Internal keel reinforcement

[fishboat]

There was a post a while back about a sailboat that had an internal keel that wiggled on a Gladiator 24. The Cal 25 was also mentioned as having a similar problem(?). I have a Cal 25 and would like to do some reinforcment of the keel to prevent the "wiggle". The keel on this boat has 1700# of internal lead ballast. It has minimal reinforcement (floors?) and due to this the lead at the base of the keel tends to move athwartships to some extent, basically a pendulum-type motion with the flexing occurring at the turn of the hull into the keel. I've talked to guys that have been racing the Cal 25 (Mk-1's) in one-design fleets for 25-30 years & they say all the Cal 25's have this keel wobble characteristic. They also say they've never seen the wobble to be a problem & have never seen a failure due to this wobble. In spite of this opinion I'd still like to stiffen things up.

If you guys could give me a reality check on how I plan to do this it would be greatly appreciated. I've attached two jpg files. One is a picture of the cabin sole & into the bilge/keel. You can see one of the original reinforcements with a port-side tabbing failure. The reinforcement is very light weight. They're basically 1/2 inch pieces of wood with a single tab to the hull/keel. They are not tabbed into the turn of the hull/keel nor are they attached to the cabin sole. The second jpg is a crude drawing of what I plan to do to reinforce the keel.

I plan to epoxy three 1 inch thick sealed plywood floors into the keel (orange section in picture) and tab this into the interior keel surface. The cabin sole/keel interior is about 5.5 feet long, 20 inches deep, & 11 inches wide at the widest point. I plan on doing this without removing the cabin sole. Not removing the sole gives me limited ability to tab the floors into the hull from the top (no room) so the tabbing will just barely reach the turn of the keel/hull. I'll use epoxy for sealing the wood & tabbing into the hull.

Questions:

>Does this make sense?

>Will it limit the wobble?

>Will I introduce stress to anywhere I shouldn't?

>Should I tab the floors into the underside of the cabin sole (1/2 plywood)? The sole is tabbed to the hull around it's complete perimeter. The tabbing is very solid & the plywood is original, but still in good shape.

>Is there a better way?

thanks for you help

[fishboat]

One more question...do you think it would make a difference if the repair was done while the boat was in the water or blocked up with stands on land?

[jehardiman]

Tread very carefully here! This is a place where you could make a problem by causing point loading of the structure. Many people equate deformation with high loads, but this is not the case. Like a fishing rod, many structures are designed to bend, not break. In bending, they spread out the load along the length of the structure which lowers the overall load on any one portion of the structure. In this case, deformation energy in an unstiffened composite structure flows in the outer skins. Adding a stiffener to prevent deformation prevents energy dissipation and increases the load at the rigid point. An analogy is slipping a short heavy steel tube over a fishing rod, the rod brakes at the intersection of the tube and the glass.

Because yours and other class hulls have survived so long without problems, I think this "wiggling" is the effect of a conscious design decision. Without doing a complete structural and layup analysis to ensure proper load pathing, adding stiffening seems like a bad idea in my opinion.

[asathor]

Jehardiman makes an excellent point but you can still use elements of your idea to good effect. Since the hull apparently is strong enough what you really need is damping. Soundcoat makes a constrained layer damping material called Dyad which is expensive but you won't need much so that doesn't matter. You need a layer of this material or something similar (low viscosity - high restoration force/memory) between the keel sides and the suggested new barriers - the vibration is at a very low frequence (probably like the Cal 30 I was just on) so your stiffeners will need a greater surface than a sheet of plywood - since no-one will be looking try a 2x12 treated lumber for now. Fit it with room for the damping material (2-3 layers) pretty much uncompressed and then epoxy it in place on all the layers contact surfaces - do not seal it off as you want it to be able to work. If you want to experiement before committing try some sheet vinyl (clear) like what they have for table/shelf cloth at your hardware store (they don't give specs but if it has adequate memory - that is pull it as hard as you can and see if it resumes the original for it might work just fine). You can still glue it in - if you want to get it out cut the wood down the middle and twist it off.

You should look at doing the same between hull and floor since that location could just as easily be the source of the noise. Here you could fit a vinyl pocket and then fill it with Bondo or something but it would be hard to reverse.

Ask for the Dyad brochure from soundcoat or read up on constrained layer damping elsewhere. Note that most of those types of damping materials are for much higher frequences.

If this fails or doesn't appeal to you, try to borrow a millitary sub from the Navy to see how they did it, they use all the tricks in the book including this one.

