Leave screws in?

[Steve Miller]

Have my GLen-L Utility skiff plans now so I need to order hardware. Its a basic ply on frame skiff. Using epoxy for glue would I leave the planking screws in or pull them? Its hard to counter sink much in 1/4" ply.

That also opens the question of number of screws. Do I really need all of them when planking? Seems like with epoxy that the spec 3" spacing is a bit much. I know the plans were done before epoxy was common so what do you guys think?

Use screws as needed to secure the ply to the frame - say ever 4 - 6 inches with more at the curves (bow, stem)?

Since this is my first ply on frame boat I want to check with you guys before doing anything.

Thanks.

[NormMessinger]

Just to get the discussion going: Take the screws out. After the epoxy cures the are just extra weight. Should you try to pull a plank from a rib you are as likely, or more so to rip the plywood apart before you get it off the rib.

[rstclair]

Steve,
I went through the same thought process with my Penobscot 14. What I found was that using the screw spacing suggested in the plans was the best idea. Then the screws can be removed with out a problem if you remove them soon enough. I think witin 24 hours is about right. If you leave them in to long it can be tough getting them out without problems. Even after 12 hours if you are not careful its easy to tear out the plywood top layer.

Using the spacing suggested will make sure the plywood is pulled down eavenly and fair.

Bob

[Bruce Hooke]

I agree with Bob...I don't think the plywood will pull down nicely if you spread the screw spacing out.

If you are going to pull the screws out after the glue sets it seems like you could probably use drywall-style screws rather than regular wood screws. Just make sure you get all the screws out and hope that you don't break any off when taking them out. If you use drywall-style screws I highly recommend getting good ones, such as those sold by http://www.mcfeelys.com/

Do watch out for places where screws might be called for to carry a concentrated load.

[NormMessinger]

Now we can start telling you stuff you probably already know. Dry wall screws as okay IF! Ya should drill a pilot hole in the top piece so there will be no resistance to pull down. I prefer pan head sheet metal screws and with a washer for those areas that need extra force for draw down (sometimes called pull down). Now, how to be sure you fill the screw hole completely. Wet the hole, dip a wooden peg in epoxy and tap it in to the bottom of the hole. Peg can be toothpick depending on the size of your screw.

Have at it.

[Frank Wentzel]

To make sure you can remove the screws you could dip them in melted parafin wax. If the screw is hot enough the wax will run off leaving a thin film that epoxy - or any other adhesive - can't bond to. The wax will also make the screw drive much more easily.

/// Frank ///

[ 11-07-2004, 09:14 AM: Message edited by: Frank Wentzel ]

[Bruce Hooke]

But will the remaining wax prevent the epoxy that will later be used to fill the hole from getting a good bond with the sides of the hole?

[Bob Smalser]

Not an area I have much experience in, but I'd probably use galvanized or SS ring shank nails, countersink and epoxy-butter them....and leave them there. It'd make those expensive, fat epoxy fillets less critical.

[mmd]

I'd pull them out, and waxing the screws before using will make the job a lot easier. (I don't know if the tedium of individually dipping them in molten wax is better that merely having a piece of wax handy to give a quick swipe over the threads prior to screwing the ply down. Incomplete lubricant won't be an issue, and any "dry spots" will reslove the issue with the subsequent epoxy plug not adhering.) As for filling the screw holes, I've always liked the trick of using a syringe to squirt slightly thickened epoxy into the hole from the bottom up. Don't worry about the plugs not adhering due to the residual wax and falling out - the epoxy plug will have taken the shape of the screw impression in the wood and it is unlikely that it will unscrew itself. Paint will prevent that, and if you tape the seam or sheath the hull in 'glass, more's the better.

[Steve Miller]

Good info everyone.

I had not thought about the ply laying flat vs the screw spacing - I was just thinking of the strength issue.

I did not have any trouble removing the screws when I did my glued lapstrake sailboat. Epoxy in the laps and screws to clamp. About 24 hours later they came out pretty well. Seems like the quick tork from the power driver popped them out. A few stubborn ones needed the heat from a soldering iron to release.

I like the pan head and washer idea Norm. I have used the toothpick plug idead before but had forgotten about it.

[JimD]

I fastened my Utility with the bronze fastening kit sold by Glen-L for the boat which includes both screws and ring nails. I finished the boat almost entirely bright so I didn't want screws showing everywhere. I used screws and nails permanently in place where I could easily hide them with rub and splash rails and other trim such as along the chine and sheer but had fasteners left over after completion because I did not follow the schedule exactly. If your going to paint the boat it ought not to matter. Countersink the fasteners in just a fraction below flush, fair with a dab of thickened epoxy, and glass over if you intend to glass. Fasteners left in place will make the boat stronger and prevent the plywood from sheering off the frames at the glue joint. Since this is a power boat the hull may take quite a pounding over the years.

[Tom Lathrop]

1. In most cases, you don't need to leave the screws in. For high stress areas like attaching ply to the stem piece, use your good judgement.

2. As said, predrill the top layer of ply. It works better and leaves a neater hole to fill.

3. Use small scrap pieces of ply as washers under the screw head. The indentations left from removed screw heads have a long term memory under the finish.

5. I would say nix on wax unless driving really big screws and you surely won't be needing those on plywood.

4. If the plywood is laying on the sub structure with no gap, you don't need a screw right there. Put them only where needed to make th ply conform. Use you own judgement on this. 3" spacing on ply over epoxy is way overkill in most instances.

5. Screws should be removed before the epoxy completely cures which is usually a few days. I take them out the next day. Some dry wall screws will break if set in cured epoxy, especially the long ones. Heat will get them out if there is enough shank to grip with vice grips.

[ 11-07-2004, 12:05 PM: Message edited by: Tom Lathrop ]

[Rogue Sailor]

Another thought. Unscented hair spray is a very effective mold release for epoxy.... and its cheap and easy to apply.

[Gary E]

If you remove the screws...

..The joint is now depending 100% on the glue, or epoxy to bond the inside ply of the plywood to the chine, or keel, or whatever the screw was screwed into, placing the joint in 100% tension.

..The joint is also now depending on the glue that bonds the plys to each other to not separate.

..You are spending more time to remove the screws, and repair the holes.

If you leave the screws inplace..

..The joint has all of the above plus it has the advantage of the screw holding the plywood in compression and transfering the tension load to the screw which absorbs the load. That is what screws are designed to do.

..You now have more time to spend on the next step and you go sailing or fishing sooner.

..I guess it's a matter of preference, I would leave them in, and if I was worried about the weight, I'd either skip the 2nd cheeseburger or leave the beercooler at home your choise. I'm not concerned with 5 lbs of screws or the weight of a cooler of brew, this is a boat, not an airplane where weight might matter. Once it's screwed, it stays screwed.

Belts and suspenders...

Good luck and enjoy the building.