Camber spar patent #4,503,796

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mike cunningham
Posts: 489
Joined: Sat Dec 20, 2008 11:21 am
Location: Jacqueline, F30 #3, Discovery Bay, California

Camber spar patent #4,503,796

Post by mike cunningham »

Hi all. I continue to have issues with sorting the camberspar. Due to the fact I suffered severe damage to the spar and, after repair, am experiencing issues with camberspar twist when the sail is down: It seems to roll over on itself and locks in place when I attempt to raise the sail. I must go forward and flip the sail over to unlock it. Major major pain.

I have had a discussion with Paul Dennis and he confirmed my "tacking arm" (this is what the looped bit at the aft end of the spar is called), which had been torn off during the Hawaii race, was re-welded in the correct orientation And that the sheet should be attached to the long loop of the tacking arm with the small/short loop is attached to the topping lift.

All good...except...then Paul asked about the spar chord. I told him the spar had been dramatically bent during the race and had been straightened out to appropriate shape by my sail maker here in the SF Bay area. Paul asked for the chord length of the repaired spar. in my case the chord is 16.5 inches to the center of the spar at deepest draft. New problem... looks like this chord (draft) is about 7.5 inches too great. So that may be leading to the behavior I am seeing, not to mention the obvious implications for performance.

In any event, it the process of trying to get my brain wrapped around this spar, I found Bierig's original patent which provides a thorough overview of what the parts are called and exactly how the thing is supposed to work. I have attached it here for posterity.
camberspar patent.pdf
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Mike Cunningham
Freedom 30 (Mull) Hull #3
Build date...June, 1986 . Freedom Yachts USA, sloop, shoal keel
Gun Mount and pole retrofitted (purchased from a Hoyt Freedom 32)
Yanmar 2gm20F , 1600 hrs fixed two blade prop
e-rud and ocean racing equipment

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gamayun
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Joined: Thu Dec 06, 2012 9:14 pm

Re: Camber spar patent #4,503,796

Post by gamayun »

Mike, nice to see the patent on this. I am not sure staying true to the original form is the way to go. I have gone round and round with Michael Jefferson (Mouton Noir) about the camberspar and the sail in general. He absolutely hated it and thought I was going to kill myself for using it. I am fine with it and plan to keep it but believe there's a better place in the middle to land with this issue. We designed a new headstay attachment but it is a problem too for other reasons, mainly having to do with the length of the spar relative to the sheet block. My spar seems to be too long and presses out on the forestay which causes a lot of friction and dry works the wire stays. After my last roundtrip to Hawaii, I now have even more thoughts on what works and what does not. Happy to get up with you next time you're in the main bay or I can take a drive to you. Maybe we can get Tony Bourque (Circe) and others in the bay area involved to have a brainstorming session. I can bring my camberspar and notebooks!
Kynntana, Freedom 38

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mike cunningham
Posts: 489
Joined: Sat Dec 20, 2008 11:21 am
Location: Jacqueline, F30 #3, Discovery Bay, California

Re: Camber spar patent #4,503,796

Post by mike cunningham »

Carliane,
I have had some misgivings about the camberspar (CS) as well. The CS really limits one's ability to tweak the sail plan based upon conditions. I believe you had a standard genoa made for your boat? I should get down to the Bay and look more carefully at what you have done.

I am really torn on this.

Pro's

Super simple to manage, esp as a singlehander.

With the gunmount and spin pole aboard, the pole can be centered and fixed orthogonal to the boat and the jib poled out and locked using the spinnaker sheet. This technique can also be used as a sort of mainsail preventer. The result is a remarkably stable downwind sail configuration and was a key factor (along with weather, admittedly) in my much improved performance in the 2018 SHTP vs 2016. I rode downwind for days in this configuration. Minimal stress. Squalls were manageable, etc.

Cons

Removing/changing the CS jib at sea is a royal pain. There is a rapid removal configuration for the camberspar which makes removal much easier but, of course, we are still stuck with the awkward and heavy 9 foot spar. I suppose one could simply drop the CS and hank on a jib but then we need additional deck hardware to manage a traditional jib although that same hardware might be useful for spinnaker management. We would also have a CS jib flopping around on the foredeck.

The CS is obviously not optimal for some conditions, light air for one.

The ability to tension the Forestay is limited. It is almost not a forestay in the traditional sense. I need to chat with you about your experience with the genoa re this issue.


That is all that immediately comes to mind but there are a more pros and cons out there.

In summary, it would be good for me to take a look at your set up and continue the debate.
Mike Cunningham
Freedom 30 (Mull) Hull #3
Build date...June, 1986 . Freedom Yachts USA, sloop, shoal keel
Gun Mount and pole retrofitted (purchased from a Hoyt Freedom 32)
Yanmar 2gm20F , 1600 hrs fixed two blade prop
e-rud and ocean racing equipment

SunnyIsleMark
Posts: 60
Joined: Sun Oct 17, 2021 8:42 am

Re: Camber spar patent #4,503,796

Post by SunnyIsleMark »

Hi Mike- thanks for posting that patent application! It was a very interesting read and such a clever way of adjusting the draft in a small jib as the spar is rotated. In the Freedoms, the jib becomes much more useful and powerful than a standard working jib, and downwind it becomes like a built in whisker pole. As for your 16” draft, that seems far too deep, however I would think that potential depth should only be reached if the spar is rotated to the horizontal, otherwise it should only be partially rotated. My guess is that maybe your fabricator used the curve of your luff pocket to determine the spar curvature? If the full draft is never realized by lack of rotation (as when sheeted in) I’m not sure it would be a big issue.
Mark

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mike cunningham
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Joined: Sat Dec 20, 2008 11:21 am
Location: Jacqueline, F30 #3, Discovery Bay, California

Re: Camber spar patent #4,503,796

Post by mike cunningham »

Mark, last sentence of your post is right on. I finally understood that as we get closer to the wind and sheet in we are taking draft out of the sail. Duh on me. I also remeasured the draft and I am around 14 inches. If I use the formula CS length in inches ( mine is 96) then multiply by 13% you wind up with approx 12.5 inches. So I am pretty close. Then the article Geoff posted mentioned "eyeballing it" so eyeballing implies you got some wiggle room. I plan to use the wiggle room and take no action on the bend.

However. Now that I finally understand how the thing works. I am going to really focus on trying to get the sail shape cleaned up. My new sail should help a lot!
Mike Cunningham
Freedom 30 (Mull) Hull #3
Build date...June, 1986 . Freedom Yachts USA, sloop, shoal keel
Gun Mount and pole retrofitted (purchased from a Hoyt Freedom 32)
Yanmar 2gm20F , 1600 hrs fixed two blade prop
e-rud and ocean racing equipment

SunnyIsleMark
Posts: 60
Joined: Sun Oct 17, 2021 8:42 am

Re: Camber spar patent #4,503,796

Post by SunnyIsleMark »

I had never fully appreciated how much thought went into the design and how clever it was until I read the patent application.
Here’s another article to add to the collection…
Mark
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