View Full Version : Douglas Fir
03-11-2005, 11:11 AM
I noticed in some local clasified ads, someone had a large quantity of douglas fir boards. Since I am still a novice boat builder could someone outline which parts of a boat I could use this on. Also, would it make good flooring or decking for a new home we are building soon? For example he wants 20 dollars for a 2x10 x20'- all planed. Apparently recouped from some old buildings. Thanks in advance.
03-11-2005, 11:35 AM
What size boat do you have in mind? Which woods are good for a given part on a boat can vary a bit depending on whether you are talking about a 12' skiff or a 90' schooner! ;)
Doug Fir is one of the best strength to weight ratio woods for boatbuilding... plus has good rot resistance and is easily worked. Heavier than cedar, it can be used for strip-planking a hull if weight is not a primary concern. Reuel Parker uses it for laminating masts and in hull tongue and groove construction...other uses are deck beams, stringers, cockpit combing, and other misc structrual uses. Air dried doug fir is overall a great boatbuilding material.
On pricing...I am sure many others here can offer input.
[ 03-11-2005, 12:45 PM: Message edited by: RodB ]
03-11-2005, 12:01 PM
Early Dovekies were built with laminated Mahogany leeboards, 1-1/2" thick. My boat came with a pair of later model fiberglass leeboards.
When designing a pair of custom Higher-performance leeboards, I chose Douglas Fir for price and strength considerations. Finished with six coats of Deks Olje #2, kthey gave nothing away in aesthetics to anyone's Mahogany boards. I would not hesitate to use Doug Fir again.
03-12-2005, 09:20 AM
D. Fir is great, in the right places. One nice thing about it is that you can get long pieces with straight grain, at reasonable prices. It glues well and is fairly easy to work. If there is runout in a plank, it will trend to split off at the edge or grab your plane, but this is not a big problem. I just laid up a hollow mast, 4" dia., 24' long, using D. Fir decking material. This comes S4S, with finished dimension of 3/4" X 3 1/2". The stock I bought was almost true quarter sawn, though I did not pay a premium for that. It's heavier than spruce but stronger, so you can reduce the dimensions of a fir spar and come out in almost the same place on total weight.
03-12-2005, 10:15 AM
The price works out to a hair over 60 cents a board foot. Cheap at twice the price.
03-12-2005, 10:18 AM
I use a lot of it because I grow it and mill it as part of my living.
I use the "20% Rule + Fudge"....I up the scanting size 20% when I'm substituting DF for White Oak in a design....and I down the scantling size 20% when I'm substituting DF for Sitka Spruce (which I don't have) in a design.
"Fudge" means that while DF is around 20% weaker than WO and 20% stronger than SS, that ain't true for all the strength and stiffness parameters and you have to look at what that member does for its living in the boat and whether the design is overbuilt.
For example, a glued lapstrake or seam batten plywood boat using the same scantling size for frames as the same traditionally-planked boat often has plenty of strength without plussing up the frame size because of a species substitution. In solid spars, DF isn't any stronger in shear strength than spruce (but stronger and stiffer in every other parameter) and I'm more conservative than I am with many framing applications.
The tighter the growth rings on your wood, the stronger and more rot resistant it is.
Make sure you don't allow any sapwood in your boat. Any kind of sapwood....so pick your boards carefully as sapwood isn't a consideration for the building construction those boards were milled for.
While a great structural wood, DF doesn't finish "crisply"...it is a bit gummy, fuzzy and stringy to plane, chisel and scrape and isn't at its best in high-finish applications where you'd use mahogany or teak.
03-16-2005, 01:14 PM
I've used a lot of DF in homebrew boatbuilding. Thankfully, it's available quite easily, stocked by all Home Depot and Lowes big-box stores, as 'porch floor decking', in 1" x 4" and 1" x 6" dimensions (the 1 x 4 is actually 3/4 x 3 1/2). While every piece isn't perfect, it's not hard to select what you need from the pile, and you can usually get clear vertical or quartersawn pieces. They stock 8', 10', and sometimes 12' and 16' lengths.
I've used it for strutural work, and also for mast and boom projects... it laminates nicely. One thing I have found is that the disparity in density between the rings and the softer wood between the rings means that you often get a slightly rippled effect on a sanded surface... but it isn't objectionable. It holds up well, when varnished.
Finally, it's cheap. I don't recall the big-box store price, but the local fine lumber dealer gets $2.69/bd-ft, I think.
03-19-2005, 02:35 PM
I'm a little confused every time I see somebody say that Douglas Fir has good rot resistance. In my experience it is not rot resistant at all. All of the wooden boats I have seen in in the yard at my marina undergoing major repairs due to rot were made of Douglas Fir. I guess this is relative, but Douglas Fir definately isn't even near the top of the list. It does have other good properties, but rot resistance isn't one of them.
Rot resistance is relative. At the most resistant is black locust, osage orange, and red mulberry, at the least resistant you will find birch, willow, yellow poplar, and the sapwood of most species. You will rarely find long, straight, clear pieces of the first three species but you can find lovely clear pieces of yellow poplar. D. fir is closer to the rot resistant end of the list than most of the other commercially available species.
03-19-2005, 03:45 PM
I've got old-growth DF logs that have been either immersed or floating in my beaver ponds for literally thousands of years.
The floating snags, of course, are now 8-10" long spindly sticks instead of 40-60" boles....the sunken ones are still just fine, however. All the non-durable species in those creek bottoms when the beavers dammed them up like hemlock, alder, willow and maple are the 4' of humus comprising the pond bottoms.
Rot resistance is all about resin content. The darker, tighter and smellier the DF...the longer it will last. In general, it's rated as "moderately durable" like the more resinous pines as opposed to "highly durable" like most cedars...
...but it beats the heck out of any spruce and all but a very few pines in that regard.
[ 03-19-2005, 07:42 PM: Message edited by: Bob Smalser ]
03-20-2005, 08:23 PM
How would it be for planking up a Haven 12 1/2? Calls for 1/2" cedar.
03-20-2005, 09:21 PM
Originally posted by Brent Cummings:
How would it be for planking up a Haven 12 1/2? Calls for 1/2" cedar.55% heavier....and moves 3 or so times as much seasonally. Not a problem in a 30' troller in the water year round but I'd be reluctant to use it in a trailer boat, even in a cold climate, and even in lapstrake.
For knees and beams, I can come real close to the weight of spruce by using the stronger DF in smaller scantlings. But I don't think I'd try quarter-inch carvel planking in DF to replace cedar....even if it were steam-cupped instead of backed out. Besides, as I said before it isn't the most pleasant wood to finish.
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