[PAR]

Judging by the drawings you've provided, I'd say you need to center the ballast, but in a fashion not locking it down to the hull. Basically it's flopping around a bit while under way and I'd be thinking about some well placed blobs of 3M 5200 around the sides and front and back of the casting. Not enough to seal anything, just to keep it from rocking around in there. The polyurethane will be flexible enough to permit some movement, but keep it from banging back and forth. A single cartridge of 5200 would do the trick. I'd squirt a large blob forward, aft and at a few spots down each side. You're not trying to pull a bead, rather fill the void in a localized area at spots around the casting. Loading wouldn't be transferred (not much anyway) and if you felt this was an issue you could slip a piece of wax paper between the hull and casting before you squeeze in a blob of goo. This would be left for a week or so to allow the cure to complete and then could be removed. The result would be complete isolation and no solid attachment to the hull.

It's likely the hull is built strong enough to tolerate the sloppiness of the casting to hull fit. I don't think this is a function of the design or intent by the designer. It must be unnerving to have a clunk or thump at every trim shift or maneuver.

[fishboat]

Thanks to all for your thoughts so far.

jehardiman,
I understand what you're saying & this is why I'm looking for comments here...there's a lot of talent on this board. The fishing rod analogy is also familiar. I've stressed a rod & made the mistake of touching a hard edge while a rod is under stress....SNAP! I'm looking for any & all info I can find on a reinforcement like this as I realize I could focus the loading & create a problem where previous one didn't exist. If it's of any help, Bill Lapworth desing the boat & they(Jensen Marine) made around 2000 MK-1 25's over a ten year period. Just in sheer numbers you'd guess that if the flexing was an issue it would be well known at this point(at least on the internet). I've done LOTS of searching & all I come up with is that the flexing is known to exist...but no one cites a failure due to it.

asathor,
regarding your "...the vibration is at a very low frequency "...I don't notice any vibration or sound at low or high frequency. The flexing happens due to 1700 pounds being at the base of a basically hollow & pretty much unsupported fin keel..other than the laminate of the hull & fin/keel shell. It doesn't wobble or flex (in some sort of resonance) while underway. I notice the wobble primarily as I rapidly shift my weight from port to starboard as I stand over the keel. I'm sure it does flex downward to some extent while on a tack, but you'd never notice it as switch tacks (p-s).

PAR,
The ballast itself is secure and doesn't move within the shell of the fin-keel. There isn't any space between the lead ballast & the keel shell itself, it's a tight fit & looks to be in good condition. What flexes is the entire fin-keel. While the glass laminate at the turn-of-the-hull-into-the-keel(not sure what to call this area) moves very little, 20-30 inches below this point is 1700# of lead that can move port to starboard by an inch or more. Lapworth was a very prolific designer. Building with fiberglass wasn't as much of a mystery back in the 60's-70's as many folks believe. I almost have to think(?) that Lapworth knew the keel would flex..if that's the case then thee isn't much to worry about. I did have the boat surveyed and the hull/keel is completely sound and dry as a bone. I've attached another picture to help you visualize what I'm talking about. More thoughts are more than welcome.

[PAR]

Have you tried the "Old Cal's" site http://pages.sssnet.com/go2erie/calhome.htm?

I think Bill Lapworth is retired and living in Virginia somewhere, have you tried him?

I have to admit, I was miss led by the drawing, showing an air gap or space around the casting, of course thinking that was what was moving. You need to determine what and where the movement is before you attempt a repair.

My first efforts would be to empty the boat of everything that's not bolted down snuggly (I mean everything, anchors, spare line, rode, etc.) and have someone else rock her while I was below looking and using a probe (wooden dowel held to the ear and to the surface of areas I think the noise may be coming from) The dowel in the ear trick is a very good way to track internal noises quickly (it get progressively louder as you near the source) ask any auto mechanic. It works better then the screw driver some folks use, trust me. I'd perform the same routine with the mast and it's rigging removed as well, in fact, I'd do this first with the rig completely stripped off the boat and ashore. This would insure it's in the boat and not the mast or compression post pumping sideways in the step or something.

I took a very quick look at the site listed above and there is a message board with many references to your first generation Cal 25. I'd think this problem would have been questioned there. There may not be a reasonable answer, but you'd have the "pick of the litter" in the repair attempts and the successes to take a look at, before you start spending money and effort on an issue you don't completely understand yet.

I use to have a 35' Choy Lee (Arthur Robb design) that made a noise in the keel area, similar to what you describe. It turned out to be the casting deforming the fin and flopping from side to side. It didn't do it all the time and had me baffled for a while, until I remembered that I'd run her hard aground all standing a few weeks earlier. The iron in this case, seemed to be tight in the keel, really wasn't. This was a CCA style hull (built down rather than the fin of yours) and the castings were bedded in concrete which had lost contact with the keel sides. Under load (heeling) the 'glass would deform because the casting was moving around in the keel, which would clunk every so often. The cure was hot tar poured around the edges of the concrete. I was faced with removing the several ballast pieces or this fix, which worked fine as long as I had the boat and I sailed her hard most of the time, because she was so much fun on her ear.

