CD-28 mast flex

[Steve Bernd]

After reading the recent "Sailing" article about tuning your rig, I lay on the deck and sighted up the mast in about 15kts of wind and some moderate swells. I obsevered the masthead is moving about 1ft fore-aft as the sail is alternately loaded/unloaded due to the swells. The mast remains rigid up to the stays and the flex occurs above that point. It doesn't flex starboard-port. My instict is that the fore and aft stays need to be tightened but don't have a good idea of how much fore-aft motion is 'normal'or if the 1ft I observe is 'normal'.

Any ideas?

Steve Bernd
Valhala
CD-28 #359
Ventura, CA

[Larry DeMers]

The Cape Dory masts I am familiar with (CD26,27,28,30,33,330 and 36) are all made to stay in column under all conditions. No mast bend needed in this application. Get a Loos Tension gauge and check the tension fore and aft vs. athwartship. These are all the same size shrouds so should be tensioned the same..to approximately the 40% point on the Loos Gauges scale..for the wire size you have. I arrived at that 40% number by experimenting with as much as 60% and as small as 30%. I liked the 40% number best of all, and could not determine if the 60% number gave me anything for that high a tension..and of course the danger is to damage your boat if the tension gets too high (Bananna Boat Syndrome).

You do need that gauge to tell where you are at though. You cannot do an accurate enough job with eyeballing it, or as one guy tried to tell me..he tuned by the note the shroud makes when struck with a screwdriver! heh..probably were all as tight as a piano string. hmm, middle C no doubt.

Best of Luck,

Larry DeMers
s/v DeLaMer
Cape Dory 30 Lake Superior

After reading the recent "Sailing" article about tuning your rig, I lay on the deck and sighted up the mast in about 15kts of wind and some moderate swells. I obsevered the masthead is moving about 1ft fore-aft as the sail is alternately loaded/unloaded due to the swells. The mast remains rigid up to the stays and the flex occurs above that point. It doesn't flex starboard-port. My instict is that the fore and aft stays need to be tightened but don't have a good idea of how much fore-aft motion is 'normal'or if the 1ft I observe is 'normal'.

Any ideas?

Steve Bernd
Valhala
CD-28 #359
Ventura, CA

demers@sgi.com

[D. Stump, Hanalei]

Captain DeMers,

I don't believe Loos recommends 40 to 60% of breaking strength for ANY use! More like 12-15 to a maximum of about 20%! 60% would drive your mast right through the cabin top in my estimation. I do agree with you that all the CD masts must be "in column". If you actually tune to 60%, I bet you could play her rig like a violin!!!!!

D. Stump
Hanalei

[D. Stump, Hanalei]

Captain DeMers,

I don't believe Loos recommends 40 to 60% of breaking strength for ANY use! More like 12-15 to a maximum of about 20%! 60% would drive your mast right through the cabin top in my estimation. I do agree with you that all the CD masts must be "in column". If you actually tune to 60%, I bet you could play her rig like a violin!!!!!

D. Stump
Hanalei

[Bill Goldsmith]

Steve,

I initially hesitated to question your observation about the 1 foot play at the masthead, but then I had to make a comment. I am hoping that the 1 foot of fore 'n aft play was an optical illusion--the forestay and backstay attach at the masthead, so if there was 1 foot in play up there your backstay would be obviously flailing around and the same with the forestay. This is a safety issue. Sailing in 15 knots with essentially loose forestay and backstay could dismast the boat. Do you have a roller furler on the forestay? If so, you could damage it significantly. And if not, I would think that when hanking on the foresail you would notice that the forestay has no tension. If there is **any** tension at all on the forestay and backstay there should be no fore 'n aft play like that. As a safety measure, tighten up the forestay and backstay while the mast is vertical to eliminate this play before sailing any more. Then play around with a tension guage to get it tuned up.

If you are still getting that much movement up there after tightening the stays, you might want a rigger to take a look.

All the best,

Bill Goldsmith
CD27#173
Second Chance


A : After reading the recent "Sailing" article about tuning your rig, I lay on the deck and sighted up the mast in about 15kts of wind and some moderate swells. I obsevered the masthead is moving about 1ft fore-aft as the sail is alternately loaded/unloaded due to the swells. The mast remains rigid up to the stays and the flex occurs above that point. It doesn't flex starboard-port. My instict is that the fore and aft stays need to be tightened but don't have a good idea of how much fore-aft motion is 'normal'or if the 1ft I observe is 'normal'.

Any ideas?

Steve Bernd
Valhala
CD-28 #359
Ventura, CA

goldy@bestweb.net

[Leo MacDonald]

Hi Steve,

Exactly what do you mean with;

The mast remains rigid up to the stays and the flex occurs above that point. It doesn't flex starboard-port.

