Splicing for a Birdsmouth Spar

[Dave R1]

I'm thinking about building a new mast for Julie K using the birdsmouth method. Due to availability issues or lack there of, I think I'm going to have to splice pieces to get the desired length. So my question is this, would you set the splices as I have drawn them or would you stagger them by swapping some of the pairs? Note: I drew the spar so the staves are scaled correctly in section but I used a 1:12 scale for the length so that the splice is easier to see. The splices are drawn at 2 inch intervals but I would use a 24 inch interval when cutting the actual wood.

[umop_apisdn]

First a disclaimer: I know far more about physics than I do about woodworking.

If you are using a butt joint for the splices, you are going to want them staggered randomly, with the joints for adjacent staves a considerable distance from each other.

In theory, by stairstepping them like that, you are making your mast susceptible to rotational forces. Whether that matters in practice, I will leave to the woodworkers to answer. :-)

I think that scarf joints would be far superior to butt joints for this, and then it wouldn't matter where you put the joints.

Noel

[capt jake]

I would definitely scarf the joints. Then I would also stagger those joints as well.

[Charlie Jones]

When I built the 22 foot spar for the gaffer over in Florida I used 24 foot staves (2 12s) and scarfed them. Then I reversed half of them so the scarfs were alternating around the spar and offset by a foot each way - actually more than a foot, but you get the idea. That left ends sticking out at each end of the spar, which I trimmed once it cured.

By the way- I had really good experiences with not glueing the opposite sides the first time so I could pop the spar back apart and lay in closely fitted blocking where needed.

[Dave R1]

Thanks guys. I should have taken the time to draw in the scarfs or I should have be more clear about my intentions. Scrafing was really what I had in mind for those joints. I was really just asking about the staggering part.

Charlie, I hadn't thought about reversing the pieces to get the scarfs reversed. That seems like a great idea.

I would just glue up halves as you mentioned so I could install plugs at strategic points as well as add wiring for masthead lights.

OK, now I just have to find some clear lumber long enough. What if I had 4 or 5 scarfs in each stave? :roll:

[jimw]

Dave,

What graphics program did you use to create the drawing?

JimW

[Dave R1]

Jim, the software is called SketchUp. It's an architectural sketching program and although not intended to be considered a CAD program, I find it extremely useful for doing drawings I can work from in the shop.

Here's my model of the Weekender. It isn't complete yet but it looks like a boat. I drew it from the plans plotting offsets just like you would on the real wood.

[Barry Pyeatt]

Dave,

Shouldn't be any problem scarfing together shorter pieces. Just stagger the joints as much as possible so no two are adjacent or within about 12-18 inches of each other.

[Howard]

This may seem like a dumb question, but of the two scarf patterns I've drawn, which is most correct for scarfing stave lumber? A or B? The reason I ask is that I've seen both used on wood. A is used on plywood.

Would finger joints work to scarf these staves together?

[Dave R1]

I think B makes more sense for solid wood because it creates a joint that is much closer to being a long grain to long grain joint and because the faying surfaces are so much larger.

A makes sense on plywood though.

[Charlie Jones]

Howard- use B

And I personally would not trust a finger joint in this type of application. Finger joints are fine for unstressed use, but there will be a bending load on a mast- I'd go for the longest scarf and glue surface possible. Which is "B" in your drawings. That will also make the nicest looking joint in the finished spar.

[umop_apisdn]

I think the best choice depends on how the wood will be bent, doesn't it?

It seems to me that B is going to be more prone to splitting if the joint is bent around a compound curve (say a rubrail), won't it? In other words, of you both twist and bend the wood, won't the rotational force cause the B joint to bend and break? (Which is why B is bad for plywood, it would break as soon as you bend the plywood)

For the mast, though, I think B would be the superior one.

Noel

[Howard]

Scarf B is what I would have guessed, but I have a book in which a large 50 foot mast was built using A. They built a jig to use a Skilsaw to cut the scarf, but had to finish them with a handsaw, as the circular saw blade could not cut all the way through.

I'm contemplating building a birdsmouth mast for my Spindrift....don't need to make it out of wood, but it might make good practice for a bigger B&B later on.

Anyway, the wood mast option calls for a SOLID mast that is 2 1/4" at the base, tapering to 1 1/4" at the top. If I have this right, assuming a centered birdsmouth joint, my panel widths are going to be around 15/16ths inches (a bit too large to finish at 2 1/4"), but can be planed down) and the panels will have a thickness of around 7/16ths (about 20% of mast diameter). If I used a 12 inch scarf, I'll have close to a 12:1 scarf. I'll core the base to the point where the boom attaches, hollow above that, and plug the top 6 inches or so. Instead of ripping these (no table saw here), I may use a 90 degree bit on the router table. And build a shooting board or some other way to get an even taper on each panel. I'm just guessing on the panel thickness. At 20%, it may wind up too stiff.

I have a 16' 2x8 stick of Doug Fir leftover from when my house was built. Have never had a use for it, and this is as good as any. But I can only find some lengths in that board of 8 to 10 feet that are clear...then a knot will show up. So scarfs would be required, and lots of them. Grain is average to coarse.

Plan B is to use Hem Fir. The local yard had some of those that were pretty clear and it's tight grained. It's what I'm building my boom out of. That way, the two would match, asthetically. Or shop for a better stick of Doug Fir. Some of the best I've seen are in my basement, installed as floor joists. Some of them are tight grained and clear like in my dagger board below. That was made from a scrap I've had for years. What are the odds that one of those would be missed? :wink:

[Dave R1]

Noel, if the glue joint is made properly it will be stronger than the wood. There shouldn't be any problem with using scarf B in a compound curve. The one problem might be that the piece might have a hard spot where the scarf is and wouldn't make a smooth, fair curve.

