Mast Inversion - Selden Mast

[Jaramaz]

Agree with Chris.
The usual way to set up the rig is to firstly tighten the upper (top) shrouds. They should be really tight (Selden use to recommend 15-20% of breaking load, which I personally think is to much - but it says someting). Lowers and stays are used to strighten the mast or give it the bend one would like it to have.
When tensioning the uppers one follows with the lowers and stays, in order not to get too much unwanted bend.
Do remember to oil the turnbuckles, they are too easily destroyed by the huge forces.

The aft and back stays should normally not be set very tight, they are for trimming the mast.

/Jaramaz

 

[bignick]

When its all set up, sailing to windward in 15 knots the lee shrouds should be just loose - ie not drum tight if you see what I mean! The lowers must be very tight on both sides to avoid them jarring as the boat pitches.

With respect, I'm not quite sure about that - my understanding is that with aft-swept spreaders the D1s ans D2s are pulling the middle of the mast aft. The tension in the cap shrouds (V1 v2 v3) is compressing the spreaders which push the middle of the rig forward. By having the cap shrouds (V1-V2-V3) loose and the D1 and D2 tight you will straighten the rig, or possibly invert it, which is the problem already evident.

I would show the pictures to the rigger who set the mast up and ask him first.

Agreed, very good idea.

 

[Chris_Robb]

With respect, I'm not quite sure about that - my understanding is that with aft-swept spreaders the D1s ans D2s are pulling the middle of the mast aft. The tension in the cap shrouds (V1 v2 v3) is compressing the spreaders which push the middle of the rig forward. By having the cap shrouds (V1-V2-V3) loose and the D1 and D2 tight you will straighten the rig, or possibly invert it, which is the problem already evident.


Agreed, very good idea.

The lowers are in opposition to the baby stay - or foreward lowers. So if set correctly - but tight - will serve to keep the mast rigid to the lower spreaders.

Its the cap shrouds that are the problem here. They work in both compression on the spreaders and tension on the mast. Much more difficult to understand.....

 

[fireball]

you also have to look at where the intermediates are terminated - many will terminate on the outer end of the lowers - and the shrouds are split here too - so tightening up the shrouds just tensions the intermediates too ..

Mines a fractional rig - so slightly different in set up - but basically we put the mast up roughly ... fixed forestay so that was easy ... then straightened the mast vertically (side to side) ... then applied the text-book tension to the shrounds - slackened it off a bit because it seemed too tight (should get a proper rig tension guage really!) then did the lowers before going up the mast to do the intermediates.
Crew checked the mast as I tightened them up to ensure the mast wasn't being bananad - which it was a bit till we sorted the lowers and intermediates out ...
Been set for 18 months now (checked a few times) and all ok (touchwood!).

 

[bignick]

The lowers are in opposition to the baby stay - or foreward lowers. So if set correctly - but tight - will serve to keep the mast rigid to the lower spreaders.

Agreed, if you have twin lowers or a babystay. Not if there are only single lowers and no babystay, as per the pictures of his rig at the start of the thread surely?

 

[dt4134]

I think Selden are giving you very good advice advising you not to sail the boat until you get it sorted.

You clearly have a mast join so I'd guess the rig would be at least 50' or more. Advice given to me by a professional rigger is that you can't overtension a rig with 8" spanners. This is a rule of thumb and we were talking about a 40' plus boat so maybe it doesn't apply to body builders tensioning the rig on an average twenty footer, but on your size of boat you should be OK.

Do you really have discontinuous rigging where you have to separately tune the D1s & D2s? Usual giveaway is the rigger has to be hoisted up the mast with a couple of spanners. It would be more a cruiser-racer thing rather than something I'd expect to go hand-in-hand with in-mast furling and a deck-stepped rig.

I can't see a baby stay in the photos and you do seem to have swept-back spreaders, so the only way you'll get prebend is to ease the intermediates and tighten the caps. If you really have discontinuous rigging the means going up to the first spreaders to reduce the rig tension up there on the D1s. Obviously with in-mast furling you can't go for too much prebend, but there should still be some.

Inversion is pretty much the worst thing you can have as the aft wall of the mast is the weakest, so if you need to yank on the backstay to keep it under control that is better than just letting it persist. The mast seems really kinked and maybe that is the cause of the creases in the mainsail. Diagonal creases usually mean too much mast bend (that's too much bend the right way rather than too much the wrong way like yours) and are usually something that happens on racers who've yanked on too much backstay in lighter winds.

 

[William_H]

That is a pretty brave statement which i would generally disagree with. However inversion is a bad thing.

I would suggest to the OP that he check the spreader bases very closely. They need to be very rigid and strong in holding the spreader back at the angle. This pressure on the spreader tip provides the push forward to the middle of the mast.
Further if the mast has too much rake then the cap shrouds will not be diverted aft at the spreader tips so there will be less pressure pushing the spreaders forward. So the amount of mast rake then is limited by the location of the chain plates (the distance aft of abeam the mast). Less rake make improve the situation. (or more spreader angle aft)
good luck olewill

 

[dt4134]

That is a pretty brave statement which i would generally disagree with. However inversion is a bad thing.

Interesting! Which bit do you disagree with? That the aft wall isn't the weakest. Or that there are things that are substantially worse in tuning your rig (ruling out silly things like not even connecting shrouds or stays or forgetting the odd spreader).

Anyway, we'll not have an argument about it as I won't get to log in for a couple of days, but it'd be interesting to see why you laid into the post. And if it's *******s might come back in a couple of days and have the argument anyway.

