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Increasing mast rake in stronger winds

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=222
Printed Date: 10 Aug 20 at 6:12am
Software Version: Web Wiz Forums 9.665y - http://www.webwizforums.com


Topic: Increasing mast rake in stronger winds
Posted By: Andi
Subject: Increasing mast rake in stronger winds
Date Posted: 10 Sep 04 at 12:35pm

The accepted wisdom is that raking the rig back in higher wind strengths depowers it and/or makes the boat more balanced.   No-one has explained this to my satisfaction.  I sail an RS200 by the way.   When it's windy ( I'm talking about over-powered to the point where one is sheeting out the main regularly to keep the boat flat ) the main forces on the mainsail are ore towards the leech  and as this is further aft than the usual centre of effort I should have thought that raking the mast forward would bring the centre of effort and the centre of lateral resistance from the foils more in balance.

I know all the arguements about the jib slot being opened, the spreader angle changing and the jib fairleads being effectively raised so reducing jib leach tension but all of the these are miniscule effects when compared to the mast shape control caused by block to blocking the kicker.

Can any one help?  I've sailed all this year on one set of rig settings and have not noticed any difference in performance - we always come somewhere between 20-33% back form the winning boat at major events.

Any info welcome - Andi  ( PS sorry about the duplicate message in the wrong category )




Replies:
Posted By: Stefan Lloyd
Date Posted: 10 Sep 04 at 2:06pm
Originally posted by Andi

Can any one help?  I've sailed all this year on one set of rig settings and have not noticed any difference in performance - we always come somewhere between 20-33% back form the winning boat at major events.

I've never read a convincing explanation as to why increased rake de-powers, but it works. Why not try it next time it is breezy? How do you hope to get better if you won't experiment with different rig settings, or at least copy the ones the winning boats use? 



Posted By: Andi
Date Posted: 10 Sep 04 at 2:32pm

My point is that in the past I have changed mast rake in different conditions like every one else.  This year, 2004 I have made a decision not to and we don't seem to have made any loss in windy conditions in fact our best result this year - 8th overall was in a very windy Winter championship sailed in 30mph winds using what most people would call light wind mast rake. 

I'm not saying raking the rig doesn't work, I'm saying I don't know why it does and no-one ( including the experts I have asked ) can tell me why it should work ( at least not in a way that makes sense to me - and I have a very strong science background )

   - Andi



Posted By: JimC
Date Posted: 10 Sep 04 at 2:49pm
Originally posted by Andi

This year, 2004 I have made a decision not to and we don't seem to have made any loss in windy conditions


   - Andi



The truth is that boat tune really doesn't make very much difference. Your position in the fleet - any fleet from the tightest one designs to the most open box rules - is primarily defined by how good a sailor you are. Boat speed just represents a place or two each way. At the top of the fleet of course a place or two can be critical - the difference between 1st and 2nd. You beat the guys you would normally beat in HW while your mast is set up for lighter stuff because you're a better sailor than them in heavy weather. What tune might make a difference is between you and that bloke you're always scrapping with.

The other thing that everyone always forgets is that there is no scientific rule that says the most talented sailor must have the best tuned boat, but the best sailors boat is the one everyome wants to get the settings off.


Posted By: Andi
Date Posted: 10 Sep 04 at 3:04pm

A lot of good points in what you say.  My question about mast rake wasn't really about trying to improve our results - we've got a list as long as your arm of areas we need to improve; I was really trying to get my head round WHY raking the rig works ( if it does ) and what are the feedback effects evident in the way the boat handles and  experienced by the helm and crew that might confirm that the rig change was worth doing.

   - Andi

 



Posted By: redback
Date Posted: 10 Sep 04 at 5:02pm

I'd love to know why too, but remember keeping the boat level makes a huge difference to weather helm - more than mast rake, rig tension or whatever.  One significant way of affecting the relationship between rig and hull is to move the lateral resistance back - swing the centreboard back.  This also reduces the leverage and area, both commendable.  Even though it doesn't move it back, it helps on a Laser to raise it.

I wonder if by raking the mast back it puts more tension on the jib luff?

Further up the forum somebody said boat tune only makes a little difference to your fleet position.  I agree in most conditions, but in a real big blow it can make the difference between getting round or repeated capsizes and in some classes it makes the difference between keeping the stick in the boat or breaking it.



Posted By: redback
Date Posted: 10 Sep 04 at 5:09pm
I sail a 4000 and it is a great strong wind boat - if the tune is right.  If the sail is too full it flogs and this really slows the boat.  My rig is adjustable enough to almost completly flatten the top third of the sail and open the leaches which means that in winds of 30mph the sail isn't flogging and the boat really motors.  I would have thought the RS200 is equally capable - the RS400 certainly is.


Posted By: ChrisJ
Date Posted: 10 Sep 04 at 5:20pm

Is it: Rake the mast back in strong winds that helps in strong winds?

