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Keel trunk "flex" continued

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JoergK
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USA
140 Posts

Initially Posted - 06/21/2004 : 14:00:53

… more on the keel trunk problem …
I removed the side of the wooden box that covers the “boot” of the keel trunk and closely observed it while sailing. When the keel hits the side of the boot, the boot sways sideways, approx ¼ inch at the top. The boot itself looks ok, no “mushy” spots like I read in one of the other threads. I should add that Second Wind draws an appreciable amount of water which appears to enter somewhere in that general area.

I had her hauled yesterday. The main section of the trunk appeared to be fine, also the area where the four keel-bolts hold the castings/pin assembly. However, I could not inspect the most critical area – the inside of the boot itself because there was no time to remove the keel. My guess would be that somewhere at the base of the boot there are cracks. I cannot inspect these areas from the inside of the cabin because the cabin floor is in the way.
In an act of futility maybe, but I then epoxied shims to the side of the keel to minimize sideways movement. She is going back into the water today. I hope I can save a part of my season with weekly bailing and babying her while sailing, and resort to major repairs in the fall.
In anticipation of that I would be grateful if you shared your expertise /opinions : (a) to expose the entire base of the boot, how much of the cabin floor would have to be cut away, and how involved/expensive would this – and the subsequent fixing of keel trunk boot and cabin floor – likely be? (b) if I chose wing conversion, would the fitting and epoxiing of the wing keel at the same time fix any cracks problems in that area? I don’t know if the flange of the wing totally covers the void where the swing keel top normally retracts into the boot when the swing is lowered, and thus automatically seals any problem areas.

Joerg
2002C250 WK "BerLyn"

Edited by - on

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 06/21/2004 : 14:43:47

Borrow a fin keel trailer for a couple of days, put the boat on it. Build the wooden frame you see. Use the all thread method. Drop the keel and inspect the inside of the trunk housing. Repair as needed.

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JoergK
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USA
140 Posts

Response Posted - 06/21/2004 : 16:27:40

Frank, are you saying that I could possibly repair this from the outside??? This never occurred to me. If so, that would be a huge relief.

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Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 06/21/2004 : 16:46:27

We all wait for Leon or Dave to chime in on big maintenance issues, but yes I believe so. A seriously messed up trunk has been the impetus for a wing in the past and rumor has it the cost was the same as a repair. You sound like you should be able to repair from the bottom. The dropping and inspection will probably decide for you. I would go to a wing before I cut out my floor. Of course as Dave will tell you, after you go to a wing you can cut out your floor and replace it with a teak and holly flat floor! Ain't life complicated?

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Dave Laux
Captain

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318 Posts

Response Posted - 06/21/2004 : 19:15:53

Ok , I'll bite. Joerg you have a potentially very dangerous condition. The bolts that hold the keel to the boat were never intended to hold the keel when the boat heels by themselves. The engagement of the tongue on the keel into the trunk is what takes the load. Yours is cracked and beginning to leak. Some time in the future it will break off and you will have a 4 inch by 12 inch hole in the bottom of the boat. If you are particularly unlucky the keel fasteners will fail at the same time. Leaving the keel hanging on the winch pennant and a large hole in the bottom. If I remember correctly a Cat 25 was lost this way a couple of years ago on the Great Lakes. Make sure your insurance and affairs are in order. Actually I'm overdramatizing the situation but not by much and all bets are off if you took it out in big waves. One of the boats we looked at had experienced this when the keel pennant broke and the damage was considerable. I wouild make plans to fix it one way or the other. Dave

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Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 06/22/2004 : 00:43:19

I really hate to disagree with Dave, who is very well qualified to discuss these technical matters, but I'm inclined to believe that the four 3/8" swing keel bolts can handle the normal forces imposed by the keel, including sailing and motoring in breaking ocean waves up to deck level. That said, I did install backup hardware to take the forces on the keel bearings if any of the stock bolts were to fail. So far, so good.

I was originally under the impression that the heeling forces from the C-25 swing keel were intended to be transfered to the hull through head of the keel trunk (as is the case with many swing keel designs). However, when reconditioning my keel, I looked at the large clearances between the head of the keel and trunk, and discussed pivot pin bushing tolerances with someone at the Catalina Yachts factory. I came around to believing that the swing keel heeling forces in a C-25 can and should go through the pivot.