Good Luck,

[fishboat]

PAR,
Thanks again for your thoughts.

I have checked everything on the calhome site as well as the cal25.com site. The wobble is mentioned, but no one on these sites has actually done the reinforcement. I do know there are people that have reinforced the keel (Long Beach, CA C25 Fleet), but I haven't been able to get in contact with any of them. I also joined the Cal email list on sailnet.com. The group is full of info...but not on this topic.

Regarding your suggestion: I guess I'm having hard time explaining what what we're looking at or I'm considering. There is no noise or vibration coming from the flexing and I don't think there really is any "repair" to speak of as I don't think there is anything really 'broken'(other than the loose tab that exists already..you see it in the picture). The boat sails beautifully. The standing rigging & mast support (one main laminated beam over the main bulkhead that's tabbed into the hull continuously, no compression post) is dry & in good shape. If you were on the boat & trimmed or tacked you wouldn't notice anything amiss. It's a responsive & fun little boat. As with any older boat one wants(needs) to keep it maintained and fix things before they get worse. In this "what can I update" mode I noticed what every other C25 owned has noticed (well, not all...as the PO had this boat for 13 years & was never aware of the keel wobble) that the keel flexes alittle. Since I haven't experienced a flexing like this before I tend to think..."I can stiffen this up a bit...it doesn't look too hard to do...". The question, as was brought up earlier, is whether I should stiffen it up & whether (using the specific plan I had in mind) I would be creating a problem where (maybe) none existed before. The owners I have talked to (a couple guys in the Detroit One-Design Fleet & a couple on the sailnet list) said they were aware of the flexing and don't see it as a problem. Their suggestion was "go sailing". Maybe that is the answer and I just need to accept it's the nature of the beast.

I wasn't aware Bill Lapworth was still around. Seems like contacting him is a reasonable move. From a quick search it looks like he's in the Tidewater, VA area.

As always...any additional thoughts are more than welcome.

[PAR]

I'll bet the most competitive in the racing fleet(s) have addressed this issue, thinking (and rightly so) that it would have to improve things, even just a small amount. As you describe it, a wobble, this would drive me nuts, especially if I was near the front of the fleet. This is a solid chopper layup with a casting dropped in the bottom of the fin as ballast. This shouldn't wobble and if it was the fin, you have to have stress cracks or other signs of movement.

Does this boat have a liner? I've seen mystery noises and wobbles when things get between the liner and hull in a void and roll around. This is a feeling not a noise? Have you had someone rock the boat while you have your head in the hole at the top of the fin? Try placing your hand on the side of the fin as the boat rolls, does it move? Buckle? Does the ballast casting move when you feel this wobble? Personally, I'd want to be as close to or better yet in contact with (my hand or bare foot) the area that is wobbling, so I could get a better understanding what's going on.

[fishboat]

Par,
Thanks for sticking with me here.

The Long Beach, CA one-design fleet has done some reinforcement...I hear there is some pretty tough competition out there. The Detroit fleet hasn't done any keel reinforcement. I think one of the Detroit fleet took 1st in a C25 nationals race recently in Annapolis. The boat is very well rigged & taken care of..wobbly keel and all.

When I say "wobble" it might imply that the keel is continually moving /flexing/oscillating while underway. This isn't the case. I'm sure it flexes to one side slightly & sits there until I tack to the other side. The only time it really wobbles is when I make it do that by quickly transferring my weight back & forth to each side of the keel. The flex is most easily seen at the base of the keel down by the ballast. Up at the turn of the hull into the keel there is very little movement. (think of how a pendulum moves at the bob-end (ballast in this case) versus the the opposite end where the pendulum is attached.

The hull/keel laminate is all hand laid. There was no chopper gun was used in the layup. There are no stress cracks or any sign that anything is amiss. I've gove over it with a very bright light & mirror or magnifying glass. The surveyor has gone over it too & everything seems to be fine.

>"Does this boat have a liner?" No. The cabin sole is tabbed directly to the hull & the inside of the keel is completely accessible. All external hardward through the deck/hull is completely accessible from inside the cabin (a good thing).

>"This is a feeling not a noise?" No feeling, no noise. The only evidence of the flexing is that I see it when I transfer my weight quickly over the keel & to each side of the keel. Naturally when I'm shifting my weight I can feel the flexing a little as there is 1700 pounds moving port to starboard to port to starboard.....as long as I keep shifting my weight.

>"Have you had someone rock the boat while you have your head in the hole at the top of the fin?" Don't have to. I can do both...rock the boat & see the keel/ballast just by standing/straddling the keel.

>"does it move? Buckle?" It does flex, I can see it, but no buckling or anything dramatic...just a gentle flexing port to starboard as long as I keep shifting my weight.

