Adventures on the Blue

I'll let the video do the talking. :D

Sunday, April 27, 2008 Leave a Comment 0 comments

This is for all those people out there who don't know which way to read a tide and current book. I've been working on a nice little worksheet to remind myself about what the tides and currents will look like day to day. These worksheets use data from the Canadian Tide and Current tables and allow you to pencil the information into boxes. I know there are some online utilities and atlases to get the same info, but I find I commit things to memory better by writing and calculating, and in the end I'll get a doc that I can take on the 'yak for reference. After a while these sheets will just become Dumbo's magic feather, and you can know all the reference ports in your usual paddling areas off heart. The point of these sheet is to have all the adjusted data for quick review and learn a little about the area while you're at it.

download the worksheet  Download the Worksheet Here »

The formula is pretty much adopted right from the instructions in the guide. I suggest filling them in with waterproof and smudgeproof pencils or a pen with truly waterproof ink if you intend to bring the sheet on your trips. Normal ballpoints will bleed when the paper is accidentally exposed to water. Also print them on a laser printer instead of an inkjet.

Without further ado, here's the instructions on using the worksheet.

The first section is tide heights. Before you can predict any of this stuff, you need to know where you're paddling. For example, I want to paddle in a part of Victoria BC called Oak Bay. So the first thing I want to do is flip to the Reference Ports near the back of the book and have a look at the area. In Secondary Reference Ports, I see Oak Bay, and it's primary Port is Victoria.

The Reference port is Victoria, so just go ahead and copy the information for the day you'd like to paddle into the top set of times and heights using Victoria's data from the front of the book, you'll adjust it in the next steps. Flip back to that secondary information about oak bay. You'll see position coordinates and a set of adjustments that match up to the worksheet. Fill in this info. At the end of the row, you'll see an indication of what is considered a "large tide" for the area. If any of your tide predictions exceed that number, you will use it in calculating one full tide cycle.

You're ready to fill in the adjusted data area. If you noted a large tide, check the boxes for the affected tide cycle. Otherwise, fill in the adjusted time if the book says 0326 and the time difference is +058 you add 58 minutes to that number to get your watch time. The book is published in PST in my part of the world, so in the spring I spring forward an hour. The total time difference would end up being 1 hour 58 minutes. This rule goes for calculation of currents later on.

Calculating tide height is just simple addition or subtraction. If this cycle is a Large tide, use the large tide numbers, otherwise, use the mean tide number to modify your high and low values. You will now have a time you can reference with your watch
and an easy to read high and low tide level.

The next section is Currents. You know where you want to paddle, so head back to the reference and secondary current stations section. The nearest feature to oak bay in my case will be a narrow channel called Baynes channel. You can find a nearby current station quickly on a chart if you are unsure of the location of current measurement stations. As with tides, you will often use predictions at a secondary current point. Baynes Channel's reference is Race passage, so I'd copy the reference data from Race passage into my sheet.

Read the information on the secondary or primary station and you will see differences in turns and maximum flow values. The turns are generally considered slack water, that is no appreciable current is predicted at these times. The maximum flows are the fastest speed the current will reach at the station. There's also a flood direction so you can expect an angle that you will drift if you are not paddling parallel to the current. a nice reference to have is a magnetic bearing so you wan use your on board compass to stay on course. Use the position area in the Tides section on the NOAA declination calculator to find how you can compensate for magnetic north.

As with the tides, use the turn and flow differences to calculate the watch time for turns, and max flow. Adjust the rates according to the percentages for flood and ebb flow. A negative number indicates an ebb; a positive number indicated a flood. Indicate the adjusted flood direction in the box on the left and you'll have a completed worksheet with all the info you need for the day's paddle. Always remember to compare what you see and experience on the water with the predictions. I found this was a great way to build confidence in going with nature and not head on into its fury :). Have fun and I hope these help to be safer on the water.

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