I think some of the confusion about how the heeling forces should be handled has to do the the unfortunate "high mileage" wear that has occurred in the cast iron of all the swing keels by now. Realizing how unhappy owners of C-25s would be to hear that they really needed to install close tolerance bushings to correct the wear, Catalina Yachts, boat repair yards, and resourceful individual C-25 owners came up with various jury rigs to deal with the wobbling and clunking keels without resorting to clamping a 3/4-ton, 8' long, hunk of cast iron on a vertical mill.

When I first got my 1979 C-25, the pivot was very loose, and the keel did rub inside the trunk, leaving deep scars in the fiberglass, and causing the head of the trunk to flex in ocean waves, as described by Joerg. As I mentioned in [url="http://www.catalina25-250.org/forum/topic.asp?TOPIC_ID=6868"]the thread that preceded this one[/url] on the same topic, when I installed a bronze bushing in my worn swing keel, I had a machine shop bore it to 0.030" radial clearance on the new pivot pin. I also set up the axial clearance to maybe 1/16" when I had the new pivot bearings milled. As a result, the head of my swing keel can't touch the sides of the trunk, it only touches the down stop area.

During the production run of the C-25, Catalina Yachts increased the strength and stiffness of the entire swing keel trunk. They also have a sort of service bulletin dated 6-16-80 titled "CATALINA 25 TRADITIONAL INTERIOR KEEL TRUNK REINFORCEMENT INSTRUCTIONS" which describes a quick and dirty modification to brace the head of the swing keel trunk in the traditional interior boats. In my forward dinette locker, I added bracing to transfer any trunk rocking loads to the hull and liner. Even though my keel no longer rubs the trunk head, the braced trunk serves to stiffen the area of the hull where the keel bolts are attached. I also added as much of the later year trunk stiffening as was practical without removing and replacing the entire cabin sole -- it's not a task for the faint of heart.

This trunk head flexing in waves is a separate issue from the damage that can occur if the keel pendant breaks, allowing the head of the falling keel to strike the down stop portion of the trunk.

This thing has gotten too long for me to keep track of how it's organized any more, so I'm going to hit [Post].

-- Leon Sisson

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Dave Laux
Captain

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318 Posts

Response Posted - 06/22/2004 : 07:06:07

Hi Leon, I just did a calculation of the load on the bolts in the situation of the boat lying on its side. It approximates the breaking strenght of the bolts. I think that engagement with the trunk is necessary. I believe that the pins and bushing can get too loose and allow too much misalinement but if the boat is healed significantly its touching and bearing part of the load. What else would be flexing Joerg's trunk. Also look at the shape of the keel. Why bother with the piece to the front and above the pin at all if its not necessary. If Jeorg's boat is leaking around the base of the trunk the resin is fractured and probably some of the glass fiber is broken. I think this is cause for serious concern. Why bother to strenghten the trunk on your boat if it was doing nothing. This is no different than a normal centerboard boat with the board pivot on the outside of the hull and integrity of the trunk is absolutely essential. Dave

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JoergK
Navigator

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USA
140 Posts

Response Posted - 06/22/2004 : 10:23:02

Dave and Leon and Frank sharing their ideas is invaluable for someone less experienced, like I. Thank you. I am fascinated by your comments. It seems to me that if Dave is right, it may actually be disadvantageous to have a too tight fit of pin vs. bushing, and castings vs keel, which would prevent any contact between keel and trunk when heeling, and always assign the entire load to the bolts. To purposefully "loosen" the tolerances, on the other hand, seems counterproductive, too. So, this may boil down to the question if Dave's load /breaking strength calculations for the bolts are right (please, no disrespect here). To throw in another "but" - the observations regarding the shape of the keel head and trunk stiffening seem to have merit, too. Those, however, may have been added to the design as a "back stop" measure, anticipating some wear and tear on the keel hole over time which would negate the initial design concept. I guess, only Mr. Catalina could tell.

Permit me to return to my acute pains: has anyone ever fixed cracks in the base of the keel trunk boot from the outside? Wouildn't this too much restrict the width of the trunk, impeding the keel head to enter?

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svmoxie
Past Commodore

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USA
331 Posts

Response Posted - 06/22/2004 : 12:27:41

Joerg,

I don't think you could do a good repair from outside as it would be very difficult to grind back enough glass to get an appropriate bevel for the new glass.

You still need to drop the keel down enough to look at the pivot pin and bushing to see if they are out of round. It is my opinion that the keel trunk is not designed to carry the load by allowing the head of the keel to press against it. However it seems that is exactly what is happening in your case. That indicates to me that the bushing is out of round.

