Offshore conditions: go/no go

[NATBF]

I am planning to go practice for a hoped future LongPac, and would appreciate advice on sea conditions. Boat in question is an Ericson 34.

Tradewinds Sailing, in Pt. Richmond, has a nice discussion of making a go/no go decision re: going out the Gate:

Exiting Chrysopylae … “The Golden Gate”

Also known as … is it safe to head out the gate? For over two hundred years, the Golden Gate hid its existence from the Europeans transiting and exploring the coast of California by boat. Fi…

www.tradewindssailing.com

However, on a multiday (~ 5 days) trip things may change once you're out, and as I keep an eye on the weather to get a feel for things I notice that this weekend the offshore (to 60nm) report is:

SUN
NW wind 15 to 20 kt. Seas 6 to 8 ft. Wave Detail: NW 8 ft at 8 seconds and S 2 ft at 14 seconds.

Obviously 20 kts is no problem for anyone who sails in the bay.
My question is about the seas: 8+2=10 ft at a primary of 8 sec exceeds the go/no go recommendation from Tradewinds, which is that the combined seas be under 12' and less than the period, and that the primary period be 9s or greater. I realize there are two issues here: a period < 9s, and separately a combined wave height > period. I am curious about both.

I am unsure if the requirements above are more about not wanting to face those conditions across the SF Bar / in the main shipping channel, or whether it is a more general "avoid being out if there if anything like that in the forecast", even if one would be well offshore by the time that weather hit.

For clarity: my question is not "should I go out the Gate on Sunday in those conditions." I would not. Rather, it is "would you go on a 5-day trip like the LongPac if something like that was in the forecast for later on, when you would be out far past the lightship/SF1?"

Any advice/comments/suggestions would be appreciated.

 

[BobJ]

Hi Neil,

Once you're far enough offshore that current is less of a factor, the wave state is determined mostly by the wind. So the wind forecasts will suggest the expected sea state. You can also get wave forecasts: passageweather.com is one option. Take a look: once you select an area, scroll to the bottom panel for their wave forecast. There are exceptions: Hurricane remnants have deteriorated the sea state at the end of Hawaii races. The passageweather charts (as one example) would show those.

If you're using the LongPac course as a qualifying sail (and going out when you want), you can plan accordingly. It's when you HAVE to start on a particular date for the SH TransPac or LongPac that you may have to sail in harder conditions than you'd like.

Other factors are how hard you want to push, and your boat's weight and hull shape. My J/92 was light and relatively flat-bottomed. It tended to pound when pushed. I won the 2011 LongPac because I was willing to stay close to the wind and push hard going out, when the other boats cracked off and slowed down. I had to steer through the waves to reduce the pounding - how much you hand-steer also has a big effect on what you can handle.

Not sure if I'm answering your question so write back if I'm not.

Bob J.

 

[NATBF]

Many thanks, Bob!

My question is actually a little different; apologies for the dense phrasing. For purposes of this question, I am assuming the NOAA forecast for 60nm is correct, and am wondering how to interpret the figures in terms of whether or not to go out.

What I am really asking is:

--> Is it a bad idea to go out for a 5-day trip if the predicted seas 60nm offshore are 12 ft (combined swell and wind waves) at 8 seconds?

and, more generally,

--> what predicted sea states out past the Farallones would cause you (any of you, not just BobJ) to delay your trip?

I ask because there seems to be a good bit of agreement on various forums that it's a bad idea to go out the Gate in swell periods < 9s and/or when the period < wave height, so I would not go out in that. But I am curious whether that advice is specific to getting past the SF Bar, where it is shallow, and the advice may be different for deep water, i.e. if the forecast seas weren't showing up until later in the trip.

Much appreciated!

PS: As waves hit shallow water, the slow down and get closer together (wavelength shortens). A 9s period in deep water has a wavelength (wave spacing) of ~ 400 ft, per Bowditch, while I have seen them much closer together just South of the Potato Patch (obviously pretty shallow.) Hence my question: maybe the spacing is part of the concern, and that changes and becomes less of an issue as one gets to deeper water.

PPS: Definitely appreciate the steer to Predictwind! It looks sort of like the 'Windy' website, which gives windspeeds and also wave heights; will have to see what the differences between the sites are.

Professional weather forecast

50+ weather layers, weather radar and satellite

www.windy.com

 

[BobJ]

Double-digit height with a single-digit period = would not go. What you're reading is good advice.

 

[Philpott]

052215

At the Skipper's meeting last night Rick Elkins asked for a show of hands from those people who were doing the Farallones race for the first time. There were a lot of hands. Last year or the year before that ... I asked Bob Johnston for advice. Here it is:

Well first, that's an average for the whole day and 15-25 is a broad range. The last time I looked it was going to be more like high teens out at the Farallones = a piece o'cake. It is forecast to get windier at the end of the day, with gusts as high as 31 knots. Therefore if you're not around the island by mid-afternoon you might want to head back, but see how it's going and how you're feeling.

On the way out, once the breeze picks up keep your sails flat - plenty of halyard tension, cunningham and outhaul on the main, halyard and sheet on the jib (grind it in flat). If you're still heeling too much you can reef of course, and also try to move the jib leads aft to open up the jib's leech a bit while keeping the foot tight.

On the way back you can ease everything some. A looser vang will help to keep you from broaching and of course, ease the mainsheet well out if it's getting broachy. If the jib is a little on the tight side (overtrimmed) it will hold your bow down better coming back, also reducing the tendency to broach. If you have an outboard jib lead (like out to the rail) use that - it will also want to led a little farther forward. This will keep the top of the sail from luffing when you ease it out on the reach home.

If that forecast (SAT...NW WINDS 15 TO 25 KT. WIND WAVES 3 TO 5 FT. NW SWELL 6 TO 8 FT AT 9 SECONDS. .SAT NIGHT...NW WINDS 15 TO 25 KT. WIND WAVES 4 TO 7 FT. NW SWELL 7 TO 9 FT AT 8 SECONDS. ) proves correct and the wave period is that short, it's going to be a bit sloppy. Remember though - just close up the companionway and turn around and it becomes more manageable/comfortable coming back. So keep going until you're not having fun anymore and then turn around. Hopefully that will be at the island!

Just a reminder on the rounding: You see the knob on the NE corner of the island from way off so it's pretty easy to plan to pass it at a seamanlike distance. Once you do that, don't bear off - hold a heading of 255 Mag (270 True) i.e. due West, even though the island tapers off to the south as you proceed along the north side. Watch for breakers off your STARBOARD bow. If you see any big ones, tack over and get farther North. Then don't bear away around the west end of the island until you're almost past it. Simply said - sail due West across the top, don't cut the corner.

Then once around and in the lee of the island (on the south side), use the head and get everything out in the cockpit you're going to want during the trip home. Then relax and enjoy the ride. It's nice to know the bearing back to the Gate since you won't be able to see it until you get closer in. Don't forget to turn on your running lights (I do it early), call in your approach to the finish and jot down your finish time in case the R/C misses it.

Let me know if you have any other questions.