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South San Francisco Bay Charter's Handbook - Bay Conditions
By Bob Diamond

San Francisco Bay Conditions

The sailing conditions on San Francisco vary by time of year, time of day and even by exact location. The windy season begins by mid spring and lasts until September. In the fall the sailing gets mellower and mellower until, by winter-time, there are many days when there's hardly enough wind to make sailing worthwhile. But there are a few good days in winter, usually after storms have passed through the area. The spring and summer is the windy when we get small craft advisories almost every afternoon. The wind peaks mid to late afternoon and locally tends to be a little stronger at the San Mateo Bridge. The normal direction is from the northwest but it tends to blow a little more from the west as it gets stronger in the afternoon.

There are some spots that routinely get stronger wind. Right through the Golden Gate towards Berkeley, it's called the "slot" because so much wind is forced through the area between San Francisco and Marin County. There are other areas known for strong wind. The San Bruno Gap blows through the area near Oyster Point Marina and The Crystal Springs Gap focuses wind from about Coyote Point to the San Mateo Bridge. It's important to note that where there is strong wind blowing over a greater distance of water, there will be larger waves. This is called "fetch". For a given wind strength, the longer the fetch, the larger the waves.

Boats usually don't have to travel far in San Francisco Bay to find shelter from the wind and the waves. On the south side of the "slot" there's some shelter behind Treasure Island and directly behind The City. On the north side there's shelter behind Angel Island and Tiburon. The wind in one area can be 30 to 35 knots while a few hundred yard away it might be only 10 knots. Knowing what lies ahead, smart sailors will find the easiest places to hoist sails or reef.

There's more commercial traffic in The North Bay including tug boats, ferries and ships. All of them are a lot faster than small sailboats. It can take as long for a small boat to cross a shipping channel as it takes a large ship to travel up to two miles. Keep a constant look out for all commercial traffic and especially the ships which can not deviate from their channels. You need to start moving out of their path well before they become close to you. Get a chart briefing from any of the various members of the Spinnaker staff who are familiar with North Bay commercial traffic patterns before heading there for the first time.

Fog can be an additional factor in the North Bay. Sometimes the bottom of the fog layer is far enough above the water that you can see traffic on the bay but sometimes it comes right down to the deck. When this happens, extraordinary measures must be taken to avoid colliding with other vessels or obstacles. The fog tends to limit itself to the area from the Golden Gate to the Berkeley side of The Bay between Richmond and Emeryville. It also tends to be heavier in the west. Transiting this area when the fog is on the deck is extremely dangerous and should be avoided if at all possible. If you're stuck in the fog have to move, try to stay completely out of shipping lanes or if you do have to cross one, do so at right angles and with extreme caution. If you have VHF radio, you can listen to channel 14 to learn what the commercial shipping traffic is doing.

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Bob Diamond has been the head sailing instructor at Spinnaker Sailing since 1984

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