I also suspect that you will need to cut back part of the floor to gain adequate access to the entire keel trunk so that a proper repair can be made.

Converting to the wing retrofit does on fact seal that entire area if properly done. Considerig the cost of having a new bushing set in the keel it might well be cheaper to convert to the wing.

Tech Tip Links
http://www.catalina25-250.org/tech/tech25/dragn2.html
http://www.catalina25-250.org/tech/tech25/wingcon1.html

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ronrryan
Admiral

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USA
561 Posts

Response Posted - 06/22/2004 : 12:33:33

Joerg, it seems to me there are two issues in play. Your first post says there does not seem to be any "mushy" part to the trunk that you can see or feel, even though it flexes under load. Your second post says she "draws" water in the general area. By "draws" I assume you mean leaks, or admits, or weeps water but not at a rate that requires you to do more than sponge or bail on a weekly basis. This water coming in is NOT visible at the trunk, or anywhere you can visibly inspect. IF this is the case, first I would make every effort to isolate the point of leakage to be absolutely sure it is related specifically to the keel trunk, as there are some other places water might be entering ( see archives). As to rerpairing of exterior cracks, I believe you said you think there are cracks, but do not mention if you can actually SEE and inspect them. Cracks are pretty simple to fix: cracks caused by structural failure are generally not fixable with cosmetic remedies, as you have already surmised. As to keel trunk strength etc, this has already been addressed by others more competent than myself. Good luck and God bless, ron srsk Orion SW FL

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ronrryan
Admiral

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USA
561 Posts

Response Posted - 06/22/2004 : 12:36:52

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Dave Laux
Captain

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318 Posts

Response Posted - 06/22/2004 : 17:51:59

Joerg, If the trunk is cracked you will have to fix it from the outside by grinding down at the cracked area and rebuilding the ground out area with glass and resin maintaining original profile. Then you will have to grind out the inside until you almost reach the material you put in from the outside and then build back to original thickness or more. I think that the trunk and the bolts are necessary to support the keel in a healed position. Either by itself would not be up to the job. In your case you probably have some wear in the pin bushing area and if you have damage to the trunk some weakness there. Remember this is a low tech glass structure and flexible is the name of the game. In other words I would not be upset by minor movement of the trunk if there is no leaking accompanying it. Dave

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Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 06/25/2004 : 21:52:58

Dave and others, thanks for your thoughtful input.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">I just did a calculation of the load on the bolts in the situation of the boat lying on its side. It approximates the breaking strenght of the bolts.<hr height="1" noshade id="quote"></blockquote id="quote">I'd be curious to learn more about those calulations, and the assumptions about C-25 swing keel geometry they are based on.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">I believe that the pins and bushing can get too loose and allow too much misalinement but if the boat is healed significantly its touching and bearing part of the load. What else would be flexing Joerg's trunk?<hr height="1" noshade id="quote"></blockquote id="quote">I agree that's what's probably flexing Joerg's swing keel trunk -- that's what was going on with mine when I first got it.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Also look at the shape of the keel. Why bother with the piece to the front and above the pin at all if its not necessary?<hr height="1" noshade id="quote"></blockquote id="quote">Because the designer knew full well that the pivot would eventually develop enough slop to allow/require the head of the trunk to support the head of the keel.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">If Jeorg's boat is leaking around the base of the trunk the resin is fractured and probably some of the glass fiber is broken. I think this is cause for serious concern.<hr height="1" noshade id="quote"></blockquote id="quote">I quite agree, and I urge Jeorg to determine exactly where the water is getting in, and if his keel trunk is damaged.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Why bother to strenghten the trunk on your boat if it was doing nothing?<hr height="1" noshade id="quote"></blockquote id="quote">I'm assuming you mean literally, the particular C-25 I own. When I first got it, the head of the keel was bearing against the walls of the head of the trunk. This was consistant with the way my previous two boats worked. (A Lightning and a Venture 22.)

But more importantly, as I was grinding off a botched barrier coat from the previous owner and preparing to do blister repairs, I began to discover delaminating repairs and other strainge stuff below the waterline. Since I was going to be doing a lot of grinding and filling anyway, I got to poking around with the grinder where ever I saw anything suspicious. And there was plenty to suspect, much of it in and around the keel trunk.

