Mast Diameter question

[mkrautha]

Hello,
I have a hurley 22 and I want to replace the aluminum mast with a solid wooden mast. I live in VT where pine lumber is cheap, and so my plan is to laminate up a few 2x6s and then use my saw and power planer to get the right shape. The current mast is stepped on deck, so the base of the new mast will be squared to fit the mast step, but I wonder, any suggestions for the appropriate mast diameter? This is a 22' (LOA) 3900 lbs disp. twin keel sloop rig that carries a 103 sq ft. mainsail. The forestay attaches to the mast, and the no 2. genoa is 187 sq ft. The working jib is 100 sq feet.

I'd appreciate any suggestions.

[JimConlin]

A solid pine mast will certainly be heavier than an aluminum mast of the same strength. This will make the boat heel more and pitch more in any sea. It will also need more maintenance.

Why would you do this?

[Bob Cleek]

It can be done, but it's not as easy as you might think. I'd doubt pine would be particularly good for spar purposes. You want a wood with a high compression strength, such as Sitka spruce or Doug fir. Then there are weight issues. A wood spar is considerably heavier than an aluminum one, and a solid wood spar MUCH heavier. That much additional weight aloft may alter the stability characteristics noticeably. Most wooden spars in Marconi rigs are hollow due to weight considerations.

I'd suggest you get a good book on mast construction.... Chapelle's "Boatbuilding" or Steward's on wooden construction, and also the book on "Boat Strength" that WB Store sells, which will contain all the engineering data you should need to determine the strength needed and the corresponding size for the various species of wood you might use. That will tell you whether you can use a wooden mast of the same diameter as your aluminum spar... which you probably can. Those books will also tell you how to build hollow wooden spars. There's more to it than laminating up a beam and whittling it down to size, but it can be done. Then, again, why would you want to?

[mkrautha]

More work to maintain perhaps, but less work to make adjustments to my rig, add/remove cleats etc.

I have spoken to some spar builders who say that the difference in weight aloft is not so considerable that it will make a major difference in stability. Also, that while sitka spuce is most desirable, that fir or pine would also work.

My boat and aleutka are similar boats in terms of specs, with aleutka being slightly heavier but also a bit longer. John Letcher instructs:
"The prototype Aleutka has a solid fir mast,
box section, 3 5/8 inch square and tapering in the upper third down to
2 inches square. This was made by gluing two full-length clear 2x4's
together. It has never given any trouble, but it is a good deal
heavier than it needs to be. First, spruce could have saved
about 15% in weight; second, a hollow mast with 1 inch walls would
have saved about 20% more, for a total saving of 1 - .85 x .80
32% , This would be my choice for dimensions for a wood mast."

So I am not swayed by arguments of weight. I realize there are trade-offs.

I am just wondering if there are formulas based on sail area, displacement etc.

I will check Chapelle and go from there.

Thanks for the advice.

[SBrookman]

My 19' sharpie called for 2 masts of DF, 22' and 20', which I laminated out of ripped 2x6's with 1" spruce. The masts are unstayed so are larger and heavier than what you'd be making. Still that's a lot of weight. You might want to ask other Hurley owners what they think of the idea.
http://otterwater.com/Sharpie/SparsOiled.jpg

[Thorne]

As above, go for Doug Fir or Spruce -- there are many good reasons these are used for masts all over the world.

[kc8pql]

I'd appreciate any suggestions.
Don't you just love it when someone asks for suggestions and then, when everyone says he may want to rethink what he plans to do, he says he's already made up his mind and doesn't care what anyone says? :rolleyes:

[ssor]

Why not just cut down a small tree and peel the bark. That is how traditional masts were obtained. It will check a little but that won't hurt. It will come with a nice taper.

[ishmael]

Some good comments. A solid pine mast won't befriend your stability curve, but we're not talking crossing the Atlantic in the boat. As said, spruce is better.

How about this? Study up and make the mast hollow.

[JimConlin]

If you're contemplating replacing an aluminum mast with one of solid pine, may I suggest an experiment that might illustrate the effect. Wait for a windy day and lash four one-gallon jugs of water to your main halyard shackle, raise the sail and go sailing. Take careful note of how much the boat heels and pitches when going to windward. Let us know if you think the boat's improved.

[gavinpascoe]

Hurley 22s are awesome. Stay with an ali mast, and you'll cross oceans. If you want some wood in there somewhere, make it the boom instead. Like some Pearson Tritons I've seen.

[mkrautha]

Okay okay, I will continue to think about the choice.I know of course that wood will be heavier but it isn't as though boat weren't build this way for centuries. The H22 is a heavy boat for her size with 40% (or 50% depending on who you ask) of her displacement in the keels
Sorry if I gave the impression that I was not appreciative of people's opinions one way or the other-- in my original post I first wrote: "any suggestions for the appropriate mast diameter?" not simply 'opinions sought' as implied by kc8pql.
A hollow mast or a tree are other ideas I am considering.

