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Old 02-02-2014, 10:20   #31
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Re: Plywood for core

Glassed.
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Old 02-02-2014, 10:20   #32
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Re: Plywood for core

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Originally Posted by bletso View Post
No marine ply, in addition to the glues, has no voids between the layers. Regular exterior or interior ply can have some rather large voids between the layers. Here is a site which has some info. Marine Plywood by Homestead - Douglas Fir

Some technical specs can be found at Boat Builder Central - Help

You should certainly be able to source marine ply in your area or up in Houston.
Yes I understand that, but it's the same glue and the same wood..albeit with a few voids. For coring I cant see much problem.
I definitely wouldnt put some exotic expensive marine ply as coring (does anyone know a builder who did that?) And yes those exotic plys fail in water saturation. I know, I put a small square piece (less than 12x12) of bruynzeel mahogany that was 3/4"+ thick under the jack on my runabout last year. But the following summer it was coming apart!
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Old 02-02-2014, 10:22   #33
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Re: Plywood for core

Green trim the edge and pull peel ply.
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Old 02-02-2014, 10:25   #34
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Re: Plywood for core

Then flip em and glass the bottom. Wrap edges with the bottom lam. Only matts and boat cloth will go around this small a radius.
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Old 02-02-2014, 10:27   #35
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Re: Plywood for core

Rough sand and check fit.
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Old 02-02-2014, 10:29   #36
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Re: Plywood for core

I'll go through the rest of the process later, my paint is now dry enough for recoat. Stuff to do!


You can do curved hatches like this too, but it's trickier.



These hatches come out weighing less than half as much as the originals, very strong, will not warp or rot. And less likely to mash yer fingers!
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Old 02-02-2014, 10:48   #37
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Re: Plywood for core

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Coosa will tell you you can tap into it, and you can. But it ain't wood. Higher torque settings on a cordless clutch may strip out your tap, and due to the friability of foam I don't trust a fastener done that way to last through repeated load cycles. I would not tap fasteners into chopped strand and cabosil either. Too brittle. G10, however, is excellent for tapping. Just make sure to start with a regular tap and finish with a bottoming tap.
Yes, tapping for machine screws is a whole different story, but I was asking about screwing things into it - wood/metal screws and not bolts or machine screws. I also wouldn't tap chopped strand and cabosil. I'm doing something similar right now, but I'm glassing in 1/4" SS plates for tapping.

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Old 02-02-2014, 10:54   #38
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Re: Plywood for core

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First, throw the original hatches away. They are usually warped, cracked, poorly built and poorly fitted. More trouble than they are worth.
Give Raindog a break! If he has 1/4" skins, it is likely his hatches are in good condition and, being a Pacific Seacraft, very likely well-built and fitted. Your point about lighter weight and less likely to slam hard is very good, but I wouldn't throw away a perfectly good hatch needing a few dollars in materials and a couple of hours of time to go for a much more expensive and time-consuming solution.

Cutting out the bottom skin, recoring and glassing the skin back on is not very difficult and all that is needed if the skins are in good shape.

I just did this to a bow seat and it was easy (and inexpensive).

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Old 02-02-2014, 11:08   #39
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Re: Plywood for core

Minaret,

Great information and pictures. I've used Coosa BW26 for deck lids, bulkheads, etc. with additional biaxial cloth/matte medium weight applied to both sides using West epoxy. I have found that Coosa is not adequate for screws/through bolting unless the holes have been cored well oversize and filled with a hardware-focused filler. Moreover with cloth on both sides, properly prepared hardware holes can adequately support a backing plate if necessary.

I have some Coosa board pieces as they were delivered that have been exposed to weather for several years and have no obvious damage or indication of water saturation. I should have weighed them; next time I get back to the boat, I'll do a comparison with my moisture meter.

Great Stuff.

