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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

Swing Keel Lock down

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albert
Captain

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USA
262 Posts

Initially Posted - 12/18/2002 : 13:37:29

Any ideas on how we can add a lock down option to our swing keels? The lock down should be "disposable" in that it should breakaway if we run aground then be easily replacable from inside the cabin.

Is this necessary? 20' to 22' swing keelers have them. I would feel safer in rough weather knowing that my keel isn't going to be swinging around unexpectedly. Maybe our 1500lb keel moves less than the 500lb keel on the 20 to 22 footers.

Albert Iturrey
al@comhertz.com
Abacus': http://www.comhertz.com/abacus

Edited by - albert on 12/18/2002 13:42:25

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Steve Milby
Past Commodore

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USA
5895 Posts

Response Posted - 12/18/2002 : 14:30:03

Albert,

I was not privy to Catalina's thinking, but, because the C-22 was designed and built before the C-25, and the C-22 has a lock-down device, I have always believed that Catalina probably considered adding a lock-down device to a C-25 and intentionally rejected it. They probably rejected it for two reasons. (1) The structure of the boat would have to be enormously reinforced to support the keel when the boat is inverted, and they probably thought it would be unnecessary and impracticable. It's one thing to provide inverted structural support for a 500 pound C-22 keel. It's quite another to provide inverted structural support for a 1500 pound C-25 keel. (2) The keel would not fall into the bottom of the boat unless the boat is in big, steep seas that are capable of rolling the boat over. The boat isn't designed to be used in the kind of conditions that could roll the boat over, and owners should not put the boat in that environment. In other words, if the boat is used as it is intended to be used, a lock-down device should be unnecessary.

Steve Milby "Captiva Wind" C-25 T/FK #2554

Edited by - on

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 12/18/2002 : 22:43:19

"Any ideas on how we can add a lock down option to our swing keels? The lock down should be "disposable" in that it should breakaway if we run aground then be easily replacable from inside the cabin." - Albert

If it were "disposable" or broke away when running aground, it would probably do the same if the boat inverted and the weight of the keel was put upon it.

My Venture 25 swing keel(625lbs) had a lock down bolt, but I never used it. The reason was, the hole in the trunk the lock bolt went into to secure the keel was no longer a hole, but a 3 inch arc(like a smile <img src=icon_smile.gif border=0 align=middle>) that was ripped into the fiberglass trunk. Apparently the PO had locked the keel and then ran aground, which caused the lockbolt to rip through the trunk. I never repaired it because if I ran aground, I wanted the keel to give. Additionally, as Steve said in his post, I never took that boat out in conditions that it was not designed for.

Don Lucier, 'North Star'
C25 SR/FK
On the hard, 200ft from Lake Erie

Edited by - dlucier on 12/18/2002 22:45:11

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mroettersr
Navigator

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USA
148 Posts

Response Posted - 12/18/2002 : 23:32:35

I had a Venture 225, 17 and a Catalina 22. The Ventures had oblong holes where the keel lock down bolt went through the keel trunk. There was a lot of debate on the Catalina 22 site about sailing with the keel locked down or leaving the keel unlocked. Mine (1976 model which I owned from 1998 - 2001) had a nice smile worked into the keel from years of movement with the keel locked down. I locked the keel down when I used the boat to reduce the keel klunk and I'm not sure the lock down mechanism would have held if the boat turned turtle. I noticed the Venture 17 and the Catalina 22 seemed to dump air when heeled beyond a certain point which gave me some comfort when sailing in heavy air. The best advice has been offered to respect the boat's limitations. I didn't lock the Ventures due to the shallow water I sailed in in extreme Western Lake Erie (Maumee Bay).

Mike Roetter
'83 C25 #3568 SK/SR
Marblehead on Lake Erie

Edited by - on

Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 12/19/2002 : 00:35:20

Albert,

I agree with what Steve Milby said.

You'll note that the C-25 swing keel, fully extended, hangs down at maybe a 45 degree angle.

Using some highly questionable quick & dirty estimates, let's assume:

The center of gravity of the extended swing keel is maybe 4 feet aft of the pivot.

The portion of the keel mass forward of the pivot is proportionately so small that we can ignore it.

The radius of the keel head is maybe 18 inches. (I think it's actually closer to 17".)

Assuming an inverted C-25 with keel fully extended, for simplicity, let's say there's 1,500 lbs. 4' aft the pivot trying to force the keel toward the trunk. Multiply that by the difference in radius at the most practical location for a lock pin. The result looks to me like maybe 4,000 lbs shear force at the lock pin. (And at the pivot support bolts?) But that doesn't take into consideration the peak dynamic forces that would be produced by steep waves passing under the inverted boat. I seem to recall that the industry standard safety factor for keel bolts is somewhere around 10:1. So, how much modification would be required to impliment a 40,000 lb. shear lock pin?<img src=icon_smile_big.gif border=0 align=middle>

I know of one swing keel design slightly lighter than the C-25 that does have a lock pin, the Parker-Dawson 26. However, the PD26 swing keel dangles straight down, not back at an angle, and that keel weighs only 1,200 lbs. Their lock pin is stainless steel, maybe 3/4" minimum diameter, threaded into a metal insert built into the top of the swing keel trunk and hanger assembly.

I've had paranoid daydreams of fabricating such a keel lock down system for my C-25. However, I then got a grip on reality, and decided that it would be far more prudent to avoid circumstances that might cause the keel to crash up into the trunk in the first place. The Catalina 25 was never designed to be used as a blue water cruiser. I doubt the swing keel is the only Achilles' heel that would be revealed by subjecting one of these boats to offshore survival conditions.

-- Leon Sisson

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 12/19/2002 : 09:44:56

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>
The Catalina 25 was never designed to be used as a blue water cruiser. I doubt the swing keel is the only Achilles' heel that would be revealed by subjecting one of these boats to offshore survival conditions.
<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>
Amen, Leon... I was thinking about the same calculation, which essentially quantifies the leverage as well as the mass working against a locking device that's very close to the pivot point. The leverage is what causes the "smiley" bolt holes mentioned on other boats.

Another difference with the C-25 is that if it runs aground with the keel locked, the momentum of a 5000-6000 lb. boat will put a lot more stress on that lock--also magnified by the leverage--than a C-22 or Venture would. That's why fixed keels on all but the really fragile racers are relatively long (horizontally) at the hull joint. You don't want a grounding to rip the keel (and part of the bottom) off the boat!

Dave Bristle - 1985 C-25 #5032 SR-FK-Dinette-Honda "Passage" in SW CT

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