OR is it: Rake the mast forward in light winds helps in light winds?

Which is the "normal" setting for the boat? The normal setting for sailing is the light/medium wind setting, because that is the general winds we have in the UK. But is this the best setting for the boat?

 

If the strong wind setting is the correct one (wind travels across boundaries at right angles, the nearer vertical leach helps with the wind exit from the sail, this also helps to prevent the wind flowing up the sail and helps with it flowing horizontal), then raking the mast forward in light winds helps because:

Less wind means more power is needed. This means a straighter mast held in place by the spreaders and rig tension. Closed slots to keep as much wind as possible doing good work etc.



Posted By: Andi
Date Posted: 10 Sep 04 at 6:58pm

I have tried moving the centre-board back as an easy-to-do alternative way of making heavy weather beating more effective.  There is a very definate reduction in pointing angle or maybe it's just the tracking angle - either way we certainly dropped lower and lower compared with other boats.  Angling the centre-board back moves the centre of lateral resistance aft - this is the opposite of moving the centre of effort in the sail plan back so perhaps angling the board back needs to be coupled with super mast rake settings to get things back in balance or maybe the small reduction in foil area is responsible for the poor course made good.

I have not tried the combination of angled back c/b and super mast rake aft as in an RS200 the boom gets so low that the boat is hard to sail.  I did have a Topper Spice for a while and the accepted wisdom in that class was to rake the mast and raise the dagger board as much as 30% in high wind so maybe there is something in this idea ( it's just that no-one does it in the 200s ( yet! ) ) 

I find that as the wind pipes up we point higher and higher until we reach a point where we stall the foils and then we have to change mode completely and let the jib out a bit.  The extra fullness in the eased jib creates so much power that the main needs to be dumped a long way out to keep the boat up-right. This occurs about 25mph wind, after this point we are great at surviving but are well off the pace with a very poor pointing angle.

   - Andi

 



Posted By: Garry
Date Posted: 10 Sep 04 at 7:46pm
Have you tried moving the jib lead aft (further out) rather than easing the jib combined with increasing the luff tension (but not the rig tension)? Thus twisting the jib leech open at the top. Also is the reason you're pointing higher, because you're pinching, rather than easing a flattened main?

-------------
Garry

Lark 2252, Contender 298

www.cuckoos.eclipse.co.uk


Posted By: Andi
Date Posted: 10 Sep 04 at 8:27pm

RS200 jib leads do not go out sideways unfortunately.  They are quite long fore and aft but they are angled so that the sheeting angle from the centre-line is constant.  We sailed a Lark many years ago and you could adjust the jib sheeting angle in, out, up/down as you choose.  Some people do use a jib cunningham effect in the RS200 ( we are not allowed to have an adjustable jib cunningham but by tweaking the jib luff tie down you can get something of a downhaul effect but it never looks impressive enough to be worth fiddling round with 1mm string in very tight knots.)  I will have a go at this though as I am running out of options.

Yes we do end up in effect pinching but this is the only way of getting both the windward and leeward telltails flying in the higher wind speed with the very flat jib camber.  I would love to have an outward pulling barber hauler or a sideways track ( too much National 12 sailing I guess. )

If we have to ease the jib, it has to be eased a long way until the extra power from the fuller camber is countered by the increased twist and if necessary allowing the luff to lift upto 30% back from the jib luff wire.

We are getting the main nicely flat - we have a good downhaul and kicker and we are getting a nice barn door effect within the limits imposed by a soft mast comparable with the Proctor C on the Lark.  I am interested in your comment about pinching by having the main too far in.  Our pointing angle is surely set by the need to get the jib streaming efficiently and the main then comes in as far as we can get it while still keeping the boat flat.  ( We do sail very flat. )  Am I wrong in taking this approach?  Some one at the recent nationals said we were pinching.

   - Andi

 



Posted By: redback
Date Posted: 10 Sep 04 at 11:29pm
In the 4000 we ease the jib, but with the power of the trapeze the extra speed more than makes up for the extra distance.   I find pinching a mistake in any boat when its survival conditions.  In the Laser I used to raise the board and try and drive the boat off - the extra speed made the boat more responsive and thus less likely to go into irons.


Posted By: Andi
Date Posted: 11 Sep 04 at 8:21am

Yes, I still race a Laser at times ( usually a Radial at 10.5 stone ) The new Radial rig seems to be able to point high even in seriously windy conditions without stalling and without the need to raise the Dagger board.  Like you, I also used to sail with the dagger board upto 30+% up just to keep the boat moving without it going into irons.

