Wood for Strip Planking

[Sakari Aaltonen]

The wood most often specified for strip planking is surely Western red cedar. It may, indeed, be a wonderful choice; it's just that it doesn't grow where I live, and I have a - possibly sentimental - urge to use local wood, pine, say. Or... Alder?

In any case, the "local" wood will certainly be denser, that is, heavier than WRC. Does this mean that the strips can be thinner?

On the other hand, if the strength of the structure comes from glue rather than from wood, then would not thinner strips mean narrower - and weaker - glue lines?

[JimD]

Hello, Sakari
Steward discusses 16 varieties of wood in 'Boatbuilding Manual'. White pine is second last in the strength department, beating out only WRC. White pine is nominally heavier as well. WRC however is highly rot resistant not to mention beautiful in colour. Steward describes white pines as having dubious durability.

Yellow pine is strong and durable but would almost double the weight of your boat unless you made your strips extremely thin and then as you have forseen you wouldn't have much of an edge to glue. Since WRC is also the lightest wood suitable for planking you can make the strips wide enough to edge glue strongly without the boat being too heavy. I have no experience edge gluing very thin strips but somehow it doesn't sound like a very good idea. Perhaps someone else will chime in who has tried it.

[Sakari Aaltonen]

I have a problem with Steward in that I don't understand, exactly, what his "yellow" and "white" pine are. My local variety is Pinus sylvestris. (The two local varieties of alder are Alnus incana and Alnus glutinosa - the latter is particularly pretty.)

[Venchka]

The local Finnish birch? Suitable?

[Nicholas Carey]

Originally posted by Sakari Aaltonen:
In any case, the "local" wood will certainly be denser, that is, heavier than WRC. Does this mean that the strips can be thinner?The strength and ridgity of a composite panel like a stripper hull—two 'glass skins with a core material in the center—comes primarily from the two 'glass skins and the distance separating them. When a composite panel (or, for that matter, any beam, from the engineer's POV) like that is stressed, one side is placed in tension and the other in compression.

The load on the material varies with the distance from the center axis: that's why you can build a hollow wooden spar that's lighter and just as strong as a solid wood spar and that's why a steel I-beam works. The material in the center of the beam contributes little to its ultimate stiffness or strength.

In a steel I-beam, the two flanges are what carry the load; the height of the web separating them gives it its stiffness.

In your strip-planked panel, the two glass skins act as the I-beam's flanges and the core material—the wood— acts as its web.

Even though the wood is heavier and stronger, reducing the distance between the skins will greatly reduce the panels ridgidity.

[TimothyB]

That of course assumes we are talking about Epoxy strip planking.

If we were talking about traditional strip planking, then it would be a different ballgame. The wood would be forming a momocoque vis a vis the 3 point nailers in her edgewise and the well bevelled edge plus an oily bedding like thick paint.

Then there is also the option of traditional double strip, which puts thin boards as layer #1 diagonal on the frames, then you layup strips like normal fore and aft. Between you use canvas and mastic, or white lead etc. Similiar to an old time canvas deck.

http://www.sredmond.com/strip_plank.htm

--T

[Nicholas Carey]

As far as wood goes, here's the FPL data on Western Red Cedar's engineering properties as well as common North American alder and aspen.

</font><blockquote>code:</font><hr /><pre style="font-size:x-small; font-family: fixed;"> Static Bending Compression
------------------------------- ------------------------ Shear Tension Side
Moisture Specific Modulus of Modulus of Work to Impact Parallel Perpindicular Parallel Perpindicular Impact
Common Name Content Gravity of Rupture Elasticity Max. Load Bending to Grain to Grain to Grain to Grain Hardness
----------------- -------- -------- ---------- ---------- --------- ------- ---------- ------------- --------- ------------- --------
Western Red Cedar 12% 0.32 51,700 kPa 7,700 kPa 40 MPa 430 mm 31,400 kPa 3,200 kPa 6,800 kPa 1,500 kPa 1,600 N
Alder, Red 12% 0.41 68,000 kPa 9,500 kPa 58 MPa 510 mm 40,100 kPa 3,000 kPa 7,400 kPa 2,900 kPa 2,600 N
Aspen
Bigtooth 12% 0.39 63,000 kPa 9,900 kPa 53 MPa - 36,500 kPa 3,100 kPa 7,400 kPa - - N
Quaking 12% 0.38 58,000 kPa 8,100 kPa 52 MPa 530 mm 29,300 kPa 2,600 kPa 5,900 kPa 1,800 kPa 1,600 N</pre>[/QUOTE]And here's the only data comparable data I could find on Pinus Sylvestris was its specific gravity. It's about 0.51, so considerably heavier than WRC. Pinus Sylvestris is also known as Red Deal in the UK...maybe some of our Brit friends could help us here.

I think that your alder or aspen, if you can find it, is a better alternative to WRC than the pine, at least for a strip-planked boat that's glassed and drysailed.

