I once heard of a cruising catamaran which was designed so that the rig would blow off before the boat would capsize. I’m not sure if this is common practice for cruising cats, or whether it’s just because the righting moment is so big that it’s difficult to design a rig which will stay attached, but it was touted as a safety feature. Probably not what you want for an off-the-beach boat though. 😊

Mal.

Mal Smith - 12 May 2014 07:22 PM

I once heard of a cruising catamaran which was designed so that the rig would blow off before the boat would capsize. I’m not sure if this is common practice for cruising cats, or whether it’s just because the righting moment is so big that it’s difficult to design a rig which will stay attached, but it was touted as a safety feature. Probably not what you want for an off-the-beach boat though. 😊

Mal.

This is fairly common with cruising cats. Believe what you may regarding feature or bug (I do!), but to the best of my knowledge, it’s a fact. Not hard to design to if you think about it; max RM is fairly easy to calculate, as is max force a rig can absorb. Keep A > B and everything else sorts itself out.  😉

Dave

Update

Rather than fab a whole new wing, the existing is being ‘rebuilt’, the decision came after discussion and showing the thing to an old friend who’s a retired air force pilot. Spar cap was spliced and the trailing edge splinted with some uni carbon. New leading edge is all hotwired solid 1# foam with cut out for mast tube. After fairing the thing out, will cover leading edge with 4 mil mylar. 3M’s NP 30 contact cement appears to be the premium method to stick mylar to foam. Also found Rene 41 resistance wire is superb for hot wire cutting.

Most interesting though is the mast tube. Originally I missed the minor fact that the 53” long tube had about a 1” bend in it. Hmm, it was bent in a direction that corresponded with ninety degrees to the 20+ mph wind that day. So I now surmise that what really happened was one of the control cables hopped off a pulley and let the wing assume an angle of attack sufficient to load up the aluminum tube past its yield point and then the plug popped out of the top of the tube. Working backwards with a lot of suppositions, yield strength, wind speed etc. the wing was probably at a lift coefficient of 1.2 or so when the tube yielded, not bad for a symmetrical section.

John Wright had a 20’ stick of 1-1/2” schedule 40 aluminum pipe at hand that didn’t have a project assigned to it and graciously donated it to the cause (thanks John). In a massive burst of serendipity, the 1.9” OD of the pipe was a nice snug fit in the tube once a little heat, 3# rubber mallet and a straightening of the tube (with a 20’ piece of 1-1/4” steel pipe) were applied.

Cheers,
Skip

Skip - 04 June 2014 03:03 PM

Update

New leading edge is all hotwired solid 1# foam with cut out for mast tube. After fairing the thing out, will cover leading edge with 4 mil mylar. 3M’s NP 30 contact cement appears to be the premium method to stick mylar to foam. Also found Rene 41 resistance wire is superb for hot wire cutting.

Hmmm, do you mean *actual* mylar (polyester film), or the stuff they make “mylar” balloons out of (actually nylon film with a different plastic laminated on for thermal adhesion)? Or do you mean shrink-wrap as before? (I’m so confused…  😉

I love 3M adhesives, have never found anything Super 77 couldn’t permanently adhere. As it’s an aerosol you can use from a light misted coat (as for gluing 1/4 oz spinnaker cloth to itself) to a full double coat for sticking formica to countertops. Widely used by pro sailmakers—and pro kitemakers) It gets expensive for large projects, but it’s the bees knees for anything smaller than a pickup truck. Plus its shelf life—even a partially used can—is measured in years. I can’t personally vouch for it in heavy coats onto styrofoam—as I just mist the stuff on, but it’s awesome sticky, and very permanente.

For hotwire, I’m a fan of plain old stainless wire. Often free, never very expensive. I have several hundred yards of .012 I found at some garage sale, but you can get it as stainless fishing leader at Amazon for less than $10 for 10-15 yds. It has lower resistance than nichrome, so uses a little more juice, but it works totally fine.

Dave

daveculp - 04 June 2014 03:41 PM

Hmmm, do you mean *actual* mylar (polyester film), or the stuff they make “mylar” balloons out of (actually nylon film with a different plastic laminated on for thermal adhesion)? Or do you mean shrink-wrap as before? (I’m so confused…  😉

Real mylar, drafting film in this case, got a full roll of it.

I love 3M adhesives, have never found anything Super 77 couldn’t permanently adhere. As it’s an aerosol you can use from a light misted coat (as for gluing 1/4 oz spinnaker cloth to itself) to a full double coat for sticking formica to countertops. Widely used by pro sailmakers—and pro kitemakers) It gets expensive for large projects, but it’s the bees knees for anything smaller than a pickup truck. Plus its shelf life—even a partially used can—is measured in years. I can’t personally vouch for it in heavy coats onto styrofoam—as I just mist the stuff on, but it’s awesome sticky, and very permanente.

I use the 77 also’ super stuff, but it is pricey for big areas and melts foam

For hotwire, I’m a fan of plain old stainless wire. Often free, never very expensive. I have several hundred yards of .012 I found at some garage sale, but you can get it as stainless fishing leader at Amazon for less than $10 for 10-15 yds. It has lower resistance than nichrome, so uses a little more juice, but it works totally fine.

