Tides and Currents Rough Agenda: Day 2 (Mike): Start tides and currents presentation as usual and stop after tides to have students breakout to fill out tables, then stop, regroup and review. Then ask students when tide timing works out best for travel. Next, go on to current theory then stop for a breakout to have students compute tables. Possible breakout question: how fast water is moving at slack? Then go back to lecture to review then ask what’s best time for travel. Then leave them with Hope/Skagit Islands homework (optimal trip and non-optimal versions).

General flow of water into Puget Sound and the Salish Sea FLOOD

General flow of water out of Puget Sound and the Salish Sea EBB

Tides

Tides Tides are the VERTICAL movement of water caused by the gravitational influences of other celestial bodies and the centrifugal forces as the earth rotates. Tides measure the HEIGHT of the water at a specific TIME. Several places to look up tide predictions: NOAA https://tidesandcurrents.noaa.gov/tide_pre dictions.html Paper tables Websites Apps

Primary Tide Stations Port Townsend Seattle These two stations are the primary tide measuring stations in the Puget Sound. All other tides in the region are calculated as offsets to the primary stations. 4/4/19 – with the 2015-17 studies by NOAA, there are many more than 2 tide stations. They are now designated as harmonic or subordinate stations. Port Townsend Seattle

Secondary Tide Stations There are LOTS of them! These stations are the locations where calculations have been established to allow tide predictions for an area closer to where you are boating. Predictions for these stations are calculated as offsets from the primary stations. Offsets are both HEIGHT and TIME.

Tide station list for Rosario Strait from the NOAA Tidal prediction website

Reading Tide Tables Tide tables are samples of the tide curves at the most important points. Specifically, the tide tables provide height and time information for the two primary tide stations, either Port Townsend or Seattle. What if you’re not at one of those two stations??? Point out that the table entries correspond to the HIGH and LOW points on the plot from NOAA. Talk about WHY we read the tables. NOTE: for explanations and footnotes, refer to pages 2 and 11 of the Tidebook Company Tides & Currents Puget Sound

Tide Table Offsets Each secondary station has a time and height offset that can be applied to the corresponding primary station to determine the predicted tide at that location. You can find the offsets in the front of the book under “TIDAL DIFFERENCES.” To use the offset: Add or Subtract the time offset (in minutes) as indicated. Multiply the height as indicated. Note that time/height offsets are provided for both high and low water. Show what the offsets look like and how to interpret them. Note: Sometimes the offset has NO multiply (*) sign – this implies an offset *NOT* a scale.

Reading Tide Tables Example: Point Vashon on April 13, 2019 Primary Station Time Secondary Station Time Offset Secondary Station Time Primary Station Height Secondary Station Height Offset Secondary Station Height High Low Reading Tide Tables Example: Point Vashon on April 13, 2019 Find your nearest secondary station. Determine the primary station. For the desired date, read the entries in the tide table for the primary station. Lookup the offset (time and height) for the secondary station. Compute the adjusted time and height for the secondary station. Do an example, showing primary and secondary pages. Then fill in the table below.

Reading Tide Tables Example: Point Vashon on April 13, 2019 Primary Station Time Secondary Station Time Offset Secondary Station Time Primary Station Height Secondary Station Height Offset Secondary Station Height High Low Reading Tide Tables Example: Point Vashon on April 13, 2019 Find your nearest secondary station. Point Vashon Determine the primary station. Seattle For the desired date, read the entries in the tide table for the primary station. Lookup the offset (time and height) for the secondary station. Compute the adjusted time and height for the secondary station. This is a little contrived; we gave them the SECONDARY station “Point Vashon”. Explain how “Seattle” is chosen as the PRIMARY station.

Reading Tide Tables Example: Point Vashon on April 13, 2019 Primary Station Time Secondary Station Time Offset Secondary Station Time Primary Station Height Secondary Station Height Offset Secondary Station Height High 00:55 10.5 Low 06:45 7.2 11:16 8.9 18:20 0.00 Reading Tide Tables Example: Point Vashon on April 13, 2019 Find your nearest secondary station. Point Vashon Determine the primary station. Seattle For the desired date, read the entries in the tide table for the primary station. Lookup the offset (time and height) for the secondary station. Compute the adjusted time and height for the secondary station. Do an example, showing primary and secondary pages. Then fill in the table below.

