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preventing keel drop catastrophe?

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Merrick
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USA
192 Posts

Initially Posted - 04/19/2011 : 19:07:37

On the standard layout the keel trunk is easily accessible by removing the wooden housing around it. I am wondering if it would strengthen the keel trunk if you epoxied several layers of fiberglass cloth to reinforce it? And would it add enough strengthen to make a difference if the keel dropped?
I've also wondered if a piece of wood maybe 2" thick was glued to the inside of the keel trunk, would it help by spreading the impact and also absorbing the some of the impact instead of having metal hit fiberglass.....
Guess I stay worried about the keel dropping scenario, now after reading the topic below, been thinking about how my winch is making noises lately.

1981 #2555 "Aero"
sk/sr
Coosaw Island, SC

Edited by - Merrick on 04/19/2011 19:32:14

Stinkpotter
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Djibouti
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Response Posted - 04/19/2011 : 20:29:16

Do you have to leave it up? (I know that leads to a debate...)

Edited by - on

Dave5041
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Response Posted - 04/19/2011 : 20:32:21

Check your winch , cable, attachment, and pivot every year and replace as necessary, that is all it takes. You could add a layer of high density rubber forward of the keel, but routine annual maintenance is all your keel really needs.

Edited by - on

Prospector
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Response Posted - 04/20/2011 : 05:49:37

Caveat #1 - I have a fin keel.
Caveat #2 - I work in engineering and tend to overthink things

I wonder why no one has developed some sort of a sacrificial "marshmallow" that would crumple, absorbing the energy of an accidental keel drop. In guide rail installations we install extruder end treatments that are designed to deform the guiderail, absorbing the energy of a hit, and preventing the guiderail from spearing the car. Seems to me a similar "brake" would be easy enough to build into a swing keel trunk, and would mean replacing a shock absorber rather than rebuilding the keel trunk.

Edited by - Prospector on 04/20/2011 06:02:43

britinusa
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Response Posted - 04/20/2011 : 05:53:05

that has always crossed my mind to Chris. On our 250 it's barely an issue a the 'keel' ('board', whatever) weighs a fraction of the C25 swing keel.

I had thought of stuffing some polystyrene at the front of the keel well. But I guess it would have to be more substantial for the C25.

paul

Edited by - on

DaveR
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Response Posted - 04/20/2011 : 06:04:52

An "absorber" would prevent the keel from being lowered completely and by it's very nature would take on water over time unless it was a automotive styled device. I don't think there's a good answer to prevention other than annual inspection. And even then, how can you tell if a bushing in your winch is ready to go?
Oh, and to answer your question Merric, IMHO I don't think extra fiberglass or wood would slow the keel down at all.

Edited by - DaveR on 04/20/2011 06:06:29

Prospector
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Response Posted - 04/20/2011 : 06:18:07

Dave, I respectfully disagree.

I think a plastic extruder head could absorb enough of the energy to preserve the keel trunk. We don't have to absorb ALL the energy, just enough to prevent irreversable damage. Here is the highway installation we use for guiderail...

The way that works is the metal guiderail is flattened into a ribbon if a car hits the guiderail end-on. A similar installation could be fit into the keel trunk if there is about 6" of free space. A sacrificial "brake" of plastic would be squeezed through the extruder. Deformation of the plastic would convert the energy of the falling keel into friction (heat) and extrusion energy. I am not talking about compressive energy like in a shock absorber, I am talking about a sacrificial extrusion.

How much space is in the keel trunk? How much space is there forward of the keel trunk that this could be fit into? A miniture extruder could take a lot of energy out of the drop and prevent catastrophic results.

Edited by - Prospector on 04/20/2011 06:38:32

Stinkpotter
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Djibouti
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Response Posted - 04/20/2011 : 06:28:49

Chris--could you shrink that image down a bunch? It makes the thread very difficult to read, and even puts the "reply" text box out of sight.

Regarding the energy involved, remember you have a 5' lever weighing 1500 lbs. and the contact point on a free-fall is very close to the pivot, with virtually all of the weight out on the lever. I suspect that would require a pretty robust cushion--perhaps more than there is space for in normal operation.

Edited by - on

Prospector
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Response Posted - 04/20/2011 : 06:47:14

Sorry Dave, I was hunting for a smaller version while you typed that.

Considering that teh design above handles the weight of a Suburban travelling at 90 mph, you could likely get close. The energy absorption isn't all in the deformation of the material, part of it is in the process involved in the deformation. This is a little different than the crumple zone we are used to thinking of.

In the pic above you can see where the end of the guiderail is flat and curled around the end of the extruder. A hit forces the extruder head to travel along the guiderail flattening out the channels into a flat cross-section and feeding it away from the car. This happens over about a 15 ft travel. For our application, turn this on its side. Put a 1" thick hunk of plastic in place of the steel guiderail. Put the extruder head at the back of the keel trunk and let teh keel feed the extrusion through the head (rather than the other way around). Teh energy of the drop would flatten the plastic, and create friction with the outfeed below the boat. You can play with plastic polymers until you get the right formula so that it will deform at the needed rate to absorb the energy of the fall.

