0

I want to secure a dock ladder to a wooden dock with 4 lag screws. The wooden dock surface is 2"thick wood.

2
  • Hi, welcome to StackExchange. You've given two of the relevant bits of info but missed another, the species the screw will go into. Species (or at least general wood type) is important for properly sizing pilot holes in wood. While wood is a reasonably forgiving material in this respect (so close enough will often do) where strength is important or vital, as it is here, you do want to get as close to textbook as poss.
    – Graphus
    Jun 30 at 20:54
  • And further to the strength issue, just 4 screws doesn't seem enough to me given their relatively short length. My gut tells me I'd want to either use longer screws (3" or longer) or more of them, and maybe even both just to be on the safe side.
    – Graphus
    Jun 30 at 20:54
3

If the dock is made from hardwood, then you want about a 7/16" pilot hole. If it is softwood, about 3/8"

If possible, don't use screws at all, but rather use through bolts with nuts and washers. They will be much more secure long term.

In general, you want the size of the pilot hole to be about that of the root diameter of the screw around the threads. See this thread from DIY Stackexchange

5
  • 1
    Given screws are used to construct most patios, decks and similar I don't think they can legitimately be thought of as less secure long term unless (assuming the appropriate gauge, length, and number are used). I've seen the same thought posted more than once, about how to undermount heavy iron vices, and how lag screws can't be trusted to withstand the weight, plus all the shocks and vibration..... but then you get guys who installed their vices 10, 20 and even more years before using lag screws chiming in going "Waddya mean lag screws aren't up to the job?" :-)
    – Graphus
    Jun 30 at 21:22
  • 1
    I never said lag screws weren't sufficient, I just said that through bolts were more secure. In use case above, the wood will experience many wet/dry cycles, the fasteners not checked for tightness on a regular basis, and failure of fasteners could result in injury. This is not comparable with a tool in a dry environment that can easily be tightened as soon as it feels loose.
    – LeeG
    Jul 1 at 17:28
  • I didn't say you did Lee, I said they can't legitimately be thought of as less secure (the direct implication of the statement that nuts and bolts are "much more secure"). Yes, obviously something can happen to screws in real-world scenarios, but equally, nuts can and do work loose where there are cycles of strain and release, or vibration, unless steps are taken (old-school methods for locking nuts), or or something other than a standard nut is used.
    – Graphus
    Jul 1 at 18:55
  • "This is not comparable with a tool in a dry environment that can easily be tightened as soon as it feels loose." The point was that the lag screws never do work loose. On the other hand I can't tell you the number of times I've heard of people having to tighten the nuts used in their workbenches.....
    – Graphus
    Jul 1 at 18:58
  • @Graphus In a marine environment, you have to expect all wood to rot eventually, and all metal to corrode. If the OP was screwing long lag screws into a thick timber, you're probably right -- the ladder will likely disintegrate long before the screws come loose. But there's only 2" of wood here, and because it's a ladder it's pretty important for the fasteners to fail gracefully -- the ladder should get noticeably loose long before the fasteners pull out. Bolts with washers and preferably nyloc nuts seem like an excellent recommendation.
    – Caleb
    Jul 1 at 21:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.