MERLIN ROCKET FORUM

Topic : Tide

If you're planing over it, is the effect of tide significantly reduced?


Posted: 10/04/2008 19:31:15
By: Ben 3634
Friction applied by the water is related to the surface area in contact with the water. If you are in a foiling moth then the surface area is dramtically reduced, if you are in a merlin at planning speed the surface area in contact is reduced but not by a massive amount, maybe one third (guess).  SO in my humble opinion, the effect of tide is reduced, but what do you consider to be significant?


Posted: 10/04/2008 19:44:39
By: AlanF
Yes and no. Drag is still there but the speed proportional to tidal speed is less. However, if sailing across the tide tranist lines are still important and you will always be slower than the guy sailing out of the tide. Also the wave size may be greater so generating greater resistance. Best stay in the weaker flow if sailing against it as much as possible.
BFN


Posted: 10/04/2008 19:45:55
By: Barnsie
But, if you want to cross the tide... the quickest way would be to plane across, baaah


Posted: 11/04/2008 10:20:45
By: Shaun
It all euclid and pythagorus and basic level one yachtmaster or aviation navigation or rifle shooting (Laying/aiming off!)


Posted: 11/04/2008 10:23:11
By: Bitzer
The answer must be NO. You are attached firmly to water that is moving, you must move with. Time taken, vectors and VMG change as speed increase. True Vs apparent wind change with tide, as does apparent with speed. However the moving carpet stays the same.

Now getting late on a Friday night, lets have the leebow debate!


Posted: 11/04/2008 20:49:11
By: Blind Squirrel
It is all relative and what debate is there about lee bow it works.


Posted: 12/04/2008 10:26:31
By: Einstein
"You are attached firmly to water that is moving". ???? I don't think so. If you were attached firmly you would never plane, and power boats would never go airbourbe over waves.


Posted: 15/04/2008 20:31:44
By: AlanF
The efect of the tide is reduced because you are travelling faster over it, if you were travelling slower the effect of tide on your progrees increases until you actually stop moving and start going backwards.  If the tide is with you, planing will obviously make you go faster, but you have to remember the whole body of water is moving not just the surface. It is akin to running on a travelator... baah


Posted: 16/04/2008 09:49:21
By: Shaun
There's some very dodgy physics going on in this thread.  The tide is merely that the water you are sailing on is not stationary.  You can sort out the effect using vectors for speed and direction of wind, boat and tide.  The only thing that changes when you are planing is that you are going faster.


Posted: 16/04/2008 10:12:31
By: Andrew M
Is it as simple as saying that the effect of the tide (and water) is proportional to the amount of wetted hull area in contact with the water? 

If the boat were fully airborne there would be no effect of tide or water drag at all.
If the water is stationary and the boat travelling forwards at 5 knotts then the forward speed is 5 knotts.
Travelling against a 10 knott tide the 5 knott boat is going to be going backwards, relatively speaking. The if only half of the wetted area was in contact the water, it would theoretically be able to reduce the drag on the hull and travel forwards a little faster - how much faster would be down to more hydrodynamics and which bits of the hull were touching the water.
Presumably the lurching / choppy behaviour experienced would be a result of being subject to less drag momentarily, then more, then less, etc, as different amounts of hull made contact with swell, waves etc.


Posted: 16/04/2008 12:26:27
By: Waiting for varnish to dry.
It is surely a matter of speed and course made good over the land (Or bottom of the sea!)As someone has already pointed out, vectors etc.,basic Yachtmaster Navigation; without instruments in dinghies and small keelboats some are better at it than others.


Posted: 16/04/2008 12:49:30
By: Ancient Geek
Tide is the whole body of water on the move just like a river flowing except it changes direct at predicted intervals.  No matter how fast you travel with against or across it you will be deflected, slowed or accellerated.  If we carried tide tables, tidal flow charts dividers parallel rules or plotters we could more or less accurately work out which course to steer.  We may need to make adjustment for compass deviation and magnetic variation as well as predict out particular craft's leeway.  By the time we have done all this we will have hit the bank/mark/committee boat/opposition so in all its best to head up tide and go downtide to the mark either planing or drifting.


Posted: 16/04/2008 13:26:47
By: Jonathan

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