Reading Tide Tables Example: Point Vashon on April 13, 2019 Primary Station Time Secondary Station Time Offset Primary Station Height Secondary Station Height Secondary Station Height High 00:55 +0.02 10.5 *1.02 Low 06:45 7.2 *1.01 11:16 8.9 18:20 0.0 Example: Point Vashon on April 13, 2019 Find your nearest secondary station. Point Vashon Determine the primary station. Seattle For the desired date, read the entries in the tide table for the primary station. Lookup the offset (time and height) for the secondary station. Compute the adjusted time and height for the secondary station. Do an example, showing primary and secondary pages. Then fill in the table below.

Reading Tide Tables Example: Point Vashon on April 13, 2019 Primary Station Time Secondary Station Time Offset Secondary Station Time Primary Station Height Secondary Station Height Offset Secondary Station Height High 00:55 +0:02 00:57 10.5 *1.02 10.7 Low 06:45 06:47 7.2 *1.01 7.3 11:16 11:18 8.9 9.1 18:20 18:22 0.00 Example: Point Vashon on April 13, 2019 Find your nearest secondary station. Point Vashon Determine the primary station. Seattle For the desired date, read the entries in the tide table for the primary station. Lookup the offset (time and height) for the secondary station. Compute the adjusted time and height for the secondary station. Do an example, showing primary and secondary pages. Then fill in the table below.

Tides Exercise Compute the TIDES on July 6, 2019, at Snee-oosh Point. What times are the low-tides? What are the heights of the low-tides? What times are the high-tides? What are the heights of the high-tides? Group exercise starts here. Snoo-oosh – from the Lushootseed language; meaning “look the other way.”

Tides Calculation Worksheet Date: Trip Name: Primary Tide Station Name: Secondary Tide Station Name: Tides Primary Station Time Secondary Station Adjustment Secondary Station Time Primary Station Height Secondary Station Height Low High

Tides Exercise ANSWERS Primary Station Time SecondaryStation Time Offset Secondary Station Time Primary Station Height Secondary Station Height Offset Secondary Station Height Low 02:35 +0:39 03:04 6.2 *0.90 5.6 High 07:27 +0:32 07:59 10.0 *0.97 9.7 14:19 14:58 -2.2 -2.0 21:37 22:09 12.4 12.0 Tides Exercise ANSWERS Compute the TIDES on July 6, 2019, at Snee-oosh Point. What times are the low-tides? What are the heights of the low-tides? What times are the high-tides? What are the heights of the high-tides? SECONDARY STATION: Sneeoosh Point PRIMARY STATION: Seattle Review table, answer questions. Again, point out our computed table matches the NOAA model.

Currents

Currents Currents are HORIZONTAL movement of water occurring in conjunction with the rise and fall of the tide. Currents measure the SPEED of the water at a specific TIME in a specific direction (ebb or flood). Several places to look up current predictions: NOAA https://tidesandcurrents.noaa.gov/noaacurr ents/Regions Websites Apps Paper tables

Primary Current Stations These stations are the primary measuring stations in the Puget Sound. There are 5 of them. All other currents in the Puget Sound are relative to one of these 5 primary stations. 4/4/19 - with the 2015-17 studies by NOAA, there are many more than five primary current stations. In fact, there are now more than 130 harmonic stations and very few, if any, secondary stations. San Juan Channel Rosario Strait Deception Pass Admiralty Inlet The Narrows

Secondary Current Stations There are LOTS of them. Secondary predictions are calculated as offsets to the five primary stations. Offsets are both SPEED and TIME. Direction is indicated as ebb or flood. Note: As of 4/4/19 the Navigation committee has discovered that NOAA conducted current studies during 2015-17 which have updated the secondary stations and now they are considered “harmonic” and stations in their own rights, not calculated based off of primary stations. It is our opinion that it may take a little while for third party apps and books to catch up to this new structure. We also advise double checking any current predictions calculations against the official NOAA current predictions.

Current Tables For a given date, current tables tell you the SPEED and DIRECTION of the water, at a specific TIME, for a specific primary current station location: San Juan Channel Admiralty Inlet The Narrows Deception Pass Rosario Strait What if you’re not at one of those primary stations? Show how the tables match the graph from NOAA.

Current Table Offsets The secondary station offsets for the primary current stations are shown at the front of the book under “CURRENT DIFFERENCES & OTHER CONSTANTS.” Each secondary station has time and speed offsets. To find the predicted current at a secondary location, apply the secondary offsets to their primary current station data for that date. Show the offsets and how to read them. For currents, there are more offsets.

