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Old 30-09-2016, 13:31   #1
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Sailing with or against current

Here is a newbie question -

Assume my boat has a top speed of 5 knots. I know that if I'm sailing against a tide my speed over ground will be slower and the opposite if I'm sailing with the current. I also know that the current will affect how quickly I can turn - or more accurately the distance I'll travel when making the turn.

Beyond that - what other current conditions would affect the ability to control the boat and in what way?
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Old 30-09-2016, 13:33   #2
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Re: Sailing with or against current

Wind against current will produce bigger and steeper waves than wind with current.
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Old 30-09-2016, 14:43   #3
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Re: Sailing with or against current

So, is the potential for waves the only other issue to know related to sailing with/against current?
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Old 30-09-2016, 14:59   #4
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Re: Sailing with or against current

dmksails,

Well, suppose you are motoring your Tashiba towards an anchorage, and the current is with you.... Can you explain how fast you will have to motor in order to have steerage way in a 5 knot current? You need to get clear on this because there are times to not go somewhere if you cannot make headway against the current when you turn up to anchor.

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Old 30-09-2016, 15:31   #5
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Re: Sailing with or against current

in indonesia I passed through a straight which featured 11 knot current. This is between the islands of flores and rinja

This produces many overfalls, whirlpools etc. In this situation it was impossible for me to travel against the current, but I witnessed local boats crossing the fast moving water to reach backflows, loosing ground in the meantime.

This makes the course not straight bu getting there:

Also, apparently it's possible to use anchors and with a current you can work your way against it actually powered by the current as the keel causes the boat to ride up over the anchor, you place a new anchor ahead of the previous one.


Also swift narrow currents can spin a boat when you enter them as the front of the boat reaches the current before the back.
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Old 30-09-2016, 15:31   #6
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pirate Re: Sailing with or against current

I can remember sailing into the Solent past the Needles.. unfortunately I'd missed the flood and slack water.. I sat there with a good heel and water creaming past staring at the Needles for 5hrs with my log reading 6kts before I started making any headway.. it was a big spring tide..
Also.. be careful making a turn against the tide in a restricted waterway.. or close to rocks etc.. chances are at least 60/40 you'll end up in a sticky situation.
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Old 30-09-2016, 15:38   #7
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pirate Re: Sailing with or against current

Quote:
Originally Posted by boat_alexandra View Post
Also, apparently it's possible to use anchors and with a current you can work your way against it actually powered by the current as the keel causes the boat to ride up over the anchor, you place a new anchor ahead of the previous one.
I use that technique to raise the hook without engine.. raise the main, centre the traveller and sheet tight.. the boat then starts doing a series of little tacks and one hauls in at the extreme of each tack as the boat falls off before starting the opposite tack.. then lock and hold.. repeat till the hook breaks free.. ensuring your on the safe tack for that moment.
However I cannot see how one would place the new anchor ahead of the previous one as you describe..
The technique the Indonesians were using is known as 'Crabbing'.
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Old 30-09-2016, 16:47   #8
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Re: Sailing with or against current

Quote:
Originally Posted by boatman61 View Post
I cannot see how one would place the new anchor ahead of the previous one as you describe..
I did not grasp that either.
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Old 30-09-2016, 16:49   #9
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Re: Sailing with or against current

In the San Francisco Bay area, which is a deep body of water so this will work in similar places, there is a counter current near shore that you can use to work your way against the prevailing current. How close to shore that counter current is depends on a number of factors, most importantly of which is how much you're willing to risk dinging your keel.
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Old 30-09-2016, 17:00   #10
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Re: Sailing with or against current

I try to time my travels to go with the flow. UNLESS the winds and tides opposite and I'm going windward. Then I try to catch the last of the income tide before the outgoing current and winds build big square waves on 3 second period. Always fun when that happens.

I have sailed at 2 knots against the current and gone 8-10 knots with the current. I sail at 5-6 knots on average.

