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The formula to height

Printed From: Yachts and Yachting Online
Category: Dinghy classes
Forum Name: Technique
Forum Discription: 'How to' section for dinghy questions and answers
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=13156
Printed Date: 21 Sep 19 at 11:33pm
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Topic: The formula to height
Posted By: ClubRacer
Subject: The formula to height
Date Posted: 28 Aug 18 at 7:42pm
what is the key to pointing high when you've got sufficient wind over the sails that flow isn't important 

jib car positions/jib luff tension/jib leech tension

Mast rake/kicker/downhaul 

what does each of these do to your pointing



Replies:
Posted By: Sam.Spoons
Date Posted: 28 Aug 18 at 9:57pm
It's different for every boat so look at the CA tuning guides and tips from their top sailors. But, for detailed, non class specific advice buy a copy each of "Start To Win" by Eric Twiname and "Expert Dinghy Racing" by Paul Elvstrom.

FWIW jib car position affects jib leech tension and twist, set it so the twist matches the mainsail and adjust the slot to suit, jib luff is usually dictated by rig tension so see above, more rake is faster upwind but slower down, cunningham (downhaul) depowers and flattens the top of the sail by bending the mast, kicker increases leech tension and reduces twist (so more power offwind) but upwind bends the mast which depowers the sail and, depending on the class, you'll be controlling mainsail leech tension with the mainsheet so the kicker will be slack or with the kicker with the mainsheet controlling sheeting angle only. Every class has it's foibles and needs specific advice.


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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: Chris 249
Date Posted: 29 Aug 18 at 1:16am
As SS said, look up the class guides. As very general rules;

jib car positions - class dependent, as it relates closely to the slot which relates to hull shape, permitted sheeting angle, sail depth etc.

jib luff tension - easing luff tension allows for a flatter entry because the point of maximum draft moves aft, therefore increasing pointing.

jib leech tension - as with car position.

Mast rake - less rake equals higher pointing generally, but there's a lot of inter-relationship with other factors.

kicker - class dependent. On some boats, tighter kicker can tighten the leach and flatten the sail and allow you to point higher. On others, tighter kicker bends the mast and allows the mid leach to sag open.

downhaul - less equals higher. The draft moves aft, flattening the entry and tightening the leach. 


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Posted By: Rupert
Date Posted: 29 Aug 18 at 7:02am
And spot the lifts.

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Firefly 2324, Lightning 130, Puffin 229, Minisail 3446


Posted By: Sam.Spoons
Date Posted: 29 Aug 18 at 9:54am
BTW, the key is VMG which is a balancing act between pointing angle and speed, too high and the extra angle isn't enough to compensate for loss of speed, too low and the higher speed can't make up for the greater distance travelled.

Apologies if you already understand this (which I suspect you may well).......


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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: mozzy
Date Posted: 29 Aug 18 at 9:58am
anything which narrow the angle of attack is good, but the trade off is that many of these things also move the draft further back, close the slot and hook the leech. This stops the air leaving the aft of the rig efficiently, and chokes the sail, which will harm pointing (and massively speed). 

In practice, a lot of it is feel. There is a very fine line on slower dinghies between VMG and too high. 


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Posted By: davidyacht
Date Posted: 29 Aug 18 at 10:35am
In the original post, it is unclear whether you are looking for the ability to point high for short periods, or whether you have an inherent pointing problem.

If you are looking for short term pointing ... to lay a mark or squeeze another boat, then probably best to look at the controls and sheets to find a solution.

However if you feel that the boat simply doesn’t point, then you probably need to look at fundamentals ... such as mast set up which the tuning guides tend to cover well.  Also consider the condition and symmetry of your foils.  Sail upright and minimise rudder movements.

Whilst the ability to point when tactically required is a good thing, sailing free and fast, even if it is a knotch off pinching is in most classes a good thing.  Where I sail, occasionally it is important to pinch to get to windward of a moored boat, at this point it becomes blindingly obvious that pointing too high is slow.

In the Solo it pays to let a little foot off, and pull on some kicker, to get the lower leech to stand up if I want to point high.  In the Yawl, similar plus sheeting the jib hard to flatten the entry.

