Choosing wood for a wood/glass Chris Craft Coho

Good to see you're back F14. You're where I was about 5 years ago with my 73 Silverton. Take a lot of photos, and I mean a lot from all different angles and notes as you proceed with your disassembly.

As far as covering countersunk screws, I've used two methods. Originally I thought I'd cut plugs. This is fine for bright work but since I was painting most of my boat I decided to generally use epoxy as the filler. On horizontal surfaces I just mixed up neat epoxy and filled the depressions. On vertical surfaces I added some silica (cabosil) to the resin to keep it in place. Once the holes are filled seal the wood with a couple of coats of resin. Once sealed all exterior surfaces were covered with 4 oz. fiberglass cloth primed and painted (I used interlux epoxy prime coat and Perfection).

Regarding wood. For all structural parts I used philippine mahogany. Decks are douglas fir plywood (i wished I'd used okoume marine ply as it looks better finished but douglas fir was less expensive - you live and learn!) cabin top and all load bearing vertical panels are okoume ply. For all interior panels and non load bearing vertical panels including my new flybridge I used a product called Arauco plywood. This product is available at some but not all Lowes stores. It's much less expensive than okoume or douglas fir ply but is a bit heavier. If you can find it take a look. I found it to be an excellent product for the money and when finished properly (two seal coats of epoxy, 4oz cloth with two more coats a couple of coats of primer and two finish coats - that's 8 layers of protection) I see no reason why it won't provide many years of excellent service. You also need to pay close attention to any point where to put in a screw or bolt. More about that another day.

http://www.boisenortheast.com/boisenortheast/arauco/arauco.html

I'm doing exactly what you are starting to do so you might take a little time to look at previous posts. One especially problematic area will likely be the windshield area and the roof pillars that form it. You'll probably find that the entire front of the cabin has rotted and settled over the years. The angle of my windshield frame was actually 39 degrees. Clearly it was built as a 45 degree but sagged. You may want to consider redesigning the windshield area to strengthen it. ANother area I found really poorly designed was the fore and aft beam that supports the side decks next to the cabin side walls. The beam was just Southern Yellow Pine and pretty thin/weak. Over the years increasingly overweight people stepping onto the boat caused the deck to begin flexing. Water made it's way in to the area where the cabin walls meet the side deck aft and rot did the rest. I replaced that original beam with a larger one made of Phillipine Mahogany.

Regards and good luck for now,


MIA

 

I dunno...I'm still undecided on whether I should coat the exterior stuff with glass or coat with epoxy (deck will be glassed though) or just prime and paint. I like the idea of it being sealed but possible penetration is what I'm worried about. At any rate counting that the paint is kept up and the limber holes for the side windows are kept open it will probably last as long as it did. It's in bad shape now but neglect didn't help. Not sure if Ill be keeping it another 40 years at any rate.

 

You can seal the vertical parts with epoxy (the standard regimen is 3 coats on all 6 sides). The problem is that you'll see the seams where parts butt. I've found that the light fiberglass cloth made it easier to hide the seams. So far the cabin has been in place for about 3 seasons and there are no signs of the seams opening up or cracking. I believe that the cloth helps to keep the parts dimensionally stable. Painting the boat white probably helps too as it minimizes temperature cycling.

I glassed where I thought it was to my advantage. Besides 4 oz. cloth isn't very expensive, doesn't soak up much resin and is relatively easy to apply to vertical surfaces as it's light weight.

Some photos for thought. 1. Do most sealing / epoxy coating off the boat. It's easier to do on a flat surface. Note that wife's car is often kicked out of garage. Boat builders old Z always stays inside! 2. Zoom in to see epoxy "bungs". These decks will never come off. Look carefully and you'll see I'm a healthy eater! Those yogurt containers make great mixing pots. 3. Bare plywood can be painted. 4. Wouldn't you rather paint over a sealed epoxy coated deck? This photo just shows the seal coats, the glass cloth was applied afterward.

MIA

 

Eating epoxy isn't especially healthy Bart . . .

 

as in epoxy can't rot?

 

True PAR but the yogurt really masks that bad resin aftertaste.

 

I prefer mine over greens, maybe on a bed of pasta.

