Sitka Spruce vs Douglas Fir

[Aggie]

I'm finding that locating a supply of sitka spruce in Texas is like trying to find a cowlick on Jesse Ventura. I've read that douglas fir is a close second. I'm working on a gunter sloop. Will douglas fir be an acceptable choice for mast, boom, and gaff? Thanks!

Aggie (TAMU '82)

[ishmael]

Yes. That is the short, workable answer. Search the forum, if you wish, as there are discussons of this regarding strengh weight ratios etc.

Or... just build the spars and enjoy your boat. Not to worry.

Look for good stock; much more important than species here.

[Don Danenberg]

Ahh, Ishmael, gird thy loins, (proper)Douglas Fir grows as far from Texas as Sitca Spruce; Individual 'sailing style' can be bastardized by heavy sticks on little boats. Sitka Spruce is available and cheap. The proper materials are still cheaper than the labor. Don

[ishmael]

Gird my loins? Don, have you a new mount, lance and shiny sword? I am on guard!

I'd be all for Sitka spruce, but was under the impression that the correspondent had found it someway beyond his means. And, doug fir closer to spirit and bump.

Don, I think, is asking for other design parameters. A good question, so let's go with it.

I do tend toward hastiness. A nasty habit of my sorta-commercial shop days.

In short, if your boat is a "skinny" one, the extra weight aloft from the fir may (will) make some signifigant difference in performance. Whether it accounts for much is probably a personal matter. If the boat is "stouter", I still wouldn't worry over it.

You might also consider some the hollow spar techniques discussed here on the forum. Search under "birdsmouth." A hollow mast, in either material, would likely obviate all further discussion. The technique, for an engineer (I peeked), should be relatively easy.

What sort of boat ARE we talkin' bout?

Good luck, with us as much as the boat.

[This message has been edited by ishmael (edited 08-26-2000).]

[This message has been edited by ishmael (edited 08-26-2000).]

[Charlie J]

Don - Here in Texas, Sitka Spruce AIN'T available, except delivered by truck - That isn't cheap. Doug Fir on the other hand is used heavily in the construction trade for Facias and trim. It IS available in long clear lenghts. If it were me, I'd use the fir- The weight difference on a small boat isn't gonna amount to very much. Maybe two or three pounds total. And if you are careful in selecting the wood, maybe not that much.

[Ian McColgin]

If you make the spar with that nifty bird's mouth approach, the hollow spar will be so light in either wood that, as my Oklahoma cousins say, 'twon't make no never mind.

[Aggie]

Should have included this in the initial post... I'm building the Penobscot 14 by Arch Davis.

Length: 14'
Beam: 4' 6.5"
Weight: 155 - 175 pounds

[wandiwise]

Aggie: You asked if D. fir could be substituted for S. spruce. Yes, of course. But, it would be a poor substitute. Assuming you purchased the plans from Arch Davis, the designer, why not ask him?

Remember, the fir was delivered to your lumber dealer by truck, also, though in large amounts. Have you asked for a quote from Edensaw in Port Townsend? Just the difference in working the spruce compared to the fir would make a few bucks worthwhile.

Good luck with your project.

www

[NormMessinger]

Douglas fir, a poor substitute? Hmmm. I had the impression from reading this forum and other sources that Doug fir was a close second. What they call fir in the lumberyards around here isn't Doug fir and would indeed be a poor substitue.

However carefully selected hem-fir or SPF would make an acceptible mast until you can score some spar grade sitka spruce. I got my Sitka spruce from Flounder Bay in Antecortes WA but you don't need enough to justify the shipping unless you get pieces short enough for UPS. Your second spar will be better than the first anyway so charge the first off as practice, go sailing, and have fun.

I've wondered what sort of spar cypress would make for a boat that is not going to be sailed hard. Its light, cheap and beautiful.

Best wishes.

--Norm

I'm useing a pushpole in the launch that was made from a 16' Western Red Cedar 2x4 15yrs ago. This thing gets a lot tougher workout than a spar. It is a bit more limber than spruce, alot lighter than fir, not as good as its cypress predicessor that got "liberated". Closeness of growth rings, lack of knots, no grain runout, are all more important than species. If you can manage legal access to some spavined understory cypress, it would well be worth riving some out with a froe.

[NormMessinger]

"...riving some out with a froe."


