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Discussion Starter · #1 ·
Hi,

I've been sailing up and down the East River for years and I've always used Eldridge to check the window of opportunity with the tides in each direction. You can also get the rules of thumb from Eldridge or offshoreblue.com. Both require that you look up some reference datam and add some time or remove some time. Neither one really accounts for boat speed and yet the guidelines work.

I started to create a table, later to be an online resource, that just lists the tide windows for every day of the year Northbound and Southbound. No cross-references, no modulo math to add add hours and minutes. So for example, using Eldridge or offshoreblue, on Saturday, April 10th 2021, there are 2 times when the tides are favorable for a fair passage north - 3:50 am to 6:35 am or 4:07 pm to 6:52 pm. Go under the Brooklyn Bridge between those times and you'll have a fast, current assisted trip. Now wouldn't you love to just look that up rather than buy Eldridge or download the high and low water data at the Battery and do some calculations?

If you've read online about traveling the East River, lots of people talk about timing the trip around slack water at Hell Gate. There are apocryphal stories that imply that it's because the whirlpools at Hell Gate are minimum then. (BTW, lots of scary stories, but if you're in reasonable length sailboat that can do 3 kts, I think their highly exaggerated.) I suspect the real reason is that, with the tide turning at Hell Gate, you get to ride the tide one way up to Hell Gate and then ride it the other way away from Hell Gate. It's similar to riding the tide out the Race and landing off Newport just as the tide turns so that you can ride it up Vineyard Sound without having that strong current against you.

Anyway, the more I thought about it, tghe more I wanted to actually calculate the transit times each way on the East River. I've downloaded the current data from NOAA at the 15 current stations between the Throgs Neck Bridge and the Brooklyn Bridge. NOAA also gives the precise LAT/LON of each station. So with the water velocity and times we should be able to calculate transit times at various boat speeds. Yes???

I'm looking to see if there are any other nerds out there who what to help me crowd source the calculations so that we can create a really nice lookup table for mariners. If a few of you reply, I'll lay out how I calculate the transit time in a subsequent post and we can all check each others math.

Sound like fun? Looking forward to hearing from you!

JJ
 

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Sounds like a good idea for a web site... Maybe it should include your vessel's motoring speed.
 

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JJ, Welcome to the sandbox! That sounds like a little too much work to me, for a 15 mile trip up the River.

Whenever I go up or down the river, there are usually other considerations besides just that 15 mile stretch in say a 70 mile trip. . i.e. when Can I leave where I am. ( sometimes there are constraints) when do I want or need to arrive where I'm going. Do I want to also carry a fair current east in the LIS, or a Fair current down and out through the narrows. So, sometimes it works to hit the full flood, or ebb depending on direction, other times, it's the tail end etc.

Those calculations are pretty easy imo. Once I know what the circumstances are of the entire trip.

But, I'd be interested to see what you come up with.
 

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I just transited Vineyard Sound yesterday. Wind on the nose and waves on the nose. They always knock down boat speed measurably, even when motoring. These impacts vary greatly by boat and are dependent on weight, hull shape, windage above the water, etc. There are several navigation apps that will calculate a timed course, based solely on speed and distance traveled (Navionics for example). I find, by playing with speeds +/- my anticipated average SOG, I can manage current windows well enough.

There can be more to it, as well. More than once, I’ve had the current nicely timed behind me traveling westbound in the Cape Cod Canal. Then exit into Buzzards Bay which had a stiff SW wind and found 4-5 ft steep waves stacked up at the exit (current opposing wind). An hour of crawling along, while submarining the bow through the steep waves really messes up the plans. This condition is not uncommon at the Race, as well.
 
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There are many locations in LIS thru Southern NE with strong currents mostly occurring at and near narrow passages. One really needs to plan and consider the winds and how long strong and how long they have been blowing, direction and fetch. I've gone through Plum Gut...one of these locations for years enough times to know that unless conditions are favorable the passage will be difficult and unpleasant... I am usually not "on a schedule" when I am sailing... or try not to be and plan passing these locations in favorable conditions. Fortunately the motor can power the boat through even if messy and slow. Current is something LIS sailors deal with all the time and if you are doing a long run east or west it will make a big difference in the time.
 

