Riding the Tide
 

I found some current charts for some areas, they give slack, max ebb,
and max flow. this I understand.
For other areas I find only the H & L tide chart. I want to make max
use of the tide (ebb). Say H is at 0800 and L is at 1400. is it simply
a matter of shoving off at 0800 and 'ride the out going tide till
1400?
TIA

Scotty

Bobsprit wrote:
I want to make max
use of the tide (ebb). Say H is at 0800 and L is at 1400. is it simply
a matter of shoving off at 0800 and 'ride the out going tide till
1400?


GADZOOKS!!!! Bwahahahahaha!


RB

Good answer!

Cheeers
Marty

It depends of the area and of the duration of the trip.

There is 3 sources of tidal current: Tidal current tables (ATT), Tidal
current charts and tidal currents shown in the sea charts.

If you only know the time of HW and LW, you can assume that the curve
of the tidal current will look a bit like a sinus curve.
Generally there is a period of relatively weak currents around HW and
LW and the current will run faster halfway between HW and LW.

If the trip is expected to take 9 hours it would best to leave around
6.30
so you can sail in two periods of slack (weak currents) and one period
of favourable current.
If the trip is expected to take 3 hours, if you leave around 9.30 you
should be able to sail the whole trip in favourable current.

I'm sure Donald or some of the others who sail in areas of strong
tides could elaborate further, but they probably think that you need
the mental exercise of figuring it out yourself.

Peter S/Y Anicula

"Scott Vernon" skrev i en meddelelse
...
I found some current charts for some areas, they give slack, max
ebb,
and max flow. this I understand.
For other areas I find only the H & L tide chart. I want to make
max
use of the tide (ebb). Say H is at 0800 and L is at 1400. is it
simply
a matter of shoving off at 0800 and 'ride the out going tide till
1400?
TIA

Scotty

"Peter S/Y Anicula" wrote in message
...
It depends of the area and of the duration of the trip.

There is 3 sources of tidal current: Tidal current tables (ATT),
Tidal
current charts and tidal currents shown in the sea charts.

If you only know the time of HW and LW, you can assume that the
curve
of the tidal current will look a bit like a sinus curve.
Generally there is a period of relatively weak currents around HW
and
LW and the current will run faster halfway between HW and LW.

That's what I thought, but I want to be sure.



If the trip is expected to take 9 hours it would best to leave
around
6.30
so you can sail in two periods of slack (weak currents) and one
period
of favourable current.
If the trip is expected to take 3 hours, if you leave around 9.30
you
should be able to sail the whole trip in favourable current.


Should take about 8 hrs., but you know sailing, could be longer.
At a different location there is a narrow channel , with strong
currents, to go through. this should be done at slack tide.


I'm sure Donald or some of the others who sail in areas of strong
tides could elaborate further, but they probably think that you need
the mental exercise of figuring it out yourself.

Nah, they know me better than that.

Thanks, Peter.

Scotty

"Peter S/Y Anicula" wrote...
If you only know the time of HW and LW, you can assume that the
curve
of the tidal current will look a bit like a sinus curve.

Yes, that's true. The current will also follow the 'rule of 12s'
somewhat, lagging because of the momentum of the water in motion.

In the absence of current tables, assume the max current is at 7/12s the
interval between high & low water.

DSK

DSK wrote:

"Peter S/Y Anicula" wrote...

If you only know the time of HW and LW, you can assume that the

curve

of the tidal current will look a bit like a sinus curve.


Yes, that's true. The current will also follow the 'rule of 12s'
somewhat, lagging because of the momentum of the water in motion.

In the absence of current tables, assume the max current is at 7/12s the
interval between high & low water.


Got that wrong Doug. Tidal stream is generally strongest at the time of
the fastest rate of change of tide height. That is most often about
halfway between high and low water. Look it up.

Cheers

"Scott Vernon" wrote in message
...
I found some current charts for some areas, they give slack, max ebb,
and max flow. this I understand.
For other areas I find only the H & L tide chart. I want to make max
use of the tide (ebb). Say H is at 0800 and L is at 1400. is it simply
a matter of shoving off at 0800 and 'ride the out going tide till
1400?
TIA

Peter has given an excellent answer!(even if he got my name wrong).

I would only add one thing. You need to use "slack water" as your
reference, instead of HW, or LW.

Geographical features can have a major impact on the tides. For example, at
Portsmouth the current changes direction 2 hours before HW (or LW) because
the proximity of the Isle of Wight. The Island produces a "circular" effect
which completely changes the normal flow.

It is also worth knowing that the current will be much smaller in shallow
water. If the current is with you, then you should get into the deep water.
If it is against you, then you should get into shallow water.

Furthermore, you may be able to benefit from back eddies. A good tidal
stream atlas for your local area should show where the back eddies are.



Regards


Donal
--

"Donal" wrote ...

"Scott Vernon" wrote in message
...
I found some current charts for some areas, they give slack, max
ebb,
and max flow. this I understand.
For other areas I find only the H & L tide chart. I want to make
max
use of the tide (ebb). Say H is at 0800 and L is at 1400. is it
simply
a matter of shoving off at 0800 and 'ride the out going tide till
1400?
TIA

Peter has given an excellent answer!(even if he got my name wrong).

I would only add one thing. You need to use "slack water" as your
reference, instead of HW, or LW.


That's what I was asking, as I only have a HT- LT schedule for the one
area.


Geographical features can have a major impact on the tides. For
example, at
Portsmouth the current changes direction 2 hours before HW (or LW)
because
the proximity of the Isle of Wight. The Island produces a
"circular" effect
which completely changes the normal flow.

It is also worth knowing that the current will be much smaller in
shallow
water. If the current is with you, then you should get into the
deep water.
If it is against you, then you should get into shallow water.

Good point!



Furthermore, you may be able to benefit from back eddies. A good
tidal
stream atlas for your local area should show where the back eddies
are.

I may not be going anyway , if these damn hurricanes don't stop.

Scotty

Nav wrote:


DSK wrote:

"Peter S/Y Anicula" wrote...

If you only know the time of HW and LW, you can assume that the


curve

of the tidal current will look a bit like a sinus curve.



Yes, that's true. The current will also follow the 'rule of 12s'
somewhat, lagging because of the momentum of the water in motion.

In the absence of current tables, assume the max current is at 7/12s
the interval between high & low water.


Got that wrong Doug. Tidal stream is generally strongest at the time of
the fastest rate of change of tide height. That is most often about
halfway between high and low water. Look it up.

Cheers

Personally, I disagree. You need to know where you are (narrow
opening/wide opening) and various given conditions before you start to
apply any particular rule. Compare your tables (tide/current) for the
particular locale, then see if a particular rule applies at all times or
only sometimes.

otn

Scott,

You've seem to have forgotten "The Gulf Stream Master" Jax. I'm sure he
can help you ride the eddies:^) Maybe even find you a stray current
heading south (g)

Now, for what's it worth. The Tide Flow is a sine wave. Us common folk
understand that slack water is at the top and bottom of the wave. So
slack is, roughly about a hour and it is roughly in the upper 30%
counting the end of the rising tide and the beginning of the Ebb. 15% to
the HW and 15% roughly to the Max Flow. That means about two hours to
max flow, 8 hours of max flow and then another couple of hour of
diminishing flow to LW.

That doesn't make allowance for land masses, rivers, depth, etc. Also
the time differences of where the HW takes place. So if you are sailing
a Riding Tide you can increase your Max Flow by watching your location
and tide tables times.

From your fat, old sailor,
Thom