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Mast Stiffness

Postby fitzwarryne on Sat Jul 16, 2005 8:25 pm

I own 266 with the original mast. The mast appears to be very stiff making it difficult to bend and flatten the sail.

Q 1 Does anyone have any bend characteristics of a Sabre Mast? For example when my wife sailed a NS 14, they measured the mast bend characteristics by supporting at the ends and hanging a 28lb weight at the hounds- thus everyone had a standard measurement system.

Q 2 Does a mast case harden over time to become stiffer, 25 years sailing is quite a lifetime?

Q 3 In an earlier thread Stephen Early gave a method of softening by heating and slow cooling, has any one tried this and with what results?

Q 4 I noticed Binks in SA is selling Sabre masts, how does this compare with those sold in Victoria? Freight from Melbourne is expensive.

Q 5 Is it within the rules to use a mast with the track pop rivetted on, for example an ex Cherub mast which fits the rule dimensions?

I would be very grateful for any advice as its several hours travel to the nearest sabre Guru.
fitzwarryne
 
Posts: 58
Joined: Fri Jul 09, 2004 12:18 am
Location: St George, Bermuda

Sabre mast characteristics

Postby Barry Eastgate on Sun Jul 17, 2005 5:34 pm

I can't answer all your questions.
I believe it would be illegal to pop rivet a mast track on to the mast.
I have used the same mast since 1992 and I don't think the bend characteristics have changed.
It is a fairly light (not as light as John Dick's mast - 1275).

My mast bends as much as I want it to - which is very much controlled by the amount of luff round built into the sail.

Lindsay Irwin measured the bend in my mast before designing his current model sails and discovered that max point of bend was lower down than was previously in his computer...hence his current sails have a lot of fullness down low.

Interestingly, when Lindsay is asked to build a sail for 14 footers, he measures mast bend which is all he needs for his computer modeller to design a sail... 14's are not one-design like the Sabre.

FYI masts in Vic are relatively very cheap...purchased in bulk by SSAV in conjunction with other classes using the same section. I'm not sure what the current retail cost is, but they used to be about $100 cheaper through SSAV.
Barry Eastgate
 

Postby fitzwarryne on Tue Jul 19, 2005 12:43 am

Thanks for your rapid and informative response.

As a result I spoke to Lindsay Irwin who advised that while he could cut a sail to any bend characteristic, a stiff mast is the quickest way to the back of the fleet. That might explain in part why I am there!

Lindsay put me in touch with Bob Keely who said most likely mine was an original Alcan mast which was far thicker, heavier and stiffer than modern masts. He also told me it was illegal anyway as the class rules required a cut out for the sail rather than the track being opened up. That interpretation must have got lost at the SA border.

regards
fitzwarryne
 
Posts: 58
Joined: Fri Jul 09, 2004 12:18 am
Location: St George, Bermuda

Postby Guest on Tue Jul 19, 2005 5:27 pm

The Old masts were a lot stiffer and if anything masts tend to get softer with age. As for the cutout Lindsay is wrong. You can open up the track. My current mast was passed by the measurer and has an open track with no cutout. The problem is you still need the opened part to fit within the measurements. I would advise no one to cutout the mast as per the building notes as this leaves a weakness and has lead to broken masts. If you are going to cut out the mast only go just deep enough to allow the sail to enter.
As for the effect of stifness most like the flexable masts particularliy with the Irwin sails. The Hooper sails are said to perform better with a slightly stiffer mast or at least that was the logic a couple of years ago.
Dont forget that rig tension can make a mast softer but it will have only a small effect with those old masts.

Stephen Early
Guest
 

Postby fitzwarryne on Tue Jul 19, 2005 6:33 pm

Thanks Stephen for the response on mast cut out, the information was given to me by Bob, a real old time sailor/sailmaker from Adelaide.

My mast is ultra stiff but matches the original 1976 Ray Brown sail. I recently acquired a 1999 Hooper from Shane Nevin. As I said in a different topic. while attempting to flatten the sail by pressure my foredeck collapsed under the strain!

What I hoped to obtain in this topic was results from an objective method of measuring mast bend, for example by measuring the deflection caused by a specific weight suspended at the hounds. I thought of taking your advice on heating/slow cooling the mast to soften it but for some reason my wife vetoed the use of her hair dryer.

regards Paul
fitzwarryne
 
Posts: 58
Joined: Fri Jul 09, 2004 12:18 am
Location: St George, Bermuda

Linsay Irwin's method of measuring mast bend

Postby Barry Eastgate on Tue Jul 19, 2005 10:55 pm

Paul, I thought it worthwhile to describe how Lindsay measured my mast bend.

1. Rig the boat with your normal rig tension and lay the boat on its side.

2. String a light cord down the mast track between the top black band and bottom black band...wind tape around the mast to hold the cord tight against the black bands.

3. Attach the main halyard to the end of the boom and tension the halyard so that the boom is approx the normal sailing height off the deck.

4. Tension the vang and mainsheet to how you would have it in heavy, moderate and light conditions.

5. As the mast bends a gap will open between the mast track and the measuring cord...make sure the cord is always tight as it may slacken off as the distance shortens with more mast bend.

6. Mark about 4 different positions on the mast from which to take measurements and record the distances between the outside mast track and the tight cord for each simulated wind strength.
I can't remember the exact positions where Lindsay measured so it might be worthwhile checking with him...I am sure he would welcome feedback from anyone who does this so that avegare mast bend for sabre can be established.
Barry Eastgate
 

Postby fitzwarryne on Wed Jul 20, 2005 1:50 am

Barry, I will measure the mast bend as you suggest as soon as it becomes warm enough to sail so I can datum mark the sheets and controls. One method I have seen of keeping the measurement line tight is to use light shock cord.

At least it will be easy on a Sabre. I have seen a trailable yacht prior to ordering an Irwin sail tape a ruler to a halyard and hoist it then use binoculars to sight the results!

Thanks for your help, all I need to do now is learn to sail.

Paul
fitzwarryne
 
Posts: 58
Joined: Fri Jul 09, 2004 12:18 am
Location: St George, Bermuda


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