Drill bit type for drilling +1" cored deck

[jclays]

I will be drilling 4-1" holes thru my cored foredeck on my Mainship 350 In order to install a mooring bit/Sampson post.
What style/type bit would you guys who have drilled fiberglass decks before would recommend? I have hole saw, standard style drill bit, Forstner bit, and spade bit. The hole will be 1" in diameter and +/- 1" deep.
Thanks
Jim

 

[Cigatoo]

I will be drilling 4-1" holes thru my cored foredeck on my Mainship 350 In order to install a mooring bit/Sampson post.
What style/type bit would you guys who have drilled fiberglass decks before would recommend? I have hole saw, standard style drill bit, Forstner bit, and spade bit. The hole will be 1" in diameter and +/- 1" deep.
Thanks
Jim

 

[KnotYet]

The 1" hole saw would be my first choice, maybe drilling the guide hole first.
Use the slower speed if you have a choice.

 

[CharlieO.]

I used a 1" spade when drilling into my keel, worked fine until I hit the concrete.

 

[Eagle Pursuit]

I would use a hole saw with a center guide bit. Start the project by making the area of each hole. Then begin your drilling and stop just before the teeth of the hole saw hit the deck. Reverse the drill and score the deck going backwards to create a groove in the deck to prevent chipping off the deck outside your new hole. Then drill in the forward direction until the center guide drill comes out the bottom. Now finish the hole from the bottom. This will allow the hole saw to complete the hole through a thick deck.

 

[Cigatoo]

I am going to complicate things a bit. Here goes......
I think a hole saw might work best.
First I would drill a 1 1/2 or 2 inch hole through the top layer of glass, down through the core, and down to but not through the bottom layer of glass. Fill that hole with thickened epoxy and let the epoxy cure. Then drill the necessary 1" hole (with maybe a spade bit) through the epoxy. Do this for each hole. The epoxy will seal the core so that if you should have a leak the core will not become compromised.

 

[CharlieO.]

I think Eagle has given the best method to get a clean hole on both sides

 

[rslifkin]

I would use a hole saw with a center guide bit. Start the project by making the area of each hole. Then begin your drilling and stop just before the teeth of the hole saw hit the deck. Reverse the drill and score the deck going backwards to create a groove in the deck to prevent chipping off the deck outside your new hole. Then drill in the forward direction until the center guide drill comes out the bottom. Now finish the hole from the bottom. This will allow the hole saw to complete the hole through a thick deck.

I am going to complicate things a bit. Here goes......
I think a hole saw might work best.
First I would drill a 1 1/2 or 2 inch hole through the top layer of glass, down through the core, and down to but not through the bottom layer of glass. Fill that hole with thickened epoxy and let the epoxy cure. Then drill the necessary 1" hole (with maybe a spade bit) through the epoxy. Do this for each hole. The epoxy will seal the core so that if you should have a leak the core will not become compromised.

Seconded on both counts.

 

[Bmarler]

you can also set in some gpo-3 with thickened epoxy as described by drilling through one side and the core.
i like the gpo3 as it's got great compressive strength.
use the same hole saw to make the inserts as you did for drilling out the core.

 

[Comodave]

Check marinehowto.com on how to drill mounting holes in cored decks. I would use a hole saw running in reverse to drill through the top fiberglass. Then drill through the core but do not drill through the bottom fiberglass. Pop out the core and then reef out the core around the hole. Tape the pilot hole closed under the bottom fiberglass. Then fill the holr with thickened epoxy after painting the exposed core sides with unthickened epoxy. Let the epoxy setup and then redrill the original hole. By reefing out the core and filling with thickened epoxy you will stop the fiberglass from collapsing when you tighten the bolts.

 

[jclays]

I am going to complicate things a bit. Here goes......
I think a hole saw might work best.
First I would drill a 1 1/2 or 2 inch hole through the top layer of glass, down through the core, and down to but not through the bottom layer of glass. Fill that hole with thickened epoxy and let the epoxy cure. Then drill the necessary 1" hole (with maybe a spade bit) through the epoxy. Do this for each hole. The epoxy will seal the core so that if you should have a leak the core will not become compromised.

That’s pretty much what I am doing however there is a modification. I will be inserting 7/16x14 stainless threaded inserts into the thickened epoxy instead of re-drilling. 1” holes should be sufficient for 5/8” OD inserts. I will use an Allen wrench chucked in my drill to hog our the coring so that the thickened epoxy will key into the deck.

 

[luna]

I'm not familiar with the construction details of the foredeck on you Mainship, the specs on the 7/16" SS threaded inserts that you mentioned, nor the design of the Samson Post.

That being said, I suggest you have a good think about what kind of loads a stainless insert epoxied into a 2" diameter by 2"+/- deep hole can resist.
Then think about what bond is stopping this entire epoxy column from coming up through the upper skin of the cored deck. Wouldn't that be the bond to your coring? Is the bond and the coring itself suitable for this?

