How do you gauge your speed

Discussion in 'Laser Talk' started by Skygod1, Jun 8, 2007.

  1. onetwoMeny

    onetwoMeny New Member

    Likes Received:
    0
    Trophy Points:
    0
    very confusing indeed...

    so faster you go the further away "aparent wind" is from "true wind". thus not allowing you to point as high.
     
  2. viktor188924

    viktor188924 New Member

    Likes Received:
    0
    Trophy Points:
    0
    Exactly. It is confusing. Sorry merrily. I should never had brought it up. It's a confusing concept... I'm not even ready for it.
     
  3. onetwoMeny

    onetwoMeny New Member

    Likes Received:
    0
    Trophy Points:
    0
    so lets streighten up some confusion. if this is a complicated topic maybe meny minds can help us solve it.
     
  4. Ross B

    Ross B Guest

    Summary: this is all you need to know from this thread





    might what to also figure out the BASIC'S of how to read telltales

    KISS: Keep It Simple Stupid
     
  5. Chainsaw

    Chainsaw Brmmm Brmmm

    Likes Received:
    0
    Trophy Points:
    0
    The faster you go, the further forward the apparent wind becomes when compared to the actual wind direction.

    e.g.

    If the wind was blowing in your right ear at a stop, as you accelerate, the wind now blows in your right eye.
    The actual wind direction has not changed. The apparent wind direction has changed, moving forward.
    Again: If the wind is blowing steady Easterly and you accelerate to the North, the apparent wind moves forward to ENE.

    You cannot point higher than your boat is designed to go just because you are going fast,

    i.e. breaking the rules of sailing theory. At some point you will reach head to wind, regardless of how fast you're going.

    but you are pointing higher when compared to the course you were sailing at the slower speed

    and when compared to the actual wind

    and when compared to any other boat that is not going as fast as you, on the same course as you.

    This is why fast is good while racing. :D

    You are not pointing higher by your own choice, but because you must use a higher course to keep your sails trimmed correctly, because your speed has changed the apparent wind.

    Your sails use only apparent wind from the time you start moving. Actual wind direction is just a point to measure from.

    As you slow down the apparent wind moves back towards the actual wind direction.

    Slow is not good when racing. Avoid it at all costs.

    Unless an obstruction is approaching fast, and your apparent speed towards the obstruction is increasing, then I recommend you use all the slowness you can find to avoid the hitting the obstruction with a high apparent speed.


    If this has not increased you confusion, I will be very disappointed.
     
  6. Merrily

    Merrily Administrator Staff Member

    Likes Received:
    14
    Trophy Points:
    38
    So faster means pointing higher--or not?!
     
  7. Chainsaw

    Chainsaw Brmmm Brmmm

    Likes Received:
    0
    Trophy Points:
    0
    yes, you will be pointing higher.

    Speed is a tactical advantage.
     
  8. viktor188924

    viktor188924 New Member

    Likes Received:
    0
    Trophy Points:
    0
    three cheers for chainsaw!
     
  9. Chainsaw

    Chainsaw Brmmm Brmmm

    Likes Received:
    0
    Trophy Points:
    0
    hooray

    hooray

    hooraay!

    so... what was the original question?

    who's chainsaw?
     
  10. Looper

    Looper New Member

    Likes Received:
    0
    Trophy Points:
    0
    Chainsaw that somehow doesnt seem right but as a relative novice I may be missing something. Surely the highest you can theoretically point to absolute wind is when moving relatively slowly when actual and apparent wind are fairly close. Say the highest my boat can point is 45deg (to apparent wind). As soon as I start to move forward at 45deg the apparent wind moves forward (away from actual wind) so i have to bear away to avoid the dead zone (which also shifted forwards). So now I'm going faster, still at 45deg to apparent wind but now at 50deg to actual wind so even though I'm going faster it's at a more oblique angle so I may not actually make any more progress to windward even though I'm going faster. I am not sure if the optimum tradeoff between increasing angle away from wind direction and resultant increase in absolute speed can be calculated but isn't it possible that the optimum angle for absolute speed might turn out to be different to the optimum angle for progress to windward so maximum progress to windward might be achieved at an angle other than that which gives maximum absolute speed?
    However I may be failing to take into account a possible change in the angular size of the dead zone with increasing speed? Does this zone shrink when speed increases? The above manouevring is assuming that all this is done with sails fulling sheeted so we are only using directional change to keep the sails full sheeting. If you take the apparent wind argument to its logical conclusion - the fastest I can possibly go might be on a screaming reach somewhere approaching 90deg to actual wind but at that point I may be making very little progress to windward?
     
  11. Merrily

    Merrily Administrator Staff Member

    Likes Received:
    14
    Trophy Points:
    38
  12. Chainsaw

    Chainsaw Brmmm Brmmm

    Likes Received:
    0
    Trophy Points:
    0


    Have you changed the point of sail by bearing away though?

    If you are planing close hauled, you are making gains to windward. If you bear away to a reach, you are not making as much gain but your speed increases. If you want to slow down while on that reach, you’d move to a broad reach that would in its extreme either make you luff (easing the mainsheet without bearing away) or you would have to bear away and go lower, for your point of sail.

    If you’re in a laser, you won’t be planing to windward, so will make best gains to windward at maximum displacement speed. You will be pointing higher to some extent, but not as much as the angle between points of sail. As mentioned earlier, the phrase “pointing higher” gives the impression of tremendous gains rather than the reality which may be measurable, but not startling.




    Yes, I think this is what is highlighted above. Perhaps we could further complicate the “ifs and buts” of these “rules” by adding:

    "So faster means pointing higher...within the point of sail"

    If the apparent wind has moved forward, it’s moved forward on both tacks. (obviously)

    Once you tack, would you not be covering less ground, and faster, over the same course as at a slower speed? (ruling out the possible changes that happen in real life such as wind shifts etc)



    This is the same problem you have at slow speed. How fast to sail to gain optimum speed and make the highest gains to windward.




