Understanding Equal Load Distribution for Rowing Team: Help Needed

[Kitkatje]

I'm hoping someone can help me. I have only a rudimentary knowledge of physics, but have strong scientific instincts, as well as a background in science, but not physics.

Our rowing team recently has engaged in a debate about the distribution of a load while carrying a heavy rowing scull (about 60 feet long and weighs over 250 pounds).

Currently, the way we carry is to have four tall people in one end, and four small people in the other. Sometimes the height difference is over 24 inches. When the boat is carried tilting down due to height differences, it feels as if the boat is heavier in the lower end. Initially we used the method of every tall person spread out along the boat, but they end up carrying a heavier load because the boat sits on their shoulders, and the shorter teammates carry less, because the shorter team members are essentially unable to fully assist as the boat is above their shoulders.

Thus, we changed to the current method, grouping together to spread the load. This works well only when everyone is similar in height. Spreading out along the boat evenly results in more load on each individual. A few members think the load distribution is "even" when the boat is tilting downwards, and their explanation is "gravity is gravity" (they probably never studied physics). Anyways, it sure feels heavier for those of use in the short category.

Additionally, my thoughts are that if I'm carrying 50 lbs and I weigh 110, proportionally my load is heavier than a 280 pound person carrying 50 lbs.

How do I explain the difference in load in a way the average person could understand, and come up with an equitable solution for load distribution for the team going forward?

Any help is sincerely appreciated.

Thanks!

Kate

 

[berkeman]

I'm hoping someone can help me. I have only a rudimentary knowledge of physics, but have strong scientific instincts, as well as a background in science, but not physics.

Our rowing team recently has engaged in a debate about the distribution of a load while carrying a heavy rowing scull (about 60 feet long and weighs over 250 pounds).

Currently, the way we carry is to have four tall people in one end, and four small people in the other. Sometimes the height difference is over 24 inches. When the boat is carried tilting down due to height differences, it feels as if the boat is heavier in the lower end. Initially we used the method of every tall person spread out along the boat, but they end up carrying a heavier load because the boat sits on their shoulders, and the shorter teammates carry less, because the shorter team members are essentially unable to fully assist as the boat is above their shoulders.

Thus, we changed to the current method, grouping together to spread the load. This works well only when everyone is similar in height. Spreading out along the boat evenly results in more load on each individual. A few members think the load distribution is "even" when the boat is tilting downwards, and their explanation is "gravity is gravity" (they probably never studied physics). Anyways, it sure feels heavier for those of use in the short category.

Additionally, my thoughts are that if I'm carrying 50 lbs and I weigh 110, proportionally my load is heavier than a 280 pound person carrying 50 lbs.

How do I explain the difference in load in a way the average person could understand, and come up with an equitable solution for load distribution for the team going forward?

Any help is sincerely appreciated.

Thanks!

Kate

Welcome to the PF.

It seems a better way to work it would be to distribute the 4 tall people evenly along the underside of the scull, each pushing up on the hull, and distribute the 4 shorter people evenly on either side of the scull pushing up on the gunwales. You carry the scull inverted, right?

 

[berkeman]

Oh, and 250 pounds divided by 8 is closer to 31 pounds, not 50 pounds.

 

[Kitkatje]

Thanks for the welcome, and your response, and the math correction, too (I was giving it a ballpark estimate) :)

Yes, the boat is carried with the keel facing up. If you have taller people on one side, would that create more of a load for the lower side? Are there any equations to try to figure out load per person in this situation, based on height, weight of boat, weight of person, angle of the boat away from the ground along the length (maybe from the midpoint of the hull), and angle of the boat away from the ground across the beam/width? Thanks again!

Kate

 

[Kitkatje]

Sorry, I'm probably not communicating my question clearly.

I re-read your point about the weight distribution. If the load was distributed evenly, each person would carry 31 pounds. My question is actually a) what is the amount each person carries based on the angle of the boat when carried (does it stay the same, and if not, how do you determine that, and b) does the amount of effort carrying related to the relative quantity of weight carried (based on the weight of the person) vary; ie. 31 pounds is still a greater percentage of my body weight to carry than if I weighed 280 pounds.

Thanks again.

Kate

 

[I like Serena]

Hi Kate. :)

When the boat is at an angle of say more than 10 degrees, it will have a tendency to slide down.
Someone will have to prevent it from doing that, and usually that is the person at the lowest point.
It also depends on the actual direction that the people are pushing.

I don't know for sure, but I can imagine that ik may help if the tall people are in front, instead of in the back.
At least as long as you're walking with the boat, since they will have a tendency to lean forward.

And yes, a bigger person can carry a bigger load.

 

[Kitkatje]

Thanks much for your response. Now we have at least two different methods to try.

Hopefully, this will help as I appear to be losing height rapidly as my spine compacts from the extra load at the short carry end of the boat, which is always leading the way ;)

Kate

 

[AlephZero]

You should be able to settle the argument by measuring the weight at each end with two sets of bathroom scales.

It is quite likely the load is different at the two ends of the boat whether or not it is sloping, because unless it is completely symmetrical the center of mass will not be half way along its length. You didn't say if it makes a difference whether the tall people are at the bow or stern end.

But people's perception of the load isn't necessarily the same as what you measure, because there is no way that a short person can know first hand what it would be like they were tall and carrying the other end of the boat!

If the boat is sloping from side to side, there will be a bigger weight on the low side. You can understand that without any math. Suppose the boat is resting on the ground, upside down, and you pick up one side, If you lift it far enough, the weight on the side that you pick up will reduce to zero, and the boat will roll over unless you hold it down rather than lifting it up. (But you probably don't want to try that experiment unless you have a boat that is ready to be scrapped!)

The same argument applies in principle if the boat was sloping end-to-end, but as you can imagine you would have to lift it almost vertical before it toppled over, and in practice the angle of slope would be much smaller end-to-end than side-to-side, so the effect would be much smaller.

 

[Kitkatje]

Thanks for your answer! Good point about perception, and another very variable factor would be strength and conditioning of each person. It doesn't seem to make a difference which end the tall people stand, and the boat appears to be symmetrical, although I'm not certain of it, and I will check to make sure.

How would you recommend a bathroom scale be used? I can imagine holding the end opposite the scale up in the air (at the same distance from the ground as the distance from the shortest to tallest person), letting the end of the boat rest on the scale, and then switching the ends that the scale is under, next placing the scale under the end suspended in the air. Would that give an accurate measurement on the end up in the air, or would it provide a false measurement because of the effort involved in pushing up the boat to sustain the height needed to effect the angle for the purpose of using the scale? Would it help to hold the boat in the exact middle point (given that the boat is symmetrical) and pivot the ends to rest on the scale at the required distance from the ground?

Thanks!

Kate

 

[AlephZero]

You could use one scale to weigh each end in turn, or two scales to weigh both ends at the same time.

Any vertical force you apply to the boat while holding it will affect the results, but you probably will need to hold the boat somehow, with the minimum force possible, to stop it falling off the scales.

On level ground you might need to put something like a wood block on top of the scale to keep the boat off the ground. You can then subtract the weight of the block from the total weight.

You should be able to find something (e.g. a chair, or part of the trailer you use to transport boats) to support one of the scales two feet higher than the other, to weigh the boat when it is sloping.

Actually the easiest way to do the weighing probably be to lift the boat with a rope and sling at each end, and measure the tension in the ropes, if you had the equipment to do that - but you are more likely to have some bathroom scales available than a couple of spring balances that can measure up to say 150 pounds.