Tree species for a big mast

[ShaneK]

Hi all. Can you advise me of a tree species for a BIG mast, preferably something that is grown in Scotland or possibly Scandinavia. I KNOW that just about everything grown in Ireland is crap for this purpose !

I want to construct a 25 - 30m cantilever mast with a hollow section and probably reinforced with inlaid glass or even Kevlar unidirectional roving.
I am familiar with wooden aeroplane propellors being made in similar fashion.

Thanks-in-advance.
Shane

 

[jehardiman]

You may get more/better answers if you go ask this question on the Wooden Boat forum.

http://forum.woodenboat.com/

Tight straight grained spruce or fir is most likely what you need, but even in the early 19th century there weren't enough suitable tree left so masts began to be pieced. Even a hollow birdsmouth mast that big is going to be very heavy compared to an alloy or carbon fiber mast.

http://duckworksmagazine.com/06/howto/birdsmouth/index.htm

 

[Petros]

I have many years experience engineering wood structures, and a cantilever mast that size made out of wood is going to be very large, and there are not many species that would be suitable. I do not think there have ever been all wood cantilevered masts that large, almost all of them taller than about 10 meters would have been braced or use shroud lines.

Unless you intend to use the wood as a hollow plug and the composite skin is going to provide all of the strength, it will be VERY heavy.

You should also get some competent assistance on designing and detailing the design of such a large structure. Either a Navel Architect familiar with hand build cantilever masts or a structural engineer familiar with wood design.

Good luck.

 

[gggGuest]

Carbonus Fiberensis is surely the most suitable species... You could vac bag on some pine veneer if you are feeling picky...

 

[PAR]

Douglas fir is the logical choice, but why a solid mast? There's no reason to burden any boat with this type of arrangement. There's also no need or desirable trait for 'glass or other sheathings on a solid grown timber mast, so skip this step.

 

[Stumble]

Shane,

I think you are barking upan incredibly difficult tree. A cantilever mast this size is not only going to be incredibly heavy, but also very expensive to build well. In fact I would posit that it would be the largest wooden mast of its type ever built, which leads me to think there may be a terminology issue here more than a technical one.

Every mast I have seen in this size for the last decade have been carbon fiber, and there are a lot of good reasons for it. Could you provide more information on why a free standing mast of this size, made from wood is even desirable?

 

[Tad]

The biggest unstayed masts I can think of are those in Norfolk Wherry's. Below is Albion, around 58' by 15'. Her mast is only 42' overall and around 14" in diameter. The sail is about 1200 sq ft.

 

[bregalad]

Bolger's 50 foot Tonweya (in 30-Odd Boats) has a 55' 6" unstayed hollow wood main. 10-1/2" diameter with some carbon fiber let into the rounded corners. I don't know if that was his largest though.

 

[rasorinc]

I can get you one just a little smaller in diameter then this one. 1.2 million board feet, 180' tall. estimated weight 800,000 pounds. http://www.monumentaltrees.com/en/trees/giantsequoia/biggest_tree_in_the_world/ Price --Make me an offer.....................

 

[Eric Sponberg]

The best species are Sitka Spruce and Douglas Fir. You need to hand-select each piece to make sure there are no knots or imperfections in the wood. Cut and splice as necessary. Use epoxy resin.

Reinforcement with fiberglass or Kevlar is folly. Glass has similar strength and stiffness to wood, but it is heavier than wood, so you would do better to simply increase the wood thickness than adding fiberglass. And Kevlar has very poor compression strength. Wood free-standing masts fail in compression, so Kevlar is not going to help. If you want to reinforce with anything at all, in my opinion, it should be carbon fiber.

For guidance on size, you can use the book "Practical Junk Rig" by Hasler and MacLeod to get an idea of how big your mast will be. That book also gives guidance on making a hollow section mast with the appropriate wall thicknesses and section tapering. The authors admit to NOT being engineers, so take that seriously. The size of your mast is quite large, so you may want to consider hiring a professional to do the mast design for you.

