Please help me straighten my mast

[Richard10002]

1st sail of the season a couple of weeks ago..... leeward shrouds so saggy as to be dangerous. backstay ditto.

Deck stepped mast.
2 sets of aft swept spreaders.
cap and intermediate shrouds
fore and aft stays, (to just below 1st spreaders)
Roller reefing on forestay
Backstay
Roller reefing main

tightened caps and intermediates very hand tight. Then tightened them again 2 turns when they were leeward shrouds, so now reasonably tight.

all seems fine.

Thursday and Friday, roller reefing main refuses to roll out easily.... bunches up in the groove, and the bunch tries to roll out as well as the leech, thus jamming.

Look up the mast today and it has a bend in it from about the first set of spreaders to the top. This means that the top of the furling gear is aft of the bottom of the furling gear, thus pressing the rolled up sail against the back of the mast, resulting in the problem.

The mast obviously needs to be straighter, so the furling gear lines up inside the mast without being pressed against the mast.

Selden manual says:

".......... check the mast’s fore-and-aft tuning.
The mast should have a slight forward bend at the
spreader area. Sight along the mast from deck level.
Adjust if necessary using the lower shrouds. "

It therefore looks like I loosen the forward lowers and tighten the aft lowers to straighten the mast.... does this sound right?

Cheers

Richard

 

[fireball]

Yup ... sounds right - the methodolgy for straightening that is ... not sure I'd like an inverted mast though ... do they really expect the mast to bend FORWARDS at the spreaders?!
Did you have the presence of mind to take a photo whilst you were there?

 

[Lakesailor]

Presumably you still have a topping lift or something at the mast head you can lead down to the gooseneck. Hold it taught and you can see objectively if the bend is forward, aft or sideways.
Adjust the mast rake using forestay and backstay.
Adjust uprightness (is that a word?) across the beam using the cap shrouds (measure side to side using a spinnaker halyard).
Then set the mast bend using the fore and aft lowers. I would have thought you needed very little pre-bend with inmast furling.

No claims if it all falls around your ears!

 

[Richard10002]

[ QUOTE ]
Yup ... sounds right - the methodolgy for straightening that is ... not sure I'd like an inverted mast though ... do they really expect the mast to bend FORWARDS at the spreaders?!
Did you have the presence of mind to take a photo whilst you were there?

[/ QUOTE ]

I'm still here so may be able to take a photo in the morning.

Having said that, it's quite hard to see the curve/bend unless looking up the mast with one cheek on it, (if you see what I mean), so it may not show on a photo

I think they mean it has a curve from the bottom to the top, such that the bit at the spreaders is forwards... the opposite of inverted.

I'll be giving it a go on Saturday.

many Thanks

 

[Richard10002]

[ QUOTE ]
Then set the mast bend using the fore and aft lowers. I would have thought you needed very little pre-bend with inmast furling.

No claims if it all falls around your ears!

[/ QUOTE ]

The pre bend is what is causing the problem, and I'm guessing it has happened as a resut of tightening the caps and intermediates, which are raked back.

Note your disclaimer, but you are only confirming what the manual says... which is good enough for me!

 

[Kylora]

[ QUOTE ]
so saggy as to be dangerous. backstay ditto.

[/ QUOTE ]

you need to check the rake of the mast to decide if you need adjust the lowers or adjust the back/fore stay.

A mast would normally bend forward in the middle, but with in mast reefing you can't afford much.

If you have an adjustable backstay, then you might be better to take the pressure off when reefing/unreefing to allow the mast to straighten.

If the lowers are holding the mast at the correct rake, then you need to lengthen the backstay/shorten the forestay.

Ash

Edit - Been LakeSailored

 

[fireball]

[ QUOTE ]
A mast would normally bend forward in the middle, but with in mast reefing you can't afford much.

[/ QUOTE ]

Can you clarify what you mean ... if the left side of the page is the bow (and the right side the stern duh!) ... then an open bracket ( would be an exageration of how I'd expect a mast to look - ie it bananas towards the stern - the middle may be slightly forward of the base .... if you've got a close bracket ) then I'd think (from my experience) that that is wrong...

 

[Kylora]

Agree with your opening bracket description, ie midheight of the mast would be nearer the bow than the top and bottom.

Sweptback spreaders are designed to induce the prebend.

Ash

 

[Richard10002]

[ QUOTE ]
[ QUOTE ]
A mast would normally bend forward in the middle, but with in mast reefing you can't afford much.

