Hi all

On Friday we went for a sail down the river in the 349 and on the way beating back up in 15 to 20 knots of breeze from approx 1.30 pm to 3.30 pm the log was reading roughly 1 to 2 knots faster than the speed over ground reading (most of the time the log was reading 6 to low 7 and SOG at the same time was just over 5)

The tide on Friday was a low at 11.29 am of 0.42 m followed by a high at 6.04 pm of 1.15 m so the tide was on its way in

Also looking at the river plot there was about 1000 megalitres a day flowing down the river upstream of where we were so we were going against that

The section of river we were sailing in was approx 1.3 nm wide with average depth of approx 60 to 80 feet and we were able to sail the 9 nm length of the river without tacking

Any thoughts would be appreciated

Regards Don

Hi Shaggy

In theory we were going with the tide flow (we started at the mouth of the Huon and were sailing towards upstream towards Port Huon) and the tide times i gave were for Port Huon, but against the flow of the river so if you take the river flow out of the equation the tide should have been helping out SOG

I guess my question might be does the 1000 megalitres of water per day flowing down the river counteract the incoming tide

Regards Don

Q=va

1000ML x 1000 / width (m) x depth (m) = v (m/s )

If you work it out the flow velocity induced by the 1000 megalities will be approximately sfa. Hope that helps

Trek said..
Sounds like if you anchored in the middle of the river your log would say 1 to 2 knots boat speed although you sog would be zero.

Hi Trek

That is pretty much correct if the log is reading correctly

Regards Don

The fresh water runs out over the top of the salt water in some rivers, saltwater is more dense than fresh, the tide pushes in from underneath.

Lets run the numbers. A river 1300m wide by 10 m depth has a cross section of 13,000 sq m. A magalitre is a million litres, or 1000 cubic metres. So if the river flows one m you have moved 13 Megalitres (Ml). 1000Ml would therefore span about 77m of river length. And its got all day to flow that 77m, so the runoff flow velocity is negligible.

Shags...there is no one smarter than you...you bought the Pogo...remember?.

Yara...or should I say Professor Yara. Gotta love your analysis. Wish I could understand it.