[mkrautha]

I found an interesting calculator online:
http://www.carlsondesign.com/#Fun_Shareware

The dimensions it computes for the mast I am interested in: solid mast with a taper beginning 4' from the partners, 4.13" tapered to 3.57 inches at the mast head. Using Douglas fir the wieght is calculated at 78.9 lbs with a center of gravity at 159.33 inches. Hollow mast dimensions are slightly bigger (3.2" at the base to 3.7" at mast head) and about 20 lbs lighter.
It would be interesting to compare these to the weight of my 28' aluminum mast...

[alkorn]

Chappelle's Yacht Designing and Planning gives mast diameters and tapers for a wide variety of craft, but only for solid masts. It looks - like much of what Chappelle presents - that it is not the result of analysis but simply a survey of existing practice.

Kinney's Skenes Elements of Yacht Design gives design info for both hollow wood and aluminum masts. If you have the measurements of your aluminum mast you should be able to use the info he presents to translate it into an equivalent wood mast.

My opinion on wood-vs-aluminum for weight aloft: for the same strength and stiffness an aluminum section is lighter than a wood section. But tapered aluminum sections aren't available. A mast needs much less beef high up than it does at the deck. Since a wood mast can be tapered, it can reduce its weight high up where it really makes a difference. The net result is that hollow wood and aluminum are roughly equivalent in weight effect.

Also:
- Wood is prettier than aluminum.
- Tapered masts are prettier than constant-section masts.
- I hate the clank-clank of halyards on aluminum.

[ssor]

If you have access to a welding shop then flag pole blanks will provide perfectly good tapered aluminum sections for building into a mast.

[kc8pql]

I found an interesting calculator online:
http://www.carlsondesign.com/#Fun_Shareware


I used a version of this software, a program to handle larger spars I got directly from Robert Tyrrell, to design my 50' sitka birdsmouth mast. It's results are quite accurate and reliable.

[gavinpascoe]

Another thing I thought of: Hurley 22s suffer from compression of the cabin-top, mostly from tight standing rigging pushing the mast downwards, but gravity does it's job there too. This problem is more pronounced in the bilge keeled ones, as there is little mast support like you can get from a support post inside the cabin down in the single keel version. A heavier mast will make that worse. You might want to check you've a mighty bulkhead installed to brace up the cabin top.

[alkorn]

If you have access to a welding shop then flag pole blanks will provide perfectly good tapered aluminum sections for building into a mast.

I'm not sure it's correct, but I've heard that tapered flagpoles and lampposts are "spun" from tubing. If so, they are thicker where the diameter is smalller so that the weight per foot is the same along the whole pole.

[ssor]

Link: http://www.flagpolesetc.com/flagpoles/external-halyard-flagpoles-commercial.html

[mkrautha]

Great resources. Thanks!

[JimConlin]

I used an aluminum flagpole as a mandrel for a carbon mast.

[paladin]

all things considered....with care, you can make a wood mast almost as light as aluminum, using extreme caution, and reducing weight of hardware aloft. If you will make a drawing of the mast with all dimensions and wall thicknesses, and masthead hardware etc that will be attached to it, you may be able to go to wood and keep things pretty much the same.
When I built my second Jim Brown Searunner 31, it weighed in several hundred pounds lighter than anticipated. The hull was specified as A-B exterior grade marine ply, I used meranti in a mm thickness just a hair thinner than the inch measurement...the wood was stronger and lighter. I also removed all screws and nails from the hull after the epoxy set, saving a few hundred pounds there. With two people on board, no supplies except a cooler with sodas and water, she would literally fly.

[MiddleAgesMan]

Why not just cut down a small tree and peel the bark. That is how traditional masts were obtained. It will check a little but that won't hurt. It will come with a nice taper.

And if a little extra weight is OK think what a LOT of extra weight will be like! ;)

If the OP is determined to do what he wants I'd say go for it and don't bother with the scantlings. Just make your solid wood mast the same size and shape as the aluminum one. Yep, adding and removing hardware on a wood mast will be so much easier. ;)

[andrewe]

I looked for Hurley 22 and 3rd up was www.hurleyownersassociation.co.uk (http://www.hurleyownersassociation.co.uk) You might want to ask there in case someone has tried it before.
Nick Vass might be the one to ask, as he offers technical advice.
A
BTW, the extra weight of the mast (if hollow) won't make much difference compared to the compressive loads on the cabin top.

[MiddleAgesMan]

I'm not sure it's correct, but I've heard that tapered flagpoles and lampposts are "spun" from tubing. If so, they are thicker where the diameter is smalller so that the weight per foot is the same along the whole pole.

That is correct. Spinning-extruding the tube to create a taper results in a thicker wall where the diameter is smallest.

I recently rigged an aluminum flagpole as a mast for my Goat Island Skiff. I was curious about its balance point once I cut it to length. The balance point was within an inch of center even though the top measured 1 7/8" and the bottom was 3".