F14, epoxy is inert when cured. It's so inert that medical implants have epoxy coated circuit boards and electrical leads, to prevent corrosion.

 

Well...

I know epoxy is really great stuff. I know that it's more or less "impervious" to water penetration, especially if well soaked with epoxy and covered in glass. I'm still worried about water finding a way in through a screw hole or something.

My other consideration is that marine plywood is really good stuff anyway, and since the wood on the boat has made it this long (41 years) without being coated in epoxy, it seems like epoxy just isn't necessary. The wood is obviously bad now but the boat has seen some neglect at least in the past few years but it's still reasonable to assume that new, un-epoxied marine plywood would last at least half that long, which is acceptable to me. Regardless of whether it has epoxy or not the paint has to be maintained.

So, for at least the exterior, vertically mounted wood, I'm not quite convinced that epoxy is needed

 

A boat in salt water, whose owner carefully prevents fresh water in its bilges, who has access to the quality of plywood available back when the boat was built (from it), can repair without using epoxy. Also, many boats go decades out of water and under cover and a later owner doesn't even know it. Such boats appear to be impervious to decay but just start using them heavily in fresh water and see how they accellerate their age.
If resourcinal was originally used, epoxy would be a good replacement for that, though resourcinal is still available. Resoucinal has to be clamped well and mating surfaces are far more exacting as resourcinal is not like epoxy, which has gap-filling qualities without loss of bond strength.
In other words, use common sense and listen to those who have gone before...

 

Hmmm...the mahogany marine ply, or in some places dimensional mahogany, could have been better than douglas fir marine ply these days.

I'm pretty certain this has always been a great lakes boat, being that it has raw water cooling. With 3400+ hours on the meters I don't think its sat inside that much though.

I think epoxy is not always needed but nevertheless a great material.

I am not saying that any of you guys have said so, but if epoxy was as great as some people have made it out to be, I would have bought a rotten 40+ Constellation for next to nothing, a 55 gal barrel of epoxy and the hardener, coated everything, launched it, and it would have been stronger and leak less than when it was new.

I like technology and modern materials but the old building methods worked fairly well

 

In most situations, repairs and restorations doesn't employ epoxy encapsulation techniques. This is simply because you can't fully encapsulate, without removing and coating each piece separately. There's a standing, unwritten rule in repairs and restoration "build to the work". This means you don't make it prettier, stronger or longer lived, just do as well as what you've got. Nothing looks worse than a repair or restoration where you can see the repair areas or restored parts and they look different of better then the remaining stuff. This phrase also means don't screw with well enough. In other words, if you have a boat that's survived a half a century, without a drop of epoxy, you can probably restore it without a drop of epoxy. This said, epoxy can be a time saver, a superior adhesive and a water proofer, so evaluate the separate situations on the boat and use epoxy where you can, but you don't have to get married to it. Typically what this means is very limited encapsulation, except on pieces you've made new as replacements, though you may find as a glue it's wonderful.

 

A lot of good advise here. Keep in mind F14 that coating with epoxy really doesn't use that much resin. I've found in my work that fiberglass layups and making fillets at inside corners are the procedures that really drive the epoxy use up. If you decide to use tongue and groove methods to join structural members that will gobble up resin too but boy does it make for a strong structure.

I'm confident that my boat will long outlive me but I've spent a few good years building that I might have had to actually use the boat. Who knows how long their health will hold up well?

It's a judgement call.

MIA

 

Thanks PAR and MIA. I like the idea of keeping it "true in spirit" or however you want to say it.

I would like to bond and tab things when the cabin structure gets reassembled...I want things to be pretty rigid

 

Don't be tempted to "bond and tab" things unless you're fully encapsulating the wooden elements. This will cause point loading and prevent neighboring structural elements from helping absorb strains and load transfers, in a traditionally built (no encapsulation) wooden structure. Simply put, if you freeze things down with goo, without disassembly and encapsulation, you often end up with a bunch of localized hard points, which tends to break things. These structures actually depend on neighboring parts sharing some of the load transmissions in traditional structures. If they're isolated with a hard plastic bond, stuff breaks.

 

PAR: I think I know what you're talking about. Would it be bad for me to do something like tab the cabin sole to the sides of the hull?