One other thing, shrinkage/movement. Here's the numbers for the above species, green to oven-dry:

Alder, Red. Radial: 4.4%, Tangential: 7.3%, Volumetric: 12.6%

Aspen, Bigtooth. Radial: 3.3%, Tangential: 7.9%, Volumetric: 11.8%

Aspen, Quaking. Radial: 3.5%, Tangential: 6.7%, Volumetric: 11.5%

Western Red Cedar. Radial: 2.4%, Tangential: 5.0%, Volumetric: 6.8%

[ 10-29-2003, 07:58 PM: Message edited by: Nicholas Carey ]

[Bob Smalser]

Our local Red Alder is a bit heavier (.37 to .32 SG) and a bit stronger than WRC, is pretty stable once dry, and should work for a glassed, drysailed boat.

Problem is getting it in long straight lengths as it's a rapid-growing pioneer species that bends rapidly as it grows to compete for light. You'll do a lot of scarfing, as getting 10' or longer lengths out of my woodlots is difficult.

[ 10-29-2003, 08:07 PM: Message edited by: Bob Smalser ]

[Steve Lansdowne]

One practical consideration may be that if you're going the cove and bead route, getting router bits for other than 1/4" wood may be a problem. I think you can use 1/4" bits on slightly thinner wood, but I'd not go too much thinner. Also, if you make the strips too thin you run the risk of getting a "too thin" spot if you don't strip perfectly (who does?) and have to sand more in a given spot. Starting with 3/16" or thinner wood gives you less room for error.

[JimConlin]

I'd look for species which are as light as the cedars. In strip composite construction, the core mostly serves to hold the glass skins a fixed distance apart.

[Sakari Aaltonen]

Originally posted by Venchka:
The local Finnish birch? Suitable?No - it doesn't like water at all, and rots very easily. Also, it's rather heavy.

[Aramas]

Just to throw a dog in amongst the pigeons, there is less weight difference from using a denser wood than one might imagine. Cedar soaks up more epoxy than something of similar density to douglas fir, so even though the heavier wood produces a heavier hull, it's not as much as one might assume. The denser wood also has structural advantages.

The weight difference would be noticable in a canoe, but in a moderate displacement cruisiing boat, I would actually prefer the denser wood. Just don't reduce the planking thickness. To compesate for the loss of transverse strength due to closer skin seperation, the added glass would weigh more than the wood.

It you're extremely weight conscious you can lower the weight by replacing the specified mat with unidirectional glass with the fibres oriented transversely - that way you only need half the weight of glass.(I contacted McNaughton regarding doing that with his scantlings, and he said it was fine).

WRC is pretty nasty stuff. I had a carpenter fit out a kitchen in entirely in WRC, and after a week of it he went out on his regular morning run - after ten minutes he doubled over vomiting up blood. And some people complain about epoxy :rolleyes:

[ 10-30-2003, 02:01 AM: Message edited by: Aramas ]

[imported_Mac]

Sakari,

I am using Scots Pine or Furu (Pinus Silvestrus)
which I bought in Norway, and had shipped to Denmark.

I used the Norwegian species because they grow very slow and have therfore very high density.

I know of someone in Finland who is using Pinus Abies (Norway Spruce or European Fir) for building a big catamaran, where weight is an issue.

Hope this helps

[Sakari Aaltonen]

Originally posted by Nicholas Carey:

I think that your alder or aspen, if you can find it, is a better alternative to WRC than the pine, at least for a strip-planked boat that's glassed and drysailed.

One other thing, shrinkage/movement. Here's the numbers for the above species, green to oven-dry:

Alder, Red. Radial: 4.4%, Tangential: 7.3%, Volumetric: 12.6%

Aspen, Bigtooth. Radial: 3.3%, Tangential: 7.9%, Volumetric: 11.8%

Aspen, Quaking. Radial: 3.5%, Tangential: 6.7%, Volumetric: 11.5%

Western Red Cedar. Radial: 2.4%, Tangential: 5.0%, Volumetric: 6.8%OK - the low shrinkage/movement of WRC is immediately apparent.

Local aspen is featureless and almost white. In fact, it looks like soap. I avoid it.

So - should I try the local alder (Alnus glutinosa)? I have not heard of anybody building a boat with it, which is kind of exciting. Then again, it has the same problems as the red alder local to Bob Smalser (Alnus rubra?). That is, getting long _straight_ lengths is very difficult.

[Sakari Aaltonen]

Originally posted by Mac:
I am using Scots Pine or Furu (Pinus Silvestrus)
which I bought in Norway, and had shipped to Denmark.

I used the Norwegian species because they grow very slow and have therfore very high density.
I don't think I want dense wood. The boat is a small dinghy - no great strength is required.

[Nicholas Carey]

Originally posted by Mac:
I am using Scots Pine or Furu (Pinus Silvestrus) which I bought in Norway, and had shipped to Denmark.

