You want battery life? I got 22 hours out of my Etrex Legend using it's factory settings (I believe with WAAS enabled and NOT in battery saver mode) by using the Energizer Lithium Camera AA batteries. They were about $10 for four ...



GPS - $280

Energizer Lithium Batteries - $5

Not having to change batteries in the middle of the night while under spinnaker in the intercoastal waterway? ... Priceless.

Hey, Gary!

I was just getting ready to email you with some ideas on our mast raking sessions because of an idea I got off of Greg Scace's article for CRAC on a Randy Smyth seminar. The matter of weather helm 'feel' was too subjective for me.



So,... I thought I would mark my tiller cross arm and rear beam center points so I could see where my rudders actually were. Then I remembered all this amazing stuff about lift off of foils and the special characteristics of symmetric foils at : http://monmouth.com/~jsd/how/htm/airfoils.html

(thanks Wouter for the link in one of your documents)

So I figured 5-10 degrees would be a good angle of attack lift/drag ratio. I did the tangent on 21" lever arm, came up with 1-7/8" for 5 degrees, and marked it on my tiller connector. I think I have lengthened my forestay 3/4" from my raking outing with you, which is about as far as I can reasonably go back and is is little further than Randy recommended. I didn't have even a half inch windward helm. Then I started thinking air is one thing and water another and I happened upon your Bethwaite info. Thanks, bro! Anyway, I hope to do some more experimenting today. I'm going to make the marks for the rudder arms because you can't tell 1/4" at the center and still helm proper. Does anyone remember how much Ackerman is? (angle offset for 2 steering points to give concentric circles) It's going to take some time and research to digest this, but I suspect Ed Norris is correct if I understand him correctly, that the changes we are making are small and we are adjusting settings around the 'sweet spot'

Were you thinking of going to the speed trials at Ivanpah? Steve

I'm glad you enjoyed the graphic Ed. The gps data is very interesting since it gives speed, heading, at various positions over time increments. I'll post more someday, since you like it. Perhaps I'll do a test to see how high I can point.



The method I described was really two different tests that you can do. One is to simply watch your average course heading to see what your tacking angle is. The gps is very good at this since not only does it make a record to later view, but you are not looking at where the boat is headed per the compass and having to deduct measured slip angle. Rather, the gps tells you your 'actual' heading.



The other test is for using the VMG to optimize trim. Using the VMG readout is a great thing to watch when you try to adjust your boat trim, either by sail trimming or by adjusting boards or your point of sail. But, simply knowing the wind direction does not allow you to project a way point that is equally centered between your tacks. First you must find your actual center of upwind resistance. (A phrase that I've coined.)



Once you've sailed the boat on each tack, you then know the center of the overall upwind resistance. The center of resistance moves away from the bearing of the wind's direction due to other forces including two big ones, current and waves. While your bow may be pointing 35º off of the apparent wind, your slip angle, current and waves reaction may have your boat moving in a course that is more like 50º off the actual wind. On the opposite tack, everything usually changes.



By averaging the boat's actual direction of travel on each of the two upwind tacks, you'll be able to form an imaginary target far enough away that the angle to the imaginary destination won't change measurably from one side of the course to the other side of the course. This will keep the bearing to the imaginary point, constant as you progress. All of this, of course, depends on some good steady wind direction!



On the rudder issue, I do believe you are beginning to enter apples vs. oranges territory. Sailing upwind is entirely different than downwind. I would expect optimum foil positions and angles to be different in each case. I was focusing on the upwind and weather helm stuff since Mark primarily had mast rake concerns. Sailing off the wind with a spinnaker gives so much lee helm that mast raking wouldn't touch it. Also, as you "heat it up" the CE moves aft and you often end up with Weather Helm. The changes are radical because the apparent wind angle changes are radical when downwinding. (When beating, your apparent may go from 40º to 10º at times. When downwinding, your apparent could move all the way from 180º to say 30º) To try to balance a boats helm for such radically changing conditions could prove to be impossible; you must steer with your sails.



Good point about the added sail area (in a square top) and how most of the influence is still at the draft pocket, not far from the mast. But I think what I was most concerned about was the fact that the area added aloft has more leverage from position changes (mast rake) due to its distance from the mast base. The top of the sail moves farther fore and aft than does the foot, when mast is raked.



GARY

Steve,



Might I suggest that you find a comfortable spot to sit on the hull and rest your tiller extension handle? You could do a set of reference marks on deck and on extension handle. Bethwaite marked his stick and gunwale and looked for 1/2".



By the way, he also states that this is to be done (this is an aussie skiff) "when the boat is being driven hard and upright. On all other points of sailing, the rudder should be central."



Have you measured your boat's side slip? You can trail a fising line and weight and place the flat side of a "D" shaped protractor on the back of your transom or crossbar. Tie the fishing line to the pencil hole at the center. The line will register on the protractor like the arm of a clock.



Remeber that you want the leeward rudder to match this angle for minimum resistance. (ref: Frank Bethwaite, High Performance Sailing -p.265)

(edit) Wrong. The rudder is to be pulled toward the windward side of the boat about .75 to 1.0 degrees. This is not the angle of the side slip (leeway). But the rudder angle desired, happens to be the same amount as how much deflection occurs to the water passing across the centerboard. So, it seems that the rudder produces the lowest amount of drag/lift when it is allowed to have the same angle of attack on the water as did the centerboard. To acheive the same angle of attack as the centerboard, you must twist the rudder to compensate for the change in direction of flow that was induced by the centerboard. The rudder will have to have its leading edge brought up toward weather, about 1º. (end edit)





On a personal note, I'd like to attend the speed trials. Thanksgiving I presume? Also, as in the past three years, I'll set up the Cats2Catalina season kick off to coincide with the land yacht nationals to allow you to attend both if you can get that date for me. Usually near March 20th.

Post deleted by Ed Norris

See! I told you I wasn't a teacher. I am confusing further, when trying to clarify.



You have got me all wrong Ed! I am suggesting the leading edge of the rudder to be turned toward weather by about 1º. Or rather Frank Bethwaite is. Not turned away, turned toward; as in me pulling on the tiller.



That happens to be the same amount of angle as the amount of deflection that the centerboard is changing the flow of water. That means that once the centerboard has passed through the water, the water is striking the rudder at the exact same angle if you pull it up to weather a degree.



I hope that clears up the mis-understanding and I encourage you to eliminate or edit your last post since it woud only confuse a reader. I will take my own advice and edit my last post.



GARY

Sorry about that guys! I went back and added an edit to the post entitled "Alas, we..."



Now here is what I got out of reading page 265 of Behwaite:



The angle that Bethwaite has measured as being the least drag with most lift, is in the 3/4 to 1 degree range, Windward, tiller pulled toward weather. And he points out that this is same amount of angle that the water passing around the centerboard is deflected by the centerboard.



So, one can deduct from that, that the best angle for the rudder is when the rudder is taking the same angle to the water as is the centerboard is experiencing.



Let's say the boat is slipping 5º and the water approaching the rudder has been twisted 1º by the centerboard. The water headed for the rudder is 5 minus 1, or 4º to leeward of the rudders leading edge. You turn the rudder to weather by 1º and now the rudder enjoys the same apparant water flow angle as the centerboard did.



You set the rudder so that it gets the same angle of attack as the centerboard gets. It is a different angle to the boat since the water is being turned by the centerboard.



I hope I am finding a better way to express my thoughts more betterer here, cuz I sho am not a very good instructionatoralist.