Westerly Fulmar - standing rigging set up/mast bend

[Tim Lee]

I discovered my mast was leaning to port the other day - subtantially - it took 15 turns on the bottle screws to straighten it up!
I now want to set it up properly from scratch and have read a bit on setting up fractional rigs so have some familiarity with the principles. What I'm not sure on though is what sort of mast bend I should be seeking to get on my Westlery Fulmar after setting up the cap and then lower shrouds. I know I can then increase bend with the backstay for different conditions, but what is the 'natural state' of bend? Anyone out there know? Or is it one of those 'not an exact science' things?

 

[vyv_cox]

There is generic information for masthead rigs at this page on my website. Prebend depends to some extent on the cut of the mainsail but about half the mast depth (width?) is typical.

 

[Tim Lee]

thanks Vyv -I came across that in my travels.

 

[Tranona]

Theres a comprehensive guide to setting up fractional rigs on the Selden website. For Fulmar specific no doubt you can get help from the Westerly Owners Association.

 

[richardbrennan]

I don't know where you are based, but XW Rigging rigged all of Westerly's boats since the year dot and know more about setting up the rigs than just about anyone. It's not that expensive to have the rig set up professionally and the gain in performance can be startling. They are based in Haslar Marina Gosport.

 

[VicS]

Theres a comprehensive guide to setting up fractional rigs on the Selden website

"Hints and advice" from this page http://www.seldenmast.com/frameset.cfm?id=6740&randnum=326715904

It's worth downloading and saving on your own computer

 

[merlin3688]

This may help from the Z Spar website.

1.1 Mast Rake

Mast rake is determined by forestay length. Rake affects helm balance - raking the mast increases weather helm.
As a starting point, use the designed rake on the sailplan (ask the boat designer, not the mastmaker). If no information is available, start at 1:30. (eg 33 cm rake on a 10m mast). To measure rake, tension the backstay approximately 60%, then check rake with a weight attached to the main halyard. (Boat must be floating level when you do this!). Adjust forestay as necessary to obtain the desired angle.
1.2 Mast Bend

Check that the mast is upright athwartships in the boat. Use the main halyard to measure from the masthead to the chainplate each side. Adjust upper (cap) shrouds to get identical readings each side (but use minimal tension in the shrouds).
A certain amount of pre-set mast bend is desirable, to stabilise the middle part of the mast and thus minimise rig pump in a seaway.
Ensure the lower shrouds are slack. Induce the required amount of pre-bend in the mast by tensioning the backstay. (Make a note of the amount of pre-bend by using the main halyard tensioned down to the foot of the mast, and measuring the amount of bend at the spreaders). Tension the cap shrouds equally, a few turns at a time, until the fore and aft bend starts to increase. Check that the mast is still straight athwartships.
Now tighten the lowers in the same manner as the caps, until the fore and aft bend starts to decrease. At this stage the caps should be tighter than the lowers.
Release the tension in the backstay, check that you are happy with fore and aft and sideways deflections.
(Once the rig is set up as described here, tensioning the backstay whilst sailing will affect the curve in the upper part of the mast only, as the area around the spreaders is fixed by the opposing forces of the shrouds).
2. Transverse Tune

Go sailing! Set full sail to windward in smooth water in enough wind to induce 10-15 degrees heel when sailing to windward.
Tension the backstay just sufficiently to straighten the forestay.
If the leeward shrouds are slack, tighten them, but NO MORE THAN TWO TURNS AT A TIME. Go on the opposite tack and do likewise, then tack again and check if the lee shrouds are still slack. If so, repeat the operation. DO NOT OVERTIGHTEN the lee shrouds, as you may bend the boat or break the mast when you tack!
Back at the dock, check that the mast is still straight athwartships.

 

[dunedin]

I discovered my mast was leaning to port the other day - subtantially - it took 15 turns on the bottle screws to straighten it up!
I now want to set it up properly from scratch and have read a bit on setting up fractional rigs so have some familiarity with the principles. What I'm not sure on though is what sort of mast bend I should be seeking to get on my Westlery Fulmar after setting up the cap and then lower shrouds. I know I can then increase bend with the backstay for different conditions, but what is the 'natural state' of bend? Anyone out there know? Or is it one of those 'not an exact science' things?

Was the mast lean based upon a spirit level, or measuring from chainplate to chainplate ? The reason I ask is that most Fulmar's seem to lean to one side when at rest.

If racing then need to match bend to sail shape. If just cruising I think we used to have a pre-bend of about 3/4 of the mast width (but that was a few years back so just from memory)

 

[Rob_Webb]

I don't know where you are based, but XW Rigging rigged all of Westerly's boats since the year dot and know more about setting up the rigs than just about anyone. It's not that expensive to have the rig set up professionally and the gain in performance can be startling. They are based in Haslar Marina Gosport.

I was going to make the same suggestion. And learn from them as they do it. Ideal.

 

[30boat]

One thing to bear in mind when setting up prebend is that the existing sail will fit well.My boat had excessive prebend when I got her and the main had been made to accomodate that so now that things have been corrected it doesn't set well anymore.I needed a new sail anyway.

 

[Powersalt]

Having owned a Fulmar for a number of years, I can tell you that getting the mast bend right makes a fantastic difference to the way the boat sails. So its worht the effort. From memory the forwd and aft lower shrouds can work against each other and create the inherant bend and the backstay the adjustable upper bend. Too much strain though and it could create mast stress. IM no expert though.

ps still got number 1 genoa if any use?

 

[wklein]

Was the mast lean based upon a spirit level, or measuring from chainplate to chainplate ? The reason I ask is that most Fulmar's seem to lean to one side when at rest.

If racing then need to match bend to sail shape. If just cruising I think we used to have a pre-bend of about 3/4 of the mast width (but that was a few years back so just from memory)

I don't trust the halyard trick as all nearly all masts have double sheave boxes aft so there is bound to be a dependency. most riggers will make cap shrouds in pairs to within a couple of mm so its a lot simpler to measure between the studs and go from there.

Also you would have to really go some to stress a mast through prebend i would say about 1 1/2 diameters as mainsail will pull some of it out. About 1/2 mast dia should be ideal.