Footing off doesn't pay in a 200 if other boats are still managing to point.  In the 200 pinching works upto about twenty odd mph wind ( as long as the waves are smooth - it doesn't work in a Grafham type chop ) and then as I said above we need to change mode and this is where we seem to go wrong - we end up easing the jib, it then powers up so we have to dump the main out a long way(pointing gone out the window) and then we have ragging sails or we bear away to get them to pull and are instantly over-powerd so we luff to depower and so we sail on the ragged edge, working like maniacs and going slowly with loads of leeway.  Maybe we just haven't enough weight in the boat to do this stuff properly ( 19.5 stone is a little light but not too bad )

   - Andi



Posted By: redback
Date Posted: 11 Sep 04 at 1:18pm
I think you're going to have to murder that main with more downhaul and keep pointing.  I hope you've got the jib fairleads further back than normal but the jib sheeted flat.


Posted By: Garry
Date Posted: 12 Sep 04 at 5:21pm
Try some of these links to links!

http://www.sailboat-technology.com/links/online_articles.php

http://www.drlaser.org/

http://www.sheridanhouse.com/reviews/physicsofsailingreview. html

http://www.wb-sails.fi/news/98_11_PerfectShape/Main.htm



-------------
Garry

Lark 2252, Contender 298

www.cuckoos.eclipse.co.uk


Posted By: Andi
Date Posted: 13 Sep 04 at 12:19pm

Thanks for the links.  Some very frightening tech stuff there and a lot of good ( hours and hours ) of study material.

On Saturday we had an open meeting at our club - Stewartby and I stuck to my "don't rake it back" guns.  It was mega windy - report on rs website and we went like a train.  I used a tad more rig tension - up from 330pounds to probably 380. ( This after reading about the jib luff sag effect.  I DON'T ACTUALLY UNDERSTAND THE EFFECT ON THE JIB LEECH THOUGH)  We kept pointing high with block to block kicker and as much downhaul as I could pull.  In the major gusts we had to ease the jib as well as the main and unlike previously we didn't get instatly over-powered.  Maybe the rig tension is the key?  Apparently our national champion doesn't alter mast rake either so maybe it's just a 200 thing.  Also as one of you helpful guys said, "Every one copies the fastest guy's settings even if he's not got the best ones.  A brilliant sailor with poor set up can still win and then the rest copy his poor settings"  I  paraphrase somewhat.  This was an entirely new idea to me.  Unfortunately it reinforces my "don't rake" stance when what I really wanted was for some one to talk me into believing that raking works so that I don't feel so lonely doing my own thing.

   - Andi



Posted By: Scooby_simon
Date Posted: 13 Sep 04 at 2:21pm

" I DON'T ACTUALLY UNDERSTAND THE EFFECT ON THE JIB LEECH THOUGH" - Bendy at the front = bendy at the back(leach) and so not the correct shape.

 

 

 



-------------
F16 GBR 553 - Hungry Monster - For sale
Wanna learn to Ski - PM me..
I also talk sport http://www.letshaveachat.com - here


Posted By: redback
Date Posted: 13 Sep 04 at 3:11pm

I think if your jib luff sags you end up with a fuller sail and a more hooked leach - not ideal in a blow.

Has anybody had the idea of having the top part of the sail curved the wrong way - ie like the top batten hasn't poped?  If you could sheet it properly you'd have a righting force at the top of the mast, in opposition to the heeling force further down!



Posted By: Andi
Date Posted: 13 Sep 04 at 3:43pm

It is starting to get a bit worrying about the amount of compression force on the mast with rig tension pushing 400pounds per shroud and eye popping downhaul plus bending it as far as the kicker will go!  Yes I know this reduces rig tension.  ( I don't know by how much - I'll have measure on Wednesday )

I'm interested to know if any one has any useful web links regarding rig tension as it affects a dinghy in the form of a more rigid jib luff.  Most books etc talk about jib luff tension in the form of stretching the cloth of the sail around a separately tensioned luff wire - ie a jib cunningham in Lark speak.

I presume that the mid point of a slack jib luff will get pulled aft and to leeward by the wind forces in the sail.  My next statements are questions really as I'm thinking aloud:  The aft deflectiion will create fullness in the mid-height part of the jib - bad.  ( Opposite of depowering the mainsail with kicker induced mast bend.)The leeward deflection would tend to increase the angle of attack at the mid height luff and also result in effectively over-sheeting the mid height part of the jib ( if there's a tight leach ) this would close the slot - bad.  But if the luff gets blown off to leeward maybe the leach goes to leeward with it regardless of leach tension, thia would be good as it opens the slot? No that's wrong probably, inless you can achive very little luff tension.  I guess this would work on a reach though where a wide slot with little jib leach tension and a twisted sail are good.

And I haven't a clue how the jib sheet forces will affect the luff shape.  I'll have to have a look at this by setting up a vey low rig tension and try sheeting the jib on hard.

   - Andi



Posted By: redback
Date Posted: 14 Sep 04 at 8:14am
I look forward to your results.  Have you noticed the forum further down on Rig Tension?


