Any ideas on how to go about to build a lightweight mastfoot? We have two old and heavyweight Tornado mastfoots which will have to be replaced as they weight way too much. Any ideas appreciated!

Rolf,
My first thought is glass reinforced polyamide 6.6
It comes in rods, tubes, plates and blocks.
Since this is just a thought, I don't know how much compression is there on the foot. The GF PA6.6 has a tensile breaking strenght of 150MPa dry and 140MPa wet.
Any ideea how much compression should it take ? The PA is lightweight -1400kg/cu meter, 2x times lighter than Al.
Very curious about the compression forces there.

There is also carbon fiber reinforced PA, and glass reinforced PEEK and carbon fiber reinforced PEEK. But GFPA6.6 is the least expensive.

Anybody good with the numbers ?

That is a good question, how large are the compression forces. I know the current mastfeet are made in silicone bronze and steel..
Shall we see. 400Kgs of sheet tension on the leech and perhaps 180Kgs of crew trapeezeing 2.5 meters from the centerline. Add a fudge factor, dynamic loads etc and I suppose the mastfoot easily have to be able to handle loads up to two tons? Just a guesstimate, I hope those who have done the calculations will chime in.

140 MPa means 1427kg/sq cm
Assuming compression strenght is higher than tensile strenght at break (it should be) if you distribute the 2 tons on an area larger than 2sq centimeters it should take the load.

Where are the engineers when you need them ?
http://www.ensinger-online.com/suche/gb/datenblatt_pdf.php?modus=PDF&ID=00122

Ah, but you need to build a mast endplate with a socket having a tight fit to the foot to make the required 2cm of contact. At the same time, it will have to rotate easily. Hmm.. Creative minds are in demand.

You can machine the whole piece from one solid block of PA.
It would be very very helpfull if you can acces a lathe, router, stationary cutting tools, drill stand, stationary belt grinder.

First shape the block to fit the inside of the mast, leaving a rim, then process the end part into a cone shape with a hole inside.

Not too much work, but this is just a fairy tale untill somebody helps with some numbers. GFPA6.6 is used a replacement material for steel to make pump housings and other industrial parts where steel can't be used due to corroding environments. It should be strong.

Ah, wonder if the guys in the repair workshop at work would allow one of their IT guys to even come close to that kind of tools <img src="http://www.catsailor.com/forums/images/graemlins/laugh.gif" alt="" />

Lets see what the australians think when they wake up in an hour or so. They might have some good and easy solutions.

This is a rough sketch of what I'm thinking about.

Rolf,
Some rule of thumb stuff.
A stainless steel mast base need not be more than 4mm thick.

Stainless is 7 times heavier than carbon per volume..
So a mast base from carbon would at the same weight would be 28mm thick. I think 1/3rd of that would be more than enough.
I'd use uni carbon because it is cheap and plain weave kevlar because it is durable and carbon does no like being drilled.
So the kevlar inclusion would be hand to counteract carbons lack of tollerance to being drilled..

So a 10mm thick plate of carbon/kevlar would do the trick. Now to a socket on the mastfoot and a pin on the beam to let the mast rotate on..

Rolf,
I have made a pin with 12mm threaded rod and a nut.
Screw the nut on. weld it in place and then grind a point of the rod. Put this through a stainless plate of the beam and bolt it in place from below. I you use a 25mm al tube with 3mm wall for the compression post you will need a hole in the beam that will be around the same size as the socket needed to do up the nut. So your mast pin transfers load directly to the compression post.

Now the fitting on the mast. Make friends with someone who owns a lathe.

Also as far as the mast base is concerned you should be able to make a mould with a mast off cut. Wrap something around the section that is say 5mm thick and make a mould say 50mm deep. lay into the mould carbon and kelvar apply a vacuum and weight until resin goes off. While still green sit the mast on top of the layup and lay in more to make a step that will locate base on the mast. So the outside edge would be 10mm thick while the centre would be maybe 20mm thick.

Also you could put a fair bit of glass in the centre to save cost of carbon especially aroun the edges keeping glass between the carbon and aluminium.

I'm 3/4 done building one at the moment. I'll post pics when I am done.

--Glenn

Looking forward to see what you have done Glenn!

I've completed my basic mast foot. A photo is attached. I'll write up the whole process with photos as soon as I figure out how to show pictures in-line. (I can't seem to get registered in Catsailor's online gallery.)

--Glenn

Glenn,

you're half way there copy the url from your attachement (open it after posting) and then go back and edit the post and hit the image button. Insert the picture's url and you're done.

Here's how I made my mast foot to mate my new SailCraft mast to my old IYE mast foot (with 2" ball) on my Tornado.

NOTE: I am *not* an expert. Mimic what I did at your own peril. I assume no responsibility for injury to you or your equipment.