[Frank Hagan]

Plan B is to use Hem Fir. The local yard had some of those that were pretty clear and it's tight grained. It's what I'm building my boom out of. That way' date=' the two would match, asthetically. Or shop for a better stick of Doug Fir. Some of the best I've seen are in my basement, installed as floor joists. Some of them are tight grained and clear like in my dagger board below. That was made from a scrap I've had for years. What are the odds that one of those would be missed? :wink:[/quote']

If the Hem Fir is really Hemlock, you might run the risk of splitting down the line. Hemlock doesn't hold fasteners well and tends to split, so I would be suspicious of it where you have to use a throughbolt or other fastener. (I also don't like the way it smells when worked ... it may only be me, but I think it smells like vomit.)

Have you noticed any problems mixing redwood with other woods? The reason I ask is that I've heard that redwood expands along its length with seasonal changes, rather than its width, and can be a bear to keep edge-glued to other woods. But it looks like you've done that with the picture you posted, and I don't see any cracks.

[Howard]

I've often thought my stuff looked bad enough to make one vomit, but it doesn't smell like it.

On the hem-fir issue, this is what I found...after they sold me the board:

http://www.wwpa.org/hemfir.htm

To save having to read all of the link....this was a summary paragraph I plucked from it:

"Hem-Fir is additionally preferred by many builders because of its: resistance to splitting in nailing and screwing; ability to hold nails and screws securely; ease of sawing without splintering; ability to hold a variety of glues and adhesives; and moderate lightness in weight. It is straight grained, stiff, strong, easy to work and relatively free from pitch."

And when I called the yard to ask about it, they told me they often sub this particular wood for Doug Fir....as the specs are very similar....was even told for some applications, it's preferred. So I guess it might be the same Hemlock you refer to, but I've found it to be like that described above. I even did a scratch and sniff, and found no smell at all.

I have a piece of clear spruce that I was going to use for the boom, but it was absurdly expensive, and I've heard that spruce...while traditional....is not all that strong or durable for use as a spar. I'm saving the piece I bought as potential oars. And all of this may be overkill for a boom anyway. I seem to recall Graham suggesting to find a piece of clear S-P-F construction lumber, and use that. They sell those for $5 at Home Depot.

As for mixing it with Redwood.....now you tell me! I have no idea if it's going to cause problems. So far it hasn't, but so far it hasn't been out of my basement. Both the daggerboard and rudder are a combination of tight grained Doug Fir, Redwood, the Hem Fir above and Western Red Cedar. All of it was scrap and I did it to get the color variations. But they were not hard to do, and if they split and blow up.....I'll do them again with only one species. Both will be glassed over, so we will see.

[wkisting]

Howard,

I'm no expert, but I used Redwood and Western Red cedar in a cedar strip kayak I built a few years ago. The Redwood was used for a stripe that wraps over the curved deck from stem to stem, so it's in a very high-stress application as there is a LOT of twist to the strips as they wrap (almost had to steam them to get them to bend). The wood is sheathed in 5 oz. glass, and so far never had the slightest trouble with Redwood swelling or de-bonding. I think if you sheathe carefully and seal thoroughly, you'll be fine. If you were only epoxy-encapsulating (without cloth), then you probably would see problems.

Again, that's based only on my experience with these woods, which admittedly is limited to that one kayak.

[Howard]

Lucky for me...my use of all these "exotic" woods has been on peripherals...spars, rudders, etc. It's not structural to the boat, so if it blows up, I can always replace it.

I started out planning to use cypress as structural lumber, thinking it would be light and would not rot. I later found out that, no it doesn't rot, but if it gets wet, it will expand and blow the glue joints apart, like Frank mentioned about redwood. So I got that stopped. I mostly used western red cedar for my cleats.

BTW....while waiting for the breakfast meat to cook this morning, I noticed a Lee Valley catalog laying on the counter. Thumbing through that, I see they are selling some birdsmouth bits for routers. They have three types...with the right angles for 6 or 12 staves, 8 staves or even 16 staves, and will handle stock to 7/8" inch thickness. Hmmmmmm.

[capt jake]

I have found it common practice amongst the yards to substitute Hemlock For DF. I agree with Frank that it is 'more' prone to spliting than DF.

There is a definite difference in the smell. Once you smell DF, you will never forget it. It smells wonderful (to me anyway).

I recently paid the premium price for DF for some oars I built. When sawing it, I really doubted their truthfulness in the species. I went to reconfirm and the swore it was. It was stamped as DF, but it did not work or smell like DF.

As with most things we use, we have used up all of (or most of) the 'good' stuff.

I have also read that the stamp 'Hem-fir' is a 'catch all' stamp that they give to multiple species.

With that said, if it is glassed and sealed, youu probably won't have a problem.

In regards to the Redwood, are we still talking about it's use in a mast? I wouldn't, it's too brittle, IMOO. In a kayak, the stresses are limited be the adjoining strips, etc.

[Howard]

Nope....redwood was only being used as a "decorative" stripe in the daggerboard and rudder. Not in a mast. Not in anything else either. Again, the redwood was just some scrap leftover from when my house was built.

The hem-fir issue was raised as a possible substitute if I couldn't find the right mix of doug fir. I do have a 16' doug fir board, again...leftover and not used for anything for close to 15 years now. Parts of it are ok, but overall, it's not that good. But if I ripped the whole thing down, I'm sure I can find enough clear pieces to scarf together 8 - 18' lengths for a birdsmouth mast.

I snapped a photo of the board in question. The other pic is an example of some of my floor joists. Some of those are really good....but alas....already used. :wink: