Sea trials of a birdwing mast

[kenjamin]

Met a guy by the side of the highway as the county deputies were filling out the paperwork on my accident. I tagged 3 inches of a corner of a Ford Expedition. I broke her tail light , scratched her bumper and completely demolished the front quarter panel of my truck. Why she stopped again after I assumed she had left the stop sign, I’ll never know, but I won’t be making that mistake again any time soon.

The good news was that the guy, David Damon, told us about a new ramp to use, towed us out to the Gulf down a long windless canal and took pictures of Xena on sea trials. Here are the results (all photos are by David Damon):

http://ford.physics.fsu.edu/Xena056.jpg
http://ford.physics.fsu.edu/Xena062.jpg
http://ford.physics.fsu.edu/Xena067.jpg
http://ford.physics.fsu.edu/Xena078.jpg
http://ford.physics.fsu.edu/Xena088.jpg
http://ford.physics.fsu.edu/Xena108.jpg

Looking at these pictures, it's obvious that there's still a lot of work to be done. Taper the battens for a better mainsail shape (thanks Todd), come up with a downhaul for the main boom, fix the angle of the offset tiller arm, and quit torturing that poor Shaw and Teeney oar as a mizzen mast. The oar is too flexible for that use and it's the wrong color to boot! Oh, and also I might try actually hoisting the jib all the way up.

All in all, though, I was pleased with the results of my experiment with this storable mast. I'm getting more and more comfortable with stepping it by myself and it can be done on any small patch of shoreline.

Special thanks to David Damon for the pictures!

[Kaa]

Quite interesting. As you change the angle of attack for the mainsail and the mast rotates, do you have to continuously adjust the tension on the jib's luff wire? And do you, basically, have to take the jib down for every tack?

Kaa

[Todd Bradshaw]

See if you can come up with a way to get some decent luff tension on the jib. That's the most glaring problem that I can see at the moment and it's likely costing you big-time. Around 85% of the say length on the hoist for the jib is usually fine on a cruising boat and helps keep it from pinching the top of the slot closed, so I don't think it really needs to go up any higher, but the amount of luff sag is off the charts. Some of this is the typical problem with trying to fly a jib from an unstayed mast and just not fixable, but anything you can do to try to bring the jib luff back toward the centerline of the boat is likely worth doing.

[kenjamin]

Kaa, I probably won't say this correctly but the jib halyard (that holds up the head of the jib) enters the mast at the center of rotation of the mast so luff tension of the jib does not affect the rotation of the mast at all, neither does the rotation of the mast affect the luff tension of the jib. You might think that the jib would have trouble getting pass the main mast on tacks but something about the curved surface of the leading edge of the mast encourages the jib to slide right on by so no resetting of the jib is necessary.

Todd, I knew you would catch me on that jib luff tension. The problem was operator error. There was so much going on. I had forgotten to step the mast while the boat was still strapped to the trailer, I had lost my glasses so everything was a little fuzzy, and I was still a little disoriented from the accident on the way over. The glue lines on the mast (and there are many of them) run fore and aft so there's plenty of stiffness there to tap into but I just couldn't see the slack luff of the jib or forgot to look.

http://ford.physics.fsu.edu/Xena098.jpg

As you can see in this photo (by David Damon) the jib halyard runs back to me (yellow shirt) and I should have given it a pull if I had thought about it. There was so much wind, I was thrilled to death just to be out there and finally sailing.

[Kaa]

Kaa, I probably won't say this correctly but the jib halyard (that holds up the head of the jib) enters the mast at the center of rotation of the mast so luff tension of the jib does not affect the rotation of the mast at all, neither does the rotation of the mast affect the luff tension of the jib. You might think that the jib would have trouble getting pass the main mast on tacks but something about the curved surface of the leading edge of the mast encourages the jib to slide right on by so no resetting of the jib is necessary.

Ah, yes, a very nice solution to the problem, provided your mast is stiff enough. You might have issues in gusty winds, though. Consider that a squall will seriously increase the force acting on the jib. That force will (among other things) increase the luff tension and try to bend the mast forward. If things get out of column, this force will also be trying to turn your main mast and change the mainsail's angle of attack. I don't know if this will turn out to be a problem in practice though :-) -- good for you for trying new things out!

Kaa

[Todd Bradshaw]

You might find something like this handy. Once rigged, it goes up quickly, comes down quickly and can be easily adjusted on the fly with built-in mechanical advantage.

http://webpages.charter.net/tbradshaw/!SELFSTA.PDF

[kenjamin]

http://ford.physics.fsu.edu/UsGuys1131.jpg

As you can see from this photo from an earlier sail, the main mast is made up of about a dozen layers of wood (fir and sitka spruce) and it is one beefy lamination. (44 lbs.) Each layer is made up of several pieces of wood with end to end splices with a 1 to 8 bevel that are staggered so no beveled splice is close to another one. Most of the glue lines run fore and aft so it's very stiff in that direction – not as stiff as a stayed mast, but very stiff for an unstayed one. When we popped out the jib it was like a jet turning on the afterburners – a real kick in the pants!

Thanks for the encouraging words, Kaa. It's been very interesting and I feel like I've learned a lot both about mast building and people's resistance to change. I just had to laugh when somebody told me if it was really a good idea, it would have been already invented. To me that's sort of like thinking the Vikings had epoxy to work with but chose not to use it!:rolleyes:

[johnw]

Penguins have shrouds on a rotating mast, so that's possible with this rig and might help with the luff tension. Any mast will bend in the puffs, and having your jib become a lot fuller and more powerful as the wind increases isn't really what you want.

