Masthead rig tuning

[DavidBolger]

I have a Sadler 34 which is a masthead sloop with one set of spreaders and a baby stay. I have noticed that my windward ability is a less than others in the fleet I race with. I reckon I am about 5 degrees off other boats. I also notice that my performance on a port tack is slighly better than on starboard tack. I have the tuning brochure from Kemp on rig tuning and to be honast I can't understand a word it says. When I look up the mainsail masttrack, the mast seems to be raked forward - I can't see the mastrack at the very top. I put three full turns on the wheel adjuster on the back stay. Should this be enough? Can anyone give me a layman's guide to mast and rig tuning?

regards

David

<hr width=100% size=1>

 

[oldsaltoz]

G'day David,

Have a look at this link, it's PDF so will take a moment or two to download.

<A target="_blank" HREF=http://www.practical-sailor.com/newspics/charts/8712mastheadrig.pdf>http://www.practical-sailor.com/newspics/charts/8712mastheadrig.pdf</A>

Hope this helps. . . . . . . . .




Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.

 

[tcm]

Re: The awful truth

Hm. There are of course lots of spannery things you could so to the rig. But, much more likely, you may simply have to face up to the fact that you are a bit crap at sailing, like me. I mean, you don't know how to tune the rig, and the others obviously do. The book is all horrible and complicated - but then so are the books about racing tactics and strategy! So, if it wasn't the rig it would be the nav, sail trim or something else a bit baffling. Somebody's got to come last in the fleet, haven't they?

<hr width=100% size=1>

 

[Aeolus_IV]

While I am no tuning expert - be aware that the back stay on a mast head rig is really only there to tension the forestay (oh and stop the mast falling forward off the boat). It will not modify any mast bend or the angle of rake to any significant degree. It sounds like you've an "inverted" mast bend (ie backwards rather than forwards), this isn't a quick set up. You'll also need to check your mast rake, roughly speaking the top of your mast should be between 6 and 10 inches vertically behind the foot of the mast.

Regards, Jeff.

 

[Twister_Ken]

David, I'm no expert but the top of your mast definitely shouldn''t be going forward (inverting). I don't know how the Sadler is rigged, but if it has fore and aft lowers one remedy is to tighten the forward lowers and slacken the aft lowers. This will, effectively, pull the middle of the mast forward and SHOULD correct the inversion you have at the top of the mast. If your rig doesn't have forward lowers, then hardening the babystay while slackening the aft lowers would have a similar effect.

As to going better on one tack than the other this is common. One cause is that the rig is not in the middle of the boat. Take the main halyard down to the toe rail by the shrouds on one side and then cleat it off. Move the halyard to the same point on the other side of the boat. Is it tighter or slacker? If so then use the cap shrouds to move the mast head to port or starboard to get it in the middle of the boat. Then use the lowers to make sure the mast is straight athwartships (look up the track to check).

If the mast is central then the probable cause of your asymmetric upwind performance lies not in the rig, but in distribution of weight. She'll be heavier on one side than the other. This allows her to sail more upright on one tack, thus making less leeway and creeping closer to the wind.

Backstay tension. It's unlikely you'd be able to overtension the backstay (depending on the pitch of your backstay screw thread, three turns is only equivalent to a few mm of movement), but as someone else said, its primary functions are to stop the rig falling forwards, and to keep the forestay straight. So tighten it if, going to windward, the forestay is curving off to leeward (which will increase the fullness of the genoa luff and damage pointing performance). If you're really keen on racing, fullness in the genoa is a bad thing upwind, but a good thing downwind, so let most of the tension off the backstay when reaching or running.

One good book on this (out of print but available through Amazon) is "Looking at Sails" by Bruce Banks and Dick Kenny. It has a simple and well illustrated section on setting up rigs. Vested interested - I was aboard many of the assorted boats when the shots were taken.

<hr width=100% size=1><A target="_blank" HREF=http://www.writeforweb.com/twister1>Let's Twist Again</A>

 

[DavidBolger]

Re: The awful truth

really helpful TCM

thanks

<hr width=100% size=1>

 

[dickh]

Another reason why it sails better on one tack than the othjer is that the keel is not dead vertical - like on my boat, only noticed when on it's trailer...

