Fiberglass patching--resizing a hole

SteveSgt

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I have interior lithium batteries, so I don't believe I need the two battery vents (unless I move to Canada). I have a modification plan to replace those vents with a connector panel for WiFi, Ethernet, ham radio, and AM/FM/TV.

E21C battery vents.jpg

The best hatch I've found is about 0.75" smaller than the opening for the two battery vents. So I will have to enlarge the width of the hole, and somehow patch the fiberglass to reduce the height of the hole.

Question #1: How would you fill a 2"W by 0.75"H bottom edge of a round hole? I think I can hide it behind the flange of the new hatch, but I need something to screw-into and something to seal to. I'm prepared to climb the fiberglass and gelcoat learning curve if that's my only option, but I thought perhaps I could do something like epoxy-in a carefully carved piece of white 1/4" ABS plastic.

Question $2: What tool would you use to enlarge the hole horizontally? I have hack saws and I have a very old jigsaw. I also have a Dremmel router and grinder. Or do I need something else?

I'm thinking I would also epoxy a couple of strips of 1"x2" wood to give something sturdy to screw the hatch into two sides of the hull.

What would the experts do?
 
Keep looking

You may be able to find a more suitable hatch. Defender Marine & West Marine come to mind as online suppliers of hatches. McMaster-Carr is a site worth looking in. Check their sources to go to the manufacturers websites. I'd start there.

The problem with epoxy attachment in your installation is inability to clamp. Using butyl tape on the hatch flange and the supplied holes in the flange, with pop rivets or S.S. screws & nylock nuts would likely be sufficient.

Just my 2 cents here.
 
Yup…keep looking

That is way to much work when I am sure there is something else out there.
Here is one on Amazon.ca 8.5 x 8 that has the mini hole hatch to feed your cables out but keeps the main door closed. One less connection if you just shove your cables inside.
Probably much cheaper in US$.
 

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That is way too much work when I am sure there is something else out there.
Here is one on Amazon.ca 8.5 x 8 that has the mini hole hatch to feed your cables out but keeps the main door closed. One less connection if you just shove your cables inside.
Probably much cheaper in US$.

What I like about the one I found is that it's a recessed box, so there's actually no opportunity for moisture, airflow, or insects to get between the inside and the outside. All of my connectors would be weatherproof.

If I used a larger hatch that did not have an enclosed box, then I would want to build some kind of box or panel behind the hatch and seal it just as well.

But point taken that I should keep looking for a better hatch or panel.
 
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If you mount the hatch with the hinge at the top (portrait vs landscape orientation) would you still need to create a 'filler strip'?

Yes. In portrait orientation, the flanges would just cover the two 2.625" diameter vent holes, but leave me barely any surface to put the weatherstrip (butyl) tape against, and nothing to screw two of the mounting screws (either the top or the bottom) into.
 
Yes. In portrait orientation, the flanges would just cover the two 2.625" diameter vent holes, but leave me barely any surface to put the weatherstrip (butyl) tape against, and nothing to screw two of the mounting screws (either the top or the bottom) into.
Then I'd go 'portrait' and work on solutions for the 'structure' that would be invisible to the outside, avoiding the tedium of crafting an aesthetically acceptable shell-patch.

IMO you're on the right track with the notion of wood 'strips' inside the shell for receiving the hatch mounting screws, but expand that idea to a four-sided 'frame'. If that frame is made just large enough to pass the recessed 'box', then that will 'back' the holes in the shell that are hidden under the hatch flange and you can build-up that shell-thickness-gap with wood, JB weld, or whatever.

It might be 'ugly' but it'll be hidden under the hatch flange, provide a level surface for your weatherstrip contact, and your hatch fasteners will be through-and-through into the wooden backing frame inside the shell.

Just for your consideration, Have Fun!
 
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Enlarge your flange

The builders big box stores carry sheets of white fiberglass, plastic sheets, etc. You could make a one piece larger flange to insert into and on your box flange to extend it. A rectangle of material with a rectangular hole in it to fit your box.

The marine hatches are waterproof. No need for a recessed container to provide watertightness. Unless you expect a lot of weight or stress, an internal frame doesn't seem necessary. One won't hurt, for sure, but does not seem required.
 
The builders big box stores carry sheets of white fiberglass, plastic sheets, etc.

Do you mean something like this White Fiberglass Reinforced Plastic (FRP) Wall Panel?

I hope I don't have to buy 32-sq-ft in order to get 1-sq-ft.

