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Stumble · 28-10-2015, 12:05

My work flow is always the same...

1) pilot hole from the top
2) forstner bit from behind, the size of the washer. Deep enough to remove the core
3) fill with thickened epoxy
4) duct tape hole
5) redrill mounting hole to proper size

As a FYI 'penetrating epoxies' of whatever type are junk. They will not provide a waterproof seal. Just use unthickened (neat) epoxy of the high solids type.

GrahamHO · 28-10-2015, 12:06

The way I do it is to use a small hole saw. I drill 4 mm or 5 mm pilot holes from above after marking where the fitting holes will be. Then from below I use the pilot hole as guide to drill back up with a 20 mm hole saw (or larger for larger fittings ) I only drill as far as the upper FG skin leaving that intact. Then some gentle levering with a screwdriver will pop the plug of core material out. I back fill the 20 mm hole with epoxy mix until it comes out the hole saw's pilot hole. Then a bit of gaffer or masking tape over the filling to stop it oozing out. Next day drill the fitting holes from above through the middle of the filler.

To get the fitting holes straight and square I use a cheap carpenters adjustable sliding square. Take the rule part right out and you are left with the cast right angle section. There is a groove where the rule part fitted in. Place the flat part of the square on the cabin top and your drill bit against the upstanding part close to or touching the groove while you start drilling the hole. It will drill a perfectly square, straight hole. The drill bit may scratch the square but they are cheap. Once you have drilled as far as you can, remove the square and the drill will continue as it started.

If I'm using 6 mm bolts ( app. 1/4") I drill 6.5 mm holes ( 8 mm; an 8.5 mm hole etc) and countersink the top or outside of the hole to give the sealant a bit more space. Underneath I use heavy SS penny washers under the nuts. They are available in a variety of thicknesses and diameters from an engineering supplier. Typically around 30 mm or 1,1/4" and more in OD.

U bolts are more tricky to line up. Best to use a screw adjustable divider to mark the span before you drill. If you get it a little wrong, make one or both of the holes slightly more oversize. You will likely need to grind a flat on one side of each backing washer so they fit together under a U bolt.

You don't want to fill the holes with sealant. Just a bead around the bolt under the fitting at the top. It will make a perfect seal forming a "gasket" in the countesink.
It also oozes into the top of the clearance hole. Don't put sealant in the bottom of the hole. In the unlikely event of a leak you don't want water trapped. A clearance hole makes a better seal giving the sealant some space.

I don't set my fittings in epoxy as some suggest. Just bolts, nuts and sealant as above. If you try to fill a blind hole with epoxy mix you will likely get an airlock and it won't fill properly. It needs the pilot hole to "vent" the air out.

My job today is exactly what I've written. I use a powerful battery drill as it's easier to control the speed. I have made hundreds of holes in core material this way.

ramblinrod · 28-10-2015, 12:38

Quote:

Originally Posted by Tessellate

I've read lots of guides on epoxy potting and rebedding deck hardware (Don Casey, Maine Sail / CompassMarine) and I love the idea in theory - but find it's not as simple as it sounds in practice. Maybe I'm doing something wrong?

Two issues:

- Epoxy potting in marine plywood core (in high load hardware areas) is way harder than Maine Sail made it sound. He suggests Dremeling out the coring with a Dremel #654 bit (1/4" router bit). I tried that - on the 5/16" holes for a U-Bolt - but it barely put a dent in the plywood. The wood is so hard that I wasn't able to remove much of it.

I don't want to overdrill the holes because it's better to keep the fiberglass skin. Also overdrilling a 5/16" hole (with say a 3/8" bit) can be a bit tricky - a big 3/8" or 1/2" bit is likely to bind on the existing fiberglass skin.

Maine Sail's site says 10-15 seconds of Dremeling was enough to remove plywood core. But I did 4 or 5 rounds of 10-15 seconds and only had about 1/64" removed. In some places the plywood looked kind of burnished / polished (shiny + smooth). I ran the Dremel at 1500-2000 rpm. I tried higher rpm (2500) for a second but that was worse (chattering and hard to control).

I don't think the bent nail / broken allen key trick would work any better.

