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Old 28-03-2020, 16:52   #1
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Cockpit core.

Today i decided to rip out a part of my cockpit core and get this right. I had known it had water in it but it was still pretty solid so i ignored it. The other day while my brother was walking on it i noticed a drip down below and figured that was a sign that action needed to be taken. The skin has pretty bad cracking from all the flexing under foot. Here is what i want to ask you guys and gals.

Would you re use the skin or start from scratch?

I purchased polyester resin because thats what the boat was built with and im not rich.

What have you used to thicken it?

What type of fiberglass mat would you use if starting from scratch? Csm? 1708? Both? Neither?

Anyone successfully brushed on gelcoat? Im against using paint because nothing is painted so far and the rest if the gel in the boat looks decent.

Anyone ever used conventional a grade plywood with excellent sealing and prep work?

Anyone know what size this plywood is? Its not easy to measure wet wood.

Other comments are welcomed.

Thanks.
-Drew
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Old 28-03-2020, 17:49   #2
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Re: Cockpit core.

First if at all possible I would have gone in from underneath. WAY less finishing work. Second youíll want epoxy for this job and you wonít need much. Three, it really doesnít matter what size the squares are, they made them that way to reduce water penetration and rot. If you use a slightly smaller sized squares and leave an 1/8Ē gap between each epoxy them all in place and spread thickened epoxy like grout and really work it in between the squares I wouldnít worry about the grade of ply. I personally would use one sheet and properly seal the binnacle as it is the most likely culprit for intrusion. Canít tell if itís checkered from your pictures but if it is, it might be best to fair out the whole cockpit and finish with awlgrip or similar.
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Old 28-03-2020, 18:00   #3
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Re: Cockpit core.

Have I missed it or haven't you told us what make/model yacht you sail?

Looking at the photo I'd say it is around 28ft so it likely has tiller steering and no helmsman seat. If that is so you won't have a problem with compression pads for seat/steering pedestals.

I'd rip out the de-laminated cockpit floor and start again using the polyester you have and 1/2 inch exterior quality ply (which is cheaper than marine ply)

https://www.homestratosphere.com/types-of-plywood/

Coarsely sand the cockpit sides up to (say) 6 inches, lay the ply in the bottom of the cockpit and use CSM X3 (fairly heavy 1708?) over the entire cockpit floor. Then CSM strips (2 inch) X2 around the floor/sides join. I'd put at least one layer on the bottom side of the cockpit floor and some strips on the join for reinforcement.

Don't forget the cockpit drains!

PS I'm certainly no fan of balsa core especially where the laminate is constantly wet (such as a cockpit floor)
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Old 28-03-2020, 18:16   #4
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Re: Cockpit core.

With the binnacle and destroyer wheel and T cockpit in the pictures Iíd say heís mid thirties in length
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Old 28-03-2020, 18:31   #5
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Re: Cockpit core.

Of considerable importance to me would be making sure the base under the skin is fully supportive of the skin. Looking at the 2nd picture it appears that the RHS is flush with the bottom of the skin whilst the LHS has a considerable gap. Is the difference perhaps stuck to the bottom of the old skin?

I would use side rails and a router with a wide surface cutter to cut the existing plywood to a good level, equally deep over the whole area and if possible able to accomodate a standard thickness of ply to come level with the bottom of the existing floor skin. Quality of ply? Phenol-bonded pine ply. Inexpensive and will last for 50 years. I would use one sheet, not a series of squares.

You mention that the skin is full of cracks. Stress cracks? Structural cracks? Because for me 1st prize would be cleaning off the ply on the underside and refitting it. Firstly it would be the correct thickness, secondly it would have the non-skid finish that youíve been used to. If it remains usable for a repair, I would use it. Getting a decent finish on a newly laid GRP floor is not easy.

The existing ply needs to be dry or no adhesive will hold. I second the use of epoxy. Acrylic resin is not well-known for sticking to old acrylic resin. Epoxy sticks very well and is not as expensive as one would believe. Use West System 105 resin with 206 (slow) hardener.

Laminate the new ply to the old, using a layer of thin chopped mat between the new and old ply and on top of the new ply, paint the bottom of the skin with wet epoxy and laminate to the ply. Use a series of weights to place even pressure over the whole area - something like a number of clay bricks. I would do this whole laminating job in one session.

When itís all set, use some epoxy with fairing thickener (micro-balloons) to fill in the seam around the edges. Fair the seam off to original levels.

Finish of with two-part epoxy paint - it has a great finish, is very hard-wearing and easy to apply with a brush or small roller. Iíve used International Perfection Topcoat with good success. If the old floor just has stress (spider web) cracks, this paint will fill them.

You will no doubt get a number of suggestions/processes from others. Look at all of them then choose what falls inside your self-perceived skill set. This is not as hard as it appears.
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Old 28-03-2020, 18:38   #6
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Re: Cockpit core.

Hey Drew,

I can see that you have a binnacle with an attached steering wheel. I can also see the tools and your sandals there, so I suspect this is about a 2x3 foot hole you cut in your boat. Is that about right?

