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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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  #11  
Old 10-12-2007
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Alcatraz can be a real PITA, especially when used as a windward mark (stb rounding) and the tide is in flood. What happens is the west and south ends tend to be a lee shore wind wise as there this a persistent shift in that area due to the shape of the hills in the city. The island and seamount it sits on also deflects the tidal current in the area so the flood hits the north point (Alcatraz Shoal), splits and runs down both sides of the island. On the city side, it has a bad habit of sweeping you towards the island. The back side splits and flushes you straight out to the Olymic Circle and Berkeley. Coupled with the wind lifting to clear the island, you can find yourself in dirty (non-linear airflow) air just when you need the power to offset the current that can run as high as 2 and half kts. Cutting inside the buoy at the shoal is not advisable unless you want to make the cover of the BoatUS magazine like a powerboat did a few years back.

Our race strategy (coming out from the Berkeley Pier start line) is to sail up inside the “cone” then run up the tide line to the south end of the island (port tack). We will go to stb tack when we get headed right at the south edge or sooner if there is a lot of traffic. The water is really deep on this side and you can get real close without hitting anything on the bottom. We will then short tack the city side of the island and will over stand the “natural” layline to the buoy that marks the shoal. With the current set being as much as one third your boat speed and you’re crawling off a very rocky lee shore, you want to give yourself extra allowance as the current set doesn’t give you much margin of error.

On port roundings, we go up the cone, favoring the “slot” side. Again, you need to over-stand the layline on your last port tack as the current doesn’t really flow down the back side of the island but rather straight down the slot to Olympic Circle. So any type of current set will put you straight into the backside of the Island where there is one heck of a wind shadow.

Kinda hard to describe what happens at Alcatraz without the aid of a chart but I hope you can get the “drift”. Alcatraz is no common lee shore.
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  #12  
Old 10-12-2007
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Oh, thats right, stupid me, brain fart, wrong side. And good lord that side is even worse!
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  #13  
Old 10-13-2007
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Mr. Ganier is on to the heart of the matter. It sounds a bit simplistic, or even condescending, but it's not being evasive to say that you cannot allow yourself to get in such a situation.

Another way of looking at the issue is by one of definition. By definition, you cannot sail off a lee shore as you are unable to point high enough to avoid grounding. If you are able to sail off a leeshore then, the point can be made, it wasn't really a leeshore; just a really intense exercise in beating (sailing to windward).

In all due seriousness, the issue arises at the point at which the determination is made that you can sail out of there as you approach the coast or shore. Making that decision without due regard to wind shifts or current can allow you to end up in a leeshore situation. The error occured earlier though, when you either did not allow for, or were aware of, the changing nature of conditions.

The best thing to do is to avoid impulses to go sight-seeing inshore, leaving those situations where you might confront a leeshore to the requirements of entering port, if then. Of course, knowing how well your boat handles to windward is of fundamental importance in determining what may be a leeshore for you.

A sea anchor and excessive ground tackle are not amiss either.
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Old 10-13-2007
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Thank you all for your replies.

You have answered my question, but in some ways it is because I asked the wrong question because of my own ignorance. What I mean is this - I didn't know the definition of a lee shore was one that you couldn't sail away from. I thought that a lee shore was any shore to the lee, one you could sail away from or not sail away from. So my original question has to be rephrased.

So now what I really meant to ask was this ...

How do you know when something is about to become a lee shore ? Of course we are always in situations where there is a shore that is to leeward, I mean, it is impossible for me to go out on the Chesapeake Bay and not have a shore to leeward AND windward, however distant they might be. So when does it become a lee shore ? I mean, what are the variables involved ? It seems like wind speed is the primary one. In a gentle breeze you aren't going to get pushed closer to the shore, you can probably sail off of it. In a stronger breeze it gets harder, and in hurricane winds I guess it's impossible to make enough progress windward to avoid being pushed on to shore. That's really what I wanted to know .. how close is safe ? How do you know when you are getting into a situation that is going to get you into trouble ? Is the only requirement that you see that you are not making progress to windward and that you are being pushed towards a shore, or is that already too late ?