This epoxy potting attempt was somewhat disappointing because I felt like it perhaps did more harm than good. Epoxy potting without removing enough core to prevent your redrill holes from exposing core is kind of pointless. I wondered if I would've been better off just rebedding the hardware and reusing the existing holes.

- Lining up the redrill hole with where it was before. How do people get perfectly aligned thrubolt holes for U-Bolts? I got the angle close to correct, but the holes were still off about 1/8" on the bottom (cabin) side. This made it hard to get the U-bolt in (and re-exposes core by going outside the epoxy pot).
The deck here is 1/4" FRP, about 3/4" plywood, then 1/8" FRP, then 1/4" foam filler (above cabin liner), then 1/8" FRP (cabin liner). So a couple degrees off on the drill can make a big difference.

In my experience undercutting core is a waste of time.

A simple and fast way to prevent future core moisture ingress is to simply:

1. Drill the hole oversize x 2 (eg. for 1/4" hole drill 1/2").
2. Tape the bottom.
3. Fill with low viscosity epoxy.
4. Redrill clearance hole for fastener (e.g. 1/4")
5. Countersink top of hole.

Deck fittings will more than cover the double sized hole skin removal (or there is not enough meat in the fitting beyond the mounting hole which is a more serious issue than covering an over-size hole).

Using a fender washer of at least twice the diameter of the oversize hole, or a backing plate on the underside, will make any loss of strength from drilling oversize, vs undercutting, negligible.

Save your time and effort, drill oversize instead of undercutting (bent nail, allen key, or dremel bit).

Ramblin Rod
www.sheenmarine.com

GrahamHO · 28-10-2015, 13:06

Quote:

Originally Posted by roverhi

The Dremel 199 bit works a treat.

As far as taping the underside before pouring in the epoxy, use a good sticky tape like duct tape. Masking tape will hot stay in position and it's a real PITA to clean the epoxy off your teak and holly cabin sole, btdt.

The blue masking tape I use stays in position. I usually use gaffer tape though.
Use a Dremel if you like or as I do, use a hole saw. To avoid a mess on the cabin sole I mask off with strips of masking tape before I drill up with a hole saw through the masking tape. You can feel the pilot hole through the masking tape. Then fill the hole and the excess goes on the drilled through masking tape. The gaffer tape goes over the whole lot. No problem. No mess.

GrahamHO · 28-10-2015, 13:22

Quote:

Originally Posted by ramblinrod

In my experience undercutting core is a waste of time.

A simple and fast way to prevent future core moisture ingress is to simply:

1. Drill the hole oversize x 2 (eg. for 1/4" hole drill 1/2").
2. Tape the bottom.
3. Fill with low viscosity epoxy.
4. Redrill clearance hole for fastener (e.g. 1/4")
5. Countersink top of hole.

Ramblin Rod
www.sheenmarine.com

An advantage of leaving as much as possible of the top skin in place is if you want to alter things later, maybe in a few years. Then you only have say a 1/4" inch hole to gel coat instead of a 1/2" hole.
That's why I drill from below with a hole saw and leave the top skin intact.

