Suitable Substitute for Sitka Spruce?

Yep, Dan was beaten up by a Douglas fir as a grade school kid and hasn't "let it go" yet. Though years of therapy have helped him cope in a much softer manor (it was much worse years back), he still can get wrapped up with the memories and some difficulty erupts.

Actually, everyone is correct, Douglas fir both sucks and can be prized, depending on what it is, where it's cut and age. Personally, I don't ever use it in finish applications as it just has way too many issues, but it's fairly light for it's strength, can be had in long lengths of straight grain and it's easy to machine, given it's particularities.

If looking for substitutes for Sitka, I wouldn't look at Douglas fir, mostly because of it's weight, though checking is a concern too. Look at the spruces (white and black most notability) for similar weights and strength.

 

Liki - good question. Wikipedia lists over 20 species under the Paulownia genus. I'm pretty sure the one being grown here is P. tomentosa - this is the one known as Kiri in Japan. Most local sales are for surfboards or cabinet work, but it is fast catching on for boat building for the reasons mentioned in my last post

A Google search yields much interesting information, including the fact that it is grown commerically in the US as well as elsewhere. See http://www.worldpaulownia.com/html/tech.html for a USD grower

Cheers

Alan

 

Yes,

P. tomentosa is the plantage grown species we use in boatbuilding. And I am promoting it here since ages now, but with little response by so far. P. elongata being the other one suitable.
(Kiri refers to all species of Paulownia in Japan, that is a bit irritating the market, but the majority of timber available is tomentosa anyway)

It even makes a perfect core for FRP layups, being several times stronger than any foam, rot resistant, and providing far higher shear strength. But the FRP "Guru´s" are even more biased than we wood heads.

Regards
Richard

 

ahem, I have built 13 wood boats, first one when I was 12 years old. I have built two wood houses, and many other structures, installed all the trim and fixtures in one of them my self. When not working in my office, besides working on old cars, I do quite a lot of wood work.

I can only explain your experience with dough fir is that the doug fir you get there is all junk wood they would not sell here. It is readily available and most I know like working with it. It is far easier to work with than most hard woods and it often stronger.

Whenever you design something, you design WITH the structural properties of the material in mind. You would not build an aluminum hull using plans designed for steel hull would you? If you blindly substitute one type of lumber for another you should not expect the same results. And with any grown material, there is a certain amount of hand selecting that has to happen, if you use junk sitka spruce you will not end up with something better than one made of qualtiy doug fir.

FYI, the FAA has approved the use of Doug fir for aircraft construction since Sitka Spruce is not available in most parts of the country. Both must pass quality control inspections, but there is a reason why Doug Fir was approved and not something else. Or do you think you are smarter than all of the engineering capacity of the FAA?

 

I wouldn't use the FAA as an example of an engineering metaphor. The FAA is one of, if not the most conservative organization going, which in this discussion is probably advantageous. I agree with Petros that Douglas fir is perfectly suitable structurally, though for spars I think it's one of the heavier substitutes.

 

of course you are referring to FAA Advisory Circular 43-13, government bulletin ANC-19, Mil-Spec-6073.
Advisory Circular 43-13 lists a number of different types of wood that may be used in an aircraft structure. Some of these are Douglas Fir, Noble Fir, Western Hemlock, White Pine, White Cedar, and Yellow Poplar.

kinda shot yourself in the foot on that one friend
each of the materials listed have there own unique qualities that make it "possible" to be used for aircraft construction
that doesn't however address in any way the financial advantages of using some species as compared to others
of interest might be that Poplar is a far more common as an aircraft material that Dougy is any day. Its got way better bending strength and better overall strength to weight ratio in nearly all categories. Makes great spars and comes in nice long pieces. My x girlfriends father is in some club that build 5 WW1 Jenny's and they used a lot of poplar.

and speaking of the FAA

ya I hate to have to stick to my guns here but I do my share of flying in small planes so I kinda have a unique view of the FAA, that and one of my best buddies has both his air frame and power plant certification and his take on it is

cheers
B

ps
its not a contest
everyone's got there own way of doing stuff and mine does not include using what I consider to be inferior materials. While it has been suggested that the DF out here is crap I have seen some folks pay top dollar for what is supposed to be "the good stuff" and have it end up with more waste by far than what they could have just got at the local yard. Mater of fact Dougy is well known in the biz for having an extremely high amount of waste at all levels of production. That nice low price for Dougy starts coming up some after you might loose some huge unknown percentage to bends bows warps cups splits and poor grain orientation or consistency all of which are critical to the construction process.

 

More on Paulownia

Richard's comment is very interesting, even though I am already a convert to Paulownia. Please understand I come at this from an Australian perspective so the cost and availability issues may be totally different to the US. However, even though it has been grown commercially here for over 15 years, virtually NONE of the local suppliers I used for WRC (strip planked hulls) and the teak (interior fitout) on my last boat had even heard of it and were certainly not aware of its properties. The boat I built before that was Douglas Fir on Spotted Gum frames - the traditional choice if Huon Pine was unavailable, or Teak too costly, so I think I can claim some real-world experience with the different timbers.

Having now built the new trimaran main hull and two amas from Paulownia, I can say without hesitation I would never use Douglas Fir again - more than twice the weight and here at least - more than double the cost. It also does not have the same rot resistant properties, is harder to work and does not form as good a bond with epoxy.

Richard, knowing how closed-minded the trade is to anything new, I symphathise with your situation.

Alan

 

Don´t forget the absolute phantastic insulation properties, the immense heat load it can bear before it ignites (more than 400°C, compared to 200° with most common timber), and the ease of machining.

That is a real "high tech" fibre, worth ten times the value of any foam cr@p in sandwich composites, and much cheaper than that.

At present I am developing a wooden sandwich with Kiri as core.

Regards
Richard

 

altho its probably been said before here, as far as i know paulownia is also used to make boxes to keep engineering instruments fairly rust free, a very particular wood

 

Yepp,

there have been coffins found (dug out) after 100 years or so, still not rotten.

 

I copied from the internet this: