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Laser Masts for CS17?

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Surely some one has thought of or tried this but my searches come up empty. Say one was to find a couple used but good condition laser masts, would they work well for the CS17 main and mizzen masts?

From my searches, Laser mast:

Upper section 2.0" .065 wall by 142" long

Lower section 2.5" .125 dia 113" long

12" lost for overlapping sections for an OAL of 20'3"

CS17 main mast: OAL 19'6" starting at 2.5" and ending at 2" with an intermediate section in between.

I am sure the bending characteristics would be a little different, but overall they seem quite similar.

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I use a Laser mast and sail on my Spindrift 12 and it sails great. I was thinking of using 2 of them on my Coresound 17 once it is built since I can't locate suitable aluminium stock to make a mast as per plans here in Australia and I don't want to go to the expense of getting them from the US. Or I may go wooden masts. Do you think the Laser masts  would not be suitable for the Coresound 17?

 

Alex.

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There's a significant sectional modulus difference between the mast scantlings spec'd for the CS-17 and the Laser. Simply put, it'll be quite bendy, more so than the luff round is designed to accept, so the sail's general shape will be incorrect for the winds typically seen in a daysailer. This said, you could have a new set of sails cut to accommodate this additional luff round, though you'll need to run some math to determine the amount of round you'll need. On the other hand, if you used the 76 ft2 Laser (International) sail for the main you'd be about 10 ft2 over the CS-17's main area, but being loose footed, you could cut it down a bit without much harm (you'd have to cut about 14" off the foot). The mizzen is about 53 ft2, so you'll need to whack off more and will likely affect the sail's abilities, with this much of a reduction, though still a possibility, particularly if you sail in light air mostly. The Laser Radial sail would work much better for the CS-17 main, without having to cut it, too (62 ft2) and the Laser 4.7 sail would also be a better choice for the CS-17's mizzen at 51 ft2.

.

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Hey Alex,

Where are you in Australia? I know 6061-T6 is rare here, but it may be possible to get it. Also, I think I remember Graham recommending another alloy that's more readily available here.

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Hi Ken,

 

I live on the Gold Coast, Queensland. I have tried all the major suppliers on the Gold Coast and in Brisbane and no one can help me. I spoke to Peter from Brisbane and he said that he had his shipped out from the US. Which is why I was thinking of using Laser masts or make wooden masts. I will have a look at the OK dinghy masts and see what I can come up with.

 

Alex.

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The lower section of a laser mast is about the right spec. Maybe a birdsmouth wooden topmast on the lower section ( a 2 piece mast instead of a 3 piece) would work well.

Cheers

Peter HK

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I did a super quick, basic, and possibly inaccurate  analysis of the two masts because I thought they would be fairly similar.  Assuming similar material specs, the top and bottom sections are pretty much identical.  The stiff lower section on the laser mast is taller than on the CS17.

 

I looked at the total maximum deflection of each mast with a 100 lb. side load concentrated at the tip.  The laser masts top section was reduced to match the 19'6" of the CS.  I get 52" of defection on the laser mast and 31" for the CS. 

 

I am not sure how significant these numbers are because of course the load from a sail is not focused on top.  I bet the numbers would be closer with the load at the centroid of the sail area or with a uniform load. 

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Yes, it definitely is.  What I meant was that the maximum deflection at the end of the mast is only part of the picture.  For example, at 113" up from the base (the top of the 2.5" section of the laser mast) the CS mast is actually deflected more because it has already stepped down to 2.25" dia. 

 

If I were less busy (read: lazy) it would be interesting to see a graphical overlay of the two masts showing the different deflection shapes with a more realistic loading from a sail as opposed to my point load.  My guess is that the CS mast has a more gradual curve while the laser mast curves more sharply towards the top.  I'd also be interested to see the solid and/or birdsmouth mast thrown in for comparison.  Any FEA guys out there?

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Laser masts are also 2 piece so there has to be a joint with some amount of play that accounts for some (maybe a few inches) of deflection. In this picture, the position of the joint is obvious to me and there is a very faint "kink" in the curve. Was the mast you tested 2 piece? just curious. Of course, if your just using the mast for it's aluminum you can join the sections permanently. 

 

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