The marine hatches are waterproof. No need for a recessed container to provide watertightness. Unless you expect a lot of weight or stress, an internal frame doesn't seem necessary. One won't hurt, for sure, but does not seem required.

They're only waterproof (or bug-proof) when they're closed. I intend to hook three or four cables up to them and then leave them open while I'm parked for a week or two.

As far as stress goes, it'll be at least as much as a full and pressurized fresh water hose.
 
Yes

I was thinking of a similar plastic as the FRP you linked to.
There are plastic supply houses. They may have a small piece. They also do fabrication, and can cut to your dimensioned drawing.
You could buy a small piece at the big box store of ABS, PC or other material. Cut and paint it if it not white. A heat gun could shape some if there is a curve.
McMaster-Carr has small plastic panels. I've got one of ABS black, maybe 18"X24".
Something is out there. The searching is the work.
 
... Unless you expect a lot of weight or stress, an internal frame doesn't seem necessary. One won't hurt, for sure, but does not seem required.
In undertaking a range of mods on my 5.0 the only things I've found that are screwed into the fiberglass shell are the tail lights and license plate bracket. Both of those items were basically held in place by the adhesive / sealant used by ETI, the screw holes directly into the fiberglass shell were essentially 'stripped'. Everything else seems to be screwed into a wood backer piece inside the shell or use an inside metal 'clamp trim' for holding fasteners.

Maybe not "required" but I highly recommend that anything fastened to the shell be either:
  • Through-bolted with backing washers and nuts; or,
  • Screwed into a wood-backer inside the shell.
.... just in the interest of long-term robust integrity and water-tightness in the face of miles of road vibrations.

As always, just for your consideration, have Fun!
 
I moved the cover plate that was setup by Escape for my cellphone booster cable over to replace one of the vents-useless anyway as the incorrect wire for a booster is used.
I did drill it out some to allow for a removable extension cord to go through.
The Home Depot cap fits the inside of the vent perfectly. I like to stuff insulation in it when not in use, and also around the wire when in use.
I did update the cellphone booster wire cover.
 

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I posted: "Unless you expect a lot of weight or stress, an internal frame doesn't seem necessary. One won't hurt, for sure, but does not seem required."

Screws with nyloc nuts, backing washers, all of stainless steel, are certainly one way.

There are expanding pop rivets for thin materials that do not need a backing washer. They expand like a moly used to hang heavy items on the wall and develop a wide toggle holding surface. They come in various sizes and lengths. They would hold an item if access to reach & tighten interior nuts is an issue. And sealant, which is an option to increase fastening strength, is another adjunct to add to holding power.

There's always a Plan B somewhere out there.
 
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Yes. In portrait orientation, the flanges would just cover the two 2.625" diameter vent holes, but leave me barely any surface to put the weatherstrip (butyl) tape against, and nothing to screw two of the mounting screws (either the top or the bottom) into.


Are your vent holes only 2.625" diameter? I'm asking because when I replaced the vents on my 21C, I found the vent holes were very close to 3.0" inches. In fact, I was able to enlarge the holes to the full 3.0" inches by just sanding around the edges.


(FWIW, i wasn't doing what you are doing - I was installing bilge blower vents for my inverter/charger cooling system)
 
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Are your vent holes only 2.625" diameter? I'm asking because when I replaced the vents on my 21C, I found the vent holes were very close to 3.0" inches. In fact, I was able to enlarge the holes to the full 3.0" inches by just sanding around the edges)

My holes may well be closer to 3" diameter. I cannot get close enough to them from the inside to measure until I move the battery box. I'm not going to remove them from the outside until I'm confident that I have all of the parts and materials in hand.

If they are 3 inch holes, then I may have to patch both the bottom and the top of the holes, but I still think the hatch flange will completely cover both of the holes.

The next things I have to do is figure out:

  1. The hole pattern to mount the connectors in the new hatch, and whether I want a sheet of aluminum (for shield and grounding) riveted to the inside of the hatch box.
  2. What cutting, sawing, and/or grinding tool(s) I should use to enlarge the hole in the horizontal direction.
  3. What tool and/or chemical I need to clean the sealant from underneath the existing vents.
  4. What kind of patch I will use to reduce the hole size vertically. I'm leaning toward a layer of Marine Rx Epoxy Repair between a piece of 1"x2" wood interior framing (epoxied to the interior fiberglass), and the hatch flange.
  5. What kind of sealant I should use around the flange of the new hatch. Something similar to what ETI uses, I hope. And NOT silicone rubber.
  6. What else haven't I thought about that will cause extra grief once I get everything apart?
 
