How do I drive wood screws into a glass hull?

[Glyn Judson]

All,

I'm soliciting the list for help with an upcoming potential problem. I need to screw a bunch of #6 bronze wood screws into my hull and personal history doing just that on a previous boat resulted in them snapping off as nice as can be. The obvious problem was that I tried screwing a tapered wood screw into the straight hole I'd drilled using a standard twist drill.

I have a bunch of tapered bits as a part of several countersinks that I use for making teak plug holes. Could I use one of these to make the pilot hole and expect the bronze screw to go in without snapping off?

Affirmation or other solutions welcomed.

Thanks in advance,

Glyn Judson, E31 hull #55, Marina del Rey, CA

 

[NateHanson]

Since fiberglass is much much harder than wood, you need to drill a larger pilot hole in fiberglass than in wood. Don't try to match the drill bit to the shaft of the screw. Go a bit larger. The teeth just need to bite a bit.

 

[Sid]

Glyn
I agree with Nate but have also I also run the screw across a bar of soap as lubricant.
By the way how long have you been in MDR. I lived on my boat there for 20yrs, still a member of PMYC. Did a lot of racing. Worked for Calif Sailing Academy, also worked in the Venice and WLA area for 27yrs then retired and went cruising in 97 and are still having fun.

Sid and Manuela
In and On "Paradise"
36c #51
http://boatbumms.blogspot.com

 

[chaco]

Grease'em and Seal'em

As I install screws in to fiberglass on exterior application I dip the screw in
3M 5200 to lubricate and prevent the fiberglass from shattering and to seal
the the hole from the Elements :nerd:
Why bronze screws and what are you fastening ?
I usually end up replacing old bronze slot head screws with phillips stainless.

Happy Fastening

 

[sleather]

Don't screw-up!

Glyn, Where on the "hull"? What's the thickness?
I've been able, in the past, to match thread pitch and dia. from a stronger sheet-metal screw(got a bizzillion) w/ the treads of a wood screw at the "holding point". Use one to "pre-thread" the hole. It all depends on the thickness, works pretty good up to ~1/4"

Another thought is to always use "sacrificial" screws to pre-thread the holes prior to installing the finished screw. I always do that w/ S.S. sheet metal screws. Using and then discarding a "tap-screw" ensures a better bite for the final screw with less chance of "bunging up" the drive slot. It's also easier to pre-thread w/o the item to be attached in place. You can usually "pre-thread" up to 1/2 doz. holes before the glass trashes the threads.

Your's truly, Screwed-up Boat Guy

 

[Glyn Judson]

RE: Don't screw up.

Steve, There are four locations on the hull that I'll be fitting bronze Wilcox Crittenden vent covers to in place of the existing chrome plated brass Perko ones. There are two on the starboard bow for the auxiliary 25-gallon water tank and one for the holding tank. Then there's one for the diesel fuel tank aft of the boarding gates on the same side and the last one on the port side aft of the boarding gates for the 45-gallon main water tank under the cabin sole. In all cases the vents are mere inches below the toe rail where the hull thickness is 1/2". I love the sacrificial (wood) screw idea and also its being steel for cutting threads for the bronze screws to follow. I'll have 12 screws in total needed to mount the four covers so it'll be a slow and cautious job of fitting them, what with the boat being in the water. I'll bed the flat edges of these triangular vents to the hull as well as using a bit extra for the screw threads. These covers are as scarce as hens teeth and I don't want to drop any of them in the drink. Thanks for all the suggestions. Glyn Judson, E31 hull #55, Marina del Rey, CA

 

[sleather]

In-the-drink

Glyn, Glad to be of service!

Another thought or two from the "experience" archives. When working "near-the-edge" or "over-the-edge"(in your case), build a temporary enclosure of sorts around the work area(cardboard and blue painters, or duct tape) I found out, the hard way, that winch needle bearings are NOT captive. Works well around nav lights and anything close to the edge.

I've also found that a piece of perforated "non-skid kitchen drawer liner" is great for keeping tools from "running-away" on a slick deck. I also use it on the dash-board of my powerboat and even coffee cups stay in place.

I guess we really do NEED that "idea-bin" sticky in the maintenance section.

 

[rwthomas1]

The only tapered drill bits I know of that come with a set of plug cutters are made by the Fuller Co? Based right here in Warwick, RI They invented the tapered drill. If that is what you have then they are probably your best option for installing tapered wood screws. A trick to try is use a stainless screw of the same size installed in the hole and then removed. It will "cut" threads much like a tap and make it easier on the bronze screws. I would also lubricate the screw. Soap, sealant or there is actually a specialized product for this that Jamestown Distributors has. RT

 

[Glyn Judson]

Tapered drills used for wood screws in fiberglass.

Rob, Those are very the bits I have. I did a series of test drills in the 1/2" thick glass bow section I have in the garage and that's how I'll fit the bronze screws through the Wilcox Crittenden vent covers and into our hull. Glyn Judson, E31 hull #55, Marina del Rey, CA

 

[ted_reshetiloff]

Am I reading correctly that you have water tank vents mounted in the hull just below the toerail near the bow? What prevents salt water from entering these vents when you are heeled over or pounding through chop? Better location would be below decks in a sink or at least to the bilge IMHO. Maybe I missed something in the posts. As for putting wood screws into fiberglass are you not just begging for water intrusion at some point? Why not drill and tap for machine threads and bed the fastener in epoxy and not risk splitting up the laminate?

 

[Tom Plummer]

For tapered bits go here http://www.mcfeelys.com/ best place I know of for this sort of thing. If you need specialty screws or or other wood working equipment this is the place.

 

[Graham Cole]

After you drill the hole, use a countersink tool to chamfer the edge a bit. Prevents gel chip out and gives a bit more area for the sealant to adhere to.