Since the F-16 forum was so quiet now, I tought I would seize the opportunity and ask a question.

Mast building is a complicated matter. The building process does not allow faults in your laminating technique, you must have the engineering spot on or it will be too stiff or too flexible (that is fixable tough?), small errors in building or engineering will make your mast come down/break, the end result will be heavier than a bought mast etc. If you goof up on the building, you have wasted a lot of money on materials (I dont put a value on my time when doing stuff I enjoy).

Now, if one still wants to build a mast at home..
Reasons to do so could be several, e.g. one can not buy the spesific wing-profile you want for a reasonable sum, you need a beefier mast, you want to try it etc.

Professional masts are made by laminating a hollow profile in a female mould or a male mandrel. For an amateur one-off project the male mandrel is probably off limits (how do you get it off the mandrel, and building the mandrel would be time consuming), as is the seamless female mould technique. Building two halves in a female mould could be done. Building two female moulds, on for the front section and one for the aft sectin could also be done. Both methods lead to a complicated joining session.

I was wondering if somebody had tought about building a composite mast with foam as distance material. The ORMA60's have used (still do?) this method, and it leads to stiff and light masts. You need to take care with the compression and shear loads tough. Building a female mould and working with foam this way should be possible, but it still leaves the two halves to be joined and a sailtrack to be attached. Building the mast flexible enough and still durable might be an challenge.
Simpler still, would be a carbon tube, H, I or U beam bought from a pulltrusion company like the one virtually in my backyard http://www.vello.no/. Adding a foam fairing and a sailtrack to the fairing should not be too hard.

Question is, what would probably give the best result with regards to weight, durability, bending properties and ease of building of the above methods? Are there other methods?

I'm not an expert in this in anyway, but for a first try I would form the full mast in styrofoam (32kg/m^3) and then vacuum a layup over this and leave it there. Should only add 2.5 to 3 kg to the whole mast and styrofoam is easy to shape and I think it it just strong enough to withstand the compression under vacuum. It is cheap, doable and has reasonably succes expectancy.

Wouter

I saw this

http://www.sailingsource.com/cherub/masts.htm

http://www.sailingsource.com/cherub/video/clips/Mast%20building.mov

I also saw another

http://www.harryproa.com/building_hg/buildinghg_wk14.htm

There was another good one, but I cant find it. I will post it tomarrow if I get the chance.

The Harry masts Rob builds are not wing sections, they are more roundish due to being buildt with carbon "strips".

The styrofoam idea sounds good for a one-off project. Styrofoam can be dissolved, so removing it afterwards is possible.

Wouter,

3kg added to something that is only 11-12kg is a pretty big step. For the expense and labor not to mention time in design and testing other than the self satisfaction of "doing it yourself" it does not seem very practical.

Polystyrene foam does not have very good compression resistance, so it will be very difficult to get the compression needed to properly consolidate a laminate that I would trust for a mast. The idea has some merrit though as we have used it for one off "lost mold" projects in the past. Poor acetone in the tube when you are done and it will disolve the foam and you have a hollow tube left over. There are some other methods that work even better, but they require yet another level of equipment.

Matt

http://www.moth.asn.au/download/DIY%20moth%20mast.gif
http://bateau2.com/content/view/114/28/
http://bateau2.com/content/view/115/28/
http://bateau2.com/content/view/116/28/

Hi Rolf,

I have heard of a number of one off wing masts being built of Western Red Cedar laminated with carbon etc. The ones I have seen where on bigger cats, but it could be possible for A or F16?

Regards Gary.

It's an academic interest just now Gary, even if I have some toughts spinning around in the back of my head. Nothing happens this year at least.

Immediately, I think WRC would be heavy as distance material in a composite mast, heavier than foam at least. But WRC is good at taking compression, so I dont dismiss the idea. Gougeon bros. said that a wood/carbon composite was excellent for handling cyclic loads (like a mast). Would be interesting to do the numbers on weight and strength (compression and buckling) for pure carbon, foam/carbon and WRC/carbon. Must try to get hold of some of my engineering friends..

Matt you wrote "There are some other methods that work even better, but they require yet another level of equipment."

Do you mind describing these methods?

Regards,
Bob

Contact kevin cook

He has posted on the board several time. Kevin has an autoclave in his back yard and has built several carbon masts, including a Tornado mast... His current project is for the big Trimaran that he is completing.

Hi Rolf,

Good to see someone prepared to go out a a limb and try something different regardless of commen sense!
I've been a lurker here for awhile but am interested to see if this project goes well. As Gary mentioned some bigger cats have WRC composite construction, I built a 15metre cedar/epoxy/glass (not carbon) mast for my 11metre Schionning catamaran. The mast was designed by Geoff Schionning for either glass or carbon construction. The WRC component however is only 4mm thick planks stripplanked over a male half mold, glassed with varying orientations of unidirectional cloth inside and out then two halves joined / faired and painted etc.

I only did this project as I like making stuff and the time it took meant I had a motor cat instead of a sailing cat for 6 months. There maybe some info at schionningdesigns.com.au as I believe he is designing an all carbon A cat as well as his usual bigboats.

Personally I think a thin ply wall would be a better option done in similar fashion with glass or carbon, maybe do-able as a one piece if all the glass goes on the outside and blocking as needed is added before gluing the ply to fwd and aft stringers.

Let us know how it goes if it does

Cheers Phil Palmer

Phil, thank you for the reply, looks like you have a very nice mast from the pictures. What is the weight of your homebuildt tube compared with a similar alu extrusion?
It seems to me like homebuilding is much more widespread "down under" than it is in Europe or the US. Perhaps there is something in your mentality or society that makes it so.