I haven't done any math to figure out the needed energy absorption or anything, but this seems doable to me at a first flush.

Edited by - Prospector on 04/20/2011 07:01:49

Steve Milby
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Response Posted - 04/20/2011 : 06:57:28

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Prospector
 Dave, I respectfully disagree.

I think a plastic extruder head could absorb enough of the energy to preserve the keel trunk. We don't have to absorb ALL the energy, just enough to prevent irreversable damage. <hr height="1" noshade id="quote"></blockquote id="quote">
It's a really interesting idea, similar to the principle that Nascar is using on their shock absorbing retaining walls to protect drivers. It raises lots of questions, such as whether there is space for a sacrificial device, whether it can be installed so that it spreads the load enough to prevent damage, whether it can be removed and replaced if damaged, and the big one; whether it is economically feasible to retrofit the boat with it?

Absent a retrofit, the remedy is to maintain the retracting mechanism regularly, and leave the keel down as much as possible. To date, I still haven't heard of a C25 swing keel failure when the mechanism has been conscientiously inspected and maintained.

Edited by - on

Prospector
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Response Posted - 04/20/2011 : 07:03:47

So now I need a spare swing keel so I can build a test jig, and start working on a device...

Edited by - on

Stinkpotter
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Djibouti
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Response Posted - 04/20/2011 : 07:13:04

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Steve Milby
 ...To date, I still haven't heard of a C25 swing keel failure when the mechanism has been conscientiously inspected and maintained.
<hr height="1" noshade id="quote"></blockquote id="quote">Oh-oh... At the risk of starting another fire, you might want to ask Val "Tinob" Bisagni about his (I believe) two sinkings. "Conscientious" is a relative term, but I recall it sounded like he was.

Edited by - Stinkpotter on 04/20/2011 07:14:53

Steve Milby
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Response Posted - 04/20/2011 : 07:24:49

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Stinkpotter
 <blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Steve Milby
 ...To date, I still haven't heard of a C25 swing keel failure when the mechanism has been conscientiously inspected and maintained.
<hr height="1" noshade id="quote"></blockquote id="quote">Oh-oh... At the risk of starting another fire, you might want to ask Val "Tinob" Bisagni about his (I believe) two sinkings. "Conscientious" is a relative term, but I recall it sounded like he was.
<hr height="1" noshade id="quote"></blockquote id="quote">Maybe Val will check in and give us the facts.

Edited by - on

Stinkpotter
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Djibouti
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Response Posted - 04/20/2011 : 07:27:29

I once noodled on how to prevent the recurrence of a broken trunk when hitting a sunken object with my Sunfish's dagger-board (sort of the opposite problem). One thought was to cut a wedge-shaped section out of the trailing edge of the board, deepest just below where it meets the bottom of the boat and tapered up to the top of the board, and implant it with hard rubber.

Edited by - on

Stinkpotter
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Djibouti
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Response Posted - 04/20/2011 : 07:57:37

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Steve Milby
 Maybe Val will check in and give us the facts.<hr height="1" noshade id="quote"></blockquote id="quote">Yup, although I also recall he's reluctant to talk about it any more than he already has... I just wanted to defend his "conscientiousness", dagnabit--whether he deserves it or not.

Edited by - on

DaveR
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Response Posted - 04/20/2011 : 13:53:58

In the end it would cost too much and there just isn't room, and whatever backed up the shock would give way. WAIT A MINUTE! What if it were a pneumatic type shock (not unlike the one on your patio door) that is engaged all the time, giving way slowly so that when you cranked the keel down it depressed but would not allow for sudden movement. It could receive and relieve it's charge by and in the water around it. Wouldn't have to be huge or able to withstand sudden large amounts of force. hhhmmmmmmmmmmm

Edited by - on

islander
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Response Posted - 04/20/2011 : 14:24:41

You might have hit on something there, More or less something like a shock absorber or bladder that has small holes in it so it is full of water all the time. The water can enter and exit fine under normal operation but will slow the free fall due to the fact that the water can't exit through the small holes fast enough in the event of a cable failure. Or just take the airbag out of your car and......

Edited by - on

Stinkpotter
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Djibouti
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Response Posted - 04/20/2011 : 18:01:28

How about a truck swing arm, shock absorber, and coil spring mounted to a steel beam that runs through the hull forward of the keel and attaches to the deck, with a V to catch the keel? You might be able to salvage the parts from an F-250. (I think a screen door closer might be a little light-duty.)

