Free Standing Masts

[Garry]

Eric Sponberg, a yacht designer in St. Augustine, really likes free-standing masts. Many of his points align directly with Graham's. His description of the the expense and complication required to build a high-tech carbon fiber mast shows that the aluminum and carbon fiber mast design that Graham used on Southern Skimmer is a significant innovation.

Here is a link to Sponberg's discussion:

http://www.sponbergyachtdesign.com/StateoftheArt.htm

[Howard]

While sold on the cat ketch and freestanding rigs, there are some things about the one's I've seen so far that give me concern. Recent posts about the trouble reefing sails by moving the end of the sprit is the main one. I'm imagining it must look like me up on the foredeck dealing with a flogging jib or genny, or trying to jab my whisker pole into the clew while it's luffing. Not something I'd want to be doing in a blow.

In the reading I've done on the cat ketch rigs, historically, rigs with sprits also had rotating masts that eliminated a lot of the problems with sails binding on track and snotter tension changing, snotters binding, etc. From what I've gleaned from all I've read, once you allow the sail to rotate forward, to avoid problems, the mast has to rotate with it.  I'm also having trouble imagining how the mainsheet works when the sail is let out that far forward. I guess you just use a really long one and just let it blow out there.

The way this guy describes the benefits of the rotating masts, the planform sail shape etc. makes a lot of sense. Have wondered why a lot of these rigs don't have the full battened sails that look like windsurfer sails or those you see on the multihulls. Seems like it would also simplify reefing by allowing you to use a jiffy reefing line to the end of the sprit. It's a horizontal reef like that on a boom and the length of the sprit doesn't change either. Seems like it should be able to work exactly like jiffy reefing with nothing flogging around.

Not sure what to do about building the masts, however. The cost of carbon fiber is an issue on our size boats and it sounds complicated to get it right if you try to build it yourself. I can build an elliptical birdsmouth to get that "wing shape", but it's not going to rotate if mounted on a tabernacle. If you wanted to run it through the deck to the keel, it could be made round at the bottom and taper above decks, but that means a hole in the deck or doing what he suggests, and having a mounting stub and fitting the mast over that. Raising and lowering the masts just got harder if you do that.

A lot to consider, but a lot to like.

[Garry]

In my opinion, a rotating mast would be a high-tech engineering and maintenance challenge and probably belongs only on boats with unlimited budgets. Yes, Sponberg can talk about efficiency gains but Graham and others have shown that non-rotating masts work acceptably well.

If you did want to combine a rotating mast with tabernacles, you could use what Sponberg calls a "stub mast" in the tabernacle with the rotating part slipped over the top portion of the stub mast.

My understanding of Graham's mast design concept which will be used on the Princess 28 is similar to the masts used on his Southern Skimmer EC 22. The bottom half of the mast is aluminum tubing where the strength characteristics are well known and weight is not as critical.

The top portion is a light birds-mouth mast reinforced with a carbon fiber tube-sock and epoxy. The compression and buckling forces are resisted primarily by the wood strips and the tensile forces by the carbon fiber. The combination is relatively easy to build, reduces the weight aloft, minimizes the cost for carbon fiber, and, as shown in the latest 2007 EC Challenge, works well.

I've been following the discussion about reefing but don't understand it yet. Instead of removing the sprit from the clew, I envision a line that pulls the reef clew down to the sprit similar to one-line reefing on a boomed sail.

[Howard]

In my opinion, a rotating mast would be a high-tech engineering and maintenance challenge and probably belongs only on boats with unlimited budgets.

On the older boats I've studied, low tech was to step the mast in a tenon on the keel and it rotated freely through the deck, if it was a sprit boomed rig. For booms, they used a yoke on the boom and laced on the sails. Eric's solutions to a rotating mast are high tech and expensive. If it's a boat I'm building, that's not happening! ;D Interesting though that he thought it important enough to go to that much trouble and expense.