>"Does the ballast casting move when you feel this wobble?" No. The ballast completely fills the base of the keel cavity with no space between the ballast casting & the glass. Actually the ballast edges look to be tabbed into the inside of the keel.

>"Personally, I'd want to be as close to or better yet in contact with (my hand or bare foot) the area that is wobbling, so I could get a better understanding what's going on." I can see it move and I can see the mechanics of how it's allowed to move (1700# is 20-30 inches away from the point where the keel-shell that contains the 1700#, is attached...given the lack of internal reinforcement in the keel I can't see any reason why it wouldn't flex. My interest here is to add to the reinforcement & thereby limit the flexing...thinking that flexing glass has to fatigue at some point. Given that the boat is 35 years old I wonder when that fatigue will become an issue. Reinforcing it just extends the point where fatigue is an issue...perhaps extending that time very far into the future. As I've said I've talked with a number of Cal 25 owners and they are all aware of the flexing, but no one has seen any failures related to the flexing....and all these boats are 30-ish years old & all are raced regularly...in a couple cases for 25+ years. One guy in the Detroit fleet has been racing his 1968 Cal 25 since 1975. He's had a forestay, shroud, & backstay fail at some point or another over the years (i.e. he's stressing the boat with racing), but no problems with the keel.

Maybe I'm worrying about nothing, but to a new owner (me) the flexing just seems odd & that makes me want to "fix" it. :-)

[jehardiman]

fishboat;

I used to race on a Cal 25 in the SF Bay. SF Bay is propably one of the most extreme environments that these type of boats sail in, heavy winds with a short chop. We sailed with a 5 man crew (foredeck,pit/grinder,jib trimmer,helmsman, main trimmer) and full spinnaker gear. And in my experience, the real problem with these boats was keeping the rig above the spreaders in the boat when you pushed them hard (several failures I saw). The boat I was on (WhimisCal) and another (Cinnabar) usually were the top boats in the fleet and for most of the racing you could throw a beer can between the two. These were boats that were fully tricked out with lowstretch lines and sails. We never did anything to stiffen the keel. I feel that the rig tuning is more important to speed than the hull flex.

As for fatigue of composites, there really is none. The concept should be progressive damage once over a threshold stress. There is a threshold that below a certian stress, flexural response is totally plastic and fatigue life is effectively infinite. This is because resin/fiber or resin/core bond is not broken. As stress increases above this threshold, the highest stressed resin/fiber bond breaks. If you reduce stress at this pont and then return to the same maximum stress, no additional damage to the laminate will occur. As you continue to increase stress, more and more resin/fiber bonds break and eventualy the plys begin seperate and/or the fibers begin to break (or core crush, etc.). The extent of these failure can be determined by UT testing, when damage reaches a certian precentage the part is removed from service. Of course, impact and UV damage also cause damage, and layup material/design may lead to progressive failure (so called zipper failures where the failure of the highest loaded fiber overloads the next which fails and overlads the next...etc, etc,etc.)

[fishboat]

jehardiman,

Thanks again for your thoughts. I've seen & been on SF bay and your right, it can be a real wash-machine. Your experience is another camp heard from in the "leave it alone" column. The Long Beach fleet has done alot of reinforcing, but within one fleet/location that might be a psychological "me too" thing as much as anything. One or two people do it for whatever reason & then everyone does it in the hope that no one has an advantage....

Elastomers & composites...I have a reasonable background in polymer chemistry (coatings) although very little experience in elastomeric or composite (mechanical) behavior. The concepts you're discussing make sense (an Instron instrument comes to mind).

A couple nights ago I had a conversation with the owner of (now shutdown) Calgan Marine of Vancouver. Apparently they were under license to build Cal sailboats in Canada. They built 25's up there as well as 20's, 28's, 29's and also their own line of Crown sailboats....18's, 23's 28's & 34's. There's a Calgan 25 and a Crown 23, 28, & 34 on yachtworld.com right now. Anyhow, I asked him about the flexing keel & he said in his memory they had no flexing. He then described how they built the keel area (just 35-40 years back) & suggested how I might do the same. What he described was fairly similar to what I've been thinking about although the bulkhead-type structures inside the keel would be MUCH thicker (4-5 inches rather than 1.5-2) than what I had in mind. Naturally the added thickness would spread out the loading. He said if I really wanted to do it right I should cut the cabin sole out, leaving the current sole-hull tabbing alone (like cutting a new, very large, hatch), build the three bulkheads, and tie them together in a frame-grid structure...then tab all this into the hull. The loads would then be spread everywhere & there would be no issues.

All this being said, I think I'm coming down on the side of leaving it alone for the time being. At least I fully understand what to do if I go that route. Winter is coming and there plenty of other upgrades that will have an immediate payback...I'll focus on them. Thanks for the help.