Oh, Dale. I just love it when you talk like that.

--Norm

[ROWE BOATS]

Cypress would certainly be an acceptable substitute. Aso you might check with your lumber yard for certified staging planks, which here in the northeast are usually eastern spruce. Bud McIntosh used them on a great many of his boats, and I have used them several times myself. Pick through the pile and find the lightest straightest grained piece that you can.

[ishmael]

My take on this is that people have been making small boat spars out of all manner of woods forever. Sitka spruce, like so much else with wooden boats, is a quasi-religious icon. If I could get 'hold of nice sitka would I use it, you bet. But it's not essential.

[John058]

re: cypress. Might be just the ticket for anything above the waterline. I have read that it tends to soak up water so might not be suitable for anything in the nether regions.

[Keith Wilson]

Aw fer Chrissake, guys, lighten up! These aren't space shuttle parts we're talking about, and he's not going to sail this boat to Bora Bora. Douglas fir spars will be a little heavier, a little stronger, and will work just fine with a Penobscot 14. The crew weighs more than the boat anyway, so a slightly heavier mast means that they'll have to sit 3/4" farther from the centerline to make her heel the same amount. If the sailing qualities of the boat would be harmed seriously by four more pounds of mast, the design has real problems (really high-performance boats excepted, which the Penobscot 14 isn't.) If you can get good Douglas fir for not too much money, use it.

[H Downey]

It is my understanding that the strength to weight ratio and stiffness to weight ratio of doug fir is almost identical, if not somewhat better. See the wood handbook for values.

That said, if you change the scantlings to achieve the same stiffness and strength, the spar will be just as light, or lighter than sitka spruce.

Of course if you build it to the specs for sitka spruce it will be heavier, as others have stated. This is, of course, not a good thing.

A spar is just a beam. You need to achieve two things. 1. Equivalent strength: you want the bending moment at failure to be the same, so strength*moment of inertia of area / (half height of cross section) should be equal to that for sitka spruce. That is (SI/c)spruce = (SI/c)fir. 2. Equivalent stiffness: you want the same deflection, so make moment of area times Young's modulus (EI) equal, or (EI)spruce = (EI)fir. Adjust cross sectional shape and area to achieve both of these. When you are finished, calculate the volume and weight and see if they aren't very close.

[Cedar Hill Boatworks]

Come on guys, you're looking a difference without a distinction. Doug fir is a perf4ctly ascceptable alternative to sitka spruce. We're building boats here, not rocket ships and laser beams.
Go with the doug fir.

[Keith Wilson]

The Wood Handbook (aka The Bible) is available to download free at: http://www.fpl.fs.fed.us/documnts/FP.../fplgtr113.htm
The handbook has excellent engineering data on most species. Be patient if you don't have a fast connection; it takes quite a long time at 56K, but it's worth the wait.

I would bet quite a lot that Arch Davis didn't do stress calculations when he was designing the mast of the Penobscot 14. He most likely specified sizes and materials like what worked in the past on other similar boats, knowing that the acceptable range is quite large. OTOH, one can easily make sure that a mast of another type of wood will be very close in strength and flexibility to the one originally specified by doing the math. Whether the original mast was really optimal, who knows? I bet Arch Davis doesn't.

[This message has been edited by Keith Wilson (edited 08-28-2000).]

[ishmael]

Ditto and amen Cedar Hill.

[Jim Budde]

Used fir for Payson Bob Cat. (12'6") Do not think I experienced any significant increased weight nor reduced strength. Have had boat in 30+knt and snapped boom, but mast held together. Agree w/ others suggestion of birds mouth mast. strong and light weigt, even if you use a heavy wood .... TAMC 68'

[This message has been edited by Jim Budde (edited 08-30-2000).]

[Will Truax]

I'm not greatly familiar with boatbuilding But am more than familiar with Doug

Old growth and 2nd are two very different animals

I would personally aviod it's use for anything structural which will be sujected to extreme stresses such as your mast

[ishmael]

Hoo boy,

I think you raise an interesting point Will, but one that it is difficult to do much about, especially in Texas.

I stand by my previous statements, particularly with regard to stock selection, and not getting too worked up over species. If the growth rings are obviously spread far apart and the wood feels "wonky", don't use it.