Worth noting that one of the easiest ways of getting past a group of back markers to windward (or leeward) is to crack off a little and sail through their lee.






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Happily living in the past


Posted By: fab100
Date Posted: 29 Aug 18 at 12:00pm
My favourite answer to "how can I point higher?" is "buy a longer tiller extension"

Michael McNamara in his talk at the dinghy show this year suggested the windward tell-tales need to be pointing vertically, not streaming horizontally - doing so gives a few degrees of extra height.

Often the elephant in room, when it comes to pointing is leeway. Ultimately, it's not which direction the boat is aimed but where it actually goes. The boat not being held flat, plate not fully down or stalled out, butting into on-coming chop and more all conspire to add leeway and result in failing to hold a lane.




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Posted By: Mike Holt
Date Posted: 29 Aug 18 at 1:58pm
Height is only really important off of a start line and when trying to hold a lane, as others have said VMG is the most important factor. Height generally comes with speed and flow over the foils. So pay as much attention to what is going on in the water as in the air.


Posted By: iGRF
Date Posted: 29 Aug 18 at 4:25pm
There's an old saying, where the head goes the body follows and until I once followed a really good lass in a Europe up a beat and then realised that there is no difference between the way I sail a board and the correct way to sail a dinghy, I didn't think it applied.
But whoever back there said about feel, that's the answer and even for someone like me who lives by feel, on sail craft, no tel tales, no little flag thing on top of the mast, it take a while to bed into a boat they are so much deader by comparison to real sailing on boards.

But having said that, twist the upper half of your body and look upwind at the same time as loosening the grip on the wiggle thing and let the boat 'hunt' for you, works wonders. Providing of course you have a well set up boat that isn't all weather helm like my little sailing joy the Solution. The Alto was equally good as I imagine would be a 505, and surprisingly if you could stop it rocking and rolling that RS200 was nicely balanced and not bad at all upwind. Now my little Mini sprint will point like a demon - and then slip sideways because it has a crap centreboard, so you have to dig the rail of the boat in a bit to try and stop that. Neither did I rate the Blaze in light weather, always thought it was under foiled,now a Phantom.. just sit there and enjoy your pies, it does all the work. Moral of the tale, they are all different but You have to learn first so you can tell the difference and that's taken me the best part of ten years.. And now I've got a boat which if you point it you die (Farr 3.7)so you have to foot it off, sail under the damned Lasers, let some speed build then the foils do the work and if there's not enough wind to get on the wire - sail something else.

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Posted By: ClubRacer
Date Posted: 29 Aug 18 at 5:36pm
correct me if I'm wrong here but my belief was

Jib luff tension (not rig tension) - would kill height by messing with the entry to the sail but open the leech of the jib. This when windy would help the slot and balance of the boat when the kicker moves the COE aft

Jib Leech tension (non boat specific, for example if you had a meter long jib car track you could go from a really tight foot to and next to no leech tension to tight leech no foot)- This is the one I'm struggling with, leech tension helps with the ability to point higher. But on the jib the leech has a second function to accelerate wind over the back side of the main, so would a tight leech disrupt this flow and kill your height more than you've gained?

Mast rake- this opens the leeches of the main and jib and moves the COE back. All i can see is this is a massive height killer, what is the purpose of raking the mast back as it gets windier?

Kicker, Moves the COE back but holds a tight leech when you need to sheet out, surely this is a big height killer too

Downhaul, Moves the COE Foward in exchange for messing with the entry to the sail. Also opens the leech at the top. 


So for maximum pointing ability you want;

up right rig so neutral helm
jib on hard with tight foot and near tight leech
jib luff tension just taking the slack so as to clean the entry to the sail up
No kicker but mainsheet tension on hard but not so hard it hooks the top leech
No downhaul- possibly to take the creases out the sail out and tidy the entry?