    Off the top of my head, I don’t know. :rolleyes:

    If it stays the same but only moves forward, it would have the same effect as being smaller when traveling to a fixed point to windward on any given tack.

    If a boat comes off the plane as it tacks, then the apparent wind suddenly moves back toward actual wind direction. Then under acceleration the AW moves forward again, until you reach the balance between speed and height again. It would seem like the deadzone had reduced under those conditions, but it may have only moved.

    However, if it does get smaller, through some aerodynamic rule...lol... I’ll look it up and tell you tomorrow.
     
  13. Ross B

    Ross B Guest

    this is getting to ridiculously complex, even for me, can we hijack to deciding if the bow eye should be made out of carbon fiber? need to get all that weight off the bow!

    If you vote me to the Laser NA board, I promise it will happen!
     
  14. Looper

    Looper New Member

    Likes Received:
    0
    Trophy Points:
    0
    I'm not sure if this is valid or not but if we say that the limiting angle of the dead zone (relative to APPARENT wind) stays the same size for regardless of speed. If we also look at the case where all manouevring is done fully sheeted in. As I sail forward closely hauled on the limiting angle and pick up speed the apparent wind shifts forward and so the dead zone limiting angle shifts to leeward so i am forced to bear away to stay outside the dead zone. Granted I may now be going faster so my progress to windward may be the same (or slightly better or slightly worse - I don't know) but I had to physically bear away from the original closely hauled angle due to the forward shift in apparent wind (and the consequent leeward shift of the deadzone limiting sailing angle) caused directly by my increased speed.
    This forward shift of apparent wind and consequent leeward shift of limiting sailing angle happens in opposite directions for opposite tacks so I can't help but feel that the effective total angle of the deadzone (relative to ABSOLUTE wind) might actually increase as your speed increases?
     
  15. Chainsaw

    Chainsaw Brmmm Brmmm

    Likes Received:
    0
    Trophy Points:
    0
    If the AW moves forward, then the deadzone limiting angle has moved to windward, not to leeward.

    As long as you don't change the point of sail, then I can't see how the limiting angle would become greater with increased speed.

    (This is what I was I was going to find out about, but you're welcome to beat me too it... whether the deadzone limiting angle reduces, moves forward or stays the same.

    I''m looking for answers... I'm looking I'm looking ...give me time man!

    lol :D
     
  16. Chainsaw

    Chainsaw Brmmm Brmmm

    Likes Received:
    0
    Trophy Points:
    0
    If the apparent weight of the bow eye is 120g, dry, how much will it weigh made out of carbon fibre, wet, at planing speeds if the apparent wind has moved forward by 5 degrees?

    Your nomination hinges on the answer. You have 1 minute. Starting...

    ...NOW
     
  17. tannerz

    tannerz New Member

    Likes Received:
    0
    Trophy Points:
    0
    well, lets see if I can confuse everyone a little more...

    My limited knowledge tells me:

    When you go faster, the AW moves forward. To maintain optimum polars you have to bear away. Your polars don't change... ever. The dead zone is still what it always was, if you don't make a correction, you are now pinching. Think of it like a wind shift, because that is what it is, the usable wind has now shifted forward. You always sail to the AW, not the TW. I really don't care what the TW is.

    This is my experience in racing the big boats. It may not apply here...

    Now, notice I never mentioned speed, just polars. So, the real question is:

    Can a laser pinch a little, while planing, and still maintain optimum VMG?

    My vote is no. Physics is Physics, and wind moving over an aerodynamic surface behaves in the same way fast or slow. The only difference is the force. If you move the angle of attack of the airfoil in relation to the direction of the wind it reacts the same at all speeds (assuming some laminar flow, and not is a stall situation for those pilots out there)

    Another magical question:

    Can you trim the sail (change the airfoil) in a way to take advantage of the new wind angle? Does moving the draft back or forward help with the angle of attack change?

    I think the only way to really know the answer to all of these questions is to fully rig a laser with instruments and go sailing...
     
  18. Merrily

    Merrily Administrator Staff Member

    Likes Received:
    14
    Trophy Points:
    38
    This is the part I don't get at all. Why would you bear away when the wind moves forward? You'd want to follow the wind up. Seems totally backward to me. Seems to me there's two issues here, also. Do you want to use the apparent wind to point better or to go faster? That's a tactical decision.

    I remember that DrLaser had a great article on this topic, including the Polars. Does anyone still have it? I tried the archives but couldn't get them to work or find the article that I needed. If anyone has the article, please e-mail it to me. (don't post it here due to copyright considerations)

    janet @ laserforum dot org
     
  19. tannerz

    tannerz New Member

    Likes Received:
    0
    Trophy Points:
    0
    I am sailing with the wind at 45 degrees to the sail...

    If I go faster the wind is now 35 degrees to the sail...

    I have to bear off a bit to get back to 45 degrees to the sail...

    The numbers are for clarification, I am not saying what the proper angle to sail a laser is.

    understanding pointing versus speed is what makes good sailors into great sailors.

    this is how I understand it:
    (the small blue lines are your boat)
     

    Attached Files:

  20. Merrily

    Merrily Administrator Staff Member

    Likes Received:
    14
    Trophy Points:
    38
    Quit showing me the diagram. I don't get the diagram. Your explanation still doesn't make sense to me. Our speed increases as we settle into the tack and the apparent wind moves forward, closer to the bow. It's like you've gotten a wind shift up. Why don't you head up? Don't tell me because the true wind is still back there, the apparent wind is driving the boat, ain't it?
     

Share This Page