Posted By: Stefan Lloyd
Date Posted: 14 Sep 04 at 7:23pm
Originally posted by Andi

I'm interested to know if any one has any useful web links regarding rig tension as it affects a dinghy in the form of a more rigid jib luff. I presume that the mid point of a slack jib luff will get pulled aft and to leeward by the wind forces in the sail.  My next statements are questions really as I'm thinking aloud:  The aft deflectiion will create fullness in the mid-height part of the jib - bad.

I don't have such web links but I did once spend several hours tuning a keelboat rig and checking forestay tension with a gauge. On a keelboat, pointing ability and windward boatspeed are very related to jib sag, which in turn is determined by forestay tension. I found the relationship between rig tension, mast bend and forestay tension was more complicated than I thought it would be. On that boat at least, you needed a fairly straight mast to maximise forestay tension. If you allowed the mast to bend much, the compression reduced forestay tension. Therefore you could increase rig tension but decrease forestay tension, which I hadn't expected before I tried it.

My point is that there are complicated inter-relations in rig tune, which are often class-dependent. Therefore general tuning guides may make statements which are not true for your class.

Now relating my first paragraph to mast rake, I wonder if more rake allows you to use more rig tension to increase jib luff tension rather than increase mast bend. I'm really not sure. On my keelboat, the whole class used the maximum allowable rake anyway, so it wasn't a tuning variable. However I used to sail Merlin Rockets and there is no question whatsoever that in that class, rake is the most effective way to depower. The whole history of rig development in the class over the last 10-12 years has been to allow easier adjustment of rake. That is why the class has moved from hog-stepped to deck-stepped masts, despite the constructional difficulties this has caused.

I also think your suppositions on why excessive jib sag is bad are correct.

 



Posted By: Andi
Date Posted: 14 Sep 04 at 7:59pm

Interesting that the Merlins are convinced about raking as a means to depower. ( I wonder if you mean de-power or mean re-balance the helm? )  I'll have to look at their web site to see if they have any theories on WHY this is so.

- Andi



Posted By: jeffers
Date Posted: 15 Sep 04 at 8:28am

After having a 2 day training session run my none other than Adam Bowers he explained all about depowering (it was a windy weekend).

Basically the effect of raking the rig moves the centre of effort back (which means you need to move back down the boat). Also it helps to open the 4th corner of the sail (along with using cunningham) and allow the wind somewhere to exhaust without creating additional power.

For those who seem sceptical try it! You can easily see the 'flattening' of the leading edge of the sails but stand behind the boat and get someone to pull the cunningham hard on and just watch the 4th corner fall away. I can spot it on mt Laser quiet easily but it twns to be mor noticable on a boat with a full length top batten (such as a Fireball, Scorpion,. Werlin) as the batten just falls away.

On a boat with a jib you also need to make sure you reset the jib cars as this has a huge effect on the jib leech which in turn affects the slot. Basically a reasonable rule of thumb is up and in for light winds (gives you a very open leech) and out and down for heavy winds (closes the leech).

Just my 2p....

Paul



Posted By: redback
Date Posted: 15 Sep 04 at 12:36pm

If you rake the mast back but maintain the same shroud tension you should find an increase in forestay tension and hence less jib luff sag.  This is theoretical and I'll check it ASAP.  Is this why the boat goes better in a blow with a raked mast? 

Here's another point, when you measure the rig tension do you measure the shroud or the forestay?  The forestay is awkward but that's where you should measure.  Next time you have the gauge on your boat you'll be able to notice that the shroud tension is higher than the forestay tension, that's because the forestay is at a wider angle to the mast.  This is not theoretical - I have measured it.



Posted By: redback
Date Posted: 15 Sep 04 at 12:56pm

If it weren't confusing enough, there are several guages in use for measuring rig tension.  Probably the most popular is the Loos guage but that comes in 2 varieties - old and new.

If you follow this link on the Laser 4000 site you'll find a conversion chart on page 1.  I think we should say thanks to the guy who took the time to produce and publish it - so thanks.

http://laser4000.lasersailing.com/docs/Tuning_Guide.pdf - http://laser4000.lasersailing.com/docs/Tuning_Guide.pdf



Posted By: Barty
Date Posted: 15 Sep 04 at 2:42pm

Jeffers

Next time you see Mr Bowers ask him if he can explain in laymans terms why mast rake helps in a blow.  I have spent a good few hours (and pints) discussing this with him and as yet have been unable to do it.  4th corners are great but try and explain it without being technical e.g. "the centreboard stops you going sideways" etc



-------------
http://www.highlandtopper.com - For Topper boats & spares in Scotland-highlandtopper.com


Posted By: Andi
Date Posted: 15 Sep 04 at 9:36pm

Before our wednesday evening race I had some time do measure some rig tensions.  On our RS200 340pounds on the shrouds gives a jib luff wire tension of about 270 pounds with our normal mast rake.  I didn't have time to alter the mast rake to test redbacks rake versus jib luff tension theory. But I did try putting full kicker on and re-measuring rig tension - the shrouds tension dropped by 70 pounds while the jib luff wire tension remained pretty much unchanged.  I can understand the drop in shroud tension - a bent mast is shorter than a straight one so the shroud tension is reduced.  I really am struggling to figure out why this doesn't lead to a corresponding reduction in jib luff wire tension.

