SF Bay Currents and Other Stuff

Hi, All. Paul, there is a set of current charts for the northern Chesapeake Bay in the Maryland Cruising Guide (chart book). It is not nearly as detailed as Allen’s for SF. Allen, what are the effects of wind driven (or other) variables in SF? On shore breeze and the like. In the Chesapeake we are heavily affected by breezes in changing the current strengths and times. Not to mention that they occasionally open the Conowingo Dam at the top of the Bay (lower Susquehanna River hydroelectric plant) with substantial effects. Item on the Tac-Tick (and other integrated instrument sets). I have found that one must almost totally involve a crew member in looking at the reams of numbers and data put out by these systems. For myself, I find all the numbers distracting to the detriment of my driving and tactical instincts (especially in the shorter around the marks races). On a CAL 25, we usually do not have a spare crew member to devote to the numbers game. (Of course, I do race one design, so the other boats are my reference for performance.) Last time I used a GPS aboard (handheld) was to check the difference between my compass course and my true course when reaching in a heavy cross current in light air (sometime last year). I realize that the data can be useful, but personally, I also see downsides. I come from the “grab you’re a** with both hands and sail the boat” school. As a “high tech” engineering person, I am a Luddite. Cheers Charlie From: Ca… [at] yahoogroups.com [mailto:Ca… [at] yahoogroups.com] On Behalf Of pw… [at] aol.com Sent: Friday, November 25, 2011 7:23 AM To: Ca… [at] yahoogroups.com Subject: Re: [Cal_Boats] SF Bay Currents Allen - Any chance you'll be doing this for the Chesapeake in the near or not so near future? Thanks - Paul In a message dated 11/24/2011 11:56:18 A.M. Eastern Standard Time, al… [at] gmail.com writes: Happy Thanksgiving everyone. I would like to share a program I have written that presents maps of the current in the SF Bay for any day and time. The program matches your desired day with a similar tide day for which I have a map then draws the map. There is an explanation on the site. It is in Beta release and I would welcome feedback. Specifically, I have created a few zones, city front, south beach, Berkeley, and a couple of others. If there are other zones you would like, or other changes or additions to the site please let me know. http://l-36.com/sf_current_new.php Here is the example page http://l-36.com/sf_current_example.php And here is a sample map for noon today (3 hours from now). The timestamp on the map is the matching day and time. [Description: Image removed by sender. city11102714.png] Allen

> > > Allen, what are the effects of wind driven (or other) variables in SF? On > shore breeze and the like. In the Chesapeake we are heavily affected by > breezes in changing the current strengths and times. Not to mention that > they occasionally open the Conowingo Dam at the top of the Bay (lower > Susquehanna River hydroelectric plant) with substantial effects. > The thing we worry about most here is river flow and I asked the question to the guy who is responsible for our bay model simulation. He worked for the USGS and now maintains the computer program in his retirement as there is not funding for it in the government. His response, below, mentioned wind driven water as well. The bottom line is that the bay is so large and there is so much water coming in that wind and river flows are fractions of a percent and not significant. We have a model of the bay in Sausalito. It is huge and was used pre computer simulation and is now a National Park or something similar so you can visit it and should if you are in the area. If you look at the water flow in and out of the bay and observe the currents it becomes clear that there is a large chaotic component that can just not be modeled. Sailing around the other day we saw whirl pools with flood on one side and ebb on the other. The models are good in predicting that there will be ebb on shore and flood out in the bay, but where the transition happens and how quickly is not shown and probably cannot be modeled. I have seen 1 knot differences in current in just a boat length, then see it happen again some distance away. Here was his reply: For a 2D model, river flow is insignificant relative to tidal flow. The tidal volume of the Bay (Mean HHigh vol - Mean LLow vol) is ~2500x10e6 cubic meters while typical winter river flows are about 2000cfs or 1x10e6 m3 in the 6 hr tidal swing. Hence river flow has little effect on tidal currents, except above Carquinez where the water slopes can be changed at peak flows. While this seems to contradict your observation of surface currents at the GG, the net water column currents do change with the tide. We have seen sustained strong winds produce similar observations (no change in the direction of surface currents for a 10-12 hour period). Allen

