87 Chaparral 235 XLC complete restore

[davedog]

This is my first post, but I feel I know so many of you already after reading this forum for years studying and preparing for this restore. I will be posting pics of entire restore going forward once I figure out the best way to do so since the old methods don't seem to work well now days. Anyway here is the deal.
I have a 1987 Chaparral 235 XLC with a Mercruiser 454 Mag / Alpha drive 1.32 gear ratio.
I have already gutted the boat and rebuilt the entire transom and was working on the stringers when I noticed under the fuel tank and under the engine area that the hull is cored with 1/2" plywood. If I had really thought about it months ago I would have sold the boat and moved on but I have gone this far so plan to finish it right which means I need to recore these areas of the hull. I have the core removed on the Starboard side only under the gas tank area. I don't want to remove too much and have the trailer bunks come busting through the hull.

* Here is what I want to know and have not been able to find an answer anywhere online. Why did the builder use approximate 7" squares instead of a single piece of plywood?

* When I re core these areas, do I have to cut the wood into squares just like it was done originally? I guess I can answer this one after I know the answer to my first question.

* Should I treat this part of the job like the transom and PB the new core to the outer skin?

* Is it OK to add a layer of CSM and 1708 to the outer skin before I lay down the coring?

Oh ya, I am using Poly for this part of the rebuild. I did the entire transom with Vinyl Ester, but just received 15 gallons of Poly from US Composites so am going to use it. (It was late and I ordered Poly instead of Vinyl by mistake.)

 

[tpenfield]

Answers . . .

* Here is what I want to know and have not been able to find an answer anywhere online. Why did the builder use approximate 7" squares instead of a single piece of plywood?

Because, that's why. Actually using smaller pieces of wood allows for curvature of the hull and depending on how it was done can provide more strength.

* When I re core these areas, do I have to cut the wood into squares just like it was done originally? I guess I can answer this one after I know the answer to my first question.

Might be best . . . are you sure you want to use wood instead of high density foam?

* Should I treat this part of the job like the transom and PB the new core to the outer skin?

The core pieces should be adhered to the hull (using resin) otherwise it will not be very strong

* Is it OK to add a layer of CSM and 1708 to the outer skin before I lay down the coring?

Sure, we will allow it

 

[davedog]

 

[davedog]

Thank you for the response and help. I have attached some pics to help show what I have going on so far and for a bit more clarification before I mess up real bad.
You will see in the pics that the coring stops right before the keel and the glass covering the core helps create that center drainage area. I outlined on one pic how much of the coring I have removed from one side leaving about 2" of the hump/glass roving still there. What I am trying to ask is should I cut out the glass all the way into the center or leave it there for support try to scrap out the remaining core wood from under it and then wedge the new coring pieces under that part? Also am I correct in only doing 1 side at a time to help keep the hull from collapsing from not enough support.

My thinking was to beef up the inside of that outer skin with another layer of mat or 1708 or something before I attach the core to it with resin since it is so thin.

 

[tpenfield]

Post some more pictures from a greater distance and different vantage points so we can get a better idea of the entirety of it all.

As far as the immediate question on what to do about the remaining core material near the keel . . . It is really a judgement call that you will have to make.

I assume you took out the coring material because it was wet/rotting?

Is the remaining core material dry/solid?

Can you remove the remaining core material fairly easily?

The better approach would be to remove the remaining core.

As far as the hull being thin and concerns about the trailer bunks deforming the hull, etc. . . . Make sure the bunks are supporting the hull in the area of bulkheads. If you have completely gutted the structure, then supporting near the chines of the hull along the boat's length would be good.

 

[davedog]

Yes the core was wet but not completely rotting which is why it is difficult to remove under that lip of glass I left next to the keel drainage area. Its dried out now that it has been cut open but at this point some areas have been dug out and others not yet. Here are a few pics from further out. Let me know if you need any other virews etc.

 

[davedog]

Here is zoom in of area I am wondering if I should cut off lip to be able to core easier and then just do some heavy glass work over it all and hopefully still be able to have that drainage area down the keel.

 

[chevymaher]

Yes grind it smooth.