Lepke · 28-10-2015, 14:46

I think you're making too big a production out of this. I am a former shipwright, etc., and have built and repaired boats of all common materials except cement.
Almost all of the "professionally built" boats I have repaired do a good job on the hull and a lousy job when it comes to mounting to the hull. Especially stanchions. I guess there are 2 crews. One for hull and another less trained or supervised crew for finishing. Quite often when fixing loose stanchions, I found not enough bedding compound and screws driven w/o pilot holes and no other system to stop water going down the screw and into the wood/core/fiberglass.
The fast, easy, permanent way to put screws in forever without eventual leaks is to drill an oversize hole 2x or 3x bigger than the screw hole. If there is room, bevel the hole to provide a larger bonding to the deck. What ever the hardware will cover. Fill it with West epoxy mixed with high density filler. I find it easy to pour and match the deck level. If you figure the surface area of the larger hole you will have 5x or more contact area for bonding to the hull/core/wood. The high density filler also has adhesive properties. Then do a pilot hole for the screw. Usually with a syringe, I add a small amount of epoxy to the pilot hole so the screw will be coated and totally sealed within the epoxy. If you bed or not, it will not leak. Later if I have to remove the screw, I have to use a small impact driver. Use a screw with a head that doesn't slip when driving.
As a shipwright or a marine service I mostly did commercial boats, back when the majority were wood and seeing rough service. But I also did many repairs to cored fiberglass where the original hardware seal had failed.
If you have core to remove, use a round fluted cutter (like a ball on a shaft, often used in steel machining) the same size as the bigger hole. With a long shank or shank extension you can go thru the hole at an angle and work your way around and carve out a fairly large void. With some effort you can vacuum the debris out. If it's dry, you don't have to get every piece since the epoxy will bond it in.
To do a horizontal hole, cover it with a piece of duct tape. Cut a small slit and fill with a syringe until you see a slight bulge in the tape. Have a 2nd piece of tape handy and cover the slit as you withdraw the syringe. After that it's the same as a vertical hole.
I use this method for any hardware that doesn't occasionally get removed. Including windlasses, etc. Just bigger holes and bolts.
I'm 67 now, but when I was young and working for wages, I could do all the stanchions on a 35' sailboat in a day unless there was core drying time involved. To dry the core, I used DRY compressed air going thru a copper tube about 2/3 the size of the bigger hole with the air at about 5psi. Usually I had to setup a manifold so I could do many holes at once. It usually took a day or two to completely dry really wet balsa core.
I've never had a loose stanchion come back. The only issue I've ever had is getting the new screws out to do other changes.
A Dremel is too small. I have one I haven't used in decades. I've used many resins, and there are good ones out there, but every time I go away from West Systems I am not happy with some aspect of the job. I won't use polyester resin for anything.

GrahamHO · 28-10-2015, 14:58

Quote:

Originally Posted by Lepke

I think you're making too big a production out of this. I am a former shipwright, etc., and have built and repaired boats of all common materials except cement.
Almost all of the "professionally built" boats I have repaired do a good job on the hull and a lousy job when it comes to mounting to the hull. Especially stanchions. I guess there are 2 crews. One for hull and another less trained or supervised crew for finishing. Quite often when fixing loose stanchions, I found not enough bedding compound and screws driven w/o pilot holes and no other system to stop water going down the screw and into the wood/core/fiberglass.
The fast, easy, permanent way to put screws in forever without eventual leaks is to drill an oversize hole 2x or 3x bigger than the screw hole. If there is room, bevel the hole to provide a larger bonding to the deck. What ever the hardware will cover. Fill it with West epoxy mixed with high density filler. I find it easy to pour and match the deck level. If you figure the surface area of the larger hole you will have 5x or more contact area for bonding to the hull/core/wood. The high density filler also has adhesive properties. Then do a pilot hole for the screw. Usually with a syringe, I add a small amount of epoxy to the pilot hole so the screw will be coated and totally sealed within the epoxy. If you bed or not, it will not leak. Later if I have to remove the screw, I have to use a small impact driver. Use a screw with a head that doesn't slip when driving.
As a shipwright or a marine service I mostly did commercial boats, back when the majority were wood and seeing rough service. But I also did many repairs to cored fiberglass where the original hardware seal had failed.
If you have core to remove, use a round fluted cutter (like a ball on a shaft, often used in steel machining) the same size as the bigger hole. With a long shank or shank extension you can go thru the hole at an angle and work your way around and carve out a fairly large void. With some effort you can vacuum the debris out. If it's dry, you don't have to get every piece since the epoxy will bond it in.
To do a horizontal hole, cover it with a piece of duct tape. Cut a small slit and fill with a syringe until you see a slight bulge in the tape. Have a 2nd piece of tape handy and cover the slit as you withdraw the syringe. After that it's the same as a vertical hole.
I use this method for any hardware that doesn't occasionally get removed. Including windlasses, etc. Just bigger holes and bolts.
I'm 67 now, but when I was young and working for wages, I could do all the stanchions on a 35' sailboat in a day unless there was core drying time involved. To dry the core, I used DRY compressed air going thru a copper tube about 2/3 the size of the bigger hole with the air at about 5psi. Usually I had to setup a manifold so I could do many holes at once. It usually took a day or two to completely dry really wet balsa core.
I've never had a loose stanchion come back. The only issue I've ever had is getting the new screws out to do other changes.
A Dremel is too small. I have one I haven't used in decades. I've used many resins, and there are good ones out there, but every time I go away from West Systems I am not happy with some aspect of the job. I won't use polyester resin for anything.

