Pointing-so whats that all about?
Printed From: Yachts and Yachting Online
Category: Dinghy classes
Forum Name: Dinghy development
Forum Discription: The latest moves in the dinghy market
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=12940
Printed Date: 03 Jul 25 at 11:30pm
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Topic: Pointing-so whats that all about?
Posted By: Oatsandbeans
Subject: Pointing-so whats that all about?
Date Posted: 21 Dec 17 at 6:17pm
Following on from a good thread on the Star event. It was mentioned how high they
point . So why is that? What makes some boats point and others don't, and how can some sailors get boats to
point higher than the rest?
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Replies:
Posted By: Guests
Date Posted: 21 Dec 17 at 6:41pm
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The angle at which a boat points is the sum of its aerodynamic and hydrodynamic drag angles. Drag angles are the arctan of lift/drag ratios. So, better lift/drag ratio = higher pointing. Given that lift is largely limited by righting moment, the best way to improve pointing is therefore to reduce drag - of the underwater and above water parts.
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Posted By: Oatsandbeans
Date Posted: 21 Dec 17 at 6:47pm
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Thats really good but your average sailor can't deal with that. How does he get his boat to point higher than his mte off the line, when he is using the same gear? Should he have a fuller sail faltter sail, sheet the jib more or what?
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Posted By: Do Different
Date Posted: 21 Dec 17 at 7:19pm
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To a large extent I've given up worrying about pointing in isolation. My biggest concern now is to stay fully powered, driving and bolt upright.
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Posted By: Oatsandbeans
Date Posted: 21 Dec 17 at 7:29pm
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I get that but being able to point higher than the rest can make life a bit easier. Getting off the line you can burn off the guy on your hip and get a clear lane. At the leeward mark you quickly get your own clear air as you are sailing higher than the rest. You end up being able to sail your own race in clear wind. So that can't be bad.
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Posted By: iGRF
Date Posted: 21 Dec 17 at 7:32pm
Pointing high 'off the line' is more a matter of having your nose ahead. Because if the boat immediately downwind of you gets his nose ahead of you, you can have the best set up rig in the world but overcoming the heading effect of the wind as it channels between you and he will be difficult to overcome (Another lee bow effect)and you will slip back, then the boat above you will also overwhelm you and you're back into the 2nd rank.
So, 1st rule start on time, in fact, start a micro second ahead of time.
I point really high, always have, can't help it I'm a lightweight, it's my style. I often wish I didn't because it is not always the fastest method of sailing, there are times when cutting loose and sailing fast and free works better, but how do you do it, we have an expression where the head looks, the body will follow, so hanging outboard looking upwind plenty of body twist, I have found exported from my windsurfing technique, seems to apply to dinghies. I picked up on it by following an ex Olympic squad lady in a Europe and Jesus she could point high and she nailed every shift. So for me it was following someone really good and emulating the way they sail.
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Posted By: Oatsandbeans
Date Posted: 21 Dec 17 at 7:40pm
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Yes its tricky if the guy to leeward has his nose in front, because then you are sailing in a header from the"lee bow effect", but if you can hang in which will inlvolve getting dropped back a bit you may then be able to climb up if you have sussed out how to point. and then can work out to windward and could finally come out on top.
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Posted By: Guests
Date Posted: 21 Dec 17 at 8:24pm
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Clean hull, good slot gasket, foils well maintained and aligned as per design intent. Boat upright and well trimmed, sails flat and slot small (jib sheeted about 9-10 degrees). I don't think there is a magic bullet, just lots of increments gains to be had to reduce drag.
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Posted By: Oatsandbeans
Date Posted: 21 Dec 17 at 8:34pm
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So its all about drag- so do you need full sails or flat sails?
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Posted By: 423zero
Date Posted: 21 Dec 17 at 8:48pm
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I was told by one of our old sailors, get well forward, dig the bows in, heel to windward for better gust response. Never done me any good though.
