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canadacatman2016
Last seen: 4 months 1 week ago
Joined: 4/2/16
Posts: 9
Deck construction ?

I just had my 1984 C36 Mk 1 surveyed  and the surveyor used a combination of a moisture meter and tapping to report there is moisture present in the side decks which could be a problem. I have often been down on my hands and knees examining the decks and tapping them for any signs of a dullness to the ring of the non-skid surfaces, swelling or sponginess and have found no apparent issues.The decks feel solid.
Does anybody have any experience with how moisture presents itself, what signs could go undetected and are these so-called moisture meters of any real diagnostic value? I've heard they require great skill to  interpret the results because  it's conductivity changes they are detecting NOT percentage of moisture.
Also does anybody know what the construction of the side decks is made of? Is it a GRP/plywood/GRP laminate or a GRP/end-grain balsa/GRP laminate?
What could be the effects on hull rigidity and ultimate strength of the boat if there is some rot starting. Is there a simple, minimally invasive technique to test the core to verify if there is a real problem developing?
I live in Ontario Canada where we sail May - October then the boats are laid up during our frigid winters.
Many thanks.
PS - He couldn't find the hull identification number said it's 12-14 characters long but all my boat has is the aluminum plate at the transom marked hull #288, Does anyone know if there's another number tucked away somewhere out of sight?

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KevinLenard
Last seen: 1 week 4 days ago
Joined: 1/28/15
Posts: 153

In 1991 the hull serial number was stamped into the gelcoat on the starboard side at the stern just below the toerail.

For some minimal info, see JPG attached.  There are also several YouTube videos from 2011 by Catalina illustrating their current build techniques.  I'm sure other owners will have more info for you. 
 

Attachments
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Kevin Lenard
"Firefly"
'91 C-36 Mk. "1.5" Tall Rig, Fin Keel, Hull #1120, Universal M-35 original (not "A" or "B")
CBYC, Scarborough, Lake Ontario, Canada

canadacatman2016
Last seen: 4 months 1 week ago
Joined: 4/2/16
Posts: 9

Hi Kevin - Thanks for this but it is really the decks to the side of the cabin where the moisture issues have been detected - basically form the cockpit forward to the aft lower shrouds and undermining the double stanchions. My hull so far seems ok execept some osmosis blisters.
Steve

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IslandTime
Last seen: 1 month 3 weeks ago
Joined: 12/18/17
Posts: 31
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Jeff D
Island Time
'84 MK-I SR/FK #273
Kemah, TX
canadacatman2016
Last seen: 4 months 1 week ago
Joined: 4/2/16
Posts: 9

Hi Jeff, thanks for the diagram - once again this is helpful but I'm still not seeing exactly what  the side deck composition is from the cockpit forward to the aft lower shroud areas.The surveyor indicated 15 sq ft was affected each side which is almost the whole deck form cockpit to shrouds.I am able to hear slight differences in the percussive sounds when tapped but the decks are in no way spongey underfoot. There a few stanchions that seem to move a little with side to side pressure but only the port double has slight signs of upper deck skin movemment. I am thinking I will have to remove the genoa track and several stanchions and all 3 shroud plates to fully access the damaged areas. I am assuming there is vertical grain balsa between the upper and lower deck skins but again the  PDF you sent does not quite seem to clarify this?​ I am hoping I do not have to take up a significant area of the non-skid side decks to access the water damaged core material, because relaying it could be difficult to get cosmetically perfect. I believe it is possible to get the mold for the diamond pattern non-skid gel coat and I may repaint all the non-skid areas after repair. 
 Just wondering if anybody else has had to tackle this type of repair or if there are any other articles on the process?
 

Floris van Bentum
Last seen: 2 weeks 6 days ago
Joined: 10/7/19
Posts: 2

Hello, I encounter similar problems on my Catalina 36MKI from 1991 which I bought a few months a go. I started to remove stancions and the like where rainwater is leaking hrough the deck and with some good marine Sikaflex kit and tape like HPX sealing tape put these parts back. That meaned I had to remove part of the inner "book case" (or what is it called) in the interior covering the under side of the deck. On the port side there is one spot of which I am afraid I have to remove the deck as well, except the upper part. Then fill this it up with PET-foam and cover it with fiberglass in epoxy. Like it is being down on youtube by, I believe an american company callled West. Before I start I am using a moisture detector to estimate which part I have to remove..