I have also sailed at 1.5 knots backwards near the golden gate. That required the engine to make a 1 knot headway.
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Old 30-09-2016, 17:15   #11
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Re: Sailing with or against current

Steerage when going with the current is very difficult. This can happen a lot in PNW marinas ..... as the current may flow differently inside the marina. When approaching a dock, observe anything you can in the area. Pilings will show how the water is flowing past them. Little pieces of litter or wood will be flowing with the current. If you have a choice when docking, turn the boat into the current to dock.
I once entered a marina I was unfamiliar with in my 47 footer. Once I went into the marina between two widely spaced main docks, (each with finger docks jutting out) I observed that the current was huge! I mean like 4.5-5 knots of current. Not enough room to make a Uturn and head back out, so I had no choice but to go for the assigned slip. I hugged the boat sterns on the opposite dock. I gunned the engine full ahead and made my turn (only way I would have steerage) I headed for my slip at 6-7 knots of speed. As the bow entered the slip I went to reverse and full throttle. The boat stopped perfectly in place for about one second and the dock boys tied the stern line just as the bow tapped the main dock. Thank god for Max Props.
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Old 30-09-2016, 19:12   #12
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Re: Sailing with or against current

Current will affect your tacking angles too. This can be used when racing. One tack is better when racing over current.

As currents can be tidal (and so the may be timed) you can prefer one side of the course going up and the opposite going down.

Etc.

In light winds try to beat with current lifting you. This creates more app wind.

etc.

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Old 30-09-2016, 21:32   #13
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Re: Sailing with or against current

One simple way to think of currents, is to consider how your ability to control a car changes on a hill. When traveling; uphill, downhill, & sideways. Especially when it comes to stopping distances, or when turning. And better yet, try it on a bicycle.

One other nasty trick that it can do to you, is that if you suddenly wind up going down current, in a very fast current. Then you may lose steerage, much as boats do when coming in across a bar, when being pushed by big waves.

What happens is that the speed of the water's flow over the rudder essentially drops to zero (relative to the rudder), when the current is running at or near your boat's speed/hull speed. So that unless & until you get water flowing back over your rudder fast enough for you to regain steerage, the current will push you around like a child's pool toy. Sideways, backwards, or however it pleases. And your helm simply won't much answer, or have any effect. As at best, all flow over it has stalled... or doesn't at all exist.

This is why you want to go fast when sailing in surfing conditions, or when crossing bars, etc. So that the span of time when the speed of the water flow drops to zero over your foils, is minimized as much as possible.

And it's a situation where having a spade rudder is a big perk. As they steer boats quite well, whether the water's flowing over them forwards, or backwards. Where as with a keel hung rudder, when the water flow over it mimics the condition of the boat backing down, the rudder doesn't function well. And subsequently, the boat will handle poorly under such circumstances, even if it appears that she's moving "forward". And she quite well could be.
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Old 01-10-2016, 06:50   #14
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Re: Sailing with or against current

My local waters are the Hudson Estuary ,so tidal currents are always there and reversing.
NYC area is maybe the strongest area,with the East River and its Hell Gate the most notorious.However all who sail here quickly learn that much needs to be calculated esp. to be a successful racer.
One of the most obvious effects not mentioned above is the often observed counter currents that can occur along the edges of a strong running tidal stream. There are many subtile nuances regarding bottom configuration,depths,etc. that make the locals hard to beat in the light airs so common here in the valley
Ian Proctor (WIND and Current in Sailing Strategy) has much info based on the British Is where those locals regularly experience all sorts of weird and wonderful effects....................worth a read.

................................luv you all....................mike....................... ....................
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Old 01-10-2016, 07:38   #15
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Re: Sailing with or against current

One thing to remember is that the strongest current is in the deepest water.

Racers use this knowledge all the time, and it can help a slow monohull make headway at times say getting in an inlet or pass against the current by using the shallowest section of the channel possible....or even out of the channel just a bit if it's deep enough

During races on beach cats sailing against the current through a pass or inlet, we'd raise our 4' daggerboards and sometimes even the rudders so we could come through in a foot or two of water if necessary far out of the channel and in very little current
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