The 'Stays' should do to the top of the masthead?? (only instrument sensors, antennas, pigstick, etc above this point)

F/W, Leo



macdoreNOSPAM@aol.com

[Steve Bernd]

Bill and Larry,

Thanks for the execellent advice. The back stay does seem to be too loose when loaded and has very little tension. I suspect both fore and aft stays are simply too lose and the load is being born by the main sheet and sail. As the sail fills, it tightens and as it looses wind, it loosens. Now I know what my next project will be.

Best Regards,
Steve

Steve,

I initially hesitated to question your observation about the 1 foot play at the masthead, but then I had to make a comment. I am hoping that the 1 foot of fore 'n aft play was an optical illusion--the forestay and backstay attach at the masthead, so if there was 1 foot in play up there your backstay would be obviously flailing around and the same with the forestay. This is a safety issue. Sailing in 15 knots with essentially loose forestay and backstay could dismast the boat. Do you have a roller furler on the forestay? If so, you could damage it significantly. And if not, I would think that when hanking on the foresail you would notice that the forestay has no tension. If there is **any** tension at all on the forestay and backstay there should be no fore 'n aft play like that. As a safety measure, tighten up the forestay and backstay while the mast is vertical to eliminate this play before sailing any more. Then play around with a tension guage to get it tuned up.

If you are still getting that much movement up there after tightening the stays, you might want a rigger to take a look.

All the best,

Bill Goldsmith
CD27#173
Second Chance


A : After reading the recent "Sailing" article about tuning your rig, I lay on the deck and sighted up the mast in about 15kts of wind and some moderate swells. I obsevered the masthead is moving about 1ft fore-aft as the sail is alternately loaded/unloaded due to the swells. The mast remains rigid up to the stays and the flex occurs above that point. It doesn't flex starboard-port. My instict is that the fore and aft stays need to be tightened but don't have a good idea of how much fore-aft motion is 'normal'or if the 1ft I observe is 'normal'.

Any ideas?

Steve Bernd
Valhala
CD-28 #359
Ventura, CA

[Larry DeMers]

Dave,

I did not mention Breaking Strength in my entire piece. I was refering to the Loos Tension Gauge's scale..30% of the scale you are using. This has nothing to do with Breaking Strength, and of course, if it had been, I would be certifiably ready for the rubber room.
I quote from my piece:

"...to approximately the 40% point on the Loos Gauges scale..for the wire size you have. I arrived at that 40% number by experimenting with as much as 60% and as small as 30%. I liked the 40% number
best of all, and could not determine if the 60% number gave me anything for that high a tension..and of course the danger is to
damage your boat if the tension gets too high (Bananna Boat Syndrome)."

I was warning folks **away** from over tensioning their rigs, as the danger of a bannana boat syndrome is very real, for all boats (none excepted).

The main point is to keep the mast in column..that is where it's strength lies. Once out of column, it has only a fraction of the strength as before.

Did I clear that up? Hope so..nobody should read that as Breaking Strength, as that would lead one to the wrong answer completely.

Cheers.

Larry DeMers
s/v DeLaMer
Cape Dory 30 Sailing Lake Superior ...in a few months now.

The Cape Dory masts I am familiar with (CD26,27,28,30,33,330 and 36) are all made to stay in column under all conditions. No mast bend needed in this application. Get a Loos Tension gauge and check the tension fore and aft vs. athwartship. These are all the same size shrouds so should be tensioned the same..to approximately the 40% point on the Loos Gauges scale..for the wire size you have. I arrived at that 40% number by experimenting with as much as 60% and as small as 30%. I liked the 40% number best of all, and could not determine if the 60% number gave me anything for that high a tension..and of course the danger is to damage your boat if the tension gets too high (Bananna Boat Syndrome).

You do need that gauge to tell where you are at though. You cannot do an accurate enough job with eyeballing it, or as one guy tried to tell me..he tuned by the note the shroud makes when struck with a screwdriver! heh..probably were all as tight as a piano string. hmm, middle C no doubt.

Best of Luck,

Larry DeMers
s/v DeLaMer
Cape Dory 30 Lake Superior

After reading the recent "Sailing" article about tuning your rig, I lay on the deck and sighted up the mast in about 15kts of wind and some moderate swells. I obsevered the masthead is moving about 1ft fore-aft as the sail is alternately loaded/unloaded due to the swells. The mast remains rigid up to the stays and the flex occurs above that point. It doesn't flex starboard-port. My instict is that the fore and aft stays need to be tightened but don't have a good idea of how much fore-aft motion is 'normal'or if the 1ft I observe is 'normal'.

Any ideas?

Steve Bernd
Valhala
CD-28 #359
Ventura, CA

demers@sgi.com