Robert Wilson
Well-Known Member
Thanks Concerto. I'll try it when my old girl is back in the water.
(Ohhh yeah !!)
(Ohhh yeah !!)
Mast-bend - setting-up & when sailing
- Thread starter Robert Wilson
- Start date
Steve The Seagull
Active Member
Backstay is really the forgotten control and one of the most powerful. Using it correctly is like putting your car into the correct gear, you can use the accelerator as much as you want (the sheets) but the back stay allows you to change through gears and get more out of your boat for the conditions.
In basic terms for upwind and close reaching you should be setting the backstay up for the conditions, for a cruiser I would set yourself 3 marks as reference, sub 10knots, 10-16, 16+, allowing your to have a small amount of headstay sag in those conditons. Doing this and adjusting it for the conditons will mean the boat is much more efficient, less heeling with more speed!
In basic terms for upwind and close reaching you should be setting the backstay up for the conditions, for a cruiser I would set yourself 3 marks as reference, sub 10knots, 10-16, 16+, allowing your to have a small amount of headstay sag in those conditons. Doing this and adjusting it for the conditons will mean the boat is much more efficient, less heeling with more speed!
Robert Wilson
Well-Known Member
I'm sorry, but am I being thick?
Tensioning the backstay surely tensions the headstay as well? (masthead rig).
If I am being thick, you are welcome to comment :encouragement:
Steve The Seagull
Active Member
Yes it will, but you want a small amount of sag to keep the boat forgiving. A pin tight headstay will allow you to point very well but will be very difficult to sail to and lack any acceleration. You are not looking to totally stop the sag but control it.
Daydream believer
Well-Known Member
Dingo??
Joker
Well-Known Member
All this is with masthead rig. Mine is fractional.
I have a 4:1 purchase to tension the backstay (difficult to describe, but it has a single wire which terminates in a pulley block, then a V shaped wire to either side of the hull). I can tighten this further using a genoa winch.
What difference does the tension make compared with a masthead?
I have a 4:1 purchase to tension the backstay (difficult to describe, but it has a single wire which terminates in a pulley block, then a V shaped wire to either side of the hull). I can tighten this further using a genoa winch.
What difference does the tension make compared with a masthead?
Concerto
Well-Known Member
Well guessed.
Javelin
Well-Known Member
Masthead with fore and aft lowers
lots of back stay
pros - will point high, higher vmg
cons - No grunt to push through waves, twitchy in terms that the sails will stall easier
Less backstay - sag in the forestay
Pros - lots of grunt to power through chop, sail setting more forgiving
Cons - Poor pointing,
Single parallel lowers and babystay masthead rigs work slightly differently and are kind of half way between the twin lower masthead and a fractional, ie there's more capacity to bend the mast on the fly.
Heavy displacement yachts will generally perform better with more grunt from full sails and look to keep powered up rather than point high.
Lighter boats can utilise flat sails settings and will point very high and have the ability to feather through the gusts.
In general the masthead rig uses the Jib for the main power upwind.
A fractional rig relies more on powering up the mainsail which usually has a much bigger roach area than a masthead main.
So the backstay on a fractional rig is a tuning tool for the mainsail as it bends the mast far more.
More backstay results in flattening the mainsail, de-powering the sail, increasing twist and opening the slot.
The raked back spreaders do the majority of the job of reducing forestay sag but also mainsheet tension helps.
Racing fractional rigs also use running backstays to increase tension on the forestay.
lots of back stay
pros - will point high, higher vmg
cons - No grunt to push through waves, twitchy in terms that the sails will stall easier
Less backstay - sag in the forestay
Pros - lots of grunt to power through chop, sail setting more forgiving
Cons - Poor pointing,
Single parallel lowers and babystay masthead rigs work slightly differently and are kind of half way between the twin lower masthead and a fractional, ie there's more capacity to bend the mast on the fly.
Heavy displacement yachts will generally perform better with more grunt from full sails and look to keep powered up rather than point high.
Lighter boats can utilise flat sails settings and will point very high and have the ability to feather through the gusts.