[kenjamin]

Todd, there are Harken sheaves mounted inside the mast for both the main halyard and jib halyard. The main halyard hoists the fiber reinforced bamboo yard past the end of the mast with its sheave mounted near the very end of the mast. The top of the jib halyard sheave is located exactly in line with the axis of rotation of the mast. The sheaves are high quality units with ball bearings and the halyard tunnels inside the mast were coated with epoxy during the gluing of the two halves of the mast. Knotted up parachute cord was used to clear the halyard tunnels of excess epoxy. The halyard tunnels emerge out of the mast where the mast changes direction and becomes a straight section with a round cross section for rotation in the mast step.

I'm sure could have put a lot more luff tension on the jib if I had just remembered to check the darn thing.

[kenjamin]

Thanks johnw, luckily for me I remembered to drill for mast stays when the two halves of the mast still had flat sides so the holes are there (straight and parallel for bolts) when I go looking for better performance. Being a novice sailor with a novice crew, I've been feeling like I'm holding the reins of a wild mustang as it is. Just now meeting people who grew up sailing (like photographer David Damon)and have offered to help sort out the boat. I planned for the stay attachments as close to the axis of rotation of the mast as possible but it wasn't possible as far as I know to get it as close as where the jib halyard enters. Still, maybe with the use of some rings, the stays won't affect the mast rotation very much. It would be good to get a close look at the Penguin rig. Thanks for the heads up on that.

[Todd Bradshaw]

You could also eyeball the rig on any Hobie Cat or modern iceboat as they all have rotating masts with the shrouds and headstay leading to a single point on the front of the mast - usually to a saddle-like fitting with a hole that they shackle to.

[johnw]

Yeah, I think it has to be on the front of the mast. That's how it is on Penguins, too.

[johnw]

You know, the thought occurs that if you put that jib on a mast that sits at the same angle the jib does, you could get by without shrouds and not have to worry about luff tension. Uffa Fox did that with the racing canoe he used to win the North American trophy, because the North American rule required a two-masted rig. Might be an easier answer.

[Todd Bradshaw]

This is how it's done on my iceboat. The fittings on the mast are made from four strips of bent stainless steel, through-bolted to the spar. The top of the mast is to the left.

http://webpages.charter.net/tbradshaw/fb%20003%20copy.jpg

The shrouds and headstay are attached to a couple more hunks of stainless and the pin on the mast fitting passes through the loop on the left. This photo shows the back (mast) side of the big piece. It's good up past 60 m.p.h. with a 7:1 mainsheet system and the sailor sheeting in about as hard as he can with his feet braced against the front wall of the cockpit, so I can't see it failing on a softwater sailboat as long as the mast doesn't break.

http://webpages.charter.net/tbradshaw/fb%20005%20copy.jpg

My last iceboat used a similar gizmo on the mast and simply used a heavy bow shackle instead of the pin and plates. The wires fit over the round part of the shackle and the shackle pin passed through the pin holes on the mast pieces.

[kenjamin]

Thanks guys, this is great information. Hey Todd, I'm assuming that this pin in this picture is mounted on the front side of the mast, right? (The last time I assumed something I hit a Ford Expedition.)

http://ford.physics.fsu.edu/ToddMast.jpg

Like I said I've already got two through holes in my mast and this strap set up looks perfect for bringing the pivot point of the stays around to the front of the mast. Good thing there's a machine shop in the basement full of guys that work in stainless all the time, and many are good friends since I've worked here 35 years. They know what to expect when I put on my beggin' face.:D

[BrianM]

Very cool boat. I really think the burgundy color of the sails adds a whole new level of CLASS.

The birdwing concept as interesting as it is technically, also adds an (I'm sorry for using this term) "Organic" touch to the boat, almost as though it is a living thing.

Great photography also!


What are the origins of this birdwing concept? What's the idea behind why it works better than a traditional straight stick?

[Kaa]

What are the origins of this birdwing concept? What's the idea behind why it works better than a traditional straight stick?

I believe it all started with Kenjamin's wish for a mast which he could take out and stow in his Caledonia Yawl hull so that it doesn't interfere with his fishing. Well, the boat's hull happens to be curved, so... :-)

Kaa

[kenjamin]

Brian, thanks for your interest and your comments.
Kaa, thanks for covering for me. My computer was down for a while yesterday for more memory and they forgot to turn file sharing back on afterwards.

Here's the story, guys, in pictures.

http://ford.physics.fsu.edu/Cobia.jpg

My fishing buddy shown here with his undersized cobia (he threw it back) complained loudly and obnoxiously about the old straight mast being in the way of fishing so I glued one up that curved around him when stored.

http://ford.physics.fsu.edu/Skiff-topview.jpg

http://ford.physics.fsu.edu/Doryskiffsailing.jpg

This worked well and when my dear mom left me money to build a new boat, I had already thought of about ten ways to make a new better birdwing mast. The new mast got so good in my brain that I thought it might be worth a patent. I gave the idea to my employer, Florida State University, so now I only own 40% of the rights to the design but FSU is paying all costs of the patent search and will no doubt defend the patent if it ever amounts to anything. I figured 40% of something is a lot better than 100% of nothing.

http://ford.physics.fsu.edu/XenaMainsail0376.jpg

I believe the design may offer some real performance benefits especially to windward where it can shed the drag of the mast better than your average stick.

Look closely at this next photo and you can also see just how well the mast stores along the gunwales of Xena's hull.

http://ford.physics.fsu.edu/Birdrack.jpg

From the beginning of her build, Xena was meant to be a working fishing boat so the finish is quite rough and I was in a hurry to finish her to show at last year's WoodenBoat Show at Mystic.

Here's one of my favorite pictures of her at Mystic with a very expensive traditional lug rigged Caledonia Yawl moored at her stern.

http://ford.physics.fsu.edu/Xena&Patina0395.jpg