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Catalina/Capri 25/250 Sailor's Forums

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Dumb Question: Drilling Holes in Cabin Walls

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MartinJW
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USA
241 Posts

Initially Posted - 07/17/2008 : 22:03:44

Hello Everyone,

I've been searching here, but I can't find the exact answer to my question. (It's probably too elementary to appear here.) So, I'll lead with my chin and ask anyway.

I'm thinking about installing boat hook brackets, a fire extinguisher bracket (inside the cabin), maybe some hand holds, and possibly a couple of cam cleats - all on the top/outside of the cabin. Here's my question:

Can I simply drill holes in the fiberglass and mount these with (stainless steel) machine screws and nuts?

Do I need a special drill bit?

Is there anything I should be aware of in terms of techniques for drilling into fiberglass/Gelcoat/wood laminates?

Should I drill over-sized holes first, fill with epoxy, and then drill final holes with the desired diameter?

For very low load items, can I simply use wood or sheet metal screws?


(I do realize that I might need to use backing plates or fender washers for some of these applications.)

Any suggestions, comments, ideas?

Thanks!

Martin

C25/250 Int'l Ass'n Member
2008 C-250 WK #973
"Bluebell"
Lake Tahoe, CA/NV

Edited by - on

Nautiduck
Master Marine Consultant

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USA
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Response Posted - 07/17/2008 : 23:18:13

Martin, I use only SS machine bolts and nuts on the exterior. I do not use wood or sheet metal screws. My theory is that everything on the exterior of the boat must be able to withstand a pounding and stay affixed. Regular drill bits are fine. I usually drill the correct size hole and then tape it off inside with duct tape, fill with penetrating epoxy, let stand a few minutes to soak the core, and then drain the epoxy out. I then bed the bolt with a good marine adhesive caulk like 3M 4200. Use good size washers on the inside to spread the load, especially on things like cleats. Since penetrating epoxy (I use Git Rot from the marine or hardware store) does not last long - 15 minutes once mixed - it is best to drill all of your holes at once and do the process for them all.

Others will tell you to overdrill the hole, rout out the core for 1/2", fill the hole with epoxy, let harden, and then re-drill the right size hole through the cured epoxy. That is, of course, best but I find that the method I use is sufficient to protect the core and avoid problems. You will note that Catalina used the drill and caulk method for the through deck fittings such as the winches which go through cored material.

That being said, I am about to mount a fixture forward of the mast for on-water mast raising and lowering. This fixture will not be permanently on the deck and I will use the more elaborate process in this instance since there will be no caulk used for the bolts.

Edited by - on

Dave Bristle
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Djibouti
10005 Posts

Response Posted - 07/18/2008 : 07:29:36

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Nautiduck
 ...there will be no caulk used for the bolts.<hr height="1" noshade id="quote"></blockquote id="quote">How will you prevent seepage into the interior?

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GaryB
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Response Posted - 07/18/2008 : 08:38:55

If you're using the over-drill method how much should you over-drill?

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Nautiduck
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Response Posted - 07/18/2008 : 10:04:30

<blockquote id="quote">quote:<hr height="1" noshade id="quote">How will you prevent seepage into the interior?<hr height="1" noshade id="quote"></blockquote id="quote">

Dave, I plan to use a rubber washer on the inside of the cabin. Any moisture that gets by the bolt head will be unable to get past the rubber washer. Since it will be encased in epoxy there will be no potential for damage. I will post photos soon of the planned new mast raising system so people can comment on its design.

Gary, I have both Don Casey's book on "Hull & Deck Repair" and the West System manual for "Fiberglass Boat Repair and Maintenance." Neither specifies how much bigger that first hole should be although they both call for routing out 1/2" of core once the hole is there. My project calls for 3/8" bolts and I am planning to drill a 7/8" hole which will give me 1/4" of epoxy all around plus the additional routed 1/2" of epoxy by the wood core.

Edited by - on

farrison
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166 Posts

Response Posted - 07/18/2008 : 10:10:44

Martin;

The overdrill and fill method might be good for areas where there might be high loads and where there might have been water infiltration in the past and the core has been compromised. In your case maybe the cam cleats, but since they are new, and going into an area that has never had a hole in it, water damage there is unlikely . But for the others, drilling the hole to fit the machine screws/nuts/washers is perfectly adequate. Seal the outside with 4200 to keep the water out of the core, that's the big item. But on all of the holes, on both sides, countersink the hole just slightly to bevel the gelcoat. This will help keep it from cracking around the hole.

