I am looking to build another mast for my Scamp. I am considering using Paulownia wood. It is very light weight and as strong as Western Red Cedar. I intend to epoxy two halves with carbon fiber tape between them. The mast I have now is made from spruce lumber and is solid not bird mouth construction. The mast I am thinking of making will also be solid. I question if this might be strong enough. I have seen a video of Paulownia being used in boat construction. I would appreciate any input on this idea of mine. I have priced the cost of custom cut mast halves, carbon fiber tape, and epoxy. The mast could be assembled for close to $150 plus my time.
https://www.youtube.com/watch?v=LZKKHAFN8mg
You're getting way ahead of my pay grade ;D I'm not familiar with that wood, and then you mention WRC and I HAVE fooled with that. Never seen carbon fiber tape, either. Which is all well and good but that mast isn't very big is it? I mean, relatively speaking. Is it that important to shave pounds? One thing you might consider is that when you get off into exotic materials, supply lines and logistics start coming into play, just to acquire such materials. And then there are special concoctions to repair it if something happens. Something ALWAYS happens, in my way of looking at it, else life would be a mundane thoroughfare of sameness. Err, do you kinda see where I'm going? When I built the catboat, I didn't even use epoxy. I used more commonly accessible items like polyester resins for the hull overlay, and even the fillets inside. Gas mask mandatory too. Resorcinol glue for the hull and mast. Yes, I learned a very lot building that boat and somehow it has held together for a long time. I HAVE used epoxy in certain situations since, after becoming more familiar with it. I'd love to build another but that probably won't ever happen. But I can't give any substantial opinion on your project because it is way beyond what I've ever done. I can tell you that I have thought of re-masting the catboat a couple of times. I'm sure a birds-mouth spar would be MUCH lighter and fun to build. BTW my mast is hollow except on the ends where it is solid for sheaves and where it fits in the step in the hull. I haven't weighed it but it's about 50-60 lbs out of fir. It cracked one year in very cold weather near the foot, and I cut a section out and repaired it. All of that is below the deck or I might have done it then. There's a kinda long story about that mast that I posted some time back. It was the most fun thing to build on the whole boat.
Look me up that story Kurt when you're not doing nothing ;) I can gauge how much of my brain has flown the coop since then :o :o :o :o :o
The Mast that came with the boat is a long story. Suffice it to say with 2 1/2 feet of 1/4" stainless steel tubing on one end and 12 feet of solid 3" tapering (most probably) yellow pine it is not light. Balancing it vertically as I stand on the roof of the Scamp's small cabana it's difficult to place over the mast stub sticking above the roof. I would consider a bird-mouth mast but that takes more time than I wish to put into it. I don't even have a carport to work under. So quick construction is and jobs that can be completed in a day is preferable. I have access to a mill that specializes in Paulownia. You treat carbon fiber like epoxying fiberglass, and I could laminate the mast in a day when the weather gives me time for it to set. then I can set it out of the weather even if it is under a plastic tarp and off the ground. I believe in 3 days of shaping I would have it round and tapered. Then it is back to 3 coats of epoxy and paint (which I have on hand). That's the plan that "Murphy" will be working with. I will also be making 2 Greenland style paddles from the wood. they are said to be as light as carbon fiber paddles. I have made a couple out of cypress in the past. If you have never paddled with a carbon fiber paddle you have no idea how much nicer one is when paddling all day or long distances.
Here is a link to the mill that I will use in SC.
https://bioeconomysolutions.com/
Doug, This link may be of some help:
https://www.wood-database.com/paulownia/
Your idea to place a strip of carbon fiber to stiffen the structure is a good idea, but may not go far enough.
You might consider installing the CF strip, epoxying it together, then cutting the mast in half again at 90º and installing a 2nd CF strip and epoxying that.
If you have been following my SCAMP progress posts you may recall that I was gifted a mast from a 16 foot Luger sailboat, that uses a Dwyer DM-284 extrusion. It has been subject to criticism from the SCAMP community, as they consider it too small and light to hold up.
I am not convinced and intend to go my own way and give it a try.
If it fails Spectacularly, :o my back-up plan is to start with John Welsford's original aluminum mast specifications:
6061 T6 alloy, 69.85mm Outside Diameter, x 1.65mm wall thickness; which is 2.75" O.D by .065" wall thickness.
I was going to start with 2.75" X .065 O.D. at the base in a 6-foot length, then follow up with a 2.5" O.D. X .065" wall thickness for the middle 6 feet, then finish with a 2.25" O.D. X .065" wall thickness for the top 6 feet.
The slight gap between sections would be coated in epoxy and have a layer of fiberglass tape (if necessary) to fit snugly together. After cure, I would pop-rivet the sections together. Three 6 foot sections overlapped internally at either 6 or 8 inches would give the correct SCAMP mast height.
With fairly aggressive metals shopping, you could get the price fairly close to $150.00 although the most prominent metal on-line suppliers typically run about 3 times that amount. I purchased two 6 foot X 1.125" aluminum yard sections for 1/3rd what a 12 foot X 1.125" section would cost. They were fastened together just like I describe above.
