Understanding Tides and Current

M

mrsrobinson

Well-Known Member
Mar 9, 2006
7,704
Virginia
Boat Info
2001 380DA
Engines
Caterpillar 3126
We are planning a 3 hour trip this weekend. I want to have the current behind us as much as I can during the trip.

In looking at the Tide Charts I see when it will be high tide at our starting point. So my thought is leave a little bit after this so the current is behind us. However, in looking 40+ miles up river, the tide time are exactly the opposite.

So, lets assume a river, 100 miles long, straight as an arrow. I am starting from one end, call it point "A" furthest east, traveling 100 miles to the other end, call it point "Z", furthest west. If it's low tide at point A, what is it at point Z? If I leave point A at low tide or slack tide, travel 50 miles, am I passing point N with the tide rising at point N? If it's low tide at point Z when we leave point A, will the current be behind us for the entire trip?

It's a little confusing to me.
 
It is very common to cruise a boat to a different tidal area or thru several to get to a destination. Technically, I guess you can determine tidal flows and currents, but this one is pretty far down my list of concerns for trip planning.

And, since nav aids and charts are based on mean low water, what difference does it make?

Current and how much of it you encounter depends upon the outflow of the tidal water. Around here, tides usually flow out of passes or land cuts so the current near then is enough to get your attention, but the further away from the point of outflow you get, the less the flow and current. In other words, your hypothetical doesn't give enough information to formulate an answer.
 
It is no wonder that it is confusting to you. You are asking an impossible hypothical question. If you tell us the name and location of the river it might help.

There are current charts available for many areas and these are even integrated into some electronic charting systems.
 
Whao..now you confused the heck out of me. Is it truly a river? If so you want to go upbound while the tide is rising and downbound while the tide is going down.
 
Understood

This is not a high priority on my trip planning list, a nice to have, as it's helps with the fuel usage.

When we did this trip in the other direction 2+ months ago we left just after high tide. It made a huge difference, adding 3+ knots to our hull speed cruise. I was hoping to plan for this going the other way but the tides are all over the place.

We will be leaving the mouth of the river, at the bay, heading west. My guess was if it's low tide, or just after low tide, at the mouth, when we leave, we will get the current behind us the entire way as the tide rises.
 
Sea Gull said:
It is no wonder that it is confusting to you. You are asking an impossible hypothical question. If you tell us the name and location of the river it might help.

There are current charts available for many areas and these are even integrated into some electronic charting systems.
Click to expand...

Yeah this feels easy, think I am over analyzing it.

Our starting point this Saturday, Aug 2nd, is Hampton, VA traveling west on the James River all the way to Hopewell, VA. Along the way we pass Newport News, Williamsburg, Jamestown and Jordan Point, so I have looked at their tides too.

From Hopewell we get on the Appomattox River all the way to Colonial Heights, VA (Petersburg in the tide charts).

This is what I use to check the tides: http://www.saltwatertides.com/dynamic.dir/virginiasites.html
 
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In your case, the river fills only from the body of water behind you (rain and river flow aside). For tidal purposes, if you travel as the tide rises, it should assist you when compared to traveling as the tide goes out.
 
On my Lowrance it has tidal zones. If I point to it, it tells me instantly where the tide is and by how much. Whether the tide is going out or coming in.

Alaska has some of the worst tides in the world. In Cook Inlet I have seen it go from a -10ft tide to a +32foot tide. That is a 42ft difference!:wow:

When you are out in it and it changes direction and is in full force, it seems like you are in a river! A 3lb lead sinker is waterskiing 200 ft behind your boat!
 
Depending on your speed, you can easily outrun the favorable tidal flow, so it may be worth your while to leave well after low tide. If you check the tide schedules at various points upriver, you can get a feel for how quickly the tidal flow advances, and plan your cruise accordingly.
 
You're onto another interesting and valuable concept in boating - tides on a river. Those who argue otherwise are really missing something.
A simple 1 or 2 knot flow can mean a 2 to 4 knot improvement in speed and resulting time compared to running against the current. Some rivers run faster. This can improve your speed (SOG) and decrease your fuel consumption and distance traveled 20-25%. That's a saving and has implications for fuel supply.

It's also helpful to know currents so you know which way you will drift if you lose power, or if the water will be getting deeper or shallower should you go aground or anchor somewhere for lunch. It can also be important to know which way the current is flowing when you get where you're going and need to manuver into a dock and tie up. Finally be aware that other boats and commercial traffic may come upon you faster than you expect. Here on the Hudson River, which flows north from New York City, commercial traffic mostly travels with the currents.

It does take some local knowledge to understand each river. The constant natural downstream river flow complicates current more than just ocean tides. It depends on the strength of that flow in your river, and the natural tidal rise.

Enjoy the research and planning and have dinner on what you will save.
 
mrsrobinson said:
We are planning a 3 hour trip this weekend. I want to have the current behind us as much as I can during the trip.

In looking at the Tide Charts I see when it will be high tide at our starting point. So my thought is leave a little bit after this so the current is behind us. However, in looking 40+ miles up river, the tide time are exactly the opposite.

