OK who likes physics ...
When sailing with the tide does it still add a uniform amount to velocity (over the ground like our GPS's measure) at planning speeds e.g. 15 Knots +
Is it still a simple matter or adding tide velocity to the velocity we have gained via the wind, or does it have a diminishing effect? The surface area of the board is much reduced due to planning and velocity is way in advance of the water's speed. The fin's contact to the water seems insufficient as to contributor and its passage through it is creating lift so it would if anything be a negative influence.
There's a few "frame of reference" issues you need to consider.
- If you were in a motor boat then "yes", you would simply add your tide/current vector to your Speed over Water (SOW) vector to get Speed over Ground (SOG).
- Wind is normally quoted in SOG terms. If you wanted to define the apparent wind you are actually sailing you would have to consider your speed vector over water and also the tide/current vector. For example, if the wind was 5kts and the tide was 5kts downwind, you would experience 0kts apparent if you weren't moving in the water. Experienced this a few times trying to beach start in a rip.
- In practice you will get a combined effect on a reach. The current might contribute to your SOG but also indirectly reduce your SOW due to changes in apparent wind (this might then reduce the SOG effect).
I think theres a few variables. I sail in current all the time. At certain angles in the direction of the current the fin cant generate any lift. Makes it a lot harder to get the board to plane in marginal conditions. Against the current though, its quite easy to get up n planing. I guess the fin sees a higher speed waterflow..
Sea trials in Cockburn Sound WA always ran with tide.
Running against tide ran risk of failing the longevity speed runs for high speed flight vessels
In my experience, the direction of current does effect speed. Running with the current is faster at Burrum Heads and Lota Creek. Also wind against tide creates standing waves which also hinders speed.
Going back to my long long ago youth sailing in Dublin Bay a place with a 4M tide, yacht racing in tide, local knowledge was crucial. Tide is a funny thing it is not linear (so just adding or subtracting is useless). What we could measure was boat speed i.e speed of vessel through the water it was in. Boat on boat in close quarters it was comparable but when you had a boat way out in the bay at east burfort mark making 7knots vs a boat inshore at east pier mark things get interesting. Sailing directly against the tide obviously is slower than the opposite tack sailing with it (180degrees) but when you start to sail at angles to the tide things get tricky, tide generates 'drag' and 'lift' at certain angles e.g close hauled and trying to beet (work) up to a mark with out tacking you may loose some speed but get pushed up to the mark and avoid a tack which would be slower than that loss of speed. That kind of knowledge of where when and what direction the tide was at was crucial. The tides don't just move in straight lines they can sweep into a deep bay or accelerate through an invisible under water channel or they crawl and creep over rocks bars sand banks etc etc and so their speed (velocity) and direction (Vector) varies constantly, their intensity varies with moon phases.Tides on the east coast of Australia are less obvious than the big ranging tides on the North Atlantic, but are still very powerful. My father who passed away at 88 just two weeks ago could still from in his head tell you the exact state of the tide at any time of the day for Dublin Bay, just years of experience and local knowledge. His older boat put him out of the automatic podium bragging rights but his local knowledge of tides often got him the place. I know displacement vs planing but you are still moving through a fluid medium which is also in motion. You would have to know the exact velocity of the water you are in its vector your vector and your velocity.
So to answer your question yes....and no!