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Posted By: By The Lee
Date Posted: 21 Dec 17 at 8:50pm
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In waves the most important thing for height is how you steer over the waves. In addition to this alot of club sailor neglect the fact that height comes from flow over the foils thereby fail to realise that to sail high you need to sail fast.
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Posted By: davidyacht
Date Posted: 21 Dec 17 at 10:24pm
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Pointing ... tight mainsail leach, a little outhaul off, flat jib entry, plumb upright, full board;
As has been said, if you crack off a little, you will reduce drag and sail faster, which may result in sailing higher.
Ref. Starting; look at some YouTube starting clips, the key is to pull the trigger at the right moment, and crack off to get speed in a space that you have created to leeward.
I wish I could practice what I preach!
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Happily living in the past
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Posted By: Guests
Date Posted: 21 Dec 17 at 10:47pm
Originally posted by Oatsandbeans
So its all about drag- so do you need full sails or flat sails? |
It's about the maximising the lift to drag ratio, rather than minimising drag per se, but generally flatter sails would help point higher, Pointing high isn't necessarily the best option though.
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Posted By: zippyRN
Date Posted: 22 Dec 17 at 12:21am
Originally posted by A2Z
Clean hull, good slot gasket, foils well maintained and aligned as per design intent. Boat upright and well trimmed, sails flat and slot small (jib sheeted about 9-10 degrees). I don't think there is a magic bullet, just lots of increments gains to be had to reduce drag. |
basically
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Posted By: zippyRN
Date Posted: 22 Dec 17 at 12:23am
Originally posted by A2Z
Originally posted by Oatsandbeans
So its all about drag- so do you need full sails or flat sails? |
It's about the maximising the lift to drag ratio, rather than minimising drag per se, but generally flatter sails would help point higher, Pointing high isn't necessarily the best option though. |
also limitations of structure and /or class rules may mean that a theoreticla optimum is either not achievable or has such as small 'groove' for a particular class that a less than optimum but #'wider groove' setup makes for a better VMG
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Posted By: JimC
Date Posted: 22 Dec 17 at 7:11am
Originally posted by A2Z
Pointing high isn't necessarily the best option though. |
Exactly so. Any boat can point higher by flattening off the sails, sheeting ultra close and pinching up, but the end result is the entire fleet footing across your bows and leaving you in their dirty air.
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Posted By: davidyacht
Date Posted: 22 Dec 17 at 8:12am
Originally posted by JimC
Originally posted by A2Z
Pointing high isn't necessarily the best option though. |
Exactly so. Any boat can point higher by flattening off the sails, sheeting ultra close and pinching up, but the end result is the entire fleet footing across your bows and leaving you in their dirty air. |
Though always quite fun to have a National 12 when starting in a Handicap Fleet ...
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Happily living in the past
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Posted By: By The Lee
Date Posted: 22 Dec 17 at 8:21am
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There is definitely a place for having an effective high mode as it will really help you to manage your lane.
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Posted By: iGRF
Date Posted: 22 Dec 17 at 11:14am
I so miss being able to pump like a b**tard whilst stuffing the arse out of it off the line until there's room to foot off into. #nofunstartingindinghies
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Posted By: 423zero
Date Posted: 22 Dec 17 at 9:06pm
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why can't a boat like the Minisail point very well ?
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Posted By: JimC
Date Posted: 22 Dec 17 at 9:07pm
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the Minisail doesn't have the best rig, foils or hull shape for pointing high.
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Posted By: Rupert
Date Posted: 22 Dec 17 at 9:30pm
Get some speed up, get the chine in the water and you can get the boat pointing if you need to. Generally better to crack off a few degrees for speed, though. A decent sail set well helps a lot.
Mind, a lot of "pointing high" is actually spotting the lifts.
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Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686
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Posted By: 423zero
Date Posted: 22 Dec 17 at 9:36pm
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Will the Laser like battened sail fitted to my Sprint allow it to point higher than the simple Topper style triangular sail ?
