Mast rake theory help please

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hydrophylic

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I have a masthead rig. Mast rake is set by adjusting the length of the forestay. The forestay length is then not changed during the adjustment of the rest of the rig. This gives a saggy forestay.

My question is, how is the forestay tension set?

When the rest of the rig is set the forestay still sags.
 
Very much depends on the design of the rig. Do you have swept back spreaders or not. In mast furling means straight stick normally whereas conventional rig often has bent mast. All these things make a difference. A photo may help as well if possible. Some rigs depend almost totally on the shroud tension and have very little tension on the backstay.
 
As per Greeny ...

But ..

1. What mast step do you have ? Blade fitting with different pin positions you can move the foot ? Or a fixed position tabernacle ?
2. Swept back spreaders without backstays ?
3. Single or dual backstays ?
4. Furling gear on forestay ?

Who told you to set forestay for 'rake' before setting up other stays ?
Are you using most fwd position on mast foot blade instead of a more aft one ?

Lots of questions before any real answer can be suggested.

But lets assume you have a conventional stayed mast and a blade mount. I raise mast pivoting on the hole 1 position fwd of mid and use baby stays and forestay to keep mast upright and 90 deg transversely. I then adjust caps to tension ... then forestay to approx as previous - I use the locking nuts to show previous setting on turnbuckles. I then tension my two backstays till all is at reasonable tension and rake as near previous - then I adjust forestay to ensure furling gear runs ok .. no sag. Check round all stays again to make sure not too tight .. not slack ...
Final job is to take either main or spinny halyard and check mast is still square to deck transverse.
I would never say I leave one stay and adjust all others without going back through the process to obtain best result.

If I wish later to change rake or position of mast ... then I can use combo of backstays and Forestay - or move mast foot on the blade.
(I have Masthead rig as well).
 
Sigma 362
Masthead rig
Fixed tabernacle
2 swept back spreaders
Furler
Main, inter, lower forward, lower aft stays
IYE single wire backstay adjuster

I'm following boat manufacturers instructions: set rake with forestay length, tension stays.
Backstay is for adjustment while sailing not for setting up rig.
 
hydrophylic said:
I have a masthead rig. Mast rake is set by adjusting the length of the forestay. The forestay length is then not changed during the adjustment of the rest of the rig. This gives a saggy forestay.

My question is, how is the forestay tension set?

When the rest of the rig is set the forestay still sags.
Click to expand...
If there is not a rigging screw then the forestay length is fixed, presumably to give the rake set by the designer. If it does not then the forestay may be too long.
 
If you haven't got backstay tension, what amongst the rest of your rig will stop the top of the mast dipping forwards?
 
hydrophylic said:
Sigma 362
Masthead rig
Fixed tabernacle
2 swept back spreaders
Furler
Main, inter, lower forward, lower aft stays
IYE single wire backstay adjuster

I'm following boat manufacturers instructions: set rake with forestay length, tension stays.
Backstay is for adjustment while sailing not for setting up rig.
Click to expand...

Fine ... but that means that forestay must be set to its length so its tension obtains the rake at finish in combination with all other stays incl backstays.

Sorry but I cannot see any way to set rake before you tension up whole system.
 
Pye_End said:
https://support.seldenmast.com/files/595-540-E.pdf

Worth a read.

Swept back spreaders will offer some tension, but you need backstay to tension the forestay. If you have none on then the forestay may well sag, but the time you want the tension (ie bashing to windward) then presumably you will tension the backstay and to straighten the forestay.
Click to expand...
With the correct rig setup as per the manual the backstay hasn't enough adjustment to straighten the forestay on the mooring.
 
I'm not clear on how you've started the setting up. Some guides give a dimension to which you set the forestay length (easiest before stepping), others give a distance that the masthead should be behind the foot by measuring between the aft face at the bottom and a dangled weight on the main halyard. Which way have you set yours up, and how much rake do you have now?

And... how saggy is your saggy forestay? Do you have access to a tension gauge?
 
anoccasionalyachtsman said:
I'm not clear on how you've started the setting up. Some guides give a dimension to which you set the forestay length (easiest before stepping), others give a distance that the masthead should be behind the foot by measuring between the aft face at the bottom and a dangled weight on the main halyard. Which way have you set yours up, and how much rake do you have now?

And... how saggy is your saggy forestay? Do you have access to a tension gauge?
Click to expand...
Manual says 'Adjust the rake of the mast. This is measured at the gooseneck by using the main halyard as a plumb line, there should be approximately 9". This is obtained by adjusting the bottleneck on the forestay' - now a Furler.

I have a tension gauge but the forestay wire is obscured by the Furler gear so can't be tested.

Forestay foil is approximately 20 cm off straight at the centre.

The weight of the foils and Furler can't be helping the bend.
 
hydrophylic said:
Manual says 'Adjust the rake of the mast. This is measured at the gooseneck by using the main halyard as a plumb line, there should be approximately 9". This is obtained by adjusting the bottleneck on the forestay' - now a Furler.

I have a tension gauge but the forestay wire is obscured by the Furler gear so can't be tested.

Forestay foil is approximately 20 cm off straight at the centre.

The weight of the foils and Furler can't be helping the bend.
Click to expand...

Bingo !!

That is NOT what you say in first post ...

In first post you say you set forestay for rake and then tension all others - with Forestay then having sag ...

Please go back to my description of how I set my mast ... I get it upright and 90 to the deck transversely .. Then I start tensioning up ..... the rake is set by FINAL tensioning NOT at the start ...

Tension / rake is a balance of ALL stays ...

That is where I think you are erring.
 
Refueler said:
Bingo !!

That is NOT what you say in first post ...

In first post you say you set forestay for rake and then tension all others - with Forestay then having sag ...

Please go back to my description of how I set my mast ... I get it upright and 90 to the deck transversely .. Then I start tensioning up ..... the rake is set by FINAL tensioning NOT at the start ...

Tension / rake is a balance of ALL stays ...

That is where I think you are erring.
Click to expand...
Nonsense. You set the approximate rake by measuring the forestay length or as the poster says, by measuring the actual rake. Then you tension everything. And you will find that the rake has increased a tiny bit because you stretched the forestay. So you then readjust if that tiny bit bothers you. It's a starting point - you've not offered one.
 
hydrophylic said:
Manual says 'Adjust the rake of the mast. This is measured at the gooseneck by using the main halyard as a plumb line, there should be approximately 9". This is obtained by adjusting the bottleneck on the forestay' - now a Furler.

I have a tension gauge but the forestay wire is obscured by the Furler gear so can't be tested.

Forestay foil is approximately 20 cm off straight at the centre.

The weight of the foils and Furler can't be helping the bend.
Click to expand...
Ok, all the first part makes sense. How much wind does it take to get that 20cm sag?
 
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