I just love this kind of talk! Isn't great when they talk dirty? Here was his reply: For a 2D model, river flow is insignificant relative to tidal flow. The tidal volume of the Bay (Mean HHigh vol - Mean LLow vol) is ~2500x10e6 cubic meters while typical winter river flows are about 2000cfs or 1x10e6 m3 in the 6 hr tidal swing. Hence river flow has little effect on tidal currents, except above Carquinez where the water slopes can be changed at peak flows. While this seems to contradict your observation of surface currents at the GG, the net water column currents do change with the tide. We have seen sustained strong winds produce similar observations (no change in the direction of surface currents for a 10-12 hour period). Cheers Charlie From: Ca… [at] yahoogroups.com [mailto:Ca… [at] yahoogroups.com] On Behalf Of Allen Edwards Sent: Saturday, November 26, 2011 11:09 AM To: Ca… [at] yahoogroups.com Subject: Re: [Cal_Boats] SF Bay Currents and Other Stuff Allen, what are the effects of wind driven (or other) variables in SF? On shore breeze and the like. In the Chesapeake we are heavily affected by breezes in changing the current strengths and times. Not to mention that they occasionally open the Conowingo Dam at the top of the Bay (lower Susquehanna River hydroelectric plant) with substantial effects. The thing we worry about most here is river flow and I asked the question to the guy who is responsible for our bay model simulation. He worked for the USGS and now maintains the computer program in his retirement as there is not funding for it in the government. His response, below, mentioned wind driven water as well. The bottom line is that the bay is so large and there is so much water coming in that wind and river flows are fractions of a percent and not significant. We have a model of the bay in Sausalito. It is huge and was used pre computer simulation and is now a National Park or something similar so you can visit it and should if you are in the area. If you look at the water flow in and out of the bay and observe the currents it becomes clear that there is a large chaotic component that can just not be modeled. Sailing around the other day we saw whirl pools with flood on one side and ebb on the other. The models are good in predicting that there will be ebb on shore and flood out in the bay, but where the transition happens and how quickly is not shown and probably cannot be modeled. I have seen 1 knot differences in current in just a boat length, then see it happen again some distance away. Allen _._,___

Here is the clean version. If you have a bathtub amount of water flowing into the bay and you should not worry about 1/3 cup changing the flow. Allen On Sat, Nov 26, 2011 at 10:23 AM, Husar, Charlie [USA] (ASE) < hu… [at] bah.com> wrote: > ** > > > I just love this kind of talk! Isn’t great when they talk dirty?**** > > ** ** > > Here was his reply:**** > > ** ** > > For a 2D model, **** > > river flow is insignificant relative to tidal flow. The**** > > tidal volume of the Bay (Mean HHigh vol - Mean LLow vol) is ~2500x10e6*** > * > > cubic meters while typical winter **** > > river flows are about 2000cfs or 1x10e6**** > > m3 in the 6 hr tidal swing. Hence **** > > river flow has little effect on tidal**** > > currents, except above Carquinez where the water slopes can be changed at* > *** > > peak flows.**** > > ** ** > > While this seems to contradict your observation of surface currents at the > **** > > GG, the net water column currents do change with the tide. We have seen*** > * > > sustained strong winds produce similar observations (no change in the**** > > direction of surface currents for a 10-12 hour period).**** > > ** ** > > Cheers**** > > Charlie**** > > ** ** > > *From:* Ca… [at] yahoogroups.com [mailto:Ca… [at] yahoogroups.com] *On > Behalf Of *Allen Edwards > *Sent:* Saturday, November 26, 2011 11:09 AM > *To:* Ca… [at] yahoogroups.com > *Subject:* Re: [Cal_Boats] SF Bay Currents and Other Stuff**** > > Allen, what are the effects of wind driven (or other) variables in > SF? On shore breeze and the like. In the Chesapeake we are heavily > affected by breezes in changing the current strengths and times. Not to > mention that they occasionally open the Conowingo Dam at the top of the Bay > (lower Susquehanna River hydroelectric plant) with substantial effects.*** > * > > ** ** > > The thing we worry about most here is river flow and I asked the question > to the guy who is responsible for our bay model simulation. He worked for > the USGS and now maintains the computer program in his retirement as there > is not funding for it in the government. His response, below, mentioned > wind driven water as well. The bottom line is that the bay is so large and > there is so much water coming in that wind and river flows are fractions of > a percent and not significant.**** > > ** ** > > We have a model of the bay in Sausalito. It is huge and was used pre > computer simulation and is now a National Park or something similar so you > can visit it and should if you are in the area. If you look at the water > flow in and out of the bay and observe the currents it becomes clear that > there is a large chaotic component that can just not be modeled. Sailing > around the other day we saw whirl pools with flood on one side and ebb on > the other. The models are good in predicting that there will be ebb on > shore and flood out in the bay, but where the transition happens and how > quickly is not shown and probably cannot be modeled. I have seen 1 knot > differences in current in just a boat length, then see it happen again some > distance away. **** > > ** ** > > Allen**** > > ** ** > > _._,___**** > > >