Paul

Edited by - on

Dave5041
Former Mainsheet Editor

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Response Posted - 07/18/2008 : 17:35:08

I over drill about 1/8" and dremel out the core to back fill with epoxy/chopped glass paste; for light loads, I sometimes just fill the hole and re-drill. I would suggest polysulfide instead of 4200, it is the bedding compound of choice in the marine environment. 4200 is an effective adhesive sealant, and you don't need the additional adhesive strength.

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delliottg
Former Mainsheet C250 Tech Editor

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Response Posted - 07/18/2008 : 19:35:35

The Gougeon Brothers (WEST System Epoxy) recommend no more than an 1/8" ring when over drilling & back filling. They also recommend that you fill with un-altered epoxy (no fillers), and then drain, then mix fillers into the epoxy & refill the hole. You want to make sure that you either route out the intervening material if it's cored, or make your hole slightly cone shaped with the pointy end toward the pull so you can't possibly pull the plug out. I've personally never seen this happen, but I have a friend who has.

As Randy said, normal drills are fine. Wear gloves & long sleeves unless you like to itch. If you decide not to, when the itching starts (and it will), go take a shower & scrub the afflicted area with a nylon puff ball or scrub, with soap. This will remove the fine filaments of glass you've got embedded in yourself and make the itching much more tolerable (I learned this the hard way, several times).

If you're mounting relatively light things on the interior, you can probably get away with SS self tapping screws, but I like to mount everything with SS through bolts and if they're going to show, dress them up by using oval head bolts & collar washers (that's not the right term, but can't come up with it). If you're mounting heavier stuff, you definitely want them through bolted and backed, especially if there's ever a chance what you're mounting will become a grab bar, and that's pretty much everything on the exterior of the boat. If your boat isn't on salt water, you can maybe get away w/o using bronze or SS. Personally, I use either bronze or SS on everything.

When you're drilling into gelcoat, you want to make sure you make a clean cut into it or it's going to chip out. If you're drilling from the inside of the boat through the hull, first make a cut from the outside in to cut the gelcoat cleanly. Saves on chip repairs (learned this the hard way too).

I concur with using polysulfide to bed whatever you're mounting, unless you need the adhesion of 4200 or 5200 (which I don't use any more, it's way too hard to get something back off when you use 5200).

I'd recommend picking up a copy of Don Casey's book Hull & Deck Repair, he goes over this stuff in detail, including why polysulfide's basically your best friend.

Go oversize on your backing plates/washers, etc. It can never hurt to have bigger backing plates than you need, unless you're trying to save weight because of racing. But if that were the case, you wouldn't own a Catalina.

Edited by - on

Stardog
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Response Posted - 07/19/2008 : 22:42:59

Normal drill bits will work, but they will wear out very quickly if you do much drilling. Glass is harder than most steel and will quickly wear the cutting edge off a drill bit, even though the glass is only in fiber form. If you're going to be doing much drilling, including boring holes in aluminum and stainless steel which is so common on these boats, you'll do well to get yourself a set of cobalt bits, they cost about three times as much as high-speed steel, but they will also last for many years.

For any screw you put into the outside of your boat, you should fill the holes with either marine sealant or silicone before you insert the screw. If water is getting past your seal, you want to know about it so you can fix it. Water inside the core is one of the most destructive things that can happen to a boat.

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jimmy_boots
Deckhand

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Response Posted - 12/31/2008 : 01:03:16

Hey all,

Where do you find nice SS backing plates? I'm getting leaks through my bottom gudgeon bolts, the wood core around them is all rotted, and i want to go to town with some sealants and make sure it all stays strong. i can't seem to source any suitable flat metals nearby.

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delliottg
Former Mainsheet C250 Tech Editor

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4479 Posts

Response Posted - 12/31/2008 : 02:50:56

Jimmy,
I'm not sure how useful this is, but here in the Seattle area, we have a place called Pacific Metals, they're resellers of scrap metal. They sell all kinds of stainless, aluminum, plastics, you name it. Maybe there's a similar place close to you? I love walking around the place, and always seem to find something I didn't know I needed.