I'm not sure who's making a big production??

Nicholson58 · 28-10-2015, 17:42

I over-drill the outer skin but do not penetrate the inner. back fill with Marine Tex gray. Then drill through after the putty cures. If you want more strength then back fill with epoxy & chopped glass. You could over-lay with a circle of woven glass. Dremmel bits are pretty much junk. You can get carbide burrs with either 1/8" shanks for Dremmel or 1/4" shanks for a router or die-grinder. I used an electric panel edger for many years. Available from Harbor Freight or most hardware or lumber stores.

Follow the link for carbide burrs. The set is the way to go. Cut anything quickly with these. Note - high speed for most things. Low speed for aluminum or the bit gets gummed up with metal.
McMaster-Carr

ramblinrod · 29-10-2015, 07:47

Quote:

Originally Posted by GrahamHO

An advantage of leaving as much as possible of the top skin in place is if you want to alter things later, maybe in a few years. Then you only have say a 1/4" inch hole to gel coat instead of a 1/2" hole.
That's why I drill from below with a hole saw and leave the top skin intact.

Everyone develops their own best practices that suit them.

For me, time and materials difference to fill a 1/4" hole vs 1/2" hole = 0.

All mounting holes have to be bevelled anyway, so a 1/4" undercut mounting hole is actually 3/8" diameter on the surface anyway, so we're really talking the difference between a 3/8" and 1/2" hole.

For all gelcoat defects less than 1" diameter, I generally estimate, 3 hours for first, 1 hour for second and 1/2 hour for each additional.

So I always ask the customer who calls me to fix a dock scar, "Got any more issues, cause it's a lot cheaper to fix them while I'm here with the tools already out and the gelcoat already mixed."

To date, the most prolific boat had 54 manufacturing void and battle scar defects to be repaired. (This was just fill and far as the customer was painting after completion, so it ended being about half the labour of a true gelcoat job that would require pinhole touch ups, blending, and polishing.)

Oh, another issue, when undercutting, the skin is often so thin, that there is very little meat left in it when bevelled. So the argument that the outer skin adds strength just doesn't wash with me.

To each there own; just know that there are differing opinions on best practice tempered with practical issues. Consider the options, try various methods, and use what works best for you.

Ramblin Rod
www.sheenmarine.com

UNCIVILIZED · 29-10-2015, 08:41

There's a KISS solution to this.

Drill an oversized hole from below, Through both the inner glass skin AND the Core.
Tape over the hole from below, & fill the hole with epoxy.
Drill your new epoxy plug for the fitting.
BOND the backing plate to the deck underneath. It'll more than make up for the missing skin, strength wise.
Bed the new fastener in place.

And if you're good, several of these steps can be compressed into one shot.

PS: If the hole is going to be a size of any significance, mix the epoxy with some chopped or milled fibers. They both thicken, & strengthen the resin. Making for a better quality plug.
Also, there are a menagerie of other ways to do this.

GrahamHO · 29-10-2015, 11:40

Quote:

Originally Posted by ramblinrod

Everyone develops their own best practices that suit them.

For me, time and materials difference to fill a 1/4" hole vs 1/2" hole = 0.

All mounting holes have to be bevelled anyway, so a 1/4" undercut mounting hole is actually 3/8" diameter on the surface anyway, so we're really talking the difference between a 3/8" and 1/2" hole.

For all gelcoat defects less than 1" diameter, I generally estimate, 3 hours for first, 1 hour for second and 1/2 hour for each additional.

So I always ask the customer who calls me to fix a dock scar, "Got any more issues, cause it's a lot cheaper to fix them while I'm here with the tools already out and the gelcoat already mixed."