Yeah, but in the northern Chesapeake Bay, the bathtub only has an inch of water in it. Cheers Charlie From: Ca… [at] yahoogroups.com [mailto:Ca… [at] yahoogroups.com] On Behalf Of Allen Edwards Sent: Saturday, November 26, 2011 2:11 PM To: Ca… [at] yahoogroups.com Subject: Re: [Cal_Boats] SF Bay Currents and Other Stuff Here is the clean version. If you have a bathtub amount of water flowing into the bay and you should not worry about 1/3 cup changing the flow. Allen On Sat, Nov 26, 2011 at 10:23 AM, Husar, Charlie [USA] (ASE) <hu… [at] bah.com<mailto:hu… [at] bah.com>> wrote: I just love this kind of talk! Isn't great when they talk dirty? Here was his reply: For a 2D model, river flow is insignificant relative to tidal flow. The tidal volume of the Bay (Mean HHigh vol - Mean LLow vol) is ~2500x10e6 cubic meters while typical winter river flows are about 2000cfs or 1x10e6 m3 in the 6 hr tidal swing. Hence river flow has little effect on tidal currents, except above Carquinez where the water slopes can be changed at peak flows. While this seems to contradict your observation of surface currents at the GG, the net water column currents do change with the tide. We have seen sustained strong winds produce similar observations (no change in the direction of surface currents for a 10-12 hour period). Cheers Charlie From: Ca… [at] yahoogroups.com<mailto:Ca… [at] yahoogroups.com> [mailto:Ca… [at] yahoogroups.com<mailto:Ca… [at] yahoogroups.com>] On Behalf Of Allen Edwards Sent: Saturday, November 26, 2011 11:09 AM To: Ca… [at] yahoogroups.com<mailto:Ca… [at] yahoogroups.com> Subject: Re: [Cal_Boats] SF Bay Currents and Other Stuff Allen, what are the effects of wind driven (or other) variables in SF? On shore breeze and the like. In the Chesapeake we are heavily affected by breezes in changing the current strengths and times. Not to mention that they occasionally open the Conowingo Dam at the top of the Bay (lower Susquehanna River hydroelectric plant) with substantial effects. The thing we worry about most here is river flow and I asked the question to the guy who is responsible for our bay model simulation. He worked for the USGS and now maintains the computer program in his retirement as there is not funding for it in the government. His response, below, mentioned wind driven water as well. The bottom line is that the bay is so large and there is so much water coming in that wind and river flows are fractions of a percent and not significant. We have a model of the bay in Sausalito. It is huge and was used pre computer simulation and is now a National Park or something similar so you can visit it and should if you are in the area. If you look at the water flow in and out of the bay and observe the currents it becomes clear that there is a large chaotic component that can just not be modeled. Sailing around the other day we saw whirl pools with flood on one side and ebb on the other. The models are good in predicting that there will be ebb on shore and flood out in the bay, but where the transition happens and how quickly is not shown and probably cannot be modeled. I have seen 1 knot differences in current in just a boat length, then see it happen again some distance away. Allen _._,___

You got me, Allen. Around here, over a knot is pretty strong, and over 2 knots is rare. Sure would be good to sail/motor a boat that can do over 6 knots at your place. I was once on a boat entering the Solent off Isle of Wight in UK. It was early AM and a sailboat race was going on. Must have started at dawn. I think the idea was if they did not make a certain turning mark before the tide/current changed, they would never get there. Cheers Charlie From: Ca… [at] yahoogroups.com [mailto:Ca… [at] yahoogroups.com] On Behalf Of Allen Edwards Sent: Saturday, November 26, 2011 2:23 PM To: Ca… [at] yahoogroups.com Subject: Re: [Cal_Boats] SF Bay Currents and Other Stuff

