On my Severne race sails, I've generally used the top eyelet in the clew.
Some sailors use the bottom one when fully powered blasting for better control.
What is the general concesus which hole? Does it really make much difference.?
To be honest I can't really tell much difference.
I suppose on which sails .
I'm not fast by any means , but can tell a lot of difference between the two .
I always use the top hole , but if the wind increases and I start struggling, I change to the lower hole and lower the boom an inch . It's kinda half way between going down a sail size .
I have always used the lower one on Code Red sails, but I'm also quite lightweight so control is usually more important than low-end power. On the later race sails I've simply used the one that is provided to go with an adjustable outhaul.
Clew cringle options, a discussion:
1) Do they make a difference in power delivery? Some say they do. Some people waffle on about 'control' over the rig or about 'leech twist'. Personally I think that's rubbish because we load our booms outwards and downwards with body weight, and clew height is not as important as our sailing stance and our body weight as applied to the rig. Many sails only have one clew height option, and those sails work just fine.
If you are speed sailing, then why not test the difference with your GPS. Then stick with one boom setting and check again with all the other tuning variables at your disposal - like mast foot position, footstrap placings, downhaul, outhaul etc.
(Then do the same test again at a different launch spot and/or on a differtent day and you'll probably find a different result )
2) Do they change the boom height? Yes they certainly do, at the back end of the boom and, more importantly, at the point of the boom where you hook in. Some taller people simply match a higher clew cringle with their higher chosen mast setting on the mast.
If you are so tall you use the top of the boom cutaway for the front of your boom, then you should certainly try the upper clew option.
Another option with boom height is to shift your mast foot back in the track - which brings the mast more upright and sets the boom higher.
3) Can changing clew cringle change the outhaul tension of the sail? Yes it can, because it changes the angle of the boom on the mast, reducing or increasing the boom's effective length. So that in itself has an effect on the power delivery of the sail.
4) We really control the power of the sail with downhaul and/or outhaul, and mast foot position. Not boom height.
The bottom hole moves forward, the contact point of boom batten and boom, s-bending the boom batten laying off the sail down to the boom. No advantage with a wide arse boom.
It's real and a great tuning tool. I'm on NP sails and when going to the lower clew position it usually means that I can Sheet in, fully , while in the top I was feathering for control. Someone mentioned that the lower clew position equates to approx 0.5m less sail. I'll start in the upper position. I'll drop boom height before I drop clew position. I rig with the same DH on my sails.
I generally use the upper one until I'm getting out of control or expect to be very overpowered. I'm a lightweight and they do make a difference.
I've 'played' or 'tested' mine on duotone 2021 7.7 warp quite a bit, I don't get any noticeable benefit from the bottom hole as verified by GPS - I find on the bottom hole the sale feels dull and a bit dead - can't think of a better way to put it. Perhaps in flat water conditions it could be different, in our chop it feels like the twist becomes too much.
Worth noting I'm ~100kg, usually on a size bigger than other sailors and by the time I am trying the bottom hole on 7.7 really its time for the 7m :)
I just pull on more Downhaul. To be honest l have never noticed any difference top or bottom clew settings.all my sail are pryde & North's.The mast track further forward l do notice.just my opinion 
I remember when old race sails had three eyelets. That would of confused a lot of people ??
On my severne gator the bottom eyelet is approx 3cm further towards the mast than the top one, so are you supposed to reduce the boom length by 3cm when using the bottom one because the outhaul measurement has only one length and this has always confused me 
unlike my north sail that gives separate boom lengths for top and bottom clew
Select to expand quotedkeating said..
On my Severne race sails, I've generally used the top eyelet in the clew.
Some sailors use the bottom one when fully powered blasting for better control.
What is the general concesus which hole? Does it really make much difference.?
To be honest I can't really tell much difference.
I've never had a sail with more than 1 clew eyelet to test. Do you have a GPS?
But then I dont own race sails. I guess if sails have them then you could use them.
I thought I'd look to see who has them.
