Mast rake theory help please

IF the mast is at the correct rake, and the forestay is too loose, it needs tightening.

However, IF the mast is at the correct rake, and the backstay is at it's tightest limit but still insufficient tension, then it is too long.

Assuming the mast is stepped in the correct place, and any pre-bend is correct.

Is it stepped correctly? Some have more than one option.
 
Does the forestay have a turnbuckle hidden by the drum of the furler? The odd ones that I have worked on do. Bit of a pain to adjust, but that might be where your extra length of the forestay is hiding. You mention the furler is adjustable at the bottom, but this is usually straps with several holes that move the furler up and down the forestay, not change the forestay length.
Face with a similar problem a while back, I chopped off the backstay swage and fitted a Norsman. Obviously too short then, as about 15cm was lost. So used a short link of stainless bar to get back to where it could be tensioned.
 
coveman said:
This may be helpful - How to set up your rig: tension your shrouds on masthead or fractional - Practical Boat Owner
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Or maybe this:
1d854a4e35b37fa84c0582658741e4e4.jpg
 
This is a deck stepped mast in a tabernacle? (so nothing pushing at deck level)
Does it have forward lowers?
A baby stay?
Any other bit of string pulling the mast forwards or resisting the shrouds pulling it back?
No halyards parked on the bow? Pole uphaul?
Boom not pushing forwards at the gooseneck?

I've skimmed the thread and maybe the forward lowers are the thing we're all ignoring?

Remove all the other inputs and the forward component of the forestay tension must pretty much equal the aft component of the main shrouds. (and backstay if that's not slack).
Are the jib sheets bar tight pulling the 'sag' into the furler?
You can get a bit of 'feel' for the tension in the forestay by seeing how ir deflects sideways when you push on it, compared to the shrouds whose tension you can measure.

When talking about 'tensioning shrouds to n%' it's important to be sure the rigging is the size of wire that the designer had in mind, and that you're not trying to stretch dyform like 1x19 stretches. Likewise I believe some tenson gauges over-read on dyform, specially at low tensions?

The traditional Sigma 33 tension test involves 'can you still open and close the bog door?.....'

For a dinghy, the first thing to check is usually spreader length and angle. Could that be wrong?
 
hydrophylic said:
The backstay has limited movement and is designed for use when sailing rather than setting up the rig.
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You said this initially. In post #7 I asked what else there is to create tension on the forestay. Jumbleduck asks the same thing in post#45.
The only way you can apply tension to the forestay is to pull back the top of the mast. Nothing else bears on the cap in the right direction. The speaders apply pre-bend which according to your book is only 3". The more tension you put on the spreaders the more likely the mast is to develop an 'S' bend.
It must be worth getting a pro rigger in to show you where to make the adjustments.
 
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.
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Yes. Page 37 makes it clear the backstay provides the forestay tension.
 
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.
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It seems like you are following a procedure designed for a wire forestay but actually have a furler? This may be the source of your problems. Further it seems like you are adjusting the forestay until you get the correct rake but with a slack/curved forestay? Then you find that you can't tighten the backstay enough to straighten the forestay?

If all the above is correct then all you need to do is use the backstay to provide a bit of tension while you adjust the forestay. You need to get to the correct rake with a straight forestay. The weight of the mast would probably be enough to hold a wire forestay straight while you do this, but with the added weight of a furler you need to help things along. So: pull the forestay straight using the backstay, measure the rake, slack off the backstay and adjust the forestay, pull the backstay back on and re-measure, etc. Once you have the forestay at the correct length you can release the backstay and set up the rest of the rig as per instructions.

Apologies if I have misunderstood your situation.
 
hydrophylic said:
That doesn't mention setting up a masthead rig with 2 spreaders. For single spreaders it says 'Adjust the forestay and backstay', I have no set up adjustment on the backstay.
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No adjustment of any sort on it? No rigging screw? No block and tackle? Nothing? How do you do the "adjustment for sailing" you mentioned in post #5?
 
hydrophylic said:
That doesn't mention setting up a masthead rig with 2 spreaders. For single spreaders it says 'Adjust the forestay and backstay', I have no set up adjustment on the backstay.
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The backstay is the only control you have over the mast above the upper spreaders.
If you have no adjustment on the backstay then a previous owner has removed it. You have quoted the handbook up until it suggests using the backstay.

s2107-rig.jpg
 
hydrophylic said:
I still don't understand either. Following the manual, all rigging is de-tensioned ten the forestay length adjusted to set the rake. The forestay is not readjusted then at any stage. With the weight of the wire and the furler foils there is a saggy forestay with no tension. How is a forestay tension of over 500kg ever achieved?
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You're not thinking this through. Tighten your cap shrouds to a base level of 15%. You may want more in future. (I sail with 22% when it's breezy). Your visible forestay sag will be minimal . Go sailing in light airs and you want some genoa luff sag, use the backstay to control it. In lighter wind you don't want lots of forestay tension. Go upwind in a blow and whack on a load of backstay. Sheet the main in hard and both will combine to give you the 500kg you seek.
 
TLouth7 said:
It seems like you are following a procedure designed for a wire forestay but actually have a furler? This may be the source of your problems. Further it seems like you are adjusting the forestay until you get the correct rake but with a slack/curved forestay? Then you find that you can't tighten the backstay enough to straighten the forestay?

If all the above is correct then all you need to do is use the backstay to provide a bit of tension while you adjust the forestay. You need to get to the correct rake with a straight forestay. The weight of the mast would probably be enough to hold a wire forestay straight while you do this, but with the added weight of a furler you need to help things along. So: pull the forestay straight using the backstay, measure the rake, slack off the backstay and adjust the forestay, pull the backstay back on and re-measure, etc. Once you have the forestay at the correct length you can release the backstay and set up the rest of the rig as per instructions.

Apologies if I have misunderstood your situation.
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I understand what you're saying and that that will achieve the correct rake and forestay length. If I then release the backstay and tension the rest of the rig won't this still result in a loose forestay at rest?
I'm beginning to think the backstay is just too long for some reason and needs a method adjusting the length during set up.
I'm away from the boat now so can't test.
 
Caraway said:
The backstay is the only control you have over the mast above the upper spreaders.
If you have no adjustment on the backstay then a previous owner has removed it. You have quoted the handbook up until it suggests using the backstay.

s2107-rig.jpg
Click to expand...
There's no mention of the backstay in the manual.
 
On one of my earlier sailing boats, a moody I think, the mast was deck stepped, I could never get the correct tension in the rig. I eventually discovered that the mast step had deteriorated and the coach roof was sagging under tension. I had to take the whole lot off, renew the base and install a pole inside under the mast down to the keel. It worked well, but I couldn't close the head door so i removed that and put a curtain up.
 
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