| Author | Message | ||
     ed hooper |
And it is not clear to me that the unexalted are allowed to experiment with the wind. | ||
| ed hooper |
Our course and sail trim were designed by the Professor. And we made plenty of leeway when we lost steerage, if leeway is still the issue here and not coming in first. | ||
| David |
You have to do the experiment with WIND. The drifting around we were doing Friday was so light that you cannot draw too many conclusions from it. But pinching was not the right thing to do under the circumstances. BD was sailing close to the wind, but we fell off every time speed dropped even a little. Can't tack quickly or effectively with no momentum. We also sailed faster than the rest of you  | ||
| ed hooper |
Seems like pinching is what we were all about last Friday. When we tacked, we lost headway and steerage, so it behooved us to pinch on that starboard tack in order to make it up the channel. I didn't notice any leeway at all, and I think it would have been very obvious. Empirical enough? | ||
| hughston (hughston) |
Ed, go out and get your own empirical data. Try it sometime and see what happens! :-) | ||
| ed hooper |
Illogical that pinching increases sideslip. | ||
| david (david) |
Yes, pinching will slow the boat down, although I don't think very many people do it for that reason. Pinching makes the boat somewhat less stable, as it's very easy to head up from a pinch into irons. You might theoretically reduce the number of tacks on a given course, but you would surely get to wherever you're going in a longer period of time and you may do an unintentional gybe if you get into irons. That jibe could get very interesting in a narrow channel. If you're intentionally pinching, you're also going to have more trouble coming about because your speed is lower. You need momentum to carry the boat through the turn. I have a suspicion that the boat also side slips more when pinching, but I haven't done the analysis. It would seem that if you trim the sails to point as high as possible, the forward force vector is reduced but perhaps not the vector to the beam. I think you are correct in your earlier observation that you may have to fall off an intended course in the interests of sailing efficiently. Your "velocity made good" to your destination will be better if the boat's sailing efficiently even if the price is that you take a few more tacks. Particularly if you do not have an army of sail trimmers aboard to respond to every shift in the wind, you normally would alter your course a little from time to time to keep the boat sailing efficiently. When you get far enough off course it's probably time to tack. | ||
| ed hooper |
And then "pinching" would not only slow the boat down, it would move the wind aft and give you a lift. It would seem that this would be a useful tactic in a narrow channel reducing the number of required tacks. | ||
| unclemark (unclemark) |
Yes Ed; You have it exactly right. That's why, as we said last time, catamarans and ice boats have so much more dramatic an effect since their speeds are so much greater. | ||
| ed hooper |
So, as the boat speed is picking up, we are constantly falling off, in order to maintain and/or increase boat speed. Otherwise, the effect of being headed (by the apparent wind)would be to slow the boat down, which would move the apparent speed aft, and give the boat a lift. So, if I understand this correctly, a knowledgeable helmsman would plan for this effect, knowing that as he increases his efficiency, he is moving away from his desired course. I await with anticipation watching this in action, as, in my few months of sailing experience, I have never seen this practiced or discussed. | ||
| unclemark (unclemark) |
Apparent wind is a function of true wind and the wind you produce with the speed of your boat. Like the bicycle rider pedalling down the road, you generate more wind by speeding up and you shift the wind so's it hits you more in the face. The opposite if you slow down. On the other hand, if the true wind speed increases it works the opposite. In fact, consider that if the wind is extreme, the difference between the directions of the true and apparent winds are negligible because your boat speed is such a very small proportion of the total. Look at the diagram in the syllabus and if this doesn't make sense, bring it up in class. | ||
| unclemark (unclemark) |
Message from Ed Hooper: Let's see: 1. I rec'd your email. 2. I opened it without any foreknowledge that you would query about "electricmarine." Therefore, I, at this juncture in my life, know nothing about the aforementioned (except what was discussed in class). 3. I understood that it was an either/or on email or the chat site. Has that changed? 4. Will you be discussing apparent wind and the effect of wind shifts in both velocity and direction? |
