Monday, March 10, 2014

Centerboard Solutions

I know our followers have been anticipating a follow up on our centerboard saga.  Some more than others – you know who you are.

To recap, the 1/4” stainless steel cable that we use to raise and lower the centerboard broke back in the Bahamas in 2011.  We have been sailing since then with the board pinned in the “up” position. Because there are no drawings of the cable attachment design, we have been limited to a trial and error approach, learning a bit more about the design (and repair) when we haul and launch Saralane annually.  Now finally (at least since we launched in Antigua last fall) we are up and running – and what a difference the board in the “down” position makes!  Weighing in at about 800 pounds, it really makes a stability difference when lowered – not to mention it helps our upwind performance.  The depth of Saralane is 8’6” with the board down, and 4’9” with it up – when we are at rest. 
The raise/lower design is poor at best, due to the fact that the cable attaches very close to the pivot point.  The result is a huge amount of force needed to tension the cable and lift the 800 pound board.  From the attachment point on the centerboard, the cable runs vertically up through the cabin in a stainless steel conduit, through the cabin top, over a sheave, and then horizontally aft to a winch.  A 4:1 block and tackle is also incorporated to increase the mechanical advantage.

Stainless Steel Pipe with cable running inside up to deck
Cable exits pipe, runs over the sheave and along the deck


 
Cable turning aft to cockpit
 
Cable connecting to 4:1 purchase


 
Finally led to the winch (black line).

When the board is down there is little or no tension in the system as it is essentially hanging on the pivot pin.  However, when the board is up (which is most of the  time) – everything is banjo tight.  Most worrisome is the huge compression that is put on the cabin structure where the cable turns from vertical to horizontal, behind the mast and along the deck.  Other C&C 40s with this centerboard arrangement have elaborate owner inspired bracing systems for the cabintop compression.  We too are considering ways to oppose this compression, without much luck, but have settled on a tropical, warm water solution.

When we had the board pinned up all was well and we could release the tension on the cable and let the pin do the work - but the pin was very difficult to insert/remove.   Now  we use a simple short length of spectra line with a loop spliced at each end. 
Made up Spectra strap
 
Spectra is fantastically strong (like steel) and easy to work with.  When we were preparing to launch last November in Antigua, I drilled and tapped the keel (port and starboard) and inserted 3/8” machine screws with bolt heads on each side so that the heads were well exposed.  I made up the spectra strap to just the right length so one loop hooked over one bolt, then passed under the keel, and then the second loop hooked on the oppsite side – simple, soft, and easy to do. 
Strap looped over bolt heads
When we're settled in an anchorage after sailing, the board is raised with the cable and one of us dives under with the spectra and hooks it on. 
Spectra "sling " in place
Then we release the cable and the centerboard drops a bit and rests in the spectra “sling”.  We reverse the proccess when we head out.  If we have a downwind sail ahead of us we don’t bother as the board doesn’t contribute anything on that point of sail.
 
We have one more bit of centerboard maintenance to do.  While in Guadeloupe last fall, we were in a rather rolly anchorage (Pigeon Island) so we put the board down to dampen the roll. It did help, however, during the night the wind died and we spun around, causing the anchor chain to rub against the front of the centerboard and wear a chunk out of it.  Nothing serious, but one more thing to tend to.  The board is solid fiberglass up there, so I’m not worried about water intrusion.  However, it will need a good drying before patching, so when we haul out this summer, we will just let it dry for a few months, then patch it before we launch in the fall.


The board down with a chunk out of it.
Close up of the "bite!"
So at the end of the day all of the centerboard hype boils down to a 12 inch piece of rope - we like to keep things simple.  All of this effort would be moot if we were able to enjoy the mythical “downwind sailing” we have heard about, but now we are ready for anything.

14 comments:

miles said...

It was worth the wait. Seriously. And yes the best part is the simplicity. One question. Looks like where the spectra is located that it could potentially slip off the board. Is there just so much tension on it that its an impossibility of that happening. Or maybe the spectra is also too short for that to happen also. Either way, nicely presented. I would be willing to be the full time spectra putter onner...

Skip said...

Yes, it is close to the end, but can't slip off. You may want to reconsider your offer when we get into cold water some day!

clay said...

That was my thought, how to connect in cold dark Maine water.Once I was in Maine sailing my trap skiff and got the centerboard tangled with a lobster pot I thought no big deal, jump over the side and untangle, easier said than done. However a good and inexpensive fix for where you are now.

danbarnardjr said...

I was seriously impressed with Maddie's grasp of the technical aspects involved here, but became suspicious as the blog continued. The centerboard story is interesting and nearly four years in the making. Thanks for sharing..

Madeline said...

Now now Dan.... a little credit please! I actually do understand the technical aspects here. OK so I would've called the '4:1 purchase' a 'thingy' but nevertheless, I do get it! I'm happy just to be one of the spectra sling operators underwater here, but Miles, if you want to give it a try, come on down!

Kim said...

Thank you, Madeline.

danbarnardjr said...

Well, I admit the "posted by Skip" was another clue. But I certainly don't dismiss or diminish your technical comprehension. It was only the "Spectra is fantastically strong (like steel) and easy to work with. When we were preparing to launch last November in Antigua, I drilled and tapped the keel (port and starboard) and inserted 3/8” machine screws with bolt heads on each side so that the heads were well exposed. I made up the spectra strap to just the right length so one loop hooked over one bolt, then passed under the keel, and then the second loop hooked on the opposite side – simple, soft, and easy to do" that I became suspicious.
Kim, I love Maddie. She knows it; you should, too.

Madeline said...

Aha.... your suspicions are well founded Dan. And that 'posted by Skip' bit gave me away again. Drats. Since my Mac crashed I'm going to encourage more 'posted by Skip' blogs, so stand by!



Dana Greyson said...

Thanks!

It was even better than we expected!

:)

Wayne

clay said...

I can't tell from the pictures,but would it be possible to relocate the lifting gear to the rear of the centerboard. That way when you come to Maine you wouldn't have to go overboard?

Madeline said...

Clay, We've considered relocating the cable. but it would wind up in the middle of the cabin and require a routing system that would need some sort of gland to keep the water out - all told, it would probably cost ore than the boat is worth!

clay said...

That's too bad. I guess you will have to buy a heavy duty wet suit, and underwater headlamp when you visit Maine.

Madeline said...

Actually.... we thought we'd just invite you to sail with us there, since y'know... you probably already HAVE all that equipment and are good at using it!

Clay said...

Sounds like a plan.