Kind regards,

Floris

canadacatman2016
Last seen: 4 months 1 week ago
Joined: 4/2/16
Posts: 9

Hi Floris, Thank for your comments and suggestions. My marina quoted me Can $6-7000 to "tear up the deck" on the port side which apparently is the worst affected then cover the evidence with kiwigrip anti skid. Lord knows what it would like like afterwards and likely I'd then have to pay them to tape out and apply kiwigrip to every other area of non-skid so at least the rest of the decks match the repair. Not a very appealing situation at all !
 I have decided to wait till the spring and  really examine what is going on in the deck laminates. I have purchased a high end moisture meter and have done a lot of research on the structure of the C36 decks.
If I am able to easily identify the worst areas,  I will cut out about a 2" circular section of the non-skid with a hole saw and try and save the section. I will then use a tool to undermine and remove all the rotted wood from in between the upper/lower deck skins. My intention then is to apply a vacuum film over the hole and using heat and vacuum "evaporate" the remaining moisture out of the core using the principle of "reducing the boiling point of water by lowering the air pressure". This is simple physics.
The equipment to do this is readily available from the HVAC  and Fiberglass industries . There is an article by a C34 owner who did this on his boat. he then also used the vacuum to suck penetrating epoxy into the void but I intend to try a slightly different approach.
After getting the moisture levels as low as possible I will then use Gougeon Brois "ProSet" 2 part epoxy foam to fill the voids. This material is a closed cell structure which gives structural strength wheras PET foam does not.. Having repaired the section I will either replace the cut out or use Flexmold Non-skid pattern molds from Jamestown Distributors to perfectly match the Catalina non-skid pattern.( see The Flexmold website for finding the correct Catalina non-skid pattern) The repair can be done with either color matched gel coat or better still polyurethane paint. Details of using this are on You Tube" Boatworks Today". The technology for digital color matching paint is now readily available.
Wish me luck. I will make a photgraphic record of the job and if I am successful it may be of use to other members. Any comments , advice or warnings about my intended method would be very much apprciated as I have several months of winter to get through before I raise the scalpel!

LeslieTroyer's picture
LeslieTroyer
Last seen: 5 hours 23 min ago
Joined: 3/13/16
Posts: 511

My surveyor notes several areas on the deck that were moist.  The worst was on the foredeck behind my windlass and around the fuel fill.   I rebedded the windlass then checks the area with a moisture meter and found it was still wet, using the meter I've found the source was a pad eye for either a fore guy or jack line point that was installed poorly - something for me to work on this spring   

ive used the meter on other boats to trace illusive leaks to the source   Can meters me misleading, absolutely!   You can get reading changes as the structure under it changes (ie a bulkhead)   

My experience is you get moisture intrusion at places where the glass skin has been drilled/sawed / opened up.   Stanchions are more likely be a problem than the hull/deck joint, which may leak water into the boat, but not into the balsa core.

hope this answers your question.   A great product for sealing problem leaks is butyal tape.  IMHO the best is Beddit Butyal from compass marine ( MarineHowTo.com)   While your there read his writeup on proper way to bed fixtures   

 

 

 

 

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Les & Trish Troyer
Mahalo 
Everett, WA
1983 C-36 Hull #0094
C-36 MK 1 Technical Editor. 

Commodore

 

Floris van Bentum
Last seen: 2 weeks 6 days ago
Joined: 10/7/19
Posts: 2

Hello, I removed a small part of the underlying deck yesterday, that is on the port side underneath the stancion inside the cabin. Just because I wanted to see what was causing dripping of water behind the bookshelf to know where the problem lies. Well, interesting: almost all deck plates, genua rail and stancions in that area are leaking water. Just small drips but enough to make it irritating. No damage to the construction I guess, however it was quite easy to remove the underlying section of the deck (where also this so called flange is). I can make a picture of it next weekend if anybody's interested. Now I am using butyl tape to make every deck through-hole watertight, drying the deck from inside and probably put it together with epoxy and perhaps fill the very small gap between upper and underlying structure with pet as well. Some fiberglass to make it one structure again, that is it I hope.
My view at the moment is that 1) it is nothing to worry about in the sense that there is no structural problem because there is no balsa wood anywhere, just fiberglass and 2) both sides of the deck are amazingly thick and rigid. And 3) satisfy myself that it is impossible to solve all of these relatively small problems myself and I do not want to spent a lot of money to an expensive shipyard who certainly can tackle all of these problems. I guess 90% of the perfect shape it once was, will have do for me just fine taking into account the age of 29 of my Catalina. 

Still I am very interested in construction schemes of the hull and deck to make sure what is what and how to tackle present and future problems. Does anyone in America has good connections with the catalina yard to obtain drawings/schemes or something comparable perhaps? 

Kind regards,
Floris van Bentum 

LeslieTroyer's picture
LeslieTroyer
Last seen: 5 hours 23 min ago
Joined: 3/13/16
Posts: 511

Any leaking thru the deck is cause for concern.   Look at marinehowto.com for bedding methods and buy their butyl tape. The key in my mind ts two fold 1) a good chamfer on the top surface to allow a thick layer of butyl and 2) roll the tape into a rope and go around all screws, chain plates....    For high stress areas Binicle and gates, use a router and epoxy in addition to the butyl (described in article referenced above)

 

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Les & Trish Troyer
Mahalo 
Everett, WA
1983 C-36 Hull #0094
C-36 MK 1 Technical Editor. 

Commodore

 

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