Thursday, April 30, 2020

Key West - Our first day out of Key West was a doozy

Goodbye Key West - we left at 7;00 am
We left Key West with a wind in our face of about 18 kts, it was supposed to be 10 to 15. Okay, we thought, it's predicted to lessen by 11:00 to 10 kts and then to 5 kts or so after that and change to out of the west, just the right direction to push us east. It was not to be. The 15 to 20 kts lasted until just past 1:00 and the direction was out of the south, plenty of fetch in that direction. It was a very bouncy ride, not what was predicted by Grib or PredicctWind - or any of the weather apps nor by the text weather advisories by NOAA for the coast. They were all uniformly wrong.

A nice sunset after a rough day
As added spice, just as we headed into our anchorage at Long key, a storm rolled through with top winds of 42 kts in driving rain (with crab pots around!) This was as I negotiated a narrow channel to stay away from shoals. I was often at a 45-degree angle to my forward progress vector trying to stay on course and also avoid the random crab pot here and there in the driving rain.

As I motored up the channel, my speed dropped to 3.8 kts, I thought there must be a heck of a current! A glance back provided a source of the problem - my dinghy had flipped over upside down in the high winds. It made a good storm anchor. Now the problem was how to right it?

An aside: Ann and I have five grandkids trying out the learn-at-home mode of acquiring knowledge. I suggest a home exercise in physics, after all, what else do they have to do? Let's assume a 9 x 4 ft square (we physicists love to approximate things, it's the technique, not the measurements) dinghy that's upside down.  It has been dragged by a boat for some while which has resulted in a partial vacuum between the dinghy and the water it's immersed in. The soft dinghy provides a very good seal against the water. If you try to pull the dinghy vertically to right it, you will create even more suction - resisting your efforts to pull it vertically off the water surface.

Problem 1:  Assuming a flat 9 x 4 dinghy with a rubber seal (the inflated tubes, 2 feet deep)  against the water surface, how much force is required to lift the dinghy one foot (the dinghy weighs 120 lbs).

Problem 2:  How would you propose lifting the dinghy to right it? Brute force or finesse? What method would you use and why?
Problem 2A - If brute force, how much is required?
Problem 2 B - If finesse, what technique would you use? Finesse is the essence of the solution, go for it but don't damage my dinghy! Describe the finesse technique in detail.

Problem 3: Depending on the technique, how much force would be applied to the point of attachment on the dinghy for righting and what would you use on Fleetwing for that force?

Answers will be graded and due at our Sunday Sherer meeting! (reward certificates will be given! - non-monetary! - learning is its own reward.)


Marty said...


Changes in L'Attitudes said...

Well, certainly a 'insert adjective of choice here' start to your trip north. I was wondering about the little jocking on your Spot track just as you were poised to turn west into the anchorage area. NOAA Charts only show ~5ft in that area, Navionics Sonara a bit more. Looks like you're above 0 in tides on your ride in and through Friday morning when you leave. What kinda depths did you see? Did you just go to a hole you had stayed in before?

Anonymous said...
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Bob423 said...

ScottnKit, you got it exactly right, of course. I removed your solution so the grandkids didn't see it, I may have been too late. I should have mentioned in the blog that it was a test for the kids!