That said, I backed up my new Tohatsu engine with 1/4" thick plates of aluminum that I bought at the local Ace Hardware (or maybe Lowes or HD, not sure).

Edited by - on

britinusa
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5404 Posts

Response Posted - 12/31/2008 : 06:02:19

If you do use self tapping screws (Stainless Steel!!!!) then make sure they are self tappers, a lot of ST screws only have tapered tips, they are fine for non-marine wood, but on-board you don't want to risk splitting wood or cracking the outer coat of fiberglass (gel-coat)

Take a dremmel and cut a slot along the side of the threads from the tip towards the screw head. That slot will act like a drill when you screw it into a pilot hole, avoiding cracking the gel-coat. Make sure the pilot hole is at least the diameter of the screw core.

Paul

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DaveR
Master Marine Consultant

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2015 Posts

Response Posted - 12/31/2008 : 07:36:02

Hmmmm Martin,
Seems it wasn't a dumb question at all. A lot of good info here, thanks guys!

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Dave Bristle
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Djibouti
10005 Posts

Response Posted - 12/31/2008 : 09:52:43

As long as we're back on this, a couple of other nits:

- After drilling through and using penetrating epoxy in the hole, put a larger bit in the drill, switch the drill into reverse, and use the bit to bevel the outside of the hole. (Reverse is to prevent the drill from biting and going too far in.) This allows for a better caulk "gasket" around the bolt.

- After caulking and setting the hardware in place, lightly tighten the nuts just until caulk squeezes out, allow to set up for 24-48 hours, and then tighten the nuts further, keeping the bolts stationary from the outside so the seal around them isn't broken. This makes a compressed gasket--the best seal you can make.

Happy New Years... Only three weeks to go!

Edited by - Dave Bristle on 12/31/2008 09:56:44

Merrick
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USA
192 Posts

Response Posted - 12/31/2008 : 12:32:06

quick search for polysulfide found a good page on sealants:
http://www.boatus.com/boattech/casey/35.htm

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glen
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359 Posts

Response Posted - 12/31/2008 : 12:56:28

I know this has been covered a number of times so far but here goes my two cents. The reason you bevel the gel-coat is to prevent it from chipping when a screw is tapping or cutting its threads into the glass. Think of the gel-coat and glass as two different items. The gel is thin and very brittle, which is why you don’t want the threads of a screw to toutch it when cutting into the glass body. If you use a machine screw (which resembles a bolt) the Gel-coat beveling is less of a requirement, but still not a bad idea.

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glivs
Admiral

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836 Posts

Response Posted - 12/31/2008 : 14:57:04

Lot's of good advice and heed glen and others about beveling the gelcoat on the entry side before drilling to reduce chipping and then afterwards to facilitate bedding. If drilling through, my personal biases are also to tape (painters masking tape) at least the exit surface to reduce chipping and if need be, drill a small diameter pilot hole before drilling the actual hole. Do not rush or push hard or you will chip the exit surface. For those situations that you want to over-drill, fill with epoxy and redrill, routing the core can be done easily simply by bending a small finishing nail 90º, put it into your drill chuck and route out the core around the oversized hole. A 1/4" lateral radius would be fine for many light applications. [We owe this tip to another member of this forum who as I recall used motorcycle spoke wire.] Last, realize that cabin wall thickness varies greatly depending upon location. Do not drill through unless you really are planning to.

Edited by - glivs on 12/31/2008 14:59:02

Dave5041
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3758 Posts

Response Posted - 12/31/2008 : 20:13:57

I thought you question was about interior mounting. If it is, drilling through bulkheads is straight forward. The interior fiberglass is a liner and adequate for boathooks and things like that with self tapping screws, but a backing washer and machine screw is always best if you have access. There is no reason to bed if you are only attaching to the liner. The aft interior cabin/cockpit wall is cored, so there is no room for a nut. The overhead above the quarterberth is empty above the liner and easily accessible, it is cored in the main cabin and v-berth areas. For the forward wood bulkheads, through bolts with washers and cap nuts work well and look good from both sides. Don't use wood screws in plywood

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