More specifically, the longitudinal edges where the trunk meets the hull were sharp edged, not a radius consistant with proper fiberglass production mold design. As I dug into the square edge, I quickly exposed a long narrow air pocket. Hmm. I followed that air gap with the grinder about the entire length of the keel trunk! I then flooded the bilge with a garden hose. There was a curtain of water leaking out along that entire seam. And let me restate here that I hadn't ground through anything that impressed me as structural layup. That's when I began to look into reinforcing my keel trunk.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">... the observations regarding the shape of the keel head and trunk stiffening seem to have merit, too. Those, however, may have been added to the design as a "back stop" measure, anticipating some wear and tear on the keel hole over time which would negate the initial design concept. I guess, only Mr. Catalina could tell.<hr height="1" noshade id="quote"></blockquote id="quote"> Just so.

Around Sept. 1999, I spoke with David Graas and/or Gerry Douglas at Catalina Yachts about some of the technical details of C-25 swing keels and related production methods. They confirmed that what I was seeing was odd indeed. We discussed the strengths and potential weaknesses of the design.

To sumarize:
<ul><li>The cables can fail if neglected.</li>
<li>The winches don't last in saltwater.</li>
<li>If a cable failure allows the keel to swing full range without restraint, it can do a lot of damage.</li>
<li>The later year C-25 swing keel trunks were built thicker and stiffer than the early years.</li>
<li>The pivot area has not been a notable source of problems, no matter how under-engineered it looks to us.</li>
<li>The pivot pin radial clearances should be in the 0.020" to 0.030" range.</li>
<li>The proper way to correct a loose pivot is by installing a bushing in the keel. And no, it's not easy and/or inexpensive to do so.</li></ul>
So, I ground back a frightening amount of porous roving layup along that one side of the keel trunk, esentially cutting one side of the trunk free from the hull. I tapered several inches back into good glass, and laid in many, many layers of cloth and epoxy to build it back out to what I thought it should have been in the first place. After doing that side, I repeated the whole process, garden hose, waterfall and all, on the other side. At least whoever screwed up was consistant! I was aided and encouraged by the marked up production layup schedule generously FAXed to me from Catalina Yachts.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">This is no different than a normal centerboard boat with the board pivot on the outside of the hull and integrity of the trunk is absolutely essential.<hr height="1" noshade id="quote"></blockquote id="quote">I agree that the water-tight integrity of the trunk is essential. I believe that the strength of the trunk plays an important role in stiffening the broad flat run of the hull, and in distributing the loads from the keel pivot bolts, as well as the mast compression post. I don't believe that the walls of the trunk are needed to guide or restrain a C-25 swing keel with proper pivot clearances.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">If the trunk is cracked you will have to fix it from the outside by grinding down at the cracked area and rebuilding the ground out area with glass and resin maintaining original profile. Then you will have to grind out the inside until you almost reach the material you put in from the outside and then build back to original thickness or more.<hr height="1" noshade id="quote"></blockquote id="quote">Yes, that is how I would proceed, although I don't feel the need to add fiberglass from the inside, especially in those areas not readily accessable from the bilges. I did do some minor surgery on the liner at the ends of the trunk to gain access for adding reinforcements and other modifications. The factory installed reinforcements were of course added from inside the the hull, as the mold was not modified.

Respectfully,

-- Leon Sisson

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Dave Laux
Captain

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318 Posts

Response Posted - 06/26/2004 : 09:47:23

Leon, I just did a quick calc using bending moments generated by 1500 lbs held out with a CG about 2.5 ft from the pivot. Thats 3750 foot lbs. From the picture above I decided that the bolts were about 4 inches apart. Thats 11,250 lbs on each pair of bolts plus shear forces. 3/8 SS bolts (3/16 squared X pi x 40,000 lbs yeild) are about 4400 lbs apiece. Also we are talking about a low tech GRP stucture that is quite flexible and a steel casting that is quite ridgid. I believe that even if there was no clearace in the bushings that the head of the keel would rest against the inside of the trunk for some of its support when the boat is heeled significantly because it would flex the support stucture enought to do that. Also as I guess you found out the lay up was not done to the highest standards to begin with. Dave

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Gloss
Master Marine Consultant

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USA
1916 Posts

Response Posted - 06/26/2004 : 13:27:22

I'm always impressed with the inventiveness and ingenuity of folks who find ways to work on their wing keels. Like I did with my Catalina 22 swing.
It makes putting a man on the moon seem easy.

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