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CS 17 Masts


fstauss

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Concerning masts for the CS 17. If I wanted to use ONE piece of aluminium for the masts (not 3 as the plans call for) the following questions come to mind.

1. Would this be a problem?

2. What aluminium thickness should I use?

3. Any problem because the mast would not be taperd to the top?

It seems to me that it would be easier to construct instead of making it a 3 parter. I plan to use the sail track for the sails so I would not be taking the masts apart anyway.

Any thoughts would be greatly appreciated.

Thanks, Frank

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Because the masts are free standing, the maximum load is where they leave the deck or thwart. The load almost tapers to zero at the head. To make one piece masts they would have to be the same size as the lower section.

By keeping the masts to UPS shippable lengths and stepping the diameter down at each joint we can approximate the strength to the load and save on aluminum which in turn saves money and saves weight and windage.

The weight may seem insignificant at first blush but after you step and unstep the mast a few times you will appreciate the extra weight off of the top of the masts, not to mention if you ever capsize. No performance sailor worth his salt want any more windage aloft than he needs.

What is not to like about three piece tapered masts?

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Graham:

Thanks for the reply. I agree that any extra weight in a mast when you are stepping same will add to the burden. I also agree that the shipping may have to be done by freight carrier (as was your kit), and this will add to the cost. You ask what is not to like about the 3 part mast? Well I have not built one yet but everything I have read tells me that it is a pain in the butt! From making the bearings (and trying to remove them after they he been made) to possibly having to bore the pipe for the pieces to fit seem like a big problem. A problem that could be handled by a one piece mast.

You mention that the thickness of a one piece mast should be what the lower section is. On the plans I ordered from you last summer the thickness is .083. A friend received plans from you in the fall and the thickness is listed as .125. Through this web site many have opted to use .065 as a lower mast thickness because of an inability to obtain thicker tube. What thickness are we talking about? I also wonder just how much extra weight the mast would be if it were all the larger thickness?

Please any other observations would be very helpful. I have not decided what to do as of yet any any help would be great.

Thanks, Frank

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Frank,

I went with the lower section  of mast being 8' tall at 2.5" diameter with a .125"wall thickness, and a "middle"section of 8'  of 2.25" diameter by .0625"wall thickness.

According to the Online Metals web page( where I bought the tubing...) the 2.5" tube weighs about 1.1 lbs per lineal ft., while the 2.25" tubing weighs .52 lbs. I plan to use a wooden "upper" section for my rig.

If you don't plan to take the rig apart anyway, I'd go with the "tapered" version...

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Frank,

Experiences vary. When my son and wife and I built such masts for our CS20,  each mast being made from 3 lengths of aluminum tubing,  the experience was one of the easier projects.  (No pipe boring involved.  Don't know what you mean by "trying to remove them after they've been made".)  It involved 5 kinds of effort: sanding/polishing the tubes; wetting out long narrow (~1") strips of fiberglass cloth; winding same around the tubing;  sanding same later to adjust fit;  epoxying, priming and painting.   Intent is that the tube sections are permanently joined;  this is not a take-apart mast.  Relative to other steps of the CS20 construction, it was rather quick and easy.   "Your milage may vary." 

--Paul

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Frank-

We just finished masts for a CS17 using a hollow wood tapered upper sections.  Took a lot of unneeded weight off the top and wasn't hard to build.  The mast is still heavy enough when you're stepping it.  The further weight is above the waterline, the more it wants to heel the boat.  The mast dimensions & tubing specifications Graham recommends appear to be the best compromise of needed strength, weight & availablility.

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Frank,

I think that you are mixing information. The design requires a minimum of .083" for the lower section. Which is 14 gauge. It seems to be getting harder to find and a lot of people are substituting .125" which while heavier is at the lower end of the mast. If anyone used .065" without increasing the diameter it will break. The upper sections are .065 which is perfectly adequate and readily available.

You may be mixing the mast tubes with the bushings which some people have had trouble getting off. Tom Lathrop solved that problem which has been discussed on this forum and you can do a search.

As Paul mentioned, the bushings are just a matter of winding wet out glass tape around the upper mast sections until you get to the ID of the section below it.

The mast tube is needed to keep water out of the forward compartment and has nothing to do with joining the mast sections.

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Might be repeating a few folks here, but... I thought assembling the 3-piece masts was surprisingly easy. I built both masts in a single day, not including the mast track, which took another day to put on after painting. The bushings are easy to assemble. I used a marked block of wood to approximate depth for each bushing, then used this as a visual guide while wrapping the bushings. I overwrapped by 1 or 2 turns, let the epoxy cure, then sanded off the excess little by little until I obtained a nice, tight fit. Once that is finished, making the collars at each joint is very quick and easy, though a little messy.

I also took the difficult route of backing all of the hardware fasteners with nylock nuts instead of just threading the bolts into the aluminum tubing. It took a lot of patience (about 2.5 - 3 hours total to do both masts), but basically, we taped a wrench to the end of a 5' long stick, taped the nut into the wrench, then fished it up the tubing while my wife sighted through the pre-drilled hardware holes. Once aligned, my wife gently turned the bolts into the nuts. Once it bites, you just have to hold the wrench snugly to draw things tight. We used a dab of 3M 5200 on each fastener to increase bond strength and to isolate the stainless hardware from the aluminum tubing (to prevent corrosion).

In retrospect, I wouldn't do the masts any other way. The resulting masts are nice, light, flexible, and look attractive when painted. If I could re-do anything (which I will have to re-do anyway), it would be the paint. I should've used an etching primer, but at the time, I was assured by tech support that roughing the aluminum would be adequate to bond the Systems 3 Silvertip Yacht primer and LPU topcoat I used. No such luck. Less than a year later, it is flaking badly, especially at the high wear areas (where the sprits rub, where the masts slide through the deck/thwart, and where the metal sail feet slide along the sailtrack). I also wish my masts were taller because my slightly oversized sails come down too far into the cockpit, impeding visibility and requiring us to duck low while tacking... a minor gripe.

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