# of eyelets and position of the highest compared to low one.
Point-7 - 1 clew eyelet
Duotone - 2 not that much higher, but a bit more outward
Loft - 2 not that much higher, but a bit more outward
Pryde - 2 even less higher, but a bit more outward
GA - 2 higher and slightly outward
Severne - 2 most height difference of those I've looked at, boom length looks the same between the eyelets.
Select to expand quotemob dog said..
On my severne gator the bottom eyelet is approx 3cm further towards the mast than the top one, so are you supposed to reduce the boom length by 3cm when using the bottom one because the outhaul measurement has only one length and this has always confused me unlike my north sail that gives separate boom lengths for top and bottom clew
Moving the clew position wouldnt make much difference to boom length if the 2 eyelets are the same distance from the mast, ie one directly above the other. Are the North eyelets set with 1 closer to the mast, so shorter boom required?
Select to expand quoteBasher said..
Clew cringle options, a discussion:
1) Do they make a difference in power delivery? Some say they do. Some people waffle on about 'control' over the rig or about 'leech twist'. Personally I think that's rubbish because we load our booms outwards and downwards with body weight, and clew height is not as important as our sailing stance and our body weight as applied to the rig. Many sails only have one clew height option, and those sails work just fine.
If you are speed sailing, then why not test the difference with your GPS. Then stick with one boom setting and check again with all the other tuning variables at your disposal - like mast foot position, footstrap placings, downhaul, outhaul etc.
(Then do the same test again at a different launch spot and/or on a differtent day and you'll probably find a different result )
2) Do they change the boom height? Yes they certainly do, at the back end of the boom and, more importantly, at the point of the boom where you hook in. Some taller people simply match a higher clew cringle with their higher chosen mast setting on the mast.
If you are so tall you use the top of the boom cutaway for the front of your boom, then you should certainly try the upper clew option.
Another option with boom height is to shift your mast foot back in the track - which brings the mast more upright and sets the boom higher.
3) Can changing clew cringle change the outhaul tension of the sail? Yes it can, because it changes the angle of the boom on the mast, reducing or increasing the boom's effective length. So that in itself has an effect on the power delivery of the sail.
4) We really control the power of the sail with downhaul and/or outhaul, and mast foot position. Not boom height.
2) I think even the taller PWA sailors dont have their boom at the top of the cutout. This has been mentioned before iirc.
If I want to change the boom height, I move the boom, I dont move the mast foot.
3) with race sails people normally use adjustable outhaul systems, so outhaul tension would be changed even with 1 eyelet.
4) "We"?
I use boom height for controlling the power of the sail, also mast foot. Only when the wind is too much and I never change more than 1cm on either. Flatter water I'd move the boom 1st. This is all on freerace type boards and freeride sails though.
The theory I think, is moving the clew point shifts the pivot point of the boom batten where it touches the boom. The further inboard the pivot point the more reflex is generated, stopping shape moving aft, stabilising sail and reducing lift. The lower the clew point, the further in the pivot point.
I don't know why the different clew holes make a big difference, and I don't care. But using the lower clew hole makes quite a bit of difference for me when fully powered to overpowered, with more control using the lower hole. I'll start with the lower hole if the wind is at the upper end for the sail I use, or predicted to go down. If the wind is likely to increase, I'll start with the upper hole and switch to the lower hole when the wind gets stronger. This is with Loft Racing Blades, usually on RDM masts.
Select to expand quotePhilUK said..mob dog said..
On my severne gator the bottom eyelet is approx 3cm further towards the mast than the top one, so are you supposed to reduce the boom length by 3cm when using the bottom one because the outhaul measurement has only one length and this has always confused me unlike my north sail that gives separate boom lengths for top and bottom clew
Moving the clew position wouldnt make much difference to boom length if the 2 eyelets are the same distance from the mast, ie one directly above the other. Are the North eyelets set with 1 closer to the mast, so shorter boom required?
Both sails have bottom clew closer to mast, north has 2 different outhaul measurements for this but severne only one