Now you know there is a leak...your first problem is to find the source of the leak and stop that. I saw the port on the port side of the cockpit and suspected that at first, but the water saturation seems to be on the starboard side of the cockpit. It also sort of looks like your binnacle could be the culprit.

As for the repair itself, RBK is right....you're going to need epoxy resin. Poly will adhere to poly, but epoxy will definitely bond and give you more peace of mind.

You could use exterior grade plywood, but if it were me I would recommend a closed cell foam.

WRT a thickening agent, some people use industrial talc powder. (Honestly, I've used Johnson's baby powder in the past in a pinch, but its more expensive than industrial talc.) However, using talc as a thickening agent is heavy and adds a lot of weight. A better agent for thickening is micro-bubbles (wear a respirator).

Just out of curiosity, are you planning to reuse the cockpit sole, or lay in a new sole altogether?
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Old 28-03-2020, 19:05   #7
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Re: Cockpit core.

Quote:
Originally Posted by rbk View Post
With the binnacle and destroyer wheel and T cockpit in the pictures I’d say he’s mid thirties in length

Yep! I won't argue. (I didn't spot that. I was looking at the profile picture)

Now you've pointed that out I would be even more inclined to use ply instead of core. I'd make the pedestal bases proud of the cockpit floor.
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Old 28-03-2020, 19:08   #8
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Re: Cockpit core.

Sorry folks, I forgot to mention the boat info. This is a 1985 hunter 34. The reason it looks uneven is because i tool all of the blocks out of the stbd side in onr of the pictures. The cracks in the skin are all directly over the places that were wet because the deflection allowed the skin to flex. The core behind the wheel is all sound and does not have any cracks at all. I tapped the whole area before surgery and the thud sounds were all in front of the wheel. I would hate to grind that area down.
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Old 28-03-2020, 19:25   #9
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Re: Cockpit core.

you need to have a small space between each piece of plywood so the resin can flow around it and prevent moisture from spreading in case of leaks. i would use smaller pieces than Hunter did. it looks like the wet wood extends further than your cut out area
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Old 28-03-2020, 20:42   #10
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Re: Cockpit core.

After removing the core, use plenty of (denatured) alcohol to rinse it dry. Use heat gun as well, nit at the same time of-course.

When fully dry, wet everything out with epoxy (use wide chip brush). Now thicken epoxy with microfiber to a ketchup consistency and use a notched spreader to put a coat over the brushed epoxy. Take a new piece of plywood, fully coat it with the unthickened epoxy and put it in, like tiling. Finish all the pieces. On top of that another layer of thickened epoxy, working it in between the plywood pieces and leaving a coat with the notched spreader. Put the original top layer of glass on top after wetting the underside out with resin and brush, add weights and let cure. After cure comes refinishing the cockpit. I recommend an epoxy primer followed by polyurethane paint. This takes care of all the cracks (sand the gelcoat back so they disappear).

Donít use polyester, donít use new glass as itís so much more work and the glass you took off is good enough from what I see on the picture.
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Old 29-03-2020, 06:38   #11
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Re: Cockpit core.

Everyone on this thread - if you'd like to see some lovely pictures of Drew's boat and his chronicle of what brought him to this point, here's his first official post as a CF member from a couple of days ago:

https://www.cruisersforum.com/forums...ks-232079.html

And from this thread and the above, Drew, I have to say you may have to contemplate changing your moniker to "Action Man"...

Fair winds,
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Old 29-03-2020, 07:24   #12
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Re: Cockpit core.

What about having some sort of cloth tying the top skin back togther? Otherwise that joint would be prone to cracking. Maybe put it underneath?
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Old 29-03-2020, 07:45   #13
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Re: Cockpit core.

These are all great ideas! Thanks for the help folks!
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Old 29-03-2020, 11:24   #14
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Re: Cockpit core.

Drew, hopefully you cut out the top skin all in one piece. Jedi has suggested what I would do (did pretty much the same procedure to my side decks) but I used divynicel foam, not plywood, but I think the H34 has a cabin under the cockpit? In that case, you may need the stiffness of the plywood. Be merciless about getting all the rot out and be sure everything is dry. I used bags of sand to hold the top skin back down flat, get all the edges as close to even as possible, saves work later.
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Old 29-03-2020, 12:05   #15
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Re: Cockpit core.

Quote:
Originally Posted by Sailorman Ed View Post
Drew, hopefully you cut out the top skin all in one piece. Jedi has suggested what I would do (did pretty much the same procedure to my side decks) but I used divynicel foam, not plywood, but I think the H34 has a cabin under the cockpit? In that case, you may need the stiffness of the plywood. Be merciless about getting all the rot out and be sure everything is dry. I used bags of sand to hold the top skin back down flat, get all the edges as close to even as possible, saves work later.
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In addition to weights, I drill holes in the ďlidĒ around the perimeter and screw it down so that it is exactly flush. The screws allow precise adjustment. When the epoxy has set up but way before it is fully cured, I remove the screws and fill the holes.
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