savageseadog
Well-Known Member
Ok not all!
But lots of people with no idea about swept back fractional rigs throwing in there opinions "missing stays" et al.
It's really a simple badly tuned rig that would take less than an hour to put right..
Mast Inversion - Selden Mast
- Thread starter Darrel_Walters
- Start date
Ok not all!
But lots of people with no idea about swept back fractional rigs throwing in there opinions "missing stays" et al.
It's really a simple badly tuned rig that would take less than an hour to put right..
fireball
Well-Known Member
Yup ...
Darrel_Walters
Member
Hi all.
Well a few mates and I were armed to the teeth with 2 meter rules, Verner Gauges, tape, Tension Gauges, A host of adjustable spanners, Bosuns Chair, loads of printed paper on not what to do and to do. And marched of to the yacht full of PMA (positive mental attitude).
Sods law, I was volunteered to scale the mast. (First time ever) to undo the D2s. Now forgive me, but have you ever had that feeling you’re sitting on the wrong side of the branch when cutting it, I had the same feeling undoing the D2s, scary.
We checked every thing first with the tension gauge to give us a rough idea what we did have.
Back stay was 20%
Caps 20%
D1 16%
D2 16%
V2 surprise, surprise 14%
My suspicions confirmed that indeed the D2 were to tight and as a consequence the caps were not supporting the top of the mast and all the tension from the lower part of the Cap was being transferred through the D2, I would surmise that the mast looked straight at the dock because of the tension on the backstay. The back stay on this rig is only 7mm. When we were hard on the wind in a good blow the caps were not supporting the top of the mast, only the backstay which would mean that the top of the mast would point of to lee and forward.
So after unwinding the D2 (a lot ) so they were really slack I got down from the shaky mast and undone the D1 (not so much). The mast was like Jelly (worried look on ones face).
I also slacked of the back stay to just 5%. We then measured the Caps and they had gone from 20% to about 14%. Only confirming what we thought.
We cranked up the Caps and using the Topping Lift made sure that the mast was centre of the boat we took them to just of 20%. Sighting up the luff grove we needed to adjust the port D1 (a lot) to take a bow out of the centre (1st spreader area) and not so much on the starboard. D2 and the top of the mast looked straight and fine.
By now we had a lovely bow (the right way) in the mast, we cranked on the backstay to about 22% and the bow increased, we then took a measure of the CAPS again and they were roughly the same as before.
We backed of the backstay to about 18% this reduced the bow to what we feel is adequate, and hopefully will allow us to unfurl the sail tonight.
I scaled the mast again to tighten up the D2 which had now lost all the slack I had put in to them; I tightened them up to about 12% as the same with the D1.
The mast looks sweet, perhaps a little too much bend, but we will see tonight, forecasting 15 Knots of wind.
We were very pleased with the outcome, this large chunk of metal on top of your boat that I always found quite intimidating and a black art to adjust actually is very simple and applying a logical approach seemed to work really well
I myself, found my confidence increased by going up the mast and altering the rig, the experts say not to use a tension gauge, but I found it invaluable as it allowed me to understand as a datum what is tight and what is not, however, I respect what the experts say, and I am sure if your doing it as a job it becomes second nature.
I would like to take this opportunity to say a BIG THANKS to
Nick on the forum, for giving me the details of someone to talk to at Selden
Richard Thoroughgood from Selden for his time on the phone and emails of my rig etc. and
Harry James from www.rigshop.com for his time on the phone
I am off racing tonight full of confidence in the rig; I will post tomorrow to let you know how we got on.
Cheers All
Well a few mates and I were armed to the teeth with 2 meter rules, Verner Gauges, tape, Tension Gauges, A host of adjustable spanners, Bosuns Chair, loads of printed paper on not what to do and to do. And marched of to the yacht full of PMA (positive mental attitude).
Sods law, I was volunteered to scale the mast. (First time ever) to undo the D2s. Now forgive me, but have you ever had that feeling you’re sitting on the wrong side of the branch when cutting it, I had the same feeling undoing the D2s, scary.
We checked every thing first with the tension gauge to give us a rough idea what we did have.