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[Twister_Ken]

So, some boats have canting keels deliberately, and other accidently?

<hr width=100% size=1><A target="_blank" HREF=http://www.writeforweb.com/twister1>Let's Twist Again</A>

 

[tcm]

Re: Sorry!

I have already pm'd David with apologies, but would like to do so again publicly for my very silly and unhelpful post. Obviously, i don't apologise every time otherwise 50% of my posts would be apologies.

<hr width=100% size=1>

 

[Aeolus_IV]

Seems common...

Ours certainly has a slight "twist" to one side (the lead balast on the base of the keel is slightly squint), and as a result of this (I believe) we go better upwind on starboard than port. Not a lot, but enough to sail out from under other boats while racing.

Regards, Jeff

<hr width=100% size=1>

 

[david_e]

Your mast should at least be vertical.

Sails could make at least 5% of the difference in pointing, as will the fact that most racing boats will be fractionally rigged thus allowing them to tune for better windard sailing (kicker, backstay, traveller, main sheet fine tune)

Sounds basic, but the difference between speed could be perception. Is it in all weathers and conditions or was it on one day. Often the wind is not directly over the waves so one tack will be a faster beat than the other.

<hr width=100% size=1>

 

[NigeCh]

Sorry. Disagree

The mast should have some form of prebend and have rake.

The simplest way to set up a masthead rig is to use either a Sure-Rig or Loos tension meter such that the forestay and capping shrouds are initailly set to 15% UBL and all other shrouds are set to 10% UBL. (That's for cruising. If you are racing then add another 5% to above loads and make sure that you release then when you've finished racing otherwise you will a non-hysterisis stretch and S/S work hardening which will seriously shorten the life of your shrouds)

Mast rake is best determined by sinking a shackel on the end of the main halyard in a bucket of water (to damp the swinging effect that comes from any breeze) on the deck behind the mast with the boom removed so that you can measure and calculate the rake angle. On a Sadler 34 the mast should have (without prebend) a rake of between 1.25 to 1.5 degrees with the boat in average loaded balance.

Rake determines not just tacking angle but also windward performance. With a 1.5 degree rake a Sadler 34 ought to achieve an 85 degree tacking angle with the backstay set to 17.5-22% UBL. Downwind it should be let off so that it is easy to get a 3" orthogonal pull by hand on the backstay: ie for downwind the mast should have no rake.

It's all a compromise - There is no best method. Some riggers set initial rig tensions tune by ear - Others do it with tension meters. Either way if you pluck your rigging you should get two sets of harmonics: one is the initial natural frequency followed almost immediately by the 2nd set of harmonics - If you pluck your rigging and nothing happens then it's too loose. If it zings and then the zing changes upwards you'll know that you are on the right track.

USE either a Sure-Rig or a Loos for initial static dockside tensioning. Then fine tune at sea.



<hr width=100% size=1>

 

[david_e]

Re: Sorry. Disagree

When saying at least - I mean not going forward at all is a better starting point. Agree that some rake will improve pointing.

<hr width=100% size=1>

 

[NigeCh]

Another way to determine mast rake

... is to compare your mast angle with others in a marina. Just look at those boats masts who go racing and win. Then compare their mast angles with yours.

There's no magic - It's both visual and down to numbers. At the end of the day it's all KISS - And it works.


<hr width=100% size=1>

 

[Starspinner]

Tension on the backstay should cause the mast crane to which the backstay is attached to give a forward bend to the mast centre. The instructions for my proctor mast are that it is almost impossible to overtension the backstay.

<hr width=100% size=1>

 

[loonyscot]

on our sadler 26 we always sailed better on starboard than port because the ladder is on starboard and tends to drag in the water when heeled. Try tying it up with a bit of cord

<hr width=100% size=1>

 

[Aeolus_IV]

Not sure this applies to the Sadler 34 rig. I don't believe they have a crane for the back stay - this is more typical of a fracitonal rig.

Jeff.

<hr width=100% size=1>