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Can't help with the math (Can't add very well) but always found that with hull speeds of about 5-7 knots the offshoreblue rule of thumb works amazingly well. Nothing more fun than blasting up or down the East River at 10 knots on a fair current and admiring the architecture on both sides. Only problem these days is ferry traffic. Need an app for that. ;)
 

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Discussion Starter · #8 ·
Sounds like a good idea for a web site... Maybe it should include your vessel's motoring speed.
Of course. I'm currently running my calculations for 3,4,5,6,7,8 and 9 kts to see what effect speed has on the tide windows.
 

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Discussion Starter · #9 ·

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Discussion Starter · #10 ·
JJ, Welcome to the sandbox! That sounds like a little too much work to me, for a 15 mile trip up the River.

Whenever I go up or down the river, there are usually other considerations besides just that 15 mile stretch in say a 70 mile trip. . i.e. when Can I leave where I am. ( sometimes there are constraints) when do I want or need to arrive where I'm going. Do I want to also carry a fair current east in the LIS, or a Fair current down and out through the narrows. So, sometimes it works to hit the full flood, or ebb depending on direction, other times, it's the tail end etc.

Those calculations are pretty easy imo. Once I know what the circumstances are of the entire trip.

But, I'd be interested to see what you come up with.
I get what your saying, but for planning how cool would be to know, at least for the tides, for any minute of the day in either direction how long will it take to transit the river. You might hit the BB a little early and want to know what's the time penalty or advantage more precisely. I'm thinking in addition to "high water at the Battery" and some calculations as part of your planning, you could just look up say, Sept 12 2021, at 4 pm north transit will be 5.5 hrs with a boat speed of 6 kts. Given a boat speed, time and direction, just look up how long it will take.

Anyway, I understand your point and I'm looking for some nerdy types like me to look over my shoulder and see if my calculations make sense.
 

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Discussion Starter · #11 ·
So, here's a call to all the crowd sourcing nerds: As you see from the image, the currents at every tide station are sinusoidal. NOAA doesn't give you the data they use to approximate the currents, but you can download the ebb, flood and slack times for the entire year. Do you think a linear approximation, a sawtooth, would be close enough or should I find a curve fitting tool that approximates the sinusoids? If the later, any thoughts on the tools?
 

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Discussion Starter · #12 ·
So, here's a call to all the crowd sourcing nerds: As you see from the image, the currents at every tide station are sinusoidal. NOAA doesn't give you the data they use to approximate the currents, but you can download the ebb, flood and slack times for the entire year. Do you think a linear approximation, a sawtooth, would be close enough or should I find a curve fitting tool that approximates the sinusoids? If the later, any thoughts on the tools?
This time with image.

Rectangle Slope Font Plot Line
Rectangle Slope Font Plot Line
 

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Discussion Starter · #13 ·
I just transited Vineyard Sound yesterday. Wind on the nose and waves on the nose. They always knock down boat speed measurably, even when motoring. These impacts vary greatly by boat and are dependent on weight, hull shape, windage above the water, etc. There are several navigation apps that will calculate a timed course, based solely on speed and distance traveled (Navionics for example). I find, by playing with speeds +/- my anticipated average SOG, I can manage current windows well enough.

There can be more to it, as well. More than once, I've had the current nicely timed behind me traveling westbound in the Cape Cod Canal. Then exit into Buzzards Bay which had a stiff SW wind and found 4-5 ft steep waves stacked up at the exit (current opposing wind). An hour of crawling along, while submarining the bow through the steep waves really messes up the plans. This condition is not uncommon at the Race, as well.
Been there myself. There are always additional considerations. But underneath all of them, everyone always starts with a plan and the plan starts with tides and currents. When heading to the Canal, I don't give a whit about Pollack Rip Channel and offsets. I just want to know when to be there and I'd love to just look that up.

After I work out the East River and if it's useful, we can build tools for all the interesting places we care to evaluate.
 