Back stay was 20%
Caps 20%
D1 16%
D2 16%
V2 surprise, surprise 14%
My suspicions confirmed that indeed the D2 were to tight and as a consequence the caps were not supporting the top of the mast and all the tension from the lower part of the Cap was being transferred through the D2, I would surmise that the mast looked straight at the dock because of the tension on the backstay. The back stay on this rig is only 7mm. When we were hard on the wind in a good blow the caps were not supporting the top of the mast, only the backstay which would mean that the top of the mast would point of to lee and forward.
So after unwinding the D2 (a lot ) so they were really slack I got down from the shaky mast and undone the D1 (not so much). The mast was like Jelly (worried look on ones face).
I also slacked of the back stay to just 5%. We then measured the Caps and they had gone from 20% to about 14%. Only confirming what we thought.
We cranked up the Caps and using the Topping Lift made sure that the mast was centre of the boat we took them to just of 20%. Sighting up the luff grove we needed to adjust the port D1 (a lot) to take a bow out of the centre (1st spreader area) and not so much on the starboard. D2 and the top of the mast looked straight and fine.
By now we had a lovely bow (the right way) in the mast, we cranked on the backstay to about 22% and the bow increased, we then took a measure of the CAPS again and they were roughly the same as before.
We backed of the backstay to about 18% this reduced the bow to what we feel is adequate, and hopefully will allow us to unfurl the sail tonight.
I scaled the mast again to tighten up the D2 which had now lost all the slack I had put in to them; I tightened them up to about 12% as the same with the D1.
The mast looks sweet, perhaps a little too much bend, but we will see tonight, forecasting 15 Knots of wind.
We were very pleased with the outcome, this large chunk of metal on top of your boat that I always found quite intimidating and a black art to adjust actually is very simple and applying a logical approach seemed to work really well
I myself, found my confidence increased by going up the mast and altering the rig, the experts say not to use a tension gauge, but I found it invaluable as it allowed me to understand as a datum what is tight and what is not, however, I respect what the experts say, and I am sure if your doing it as a job it becomes second nature.
I would like to take this opportunity to say a BIG THANKS to
Nick on the forum, for giving me the details of someone to talk to at Selden
Richard Thoroughgood from Selden for his time on the phone and emails of my rig etc. and
Harry James from www.rigshop.com for his time on the phone
I am off racing tonight full of confidence in the rig; I will post tomorrow to let you know how we got on.
Cheers All
bignick
Well-Known Member
Looking better already, just take it easy sailing with it for the first time. It will be interesting to see your sailing photos tomorrow. 
Well done also for taking it into your hands to find out what is actually wrong and set out to fix it.
Well done also for taking it into your hands to find out what is actually wrong and set out to fix it.
Simondjuk
Well-Known Member
William H,
I think you misunderstood, but perhaps I didn't put my point across very well.
I'm aware of how such a rig works, my point being that if such a rig isn't set up properly, ie. With some pre-bend, it doesn't work. I have a rather nice light and wippy 3/4 fractional rig on my own boat and the pre-bend is pronounced. My point was that in the absence of pre-bend, a rig with no forward running stays in highly likely to fail. No matter how many sets of swept spreaders and diagonals such a rig has, if there's no pre-bend, none of them will do anything to prevent inversion of the mast. If it's straight, the spar is already 'over centre', so to speak, and the only thing preventing in inversion induced failure is the strength of the spar section itself. Set up correctly, the pre-bend works against the tension in the caps, which prevents the mast inverting since to do so would require the mast to compress or the caps to stretch.
Clearly, we both know this. What amazes me is that the guy who set up the opening posters rig and calls himself a rigger appears not to.
I think you misunderstood, but perhaps I didn't put my point across very well.
I'm aware of how such a rig works, my point being that if such a rig isn't set up properly, ie. With some pre-bend, it doesn't work. I have a rather nice light and wippy 3/4 fractional rig on my own boat and the pre-bend is pronounced. My point was that in the absence of pre-bend, a rig with no forward running stays in highly likely to fail. No matter how many sets of swept spreaders and diagonals such a rig has, if there's no pre-bend, none of them will do anything to prevent inversion of the mast. If it's straight, the spar is already 'over centre', so to speak, and the only thing preventing in inversion induced failure is the strength of the spar section itself. Set up correctly, the pre-bend works against the tension in the caps, which prevents the mast inverting since to do so would require the mast to compress or the caps to stretch.
Clearly, we both know this. What amazes me is that the guy who set up the opening posters rig and calls himself a rigger appears not to.
