Letter: Physics Lesson on the River

We put the Hobie in the water at the mouth of McAllister Creek. One advantage of a trailerable boat is that we could be there, in the water and rigged, before a larger boat would be out of Budd Inlet.

In the past we had gone up McAllister Creek. The east bank is open and it is possible to sail up it even in light wind. It is an interesting excursion. This day we wanted to check out the abandoned hulk on the east side of the delta.

There was a Force 3 wind so we had a good sail acrossf the delta. However the wind made boarding difficult. There were waves, and no place to make contact that was not rather rough. Not wanting to let the boat pound against the hulk, we circled a few times, as slowly as we could, before giving up.

Instead, we decided to try sailing up the Nisqually River. We had to tack, but that was no problem. What was a problem was that the trees. on the bank blocked the wind. We gradually slowed down.

There came a point where our boat speed exactly matched the current. We could not go up river, but the current could not push us backwards. What happened then? We went sideways to the leeward bank.

Remember the diagram that showed you the forces that let a boat sail to weather? When you subtract the forward vector, all you have left is the sideways force, leeway.

After crossing the river a couple times, we tuned around and sailed back.

Steve Worcester, Star 6932












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