[/ QUOTE ]

Can you clarify what you mean ... if the left side of the page is the bow (and the right side the stern duh!) ... then an open bracket ( would be an exageration of how I'd expect a mast to look - ie it bananas towards the stern - the middle may be slightly forward of the base .... if you've got a close bracket ) then I'd think (from my experience) that that is wrong...

[/ QUOTE ]

I think we all mean the open bracket , and the term bending forwards refers to the bit half way up the open bracket. Negative bend is obviously a no no.

 

[Kylora]

[ QUOTE ]
... not sure I'd like an inverted mast though ... do they really expect the mast to bend FORWARDS at the spreaders?

[/ QUOTE ]

Your answer confused me - Seldon and me, and I think you are saying that the the mast should bend ( better described as bow ) forward at the level of the spreaders. They are not saying that it should bend forwards from the spreaders ( to the top)

Ash

 

[William_H]

High Ash just to be pedantic but to avoid confusion. Aft swept spreaders are not "designed to give prebend". Rather they press the middle of the mast in the prebend direction. The aft chain plate on the lowers means the lower stays are there to counteract the "prebend" middle forward. Just cos you have aft swept spreders doesn't mean you must end up with prebend.Aft sept spreaders give a similar effect to an inner (baby) forestay) ie stabilise the middle of the mast. olewill

 

[fireball]

Thanks for the clarification ... I just wanted to make sure!!

Quick question - are the spreaders fixed in a fore-aft direction? I wouldn't think so, but the reason I ask is cos on dinghies that don't have lowers the spreaders are bracketed to basically do the job of lowers ....if these are fixed then the lowers will not have the same effect as perhaps they should do.

 

[Guest]

Richard, First thing is do not play with a rig while it is sailing. The key is to keep it up right. If you can not tension it correctly statically then look for other problems like stiff turnbuckles etc.

The other point is to look for the original cause of the slack. It came from somewhere. Obviously you did not set it up slack.

So either your boat is shrugging its shoulders (Hull distortion where deck edges rise with relation to the mast base). Or the mast base is compressing.

But with swept back spreaders it could also be the whole mast went backwards due to a forestay problem. If you set it up with a slack backstay and the sail on the forestay (catenary curved forestay) then the mast will not be where it was during your first sail.

This is assuming that the wire is correctly sized. Did something give on the initial sail. Had any of the structural parts or chainplates been altered.

 

[Richard10002]

[ QUOTE ]
Quick question - are the spreaders fixed in a fore-aft direction?

[/ QUOTE ]
Pretty sure they are fixed, (perhaps a little bit of play).

Selden say the lowers straighten the mast, so I'll be giving it a go on Saturday.

 

[fireball]

[ QUOTE ]
Richard, First thing is do not play with a rig while it is sailing

[/ QUOTE ]
Beg ya pardon ... but you cannot set up a rig correctly with no sails up and everything can change once you get some pressure against it.
You HAVE to assess the rig whilst it is sailing - why do you think the racing fleet have backstay adjustment? They actively change this for different conditions whilst racing.
Instructions I've read for setting up shrouds are to sail the boat on a tight reach in a F3 and just tension up the leeward shroud, tack and do the same on the other side...

 

[Guest]

Sorry I disagree. You definitely assess a boat while out sailing to find its problems but with high aspect rigs (multiple spreaders and tension adjustments) you do not go distorting a rig while it is under load.

Back stay adjustment is to counter the force of the sail on the forestay and any mast bend is a simple bend. Adjusting a rig will put twists and dog legs into the system. How do you adjust the lowers with a sail in the way so you can not sight the mast track properly.

The other use of the sea trial is to make sure everything is bedded down properly before the final adjustment.

 

[rwoofer]

I've tuned my mast myself. You have the most control at the first spreader level, because you have forward and aft lowers, so it is relatively easy to adjust. The key point in tuning is whether the masthead is in the right position, because if it isn't then no amount of playing around is likely to achieve satisfactory results. If using the lowers does not sort the problem you can play with the inners and outers for the second spreaders, where the inners pull the mast back and the outers push it forward. In the end I started from scratch working from the mast top downwards.

Here's my approach. You are trying to get the masthead in the right position fore and aft and from side to side. This is done by using a non-stretchy halyard to measure the position from the bulwarks and distance behind the mast for rake (I went for about 10cm rake). You need to ignore the shape of the mast at this point. Tension the outer shrouds and fore/backstay until they have the right amount of tension in each and the masthead in the right position. You then work downwards with the shrouds to straighten the mast up until you get to the lowers, where you have the most control.

Hope this makes sense.

Richard