Using Sitka spruce for frames?

I'm building a 21 foot Pacific City dory (7'6" beam) which uses 1"x4" for frames. Doug fir or white Oak are recommended.

However, I just found a terrific deal on some very good looking Sitka spruce and while I know that it's been used for spar making, I'm wondering if it might serve for frames?

Any thoughts appreciated. Thanks.

 

The spruce isn't as strong as the fir and white oak is a lot stronger than either. One by four might be found from pallets used by shippers (free). It is almost always used for bed slats in case you don't know what it looks like. It holds fasteners well, which is usually a plus when you're screwing planking or plywood onto frames.
Spruce is prone to rot and won't hold fasteners too well.

 

Because it's so common here we use spruce for building anything and everything, the one place you won't see it used very often...in boats. As Alan pointed out it's too soft and it won't hold fasteners well. No matter how good a deal that spruce is I'd look elsewhere for your framing material.

MM

 

Thanks for the info. Thought that might be the case. Looks like I need to find some good clean fir or possibly white oak.

 

I reread my comment and I realized I should have said, "yellow pine is often used for pallets..", the same wood as is used for bed slats. In other words, there's a source for frames. White oak is very heavy, almost twice the weight of fir, but it's very very strong and long-lasting. You could easily reduce the width to 3" using the oak if it worked out plan-wise. It holds fasteners like nothing else too. Neither the oak or the fir are very easy to find in a lot of areas. I mentioned the yellow pine because of its use in pallets, which are free, but another wood you might find that I've found to be at least as good as fir but probably easily found in your area would be Port Orford cedar.

 

In the PNW he should have no difficulty finding Douglas fir, which is good for framing stock. He could also use the Sitka spruce, but frame spacing will need to be adjusted (considerably) and I'd recommend at least halfing what's called for. In other words, if frames are on 12" centers, then 6" should used for Sitka spruce, maybe 4" center to center, for sufficient stiffness.

 

quality doug fir should not be hard to find, even if you go to a lumber yard and pick through the pile and find some clear, straight grain planks and than rip them down to the size you need on a table saw.

If the sitka spruce is of good quality and clear, you might sell it to someone that want to make a hollow mast or to home built airplane builders. Or save it for some other project where light weight wood is important.

sitka spruce has a very high strength to weight ratio, but it is not too strong of lumber the same size as compared to the other woods, and as pointed out, does not have much rot resistance.

 

I am a little surprised at the answers. I would have thought the excellent strength to weigth ratio of sitka, plus its relatively knot-free nature and regular grain would make it an ideal wood for boat-building.

Since it is soft and has poor volumetric strength it would be appropriate to increase section size if the designer specified a stronger wood, and a larger section of a lighter material yields better beam stiffness so I don't understand why frame spacing would need to be reduced. Obviously it is best avoided in places exposed to abrasion and impact.

Its poor holding power militates against the use of fasteners but it takes glue well - better than oak at least. I can understand why it was not used in traditional construction but we have such excellent adhesives available these days, what would be the problem? Rot resistance is hardly a problem when most builders slather their creations in epoxy. I used oak for abrasion resistance and point strength only a few years ago and it has already started to rot; sacrificial pieces of spruce would have been a better choice. Surely there are places in a boat where sitka can be effectively used other than for spars.

 

Spruce is used in small craft, at least it was, until it's scarcity has left it costly. Reduced frame spacing would permit a weaker specie's use, without increasing the frame depth, which can cut into accommodations and cause other issues. Simply put respacing the frames on tighter centers has a smaller impact on the other dimensions of a build. Of course increasing the molded dimension would also help and frame spacing could remain unchanged, but soles, seats top, cleats and a lot of other elements would be affected. Decreased frame spacing would also have a higher affect on impact protection too.

 

There are a lot of variables when contemplating a design. Will the boat be dry-sailed? In salt water? Encapsulated in epoxy?
Each variable has an effect on strength and longevity.
There are still plenty on boats that will not see any epoxy at all, and they might benefit from salt water immersion. White oak is well suited in that case.
Dry sailing the same boat might lead to problems if the boat isn't well stored.
There was a time when boats were built to last only a few short years. This made sense then. The boat was used day in and day out in rough conditions. When you weren't fishing you had time to repair the boat or to begin a new construction (with the help of a lot of retirees and self-semi-employed fellows).
Things are different now. Yet a lot of people want to duplicate the old style of build, which is great as there's nothing as fine to rest your eyes on than a traditional wood boat.
But the builder has to decide which way to go. Even a very welll built tradititional build will require a lot of thought in terms of storage, use, and maintainance. Not so the epoxy-clad version. But the salty look has been diminished a bit for those few purists who hanker for the genuine old-time version.
I think this sums up what the first question should be---- and the plans will necessarily point the way----- what aesathetic do you want to achieve and what sort of convenience and abusability are you looking for?