Glassing Spars

Does glassing a solid wood mast or spar stiffen it up? I used a DF stair rail as a mast, tapered it a bit and because it seemed a bit bendier than I wanted I spiral wrapped it with 8 oz (I think...pretty heavy stuff) 4" tape and epoxy. I will recoat this evening before going to work but I was just wondering if it was going to do anything other than protect the wood.

Steve

 

I would think the fiber orientation would have something to do with it. Yours would maybe be at 45 degrees. I wouldn't think the short cross fibers would do much and the long ones are spiraled so they're not directly in line with the load. But in the end it seems it's got to stiffen the mast somewhat. I'd be interested to hear how it works.

 

Fibre type and orientatation has a huge bearing on whether you will get a stiffness increase that is noticable. The very best stiffener is uni directional carbon fibre laid along the long axis of the mast. Going to uni-axial fibreglass (if you can get it), will result in a significant reduction in stiffening effect, compared to carbon fibre. Spiralling a form of fibreglass tape, even 8 oz. will make a fairly small improvement in stiffness only, but should provide a noticable increase in resistance to breaking, but not bending. You could have asked before doing it, rather than after.

 

Well, seeing as I tried to run the cloth lengthwise and it did NOT want to cooperate and I wasn't about to spend a gazillion dollars on unidirectional anything plus wait for it to ship...all for $15 in stair rail because I don't have time to make a decent mast. It's only for a boat who's build price and effort was about $100 and a week or so. I just got a nice second hand 60 sq ft four sided sail which I I'll rig up with a sprit and sprit boom. I want to get done in time for My messabout on the 27-8-9th.

Steve

 

Anyone ever tried to make a Plywood "box" mast? I saw instruction for making one over at PolySail: http://members.aol.com/polytarp/mast.htm Seems like an easy way to put a mast together.

 

A week and a hundred bucks to a boat. You're a little more productive than me.

I can't say that I've built a mast from ply, but I have built a box mast. My concern though is the 3-ply lauan. If you're talking 3 plies of equal thickness, you'll have 2/3's axial grain orientation and I would think you would have a decent mast (application considered). If you are talking Lowe's moisture resistant ply, it's a different story. The surface plies are very thin and that leaves very little axial grain. Since a mast is axially loaded a large portion of the weight (in the cheap stuff) is providing little strength in the direction it is needed. In fact, the spruce corner pieces may contribute more to the axial loading in this design than the ply.

My mast is built out of douglas fir that Lowe's used to carry as the select pine. They have since changed to sugar pine as their "select." While most, if not all, grain was cut on the flat, I built all of my spars with the stuff and everything has performed well. My mast is a typical box section (3/4" thick) and has half of the components in cross-section of the design you are asking about. A thin section mast of dimensioned lumber will not have the cross-grain stiffness that a ply mast would have.

Provided your ply has the proper distribution of ply orientation, it looks like a good build method when given consideration to it's application.

 

I was thinking of using the better 6 mm 5 layer ply. The extra weight penalty would only be a pound or so for a small mast. I was also thinking of putting some thin stays on the stair rail and see if that would work. A dowel thru the top of the mast and the stays looped over it...just to limit the bend a bit. I think I am losing some of the shape in my sail because of excess bend. I need to lighten the boom and especially the sprit...too much weight swinging around up there.

Steve