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Catalina/Capri 25/250 Sailor's Forums

General Sailing Forum

"A " Frame material

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Jmurfy
Navigator

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USA
176 Posts

Initially Posted - 10/24/2005 : 22:16:18

Can anyone tell me if the 1" conduit described in the mast raising "A" frame system described in the tech forum is rigid conduit or EMT?

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JimB517
Past Commodore

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USA
3285 Posts

Response Posted - 10/25/2005 : 12:31:51

I used 1/2 inch steel electrical conduit from Home Depot for about $2. Plenty strong (a bit heavy). Cut down and bent to shape in my vise.

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JimB517
Past Commodore

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USA
3285 Posts

Response Posted - 10/25/2005 : 12:31:57

I used 1/2 inch steel electrical conduit from Home Depot for about $2. Plenty strong (a bit heavy). Cut down and bent to shape in my vise.

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Bubba
Admiral

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USA
542 Posts

Response Posted - 10/25/2005 : 20:26:29

I used 1" galvanized steel conduit from Home Depot. It came in 10 ft. joints, pre-threaded on both ends and included a union. By cutting each in half, I could turn the ends around and screw them together for use and break them down for transport and storage. Here's a link to my system for a C-250: http://mywebpages.comcast.net/frayed-knot/projects/a_frame.htm
It ain't pretty, but it's inexpensive and it works.

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lcharlot
Master Marine Consultant

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Antigua and Barbuda
1301 Posts

Response Posted - 10/25/2005 : 21:30:12

CAUTION: When using thin-wall metal tubing, either steel or aluminum, in any application that places the tube in compression, it's load carrying capacity can be severely reduced by even the smallest dents. Tubular compression struts made out of 1" or 1.5" EMT or thin wall aluminum, and used for Catalina 25 mast raising "A" frames, are stressed to about 200 pounds each when the mast is approaching horizontal during a lowering or raising evolution. Considering they are 120" long, the "slenderness ratio" (an engineering term), suggests that 200# compression loading is nearly the limit for 1" diameter steel EMT. Compression struts that exceed the load limit fail by "buckling", where the stress finds a weak point in the metal, usually near the middle of the strut, and causes it to suddenly bow sideways and collapse. Any dents, holes, cuts, or corrosion in the tubing can drastically weaken it at that point, as the flaw will create a "stress concentration" there. With this in mind, I recommend that every time you set up an A-frame (or Gin pole) to do a mast raising, the tubing must be inspected for damage or corrosion, and not used if it isn't in perfect condition. Compression failures tend to happen suddenly, with little or no warning, and thin wall tubing has a LOT LESS load capacity in compression than it does in tension. My "A" frames and gin poles have usually been made of 2 x 4's instead of steel EMT tubing, or 2" diameter x 3/32" wall aluminum. At least with aluminum, you don't have to worry so much about hidden corrosion inside the tube where you can't see it. "A" frames and gin poles made of steel tubing should be stored inside out of the weather when not in use, like in the rafters of your garage or toolshed, where they won't get rained on or run over by a car backing in or out of the garage.

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ed_spengeman
1st Mate

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USA
98 Posts

Response Posted - 10/26/2005 : 13:20:31

Finally bit the bullet after reading almost all of the posts on the board. Bought a Mast-Up from CD Direct. Got (2) good 2x4x10s and a nut and bolt to join them at the top after angling the boards to make a good fit at the top. A pulley is centered on the bolt. Got an "all-thread" to use as a brace in the center of the a-frame. It's about three feet long and has nuts inside and outside where it goes thru the 2x4's. I drilled holes at the bottom of each foot and put strong line thru it to tie the feet of at the stantions. The feet lean against them and are tied only to hold them in place. I mounted a Fulton Automatic Winch ($50) on one of the legs and got about 30' of good line for it. All parts were bought at Fleet & Farm.

For operation, I tie off the feet of the frame to the stantions, lean it about 30 degrees forward and tie a line from the top of the frame to the forward cleats on the deck. The jib halyard is run up near the top of the mast after the line from the winch has been attached.
Cleat the halyard.

I found the Mast Up not really worth the money. It seems to take two husky players to make it work. I just use it as a prop now.

At this point, the mast can be lifted from almost horizontal with MINIMAL help from a second person. With this type winch, you can just let go of the handle and address any needs.

My reason for boring everyone to death is that, as a newbie, I had a hard time putting all the suggestions into a rig I knew would wotk. This works on a tall rig, is cheap and 1 1/2 people can put it up - a husband and wife. Hope this helps

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thaind
Navigator

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Canada
145 Posts

Response Posted - 10/26/2005 : 13:52:06

I made mine out of conduit and watched it twist like spaghetti trying to raise my Tall rig mast. The one I now use is 1" square steel tube bolted at the top and welded to 5/16" eye bolts. I feel safer now.

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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.