Paul Thompson wrote:

Steve Wallace wrote:

So I'm looking at some steel masts and need a bit of sanity check. I've sourced some 40 foot poles that taper from 9" base to 4" top with a 3/16 wall all the way up. Using the formula from Build Your Own Junk Rig and using a safety factor of 3.5 since my Spray is is beamy and pretty stiff I come out with 9.3" so I think I'm right in the ballpark for the sail area (460 sqft). Does this seem radically off to anyone?

It's a bit on the heavy side, 1/8" would be better but the Spray design should be able to handle it.

I have the option between 11 gauge (so somewhere between 7/64 and an 1/8) or the 3/16. I was going to err on the heavier wall side just to be safe, I feel like with such a stiff boat it might be worth the extra weight.

Steve Wallace wrote:

So I'm looking at some steel masts and need a bit of sanity check. I've sourced some 40 foot poles that taper from 9" base to 4" top with a 3/16 wall all the way up. Using the formula from Build Your Own Junk Rig and using a safety factor of 3.5 since my Spray is is beamy and pretty stiff I come out with 9.3" so I think I'm right in the ballpark for the sail area (460 sqft). Does this seem radically off to anyone?

It's a bit on the heavy side, 1/8" would be better but the Spray design should be able to handle it.

Hi Steve,

Paul Thomson organised fabrication of a steel mast for Shoestring (32' Gary Underwood design and sister ship to Footprints)

It has one large single sail rig carrying 600 sq ft. See below mast dimensions.

I have only recently installed it and sailed it in  10-15 knot winds in relatively flat water.

The bottom 2 sections are 4mm thick and top three sections are 3mm.

The general consensus is that it is 'strong enough', some would say bullet proof, but I have been known to break things and will let you know how it does in windy conditions.

At some stage I intend to add some camber to the sail which could add to the overall stresses but I don't expect it will affect it too much.

The overall weight of the 'dressed' mast is just shy of 270kg. It is lighter than the original wooden mast and 2.5m longer. LAP=12.5M

I think steel is a good material for Shoestring. It has a smaller diameter at the partners than wood, and I have been able to rake the mast forward by about 5 degrees without shifting the mast step aft. The taller mast has allowed me to hoist the original flat sail a little bit higher (and further forward due to the rake), which has been enough to reduce weather helm significantly. I find the tiller is light now with very slight weather helm. 

The mast did arrive from the manufacturer with quite pronounced welds. These needed to be filled and  sanded with epoxy before painting with several layers of 2 pot polyurethane primer, undercoat and top coat. I will see if I can upload some photos for you.

Although I have had  one good sailing experience with the steel mast so far, Paul Thomson is much more knowledgeable about steel. He has had two steel masts on La Chica for some years now and is no doubt in a better position to give advice.

I hope this helps! 

Cheers

Roger

Mast Dimensions (as per email from manufacturer)

The non-standard  14.0m NMH 16 side Oclyte column with AFT=92mm and AFB= 260mm

All lapped section FW welded together plus extra 4 off plug welded the section together

·         Non-standard #1 section 3.6m 3mm  AFT=92mm, AFB=140.6mmm, , with 3mm top cap and client supply top fixing

·         Non-standard #2 section 3.6m 3mm  AFT=131.2mm, AFB=179.8mmm

·         Non-standard #3 section 3.6m 3mm  AFT=169.5mm, AFB=218.1mmm

·         Non-standard #4 section 3.6m 4mm  AFT=205mm, AFB=252.6mmm

·         Non-standard #5 section 1.5m 4mm  AFT=237mm, AFB=256.6mmm, with 5mm bottom cap and 75mm long 100x100x6 RHS welded at bottom