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Posted By: iGRF
Date Posted: 22 Dec 17 at 10:10pm
The Mini sail is under foiled, needs a bigger centre board. It goes sideways if you try to point too hard.
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Posted By: Rupert
Date Posted: 22 Dec 17 at 10:20pm
That's where digging the chine in helps, but yes, they go better with a bigger board.
The sail won't make it point higher, but the greater power will mean you can pinch at times and maybe bleed the speed more slowly. Generally, keep the boat moving. Off the start line, ensure you have space to leeward. If you pinch when going slow, you will simply go sideways, and the low rig will be stuffed in dirty air. Make sure you can tack off and tack back into a clear lane, then build speed before you point higher.
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Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686
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Posted By: Guests
Date Posted: 23 Dec 17 at 10:18am
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It's worth splitting leeway from pointing. Pointing angle is heading relative to true wind and leeway is the angle between heading and course. Bigger boards reduce leeway, but don't improve pointing angle.
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Posted By: JimC
Date Posted: 23 Dec 17 at 10:41am
Originally posted by A2Z
It's worth splitting leeway from pointing. Pointing angle is heading relative to true wind and leeway is the angle between heading and course. Bigger boards reduce leeway, but don't improve pointing angle. |
I'm not convinced that's really a desirable split.
What we call leeway is simply the angle of attack the board must operate at in order to create enough lift to balance the sails. If a board is very undersize or badly shaped it may have to operate at a significant angle of attack to create enough lift, and that's going to be especially true of any foil that doesn't maintain good flow on the windward side, but its more about lift than anything else.
Once you have a board that's operating with decent attached flow both sides then extra area won't make much observable difference in a straight line at normal speed. Board size is really much more a differentiator when coming out of a tack when the board has to operate at very low speed with a lot of side load.
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Posted By: 423zero
Date Posted: 23 Dec 17 at 10:47am
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Regarding Centreboard size, is it length or breadth ? Or is it in relation to size of sail ?
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Posted By: JimC
Date Posted: 23 Dec 17 at 11:06am
Originally posted by 423zero
Regarding Centreboard size, is it length or breadth ? Or is it in relation to size of sail ? |
All and none.
The centreboard has to provide enough lift to balance the forces coming from the sail. Bigger sail, more force. A long thin centreboard can do that, so can a short fat one. The long thin one will do it with less drag, but will be less tolerant of being given too much work to do, at which point it will stall out. The short fat one has more drag, but will continue to create lift (with ever more horrendous drag) at angles where a long thin one will simply give up.so a compromise must be made, and the best compromise will be different for different boats.
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Posted By: 423zero
Date Posted: 23 Dec 17 at 11:57am
This is centreboard fitted to Sprint (long and thin ?) approx 38" long by 14" wide at widest point. Appears looking at depth of hull and sail size to be adequate, not noticed much leeway, probably need someone following to have a proper look.https://photos.google.com/photo/AF1QipNk9rVDCqP_NCaoebt0cBIcRnrYDO4GT6AUNsyT |
Posted By: Sam.Spoons
Date Posted: 23 Dec 17 at 1:03pm
That sounds pretty short and wide with an aspect ratio of 2.7:1. A high aspect board could have an aspect ratio of 5:1 or greater. High aspect ratio foils stall at a higher speed but generate more lift for less drag when moving fast enough. What that means is that a LA board will work better in a slow boat at sub planing speeds than a HA board. Once the flow over the foil is sufficient a HA foil will be more efficient (think gliders with long narrow, super high aspect wings)
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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"
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Posted By: jeffers
Date Posted: 27 Dec 17 at 12:50pm
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Pointing is useful sometimes. Off the start line for one or if you have slightly misjudged a mark.
Speed is also good and in some classes you get a better VMG by being a little bit off the wind.
I see this in club racing, my clubmate (who also sails a D-Zero) can always point much higher then me but I always go for speed if I have the room as I feel pointing is slow. Much better to get the foils to work than get that last degree of pointing. It shows in the results (he is usually behind me).
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Paul
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D-Zero GBR 74
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