All the previous comments about not building a space ship seem relevant. Will the spar be strong enough? Only time will tell.

I think Norm said earlier that you can always make a different spar down the road. Avoid survival conditions in your 14 ft skiff. Always good advice.

[Smacksman]

Gotta chip in my sixpenneth. Treewood would be just fine for a little spar in my book; ie anything clear and true. Failing that we sometimes use Grade 3 Spruce - Clear or Better which is ally tube painted brown!

[Tom Lathrop]

In a boatbuilding class at the local Community College, we have a lot of small boat masts built. If Sitka spruce was available at a reasonable price, then it would be used but that ain't the case. Most are made from 2X construction grade Canadian spruce, with the knotty parts cut around. It works fine.

If you can do some selecting at the lumberyard, fir is fine material for masts. Don't get stuck on the listed specific weight of these species in books. The actual range can vary enough to overlap the listed weights by quite a lot. I built a laminated fir mast for a one-design racing class boat once that weighed right on the average for competive sitka spruce masts. Main thing is to avoid the heavy pieces of any species and select close/straight grained stock. Nice doug fir is wonderful wood to work with although it will split or shed splinters (sometimes into your hands) more than spruce.

I live in the heart of cypress country but would not choose to use it in masts. The best cypress has too many knots and the clear stuff is sapwood and weaker. White atlantic cedar dominates cypress as a local boatbuilding wood but I think either fir or spruce is superior for masts. I've seen masts made of about anything, including pine saplings with the bark stripped off.

[Don Maurer]

If you are building the Penobscot 14 with he sloop rig, it won't matter much what you use because the mast is stayed.

Incidentally, I just got back from Alaska. They have a big problem with spruce beetles on the Kenai Peninsula and South Central Alaska this year and are cutting the dead trees as fast as they can. Most are being shipped to Japan, I was told, but it may mean lower sitka spruce prices in the near future, if there are no restrictions on bringing the dead stuff into the lower 48.

[Will Truax]

Ish

I was saying that if Aggie was leaning towards Doug I would look for old growth from my supplier (still to be had)

might consider 2nd for lams

when I build I build for worst case seems as important to boatbuilding

[ishmael]

I don't think we disagree Will. It fact, I haven't had occasion to build small spars for quite some time so I don't know the supply issues right now. In the past, here in the North East, I'd make spars from lumberyard "spruce." It was cheap and with careful selection was quite nice stuff. I think at the time it actually was Eastern white spruce.

Ah well, you'd think a simple issue like this would have simple answers. Ce la vie these days. Best, Ishmael

[Scott Rosen]

Don hit the proverbial nail on the proverbial head. Strength won't be a factor for a stayed rig.

Sitka is popular because it is light weight. The less weight you have aloft, the less your boat will roll and pitch. Sitka is not very strong and not very resistant to decay. But who cares? The stresses on a stayed rig do not require a strong wood. A stayed rig is designed so that the stresses on the mast are compressive. In other words, there is very little "bending" stress on a stayed mast. The compressive stress is strongest at the maststep and the windward chainplates, or the backstay if you're on a run or broad reach.

But you can use any wood you like, except maybe balsa (laugh). If you really want to use Doug Fir, and if weight matters to you, then take advantage of the strength of the Doug Fir and make the spar narrower or tapered or hollow to save weight--in other words, you can play with the scantlings a little as someone else suggested.

For purely aesthetic reasons, I'd spend the extra few bucks and use sitka. Sitka is a joy to work with a saw, plane or sandpaper, and it looks real sweet with a varnish finish. But these are purely personal reasons, as I don't think the choice between sitka or Doug Fir will make any structural difference in your boat.

[Aggie]

WOW! Tons of great stuff guys! Thanks a million.

Aggie

[Kermit]

Hey Aggie, if all this has proven confusing, there's a aluminum cellphone tower down the road I'd like to see go. I hear the stuff works for masts, but is hard on tools.

[ishmael]

I now know why the good Mr. Danenberg offered me the friendly advice, "gird thy loins."

[Roger Cumming]

Actually, the correct answer is BOTH. Sitka spruce has no peer for masts where its high strength to weight ratio is paramount - higher than D. Fir. But for booms, where some weight is beneficial in stabilizing the sails, especially the mainsail, D.Fir is preferable. It is also slightly harder so it stands up better to the kind of abuse a boom encounters in a season's use. There also should be little strips of white oak where the jaws rub against the mast. The jaws themselves should be oak. And the little cap at the top of the mast should be lignum vitae.