In general the masthead rig uses the Jib for the main power upwind.
A fractional rig relies more on powering up the mainsail which usually has a much bigger roach area than a masthead main.
So the backstay on a fractional rig is a tuning tool for the mainsail as it bends the mast far more.
More backstay results in flattening the mainsail, de-powering the sail, increasing twist and opening the slot.
The raked back spreaders do the majority of the job of reducing forestay sag but also mainsheet tension helps.
Racing fractional rigs also use running backstays to increase tension on the forestay.
Robert Wilson
Well-Known Member
And here's me thinking that having the two triangular flappy things and a pole to hold them up were all I needed to know about making a boat go forwards! 
Thanks for that summary, I shall do my best to keep Khamsin sailing briskly and efficiently. I am still somewhat amazed to think anything manually operated can put any bend in that great big, thick-section metal thingy!!
As stated above, I'm not a racer but would like to make good safe progress towards where I intend to go.
Thank you one and all.
Time to get the varnishing finished, cooling system put back together, gas-locker completed, a/f done etc etc etc.
Thanks for that summary, I shall do my best to keep Khamsin sailing briskly and efficiently. I am still somewhat amazed to think anything manually operated can put any bend in that great big, thick-section metal thingy!!
As stated above, I'm not a racer but would like to make good safe progress towards where I intend to go.
Thank you one and all.
Time to get the varnishing finished, cooling system put back together, gas-locker completed, a/f done etc etc etc.
Daydream believer
Well-Known Member
Not really. I think Dingo was designed for the 3/4 ton level rating series. I sailed with the owner, Bob Stewart, father of Andrew, the designer of the Limbo's
Bob told me how the designer (forgotten who it was) got them to string the line through the boat then tighten the rigging up as much as they could whilst he measured the deflection. As far as I recall he actually only did it the once to see how his design coped with the stresses of the rig. A rumour that they did it to check tension etc each race was not actually, true but bandied about for bar room punditry for the competition
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steveeasy
Well-Known Member
Hi Savageseadog,
Forgive me as I have a limited understanding of rigging but I was under the impression that with a masthead rig tightening the backstay could not bend the mast at all. I had once a fractional rig and could understand the physics how a mast could be bent and to some extent why.
I just cant see how a masthead rig could be bent by using the backstay. surely any tension/force would would compress the mast? My current boat is a fractional rig but has jumper stays, so a little more confused
with this set upseams I'm having a problem adding images as well!!
Steveeasy
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Daydream believer
Well-Known Member
If the lower part of the mast is held fore & aft by opposing lowers then when the backstay is tightened against a slackish fore stay it will pull the mast tip aft thus bending the mast. This can have the benefit of flattening the mainsail so that reefing can be delayed a little, if coupled with other tweeks
.
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Concerto
Well-Known Member
Bob Miller was the designer. Raced against Bob Stewart and sons Rob and Andrew. Not friends of mine, but I will say no more in public forum.
Javelin
Well-Known Member
On a frac rig with diamonds as per your photos the mast will bend around the point of your steaming light.
The diamonds will hold the top section straight but from the lower hounds to the spreaders the mast is free to flex.
You set the mast up to suit the cut of the sail and conditions however on the customers yachts that have this setup I normally set the diamonds with a little negative prebend first, which is normally taken out with the weight of the boom/mainsail.
I found if you didn't do this the top section of mainsail would be too flat.
Often the top batten will be full length to induce camber but you don't have a lot of control over the top third other than leech tension/twist, when sailing.
Also when you take a reef in, due to the lower mast bent the top section can be very flat and if too much mast bend you will have issues keeping leach tension which will effect pointing and power.
Will all the rigs the best way to see what is happening is to sight up the mast track.
If you sight up and get someone to pull on the backstay, mainsheet, kicker and the cunningham you can see the effect of each.
Just had another look at your photos - its interesting that there is a sleave and mast join just below the center of mast bend.
Also, it might be due to the photo angle but it looks like the main spreaders are too flat and the ends need to be lifted by 3 or 4" to better bisect the cap shroud angle.