Last edited:
Darrel_Walters
Member
Hi all for all who have been following this thread we took the yacht out for a race last night. to our surprise the main unfurled no problem at all. winds were averaging 23 Knots and maxed out at 32 Knots.
We were on a beat, calm water, at around 23 knots and that is what the rig looked like from the images.
Sighting up the mast there was a slight bow in the middle to lee, so I am guessing we need to tighten a bit more up on the D1 and D2's this will help tension the middle of the mast, I am at 12% at the moment, so I will crank it up tp 16%.
I also noticed that having the bow in the mast flatened the main considerably. to which the manufacture of the main is allready well faltened because we have in mast furling.
Hopefull tighting up the D1 and D2 will straighten the mast and therefore, fill the main a bit more, Our helman mentioned he felt that the boat was not as fast. and unforuantly our position reflected that at coming 5th
The winds came up to around about 26 to 28 knots and the boat was feeling overpressed, we managed to hold on as the wind was quite flucky, the mast at that amount of wind, was slighty inverting.
I would say, we need to tighten the caps maybe just one turn each as well.
All in all it was an enjoyable sale, we are still 2 overall in the summer series, but we had a bad knock on points last night. I am kind of guessing if we can flaten of the mast with tightening up the D1 and D2 this would make the main a lot fuller and hopefully give us more power.
Does anyone have any views on what I am saying
Happy Days
and thanks to all
We were on a beat, calm water, at around 23 knots and that is what the rig looked like from the images.
Sighting up the mast there was a slight bow in the middle to lee, so I am guessing we need to tighten a bit more up on the D1 and D2's this will help tension the middle of the mast, I am at 12% at the moment, so I will crank it up tp 16%.
I also noticed that having the bow in the mast flatened the main considerably. to which the manufacture of the main is allready well faltened because we have in mast furling.
Hopefull tighting up the D1 and D2 will straighten the mast and therefore, fill the main a bit more, Our helman mentioned he felt that the boat was not as fast. and unforuantly our position reflected that at coming 5th
The winds came up to around about 26 to 28 knots and the boat was feeling overpressed, we managed to hold on as the wind was quite flucky, the mast at that amount of wind, was slighty inverting.
I would say, we need to tighten the caps maybe just one turn each as well.
All in all it was an enjoyable sale, we are still 2 overall in the summer series, but we had a bad knock on points last night. I am kind of guessing if we can flaten of the mast with tightening up the D1 and D2 this would make the main a lot fuller and hopefully give us more power.
Does anyone have any views on what I am saying
Happy Days
and thanks to all
KenMcCulloch
Well-Known Member
It sounds as if you are learning a great deal about your rig and how it works. In-mast mains are pretty much of a closed book to me and I intend that state of affairs to persist. However I would not be at all surprised if it were the case that the sail is cut to work with a mast with relatively little pre-bend, and that perhaps straightening your mast as you suggest will be beneficial.
bignick
Well-Known Member
The straighter it is the more easily it will invert though.
To check how much prebend there is fasten the main halyard to the mainsail's tack attachment point and tension it. You will be able to see how much the mast bends away from its straight position.
The main objective should be avoiding the mast inverting - if the main looked ok with a dead straight mast then it will definitely look different now. How does it look wrong? Have you checked draught and location of max draught with the stripes? Easiest by taking a photo and drawing lines on...
To check how much prebend there is fasten the main halyard to the mainsail's tack attachment point and tension it. You will be able to see how much the mast bends away from its straight position.
The main objective should be avoiding the mast inverting - if the main looked ok with a dead straight mast then it will definitely look different now. How does it look wrong? Have you checked draught and location of max draught with the stripes? Easiest by taking a photo and drawing lines on...
Darrel_Walters
Member
Thats great input guys, We have quite possibly been fooled/spoilt perhaps. as the top of the mast goes forward, that may have bowed the middle back a little and in doing so filled the main and gave it more power than what you would normally expsect. I think we will have to re learn the rig again and play with the shape of the sails instead of letting the mast do it for us....... ha ha ha..
Bosun Higgs
N/A
Dont judge the changes on one race Darrell - you are likely to have spent much of the race time peering at the mast and the sail shape etc rather than concentrating. Anyway, you have made excellent progress and being 2nd with in mast reefing is good going .