To date, the most prolific boat had 54 manufacturing void and battle scar defects to be repaired. (This was just fill and far as the customer was painting after completion, so it ended being about half the labour of a true gelcoat job that would require pinhole touch ups, blending, and polishing.)

Oh, another issue, when undercutting, the skin is often so thin, that there is very little meat left in it when bevelled. So the argument that the outer skin adds strength just doesn't wash with me.

To each there own; just know that there are differing opinions on best practice tempered with practical issues. Consider the options, try various methods, and use what works best for you.

Ramblin Rod
www.sheenmarine.com

Yes indeed we do our own thing. A busy professional is always trying to save time and money. As you say yourself you have had to repair work done by other professionals.

I do think that drilling a 1/4" clearance hole in a 1/2" column of epoxy, and then countersinking (as you should) it is not leaving very much epoxy around the perimeter at the top of the hole. There is quite a compression load from the bolt being tightened as you would find out if you left your thumb under the washer.

I have never considered that the top skin adds much strength but l like to have generally a 20 mm / 25 mm column of epoxy and I don't like to take that through the top skin.

A (good quality) hole saw makes very little dust to vacuum away. It does take a little more time perhaps and uses more epoxy, so your charge out will be higher and another boat builder might undercut your quote.

As for bonding fittings into foam core glass, I have seen that done by a professional and it didn't work. Do you also bond in a backing plate or heavy washer? OK as the Gougeon Brothers suggest into timber construction. If it does work for a professional, he or she is not concerned about the owner later wanting to alter or replace things, as the professional has moved on to another job.

I know the fittings can be removed by heating with a large soldering iron but I'd rather undo a nut.

UNCIVILIZED · 30-10-2015, 14:28

Quote:

Originally Posted by GrahamHO

I do think that drilling a 1/4" clearance hole in a 1/2" column of epoxy, and then countersinking (as you should) it is not leaving very much epoxy around the perimeter at the top of the hole. There is quite a compression load from the bolt being tightened as you would find out if you left your thumb under the washer.

On this one, I definitely have to concur. Odds are you'll put cracks in/rupture the epoxy's seal the first time you put a wrench onto the nut in such a scenario. You'd be better off going with a 3/4" hole, & filling it with epoxy mixed with chopped, or milled (glass) fibers.

As for bonding fittings into foam core glass, I have seen that done by a professional and it didn't work. Do you also bond in a backing plate or heavy washer? OK as the Gougeon Brothers suggest into timber construction. If it does work for a professional, he or she is not concerned about the owner later wanting to alter or replace things, as the professional has moved on to another job.

I know the fittings can be removed by heating with a large soldering iron but I'd rather undo a nut.

For bonding into foam, you're going to have to go larger than "standard" on the plugs. And either go with an epoxy, milled/chopped fiber mix. Or some G10 plugs, bonded from underneath, to the top skin.
And then, on both, bonded backing plates are part of the "recipe". Be they Aluminum, G10, or DIY G10. Also, these backers will likely need to be a touch bigger than "normal" as well.

Although, if you want to get technical abour things, it really depends on the physical characteristics of the foam in the area which you're working in. As some of them have higher sheer & compression numbers than balsa or plywood. And get used in lieu of wooden cores, given that, coupled with their being lighter (than wood).

GrahamHO · 30-10-2015, 15:29

Quote:

Originally Posted by UNCIVILIZED

For bonding into foam, you're going to have to go larger than "standard" on the plugs. And either go with an epoxy, milled/chopped fiber mix. Or some G10 plugs, bonded from underneath, to the top skin.
And then, on both, bonded backing plates are part of the "recipe". Be they Aluminum, G10, or DIY G10. Also, these backers will likely need to be a touch bigger than "normal" as well.

Although, if you want to get technical abour things, it really depends on the physical characteristics of the foam in the area which you're working in. As some of them have higher sheer & compression numbers than balsa or plywood. And get used in lieu of wooden cores, given that, coupuled with their being lighter (than wood).

Sure; that's right. At the moment I haven't got time to get technical about things. I've got some balsa core laminates curing that I need to get practical about, that I'm fabricating some components out of.