By the way full mainsheet tension caused a similar reductioin in shroud tension - mast bend again I suppose.

RS200 officionados suggest that light crews should reduce rig tension in heavy weather so that the mid mast comes up to windward and opens the jib slot, they don't talk much about jib luff sag.

An american 505 website was very imformative and gave me the idea of observing luff sag by using elastic to tension the forestay and then gauge the gap between the forestay and jib luff.  Of course the wind will cause some curvature on the forestay but it seems an idea worth trying.

   - Andi

 



Posted By: Scooby_simon
Date Posted: 15 Sep 04 at 11:40pm

forstay tension stays the same because (I think, and it's late as I was up at 05:50)

 

1, Base of the mast is fixed

2, Base of the forestay is fixed

1 and 2 mean that the base of the forstay/deck/mast triangle is fixed

3, Mast is bent so (may) move back a litte

4, Mast is bent so (may) move down a little

5, Mast is bent so the 'back' of the triangle (may) have reduced slightly

3,4 and 5 mean that the top of the tringle (may) have moved a little back and down but may still be the same distance from the base of the forestay, thus no change

Shouds are forming a different triangle where 3,4 and 5 mean the distance from the shroud plate on the Hull (or hulls  ) has reduced.

 

QED  (I think)

 



-------------
F16 GBR 553 - Hungry Monster - For sale
Wanna learn to Ski - PM me..
I also talk sport http://www.letshaveachat.com - here


Posted By: jeffers
Date Posted: 16 Sep 04 at 12:07pm

Barty,

I am unlikely to Mr Bowers until the next Fireball training event next year.

It is hard to explain the effect of cunningham and mast rake without getting a bit technical but here goes...

Basically if you rake your rig (forestay tension stays the same on a Fireball) then what happens is the wind start to travel up the sails as well as across (watch your jib tell tales, the bottom one is normally horizontal, the top one can be as high as 60 degrees from horizontal). The rake accentuates this effect allowing more wind (and with it the excess power) to effectively exhaust harmlessly out the top of the sails.

I am not going to try and explain 4th corners because I was so confused when it was explained to me. Best bet is to rig a boat and then stand behind it (with the sail sheeted in) and watch someone pull cunningham on and let it back off again, it is blindingly obvious, just make sure you are looking up near the top of the sail (top batten on a Fireball will give you a rough position).

If I get a chance this weekend I will try and get some photos becuase I am instructing and that is one area the people want to cover.

Paul



Posted By: Barty
Date Posted: 16 Sep 04 at 12:31pm

Jeffers

As I said in my previous message, I have discussed this with Adam.  I have the 4th corner/Jonny and the perfect hill T-shirt etc.  I know the three fundementals (as quoted by Aam) of a sail.  I have a degree in yacht design..........BUT and its a BIG BUT......I can't explain to a beginner why mast rake works without being technical.  Most other things like the example I quoted about the centreboard, are easy to explain without getting in cross-flows, deflection points etc.

Just a thing that amuses and drives me wild at the same time....nothing more!!!!



-------------
http://www.highlandtopper.com - For Topper boats & spares in Scotland-highlandtopper.com


Posted By: redback
Date Posted: 16 Sep 04 at 1:57pm

Getting back to Andi's rig tensions.  I believe the kicker is terminated very close the the bottom of the mast on a RS200, there will therefore be little extra tension applied to the forestay.  Just look at the Laser - because the kicker is actually terminated on the mast it does nothing to pull the mast back - it simple bends it.  My Enterprise however has the kicker terminated at the bottom of the bulkhead which gives considerable leaverage over the forestay of its deck stepped mast.

Like Andi my suspicion is that the increased kicker bends the mast and thus shortens it, which is why the shroud tension is reduced.  Mainsheet however should increase the forestay tension, but since it is applied through a flexible lever (the mast) it doesn't increase it by very much.

On larger boats they use runners to tension the forestay.  This whole discussion is very enlightening, since I have just twigged that my kicker on my Laser 4000 does virtually nothing to tension my jib luff.  What my kicker can do is break my lower shrouds but that's another story.