The largest wood mast that I ever designed was for a motorsailer called Nai'a, 120' long. The wood-epoxy wingmast was built on the beach in Fiji and was 99.2' long (30.2 meters). To my knowledge, it is still the largest wood-epoxy wingmast in the world. You can read about it on my website:

http://www.sponbergyachtdesign.com/Nai'a.htm

Eric

 

[SukiSolo]

I think Eric has summed this up nicely. Sitka is probably the best material. Collar in Oxford make masts out of it for quite a few boats and use Douglas Fir for spreaders.

I can give you the name of a UK supplier of high quality Sitka but it is directly imported from mainly British Columbia by the supplier - who is not a large timber company. PM me if you need this information.

If you use any fibre reinforcing it should be good in compression. Timber is stiff OK (for weight) but 4 to 5 times better in tension than compression. Also a lot of early carbon masts had fibres not as good in compression as current fabrics.

 

[Tad]

Sometime in the night I remembered Phouma, a Phil Bolger design stretched to around 125' by 16'. Her foremast is huge and appears unstayed......I don't know if she ever sailed anywhere......

 

[Eric Sponberg]

Phouma looks to have stayed masts--you can see the shrouds and stays in your photos. Looks to be either a gaff or junk rig by the boom on the mizzen mast. Can't tell on the main mast.

Eric

 

[Tad]

Phouma looks to have stayed masts--you can see the shrouds and stays in your photos. Looks to be either a gaff or junk rig by the boom on the mizzen mast. Can't tell on the main mast.

Eric

Okay I should have said it looks to me that the main mast is partially or un-stayed. The chanplates, shrouds, and turnbuckles on the mizzen are obvious, not so (to me) on the main. There do appear to be a couple of light runners with small tackles attached running to the bulwark just forward of the pilothouse. If I was responsible for this design I would have included these just to keep the stick under control (which is where I get partially stayed).

Phil was partial to big full-battened gaff sails on un-stayed masts. With a jib set flying........

 

[DCockey]

Phuma's main mast has stays. Also, it appears to me that the masts are metal, possibly galvanized steel light poles or sign poles. Attached images are crops from photos I took in July 2012 in Eureka, California.

Information about Phuma from documentation record http://www.st.nmfs.noaa.gov/pls/webpls/cgv_pkg.vessel_name_list:

Vessel Name: PHUMA USCG Doc. No.: 970996
Vessel Service: COMMERCIAL FISHING VESSEL IMO Number: *
Trade Indicator: Coastwise Unrestricted, Fishery Call Sign: *
Hull Material: STEEL Hull Number: 32
Ship Builder: J A GAST Year Built: 1991

Length (ft.): 121.1
Hailing Port: ARCATA CA Hull Depth (ft.): 8.9
Owner: Hull Breadth (ft.): 16
Gross Tonnage: 148
Net Tonnage: 44
Documentation Issuance Date: April 01, 1998 Documentation Expiration Date: April 30, 2001

Previous Vessel Names: PHUMA WAGL205
Previous Vessel Owners: AHR COMPANY INC
AHR COMPANY INC​

Paragraph about Phuma from The North Coast Journal, 06 December 2012 http://www.northcoastjournal.com/humboldt/backyard-of-boats/Content?oid=2185428

We motor around the Humboldt State University's big, green research boat, the Coral Sea, to marvel at another huge green boat -- the 121-foot-long, skinny, nameless and now-stalled project of retired professor J.A. Gast. Gast, who founded HSU's oceanography department in 1961, started building the vessel in 1989, thinking it would be a good instruction ship. He once called it the Phuma -- a South African term that for him evokes "unusual, different," and that also means "go out" in Zulu. It's narrow, only 16 feet wide, and light for a steel boat its size, sitting high in the water. It's only left port a couple of times. It's a labor of love. (Gast tells us later that he still has the utilities left to install but his interest has waned.)