An alternative is to go to 3" diameter at the base and progress downwards from there, if common tube sizes with .065" walls are not as available. Either way, I have to think that 11 - 15 pounds of aluminum, will be lighter than a solid wood mast, even one of a lighter material like Paulownia, which is 18 lb/cubic foot.
Food for thought,
Charles Brennan
Charles and Riley, your replies are always welcome.
I figured the board feet in the mast and this is what the pricing is based on. It is 12.25 Board feet, and this is before rounding. I did this for a 3" X 3" X 196" mast blank. There is 12 board feet in a cubic foot, so it comes to 18.36 pounds. I'm not sure how many board feet would be removed from rounding, but at 18 pounds for one cubic foot of Paulownia then It may end up being in the neighborhood of 15 pounds. I also did it with a 2.75" X 2.75" X 196" mast blank and it came out to be 10.29 board feet which comes to 15.44 pounds before rounding. I don't think the carbon fiber will change the weight negatively, but the epoxy and paint will add some weight.
I did think about splitting the mast after laminating and putting a cross section of carbon fiber. I do know one has to wear protection when sawing carbon as the small fine carbon fibers are bad news. I don't know much more than that about sawing through the carbon tape. So, I am a bit hesitant about cutting through it. However, I am considering doing so.
One more thought I could have the mast precut into quarters (I'm already having it measured to cut into halves). Then order 3-inch and 2-inch tape. Do two quarters with the 2-inch (trimming off the excess) and then use the 3-inch and epoxy the two halves together. I think I will do that.
I have a guy on the lookout for a 2.75-to-3-inch OD whisker pole as he salvages sailboats to use as a round aluminum mast. He said he would let me have it for $100 so that may be a future choice.
Doug, Something I was considering as being considerably easier to do than a birds mouth taper staved mast, (since I would be building it all by myself) was a simplified hollow mast.
Box_Mast.jpg
If you have a table saw that can tilt the blade to 45º you could easily cut the two 45º bevels off a ¾" X 2¼" strip of wood the length of your mast. Plus, they could be glued in sections working your way around, until the last piece was fitted. With birds mouth joints, all staves have to be glued at once since they have to interlock, which can get hectic.
Since the reason they cut perfectly good spars in half and glue them back together, is because the epoxy-to-wood joint is so much stronger and stiffer, this method gives you ample epoxy joints.
With this approach, you get weight reduction from the hollow, and you don't need the exotic (read: expensive!) carbon fibers for weight reduction and strength.
More food for thought,
Charles Brennan
CB, I think there is something a bit off with the dimension 1 3/4" in your sketch, s/b 1.5" if the angles are only 90 or 45/135 degrees with a 3/4" meet-up at the staves:
brennanmast1.jpg
And another thing, 2X4s aren't totally square. Some of the corners are rounded and you have to pay attention that doesn't interfere. My mast is built using that basic method. It is also tapered and I can't remember now how I addressed that fact. At any rate, once the mast is eight-sided a plane is used to knock down the high spots and then it is sanded true. Lot of sanding with the smell of the wood making up for all the work.
Quote "2X4s aren't totally square"
Or solid, or straight, I firmly believe some of the 2x4's I buy have material that exists in another dimension. I don't remember a time when you could buy a 2x4 that is over 50% bark (actually found one last time at Lowe's.) Some of what I see in the pallet of lumber qualifies as live edge.
Ditto on the quality of lumber these days.
The Paulownia I am pricing is from a sawmill and will be custom cut at a fixed pricing by board foot and not the number of cuts. So, a solid 3"X3" or four 1 1/2"X 1 1/2" will cost me the same. Since the longest board that can be cut is 15'7" and I need 16'4" it will be easy to do some offset splicing with the 1 1/2" pieces. I can then use 2" CF tape to laminate two sets of 1 1/2"X 3"X 16'4" pieces. Which will then be laminated together with the 3" CF tape. After which the next steps to make are the cuts to end up with an octagonal tapered mast to begin the rounding with rasp and plane and sandpaper. By the way Paulownia is known for its dimensional stability which means It shouldn't warp on me. So many, many details to consider. Makes me a bit tired just thinking about it. Time for a nap! ;D
When I was building the 16 foot mast for my PDR I used nice pine 1x4' with staggered offsets.
I made a 8 foot jig with a leftover 1x6 with a piece of angle iron screwed into place.
The whole works was leveled up on sawhorses and covered in wax paper (plastic film would have been better) and the pieces were coated with epoxy and the joint areas clamped in the jig both ways and the remaining ends clamped together. I have ran 4-5 projects through the jig.
Here's a sketch of it, keep in mind it is longer and there were an assortment of clamps going both ways, little pieces of wood to distribute clamping pressure, etc.
gluejig1.jpg
Thanks for the diagram, Spot! There is so much knowledge and experience on this site and so freely shared that I am thankful to be active here. I already have some aluminum angle and often use cling wrap to keep the epoxy from sticking to stuff.