San Francisco Tidal Streams
San Francisco High Resolution Tidal Streams
We are very pleased and proud that our San Francisco tidal model will be used in the forthcoming America's Cup in San Francisco Bay
San Francisco Model detail - Grib files as viewed in Expedition Software
Results for boats that used this model after its launch in 2010:
Melges World's
1st B-Lin
Big Boat Series
1st IRC Div A Vincitore
1st J105 Arbitrage
1st IRC Div C Wasabi
Melges - Big Boat Series
1st B-Lin
2nd Bliksem
3rd Red
Quotes
Dee Smith: 'After racing on the bay for more than 40 years I know the currents well. This is the best model, by far, that I have seen and it shows what really happens. Any boat, any size can benefit with this information a lot.'
Norman Davant - Vincitore: 'In a word “spectacular”. Extremely accurate, this is the first tide program that I have seen that actually works! The tide info for Big Boat Series was spot on. It really helped everyone on the boat understand what was going on, on top of that we won!'
Bruce Stone - Arbitrage: 'We loved the graphics and the granularity of the information, and found it useful in our route planning every day. It proved especially relevant and critical on the last race when we needed to finish in the top ten to secure the victory. Everyone was tacking on us, and we got pushed back into the bottom half of the fleet soon after the start. Using the tide information we ignored a lift being exploited by the leaders as the tide charts showed that taking them into late flood toward Angel Island; instead, we footed over to a ribbon of favorable ebb around Alcatraz – a classic wind vs. tide arbitrage, hence the name of our boat. Going against the grain enabled us to dig back into the top ten. From there on out we passed another five boats to finish fifth and sew up the victory.'
Q: Who built the model and what is their background?
A: Tidetech's Dr Roger Flather, one of the world's pre-eminent tidal scientists. Amongst his many achievements he was responsible for the UK Governments storm surge model, which informs decisions on whether to raise or lower the Thames Barrier in London. He spent his entire career the Proudman Oceanographic Laboratory in the UK and developed some of the key processes now used by ocean modellers worldwide. Roger F was supported by Dr Roger Proctor (also ex Proudman) who has been the oceanographer for the UK Olympic sailing team for 5 Olympics.
Q: How accurate is the model?
A: The phase (timing) and amplitude (height) of the tidal signal is within 5mins and approx 10cm of NOAA predictions in places where there is tide guage data. To increase accuracy further, we will need to include the effects of atmospheric forcing and freshwater inputs from river flow. Further development would include calibration with observations from specialist instrumention systems that can measure current.
Q: Why are there patches of faster current over shoals? - I thought that the current slowed down in shallower water.
A: It does! - but generally this is only nearshore, where amongst other things, seabed shelving causes increased friction. The acceleration of current over isolated shoal patches is caused by the Bernoulli principle, where a flow is forced to travel faster over obstacles in its' path. Water is incompressible, so the effect is very noticeable)
Q: What is the tidal profile or signature for San Francisco Bay?
A: The tides are mixed, semidiurnal dominant, with a clear fortnightly beat. This means there is a noticeable
spring-neap cycle with 2 tides per day but with one tide stronger than the other (a diurnal inequality).
Q: Do you include river flow into the model?
A: Not yet. Tests have been carried out with river flow inputs. Only with an 'extreme' event - a Sacramento river flow of 10,000 m3/s - is there any noticeable impact on the tidal flow in the model, and this is confined within the river section in the northern part of the Bay (i.e. holding up the flood tide, enhancing the ebb tide). There is more work to be done on this and on meteorological forcing (addition of wind driven surface currents and atmospheric pressure data).
Model validation against NOAA predictions
NOAA predictions in Blue, Tidetech model in Red
Golden Gate and Rincon Point 
Alameda and Hunters Point
Redwood City and Dumbarton Point
