Screws into fiberglass

[patrickkidd]

I just installed a bilge pump in a J/30 I just bought and am trying to secure the wires and bilge hose to the fiberglass. I am wondering if there are any tricks to drilling and screwing into fiberglass. I already broke a drill bit, though it may have just been low quality.

Thanks!

 

[dlochner]

Use a sharp bit. The J30 has a cored hull. Drilling into it will give water a way to enter the core. It would be safer to epoxy small blocks of wood to the hull and secure the wire and hose to those blocks.

 

[sailnoproblem]

Use a sharp bit. The J30 has a cored hull. Drilling into it will give water a way to enter the core. It would be safer to epoxy small blocks of wood to the hull and secure the wire and hose to those blocks.

 

[jaysweet]

I just installed a bilge pump in a J/30 I just bought and am trying to secure the wires and bilge hose to the fiberglass. I am wondering if there are any tricks to drilling and screwing into fiberglass. I already broke a drill bit, though it may have just been low quality.

Thanks!

In my rather limited experience, I've found drilling fiberglass to be quite easy, so perhaps your drill bit was dull (as dlochner suggested). But I have had problems getting a screw to cut threads into solid fiberglass without breaking it off. I ended up having to tap threads and use machine screws in a recent project: this worked quite well.

 

[Rich Stidger]

In my experience screws will not cut normal depth threads into fiberglass. So I use a drill that is just under a clearance dimension so that the screws will cut a shallow thread. For securing wires and such it is strong enough.

 

[Will Gilmore]

I haven't used these, but they look like a good idea.
Weld Mount - Marine Applications

No worries about chafed insulation causing corrosive contact with metal screws in bilge water.

-Will (Dragonfly)

 

[dlochner]

I haven't used these, but they look like a good idea.
Weld Mount - Marine Applications

No worries about chafed insulation causing corrosive contact with metal screws in bilge water.

-Will (Dragonfly)

I have used them and MaineSail uses them. This is a good product and solution, however they are quite pricey and the glue has a relatively short shelf life and is expensive. For just a few mounts wood and epoxy is more economical.

 

[sail sfbay]

Might see the youtube video entitled "Lumitec Minute Expert: Drilling & Screwing Fiberglass" first.

 

[patrickkidd]

I haven't used these, but they look like a good idea.
Weld Mount - Marine Applications

No worries about chafed insulation causing corrosive contact with metal screws in bilge water.

-Will (Dragonfly)

I guess the alternative is epoxy, a block of wood, and a wire tie screwed into the wood? If so, what is the advantage of this product over that?

 

[thinwater]

I guess the alternative is epoxy, a block of wood, and a wire tie screwed into the wood? If so, what is the advantage of this product over that?

Way, way stronger, and the wood won't rot. Really, do you want to use wood in the bilge?

 

[jaysweet]

Way, way stronger, and the wood won't rot. Really, do you want to use wood in the bilge?

I needed a spacer for the lower bracket on my new Groco raw water strainer, so I'm using a chunk of plywood. I happen to have some gelcoat I just used elsewhere, so I thought: what the heck, let's try it. Two coats of gelcoat on the plywood, and it's looking pretty good. I'll screw the gelcoated plywood to the engine pan (not exactly a wet bilge), and screw the lower bracket to the plywood.

 

[Will Gilmore]

I'll screw the gelcoated plywood to the engine pan (not exactly a wet bilge), and screw the lower bracket to the plywood.

Why are you using screws? Does it need the strength? I am neither for nor against screws, just seems like another step and unnecessary intrusion into the hull.

-Will (Dragonfly)

 

[quadrille38]

Just be careful. a guy I worked with popped the drill right through the the bottom of the boat when drilling to mount a bilge pump. it was thinner than he was expecting and a mini geyser erupted when he pulled the drill bit out.

