Effect of Current

Hi, can anyone help with a few "rules of thumb" about current/ tides etc when going around the course. I have read a few articles but struggling a bit with them. If there are some simple rules (Ok, there probably arent any simple rules!) to follow in various scenarios - beating, reaching, running towards the respective mark when the current is L-R, R-L, with you, against you? Alternatively, a good link would be a great help.
Thanks
R
 
Three simple rules...

On a reach or a run if the current is running across the course, line up the mark with something (like a tree) on the shore behind it and steer to keep the two in line.

On any leg if the current is running with you or against you, try and figure out if the current will be stronger or weaker on one side of the course (e.g. it will generally be stronger in deeper water) and then favor the side of the course where the current will help you the most or hurt you the least.

On a beat, current will change the laylines. For example if it's an adverse current the laylines will be further upwind than they would be in no current. And vice versa.
 
Also consider pressure. Sometimes the wind strength will negate the advantage of going off the course to avoid current in deeper areas.
 
As for knowing which side is more/less favored, there are two phenomenas that effect current. First, current flows stronger where it's deeper. Second, current flows stronger in a bottleneck (e.g. channel to shallow lagoon). These two factors often get mixed and it's important to understand the difference between the two.
 
Hi there,

Just to share abit. I did notice that the current is not always in same direction in all part of the water area. You may see anchored ships from far pointing from right to left but the exact area you race in to the windward mark may have current flowing from left to right. It could be due to objects that exist nearby, like a long wall, etc. So, be careful. This is what I just learnt. :)
 
Some really good points made - it doesn't cost anything to ask around for a bit of local knowledge. We sail in a very tidal basin where the flood tide generates a huge conter-clockwise eddie, that you can't see but the effect of stemming it unawares doesn't do much for boat speed.

To illustrate the point there's a brilliant tidal flow animation of the "Bluff Harbour Swing Basin" at the following link http://www.otago.ac.nz/marinescience/po/java/adcpti des/bluffent.htm . Zoom in for best viewing.
 
Another aspect to consider is the apparent wind direction and strength. A few knots of current e.g. on the beam will affect your pointing on different tacks and this needs remembering when looking for shifts on each tack (particularly if the predominant wind is not too strong and the current is variable across the course area).


Ian
 
paulmarshall said:
Some really good points made - it doesn't cost anything to ask around for a bit of local knowledge. We sail in a very tidal basin where the flood tide generates a huge conter-clockwise eddie, that you can't see but the effect of stemming it unawares doesn't do much for boat speed.

To illustrate the point there's a brilliant tidal flow animation of the "Bluff Harbour Swing Basin" at the following link http://www.otago.ac.nz/marinescience/po/java/adcpti des/bluffent.htm . Zoom in for best viewing.

Thats a good link but that foreshore has a pretty unnatural shape.
 
I thought the animation was pretty neat too.

The saw-tooth foreshore is actually a series of wharves all on reclaimed land.

The intersting thing to note though is that the eddie actually starts north of the wharves when the in-coming tide hits prominent rock bank (which dries at low tide).

I guess the message which reinforces earlier points is to watch for eddies around obstructions and to seek local knowledge.
 

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