Masts

[icy sailor]

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[rastydn1313`]

Ayone want to share some deflection numbers.

Old numbers 1 3/8" to1 1/2" with 100 lbs between base and 11 ft. average for heavier sailor?

My personal masts Viagra MFG. for my weight aprox 1 3/4"
glass carbon

[Icy Sailor]

Geoff Sobering was sailing the last few years with a mast stifer than he wanted.  He kept it raked excessively but still struggled with it bending in lighter air.  Taking advice from some super tinkerers, Geoff made some mods and was very much faster and looking very good in Minnesota.

Geoff, share with us what you had, did and how it worked.  THere are others with masts too stiff to bend well... 

ICY

[Bob Gray]

The stiff tip whip,which is Sherry's basic mast, bends about 1.72 inches with 100 lbs. between 11 ft centers. A few of the many ways to get a mast to bend more are: 1) loosen side stays. 2) Get a softer plank 3) Decrease the angle between the headstay and the mast. This can be done by increasing rake or moving the mast step forward without changing the length of headstay 4) increase the distance between the boom and deck. The easy way to do this is raise the sail. These changes should be done one thing at a time and in faily small incerements, then check them by sailing against your tuning patner.

[Bob Gray]

In my above reply I mentioned decreasing the  headstay to mast angle in 3). I may have overstated a fact when I suggested moving the mast step forward without changing the length of the headstay. This could give you an excessive rake angle. The solution to this would be to shorten the headstay enough to aproximate the previous rake angle. This would still decrease the  headstay/mast angle.

[dn4889]

What's the rule of thumb on mast base socket position.  A few years ago fast sailors used the back position all the time, lately people have used the middle setting mostly.  Are the mast flex's changing or are people just using this to tune their rigs differently.  I've got an older carbon whip which always seem's a little stiff and I seem to get better bend with the forward hole.

[Paul Goodwin - US 46]

DN4889

To understand your statement "I've got an older carbon whip which always seem's a little stiff and I seem to get better bend with the forward hole" ...

Moving the socket forward usually makes the mast rotate more.  The increased rotation aligns the narrow dimension of the mast cross section with the pull of the sail's leech, and the leech tension bends the mast.  However there is a drawback to this situation.  Usually you want the mast bend to flatten the sail, and the increased mast rotation does this.  But when the mast is "over-rotated" it creates an increase in the draft of the mast/sail combination by presenting the wide dimension of the mast to the airflow into the leading edge.  This creates a non-optimum mast/sail shape: a wide (or thick) leading edge with a flat foil - and the extra drag from the thick leading edge will limit top speed.

Now, if you can de-rotate the mast by pulling back on the mainsheet blocks, then the narrow dimension of the mast is presented to the airflow and you end up with a better mast/sail shape for high speed: a narrow (thin) leading edge with a flat foil.  Also, the de-rotation aligns the wide dimension of the mast with the leech and helps maintain leech tension at high speed.

However, having the socket in the forward position can lead to more mast rotation than desired, and I think most sailors are using either the middle or back socket position.  Bob Gray disclosed the way to set up your rig for more bend without moving the socket.

To increase mast bend
1) Move the mast ball forward on the hull (without changing mast rake, requires shortening the forestay)
2) Increase mast back rake by increasing the length of the headstay (and raising the halyard to maintain the same boom height from the deck)
3) Increase mast side rake by increasing side stay length
4) Use a softer plank - as the boat accelerates the increase in sail force causes more plank bend, which in turn causes more mast side rake and thus more bend
5) Move side stay tangs closer to the hull
6) Increase the distance between boom and deck by raising the halyard

Note: Items 1 through 5 will increase the amount of mast bend, and also cause the mast to bend easier (with less rig load).  Number 6 will increase the amount of the bend, but not change how easy it is to get the mast to bend.

Here is a way to use this last note to advantage.  Try to get the mast/sail/rig setup to work well in the existing conditions with the sail height in the mid-range.  Then, by raising or lowering the sail you can make subtle changes in the amount of mast bend.  This is especially effective if you are at the starting line and there is a sudden increase in wind strength.  No time for a major change in rig tuning, but you know the mast will bend too much.  Solution --> lower the sail slightly (1/2 inch makes a noticeable difference).

Have fun and sail fast!
Paul Goodwin - DN US46

[Geoff Sobering]

I was wondering if anyone could talk a bit about the differences in mast-bend that is created by sail/rig forces (ex. compression and direct side-force) and bend that is induced by leveraging the tip using leech tension.

I ask because I'm slowly discovering that my mast really likes having some bend induced through leach tension, and I'm trying to figure out the balance between leveraging the mast out of column and letting the sail-forces bend it for me.

Cheers,

Geoff S.
US-5156