Reading Current Tables Example: Saddlebag Island on August 8th 2019 Find the most applicable secondary station. Determine the primary station, not always the closest. Based on the date / time, read the entries in the current table for the primary station. Lookup the offsets for the secondary station. Compute the adjusted time and speed for the secondary station. Show how to fill out the tables.

Reading Current Tables Example: Saddlebag Island August 8, 2019 Find the most applicable secondary station. Guemes Channel, west entrance Determine the primary station, not always the closest. Rosario Strait Based on the date / time, read the entries in the current table for the primary station. Lookup the offsets for the secondary station. Compute the adjusted time and speed for the secondary station. Rosario Strait Show how to fill out the tables.

Reading Current Tables Primary Station Time Secondary Station Time Offset Secondary Station Time Primary Current (Knots) Secondary Station Current Offset Secondary Station Current Slack 00:00 Ebb 04:24 3.2E 08:30 Flood 10:24 1.2F 14:12 17:00 0.9E 19:48 Reading Current Tables Example: Saddlebag Island on August 8th 2019 Find the most applicable secondary station. Guemes Channel Determine the primary station, not always the closest. Rosario Strait For the desired date, read the entries in the current table for the primary station. Lookup the offsets for the secondary station. Compute the adjusted time and speed for the secondary station. Show how to fill out the tables.

Reading Current Tables Primary Station Time Secondary Station Time Offset Secondary Station Time Primary Current (Knots) Secondary Station Current Offset Secondary Station Current Slack 00:00 -1:24 Ebb 04:24 -0:36 3.2E *1.1 08:30 -0:21 Flood 10:24 -0:33 1.2F *0.8 14:12 17:00 0.9E 19:48 Reading Current Tables Example: Saddlebag Island on August 8th 2019 Find the most applicable secondary station. S Blake Island Determine the primary station, not always the closest. Admiralty Inlet For the desired date, read the entries in the current table for the primary station. Lookup the offsets for the secondary station. Compute the adjusted time and speed for the secondary station. Show how to fill out the tables.

Reading Current Tables Primary Station Time Secondary Station Time Offset Secondary Station Time Primary Current (Knots) Secondary Station Current Offset Secondary Station Current Slack 00:00 -1:24 22:36 Ebb 04:24 -0:36 03:48 3.2E *1.1 3.5E 08:30 -0:21 08:09 Flood 10:24 -0:33 09:51 1.2F *0.8 1.0F 14:12 12:48 17:00 16:24 0.9E 1.0E 19:48 19:27 Example: Saddlebag Island on August 8th 2019 Find the most applicable secondary station. S Blake Island Determine the primary station, not always the closest. Admiralty Inlet For the desired date, read the entries in the current table for the primary station. Lookup the offsets for the secondary station. Compute the adjusted time and speed for the secondary station. Show how to fill out the tables. NOTE: for explanations and footnotes, refer to pages 2 and 11 of the Tidebook Company Tides & Currents Puget Sound

Currents Exercise { MAP OF CORNET BAY } Compute the CURRENTS for July 6, 2019, for Skagit Bay, channel SW of Hope Island. What is the fastest current you will encounter? What time is the fastest current you will encounter? Is the fastest current on the Ebb or Flood?

Currents Calculation Worksheet Date: Trip Name: Primary Current Station Name: Secondary Current Station Name: Currents Primary Station Time Secondary Station Time Adjustment Secondary Station Time Primary Current (In Knots) Secondary Current Adjustment Secondary Station Current Slack Ebb Flood

Currents Exercise HINTS Compute the CURRENTS for July 6, 2019, southwest of Hope Island in Skagit Bay. Secondary: Skagit Bay, channel SW of Hope Island Primary: Deception Pass What is the fastest current you will encounter? What time is the fastest current you will encounter? Is the fastest current on the Ebb or Flood?

Currents Exercise HINTS Primary Station Time Secondary Station Time Offset Secondary Station Time Primary Current (Knots) Secondary Station Current Offset Secondary Station Current Slack 01:24 -0:20 Flood 03:54 -0:40 4.8F *0.4 06:24 -0:08 Ebb 09:42 -0:15 7.3E *0.3 12:42 16:18 6.8F 19:48 Compute the CURRENTS for July 6, 2019, southwest of Hope Island in Skagit Bay. Secondary: Skagit Bay, channel SW of Hope Island Primary: Deception Pass What is the fastest current you will encounter? What time is the fastest current you will encounter? Is the fastest current on the Ebb or Flood?