The main reason to drill, hog out the coring and then fill with epoxy is so that you have a solid stack that won't compress when you tighten things down with a large backing plate.

I easily pulled the 4 bolts and their washers (no joke, washers) that anchored my 3/8" chain stop through the cored deck while trying to dislodge a stuck anchor. Pretty stupid of me eh!
It took about 30 hours of work to repair/reinforce the deck and fabricate/install a new 3 square foot underdeck backing plate, constructed from 1/2" aluminum plate c/w 3" channel stiffeners.

I now sleep well at night.

Your goal should be similar.

 

[dhays]

That’s pretty much what I am doing however there is a modification. I will be inserting 7/16x14 stainless threaded inserts into the thickened epoxy instead of re-drilling. 1” holes should be sufficient for 5/8” OD inserts. I will use an Allen wrench chucked in my drill to hog our the coring so that the thickened epoxy will key into the deck.

I think the stainless inserts are a good option for many things. However, for a Sampson post, I wouldn't trust it. I bored everyone here early in the year with my mounting chocks on my deck. I molded in thread using epoxy on an area that was blind. However, I would never attempt that on something that could potentially be faced with as much force as you are talking about.

I would drill through the deck, as Cigatoo and Commodave mentioned. Then through bolt your fitting using a large backing plate on the underside of the deck.

 

[Comodave]

Agree on the backing plate. I would either use 1/4” aluminum or G10 fiberglass. Make it large and butter it with thickened epoxy before installing it. Also the thickened epoxy will fill the low spots and account for any high spots on the bottom of the deck so you have solid contact all over the backing plate.

 

[more]

I will be drilling 4-1" holes thru my cored foredeck on my Mainship 350 In order to install a mooring bit/Sampson post.
What style/type bit would you guys who have drilled fiberglass decks before would recommend? I have hole saw, standard style drill bit, Forstner bit, and spade bit. The hole will be 1" in diameter and +/- 1" deep.
Thanks
Jim

please explain why 4 1" holes for mini 35 ft boat. you don't need more of M8 bolt for tin 35 ft boat. 1" is for m24 this bolt is ok for 200-300 ft boat under 500 tonn

or you want use Chinese PVC bolt no name

 

[rslifkin]

I agree, through bolt it with a backing plate. That's an item you want to be stronger than it should ever need to be. Save the inserts for lightly loaded hardware or areas where it's not possible to access behind.

 

[jclays]

FYI.. the reason for the inserts is there is no access to the underside of the foredeck it is sealed off by the inter shell of the cabin ceiling. I already have this planned . I am just asking advise on drill bits. Thank you.

 

[Comodave]

FYI.. the reason for the inserts is there is no access to the underside of the foredeck it is sealed off by the inter shell of the cabin ceiling. I already have this planned . I am just asking advise on drill bits. Thank you.

That is why they make saws. I would not feel comfortable without using through bolts.

 

[jclays]

Thank you Comodave. Just looking for advise on drill bits.

 

[Bonkers]

I am going to complicate things a bit. Here goes......
I think a hole saw might work best.
First I would drill a 1 1/2 or 2 inch hole through the top layer of glass, down through the core, and down to but not through the bottom layer of glass. Fill that hole with thickened epoxy and let the epoxy cure. Then drill the necessary 1" hole (with maybe a spade bit) through the epoxy. Do this for each hole. The epoxy will seal the core so that if you should have a leak the core will not become compromised.

This is how I prefer to drill cored decks, with an added step. I take the core out larger between the undrilled inside fiberglass layer and the outside fiberglass layer, with a router bit set to just skim the inner glass and then adjusted to just skim the underside of the outer glass. Hole in the top glass is smaller than the final hole, allows the router bit through, and allows the router bit side swath to remove 1/4" of core larger than the final hole. Everything is thus prepared to fill with an epoxy/cabosil/glass fiber mixture after a thin epoxy pre coat wets the hole. After cure, the final hole is drilled through.

 

[Bonkers]

This is how I prefer to drill cored decks, with an added step. I take the core out larger between the undrilled inside fiberglass layer and the outside fiberglass layer, with a router bit set to just skim the inner glass and then adjusted to just skim the underside of the outer glass. Hole in the top glass is smaller than the final hole, allows the router bit through, and allows the router bit side swath to remove 1/4" of core larger than the final hole. Everything is thus prepared to fill with an epoxy/cabosil/glass fiber mixture after a thin epoxy pre coat wets the hole. After cure, the final hole is drilled through.

I also back up everything with appropriate thickness and sized 5000 series aluminum plates, with rounded corners and edges.

 

[jclays]

Used 1-1/4” hole saw rear 2 base holes. 1/2” twist bit for the front 2 base holes.