I used the Norwegian species because they grow very slow and have therfore very high density.Which is what you want to avoid.


I know of someone in Finland who is using Pinus Abies (Norway Spruce or European Fir) for building a big catamaran, where weight is an issue.I hadn't thought of that.

Some of the local Finnish spruce (Picea abies, Norway spruce aka White Deal in the UK) might be a more appropriate choice than either alder of aspen. The one reference I've found suggests that its strength properties are similar to pinus sylvestris. It's light (s.g. about the same as WRC), and purportedly stable.

[imported_Mac]

Originally posted by Nicholas Carey:
Which is what you want to avoid.
Why do I want to avoid that??
By dense wood I ment to say that the yearrings are close to each other, resulting in a tough strong species.

[Sakari Aaltonen]

Originally posted by Nicholas Carey:
[QUOTE]
Some of the local Finnish spruce (Picea abies, Norway spruce aka White Deal in the UK) might be a more appropriate choice than either alder of aspen. The one reference I've found suggests that its strength properties are similar to pinus sylvestris. It's light (s.g. about the same as WRC), and purportedly stable.Unfortunately, local spruce (Picea abies) is very knotty. i mean - _extremely_ knotty. Otherwise, it would be the obvious choice.

[Venchka]

European larch, Pinaceae Larix decidua?

This wood was used for years as planking. It's related to Western hemisphere tamarack/hackmatack. Also a boat building lumber with a good reputation. Today it may be scarce. Not sure. A Danish plywood mill is using it to produce what is probably the most expensive marine plywood in the Universe.

[Nicholas Carey]

Originally posted by Mac:
</font><blockquote>quote:</font><hr />Originally posted by Nicholas Carey:
Which is what you want to avoid.
Why do I want to avoid that??
By dense wood I ment to say that the yearrings are close to each other, resulting in a tough strong species.</font>[/QUOTE]Ahh...differences in meaning :D

My 'dense' means higher specific gravity, greater weight per unit volume. But, I'll concur that tighter growth rings are nominally better.

According to my data, P. sylvestris has an S.G. of about 0.51. Western Red Cedar has an S.G. of about 0.32, making P. sylvestris about 60% heavier than Western Red Cedar.

[Bob Smalser]

Our local Red Alder is a bit heavier (.37 to .32 SG) and a bit stronger than WRC, is pretty stable once dry, and should work for a glassed, drysailed boat. I'm a little leary of it...it rots even quicker than spruce....and it ain't gonna be a boat you can leave out in the rain all winter, glass or not.

But if you can't get larch, it's certainly cheap and strong enuf for the weight. And I'd guess our Alnus rubra has properties nearly identical to your local alder.

[George Roberts]

Sakari Aaltonen ---

It all depends on what size of boat you are building.

Tom McNaughton specifies species of wood in his scantlings.

Dave Gerr gives specific gravities for woods in his scantlings. According to him larger boats require higher specific gravities.

Both list desirable properties of the wood used.

[Sakari Aaltonen]

Originally posted by Venchka:
European larch, Pinaceae Larix decidua?

This wood was used for years as planking. .Yes; I understand that larch is very resistant to rot. And it's available, yes (I made a tiller last year from larch; it's not bad-looking.) However, it's rather heavy - heavier than pine.

Another problem is that, apparently (what I've read), larch only develops its rot resistance at a certain age, at least 50 or 60 years. Wood from a younger tree will not have the desirable property. Well, buying larch, you will normally not know the age of the tree it comes from.

[Meerkat]

Dunno if this is relevent, but there's a product called "SpeedStrip" invented and patented by a British company that is precut and shaped stripping of various diminsions. It's available in the US in White (Atlantic) Ceder (last time I checked - and the price was reasonable I thought - $1300 for a 19' Golant Gaffer hull).

http://www.maritimewoodproducts.com/images/hull1side_new.jpg
Speed Strip has been successfully used to build mono-hulls and multi-hulls up to 200' in length.


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[ 10-31-2003, 05:03 AM: Message edited by: Meerkat ]

[Sakari Aaltonen]

Originally posted by George Roberts:

Tom McNaughton specifies species of wood in his scantlings.

Dave Gerr gives specific gravities for woods in his scantlings. According to him larger boats require higher specific gravities.

Both list desirable properties of the wood used.Geography is an issue here in that I live in Europe, whereas both McNaughton and Gerr, obviously, are based in North America. Gerr, for example, says that Pinus sylvestris is not suitable for boat use. Yet, where I live, it is what wooden boats have, traditionally, been made from. Was this merely because nothing better was available?

It was noted here that North American red alder rots easily. On the other hand, the Swedish page at

http://linnaeus.nrm.se/flora/di/betula/alnus/alnuglu.html

says Alnus glutinosa is resistant to rot. Indeed, Linnaeus himself, in 1749, appears to have reported that the majority of Venice, Italy, is built on alder pilework.