In terms of spreaders i presume; More length = stiffer mast, meaning you can point higher
More deflection= more pre-bend which would open the leech and kill height
Obviously with spreaders too much or too little can break the mast so this is theoretical only 


Posted By: Oatsandbeans
Date Posted: 29 Aug 18 at 6:06pm
On this one most sailors will have their own idea on how to get that extra height.
Here's mine-95% of what has beeen said alreday I would agree can be used to give you better pointing but ther is one thing that has not been mentioned- sail depth.
It is simple -for lots of reasons flat sails will point higher than full sails. Why do you see so many sails with different fullnesses around if flat sails are so good? Its because they are awful to sail with. They have no feel, no acceleration, power, and are completely gutless. The thing is that if you sail with them a lot you learn to manage these "problems" so they are not too much of an issue as you are pointing higher than the rest and you can rely on this as your "get out of jail card " on the racecourse. Bethwaite knew about this -have a look at his 29er sails compared to other similar dinghies-not much shape there at all!


Posted By: davidyacht
Date Posted: 29 Aug 18 at 6:07pm
I was told by someone much better than me, that some weather helm is good, since it generates lift from the rudder, therefore some of your list like rake, induce weather helm, which then induces lift.

I would suggest that a National 12 May be the ultimate pointing boat, and I think the key differences with the rig to many other boats is a very narrow sheeting angle and a very controllable mainsail leech.  


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Happily living in the past


Posted By: mozzy
Date Posted: 29 Aug 18 at 7:24pm
Originally posted by ClubRacer

Kicker, Moves the COE back but holds a tight leech when you need to sheet out, surely this is a big height killer too
Kicker flattens the sail. Coupled with moving the max depth back it creates a much tighter angle of attack. Kicker is good for pointing IMO. 


Originally posted by ClubRacer

In terms of spreaders i presume; More length = stiffer mast, meaning you can point higher
More deflection= more pre-bend which would open the leech and kill height
Obviously with spreaders too much or too little can break the mast so this is theoretical only 
More pre-bend would open the leech, but nothing that can't be shut back down with shorter strops and main tension. But pre-bend will set up a flatter sail, and a flatter sail has a narrower angle of attack. 

But like I said, most of these things move the draft further back, which aids pointing, but harms the efficiency of the sail, and can choke the slot, which kills VMG.

I point best with a fairly neutral sail set up, with a nice progressive curve, then build speed and feather for height. 


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Posted By: zippyRN
Date Posted: 30 Aug 18 at 12:01am
Originally posted by davidyacht

I was told by someone much better than me, that some weather helm is good, since it generates lift from the rudder, therefore some of your list like rake, induce weather helm, which then induces lift.

I would suggest that a National 12 May be the ultimate pointing boat, and I think the key differences with the rig to many other boats is a very narrow sheeting angle and a very controllable mainsail leech.  

however the near vertical  bow and  fine entry of the  National 12  ( and also the Merlin Rocket ) help with that as well 


Posted By: Fatboi
Date Posted: 30 Aug 18 at 8:30am
Originally posted by ClubRacer

correct me if I'm wrong here but my belief was

Jib luff tension (not rig tension) - would kill height by messing with the entry to the sail but open the leech of the jib. This when windy would help the slot and balance of the boat when the kicker moves the COE aft
This is incorrect. Tightening the Jib luff will do a few things though.
1) tighten the luff and it moves the draft right forward, this can give you a bigger 'groove' to steer in when windy. If you have a loose luff the entry to the jib is much finer and you will be able to get closer to the wind. 
2)Tighter luff will also close the leech more as it stretches the jib upwards and pulls the leech tight. 

Jib Leech tension (non boat specific, for example if you had a meter long jib car track you could go from a really tight foot to and next to no leech tension to tight leech no foot)- This is the one I'm struggling with, leech tension helps with the ability to point higher. But on the jib the leech has a second function to accelerate wind over the back side of the main, so would a tight leech disrupt this flow and kill your height more than you've gained?
Generally you will want to match the leech shape of the jib to that of the main and have the slot profile matching. If you have it set like this you will be good for most of the beat and get the hull and foils working in tandem, however there are situations where you would sacrifice speed for height over a very small period of time - say pinching for a mark  for 3-4 boatlengths where you may benefit from pinching as opposed to two tacks.