Posted By: Andi
Date Posted: 16 Sep 04 at 9:52pm

You are correct the kicker in an RS200 is terminated right at the mast foot so there is no direct effect on the jib luff wire tension when you pull the kicker on.  I would have thought mainsheet tension would have affected jib luff wire tension but apparently not.  When you think about it though you have a 2:1 mainsheet system with say 35 pounds sheet tension.  Multiply by 2 = 70pounds.  This however is applied to the the end of the boom and then to the upper mast via the mainsail leach which gives a mechanical disadvantage ( mast is longer than boom ) of say 2:1 giving 35 pounds again.  The mast pulls the forestay at an angle which gives again a mechanical advantage of !!guess!! 2:1 which should give an increase in jib luff wire tension of 80 pounds.  Phew!  BUT, the mainsheet causes a lot of mast bend on a 200 which I have measured as reducing shroud tension by 80 pounds ( each side ) 160 pounds reduction in shroud force applied to the mast at a disadvantageous shroud angle ( empirically arrived at mechanical ratio of 2.5 : 1 ) gives a reduction in jib luff wire tension of 64 pounds.  This just about totally cancels out the increase injib luff wire tension caused by the aft pull of the mainsheet via the boom via the leach.

I haven't had time to do any proper maths, I need angles measuring and I need to try to remember all my old physics stuff but I think my basic point is valid that the jib luff wire tension is left pretty much unaffected by mainsheet tension because of the two opposing effects.  A stiffer mast would give very different results as the mast would not bend so much when mainsheet tension was applied so it would bend-shorten and loosen the shrouds..  A taller mast or rather higher aspect ratio would also reduce the effect of mainsheet tension on mast bend ( you are pulling back the mast aft from a more disadvantageous angle.)

   - Andi        PS  That lot has done my head in and it has left a major piece of maths work to calculate the effect of mast rake on the inter related angles and how they increase or decrease the opposing forces.  It also might be simply beyond me!



Posted By: redback
Date Posted: 17 Sep 04 at 9:10am

Of course the really good sailors get by without the maths and just seems naturally to do the right thing.  Less able guys like myself have to work it all out in the hope that it improves our performance.  What I have noticed though is that it is very easy to concentrate too much on one aspect of sailing to the detriment of overal performance.

Years ago when I moved from the sea to a lake I really got into windshifts and for the 1st season I used to tack myself to a standstill.  However the following season when I had got things back in proportion I did have the boat speed of a sea sailor and the cunning of a lake sailor - enough for club level trophies anyway.



Posted By: Stefan Lloyd
Date Posted: 17 Sep 04 at 10:24am
Originally posted by Andi

Interesting that the Merlins are convinced about raking as a means to depower. ( I wonder if you mean de-power or mean re-balance the helm? )  .

- Andi

I mean de-power.

 



Posted By: Stefan Lloyd
Date Posted: 17 Sep 04 at 10:29am
Originally posted by redback

On larger boats they use runners to tension the forestay. 

True up until a few years ago. Modern designs have almost all dispensed with runners because user-error with them results in a broken mast, which spoils your day.



Posted By: Phil eltringham
Date Posted: 17 Sep 04 at 2:01pm

I guess (and tell me if this is completely wrong) that the basic idea behing all the 'depowering' techniques is to get the mast to match the luff curve of the sail thuss making the front part of the sail flatter and depowered.  Raking the mast induces more bend (If the base of the mast is fixed - does this apply to the Meerlins??) and so the luff curve of the sail produces less shape or belly in the sail and so less 'power' is produced (also less drag). 

As far as moving the centre of effort of the sail around is concerned I guess in strong winds you are looking to move it lower predominately and also frowards to balance the probable heel on the boat (though it should be flat) and the fact that the rig is now further aft to get the sail flatter.  Pulling the kicker on tentions up the leech (especially the lower half to two thirds) curves the bottom of the mast and flattens the sail further.  The cunningham, especially on sails with a full top batten allows the top third of the sail to 'blade off' as jeffers explained, which will help to move the centre of effort down reducing the sail's heeling moment and thus the amount you have to hike

Having said all of this, there is no substitue for good boat handling, a couple of dodgy tacks or a swim in the breezy stuff will cost you at least as much as not quite having the boat set up 100%. 



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FLAT IS FAST!
Shifts Happen


Posted By: redback
Date Posted: 17 Sep 04 at 3:09pm
Agreed.  I would like to point out that all this raking the mast backwards and forwards does not affect weather helm very much at all.  A far more significant cause of weather helm is boat heel.  If the rig is over the leeward side of the boat its bound to luff the boat.  Flat is fast - especially when its windy.


Posted By: FreshScum
Date Posted: 17 Sep 04 at 4:19pm

What is the thinking behind boats that drop the rig back as they sail into gusts, 470s 505s?

Is it just about acceleration and opening the slot combined with moving the cars back or something else?



Posted By: Andi
Date Posted: 17 Sep 04 at 4:35pm

Aft mast rake doesn't do much of what every on is claiming for it.  Lots of people have talked about sail setting techniques and sailing the boat flat, but no-one has put up a significant arguement supporting aft rake in strong winds.

Raking our mast from fully forward to fully aft ( within the range described by all the tuning guides)  moves the top of the mast 300mm.  Centre of mainsail effort therefore moves aft about one third of this.  Centre of effort from jib moves aft hardly at all  This might affect boat balance - weatherhelm slightly. 

