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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

Chainplate Failure

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Jonathan Cuff
Navigator

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Cayman Island
173 Posts

Initially Posted - 06/28/2004 : 10:53:58

Hi guys

I thought I'd let you know about an interesting weekend sail. In Grand Cayman we have an annual Banks & Back race which runs from the sheltered waters of the North Sound out to sea to 12 mile banks, (as the name suggests) a shallow area of water 12 miles offshore.

We entered our Catalina 25 SR/WK and were the smallest boat to enter, the next biggest being a J/30. We had a fantastic run downwind in 15/20 knots of wind with the main and 150 genoa to starboard and the cruising chute poled out to port. At one point we reached 9.5 knots according to the GPS.

When we reached the mark it was time to haul down the cruising chute and beat back towards Cayman. Initially everything was going well and we were keeping up with far bigger boats, looking to do well with our handicap. Then there was a huge bang and the starboard aft lower chainplate gave way. We immediately tacked and used the cruising chute halyard to attach to a stanchion to give us a bit more temporary support. We reefed the main and furled the genoa and started tacking very slowly (and very uncomfortably) back to shore (3-1/2 hours).

There are several lessons we have learnt. Although the standing rigging was replaced 4 years ago the chainplates obviously needed renewing as well on a 1987 boat. I have now ordered (from CD) the necessary items. Also the engine is of little use in a big sea going upwind. I only have a Honda 5hp 20", but I wonder how much difference a high thrust 8/9.9 25" would have made under those conditions, wave height were 8ft trough to crest.

All in all an interesting experience. Looking back I'm glad we did it and went through it, but at the time I think all of us would of given quite a lot to be back on dry land!!

Pie Sees 2 C25 #5686 1987 SR/WK

Edited by - on

Ben
Master Marine Consultant

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USA
1234 Posts

Response Posted - 06/28/2004 : 11:05:42

Thanks for the heads-up, and sorry about your mishap. Fortunately you all made it back safely with what sounds like little damage.

Does anyone know how to visibly check to see if the chainplates need replacing? What specifically should we be looking for?

Edited by - on

lancej
1st Mate

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81 Posts

Response Posted - 06/28/2004 : 11:30:11

Fun Ride!!!
I can comment a little on the motor question. I sail the Great Lakes (Erie) and routinly see 6 to 8 feet, sometimes a little more. It should be noted that Lake Erie generates some very short waves however, due to it's realativly shallow depth.
I have used a 4.5 HP Mercury 20" shaft, moved up to a Evinrude 9.9 25" shaft, high thrust prop. My comments would be that there is a suprisingly small difference. The cavitation was reduced a bit, but the horsepower seemed to make little difference, and the high thrust prop is worthless other than when docking. In fact, If I were to order a brand new motor, I would do so without the high thrust prop.

One man's opinion.

Lance
85 FK/SR

Edited by - on

Tony Dillon
Navigator

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USA
168 Posts

Response Posted - 06/28/2004 : 11:37:56

Unfortunately the best way to inspect chainplates is to physically remove them from the boat, and then rebed them, the point of failure is usually hidden inside the deck where moisture and salt has had an opportunity build up and cause corrosion due to small leaks in the bedding. Chainplates should be bright and shiney for their full length. Any pitting or corrosion is a sign of upcoming failure.

Brion Toss had a good article in Crusing World regarding this subject in either the March or April issue this year. He claims the close to 30% of rig failures are due in part to broken chainplates.

Edited by - on

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 06/28/2004 : 12:00:27

I am surprised an aft chain plate would be under much strain. Most I have heard discussed are run VERY loose.

Edited by - on

rclift
Navigator

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USA
152 Posts

Response Posted - 06/28/2004 : 12:27:02

I'm curious whether these were the upgraded chain plates and where exactly they failed?

Edited by - on

Steve Milby
Past Commodore

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USA
5913 Posts

Response Posted - 06/28/2004 : 12:52:25

Chainplate failure might not be so much of a risk if you can keep the boat under 9 knots!

Edited by - on

Jonathan Cuff
Navigator

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Cayman Island
173 Posts

Response Posted - 06/28/2004 : 13:04:10

The chainplate that failed was starboard aft lower due to internal corrosion. Basically it looked fine from the outside. Underneath everything (still) looks fine with the backing plate and bolt and nut in place. The bolt was rotten in the middle and eventually was being held only by the retaining screws judging by the amount of old corrosion, i.e. it was not a fresh break. It broke while we were going upwind at 5 knots.

Cheers

Edited by - on

RichardG
Admiral

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USA
990 Posts

Response Posted - 06/28/2004 : 13:54:58

Johnathan:

Did the chainplate break or did the through-eye-bolt break? Only the uppers on mine have chainplates (bolted to the bulkhead) -- the lowers are only bolted through the deck with backing plates. Were the backing plates the original, round washers or were they the approx. 3" x 5" rectangular, stainless plates?

Does anyone know when, if ever, the upgraded rectangular backing plates for the lowers became standard equipment on new boats? Did the upgrade kit include new through-eye-bolts?

Edited by - on

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 06/28/2004 : 14:02:29

Jonathon,

You were quite fortunate that it wasn't the upper shroud chainplate that let go!

