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Spreader set up

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=12919
Printed Date: 08 Dec 19 at 10:21am
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Topic: Spreader set up
Posted By: H2
Subject: Spreader set up
Date Posted: 23 Nov 17 at 4:43pm
Please do not roast me - I am going to fess up and admit that I am not 100% sure how spreaders work!

So my mast on the H2 is one of those lovely carbon super spar things, we have an adjustable forestay but no lowers. I picked up an idea that if you are at the top end of the weight range you might want to make the spreaders longer and angle them more forward (less sweep). Can I ask why?



Replies:
Posted By: JimC
Date Posted: 23 Nov 17 at 5:06pm
Spreaders use the tension in the shrouds to push the mast about. So if the spreaders are deflecting the shrouds aft then the mast is pushed forward, and if the spreaders are deflecting the shroud forwards then the mast is pulled back. So effectively the further forward the spreaders, the straighter the mast is and the stiffer it behaves. With sideways deflection its much the same principle. However the difference is in static trim the spreaders are pushing against each other, tending to lock the mast upright. When the crew weight comes on it tends (except for trapeze boats) to increase the tension in the windward shroud and decrease in the leeward, and tries to push the mid mast to leeward.

When you get to multispreader ris with checks and things there are all sorts of complications.

Does that make sense? I could maybe do sketches later if it helps.


Posted By: Guests
Date Posted: 23 Nov 17 at 5:17pm
The mast is held up in a triangle of fore-stay and shrouds. Where the mast is held at the hounds is determined by the relative lengths of the shrouds and forestay (rake and rig tension). 

Where the mast sit further down within the pyramid is determined by the spreader rake. They push the mast about relative to the shrouds (and the hounds and the mast step).   

If you rake the shrouds forward, it pulls the middle of the mast back (relative to hounds above and mast step below). This straightens the mast. Straightening the mast pushes fullness in to the sail. Fullness means more power, up to a point where the depth is too much and you stall / can't point / close the slot. 

If you rake the spreaders back, if pushes the mast forward in the pyramid and relative to the hounds and step. This stretches out and flattens the sail. 

Spreader length or 'poke' I find harder to define. To me, the wider the spreader the more stiff the mast feels as you're widening the base of the triangle at the spreaders and making the mast more stable. So for a given rig tension it will stop the rig bending off as much under load. 

If you're light weight, you may want to rake back the spreaders to de-power and increase pointing / reduce drag. Spreaders width I think is more of a personal preference on how you want the rig to react to load, but typically in gusty places or lighter sailors it's better to go narrow to allow the mast to bend off when a gust hits. 

It's then weighing up downwind where you'll want straighter stiffer mast to upwind where you're looking to minimise drag and not stall in gusts.  

The other important thing to mention is rake. Raking the mast back will create more mast bend assuming you keep everything else the same. I find it better to set spreaders for what I generally think is good, then use rake to depower the rig before a race (but in the 200 we have to go in to iron to adjust rake on the water). Rake is usually far easier to adjust on the day and I feel has a larger impact. But that depends how easy all these things are to adjust on your boat though. 


Posted By: H2
Date Posted: 23 Nov 17 at 5:28pm
OK so if as a general rule I want more power from the rig then its logical to make the spreaders longer AND move the tips toward the front of the boat so that the mast has less bend. Lets do that first then come to mast rake! Sound right?


Posted By: JimC
Date Posted: 23 Nov 17 at 5:33pm
Yeah, roughly speaking. The big caveat is that you lose gust response if the spreaders are pulling the mast back, and you can end up with power you can't use. especially if sailing in gusty unpredictable conditions.


Posted By: H2
Date Posted: 23 Nov 17 at 5:37pm
Originally posted by JimC

Yeah, roughly speaking. The big caveat is that you lose gust response if the spreaders are pulling the mast back, and you can end up with power you can't use. especially if sailing in gusty unpredictable conditions.