Dave

I’ve used a lot of fishing leader, it works fine but the Rene 41 is better, like the difference in a regular steel saw blade and a carbide tipped,

Skip

The wing is looking really good; I’m glad you were able to re-use so much.
How is the skin kept with a concave profile on the aft section ?
Convex and flat would seem straightforward but concave ?

pr1066 - 05 June 2014 12:59 AM

The wing is looking really good; I’m glad you were able to re-use so much.
How is the skin kept with a concave profile on the aft section ?
Convex and flat would seem straightforward but concave ?

The aft section gets recovered with heatshrink film, will probably have some diagonal strapping applied on top of film. The only place skin will faithfully follow the profile is at the ribs. Keep in mind this is a proof of concept operation, next iteration if it works out will be all foam with contact cemented mylar skin.

Skip

Skip - 05 June 2014 05:23 AM

The aft section gets recovered with heatshrink film, will probably have some diagonal strapping applied on top of film. The only place skin will faithfully follow the profile is at the ribs. Keep in mind this is a proof of concept operation, next iteration if it works out will be all foam with contact cemented mylar skin.

Skip

Very cool stuff, Skip. Thanks for patiently explaining all. What tricks/techniques do you use to get the mylar contact-cemented down without misalignment or wrinkles?

Dave

[/quote]
Very cool stuff, Skip. Thanks for patiently explaining all. What tricks/techniques do you use to get the mylar contact-cemented down without misalignment or wrinkles?

Dave[/quote]

First cheat 😉 I plan on covering in sections, 30” to 60” in the broomsticks case. The traditional way to stick large areas down is to use slip sheets between the coated surfaces and slide one sheet back just a bit to initiate contact once surfaces are lined up. Biggest problem I see at the moment after doing a smaller test section is the foam geometry needs to be dang near geometrically perfect for the mylar to lay down perfectly.

The idea is to start at the leading edge and work back on one side and then do the other, will know more in a week or two.

Skip

Update (on top of previous double post)

Wing is redone, now weighs 12.5# MUCH stronger/stiffer, no longer think torsion is much of a problem but will probably still add diagonal strapping over clear skin. Mylar drafting film went on in 2’ sections, still got a few wrinkles, primarily due to foam cores not being absolutely fair. It is now much easier to mount the wing since there is a solid foam ‘tunnel’ between the bearings. Tripod much stronger due to sched 40 pipe inside tube. One hassle was the process of pounding pipe into tube moved the collar that PVC legs attached to and it took a little trial and error to get it back into correct position. Changed the attachment point of PVC legs to bolts and wing nuts rather than screws.

Since things are a little stiffer I’ll try a counterweight this time, looks like about a 2# weight on a 40” arm will be pretty close. Anyone have an idea of how critical actual balance is?

Probably be a couple of weeks before we hit the water, weather looks bad this next week and we stay away from water on major holidays.

Skip

Another thing (besides bringing post to top) 😉

Here’s my take on end rudder hinges now.
The hard hinge with some rather nice poly hinge material just won’t cut it, too many operations, pieces etc.
Webbing hinge is the way to go, this was some 1” polypropylene, actual hinges will probably be with seat belt webbing.

Skip

Mylar hinges for the wing flap ?

pr1066 - 22 June 2014 12:02 AM

Mylar hinges for the wing flap ?

Wing flap is hinged with Scotch Extreme Package tape. The tape has reinforcing fibers in both directions, very flexible, tenacious adhesive and has to be cut rather than torn.

Actually there is some mylar in the hinge 😉 Strip of mylar the width of the head of the flap is covered with tape on both sides.

tttttttttttttttttttttttttt
        mmmmmm
        ttttttttttttttttttttttttttttt

Then cut into 3” sections and applied.

Skip

Hi Skip!  Great project.  I’ve been wondering when people were going to take an interest in the cam follower. The foam you cut looks great.  You mentioned that you would go with solid foam core for your bigger project.  Have you given any thought on how you would wire cut those pieces?  Also your solid foam you added was it layered up in pieces and then cut and then cut again for the mast step with a circular cutter of some type?  Lastly did you go for a sail with it yet?

Arden - 21 July 2014 05:18 PM

Hi Skip!  Great project.  I’ve been wondering when people were going to take an interest in the cam follower. The foam you cut looks great.  You mentioned that you would go with solid foam core for your bigger project.  Have you given any thought on how you would wire cut those pieces?  Also your solid foam you added was it layered up in pieces and then cut and then cut again for the mast step with a circular cutter of some type?  Lastly did you go for a sail with it yet?

The Broomstick gets wet tomorrow! Again, third time at Somerville on a Tuesday. John Wright and Kevin O’Neill planning to be there.

The current foam cores are adequate but not exceptional, the least little bit of unfairness really futzes with mylar skin, currently has a number of bubbles/wrinkles in the covering, but it is an experimental thingy. Foam was hotwired in 30” long sections and glued together and to the existing spar. Tunnel in foam for the stub mast hotwired at the same time. Will try to remember to post a couple of pics of the templates.

Next iteration, Nomad, if this works will have wing hotwired in 4’ or so sections left and right pieces so it will be easy to cut out core for alum stub mast and some lightening holes. All glued up with gorilla type glue, some uni carbon spar caps and mylar skin.

Cheers,
Skip