I'm trying to figure out what I need to be watching for, what I need to be thinking. Obviously I am going to be thinking, hey, I don't want my boat to end up on those rocks I see on the chart. But how do I know when that is going to be a possibility ? I mean I am going to have to sail past the rocks to get out of the bay and into the ocean for example, and they are to leeward, how do I know if I am going to be able to do it ? What should I be looking at ? What conditions make it more likely that it will end in ruin ?

Maybe it's like if you get mugged in the city. In hindsight you shouldn't have been down that alley, and you "knew" before you walked down it, and you "had some idea" before you even walked down the street that the alley was off of, and you "had a feeling" before you even went downtown, but you had to go downtown to see the movie! Is a lee shore something that by the time you figure out it's happening it's already too late to do anything about it ? Is it always a surprise ? That's what I'm trying to figure out, how to avoid getting into trouble in the first place, what I should be thinking and watching out for ?

You guys must be navigating the possibilities in your mind all the time, watching out for certain things, always mindful, searching the future for things that are going to get you into trouble. What are those things out in the uncertain future that you are watching out for ? What in your mind's eye raises alarms minutes, hours, or even days beforehand that save you from being put on the rocks ?
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Last edited by wind_magic; 10-13-2007 at 01:09 PM.
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  #15  
Old 10-13-2007
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We used to sail a lot in a coastal "fiord", about 20 NM into the mainland from a largish strait.

Such geography (steep sided narrow inlet) often results in a diurnal wind pattern that sees thermal heating generating often brisk inflow winds during the day, but at night these winds reverse and blow out of the inlets to open water.

During the day cruisers would often anchor in the lee of an island or peninsula for shelter from the inflow winds. The unaware would try to stay overnight. This usually led to a rude awakening around 0100hrs when the outflow winds start up, and suddenly you are swinging toward the beach with a 20 knot breeze blowing hard onto that beach.

To me, this qualifies now as a lee shore, and my understanding was a lee shore is one where the wind is generally blowing onto it (and therefore requires beating to escape, or "claw off" as they used to say).
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Old 10-13-2007
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"I thought that a lee shore was any shore to the lee, one you could sail away from or not sail away from..."

This IS the correct definition.

You started off with the two extreams, calm and hurricane. In calm conditions a lee shore is not a major concern (but still needs to be addressed). In a hurricane, or other severe conditions, clawing off a lee shore may be impossible and would require you to allow more sea room. I would say conditions between these two extreams requires proportional sea room and caution be taken to ensure you and your vessle and crew remain safe. What proportion you use is subject to your experience, conditions, boat, etc....
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  #17  
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yeah, you have the right definition. A lee shore is one that's downwind and that you're not happy about. While you're still well away from it , experiment with sail combinations and sail trim, to see if you are moving away from it, or being set towards it in spite of all your efforts. A handheld Gps is perfect for this task, especially if the vis from rain, fog, snow, night, whatever, is preventing you from being able to tell visually. Is the long. or lat, which indicates you're opening up on it, ticking the right way? Good, then keep on keeping on, you're going to be all right as long as the conditions don't worsen. If it's decreasing, then it's a big problem, then try something else, even if it's the engine. And if all your attempts to get enough horsepower (whether from sailcloth or from iron, or combo of both) to claw off are failing, then it's time to rely on a tow off if you can find one, your ground tackle (dropped while you're still far enough off for you to get enough scope and stay seaward of the surf zone) and the holding ground, or prayer, more or less in that order.

I've found that prayer helps all the other stuff work better, but whatever works for you. If absolutely none of these work, then at some point you have to shift your focus from saving the boat to saving yourself (lifejackets, liferaft, Coast Guard, and even more prayer).

May it never come to that. But lee shores, and the ultimate inability to stay off them, are the primary reasons for most of the coastal shipwrecks, whether from sail, steam, or motor, that the scuba divers like to dive.

Last edited by nolatom; 10-13-2007 at 10:13 PM.
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Old 10-13-2007
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How NOT to sail off a leeshore...

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