Well, the trick around here is to get in the right part of the bay. Around noon today it was flooding in the center of the bay but there was an ebb along the city front MAP <http://goo.gl/N5KcE>. That is why you see boats tacking up the city front in races around here and then going way out in an arch to get into the flood on the return trip. Just cruising, is makes a huge difference if you catch the tide and are going 6 + 2 knots or if you try and go against it and are going 6 - 2 knots. The first time I tried to to out under the GG Bridge I was afraid of the tide so timed it for a flood so I could be sure of getting back in. Problem was I couldn't get out. We tacked and tacked and sailed for a long time and were directly under the bridge the entire time, just going along it. I learned that you need to go out with an ebb as you can sail back against it and although you might be making only 2 knots, at least you are in line with it and can get back. Trying to go at 45 degrees to it going out against a flood, you are only making the current and no headway. I am not sure if the AC boats will care though. As they say, a 2 knot current is a lot more interesting to a swimmer than to a speedboat. The AC boats are pretty fast. In addition, they turn fairly slowly so I am guessing the current won't matter that much. Maybe someone else knows. Allen MAP <http://goo.gl/N5KcE> On Sat, Nov 26, 2011 at 11:52 AM, Husar, Charlie [USA] (ASE) < hu… [at] bah.com> wrote: > ** > > > You got me, Allen. Around here, over a knot is pretty strong, and over > 2 knots is rare. Sure would be good to sail/motor a boat that can do over > 6 knots at your place.**** > > ** ** > > I was once on a boat entering the Solent off Isle of Wight in UK. It was > early AM and a sailboat race was going on. Must have started at dawn. I > think the idea was if they did not make a certain turning mark before the > tide/current changed, they would never get there.**** > > ** ** > > Cheers**** > > Charlie**** > > ** ** > > *From:* Ca… [at] yahoogroups.com [mailto:Ca… [at] yahoogroups.com] *On > Behalf Of *Allen Edwards > *Sent:* Saturday, November 26, 2011 2:23 PM > > *To:* Ca… [at] yahoogroups.com > *Subject:* Re: [Cal_Boats] SF Bay Currents and Other Stuff**** > > ** ** > > > > From today's tide chart for the GG Bridge**** > > 04:34 PM PST**** > > -5.78 kt**** > > Max Ebb**** > > What is it like in the Chesapeake? > > Allen**** > > ** ** > > ** ** > > On Sat, Nov 26, 2011 at 11:16 AM, Husar, Charlie [USA] (ASE) < > hu… [at] bah.com> wrote:**** > > **** > > Yeah, but in the northern Chesapeake Bay, the bathtub only has an inch of > water in it.**** > > **** > > Cheers**** > > Charlie**** > > **** > > *From:* Ca… [at] yahoogroups.com [mailto:Ca… [at] yahoogroups.com] *On > Behalf Of *Allen Edwards > *Sent:* Saturday, November 26, 2011 2:11 PM**** > > > *To:* Ca… [at] yahoogroups.com > *Subject:* Re: [Cal_Boats] SF Bay Currents and Other Stuff**** > > **** > > > > **** > > Here is the clean version.**** > > **** > > If you have a bathtub amount of water flowing into the bay and you should > not worry about 1/3 cup changing the flow. **** > > **** > > Allen**** > > On Sat, Nov 26, 2011 at 10:23 AM, Husar, Charlie [USA] (ASE) < > hu… [at] bah.com> wrote:**** > > **** > > I just love this kind of talk! Isn’t great when they talk dirty?**** > > **** > > Here was his reply:**** > > **** > > For a 2D model, **** > > river flow is insignificant relative to tidal flow. The**** > > tidal volume of the Bay (Mean HHigh vol - Mean LLow vol) is ~2500x10e6*** > * > > cubic meters while typical winter **** > > river flows are about 2000cfs or 1x10e6**** > > m3 in the 6 hr tidal swing. Hence **** > > river flow has little effect on tidal**** > > currents, except above Carquinez where the water slopes can be changed at* > *** > > peak flows.**** > > **** > > While this seems to contradict your observation of surface currents at the > **** > > GG, the net water column currents do change with the tide. We have seen*** > * > > sustained strong winds produce similar observations (no change in the**** > > direction of surface currents for a 10-12 hour period).**** > > **** > > Cheers**** > > Charlie**** > > **** > > *From:* Ca… [at] yahoogroups.com [mailto:Ca… [at] yahoogroups.com] *On > Behalf Of *Allen Edwards > *Sent:* Saturday, November 26, 2011 11:09 AM > *To:* Ca… [at] yahoogroups.com > *Subject:* Re: [Cal_Boats] SF Bay Currents and Other Stuff**** > > Allen, what are the effects of wind driven (or other) variables in > SF? On shore breeze and the like. In the Chesapeake we are heavily > affected by breezes in changing the current strengths and times. Not to > mention that they occasionally open the Conowingo Dam at the top of the Bay > (lower Susquehanna River hydroelectric plant) with substantial effects.*** > * > > **** > > The thing we worry about most here is river flow and I asked the question > to the guy who is responsible for our bay model simulation. He worked for > the USGS and now maintains the computer program in his retirement as there > is not funding for it in the government. His response, below, mentioned > wind driven water as well. The bottom line is that the bay is so large and > there is so much water coming in that wind and river flows are fractions of > a percent and not significant.**** > > **** > > We have a model of the bay in Sausalito. It is huge and was used pre > computer simulation and is now a National Park or something similar so you > can visit it and should if you are in the area. If you look at the water > flow in and out of the bay and observe the currents it becomes clear that > there is a large chaotic component that can just not be modeled. Sailing > around the other day we saw whirl pools with flood on one side and ebb on > the other. The models are good in predicting that there will be ebb on > shore and flood out in the bay, but where the transition happens and how > quickly is not shown and probably cannot be modeled. I have seen 1 knot > differences in current in just a boat length, then see it happen again some > distance away. **** > > **** > > Allen**** > > **** > > _._,___**** > > **** > > > > **** > > ** ** > > > > > **** > > **** > > >