Currents Exercise ANSWERS Primary Station Time Secondary Station Time Offset Secondary Station Time Primary Current (Knots) Secondary Station Current Offset Secondary Station Current Slack 01:24 -0:20 01:04 Flood 03:54 -0:40 -03:14 4.8F *0.4 1.9F 06:24 -0:08 06:16 Ebb 09:42 -0:15 09:27 7.3E *0.3 2.2E 12:42 12:22 16:18 15:38 6.8F 2.7F 19:48 19:40 Compute the CURRENTS for July 6, 2019, southwest of Hope Island Secondary: Skagit Bay, channel SW of Hope Island Primary: Deception Pass What is the fastest current you will encounter? 2.7F Knots What time is the fastest current you will encounter? 15:38 Is the fastest current on the Ebb or Flood? Flood

Currents Exercise ANSWERS Primary Station Time Secondary Station Time Offset Secondary Station Time Primary Current (Knots) Secondary Station Current Offset Secondary Station Current Current Direction Slack 01:24 -0:20 01:04 Flood 03:54 -0:40 -03:14 4.8F *0.4 1.9F 06:24 -0:08 06:16 Ebb 09:42 -0:15 09:27 7.3E *0.3 2.2E 12:42 12:22 16:18 15:38 6.8F 2.7F 19:48 19:40 Currents Exercise ANSWERS Compute the CURRENTS for July 6, 2019, southwest of Hope Island Secondary: Skagit Bay, channel SW of Hope Island Primary: Deception Pass What is the fastest current you will encounter? 2.7F Knots What time is the fastest current you will encounter? 15:38 Is the fastest current on the Ebb or Flood? Flood 4. But is it correct?

Currents Exercise ANSWERS Primary Station Time Secondary Station Time Offset Secondary Station Time Primary Current (Knots) Secondary Station Current Offset Secondary Station Current Current Direction Slack 01:24 -0:20 01:04 Flood 03:54 -0:40 -03:14 4.8F *0.4 1.9F 06:24 -0:08 06:16 Ebb 09:42 -0:15 09:27 7.3E *0.3 2.2E 12:42 12:22 16:18 15:38 6.8F 2.7F 19:48 19:40 Currents Exercise ANSWERS Compute the CURRENTS for July 6, 2019, southwest of Hope Island Secondary: Skagit Bay, channel SW of Hope Island Primary: Deception Pass What is the fastest current you will encounter? 2.7F Knots What time is the fastest current you will encounter? 15:38 Is the fastest current on the Ebb or Flood? Flood 4. But is it correct? Not any more, NOAA has made this a stand alone harmonic station that cannot be predicted off of a primary station. Consider the NOAA determined directions for currents at SW of Hope Island: Flood: 345° Ebb: 170°

Skagit Bay channel, SW of Hope Island (PUG1628) Depth: 10 feet Flood: 345° Ebb: 170° So according to the new NOAA determination, the flood for SW Hope Island flows close to north (the direction of Yokeko Point and Deception Pass). When you turn the corner at Yokeko Point the current there is defined as an ebb. So when we leave Hope Island to begin our way back to Cornet Bay, we want a flood, and then we will paddle into an ebb at Yokeko Point and the rest of the way back to Cornet Bay.

Trip Planning

Putting it all together Consider current speed and direction as well as tide levels in planning Identify trip start, waypoints, stops, and final destination. Identify harmonic tide station(s) and harmonic current station(s) involved. Based on the harmonic stations, identify whether the current is a flood or ebb for the direction that you need to travel. Verify that current directions are consistent with the direction you want to travel. Seek dates and times when currents and tides are favorable to the places and directions you intend to paddle.

Takeaway Points NOAA has done a 3 year study from 2015-17 for the purpose of updating tidal current predictions in Puget Sound, Admiralty Inlet, the Strait of Juan de Fuca and around the San Juan Islands Updated approximately 130 stations Many of the stations were at the same location as before, and retained the same name or were given a slight name change. Other stations moved, some of which caused a name change when a closer geographical feature or charted name made more sense to use. In some rare cases, subordinate stations that weren't re-occupied and had a quality of data that NOAA could no longer stand behind were simply removed. Each station stands on its own measurements and no longer relies on subordinate stations and corrections Flood and Ebb designations are now based on what the water level is doing at specific locations, not dependent on the primary station