Got it - but I will try not go that far and besides the mast is very good at bending in gusts and depowering already so I would rather trade some downside for more power especially as I am built like an ape and love hiking my nuts off!


Posted By: ian.r.mcdonald
Date Posted: 23 Nov 17 at 5:47pm
informed and detailed responses to a sensible question. Nice one guys!


Posted By: Wiclif
Date Posted: 23 Nov 17 at 6:12pm
Im a bit late here, but when I was learning about spreader effects I drew the mast with stays and a gentle bend (as if it had no spreaders) viewed both from the side and from the stern, so you have two separate drawings.

Then add the spreader in a choice of positions, but not connected to the stays. Then imagine the stay attached to that spreader and you can then see what effect the spreader has.

If the spreader is too long then there will be an S bend in the mast in its lateral bending. This is usually considered slow, but I did have this in one boat with this setup and it was fast. My golden rule is, if its fast then use it, it doesnt matter what the text books say. I am not necessarily recommending this setup though!

Rig tension is another variable. Most people will set the rigging up ashore to a known rig tension. Whenever you start bending the mast to what your setup would be in a blow it is quite possible to halve the rig tension on the shrouds.


Posted By: davidyacht
Date Posted: 23 Nov 17 at 6:53pm
I sailed H2 101 a couple of years back in a lot of wind and found the rig to be quite brutally on/off but I am pretty sure that this could have been improved by letting the forestay off and making the mast a bit more dynamic.

I suspect that I would concentrate on keeping the lower mast pretty straight athwartships by lengthening the spreaders, since it is not like a two sail boat where you are trying to open the slot In the gusts.  That way you could concentrate on calibrating the fore and aft bend for a given wind strength.  

One thing that I did not quite get is the absence of any control of the lower bend, but I guess that all H2s have the same set up.

If I had one I am sure that I would get great reward from buddy tuning, to help with set up and calibration.

It might also be worth talking to HD to establish how they envisaged the mast/spreader/forestay setup.


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Happily living in the past


Posted By: Sam.Spoons
Date Posted: 23 Nov 17 at 7:06pm
Deck stepped mast and no lowers is a little unusual with a modern rig, clearly the designers had a good reason and I'm all in favour of simplicity though.

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


Posted By: Guests
Date Posted: 23 Nov 17 at 7:25pm
Yeah the theory is one thing, what is difficult is matching that up against what you can feel in the boat. Isolating a single variable in changeable conditions is where the art comes in. 

One thing I will add, is I've always been a believer that you can override a 'too straight' mast set up by pulling sail controls to de-power. However, downwind you can't make the mast any straighter once your down-haul / kicker is fully off. It's always easier to rake a mast too which is often adjustable on the water, or as least without dropping the mast.

In the 200, for example, it gets to the point where the kicker is off so much you lose any leech control. I've found it better to run a straighter mast, so I can still keep a little so kicker tension and have nice depth. Then just kicker the hell out of it upwind (and not run too much rig tension). 

Obviously if you're not in a SMOD you could get a differently cut sail or different sectioned mast too... Just be glad you don't have caps and lowers and weight on trapeze wires to worry about too!




Posted By: Sam.Spoons
Date Posted: 23 Nov 17 at 9:08pm
So having the lowers (or Swatcher) tight until overpowered is a good idea?

Spice has two wires, and TBH I should work out how to maximise power with just one trapezing as I'm not the best at helming off the wire and don't have a regular crew who can compensate for my shortfalls.......

I did have a graphic demonstration a few weeks ago, a blasting day with my mate in his Blaze and me and irregular crew in the Spice, the difference between t'crew wiring and not was dramatic (should be obvious but we were just having fun reaching up and down......).



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


Posted By: Guests
Date Posted: 23 Nov 17 at 9:50pm
Yes, although, someone might correct me here as it's been a long time since I sailed with lowers and caps.

So, yes in principle the more lowers the straighter the bottom section. This will help create a bit of grunt down low. However, we never really measure tension for lowers, we just went on how the sail looked, where the starvation creases developed when increasing kicker. So, my feeling was it was more about balancing and distributing kicker forces so there is a nice even bend in the mast. 