About ready to do this...

I'm about to install the connector panel mentioned at the top of this thread in place of the battery vents.

Comm panel v2 labeled.png

As I wrote a couple of months ago...

The next things I have to do is figure out:

  1. What cutting, sawing, and/or grinding tool(s) I should use to enlarge the hole? Would a manual hacksaw work, or a small jigsaw blade of some kind, a Dremel router bit, or do I have to buy something else?
  2. Can I use a regular drill bit in the fiberglass, or do I need something special?
  3. What tool and/or chemical do I need to clean the sealant off from underneath the existing vents?
  4. What kind of patch should I use to reduce the hole size vertically? I'm leaning toward a layer of Marine Rx Epoxy Repair between a piece of 1"x2" wood interior framing (epoxied to the interior fiberglass), and the hatch flange.
  5. What kind of sealant I should use around the flange of the new hatch. Something similar to what ETI uses, I hope. And NOT silicone rubber.
  6. What else haven't I thought about that will cause extra grief once I get everything apart?

Before I dive into this, do any of you who have cut new holes in your trailer have answers to or recommendations for any of these questions?
 
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Before I dive into this, do any of you who have cut new holes in your trailer have answers to or recommendations for any of these questions?

I seem to recall some wisdom to the effect that you should stay with polyester resin and not use epoxy resin for the patch. I don’t recall why but expect it’s searchable, and/or someone else will chime in here.

Cutting fiberglass is messy. Fine tools to reduce tearing and appropriate PPE are in order.

That’s all I got.
 
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1. All 3 work. Fine tooth metal cutting blade if using the jig saw is safer, less chance of chips.

2. A twist drill works fine up to a point. Up to 1/4", just drill, small pilot hole first is best. Over 1/4" just work your way up. Don't try something large without working your way up to it. A hole saw works well. You can run it in reverse to start a groove, lessens the chance of chips.

3. Acetone is my go-to for cleaning but alcohol does a pretty good job. If you're going to bond something to the surface a wipe with sandpaper gives more tooth but it's not absolutely necessary.

4. Your plan to epoxy a wood backing on sounds fine. I'm the one who always says not to use epoxy on gelcoat repairs but that doesn't apply for your application.

5. Pretty much any sealant will work. My go-to is usually polyurethane.

6. If I knew what might cause you grief it'd mean that I'd also know what's going to cause me grief in my mods. :) There can be an unexpected bobble but that's doing mods, deal with it and move on.

Good luck

Ron
 
Thanks Ron, for sharing the benefit of your experience.

1. All 3 work. Fine tooth metal cutting blade if using the jig saw is safer, less chance of chips.

:thumb:

2. A twist drill works fine up to a point. Up to 1/4", just drill, small pilot hole first is best. Over 1/4" just work your way up. Don't try something large without working your way up to it. A hole saw works well. You can run it in reverse to start a groove, lessens the chance of chips.

I don't plan to drill anything larger than a hole for a #8 screw. So no problem.

3. Acetone is my go-to for cleaning but alcohol does a pretty good job. If you're going to bond something to the surface a wipe with sandpaper gives more tooth but it's not absolutely necessary.

Really good to know.

4. Your plan to epoxy a wood backing on sounds fine. I'm the one who always says not to use epoxy on gelcoat repairs but that doesn't apply for your application.

I wouldn't mind a more flexible adhesive if anyone has a recommendation. I don't know what might stick the pine 1x2 more or less permanently to the inside of the fiberglass hull.

5. Pretty much any sealant will work. My go-to is usually polyurethane.

Do you know what it is that ETI uses around hatches, lights, and such?

6. If I knew what might cause you grief it'd mean that I'd also know what's going to cause me grief in my mods. :) There can be an unexpected bobble but that's doing mods, deal with it and move on.

If I plan to avoid the "obvious" newbie mistakes, I'll be far ahead of the game.

Thanks again, Ron.
 
I don't plan to drill anything larger than a hole for a #8 screw. So no problem.

If I plan to avoid the "obvious" newbie mistakes, I'll be far ahead of the game.

You're welcome. There's one newbie mistake you can avoid. Drilling a pilot hole in f.g. isn't the same as drilling one in wood.

For a #8 screw in a soft wood you might drill an 1/8" pilot hole. In f.g. that would lead to a world of hurt. A snapped off screw is nasty to deal with.

Use a 9/64" drill bit. If you hold it next to the screw you might think that it's too large but it will still have lots of bite and you'll still feel some resistance.

Ron
 

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