I like the tought of building a wooden core in strip cedar over a male mould, but need to watch weight compared to a foam core (foam will have less compression strength, so there is a tradeoff) or 'dissolving foam mould'. Ply is a poor choice in my uneducated opinion, too many fibers in the wrong direction and lots of heavy glue. Cold moulding would be better perhaps.
As for doing both halves on the same male mould, what about taper? I know the Superwing section is untapered, but I would like a certain amount of taper at the top. If I build a mast, I want it to have as many aerodynamically advantages as possible within budget and time.
I also wonder about how much the extra carbon/epoxy for joining and the sailtrack+glue affects stiffness.

The Schionning designs website was nice. I especially liked the A-cat page. Lots of innovation there.. Ref: http://www.schionningdesigns.com.au/www/page.cfm?pageID=263

I think he is on to something with his spreaderless carbon mast. This is also what I have in mind, but I was thinking about adding "pre-bend" out of the mould to make it easier to trim and more responsive.

Hey rolf, I think you'll find the mentality thing is like we enjoy doing stuff the hardest way possible for the least possible return on effort! But hey I've never owned a playstation so time needs to be spent somehow.

My 15m stick (actually I sold the boat recently so its no longer mine), was supposed to be on par weight wise with an alu section of the same size, strength however is better due to the correct fibre orientation for the expected loads. The carbon version would have been approx 30% lighter again. The mast never actually got weighed so actual figures I can't give.

Regarding a f16 size mast, I'd still lean toward a base of ply and I'm only talking 1.5 - 2mm, just enough so that when bent to the desired curve it'll hold the shape while adding the carbon. As for fibres in the wrong direction, you'll still need some fibres across the grain to hold it all together, the large mast had 20% of the uni cloth running at 45 deg to the axis for resisting torsion, I'd suggest a 0.5mm layer of ply at 90 deg will add very small weight and big time in helping hold a good shape, tapering also would be easy enough, prebend maybe a little troublesome but thin ply will compound curve to some extent. Still its your mast and I'll be happy to see how the dissapearing foam trick works if you do that.

The only other main concern I'd have is that the mast will not be predictable enough to get a guaranteed sail that works with it. Maybe the first sail will need to be experimental to see how it handles the loads.

Good Luck
Phil

Hi Rolf,

I like the idea of spreaderless prebent wing mast. Crowther Multihulls designed such a mast for large Multi's, I have seen a couple in action and they looked good. One of the guy's that lives nearby has built a couple of Schionning cats, he had a home built mast on his first one, which had trouble with invertion so he kept raking back the diamonds and increasing diamond tension to prebend it, but eventualy diamond fixings failed and he broke the mast. So that's why I think building in prebend is a good idea, it can never invert I think.

Phil, it's good to see others going back to off the beach cats from big ones, although mine where not as big as your Schionning, which are very nice cats we have a couple of them on the Gippsland Lakes now.

Regards Gary.

I just discovered why the A class mast on the Schionning is left untapered. Apparently, the A class measures the largest chord when calculating mast surface area, so you loose area by doing a taper. How is this done in the F-16's ?
The Schionning mast also have 15mm pre-bend, which is not enough in my opinion. Will be interesting to see how it performs!

Current thinking on adding distance material in the mast is that it will be too stiff for efficient trim and gust response if buildt strong enough to stop panel buckling. Interesting stuff..

I'm saying for years that the A-cat rules are less simple then every thinks or is made to believe.

F16 class is only interested in the actual area of the mast ALONG the mainsail luff. For most masts this means that cord times luff length is a very accurate approximation. When you have mast taper you can calculate the real area and put the part you lost into your mainsail.

In addition the area of the mast below the boom is not included in the mast area (isn't effective in anyway) and can therefor also be put back into the mainsail area.

This is the direct reason why F16's typically have 1.4 sq. mtr. more EFFECTIVE sail area than A-cats while on the class rules it would appear that we only have 1.05 sq. mtr. more.


Do you like this news ?

Wouter

That is good news of course, simplicity is good (if it is possible).
I assume from this that there is no set procedure for measuring mast surface area, but you try to find the real surface area using whatever method is neccesary.

bending characteristic is mostly more important than pure theoretical thinking about the wing profile. most wingmast sections mostly have the problematic tendency still to be to hard fore aft and to soft sideways (compared to soft aft). I know that in the A class those guys who builded the first holland composites spars (the mould later went to austria and became fibrefoam) believe you nowadays could just use a tube profile with a thinner diameter than current A-class mast profiles and glue a sailtrack on the back of it. the aerodynamic issues could be solved within the sail for example like the windsurfers do...
but main topic than would be to get the sail right!
but you can always easily change the bending characteristic of such a tube-carbonmast by simply adding unidirectional carbon fibre strips to it...

if you go the other way (for example with a core of styrofoam) you actually will have very little control what the final bending characteristic will be like and chances to get it right are quite low...

for reusing an prefabricated carbon tube, you might not even need an autoclave...

Great post Hans.

You will have quite a round leading edge of the airfoil if you use a tube, but a sock like windsurfers (with camber inducers perhaps) Moths and certain Wharrams might work well. At least, testing can be done with this rig until one finds the correct stiffness (something I guess isn't easy to get right just by calculation), and then a lightweight/flexible glass+foam fairing can be added.

Autoclaves are definately out of the question for homebuilding. The best one can hope for is vacuum bagging and cooking in a homemade stove. I know Kevin Cook has his own autoclave, but I consider him an interesting but special case


In conclusion, there are quite a lot of alternatives if one feels like building a mast..