 

[garymalmgren]

Use what is there.
Wire tie the wires to the bilge pump discharge hose.

gary

 

[Ken13559]

Use a sharp bit. The J30 has a cored hull. Drilling into it will give water a way to enter the core. It would be safer to epoxy small blocks of wood to the hull and secure the wire and hose to those blocks.

Good advise.
This is what I usually do to try not to screw into fibreglass. No leak passage into boat/cabin.

Ken Y

 

[jaysweet]

Why are you using screws? Does it need the strength? I am neither for nor against screws, just seems like another step and unnecessary intrusion into the hull.

-Will (Dragonfly)

(sorry to divert from the original question) Because screws cost almost nothing and they're easy to attach. This is on a vertical side wall of the engine pan (engine bay). The other side of the wall is very high up in a blind bilge. I do actually have some "marine epoxy" in one of those 2-tube injector things. When I used it on something else, I noticed that the leftover from mixing it was very brittle. Would this be better than a couple of screws?

 

[Will Gilmore]

Would this be better than a couple of screws?

Not necessarily. I was just thinking, it sounded like a fairly non-critical application with little force trying to shear it off. I wouldn't be eager to pierce the layers of glass in my hull if there were other reasonable options, but I wouldn't hesitate to do it either, if it seemed like the best way to go.

-Will (Dragonfly)

 

[Davidasailor26]

This is on a vertical side wall of the engine pan (engine bay). The other side of the wall is very high up in a blind bilge.

So not the hull itself? If that’s the case it might be solid glass rather than cored, making a plain old screw an ok choice for this low load application.

 

[dlochner]

(sorry to divert from the original question) Because screws cost almost nothing and they're easy to attach. This is on a vertical side wall of the engine pan (engine bay). The other side of the wall is very high up in a blind bilge. I do actually have some "marine epoxy" in one of those 2-tube injector things. When I used it on something else, I noticed that the leftover from mixing it was very brittle. Would this be better than a couple of screws?

In the photo you posted, everything in the bilge is wood covered by fiberglass. The hull is cored with balsa wood and the the stringers or floor timbers are wood and covered with fiberglass. Penetrating the skins on these parts would put the wood at risk of getting wet.

When you talk about the engine bay, I'm not sure which parts of it you are describing. The two longitudinal ribs that the engine sits on are most likely wood encapsulated with fiberglass.

Epoxy is very brittle, it needs fiberglass or some other thickener to make it less brittle. Thickened West System epoxy or Jamestown Distributor's Total Boat epoxy would be good choices. Both West (SixTen) and Total Boat (Thixio) make epoxy in easy to apply cartridges this would be appropriate for this application.

To @thinwater's point about wood in the bilge being a bad idea, in general he is correct and I would agree with him. However, in this case it is not a critical or structural application, so I would be less concerned about the wood. If the wood should rot, then just grind it out and put in a new piece. If you can use a rot resistant wood like white oak this would be less of an issue.

A Weldmount stud would be the most durable and most expensive option. A piece of pine glued to the side of the bilge with HW store epoxy the least durable and cheapest option. Drilling and screwing directly into the hull the worst option and one the should be avoided at all costs.

 

[jaysweet]

Not necessarily. I was just thinking, it sounded like a fairly non-critical application with little force trying to shear it off. I wouldn't be eager to pierce the layers of glass in my hull if there were other reasonable options, but I wouldn't hesitate to do it either, if it seemed like the best way to go.

-Will (Dragonfly)

Since our boat was new in 2004, I'm pretty new myself to the business of modifying / upgrading boats. It hasn't needed much up to now. So I'm glad to have advice and discussion here in the forum.

So not the hull itself? If that’s the case it might be solid glass rather than cored, making a plain old screw an ok choice for this low load application.

I did end up mounting the gelcoated chunk of plywood with 3 screws. I'm pretty sure it was into solid fiberglass with no core, and no: it's definitely not the hull. More in the next reply.

Thanks for your comments!