If you find you have issues reducing forestay sag you might find adding a set of running back stays would help.
The diamonds will hold the top section straight but from the lower hounds to the spreaders the mast is free to flex.
You set the mast up to suit the cut of the sail and conditions however on the customers yachts that have this setup I normally set the diamonds with a little negative prebend first, which is normally taken out with the weight of the boom/mainsail.
I found if you didn't do this the top section of mainsail would be too flat.
Often the top batten will be full length to induce camber but you don't have a lot of control over the top third other than leech tension/twist, when sailing.
Also when you take a reef in, due to the lower mast bent the top section can be very flat and if too much mast bend you will have issues keeping leach tension which will effect pointing and power.
Will all the rigs the best way to see what is happening is to sight up the mast track.
If you sight up and get someone to pull on the backstay, mainsheet, kicker and the cunningham you can see the effect of each.
Just had another look at your photos - its interesting that there is a sleave and mast join just below the center of mast bend.
Also, it might be due to the photo angle but it looks like the main spreaders are too flat and the ends need to be lifted by 3 or 4" to better bisect the cap shroud angle.
If you find you have issues reducing forestay sag you might find adding a set of running back stays would help.
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Daydream believer
Well-Known Member
Those were the days when EAORA would get entries in the 100's & fill the harbour in Ostend from pontoon to pontoon so you could walk right across from one side to the other on boats. I know because I did it once after a few beers:encouragement: ( which I then deposited in the N sea on the way home:ambivalence
Concerto
Well-Known Member
Those were the days when EAORA would get entries in the 100's & fill the harbour in Ostend from pontoon to pontoon so you could walk right across from one side to the other on boats. I know because I did it once after a few beers:encouragement: ( which I then deposited in the N sea on the way home:ambivalence
Those were certainly the good old days of EAORA. The fun continued when boats wanted to leave and cast blocks of boats off and left it for others to winch them back into the raft. The best result we had in the Harwich Ostend was a 2nd overall, just pipped by Richard Matthews, but we way clear of the rest of the fleet.
Do you remember Dione and the other classic yachts that joined the fun. Once Dione's crew had been drinking in a bar most of the night and returned with the house band to play on the quayside and the owners children went round with caps begging for money to maintain Dione! Not that he needed any as he ran a string of nightclubs.
Sorry about the thread drift.
Concerto
Well-Known Member
Those were the days when EAORA would get entries in the 100's & fill the harbour in Ostend from pontoon to pontoon so you could walk right across from one side to the other on boats. I know because I did it once after a few beers:encouragement: ( which I then deposited in the N sea on the way home:ambivalence
Those were certainly the good old days of EAORA. The fun continued when boats wanted to leave and cast blocks of boats off and left it for others to winch them back into the raft. The best result we had in the Harwich Ostend was a 2nd overall, just pipped by Richard Matthews, but we way clear of the rest of the fleet.
Do you remember Dione and the other classic yachts that joined the fun. Once Dione's crew had been drinking in a bar most of the night and returned with the house band to play on the quayside and the owners children went round with caps begging for money to maintain Dione! Not that he needed any as he ran a string of nightclubs.
Sorry about the thread drift.
Daydream believer
Well-Known Member
There were 2 boats of similar looks, Dione & another. I forget which one it was. I think it was Dione. but Cuthbert (a cocky car dealer member of the Croaker fraternity at the Crouch YC) was navigating. They felt they were winning by miles with spinnaker up , until they ran aground all standing off the Dunkirk roads. Created some mirth in the bar I believe.
Yes you are right! it is a thread drift- but it beats Brent Swains crappy steel skips on some of the other posts any day of the week
So apologies to the OP. Perhaps we should get back to his bent mast.
savageseadog
Well-Known Member
Imagine you're pushing on the top of a vertical straw. The mast isn't a perfectly vertical column, there will be loading from the boom and main. The sheeted main will tend to bend the mast out of column and enable the force applied to induce bend into the mast.
vyv_cox
Well-Known Member
See post #4