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by lancej
 ...I have used a 4.5 HP Mercury 20" shaft, moved up to a Evinrude 9.9 25" shaft, high thrust prop. My comments would be that there is a suprisingly small difference. The cavitation was reduced a bit, but the horsepower seemed to make little difference, and the high thrust prop is worthless other than when docking. In fact, If I were to order a brand new motor, I would do so without the high thrust prop.<hr height="1" noshade id="quote"></blockquote id="quote">

With respect to the high thrust prop, my sentiments exactly, and when I get the opportunity, the high thrust prop that I installed this past spring is coming off for the very reasons you stated.

Edited by - on

Jonathan Cuff
Navigator

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Cayman Island
173 Posts

Response Posted - 06/28/2004 : 14:41:11

It was the new style upgraded chainplate with backing plate. The bolt through the hull itself failed. Underneath it looked perfect, and on the deck only what looked like a tiny bit of surface rust. The bolt was rotten through the middle.

Cheers

Edited by - on

Dave Laux
Captain

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318 Posts

Response Posted - 06/28/2004 : 18:01:40

This is a common mode of failure for Stainless Steel. The stuff is a mix of metals taht is only corroision resistant due to a surface coating that requires oxygen for its maintinence. If it sits in a small amount of water that is trapped in a closed space and particularly if the salt content is high, very rapid corroision results. Check the other bolts to see if they are going too. The other place that this is fairly common is in the lower rudder pintle bolts both thru the rudder and thru the hull. When you go to reset the chain bolts make sure that the rotten core material around them is removed and replaced with epoxy and cabosil( a bent nail in a drill is a good way to remove the core stuff) and then that the bolt is well sealed with polysulfide sealant(3M 101). How much of the deck is spongy around the chainplates and bolts?

Edited by - on

Jonathan Cuff
Navigator

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Cayman Island
173 Posts

Response Posted - 06/29/2004 : 10:23:50

Dave

I have ordered replacements for all the chainplates on the boat just to be sure, and new standing rigging too!! I don't see any evidence of soft decks aroud the chainplates but I will give it a proper check. You mentioned the rudder pintles as well. Are these worth replacing too? I did replace my rudder with a new balanced one last year, but used the existing pintles & gudgeons.

Cheers Jonathan

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 06/29/2004 : 11:23:46

May have been a 'bad bolt' too... corrosion due to a localized problem in the stainless alloy. Curious as to what you find when you inspect your other chainplate bolts... please let us know.
(part of the community knowledge bank)

Edited by - on

Dave Laux
Captain

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318 Posts

Response Posted - 06/29/2004 : 22:22:13

Actually its usually the bolts attaching the hardware that give trouble. As you noted in your original post the head and nut of the chain bolt look fine cause they were exposed to the oxygen in the air and thus maintained their inert coating. Bolts also are not elecropolished which would reduce the tendency to corrode. I have a large collection of bolts that would give you nightmares if you thought about the cosequences of their failure. Thet look perfect at the exposed ends but there is little or nothing holding those ends together. The weird part of all this is that the average guy or gal throws a fit when you say that you want a represenative sample of crictical bolts pulled for inspection. "There can't be anything wrong with them they are the best grade of stainless." Thats when I reach for my bag of bolts that I have found during surveys. Most classification societies, Lloyd's ABS(American bureau of ships) Bureau Veritas will not accept stainless for critical fasteners or for fuel tanks because of the rapid and complete corrosion that sometime occurs. You must either exclude water completely or allow oxygen or oxegenated water to surround the fitting. Either is safe but damp and closed up is really dangerous. BTW, Clam Beach, do you think that they make up the alloys in one bolt units or is it more likely that the furnace is charged with tons of material and many hundreds of thousands of bolts or whatever come out of one pour of alloy. The dramatic diferences that you see almost always come from the very specific home that a particular bolt lives in not from bad bolts. Back to Jonathan, The water that caused this trouble almost has to be soaking into the deck core around the bolts so if the deck is not soft now it will be later. The good side of this is that if you can exclude the air by sealing the holes you can reduce the rot rate and futher water inflow into the core. At least you don't have to deal with freezing too. Dave

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 06/30/2004 : 01:20:48

"likely that the furnace is charged with tons of material"

I've put 20 stainless bolts in the same environment (exposed to caustic in a pulp mill) and had 1 of the lot corrode... with the the rest staying in pristine condition. They were all 'good stuff' 316 from the same bin. Go figure. Observed same phenonema on some transom bolts in my last boat... some corroded, while others installed right along side were like new.

All that said, given the location of the boat... nice warm tropical salt water, and the nature of the failure, your explanation is much more likely than mine.

Edited by - on

Dave Laux
Captain

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318 Posts

Response Posted - 06/30/2004 : 07:08:14

Hey Clam, I see the same thing, that two or more bolts in what seems to be the same enviroment will have completely different corrosion results. I still think its mostly some subtle difference in what each bolt has around it. The other big factor in all materials is how much tension the bolt has on it. More load generally increases corrosion rates. The big deal with stainless though is oxygen starvation. Dave

Edited by - on

Ed Montague
Captain

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USA
499 Posts

Response Posted - 06/30/2004 : 12:32:39

Hmmmmm, I looked at the chain plates on my boat last night and one of them has a nice rust colored ring around it. I will definately pull that one out this weekend for a full length inspection. Thank you all for the heads up.

Edited by - on

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