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How to abandon a below water line through hull

Neil Gallagher

1984 E381
Reading the various posts on this site prompted a question. What is the recommended best practice to remove a below the water line through hull? My e381 had a generator which I removed and would like to remove the associated gear perhaps at the next haul out. I would assume an epoxy bonded backing plate then filled with epoxy fairing?
 

toddster

Curator of Broken Parts
Blogs Author
There may some diagrams in the west system how-to manual. I think you bevel out the surrounding area with a grinder and proceed to fill it in like any other fiberglass repair.
 

tenders

Innocent Bystander
You grind a 12:1 bevel around the circumference of the hole from the outside, and layer in fiberglass discs of decreasing size until the hole is filled. It can be a little bit complicated to do this when you're fighting gravity, as the glob of patch sometimes wants to slide down the hull before it's gelled. Then you fair it. I like to put a layer or two on the inside as well.
 

markvone

Sustaining Member
West Epoxyworks

Here is an article:

http://epoxyworks.com/index.php/repairing-machined-holes-in-fiberglass/

The very last example describes filling an unused thru-hull in solid 1/2" fiberglass with access from both sides.

Note that as Tenders stated you use the largest piece of fiberglass cloth first in the 12:1 beveled area (even though using small to large size pieces would seem to fit and fill the tapered area better).

The reason is the largest piece of cloth being used first has the largest bonding area to the existing fiberglass which yields a stronger repair.

Mark
 

Slick470

Member III
I filled in a hole from a decommissioned depth finder on my last haul out. I did the 12:1 trick and everything has held just fine.

A few notes:

  • when grinding out the 12:1 you have the choice to do any combination of the 12:1 from the top or the bottom. I did almost all of mine from the bottom due to access. I put a couple layers on top to seal it up though.
  • When grinding from the bottom, make sure you tape over the hole in the inside of the hull or you will get fiberglass dust everywhere inside the boat. Learned that...
  • Filling a 1/2 inch hull thickness with 10oz cloth works out to 38 layers of cloth. Which seems like a lot, because it is. (truth be told, I padded my layup with a few layers of 1708 vector ply which helped me add some thickness, still ended up with 30 or so layers though.
  • I pre-cut my circles at home and I cut more than I needed because mistakes happen.
  • I wet out my circles in a plastic plate and did a couple at a time. There was usually enough epoxy left in the plate after the previous round to get one circle wet and I didn't have to add much to get the second one wet.
  • I mixed up epoxy in small batches to keep it from cooking off while I fiddled with wetting out and applying. Even so, I kept spare cups and stir sticks handy so I could keep going in case a previous batch started to cook off.
  • Working above my head wasn't that bad and the layup never seemed to sag. Even so I supported it from below with 2x lumber that was laying around the yard once I was done with the layup to prevent it from going anywhere.
  • Disposable vinyl or nitrile gloves. Lots of them. If you do boat stuff, you should already own a large box of each anyway. Maybe even stock in the companies that make them.

In the end, it's not that hard and somewhat satisfying. Good luck.
 

markvone

Sustaining Member
Andy,

Thanks for the details. I didn't realize how many layers were needed for a 1/2 inch thick hull!

In the Epoxyworks article, the last example also describes building a 1/8 to 3/16 inch thick "puck" out of mixed epoxy of the same diameter as the hole to be filled. You dry fit this "puck" in the center of the hull laminate and bond it in with thickened epoxy, then layer glass on both sides to fill the remaining 12:1 bevel. This reduces the number of layers needed to fill a precise hole in 1/2 inch thick laminate. I didn't realize this might save close to half of the layers.

I've got an old, unused transducer that should be removed and the hole filled.

Mark
 

Slick470

Member III
Yeah, if you look at the data sheet for 10 oz cloth, which seems to be a common weight to do this sort of thing, it's only 0.013 inches thick. I did a bit of a double take when I first did the math.
 
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