Roger
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Old 02-02-2014, 11:35   #40
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Re: Plywood for core

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Give Raindog a break! If he has 1/4" skins, it is likely his hatches are in good condition and, being a Pacific Seacraft, very likely well-built and fitted. Your point about lighter weight and less likely to slam hard is very good, but I wouldn't throw away a perfectly good hatch needing a few dollars in materials and a couple of hours of time to go for a much more expensive and time-consuming solution.

Cutting out the bottom skin, recoring and glassing the skin back on is not very difficult and all that is needed if the skins are in good shape.

I just did this to a bow seat and it was easy (and inexpensive).

Mark

We all have our own definition of well built and well fitted. But yes, if your hatches look nice and fit great, but just have rotten core, recoring is fast and easy. It's just that its been my experience that by the time I get a hatch with rotten core, it has usually been that way for quite some time. This often leads to lots of stress fractures in the skins, warping, poor fit, etc. I have started over from new much more often than working with materials that are already damaged and fatigued.

I also have found that the usual reason for rotten hatches is poor fit in the first place. The way I build them, they sit dead flat on the hatch coaming all the way around, perfect fit with no rocking. This means when you sit on them the entire load is transferred to the coaming, not the hinge. An imperfect fit loads the hinge, leading to failure of bedding and fasteners. About 90% of the hatches I take apart are built like that. It makes a huge difference.
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Old 02-02-2014, 11:42   #41
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Re: Plywood for core

Quote:
Originally Posted by colemj View Post
Yes, tapping for machine screws is a whole different story, but I was asking about screwing things into it - wood/metal screws and not bolts or machine screws. I also wouldn't tap chopped strand and cabosil. I'm doing something similar right now, but I'm glassing in 1/4" SS plates for tapping.

Mark
If you screw a wood screw (even self tapping) into a fiberglass product without tapping, you are likely to fracture the skins. The whole process is much easier and less likely to damage something if you tap first. I am not talking about machine screws. Careful selection of pilot hole size and clear hole size is also crucial.


Glassing in plates works well. I often do it for motor mounts when rebuilding large engine beds. I prefer G10 above deck, due to potential for corrosion if water penetration occurs (again).
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Old 02-02-2014, 11:51   #42
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Re: Plywood for core

Easy way to tell if a hatch fits-take off the hinges and put it in place. Shim to make sure the gap is even all around. If the hatch sits perfectly flush and fair to the surrounding surface (use a batten or straight edge), with zero rocking or wobbling, it's a well fitted hatch with no warp. If not, rebuild that sucker if you want it to really last!

No, you are not allowed to do this with rubber or weatherstrip in place.
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Old 02-02-2014, 12:17   #43
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Re: Plywood for core

Quote:
Originally Posted by colemj View Post
Give Raindog a break! If he has 1/4" skins, it is likely his hatches are in good condition and, being a Pacific Seacraft, very likely well-built and fitted. Your point about lighter weight and less likely to slam hard is very good, but I wouldn't throw away a perfectly good hatch needing a few dollars in materials and a couple of hours of time to go for a much more expensive and time-consuming solution.
Indeed the hatch is in good shape and fits very well except for the core saturation. Ocean Girl will upload a picture, but I think I will take Minarets advice and use Coosa. Once i remove the bottom skin and get it really well cleaned my plan was as follows. Let me know if my plan is bad:

- grind/sand edges of existing fiberglass to taper edges
- Clean with acetone
- Lay down a bed of slightly thickended epoxy
- Put the coosa core in. let epoxy cure.
- Fill an gaps around the edges with tickened expoxy. Let it cure.
- Glass over the core with 2 layers of 1708
- Primer, paint
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Old 02-02-2014, 14:37   #44
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Re: Plywood for core

Pics. The hatch is really strong. The only indication that there was any problem was the play in the hinges. The is no spongy feeling standing on them even with the core so mushy.

I can only post one pic at a time, three more to come.
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Old 02-02-2014, 14:41   #45
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Re: Plywood for core

More pics
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