With (guess) 20 foot mast this 300mm mast tip movement corresponds to an increase in rake of 2.8 degrees.  This ain't going to cause wind to flow differently enough to depower the rig.  Neither is it going to lower the height of the centre of effort much ( about 8mm I guess!)

With a deck stepped mast the spreaders induce an extra 10mm prebend with the extra rake.  ( negligible when compared with the kicker which when on tight causes about 300mm extra bend )   With a floor stepped mast the extra prebend might get to 20% of spreader deflection ie about 30mm?  Not much then.

The only strong point in favour of mast rake is that the jib clew comes lower giving a lower sheeting angle - more foot tension and more twist but moving the fairlead back does this on most boats.

I'm not convinced about mast rake!!!!

   - Andi



Posted By: redback
Date Posted: 17 Sep 04 at 6:27pm

On my boat (L4000) I have lower shrouds and therefore rake is a quick way of adjusting them.  When I rake the mast back it opens the jib leech and eases the lowers.  It barely affects mast bend aloft.  We have discussed the benefits of opening the jib leech but easing the lowers is doubly beneficial.  1. eased lowers allow more mast bend and this flattens the mainsail and makes the slot wider.  2. eased lowers makes the rig more flexible, it has a more springy feel and this help absorb the gusts which are more violent in windy weather.  Indeed I find the boat goes better even in gusty light winds with eased lowers (which I ease by moving the pins).  It doesn't point as well though and it is less powerfull, but it accelerates much better.

Talking of flexible rigs.  You can get the same mainsail leech tension in two ways. 1. kicker, 2. mainsheet.  Using kicker gives a more accelerative rig more able to respond automatically to gust, less powerfull ultimately but makes life a lot easier for the crew since they don't have to move around so fast.  With the kicker slack and main used for leech tension the helm has to play the main a lot since the boat is less forgiving and the crew is in and out like a yo-yo, however the boat will feel more powerfull in the gusts.  Combine this with mast rake and changing the tension of the lowers and you have a fair few variables to get wrong.

On my boat it is possible to have an upright mast, tight lowers and leech tension by mainsheet and in any sort of gust the boat produces massive heeling force (even in a F2), the crew goes out on the wire, the centerboard stalls and the whole lot starts going sideway.  Those with a more forgiving rig simply sail away from you. 

I remember crewing a RS800 on several occasions when we were already moving with speed and the helm pulled the main in too far.  The boat slowed so quickly it felt like you'd sailed over a mooring warp, it then went into irons and we went swimming.



Posted By: Andi
Date Posted: 18 Sep 04 at 8:31am

IWe had a Topper Spice twin trapeze for a while and yes; mainsheet tension and no kicker and we had way too much power in 10mph wind.

I can see that on boats with stiffer masts and kicker not mounted on the mast ( ours practically is ) (and probably with a less neutral spreader setting than we use) the increase of mast rake does cause various secondary changes:  lower shrouds slacken, spreaders induce more pre-bend, jib leads effectively move up and aft.  Kicker not on the mast like in an Ent is good because you get more jib luff wire tension when you use kicker ( especially if you have stiff mast which doesn't counteract all the extra luff tension by bending so much that it slackens the shrouds and hence the jib luff.

   - Andi



Posted By: PhantomHelm
Date Posted: 07 Nov 04 at 5:58pm
I thought the idea was that dropping the mast back reduces rig tension, allowing the mast to bend off sidewards in gusts and hence depowering?


Posted By: redback
Date Posted: 13 Nov 04 at 11:01pm

Originally posted by PhantomHelm

I thought the idea was that dropping the mast back reduces rig tension, allowing the mast to bend off sidewards in gusts and hence depowering?

I've tried that and it works a bit, but in my class we move the pins for the shrouds and retension to get the same rig tension and that works even better.



Posted By: PhantomHelm
Date Posted: 14 Nov 04 at 5:07pm
Yes, you can do that but it's a hell of a lot more difficult to do on the water!  What I usually try to do it drop the mast back on an adjustable forestay when beating, and then retension the rig when reaching for maximum power.  Difficult to do this by adjusting the position of chain plates/stay adjusters.


Posted By: redback
Date Posted: 16 Nov 04 at 12:35am
Yes it is difficult but here's a cunning plan.  In strong winds put 2 pins through the end of the shrouds and this gives the extra a rake.  If the wind dies off whilst afloat you can then ease the rig tension, pull out the bottom pins and retension. And hey presto the rake is reduced and no danger of losing the rig over the side.  We don't worry too much about too much rake ruining our off wind performance since we bang up our 18m gennaker.


Posted By: Andi
Date Posted: 16 Nov 04 at 5:55pm

I like the sound of but don't understand the two pins idea.  We use two pins but the upper one is there only as a retainer to trap the wider part of shroud terminal in place - I wouldn't like to rely on a fully tensioned shroud staying in place - the pin might bend a bit.  What type of chain plate and shroud terminal do you have?