Edited by - on

GaryB
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Response Posted - 04/20/2011 : 18:55:43

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Steve Milby
 [quote]Originally posted by Prospector
 It's a really interesting idea, similar to the principle that Nascar is using on their shock absorbing retaining walls to protect drivers. It raises lots of questions, such as whether there is space for a sacrificial device, whether it can be installed so that it spreads the load enough to prevent damage, whether it can be removed and replaced if damaged, and the big one; whether it is economically feasible to retrofit the boat with it?

<hr height="1" noshade id="quote"></blockquote id="quote">
SAFER Barrier

Edited by - on

GaryB
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Response Posted - 04/20/2011 : 18:58:06

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Stinkpotter
 I once noodled ...
<hr height="1" noshade id="quote"></blockquote id="quote">
And there's your answer! Wedge a noodle in the front of the keel trunk.

Edited by - GaryB on 04/20/2011 18:59:05

Merrick
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Response Posted - 04/20/2011 : 19:41:35

An engineering challenge.....seems to me the most do-able as a retro fit would be a cushion of rubber or something crushable to give you at least some protection. Testing any method would be difficult (unless you were really confident).
Good maintenance should prevent a failure, but parts do fail. That little bracket that screws in the keel might be new but that 30 yr old metal it's screwing into can corrode away.
I'll be investing in a winch unless I can figure out how to tell if it's in good shape. I'm replacing the cable at least every two years, inspecting the rest.
I keep the keel up because when I left it down the cable got so gunked with weeds it clogged up the tube and jammed the ball to where it wouldn't rotate. i'm in a tidal creek and the cable catches junk as it flows by.
if anyone figures out that hydraulic plunger attachment, I'll buy one.

Edited by - on

dlucier
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Response Posted - 04/21/2011 : 05:30:27

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Merrick
 I keep the keel up because when I left it down the cable got so gunked with weeds it clogged up the tube and jammed the ball to where it wouldn't rotate. I'm in a tidal creek and the cable catches junk as it flows by.<hr height="1" noshade id="quote"></blockquote id="quote">

When I had a swinger, during certain parts of the season the seaweed would release from the lake bottom sometimes forming small islands everywhere, some quite large. Although you can steer around these things, my keel cable still ended up collecting a fair amount of seaweed, so much so, like you described, the keel couldn't be raised. I usually knew I had a problem when others were flying by me at hull speed and I was doing 2kts.

Then it was, lower the sails, put on the dive mask, then try to extricate the three foot ball of tangled seaweed from the cable. Yeah, I miss those days...NOT!

Edited by - on

DaveR
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Response Posted - 04/21/2011 : 06:12:10

<blockquote id="quote">quote:<hr height="1" noshade id="quote"> How about a truck swing arm, shock absorber, and coil spring mounted to a steel beam that runs through the hull forward of the keel and attaches to the deck, with a V to catch the keel? You might be able to salvage the parts from an F-250. <hr height="1" noshade id="quote"></blockquote id="quote">

WAY to much hardware.

<blockquote id="quote">quote:<hr height="1" noshade id="quote"> seems to me the most do-able as a retro fit would be a cushion of rubber or something crushable <hr height="1" noshade id="quote"></blockquote id="quote">

Once that keel gets moving some rubber wouldn't even slow it down and something crushable would have to be replaced each time.

Again, if you have a pneumatic shock that's engaged all the time it can be fairly small, simple, and inexpensive by comparison. It would take a little engineering but could be totally doable by Catalina.

Edited by - on

Steve Milby
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Response Posted - 04/21/2011 : 06:29:50

The more I think about it, the more I like the bladder idea. It could be fabricated so that it fills the available space, and that would spread the load in every direction over every bulkhead surrounding it. Also, after use, it could be recharged and re-used, rather than having to replace a crushed mechanism.

Edited by - on

dlucier
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Response Posted - 04/21/2011 : 06:33:02

Thinking outside the box, what about a device that functioned similar to the auto tilt lock mechanism on an outboard that locks in place when tilted, then when lifted a little, releases. Install it somewhere in the aft top part of the trunk so that when the keel is almost all the way up, it catches and holds, then when lifted a inch or so again, it releases. This way the cable can still take all the weight, but with a safety engaged, or maybe the latch takes all the weight, or even a percentage split. This wouldn't help if the failure occurred while lowering or raising, but it may allay fears of driving down to your boat only to find it resting on the bottom.

Or this one, developing a dual cable system so if one let's go, you have a backup.

Edited by - on

Boomeroo
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Australia
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Response Posted - 04/21/2011 : 07:37:43

Great discussion. The bladder idea is good as it doesn't need replacement . It could use water as the fluid to be forced out .

I not that my C25 rebuilt trunk is slightly tapered and tight with the keel nearly fully down . This wedging could also result in braking if the keel falls as it will drag on the edges/sides before hitting the end. .I will have a wedged keel needing a good force to free up but hope no leaks.
I Have not worked out were the water line is on the keel trunk .If I drill a hole in the top of the trunk how far is it below water?

Edited by - on

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