Share Pics of People Hauling or Towing Something Wrong

[TomSeller]

That excavator was either going to go down as it did or in the middle of the bay, I don't see a relatively narrow boat like that having the stability with the center of gravity loaded so far from the center of buoyancy. Even if it could keep it afloat.

 

[xtn]

There was a point at which he tried pressing down the far side of the boat with the bucket even harder. Like that had any chance of working. Physics, people. Don't t***** with it.

 

[IslandTractor]

There was a point at which he tried pressing down the far side of the boat with the bucket even harder. Like that had any chance of working. Physics, people. Don't t***** with it.

I'm not sure that effort broke any rules of physics. Ever tried to get into a small dinghy? It's all about keeping the boat's center of gravity in the midline. Imagine, if the down pressure on the far side was applied at the beginning and controlled with a servo linked to a level then as the weight of the excavator gradually moves from land to boat you could keep the barge level. Assuming the barge could handle the total weight it would be no different than a 200lb guy getting in a dinghy. You can't get in a dinghy by standing on the near gunwale but if you can put some weight on the far gunwale by reaching across it's easy.

 

[xtn]

Nope. No matter how hard you press down on the other side with the hydraulics, you are NOT shifting all the weight of the main unit off of the near side. No matter how hard you push, the overall center of gravity isn't changing.

Sit on one side of a dingy. Now put your foot across it to the other side. Sure, just moving your foot over there transfers a bit of weight, but pushing down as hard as you can on that far side with your foot doesn't change the fact that most of your weight is being applied under your butt cheeks.

In fact, as he pushed hard enough to tip the main body of the excavator rearward on it's tracks, he actually moved the center of gravity even more into the oh-crap zone.

 

[IslandTractor]

Nope. No matter how hard you press down on the other side with the hydraulics, you are NOT shifting all the weight of the main unit off of the near side. No matter how hard you push, the overall center of gravity isn't changing.

Sit on one side of a dingy. Now put your foot across it to the other side. Sure, just moving your foot over there transfers a bit of weight, but pushing down as hard as you can on that far side with your foot doesn't change the fact that most of your weight is being applied under your butt cheeks.

In fact, as he pushed hard enough to tip the main body of the excavator rearward on it's tracks, he actually moved the center of gravity even more into the oh-crap zone.

How do you get into a canoe from a dock? You put a hand on the opposite gunwale, one on the near gunwale and then put your foot close to centerline and balance by increasing/decreasing pressure on the two gunwales as you swing your body weight into the canoe. Same as on a dinghy. Same principle for the excavator.

When pushing on the other side of the boat with the excavator arm, the trick is to start the downward pressure while the majority of the excavator weight is still on the ground. Then you lighten the down pressure as the excavator mass moves towards midline of the boat. The excavator operator in the video simply wasn't experienced doing that. I agree that the boat was narrow for a heavy excavator but I'm pretty sure those guys had done this before successfully.

 

[Mace Canute]

It's all about physics...and where the excavator's center of gravity is. You can change that slightly by using full extension on the booms but the COG is still well back and considering the lifting capacity of them, likely to be well behind the swing axis. Pushing down with the bucket doesn't change the COG. What they did when they used the bucket to apply weight to the far side of the barge was in effect making the excavator into a Class 2 lever with the fulcrum being the tracks rear sprockets, the load being the COG and the effort being the bucket.

They could keep the barge level as they drove onto it but even with a best case scenario where no part of the tracks touched the barge until the absolute last possible moment, as soon as the excavator's rear sprockets left solid ground, all the weight the rear sprockets were supporting was instantly transferred onto the barge. Their problem was they didn't get the machine far enough onto the barge by the time the rear sprockets left solid ground and the COG was far enough away from the center line of the barge that it caused it to roll over.

 

[Jim Shooz]

That certainly will have a bearing on the failure but a major cause would be the collapse of the pier built to load the digger. As the weight is applied by the bucket the front of the tracks lift off and more weight goes on to the rear of the tracks causing the pier to collapse. The weight is then applied to the side of the boat pushing the railing under water. The rear of the boat, hidden by the digger, rapidly fills with water and over she goes

 

[dodge man]

I agree, pushing down didn't help any and once it started lifting the front of the tracks, make it worse. At first glance, pushing down with the bucket seems like it works but in fact if you are pushing down with the bucket there is and equal force pushing down on the tracks so you don't transfer any force to the high side.

I thought it looked like he should have hooked his bucket over the side to pull him self up and onto the barge but the barge might not have been strong enough for that.

 

[dodge man]

I agree, pushing down didn't help any and once it started lifting the front of the tracks, make it worse. At first glance, pushing down with the bucket seems like it works but in fact if you are pushing down with the bucket there is and equal force pushing down on the tracks so you don't transfer any force to the high side.

I thought it looked like he should have hooked his bucket over the side to pull him self up and onto the barge but the barge might not have been strong enough for that.

 

[IslandTractor]

I agree, pushing down didn't help any and once it started lifting the front of the tracks, make it worse. At first glance, pushing down with the bucket seems like it works but in fact if you are pushing down with the bucket there is and equal force pushing down on the tracks so you don't transfer any force to the high side.

I thought it looked like he should have hooked his bucket over the side to pull him self up and onto the barge but the barge might not have been strong enough for that.

Yes, pushing down on the far side with the bucket only works while there is still weight of the excavator on the shoreline. However, pushing down with the bucket does unload the weight from the front of the excavator so I think it would be possible to move the excavator towards midline of the boat while the tail of the excavator still had contact with the shoreline. What Mace pointed out earlier is the real problem....the excavator's center of mass would still not be over the boat's centerline by the time the excavator lost contact with the shoreline.

I'm still convinced that these guys (both boat and excavator owners) have done this before. They do weird things in the 3rd world but they don't throw money away. Somehow that excavator can be loaded with some variation of this technique or perhaps with the operator being more skilled. I recall from the video that he didn't try to push on the opposite gunwale until the boat was already unstable. It might also have required either more movable ballast (or men hiking out as on a Bermuda Sloop) to hold the boat steady while the excavator made it's last four or five foot crawl to midline. One idea might be to have jettisonable ballast on the opposite side like on a hot air balloon. Start with too much cantilevered ballast on the far side to balance the weight of the excavator on the shoreside gunwale. As the boat starts to heel back away from the pier as the excavator crawls on board towards midline, you just cut that outboard ballast loose.