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I just want to know when to be there and I'd love to just look that up.
I just tap on the current arrow, shown in the canal on my Navionics app. Tells me direction and velocity for any day I put it. No eldridge offsets.
 
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I get what your saying, but for planning how cool would be to know, at least for the tides, for any minute of the day in either direction how long will it take to transit the river. You might hit the BB a little early and want to know what's the time penalty or advantage more precisely. I'm thinking in addition to "high water at the Battery" and some calculations as part of your planning, you could just look up say, Sept 12 2021, at 4 pm north transit will be 5.5 hrs with a boat speed of 6 kts. Given a boat speed, time and direction, just look up how long it will take.

Anyway, I understand your point and I'm looking for some nerdy types like me to look over my shoulder and see if my calculations make sense.
Yes, when you put it that way. " What's the time penalty for arriving early or late" It could be an interesting data point.

That has happened ( arriving a 'little' early) It's not the best place to kill time, so I just head up and deal with it.
I usually budget 2 hours for the passage in my planning. 1/2 hour either way doesn't really worry me. I still enjoy the scenery.

That said, I fully realize that I am the beneficiary of a lot of nerds who have taken on projects like this and have provided useful tools. I'll never give up my eldridge but I do utilize and appreciate all the other modern electronic tools.
 

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Discussion Starter · #17 ·
Okay my nerdy friends and friends-to-be, I've just completed step one of my techno-bliss adventure. I've written some python code that downloads all the current data from NOAA for a given year for all the relevant tide/current stations along the East River from the Throgs Neck down to the Narrows.

Some of the current stations only report ebb, flood and slack currents (subordinate stations), while others report the currents every six minutes (harmonic stations). I take all that data and use a cubic spline interpolation so that I essentially have the currents at every current station for every minute of the year.

1) Do you think cubic spline is appropriate? It gives very nice smooth sinusoids. Is cosine fitting more appropriate?

For step two, I want to calculate the transit time from the Throgs Neck to the Brooklyn Bridge (I'll do down the Narrows later), for various boat speeds. I'm seeking help with my algorithm for calculating the transit times. Here's what I'm thinking:

At minute X, the Throgs Neck will have a velocity of Vtn(X) and the Whitestone will have a velocity of Vws(X). One minute later those velocities will change to Vtn(X+1 and Vws(X+1).

2) Is it reasonable to use the equation distance = (Vfinal+Vinitial)/2 x Time to calculate how far one can get in one minute where Vi would be the velocity at Throgs Neck at a particular moment and Vf would be the velocity at the Whitestone one minute later?

distance = 1/2 * ( [ Vws(X+1) + boatspeed ] + [Vtn(X) + boatspeed] * 1 minute

For each minute, I'll get a distance traveled. As I march forward, the water velocities will get updated to account for the changing current. Keep adding the distances until you traverse the East River and I should have the transit times. It's almost like a rudimentary method of calculating an integral.

All help validating the approach very much appreciated.
 

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I think the current can be influenced at times by strong constant winds perhaps... or water from flooding and rainfall... swelling rivers for example emptying into the Sound. How much? I have no idea. And what about the moon?
 

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Discussion Starter · #19 ·
From my lifeguarding days, we were taught that wind, the air-water interface, creates waves but has no real effect on current. And yes, waves are a consideration, they'll create some variability but aren't mechanistically related. With respect to the moon, because the East River isn't really a river, but is a tidal estuary, the currents are driven by the tides, which are driven by the moon. That's why I pulled down the NOAA tide/current data.

Do those equations make sense to you?
 

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From my lifeguarding days, we were taught that wind, the air-water interface, creates waves but has no real effect on current. And yes, waves are a consideration, they'll create some variability but aren't mechanistically related. With respect to the moon, because the East River isn't really a river, but is a tidal estuary, the currents are driven by the tides, which are driven by the moon. That's why I pulled down the NOAA tide/current data.

Do those equations make sense to you?
not a mathematician or a physicist.
I do know that there are currents and eddies in the ocean likely "fueled" by warm water from the tropics.
 
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