Lee-Bow..... Windsurfers...etc (Dons tin hat)

Originally posted by mozzy A footing boat will typically make less leeway and more speed for their given heading. But obviously their given heading isn't as good. A footing boat will also get a knock in apparent wind due to their additional speed. The opposite is true for a pinching boat and the best VMG is the Goldilocks somewhere in the middle. But, it's quite a complicated thing to just plug in numbers off the top of your head for and expect everyone to accept them.

Yes, I (mostly) agree. Whether you make less leeway or raise the board for constant leeway and less drag/heeling moment is debatable - reducing leeway does not necessarily improve VMG. For simplicity I assumed you raise the board to keep leeway the same and go a touch faster. If you kept the board down your leeway would have reduced from 4 degrees to 3.7 degrees, as speed through the water increased from 5.0 to 5.2kt. In the absence of tide and waves etc, we would all chose to be the green boat in Fig 1. The question is, would we all chose to be the green boat if there was a current anti-parallel to its heading? The leebowists say no, they would switch to being the blue boat and pinch up a bit.

Originally posted by mozzy Also, you have a separate vector for leeway which is created from what looks like an applied angle. This produces one obvious error that can be seen by eye which is that the blue footing boat makes greater leeway in distance over time than the pinching boat because of the 4 degree standard leeway assumed for all headings. But that certainly wouldn't be the case in real life. Their leeway over time would either be similar, or possibly red pinchers would be worse (over time, and much worse as an angle away from their heading).

I don't follow – the blue boat is pinching not footing; the red boat is footing not pinching. At any rate, as explained above, I have assumed a constant leeway angle of 4 degrees. This assumption does not materially affect the conclusion.

Originally posted by mozzy Originally posted by Peaky Second diagram, the three boats are sailing in tide at the same angle to the apparent wind (but much closer to the true wind). The red boat is pointing straight into the current but due to leeway has the current on the windward bow, the green boat is leebowing (but it’s path is straight into the tide) and the blue pincher is leebowing even allowing for leeway.  Speed through the water for the three boats is exactly the same as the first diagram without tide (as the apparent wind is the same) but speed over the ground obviously isn’t. The green boat goes literally no where to an inertial frame (land based) observer. The red footing boat slips to leeward, but VMG now matches the green boat. The blue pinching leebower slips back faster than when there was no tide! Blue and Red's VMG shouldn't be any different relative to the other boats in the tide than on the lake. Which tell me something has gone wrong, but with out you stating your assumption it's hard to work out what.  Have you measured the vectors or is all drawn by eye? Looking at the lengths of the vectors for speed though water (without leeway) they seem different in tide versus no tide.  Also, in the first diagram you compare where the aft leeward quarter is, versus bows at the end, in the second you just have a line through the starting transoms (and the gain line out right is redudant??). This artificially makes the blue pinching boat look better in the first diagram than the second, just because of how their heading orientates the boat against the VMG gain line.  Again, I'm not sure just assuming a non-specified VMG difference for footing and pinching is adequate, when essentially your whole argument is about the effect that footing and inching has on your VMG (with and without tide.  Originally posted by Peaky Moral of the story. The green boat sails best on a lake and best on the sea. It should not be tempted to pinch to leebow, but can foot off with no loss of speed. The moral of this story is to include more information about the key assumptions you are making. GRFs whole premises is that when he pinches above the tide his VMG doesn't drop, because of getting 'flow' pushing the foils, or some rubbish.  I think if the math had been done correctly, then the relative VMG differential between footing, pinching or the best VMG mode would be the same on a lake as it is on the sea. So, unfortunately your story is incorrect and unfortunately another good example of how with good intentions it's easy to spread bad advice.   In fact, the vector lines may be correct, and it's just how you've compared bows against leeward aft quarter that is making the pincher look worse in tide versus no tide. Or some combination of the both.  If you repeated this exercise but with a consistent comparison of relative positions (central axis point of the boats) and use some real life polars for angle and speed which already accounts leeway then I think you'd have something informative and useful.

So let me say first off I didn't want to get into detail on the math's, the numbers and the second order effects. I know that opens it to scrutiny but a. I'm lazy, b. I'm busy c. Most people prefer pictures to numbers d. It is unnecessary distraction. And this is the Y&Y forum, not Chesapeake Yacht Symposium or RINA Transactions. That said, I do feel the tone of your post was a little unnecessary, but maybe I’m a snowflake.

Hitcher had the excellent idea of assuming a wide groove with the boats all having equal VMG in no tide. Unfortunately, Mozzy’s diagram is misleading because it does not account for the large change in heading relative to the true wind that can be achieved. The diagram should look like this, which reinforces the point that footing, not pinching, is the way to go. All references to leeway removed to make it clearer.

Edited by Peaky - 30 Sep 19 at 6:16pm