Offshore Passage Making (OPM)
In June 2021 I finally got to do Offshore Passage Making (OPM), this was a real hoot.
Prerequisites include CPM and Celestial Navigation
I did a CPM tag cruise in May as Navigator in the same boat we would use for the OPM trip, which was a good warm up after almost a year ashore.
The goal of the OPM cruise is to sail non-stop for about 600 miles with a good percentage of that well offshore. We also had to reach a specific waypoint about 200 miles south west of San Francisco (dubbed Bikini Island) and get back by the end of the week. There was much speculation as to the facilities to be found at the fictitious island.
We ran the boat as though doing an ocean passage, and this extended to spending a lot more time checking the boat before heading out the gate than is usual for a coastal passage. I was skipper for the first 36 hours, and thereafter we changed skipper every 24 hours so everyone got to enjoy the headaches ;-)
We practiced our celestial navigation, needing to do a running fix with the Sun. My running fix ended up within 5 miles of our GPS fix, which is great and on the 3rd day I had time for a noon sight and found our latitude to with 0.2 miles of the GPS latitude - which I was very pleased with.
Shooting stars was another matter though. Volume 1 of Pub 249 provides a handy table for your approximate location that identifies seven of the of the navigation stars visible, and further indicates which will provide the best cut for a fix. I prepared a form for the first night since I could roughly guess where we would be.
With the data from Volume 1, identifying the stars in question was easy (we also had Venus visible) - they are the first stars visible at twilight, but shooting them from a small boat proved very challenging. I had switched my sextant to the traditional (half silvered) horizon mirror to maximize the brightness of the stars, but this served to halve the field of view when trying to bring them down to the horizon and the slightest jolt meant I lost them. Very frustrating.
Each day we would download weather forecast data (grib files) via Sat phone and plan the next day's sailing accordingly. Our original plan was to head down to Point Conception (near Santa Barbara) which reliably offers heavy weather, then out to Bikini but light winds for the first day meant we might not have time to reach both so Point Conception had to be bypassed.
The first night we sailed out to the Farallon Islands and (with permission from the Coast Guard) set off some expired flares and other distress signals.
Our trip south that night involved maneuvering to avoid dozens of ships waiting to dock at San Francisco. They were virtually stationary but had to be treated as underway.
We returned to the Farallons towards the end of the week in thick fog and were rewarded with lots of whales as well as seals.
We spent the last night anchored in Drakes Bay which was incredibly calm, we got to see very little though due to the fog.
| Author: | sjg@crufty.net /* imagine something very witty here */ |
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