I used the following woodworking tools:

• Chop saw
  
• - with *carbide* tooth blade.
• Table saw
  
• - with zero-clearance insert and
  
• - with *carbide* tooth blade.
• Belt Sander.
• Drill Press with
  
• - 1/4" and 1/2" speed bits.
  
• - a 2" hole saw.
• WD-40 and a respirator.
• Router
  
• - with 1/2" round-nose *carbide* blade and
  
• - with a set of router collars
  
• - on lowest speed setting.
• A bucket of water.
• A flat file.
• A compass. (Dividers with a pencil on one side.)
• A hot glue gun (or double-stick tape).
• A shop vac.

First, I matched the mast outer profile as follows:
I started with some 1.5" thick T6061 alloy tooling stock from imsmetals.com, my local metal supply house. I cut off a block a bit wider than my mast using my chop saw with a carbide tooth blade (images 145, 146). I used a scratch awl to trace the outer profile of my mast and mast web (the front wall of the track) onto the block, and used the chop saw to cut the rough outline, leaving about 1mm of extra material all-around (image 147). Then I sanded to match the traced mast outline plus an even 1mm reveal all-around (images 149 & 148). The reveal must be even all around for a good internal fit. Frequent quenching was required to keep the AL cool enough to handle.

Next, I created a rabbit (a.k.a "rebate") all around so the foot would fit inside the mast. First I installed a sacrificial fence on my table saw. (That's just a piece of plywood taped to real fence, so it's OK if the saw cuts away part of the sacrificial fence.) I installed a zero-clearance table saw insert for better support (image 150). I marked the center (high point) of my blade in pencil on the table of my saw. I then cut a small test rabbit the width of my saw kerf at the very top of the foot, and tested the fit against my mast. I adjusted the saw height until I had a snug fit in the mast.
Once the blade height was set, I removed the sacrificial fence and started cutting the rabbit in successive passes, moving the fence 1/16" per pass. I skipped about 1/8" at the top of the foot to act as a support for the other passes, and cut it away last (image 150), but in retrospect it was not necessary.
The trick to cutting an even rabbit depth is to keep the curved surface of the foot touching the table where you drew a line marking the high point of the blade.
I had to round the aft corners of the rebate with a flat file to match the inside of my mast. I achieved a nice snug fit.

Next I made and secured a template to the bottom of the foot as follows: I cut a template in 3/4" MDF with the 2 1/8" whole saw. With the compass, I marked a ~1/2 inset line on the bottom of the foot, to act a a visual guide. Then I hot-glued the template in place (temporarily), and glued and screwed blocks to the back of the template to hold the template in place over the foot (images 152 and 153).

I removed most of the metal from the hole with a 1/4" speed bit in my drill press, after setting the drill to the recommended 3000 RPM for soft metals. I set the depth limit on the press to stop my bit 3/8" above my drill press table. I drilled evenly space holes around the perimeter just inside the edge of the template, lubricating with WD-40 spray lubricant while wearing an organic vapor respirator. Cutting oil would have been better. I drilled out as much as I could without the holes intersecting. Then I switched to the 1/2" bit, adjusted the RPM down per my drills instructions (2180 RPM, if memory serves), and re-set the depth stop for the new bit, and drilled out as much as I could with that, centering the drilling on existing 1/4" holes, and making sure my 1/2" holes did not intersect each other(image 154).

Finally, I finished the mast foot hole using my router (set to its lowest speed) and 1/2" round nose bits and router template collars. I started with a collar large enough that my bits would fit through, and removed material in 1mm passes, first going clockwise around the template edge. Once I got deep enough that the router cutters were below the collar, I switched to a 1/2" router collar and re-cut all the way flush with the edge of the template, again removing material in <1mm passes, vacuuming out shavings between each pass, and lubricating with WD-40. Eventually, the whole was complete smooth, except for the pre-drilling around the edge (image 165) because I was using a round-nose cutter and didn't want to remove more material. If I had it to do over, I would not have pre-drilled quite so deep around the edge.
Note: I am very glad I pre-drilled. Removing the edge material works well with the router against the template, but removing material in the middle of the hole is a bit squirrelly, especially in the last couple of passes, which did not benefit from the pre-drilling de-bulking having removed most of the material.

The mast foot is more substantial in all respects (including weight) than my old IYE step, so I'm sure it's much stronger than it needs to be. Additional material could be removed by cutting a dado within the rabbit, and by removing material from the aft solid region. I will just KISS, however.

I will, however, be bolting an auxiliary plate to the bottom of the step to attach downhaul blocks, and to mate with my mast rotator control arm. I'll document that build similarly.

--Glenn [img]http://www.catsailor.com/forums/download.php?Number=141315[/img]