Similarly for caps, they just really supported the huge kite downwind. Upwind you'd want them pretty loose to allow the rig to work, maybe a bit more on in the light to open up the top of the sail and let it breath. 


Posted By: laser193713
Date Posted: 24 Nov 17 at 9:13am
In a boat with no lowers it's relatively simple, not having any control low down can make it harder, no mast ram or even partners at the deck to stop the mast inverting would make me a little nervous but then without a kite this might not be such an issue.

Simply put, spreader rake will control the static bend in the rig, or the amount of pre-bend that the mast gets for a given forestay tension. Once this is decided the length of the spreaders will dictate the stiffness of the mast in changing conditions, so essentially gust response. The only concern with overly long spreaders, particularly when you have no lowers at all is that the mast will sag in the middle and the tip will actually move to windward. This is particularly true when the rig is set up very slack, less of an issue when there is still plenty of residual shroud tension on the leeward side. 

I think the first thing to decide is whether the rig likes to be slack or tight, I would imagine without lower mast control or support that it would be safer to have it on the tight side. When I first got my RS100 when they were brand new I turned up at the nationals having only sailed the boat for a week, the only way I could make it feel right was for the rig to be so slack that upwind the shrouds were both slack, it was rocket ship fast but that boat has good support at deck level. In that case I just wound the spreaders back as far as they would go to help prevent the mast inverting downwind. 


Posted By: iGRF
Date Posted: 24 Nov 17 at 9:38am
I love watching them in the boat park with their 'settings' their tape measures, their loos guages, then they overstand by twenty boat lengths, or miss the start, or go exactly the wrong way up the beat, or take the circular tourist route when rounding marks...

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https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals      https://www.corekite.co.uk" rel="nofollow - New Core Kite website


Posted By: Guests
Date Posted: 24 Nov 17 at 10:16am
But 'they' probably would have made those mistakes regardless of rig set up. Better to be going the wrong way with fast boat than a slow boat, hey? 

I agree that playing around too much with the rig on the water can often be more a distraction than good. But spending time off the water on getting a decent set up seems like a good use of none sailing time at almost all levels. 

It's usually something which can be done over couple of sails to get a workable set up, then after that it's just set and forget. Most classes have a tuning guide, so with very little thinking you can just copy a setting out of their then focus on sail controls and what you do on the water. 

I think it's harder in the new classes, like H2's hadron where there is less likely to be accepted ballpark settings so you have to work out more for yourself by putting in to practice the theory. . 


Posted By: iGRF
Date Posted: 24 Nov 17 at 2:29pm
So, how given the lack of sensitivity and 'feel' in these things do you tell if what you've done actually makes a performance in terms of speed difference. I accept the better gust response and have learned that here and now directly from this thread so will check what's going on with the lump of tin attached to my lake boat, pretty sure it has spreaders.


Noooo, I've walked into it haven't I.. Go class racing then you can tell.

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https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals      https://www.corekite.co.uk" rel="nofollow - New Core Kite website


Posted By: PeterG
Date Posted: 24 Nov 17 at 4:27pm
Noooo, I've walked into it haven't I.. Go class racing then you can tell. 

That would be a good start Big smile

Better still two boat tuning - but they would have to be the same class too to learn much.


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Peter
Ex Cont 707
Laser 189635
DY 59


Posted By: iGRF
Date Posted: 24 Nov 17 at 4:35pm
Originally posted by PeterG

Better still two boat tuning - but they would have to be the same class too to learn much.</span>


And the same weight helm, my main nemesis down the lake in the same class, who I struggle to beat more often than not, is 20 + kilos heavier, but I suspect but refuse to admit the greater issue is the forty three years younger bit combined with the ten years more sailing experience and the 30 cms or so greater righting moment

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https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals      https://www.corekite.co.uk" rel="nofollow - New Core Kite website



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