter boat and improve the crew's technique.

The math says reducing the variation should increase the average speed, everything else being the same. It is a matter of how much. Small can be worth it if it is the difference between winning and losing. "Going with the lighter boat" is increasing the variation whether the technique is good or bad if the technique is the same.

I am talking small differences. The question is, how small? I don't know. It would be nice to know so people can make rational decisions instead of guessing.

[c2jonw]

Then there's this:

http://www.worldrowing.com/news/synchro ... -move-boat