how tight to screw

[olesouth]

I have a GB that has been out of the water for about 5 years and I am replacing some of the hull. but the screw that are in the hull are in good shape. but I could get another 1/4 to a 1/2 turn out of them should I tighten them or leave them, and when I put on the new hull should I just snugg the screw up or leave loss to match the others or crank them down. ??????? its Mahogany on Mahogany hull.

[Chris Woodward]

Guide boat?

[wizbang 13]

GB, Grand Banks?
Did you pull the bungs or something? How are you getting at the screw?
A quarter /half a turn is not much either way, I recon.
The part you are replacing, above water or under?
As sometimes happens , more questions than answers.

[Mrleft8]

That'd be one gigantic guide boat.

[Chris Woodward]

"Takes a big man to tame a big river"

[rbgarr]

Wood screws are for holding already tight joints together, not pulling joints tight.

[Ian McColgin]

Good thing this thread's not in the bilge.

But seriously, the existing screws could be a bit loosened up by the drying of the planks and frames. Even over just a winter this cycle is half of why a carvel boat needs to be launched and let rest a week while she takes up. The fastenings loose in their holes will wiggle about and enlarge the holes if you start motoring or sailing too soon. The other half of the swelling need is to let the planks expand and firm up against each other and the caulking. The hull is a tension structure and without that swelling, the plank strain is entirely on the fastenings, working them even more.

So back to your screws, draw the new ones down firmly so you have the plank and frame in contact but don't over-torque. If you're using a brace with screw driver bit, once you're down feeling firm, get the feel of how tight it is if you turn the brace with you hand not on the crank, but down atop the right angle between the chuck and the crank's arm. That will be about 15 foot-pounds for the average person and is tight enough.

Don't do the good screws. If the boat does not swell up correctly part of the solution will be refastening with a size up screws but before that just cranking the screws in dry wood past where they were happy when new will not help.

G'luck

[chuckt]

My thought exactly Ian (your bilge comment). I have an answer that would work here or in the bilge. It's pretty funny but at least R-rated so I think I have to keep it to myself.

[Jay Greer]

This is exactly why I still swear by my Yankee Screwdriver for driving fastenings. It allows me to feel how tight I am torquing the fastenings. Not all feel the same so it is a matter of feel rather than a setting on a screw gun.
Jay

[Ian McColgin]

Jay, I am totally with you, but almost no one even knows what a yankee is any more. My favorite (I keep at least three in my kit at any time) has the metal running up through the top of the handle so I can use it as an impact driver for easing out the recalcitrant. But, as you point out, the great thing about a yankee is that it's almost impossible to get the screw in either too loosly or over-torqued and stripping the wood.

[Chris Woodward]

I also use a yankee to set screws, each with the slot lined parallel to the waterline. This is on a guideboat with 1/4" planking. I would also take up each screw on a restoration to tighten up the planks. Don't slip though....:mad:

[Jay Greer]

A lot of the mechanics I have worked with would remove the spring from their Yankee Drivers which, of course, eliminates the pain of slipping off of the screw head and maring the wood. But, I never saw the need. I guess I am either lucky or just a bit careful. I like the spring as it is an aid if a worker has his wits about him.
Jay

[Chris Woodward]

if a worker has his wits about him.

This could be my problem.:confused: