Screw Hole repair in Plywood Bottom

[kwinsor]

1959 Penn Yan Magellan
Lapstrake side and Plywood Bottom

Hello all,

My Penn Yan is generally in good shape. However, I have about 8 screws that are loose or have fallen out of the bottom of the plywood up through the keelson / ribs.

It's not as simple as reinserting the screws because heads have either pulled through the plywood and / or rotted out and enlarged the holes.

I have taken an ice pick and poked the plywood searching for rot and it's structurally fine.

I just have the areas around the screw heads that need repair.

Any advice would be appreciated.

Ken

[Lewisboats]

bore out the holes, fill completely with epoxy, let cure then drill the centers and reinstall new screws...this will seal all the edge grain of the ply surrounding the screw shafts This is the best way...second best is bigger screws.

[James McMullen]

Agree. Use epoxy properly thickened with fibers if it's a biggish sort of hole. But if your icepicking to clear out rotten bits makes a really big hole, then you should glue in a tapered bung with epoxy into a matching reamed tapered hole.

[Thorne]

Use thickened epoxy for filling, but first application should be non-thickened and possibly heated to maximize penetration.

[Canoeyawl]

Replace them with carriage bolts.

[boylesboats]

clean out the screw holes first.. Apply CPES, fully saturating wood fibers, then fill in with thicken epoxy.. Redrill and install new screws..

[JimD]

I would not spend money on cpes for this. As others say, fill a small hole with thickened epoxy, fill a big hole with new wood glued in place with thickened epoxy.

[RodB]

What Boylesboat said...

Everyone should keep some CPES around for such things as this... this is a perfect situation to take advantage of the capabilities of CPES. . . but... if you don't want to invest in it, then the epoxy alone will work fine. Take a look at the Gougeon Brothers Book on Boat construction... they have great illustrations on fastener installation for increased strength.

RodB

[outofthenorm]

A tip for epoxy filling: On vertical or overhead surfaces, if the stiffened epoxy wants to sag out of the hole, stuff it in, then quickly put a piece of wide masking tape over the hole, trapping the epoxy in place. When it hardens, you can easily scrape or sand off the tape and make it all come out flush. Saves having to do a second application of epoxy.

- Norm

[Thorne]

Canoeyawl has a good point, bolts may be better than screws even after the holes are filled with epoxy. What material are the existing fasteners? If the "rot" problem is actually "iron sickness" around them, you can expect to have the same issue elsewhere in the boat even if you can't see it...

[JimD]

...Everyone should keep some CPES around for such things as this. . . but... if you don't want to invest in it, then the epoxy alone will work fine.
RodB

If epoxy will work fine then why the cpes? Is it really going to do anything more for the patch? I have filled at least a hundred screw holes over many years with only thickened epoxy. They are all holding up just fine. Not even the remotest hint of a problem that could be traced to not using cpes.

[James McMullen]

The CPES cult is alive and well. . . . but I can't see any reason in this simple repair to use that stinky stuff myself. No reason to complicate things by using two different resin systems.

[stevedwyer]

One little trick for dealing with excess epoxy and excess work fairing the patch...
Use some white duck tape. The white stuff is smoother, so when you scrape off the excess, it doesn't leave ridges.
I take several short strips, stack 'em and drill a slightly oversize hole. (for several screw hole patches)
After the epoxy sets up, pull the tape and use a file, then a scraper to fair smooth.