So, lets assume a river, 100 miles long, straight as an arrow. I am starting from one end, call it point "A" furthest east, traveling 100 miles to the other end, call it point "Z", furthest west. If it's low tide at point A, what is it at point Z? If I leave point A at low tide or slack tide, travel 50 miles, am I passing point N with the tide rising at point N? If it's low tide at point Z when we leave point A, will the current be behind us for the entire trip?

It's a little confusing to me.
Click to expand...

And who said those word problems in school would never help us in real life...:smt101
 
Your confusion can be cleared up simply if you account for the time that it takes the water to flow back up river. There will always be a lag between high tide (or low tide) at the mouth of the river and high tide upstream a bit. It takes your boat some time to get up river. It takes some time for the water to flow there, too.

If you leave the mouth of the river just after high tide, you'll soon out run it and be heading into the remaining outflow as upriver continues to reach low tide. If you divide the time between high tide at point a and point b into thirds, the middle third is probably close to what you are looking to find.

Where's Dr. Fluid Dynamics when you need him? Oh, that's right, playing in NYC.

Best regards,
Frank
 
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mrsrobinson said:
We are planning a 3 hour trip this weekend. I want to have the current behind us as much as I can during the trip.

In looking at the Tide Charts I see when it will be high tide at our starting point. So my thought is leave a little bit after this so the current is behind us. However, in looking 40+ miles up river, the tide time are exactly the opposite.
Click to expand...

If you are going UP river and want to have the tide with you most of the time, i would leave at almost high tide at your starting location. As you continue up river, the times for high tide will be later and you'll be going with the current. Take a look at your destination and see when high tide is. If im understanding you right, it should be a few hours after high tide at your starting point. It also helps to know how high/low the water changes are up river. The farther up river you go, i would imagine the tide swing will be less than your starting point.

Id make it easy and just leave an hour before high tide. That way you'll have the current with you on the way there, and wont have to fight it too much on the way back. :)
 
When the tides are given in my area they are given at the mouth of the Savannah River, they are at my dock 3 hours later, I am just slightly South and just West of I95 from Savannah. I am a little over 2 hours different from the entrance to Bear River in St Catherines Sound, which is where I boat. I can be in the sound when the tide turns coming back in and leave shortly aftrer and get home before the tide is all the way out at my dock and it is a hour run from the South end of Ossabaw Island to home. Like Frank said you have to figure it out so you can go with the flow.
My river is basicly tidal, it takes a lot of rain to fill the swamps around so they drain and put in fresh water to the system so my tide and currents are controled the flow, I have been drifting at about midtide out going and find I am moving at 4 to 5 mph per gps. It deffinatly affects speed going with or against that flow.
 
MAKC said:
If you are going UP river and want to have the tide with you most of the time, i would leave at almost high tide at your starting location. As you continue up river, the times for high tide will be later and you'll be going with the current. Take a look at your destination and see when high tide is. If im understanding you right, it should be a few hours after high tide at your starting point. It also helps to know how high/low the water changes are up river. The farther up river you go, i would imagine the tide swing will be less than your starting point.

Id make it easy and just leave an hour before high tide. That way you'll have the current with you on the way there, and wont have to fight it too much on the way back. :)
Click to expand...

The only problem with that is that you'll likely outrun the tide and then we going against the current. Like Frank said, dividing in thirds and taking the middle thirds is probably a better call.

Doug
 
fc3 said:
Your confusion can be cleared up simply if you account for the time that it takes the water to flow back up river. There will always be a lag between high tide (or low tide) at the mouth of the river and high tide upstream a bit. It takes your boat some time to get up river. It takes some time for the water to flow there, too.

If you leave the mouth of the river just after high tide, you'll soon out run it and be heading into the remaining outflow as upriver continues to reach low tide. If you divide the time between high tide at point a and point b into thirds, the middle third is probably close to what you are looking to find.

Where's Dr. Fluid Dynamics when you need him? Oh, that's right, playing in NYC.

Best regards,
Frank
Click to expand...

I am mathmatically challenged :huh:

Our starting point is here:

Sa 2 Low 5:19 AM -0.1 6:13 AM Rise 7:28 AM 0
2 High 11:16 AM 3.2 8:11 PM Set 9:02 PM
2 Low 5:29 PM -0.1
2 High 11:41 PM 3.5


The halfway point is here:

Sa 2 High 1:41 AM 2.5 6:13 AM Rise 7:29 AM 0
2 Low 8:37 AM -0.1 8:13 PM Set 9:04 PM
2 High 2:04 PM 2.2
2 Low 8:47 PM -0.1


and our ending point is here:

Sa 2 High 4:35 AM 3.4 6:15 AM Rise 7:30 AM 0
2 Low 11:26 AM 0.0 8:15 PM Set 9:05 PM
2 High 5:05 PM 3.1
2 Low 11:38 PM 0.1



It's a 2.5+ hour run. We want to be at the ending point by 5PM.

When should we leave to run with the current?
 
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