Oak Bluffs, MV June 21, 2012 (Part 1)

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Mark
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Oak Bluffs, MV June 21, 2012 (Part 1)

Post by Mark »

This trip report has no photos, but for everyone who took Johnnysmoke’s nav class last week (and anyone else who wants to chime in), this trip report has some navigation problems thrown in just for fun. Post your answers to the nav puzzlers and let’s see what everyone comes up with.

Dave Briggs (Briggsy) and I are planning to provide kayak escort for two long-distance swimmers who plan to swim from Falmouth to Oak Bluffs, Martha’s Vineyard next month. Since Dave had not paddled over to the Vineyard before, we decided to do a “test run” last Thursday on the HOTTEST DAY OF THE YEAR. We planned a route that would take advantage of the fast currents in Vineyard Sound both coming and going, with lots of time to kick around in Oak Bluffs in between.

When I got to the Trunk River parking lot around 9AM, I was sure I would be dying of heat stroke before day’s end. It was very hot, humid already at 9 o’clock, with no breeze, but the Sound was as calm as a mill pond and East Chop on Martha’s Vineyard was visible clear as a bell six miles away (no fog.)

NAV PUZZLER 1: If it had been foggy, and we had been stupid enough to go out in it, what would our HEADING have needed to be in order to cross directly to East Chop, given:
• The BEARING from Trunk River to East Chop is 153 degrees,
• Our paddling speed was three knots,
• The direct distance from Trunk River to East Chop is six (statute) miles.
• For simplicity’s sake, the current speed and direction was a steady 2 knots at 63 degrees.


Dave showed up, not with his Cetus, but with his surf boat – a 15.5 foot Delphin. I thought, “This is great! I might be able to keep up with him now.” (My NDK Explorer is over two feet longer than the Delphin, and should therefore be a faster boat, all else equal.) I had been wondering how I would handicap Dave on this paddle (bad seafood? an anchor secretly tied to his stern?), but he took care of it for me!

I took a dip in the Sound to cool off before getting in the boat and we took off around 9:40. It was pleasantly cooler on Vineyard Sound once we got offshore and there was even a gentle breeze. I have seldom seen such flat conditions on the Sound, and boat traffic was light. We zipped across on the 2 knot flood current, which was about at maximum (as planned). Some shoals with only 20-25 feet of water created a little “bump” as fast moving water from deeper down hit the shoals and boiled to the surface, creating small standing waves and “footprints” like you see when a whale sounds.

As we approached East Chop light, I asked Dave how good he was at estimating distances. I was working on a little nav problem in my head, trying to figure out if we were likely to get to East Chop on our then current heading or if we needed to change direction a bit to make sure we weren’t swept past it. I didn’t know how far away East Chop was, but I was guessing a mile.

“Hey, Dave do you know any easy mnemonics for estimating distances based on what you see? I need to learn some. Like, when you can see the windows in a house, you are within a mile of the house, or something like that.”

NAV PUZZLER 2: You are out in the open water off Martha’s Vineyard. You do not have GPS so you don’t know your exact location. You have a chart and compass and you can see a West Chop Light to your right and East Chop light in front of you. How do you figure out your distance to East Chop light?

Turns out we were pretty much right on target and arrived at Oak Bluffs without incident. “Well, that was too easy,” I said to Dave.

One of the things we wanted to check out was the ferry routes in and out of Oak Bluffs, since we would be escorting slow moving swimmers through these waters next month and avoiding the ferries is a big priority. Usually you can figure where the shipping lanes are by the location of the navigation buoys. “Right Red Returning” and all that. But things are kind of confusing out there in Vineyard Sound. Which way is “returning”? To the harbor on the Vineyard or to the mainland? Some of the buoys were red on the bottom and green on top. Some were green on the bottom and red on top. WTF?

NAV PUZZLER 3: You are crossing Vineyard Sound from Oak Bluffs to Falmouth in a boat and encounter a day-marker that is red on the top and green on the bottom. On which side of this day-marker should you pass?


End of Part 1

Our (approximate) route: http://www.gmap-pedometer.com/?r=5536397
cgr
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Re: Oak Bluffs, MV June 21, 2012 (Part 1)

Post by cgr »

Math is hard!
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kayakerjnj
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Re: Oak Bluffs, MV June 21, 2012 (Part 1)

Post by kayakerjnj »

Paddling a bunch of extra miles after a long day is even harder :lol:
Paddle with a big smile, its contagious 8)


Jordan
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Mark
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Re: Oak Bluffs, MV June 21, 2012 (Part 1)

Post by Mark »

kayakerjnj wrote:Paddling a bunch of extra miles after a long day is even harder :lol:


Amen!
noseykate
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Re: Oak Bluffs, MV June 21, 2012 (Part 1)

Post by noseykate »

Okay, I'll take a crack at this.

Nav Puzzle 1: Being hopeless at math, I would just overcompensate for the current by following a heading of about 180 degrees (due south) and hoping I didn't end up in the Bahamas.

Nav Puzzle 2: Triangulate. What's the compass reading of each light? Where do those lines intersect on the chart? From that point, how far to the destination?

Nav Puzzle 3: I had to look this one up. You should too!

When do we get to read part 2?

NK
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Mark
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Re: Oak Bluffs, MV June 21, 2012 (Part 1)

Post by Mark »

Nav Puzzler 1: The conventional rule of thumb is called the "Small Triangle Rule" and the math is very simple:

Ferry Angle (degrees) = Current Speed / Paddling Speed x 60

So in a 2 knot current, with a paddling speed of 3 knots, your ferry angle would be 2/3 x 60 = 40 degrees.

Add 40 degrees to the direct course bearing of 153 degrees and your heading should be set at 193 degrees.
Briggsy
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Re: Oak Bluffs, MV June 21, 2012 (Part 1)

Post by Briggsy »

OK, no-one answered so I worked it out and now find you put the answers up !!
Anyhow I worked it out with the vector drawing thing and found the 90 deg current thing after, while looking up some easy way to tell distance off shore.
001.jpg
001.jpg (27.3 KiB) Viewed 13607 times

#2, same thing ....triangulate.
#3 Either side
Briggsy
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Mark
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Re: Oak Bluffs, MV June 21, 2012 (Part 1)

Post by Mark »

#3 Either side

Well, OK, maybe the question wasn't specific enough.

What we are talking about in #3 is "preferred channel markers" that are used where the main channel splits into more than one channel. Your decision about going left or right of the red-over-green marker depends on which channel you are taking.

See if this diagram helps:

Image
Briggsy
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Re: Oak Bluffs, MV June 21, 2012 (Part 1)

Post by Briggsy »

Checked that out on the Nantucket /Vineyard Sound chart.....found plenty of the red/green buoys at the ends of the shoals.
Where did you get that diagram ?
Dave
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Mark
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Re: Oak Bluffs, MV June 21, 2012 (Part 1)

Post by Mark »

It is on this page: http://ohiodnr.com/Laws/OhioBoatOperatorsGuide/OpsGuidenavigationaids/tabid/2747/Default.aspx

I noticed that too - that they seem to be markers for the ends of the shoals. So I dug deeper:

Chart No.1 calls these "Bifurcation, Junction, Isolated danger, Wreck and Obstruction buoys".

If they are numbered, they are junction buoys, or preferred channel markers, as described above.

If they are unnumbered (like the ones on the ends of the shoals in Vineyard Sound) they are Isolated danger, Wreck and Obstruction buoys.

I knew I would learn something by this exercise!

Thanks, Dave.
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