Again, I'm learning about these rigs, but it strikes me that if you are going to let the sails run way out forward for any length of time, to avoid strain on either the sail or the sprit rigging, some type of rotation is needed. It's more than just sail shape and efficiency. It's to avoid strain and damage. The speed gain by setting sails forward to form lift vs. drag is something I'm hearing more of as I study the rigs. Fast enough that in many situations, you don't even worry about extra light air/downwind sails.

I think the combination of planform sail shape and sprit does allow for single line reefing like you mention and for me that would be the primary goal. I've seen reference to the elliptical vortex stuff he mentions and have noted that Grahams designs use that for centerboards and rudders. Almost as if he was intending them to go fast. :

As a disclaimer, or at least to let you know where I'm coming from with my concern over simplicity and reefing, I got caught out in a building wind once....the luff sail slugs on the luff of the main jammed in the slot and the main wouldn't come down. It was getting downright hairy. Near knockdowns from too much sail are not fun, and when you are out of sight of land, there is no place to hide and you have to deal with it. Reefing needs to be safe and simple to do.

BTW, Garry, if you and I were to build something today, it would probably be the same thing. I just find it interesting to talk about these different facets of the design.

[Howard]

If we were to build something....reference was to the mast and rigging.

I'd be building out of plywood!

[Gordy Hill]

When I built CS17 #11 there was no forum to call on. Graham was very helpful when I was aware enough to know I didn't know something.

I came up with a great way to make a plug for the foot of the mast....I thought. I had hole saws who's inside diameter matched the inside and outside diameters of the mast tube. I drilled through a pressure-treated 2x until the pilot bit showed out the other side and used that hole to line up the other hole saw. It created a perfectly stepped plug that I epoxied into the bottom ends of the masts. (Cross grain isn't good)

During the Great Race the block on the main swelled and I barely got the mast out in time to pass under a bridge. Of course I never stopped to think there might be something wrong and I put the mast right back. Later, while beating in a really stiff breeze I noticed the marks on the mast indicated it was about two inches out of it's hole. That's about when the fiberglass sleeve went.

I got the mast out (fully rigged) and laid it on the boat. I ripped out the rest of the sleeve and put the mast back in with the partners and about a 1/2 inch step holding everything for the rest of the race.

I made new plugs the same way with polypropylene about an inch thick. I then put a disk of about 1/4 inch poly in the bottom of the hole for the main. I never got around to fitting a disk for the mizzen.

Both masts rotated very easily!

Poly against poly is 'bout as good as the best bearings. Nylon on nylon is also really slick.

My low-tech bearings let the masts rotate in very light breezes.

[Garry]

Dang! Now you guys have me thinking about rotating masts! Will it never stop???

I wonder if graphite filled epoxy would be useful as a bearing material. It is UV resistant and completely custom fitted.

[Joe Nelson CS#35]

Graphite will wear through eventually.  We use UHMW on anything that requires a slippery surface and wear resistance.  It comes as thin as 1/4" and up to at least 3/4.  It was developed for the wood mill industry for chaifing of chains, etc..  If you need a small amount to put under a mast, I would send it to you.  It cuts with wood working tools.  It makes great bottom strake and keel protectors.  No glue will stick to it...needs to be screwed in place.

[Gordy Hill]

Brad,

I'd thought of a king plank of poly bolted in place but I don't think it would be worth the trouble.

I had sleeve luffs and drilled a 3/4" hole through the mast about 6 inches above the deck. Then had a short section of heavy walled aluminum tube welded in it. Then I could stick a short rod in it and use it as a wrench to turn the mast to wind up the sail. It worked great. I called it my mast wrench. (Graham called it a mast spanner)

Joe,

The stuff works great on trailer bunks. I had carpet covered bunks on a new trailer. and where we launched off a causeway it was about 14-16 inches deep at the end of the trailer. It took two of us with our shoulders under the boat to get it launched. With plastic on the bunks I  could do it one-handed!

[Gordy Hill]

Brad,

You would think.....

However, once you tighten up the downhaul everything seems happier when it rotates.