 

[davedog]

I quickly came to the realization last night it would be Impossible to recore this area without grinding it all down. I put on my big boy pants and started grinding. So here is what I am planning to do. Please someone chime in and let me know if I should do anything different.
1 Coat 1/2" marine plywood with poly resin really good followed by a layer of 1.75oz mat on both sides.
2 Cut sheet into 7" x 7" squares and then coat each edge with poly resin.
3 wipe down hull with acetone and or styrene real good and lay down a layer or either 1.75oz mat or 1708.
4. When that starts to kick lay down a layer of resin and place each core square with weights on top of them.
5 once that is cured put peanut butter around all the edges of core followed by a layer of mat over entire area.
6 once that tracks up lay down a layer of 1708 or woven roving
7 and keep alternating until I have encased the core very well and built up the thickness it had originally.
8 then I will start building the new stringers.

Is this a proper way to do this?

 

[AShipShow]

Sounds good to me... Still wondering why you aren't considering 1/2" hi density foam recommended earlier. The coring does not provide much strength itself, its basically a spacer that holds the inner layer of glass... The combination of the two layers of glass together provide a lot of rigidity, but the core itself doesn't do much.

You shouldn't need all that much foam so cost-wise compared to marine ply shouldn't be much different.

Obviously the biggest benefit is it can never rot, but its also lighter.

Another idea worth considering... After you cut your coring material into the squares and "glue" them down to the hull, you might want to consider doing it like a tiling job and leaving some small spaces between each piece, then go back and fill all the spaces with thickened resin with chopped fibers... Your "grout" will then bridge the inner and outer skins and make the cored hull incredibly strong and rigid.

 

[davedog]

I decided to go with marine plywood because I already have it. If it lasts another 30 years it will probably outlive me. I like your idea about the grout. The spacing filled with thickened resin should also protect each square from water should the hull get pierced allowing water into an adjacent square.
what spacing would you recommend between them?

 

[davedog]

Now you guys have me wondering how much easier/harder more/less work would it be if I used foam? Is it strong enough to core under the mounts for 454? What is the procedure compared to using ply?

 

[davedog]

Been working on removing the coring from the port side. It still confuses me why they use the squares when it's basically a flat area. I've heard some say it was to use up waste material and others say to match the curve of the hull. I would hate to think it was just to use up scrap materials. Anyway here is a pic of the port side after removing the skin as well as after removing the core material. If it lets me post 3rd pic it will be the skin removed from the starboard side engine mount bed.
Still contemplating using foam now for new core once have researched more info.

having issues uploading any pics now

 

[tpenfield]

More pictures would be great . . . If you re-size them to about 800x600 (or even 880 x 660) they should upload fine using the paperclip icon and then you can place them within the text of the post. Loading pictures as they come from the camera/phone are too big (pixels and MegaBytes) to upload.

I am a big believer in using foam. The main disadvantage is that it is wicked expensive. There is higher density foam that can be used for structural members and transoms, vs the lower density foams that are used for coring and flotation.

The main difference between using wood vs. foam is that wood tries to absorb moisture, foam tries to reject it. Water penetrates fiberglass very slowly at a microscopic level and wood readily accepts it.

I've used both wood and foam in structural work on my boats. . . Wood because it is readily available and economical, foam because it is lighter in weight and easy to cut & shape.

 

[davedog]

I have resized the images to 600x800 or less but I get a php error

 

[Scott Danforth]

there is a website picture loading issue the past few days. colonel_sanders has been trying to remedy

 

[davedog]

So when you say there are foams that can be used for structural areas like in my case are you referring to Coosa or what foam is used for this area under the engine mounts and under the entire bilge area. The coring in these areas now is 1/2" thick and are 36" x 30" sections of coring on both port and starboard.

I will be done removing all the coring by Saturday evening or Sunday afternoon so want to get moving on whatever material I end up using.
Thanks for your help!

I will upload pics once site is fixed.

 

[davedog]

test trying to show image still
If this link works you should be able to see a few pics from where I removed the core under the engine area in bilge and from under the gas tank.
https://photos.app.goo.gl/fMHXkSZnwYrgvhXi6

 

[davedog]

If you look at the pics you will see some areas that have patches of what looks like a dry layup. It is white brittle roving. I assume I need to grind these out and repair before laying new coring. Issue is they are basically last layer before gelcoat I think anyway. Any advice?

 

[tpenfield]

Testing . . . 123.

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