[Don Danenberg]

Now See, I have a lumber supplier calling me about Sitka Spruce. Have we not looked into these archives?

[JimD]

And besides, doug fir isn't a fir tree anyhoo. Its a misnamed spruce (and also not a bad substitute for white oak frames if one is epoxying)

[Buddy Sharpton]

No more than you're going to need, I'd try for carefully selected spruce construction stock at the
lumberyard. You can glue up two 2 x4's and get a blank big enough for a mast or boom.

[Bob Aberton]

What about ash?

I don't know how easy it is to get where you are, but here in Rhode Island, it can be got pretty cheaply from the sawmills.

It may be heavier, but it has flexibility and strength, righ?

[Nicholas Carey]

Douglas fir is a perfectly acceptable substitute for sitka spruce in spars.

It is harder, stronger and stiffer than sitka spruce albeit with about a 15% weight penalty.

That weight penalty can be offset, in hollow spars, by taking advantage of the additional strength inherent in the douglas fir and reducing the spar's scantlings.

The usual scantling rule (cf, Skene's, Nevens', Herreshoff's) for a hollow sitka spruce spar is that the wall thickness should be 20% of the spar section. So for a round spar, it should be 20% of the diameter of the spar. For a rectangular or oval spar is should be 20% of that axis of the spar (e.g., the forward and after planks in a rectangular hollow spar should be 20% of the for-and-aft section of the spar; the port/starboard planks should be 20% of the athwartships section of the spar.)

Since Douglas fir is stronger and stiffer, you can pretty safely reduce the wall thickness from 20% to 15% (or maybe, if you're feeling adventurous,) 10% of the spar section.

For small boats like a 14-ft sailing dinghy, the difference between hollow and solid, spruce or fir is essentially irrelevant.

A solid 2-1/2in diameter spar 16-feet long will weigh approximately 14.3 pounds in spruce or 17.0 pounds in douglas fir.

Make it hollow with a 20% wall thickness and that same spar will weigh about 9.1 pounds in spruce and 10.9 in douglas fir. Reduce the wall thickness to 15% in douglas fir and the weight drops to about 8.7 pounds.

Not a lot of difference.

If you can get quality douglas fir, go ahead and use it. Douglas fir looks awfully nice varnished too...a beautiful golden color.

There is one caveat you might want to be aware of WRT Douglas Fir: it can be hard to work because there's a huge difference in hardness between the earlywood and latewood.

And if you decide you want sitka spruce, contact Fred Tebb & Sons in Tacoma, Washington. What they mill (and have been since 1912) is spar-grade, mil-spec sitka spruce. They can be contacted at

Fred Tebb & Sons Inc
1906 E Marc St
Tacoma, Washington 98421
phone: 253/272-4107

Good luck.

[John A. Campbell]

Aggie, I'm not suggesting Doug fir over Sitka spruce but if you do decide to go with the fir, Lowes has some really nice vertical grain Doug fir here in Temple and Killeen, Texas and probably at most all Lowes stores.....check it out.

[JimConlin]

Another remote supplier of sitka spruce is Aircraft Spruce & Specialty .

Perfect stock. Spendy.

[Andrew]

I remember reading an article some years ago in an experimental aircaft journal comparing D. Fir and Sitka Spruce. The upshot was that spruce was .7 as heavy as fir but .7 as strong, so if you designed for this i.e. birds mouth construction, fir would be as good or better than spruce.

[Don Danenberg]

Sorry boys, I led you astray!
My 1959 Beetle-Cat had solid Spruce mast and booms; NOT enough to loose one, at sea.
The 70' Colin Archer ketch had two hollow, glued, Sitka-spruce masts; Let alone the booms and working jib-boom.
I have experienced, offshore, many sailboats, and the construction of the sticks that kept me alive (when younger and smaller; I was the one chosen to go aloft in a bosun's chair).
I guess I'm a bit 'too sensitive' about {mine} weight aloft.

[bret]

....Or 15,000 popsicle sticks epoxied together with, get this, "kevlar thread". Use what gets ya on the water and work on "the perfect solution".