 

[Talulah]

Well for my tuppence worth I think the mast is missing some rigging!
I have a Selden mast head rig. My spreaders are perpendicular to the mast where yours are swept back.
You only have one baby stay where I have two.
Looking at the photos your spreaders don't look swept back far enough to only have one baby stay. I would say you are missing a pair of baby stays or you need to change the spreaders mounts for ones that are swept back further.
Did the boat use to have running rigging?

 

[Chris_Robb]

Agreed, if you have twin lowers or a babystay. Not if there are only single lowers and no babystay, as per the pictures of his rig at the start of the thread surely?

Having looked at the pictures again, I agree that there is no baby stay or forward lowers. It is a mast head rig, and the spreaders are not very swept back. I don't understand this type of rig, but I do know that the lack of a baby stay requires the thrust to go down the spreaders, which I think means that the rig needs to be set up pretty tight. Somebody else suggest looking at the spreader roots - which I think would be a good idea.

 

[savageseadog]

Caps are too slack

 

[fireball]

Caps are too slack

Which won't necessarily be apparent - if tension is measured at deck level and the Intermediates are terminated at the outer end of the lower spreaders - like mine are ...

 

[Darrel_Walters]

Hi All,
Many thanks for all your comments, the rig does have sweped back spreaders, and is 7/8 th's

I have been chatting with Selden, at the bottom iof the mast is a number marked in the mast from new, this number is the code for selden to check the setup, which is being done now, hoepfully it will tell me all the measurements that I need to know to get this mast sorted.

Please keep brinign on the good feedback, I think the Caps are to loose my self. selden has said I should be looking at 20 to 21% on the caps and 20% on the back stay. so im off to try and find a tenstion guauge, I found a simple one at Jimmy greens

 

[Talulah]

so im off to try and find a tenstion guauge, I found a simple one at Jimmy greens

That looks like 10mm rigging. I doubt you'll find a suitable gauge online. (Your uppers are probably 8mm.)

 

[fireball]

7/8ths - fractional rig then ... same as mine ...

Sounds like quite a simple fix then - loosen off the lowers and intermediates ... set up the caps (& forestay) to the correct tension then do the lowers and intermediates.

 

[William_H]

Interesting! Which bit do you disagree with? That the aft wall isn't the weakest. Or that there are things that are substantially worse in tuning your rig (ruling out silly things like not even connecting shrouds or stays or forgetting the odd spreader).

Anyway, we'll not have an argument about it as I won't get to log in for a couple of days, but it'd be interesting to see why you laid into the post. And if it's *******s might come back in a couple of days and have the argument anyway.

Hello dt4134 In my experience I have built a few masts and looked at a lot more. The ones I am familiar with have a track molded into the aft wall. This would make the aft wall by far the strongest part. If it is a large section mast with track rivetted on then perhaps yes the aft wall would be no stronger than the front or sides. I guess my point is there can be a great many variations in Al extrusions. olewill

 

[bignick]

Mast rake too great, cap shroud tension too little / d1-2 tension too high, forestay length possibly having changed at rerig, mast heel not seated properly, too little backstay tension as wind increases.

There are many contributory factors which will all have an influence and it might be one, or a combination of some / all, plus more that I haven't listed.

I think its impossible to make a definitive statement from two pictures and no numbers. Definitely a risk of damaging the rig - its not designed to bend this way, so is still worth getting a rigger onboard to check it.

If original one is adamant he did it right and has been given a chance to fix any mistakes then I'd be getting a second opinion, hopefully Selden themselves can help - or recommend one of their agents to have a look.

For rigging gauges - do you know what diameter your shrouds are? I can see they're wire not rod from the photos, and I like the Pro series.

http://www.saltyjohn.co.uk/riggingtensiongauge.htm

I have PT-1m and PT-2m but I guess if you've a masthead 40' ish yacht then you may need a PT-3m (£190 !!). I don't like the cheaper ones (type A / B) as they don't seem to give repeatable results as you have to hold them in position and line up marks, where the Pro ones you just clip on and read.
At that price, and with the value of your rig, it would probably be better to get someone onboard. The gauge is only a starting point anyway - for dock-tune - and it would need on-the-water adjustment afterwards anyway.

 

[bignick]

Oops - must read more carefully - you say its 7/8.
If your caps are 7mm then you'd be able to manage with a PT-2m at a more manageable £90.

 

[haydude]

Hi,
Its Deck stepped, New rigging 2010, set up by a local rigger, who says that he tuned it all correctly. In the Marina the mast looks fine, but once you start driving the yacht at around 17 to 20 knots this is what happens, after 23 knots or so we are looking at reefing the main and genoa, this reduces the inversions, The yacht is moored in Milford Haven SW Wales

Clearly the rigger hasn't tuned the rig properly. If you have a loos tensioner, check the rig tension values. If not, it is time for a good investment.

If you have a backstay tensioner, then it is easy, just tension it tighter when sailing close to the wind, but no more than 20% breaking load.

If you do not have a backstay tensioner, then you have to induce a pre-bend in the mast.

I too have an in-mast furling main and I too had a similar problem. Riggers in general are reluctant to induce a pre-bend to the mast in case of in-mast furling because of the risk in jamming the sail, they say. In fact there is little or no risk of jam, the only issue being that the sail will furl in with creases, a minor issue compared to inverting the mast.

With back-swept spreaders tune the cap-shrouds to 20-25% of breaking load, then tighten the backstay to 15-20% of breaking load.

Or if the job is done by your rigger, then just tell him you want a "pre-bend" and if he advises against, tell him you are the owner.

 

[Darrel_Walters]

Wow so many great comments coming in, thanks so much, My Caps are 10 mm backstay 8 mm D1 10mm D2 guessing 8mm

http://www.jimmygreen.co.uk/item/428/surecheck-rig-tension-gauge

Has any one used this type of guage before ?