Thursday, August 18, 2016
What happened
Ouch, it's dangling from its hip. A case of being drawn and quartered, gone awry, and it was all done by something, but what? I know most boaters are familiar with rocks, and a few have had some up close and personal experiences with them, me included. But in southwest Florida we don't often see rocks. In place of all those hard objects we just have fluffy white sand that collects on the shores, and a hard packed version that resides in the water. I'm going to apply some marginal journalistic standards here and disclose that my information is second hand from my mechanic friend who was the verbal cell phone based first responder. He dealt with the owner throughout the incident. To protect his identity, I'm going to change his name to Ron White, mostly because he kinda looks just like Ron White. I figure the real Ron White, who actually looks exactly like Ron White won't mind. As the real Ron White says, "I didn't get to where I am today by worryin' about how I would feel tomorrow." I feel the same way, most days anyway.
Let's do the set up. It's a warm day, and the gulf's waves are about one foot. A light onshore breeze is wafting, and the tide has just started downward. A 30 foot boat backs down towards the beach, and an anchor is tossed. The stern, with slightly trimmed up outdrives is now in about 2" feet of water. The swim platform ladder is dropped, and the cast and crew head up to a beach bar. This beach has about sixty or seventy feet of very shallow water, and then it plummets down to about ten feet.
The crew can see the boat from the tiki hut and it seems fine, the waves are barely one foot. The drives started out at about one foot above the sand, but the tide is inexorably dropping, and the waves are still a measly one foot. The catch to all of this is the one foot wave lifts the 8000 lb. boat, and the small following trough drops the boat a bit lower than the mean water height. This continues until, the outdrives start to contact the sand. From 75 yards away, it doesn't look like much is happening.
Time marches on, and one wave causes a crack to occur in the gimble housing which continues to grow, and a final small wave breaks the other side of the drive free. It's still in place but only sort of. The happy crew goes back to the boat, and climbs on not noticing the drive unit is now looking a bit wonky. Engines are started, and the anchor winch pulls the boat forward and then it fails. The boat is now in deeper water, but boy is the anchor really stuck. With some hand waving, an employee from the resort swims out, and helps get the anchor hauled up. He dives off and goes to shore, the boat is put into gear.
Time marches on, and one wave causes a crack to occur in the gimble housing which continues to grow, and a final small wave breaks the other side of the drive free. It's still in place but only sort of. The happy crew goes back to the boat, and climbs on not noticing the drive unit is now looking a bit wonky. Engines are started, and the anchor winch pulls the boat forward and then it fails. The boat is now in deeper water, but boy is the anchor really stuck. With some hand waving, an employee from the resort swims out, and helps get the anchor hauled up. He dives off and goes to shore, the boat is put into gear.
Now this is all an educated guess. We went through all that we could think of to explain how this could have happened. Could the steering arm have failed, and one outdrive unit struck another? Possibly, but it has only rarely happened. The boat was fine before it was anchored, but wouldn't shift in gear when it left. The only answer is the small waves were picking up the boat, and when 8000 lbs of boat came back down the outdrives were being repeatably slammed into the sand. The other outdrive was also damaged, but not to the same out of key tune.
Waves are an awesome hydraulic force, so I thought I would expound on them for just a couple of minutes. Waves are measured from the trough to the crest. In an ideal world the trough is as far below the mean water level, as the crest is above the mean water level. At a practical level you end up with the trough a bit closer to the mean water level, but you're still lower. You're coming back from the briny and you're headed toward a pass that is normally 7' feet deep. You have nice well behaved three foot swells, and you have a 5' draft. As the swells reach the shallower water they slow down, and start to pile up getting closer together. The amplitude (height) also increases, so now your nice three foot swells are all of a sudden 5' waves. Now at the crest of the wave (2.5' + 7') your depth sounder tells you you have 9.5' of water. In the trough your depth sounder tells you you now have (7' - 2.5') 4.5', but you know that already as your keel slams into the sand. This is a pretty good example, and I have seen it in local passes. While in the trough it's scary to see how little water can be there. Every wave, and type is different, and there are many types all with different characteristics, like tidal, ocean shoaling, and wind driven. You might find it fetching to read up on them a bit. If the little 1' foot wave could cause so much damage, imagine it a squall line had caught the boat that close to the beach.
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