laminated mast- bend, layers, etc

[peterchech]

I did a forum search and little came up here, I hope there are others here who have experience with this...

I am about to build a mast for my outrigger canoe, to attach a oceanic spritsail to. It will be 17 ft long. The plans give certain taper/diameter for solid wood, though they are not specific as to species. Some flex is desireable here. My question is, on a mast of approximately 2.5inch diameter, tapered, if I laminate it from multiple thin layers of fir, or from just two pieces of fir, or anything in between, will the scantlings remain the same?

I have read that more laminations make a stronger but more flexible part, yet most laminated masts I can find pictures of are laminated from just two layers, not from multiple ones. Is there a reason for this?

[Cuyahoga Chuck]

Laminated masts are not normally made from thin layers but from billets that are positioned side by side. The cross section can be a square, a rectangle or even a circle with a hollow center.
A seventeen foot mast for a spritsail must be for one helluva big spritsail. Spritsail masts are usually short for the amount of sqares they can fly. Also a mast of 17 feet that starts out at only 2½ " is certainly going to be rather whippy. You need advice from someone who knows a lot more about wood then I do.

[kenjamin]

It's just more work to use multiple thinner layers but I think it produces a stronger piece. You probably could reduce the scantlings slightly with more layers but I wouldn't due to your use of the word "oceanic". Out in the ocean is not a place where you want something to break, especially your mast. I use 1/4" layers to make my unusual curved masts but my experience is that using multiple 1/4" layers makes for a stiffer mast rather than a more flexible one. The glue lines are harder and less flexible than the wood they replace in my opinion. Good luck with your build.

[peterchech]

here is what I mean by oceanic spritsail:

http://forum.woodenboat.com/showthre...pha-dory-sprit

[David G]

1. I'm not sure why anyone would call that a spritsail... but I know little about proas.

2. Why would you want to make up your mast of many thin laminates?

[peterchech]

I don't know, I guess I was thinking it would be easier to do because I am using construction grade 2x4's and it is easy to find a piece of wood that is good on one side but bad on the other. Laminates would allow me to use the good parts instead of having to just not use the entire piece of wood. Might mean less scarfing too. But honestly that's why I'm posting here, because I'm not sure whether its a good idea.

[StevenBauer]

If you are working with less than perfect stock the birdsmouth technique would be something to think about. I think it's the easiest way to make a tapered round hollow spar.



Steven

[peterchech]

I am def a fan of the birdsmouth technique, but now that spring is here I wanna be out on the water not building masts, so that is why a solid one that I can just buzz with the planer in an afternoon is attractive to me for this particular mast.

[Thorne]

Quick n' dirty is to epoxy two 20' 2x4's together, then cut and plane to desired size. Often recommended here is the use of three rather than two pieces of wood, so you could split the 2x4's longways and glue them up that way first. As above, that mast will be pretty flexible with those dimensions and length...

[peterchech]

Yeah it is meant to be flexible to spill wind if necessary. I am following scantlings from plans so I think they will work.

20ft 2x4's, they have to be knot-free though obviously, right?

[Thorne]

Mostly knot-free, or you may get better quality from a 2x8 and split it longways. What sort of wood is supposed to be used for a 17' 2.5" diameter mast?

[peterchech]

Doesn't specify wood type, the designer is from new zealand. Maybe I have his dimensions inaccurate, I'll check the plans again tonight, but I think I have it correct...