I have started raking the rig again in the mental winds we have been having through Sept/Oct.  I do this ONLY to achieve an open upper jib leach as the RS200 jib tracks are basically in the wrong place and don't go far enough aft.

With a single sail like a Phantom dumping forestay tension sounds like an excellent idea as a means of increasing rake ( no jib luff to worry about )  Reduced mast support at spreader height should allow windward bend and the upper mast to fall off ( even more than the ( you lucky sods) carbon stick would normally do. 

   - Andi



Posted By: redback
Date Posted: 17 Nov 04 at 12:09am
Hi Andi.  You'll find you can get two pins through the eye of the shrouds, one above the other.  Hence if you slaken the rig and pull the bottom one out the mast will rake further forward, and there's no danger of losing the rig over the side.  It can be done whilst afloat.


Posted By: Andi
Date Posted: 17 Nov 04 at 4:04pm

I like the sound of this but our shroud terminals have only a round hole the same diameter as the pin.  I will have to see if we can get some shrouds made up with the same terminal as yours - our system works securely for on the water rig changes but it is a fiddle in choppy water trying to line up the pin with the hole.

- Andi 



Posted By: Barty
Date Posted: 04 Jan 05 at 3:07pm

After extensive testing we have found that mast rake on the Playmobil Catamaran makes little difference in performance.

Can anyone confirm this?

[see 'Playmobil Review' topic under For the Magazine]



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http://www.highlandtopper.com - For Topper boats & spares in Scotland-highlandtopper.com


Posted By: NeilP
Date Posted: 06 Jan 05 at 4:32pm

The whole point of changing mast rake is that it affects many different aspects of the rig - nearly all of them in exactly the way we are looking for in a breeze. The obvious one is the slot becoming more open, but the change in spreader/shroud geometry allows the mast to bend more, flattening the main and opening the leech, which also moves the centre of effort of the main forward somewhat, helping with balance. I could go on and on, but the fact is it works. I've sailed a Flying Dutchman for some ten years now, and raking the mast in a breeze is the only way to sail it. Fully powered-up in 10 knots, and as the breeze builds we rake the mast, pull the board back in it's slot and just go faster and faster!!

If you are not convinced about rake being fast, I would strongly suggest you go for a blast in a boat that you can adjust on the water with string. If anyone wants a go, I can convince you in 30 seconds.

Neil



Posted By: Lucy Lee
Date Posted: 06 Jan 05 at 4:34pm
Did anyone else notice that this thread is mentioned in 'Roll Tacks' this week as a cheap alternative to paying for an RYA coach ?

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Fly Cherub!


Posted By: Harry44981!
Date Posted: 06 Jan 05 at 4:39pm
well there is at least 2 coaches i that are on the forum, and lots of other good sailors.

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Posted By: Barty
Date Posted: 07 Jan 05 at 7:44am
Make that at least 3 !

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http://www.highlandtopper.com - For Topper boats & spares in Scotland-highlandtopper.com


Posted By: sailor girl
Date Posted: 07 Jan 05 at 4:48pm
Who are they?

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Sailor Girl, Queen Of The Forum!


Posted By: Harry44981!
Date Posted: 07 Jan 05 at 5:00pm

Garry and Jon Emmett- i hope they don't mind me saying.



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Posted By: Garry
Date Posted: 07 Jan 05 at 5:01pm
Jon Emmett is one

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Garry

Lark 2252, Contender 298

www.cuckoos.eclipse.co.uk


Posted By: fantasia
Date Posted: 07 Jan 05 at 6:07pm

I agree that raking the rig does most of the right things in a breeze. The difficulty I have is to find the optimum upright position for light breezes. I find that the recommended upright position for my class (Wayfarer) tends to cause the slot to be too closed and easing the jib and main causes lack of pointing ability.

Therefore I usually sail with the rig raked all the time. Any ideas?

John H W7628



Posted By: redback
Date Posted: 07 Jan 05 at 6:21pm

I reckon in the really light stuff its best to rake it back a bit.  Only in light to medium strength should you use the most upright setting and even then I'd expect there to be about 20 inches of rake between the masthead and the gooseneck.  And let's face it you shouldn't worry about it being too raked for off-wind work since most of your drive will be coming from the kite.  If I was sailing a National 12 I'd be more fussy.  I'd be inclined to have a means of loosening the leeward shroud though so that the boom can go out further.

I must point out that I'm not a Wayfarer sailor though but I'm a firm believer in doing what the good guys do until you can do it better. Or to put it another way (and I've seen plenty try this) a poor sailor is not suddenly going to beat the top guys by doing something different.



Posted By: Garry
Date Posted: 07 Jan 05 at 6:39pm
I'm not a coach - only an instructor although I have been doing it for a long time both Full time and, for the last 20 years part time(maybe SI this year).

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Garry

Lark 2252, Contender 298

www.cuckoos.eclipse.co.uk



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