Anonymous wrote:

As another data point, our 40' schooner has all-aluminum masts assembled in the fashion Graeme describes.  Our 53', 10" diameter mainmast is parallel walled tube for the first 24', at this point the upper section of the mast is inserted 3' into the lower section.  The annular gap is filled with a aluminum rings at the top and bottom of the overlap with bolts joining the lower and upper mast sections through the rings.  There is some fairing that extends 4.5' above the join to smooth the transition between the two diameters.  The top section of the mast tapers down to 4.5"  Although the boat has only been a coastal sailor it seems to have held up well (masts were made in 1989).  Unfortunately, I have no idea where they got the tapered top sections from.

David, 

In the USA, the larger sizes of tube are available in 20ft lengths, and for your proposed schooner rig, you’ll be wanting lengths of up to double that. The tube is likely to be 8in or 10in diameter.

 The hybrid mast remains the practical pragmatic way to get masts of this size. I first made a hybrid mast, of alloy tube with a douglas fir topmast, in about 1976, and it’s still in service as the foremast of  Ivory Gull. Maybe I’ll be able to see how it’s holding up  this weekend, at Brixham.

I am planning my next mast (for a fairly heavy vessel) to be a solid timber pole for the bottom part, and a large tapered aluminium tube (recently acquired) for the top part. I suppose the solid timber pole will be made to fit inside the aluminium tube, at the join, but I have not yet worked out a satisfactory detail for that, and not yet quite sure how to do it.

Arne didn't call it a "split" mast, he called it a "hybrid mast" which is better terminology. ("Split" gives immediately a quite different image.)

You can make a mast from two different sections of aluminum, and this is probably the quickest way of making a pseudo-tapered mast. There are a number of ways the smaller diameter tube can be built up to fit quite accurately into the larger one. I have tried various different materials and ways to fill the annular gap between the two tubes and they all seemed to work. If the gap is small, a fibreglass bandage is a straightforward way of doing it.

I made one recently from three tubes (because that is what I had) and it looks quite good. You need sufficient bury of one tube inside the other. The final result (the join) must be robust against compression and also twisting (rotation.) The outside of the smaller diameter tube must also be built up so that the transition between the two diameters is fair, and will allow parrels to slide down easily. This fairing cone can slightly over lap the larger one below, and is easily made by a build-up of epoxy reinforced glass bandage. I am relying on this factor on its own to provide the strength to resist compression and twisting, expecting just a dab of glue inside of the join is sufficient. I I have relied entirely on epoxy glues and fillers, though I believe something like a polyurethane type of slightly flexible glue between the two tubes is probably better practice. For epoxy to stick well to aluminium, a light sanding and a pre-coat of resin on its own seems to be a good preparation and does make a difference.

There have been a number of threads which touch on this subject, the most recent being "Recommended thickness for partners/mast-support?"

Hi everyone, One of the big expenses and decisions in converting or repairing junk rig is mast replacement or purchase.  Wood technical and takes time, steel strong  and welds but heavy, fiberglass....forget about it, flag pole and light pole ali harder to source and expensive.

In comparison the cost and quality of what one could get in an untapered ali tube is a lot better.

The problem with ali is that welding in a taper weakens the tube.

Annie did untapered with a wooden top (composite?) for her Raven rig.

Now with considerable wood working skills under her belt from her build I wonder if she will do birds mouth staved tapered wood or a simple composite again.

I rather lean towards it for spars in my future (I will either buy a junk and have to replace or convert and make new ones.)

Has anyone employed an untapered ali spar or one with a small taper just at the top where it won't weaken too much?

Yes its ugly, and yes its weight and windage up high.  But it is dirt simple.

Finally would a simple tube spar need internal stiffening by way of the partners?

I look forward to your comments on this.