Mast rake- this opens the leeches of the main and jib and moves the COE back. All i can see is this is a massive height killer, what is the purpose of raking the mast back as it gets windier?
Depowers the boat and makes it easier to sail. In big wind, you often struggle to get the bow down and go fast as by being overpowered it forces pinching to lose power and you point high, but slide sideways as the foils are not working efficiently. 

Kicker, Moves the COE back but holds a tight leech when you need to sheet out, surely this is a big height killer too
Actually no. The kicker holds the leech firm and if you eased the main without it on, then your boom would rise and your leech would open. This would spill power and the height. 
With mainsail shape you want return on your leech when trying to sail in a high mode and point well.
You need to be careful though. Too much kicker means mast bend and a flatter sail, which wont help pointing either. 

Downhaul, Moves the COE Foward in exchange for messing with the entry to the sail. Also opens the leech at the top. 
Yes, only want this when depowering. Often the last control to be pulled on. 


So for maximum pointing ability you want;

up right rig so neutral helm
If you have a bit of weather helm it will mean that you can feel the pulling on the rudder and sail the boat flat but still have some feeling on the rudder. Often people set the boat up with no helm, but then heel the boat to get feel - so many things wrong with that!! 
jib on hard with tight foot and near tight leech
Would make a flat jib - might be good for flat water if you have lots of power, but if you are struggling for power you will need a bit of depth in the jib to drive the boat. If the leech is too tight, then it will backwind the main and close the slot - def not ideal! 
jib luff tension just taking the slack so as to clean the entry to the sail up
Spot on
No kicker but mainsheet tension on hard but not so hard it hooks the top leech
Depends on conditions. If lighter wind and you do not have to ease main to depower then spot on. 
When easing main to depower - start to kicker
No downhaul- possibly to take the creases out the sail out and tidy the entry?
Spot on - even some creases are fine





Posted By: ClubRacer
Date Posted: 17 Oct 18 at 8:43pm
Have had a reasonable amount of weather-helm for a long time but had the rig setup as per the guides etc so decided to do some on the water tuning this weekend

We raked the mast forward bit by bit until it slowly removed the weather-helm and did a race like it

I found the entry to the jib seemed to be a lot more flat but couldn't get my head around how. By raking forward you move the jib sheet tension more towards leech tension which would surely make the jib fuller? What ever I did it seemed to help as i was able to point a lot higher than everyone else and the boat felt like it was in a nice groove. Although now i think about it, it may have been more to do with getting my bow above the tide.

It also meant the mast rake was nearly 100mm more than the average of the class tuning guides but the rudder still didn't feel like I was used to in the 200. Could this be more to do with rudder rake? I remember I broke mine a few years ago at an open and borrowed someones new style rudder which felt completely different, so am debating re-drilling mine so its raked more forward. What is the correct position for the rudder to be raked at? My best guess would be a line from the top pintle to the bottom gudgeon extended, this line would be parallel to the trailing edge of the rudder or at least a little more raked forward 
 


Posted By: Sam.Spoons
Date Posted: 17 Oct 18 at 9:25pm
Parallel to the leading edge of the rudder surely? You definitely don't want the leading edge raked forward of vertical, that gives a very light rudder but little feel. 

From an earlier 'Club Racer' post :- "Mast rake- this opens the leeches of the main and jib and moves the COE back. All i can see is this is a massive height killer, what is the purpose of raking the mast back as it gets windier?"

I don't get this, raking the mast has no effect on mainsail leech tension (and I can't see how it affects jib leech tension but less sure about this one). Agreed that it moves CoE back. 




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Spice 346 "Flat Broke"
Blaze 671 "supersonic soap dish"


Posted By: Do Different
Date Posted: 21 Oct 18 at 7:00am
It is all so multi factored and different for every boat. Whatever you state someone will be able to find a situation that contradicts it.

Raking the mast back in wind demonstrably makes boats easier to sail and therefore faster for probably most classes but maybe for subtly different reasons.

Pointing the boat high is not the only or always the best way to get to the windward mark first. Think VMG and also remember that the boat doesn't necessarily go exactly in the direction it is pointing.



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