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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

Mast Stepping near disaster

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zsonic09
1st Mate

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USA
32 Posts

Initially Posted - 09/24/2014 : 09:10:51

I was helping a friend with raising his mast on a 1980 C25 last weekend.We used my A-Frame setup that I use on my 84 C25. We had a few guys helping us out. We had the mast raised about 75% and all of a sudden he mast plate
let go. It sheered the four screws clean off. We were able to safely set the mast back down, but it was a hairy situation there for a sec.

His boat is NOT in good shape, it needs a lot of work, but I am really surprised that the mast plate let go like that. It appears that the screws screw into the fiberglass. I looked at mine, and I have bolts through the top,with two bolts on each side of the compression post. (I do have the optional mast plate for attaching blocks to though.)

Did Catalina change the way the mast plate is attached in later years?

Edited by - on

Heartbeat
Navigator

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USA
161 Posts

Response Posted - 09/24/2014 : 09:15:21

I have bolts. 1/4-20, I think. 1985.

Edited by - on

redeye
Master Marine Consultant

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3474 Posts

Response Posted - 09/24/2014 : 09:26:46

<< It sheered the four screws clean off. >>

Sounds like somebody put a mast plate on with cheep screws/bolts. Softer metal. I think the heads of some ( aircraft grade ) stainless steel bolts have marks on them that indicate the strength of the metal.

Pretty interesting and good to know. Thanks for sharing that.

Loved to have seen that video

Edited by - on

Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 09/24/2014 : 09:57:08

All four sheared off so parts are still in the deck? Can you tell whether any of them went into the compression post? (Screwing into the deck alone would be very poor judgement--I seriously doubt Catalina would do it.) Is there any evidence that somebody changed the location (and type) of the screws? (...filled in holes in the deck, new holes drilled in the step, etc...) Do the screws appear rusted? (A little discoloring is not uncommon on stainless, but heavy corrosion indicates ordinary steel.) Do they appear to be bronze?

My '85 had two substantial lag screws through the deck into the compression post, and two bolts through the deck, too close to the forward side of the post to allow what I considered adequate washers. The step had an extension welded to it that suggested to me the method of anchoring it may have been revised from some earlier vintage. (It's apparently different from Heartbeat's of the same year.)

Edited by - Stinkpotter on 09/24/2014 09:57:36

zsonic09
1st Mate

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USA
32 Posts

Response Posted - 09/24/2014 : 10:42:42

I called Catalina Direct. All models appear to use lag bolts that go through the fiberglass into the plywood. The tech said the reason for this, is in case the mast lets go due to some rigging failure, it would not tear the deck apart. So it's a 'weak link' by design. So in this case, who knows what happened. The lag screws could have been replaced with cheaper ones.

http://www.catalinadirect.com/index.cfm/product/238_149/mast-step-mounting-kit-c-25.cfm

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Stinkpotter
Master Marine Consultant

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Djibouti
9013 Posts

Response Posted - 09/24/2014 : 11:53:31

If the CD guy is right (and I'm not convinced, based on observations), this would concern me regarding raising or lowering a mast. Short screws into the 3/4" plywood should suffice with the mast up and rigged--the forces on the step are primarily downward with minor horizontal forces. But when raising/lowering, depending on the position of anything supporting the mast, there could be substantial upward force on those screws, based on simple leverage. That "link" (screws short enough to go into the plywood without penetrating the liner) could be too weak. It suggests that any mast raising system must be designed and executed so the weight above a support point is always less than the weight below it.

Edited by - on

Heartbeat
Navigator

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USA
161 Posts

Response Posted - 09/24/2014 : 11:53:36

Hmm.

I replaced that mast step plate 15 years ago or so. I remember I had bolts because I was having trouble getting the 'screws' out. I was using a handheld impact wrench. I had some friends helping me as I was going to raise the mast just after. He gave me a hard time about using a "German Speed Wrench." I hadn't heard the term before. Eventually we figured out the reason why I was having so much trouble with the 'screws' was because of the nut and fender washer on the underside.

I wonder if my previous owner made that change? I might drop him a note and see if he remembers.

Matt

Edited by - on

redeye
Master Marine Consultant

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3474 Posts

Response Posted - 09/24/2014 : 12:06:15

Hmm.. I'd have thought the weak link would have been the one bolt holding the mast to the mast step. ( depending on how old that bolt is

)

[url="http://www.fastenal.com/content/documents/FastenalTechnicalReferenceGuide.pdf"]Fastenal Bolt Guide to strength on page 36 [/url]

A doc I work for builds/refurbishes aircraft and made me aware of the different specs on bolts.

http://www.aircraftspruce.com

Edited by - on

islander
Master Marine Consultant

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USA
3992 Posts

Response Posted - 09/24/2014 : 15:05:01

I wouldn't assume that all of the boats used lag screws... My plate has 4 bolts with washers and acorn nuts on the inside. 2 just behind the post and 2 just in front. Stainless steel will corrode when subjected to the right conditions. Usually wet without any air for it to dry out. This is why standing rigging will fail usually down in the swage. Also chain plates will fail usually just below the surface of the deck. My guess is that his bolts or screws were leaking for a long time.
Crevice corrosion

Crevice corrosion is a localised form of attack which is initiated by the extremely low availability of oxygen in a crevice. It is only likely to be a problem in stagnant solutions where a build-up of chlorides can occur. The severity of crevice corrosion is very dependent on the geometry of the crevice; the narrower (around 25 micro-metres) and deeper the crevice, the more severe the corrosion. Crevices typically occur between nuts and washers or around the thread of a screw or the shank of a bolt. Crevices can also occur in welds which fail to penetrate and under deposits on the steel surface.

Edited by - islander on 09/24/2014 16:03:12

Derek Crawford
Master Marine Consultant

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USA
3312 Posts

Response Posted - 09/24/2014 : 15:34:50

My '81 definitely had just screws securing the tabernacle. When I added a mast plate I used 4 thru' bolts, washers and nuts.

Edited by - on

redeye
Master Marine Consultant

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3474 Posts

Response Posted - 09/26/2014 : 05:50:49

Thank you Scott.. That image really brings it to life. I guess on a 30 year old boat it might be good to inspect all the bolts.

Edited by - on

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