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Old 09-06-2007, 03:28   #1
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Screws vs Nails

I have recently bought a boat (42') which needs some TLC.

Some of the hull planks need replacing and the the ones I've pulled off have been nailed in . They are 3" nails (maybe galvanised).

On a website about making a sailing boat that I looked at recently, I saw that they were screwing the planks onto the rib structure.

I would think that if I screwed the replacement planks on and then later they needed to be re-replaced, it maybe difficult and longer to get the planks off than if I nailed the on.

What do you guys think ?

Thanks
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Old 09-06-2007, 04:41   #2
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Excerpted from:

Surveying Wood Hulls ~ by David H. Pascoe
Marine Surveying : Surveying Wood Hulls - Old Boats and Yachts

”... Nailing hulls is fraught with all kinds of problems, not the least of which is the problem that nails tend to split the wood. When this happens, water gets at the fastener immediately, so whether a vessel is 5 or 30 years old may have nothing to do with soundness. Further, when water is getting at the fastener through the interface between plank and frame, its also going to corrode rapidly.

Ultimately, the problem with nailed boats involves so many factors and hazards that coming to any conclusion of soundness is nigh impossible. Nails cannot be pulled without causing much damage to the plank, if they can be gotten out at all. Inspecting the heads only tells one the condition of the head, not the rest of the nail. And tearing planks off means that they have to be renewed and the cost far too high. Nondestructive methods such as X-ray are both costly, difficult and not necessarily reliable.

Taking all these factors into consideration, steel fastened vessels are a hazard to everyone who gets involved with them.

Screw Fastened Vessels Utilizing all the techniques outlined above, along with removal and inspection of fasteners, can provide a reasonable degree of certainty as to a hull's soundness. Moreover, screw fasteners can be replaced if they have good holding ground, meaning that planks and frames are not split or deteriorated ...”

Surveying Wood Hulls PART 2: How to Survey A Wood Hull
Surveying Wood Hulls: Part 2

See also:

Guidance on Inspection, Repair, and Maintenance of Wooden Hulls
US Coast Guard NVIC 7-95

NVIC 7-95
Specificaly: Chapter 3E: http://www.uscg.mil/hq/g-m/nvic/7_95/n7-95.htm#C3

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Old 09-06-2007, 06:34   #3
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Hi Dave looks like your project is moving along. What type of nails, are they square tapered boat nails? What type of frames? I did this kind of job on the fishing boat, I had rebuilt 25 years ago. It involved removing the old boat nails with a modified slide hammer puller and using the existing holes as pilot holes to screw in over 4000, 316 ss #12 x 2 Screws. Used a thin stainless plate as a backing plate to rest the puller foot on. As not to dent the wood. I hope your having fun.
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Old 09-06-2007, 09:05   #4
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The standard wood boat fastener of recent times is silicon bronze screws. These are what I have always used and i recommend them over stainless for corrosion prevention.

Have fun with the refastening job.
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Old 09-06-2007, 09:19   #5
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I new at the time that it was preferred to use silicon bronze but they were not available in a socket type head (robertson screws) and the available slot heads were too prone to camming out. It required a lot of torque to drive these 4000 screws in. 316 SS is impervious to almost any environment so I used them we no regrets.
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Old 09-06-2007, 10:17   #6
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Thank you VERY much for your input

I have been reading the linked material which was very interesting - but it said a lot about what not to use without saying what I SHOULD be using ! I found it a bit frustrating reading !

Here are some extracts:

Quote:
E. MECHANICAL FASTENINGS; MATERIALS
Mechanical fastenings should be of material suitable for the service intended. Ferrous fastenings should be hot-dipped galvanized. Among the usual non-ferrous types brass is not acceptable in salt water applications as it will corrode from de-zincification and is inherently soft and weak.
G. NAIL FASTENINGS
Hot dipped galvanized cut boat nails have traditionally and are still being used in boat building. Barbed or annular ring nails have been successful and are suitable depending upon their application (usually smaller scantling vessels). Smooth, thinly coated or plated nails, with small irregular heads and long tapered shanks such as horseshoe nails and ordinary "cut nails" (i.e. hardwood flooring nails) will not provide sufficient holding power and should not be used. In addition, wire nails are not acceptable for hull construction.
3-5

1. Lead Holes. Lead holes for nailed joints may be 3/4 of the diameter of the nail without causing loss of strength.
2. Types Of Load. If possible, nails should be loaded across the nail and not in the direction of withdrawal. This is especially important in end grain.
3. Spacing Of Nails. The end and edge distances and spacings of the nails should be such as to prevent splitting of the wood.


Holes made by old screw fastenings should be properly reamed clean and may have the cavities filled with an epoxy mixture thickened so as to provide a filler which will hold fastenings like wood.

Since nail fastenings depend upon the swelling of the wood around them after they are driven for their holding power, this technique should not be used for holes made by old nail fastenings. Holes made by old nail fastenings should be properly reamed clean and filled with dowels set in a suitable adhesive

Use of stainless steel fastenings in underwater body salt water plank fastenings can result in early fastening failure due to crevice corrosion and should also be avoided.
So it seems that I should NOT use stainless steel screws or nails but that I should use galvanised "special boat nails" OR galvanised screws.
I should not use wire nails (galvanised or otherwise)

Is that about right ?

I don't know if the merchants here will sell silicon bronze screws (they wouldn't know what they are !)

Just one thought:
If I use screws - after countersinking them, I assume that the holes are filled with marine putty before painting. In that case, if a plank needs to be re-replced (maybe because of collisoin damage ) isn't it going to be difficult to find them and take them out ?

And how did you locate and take out 4000 nails when they must have been driven below the surface, puttied and painted ???

Thanks for all advice as I am new to this.
Dave
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Old 09-06-2007, 10:38   #7
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The screw holes are filled with what is called a "bung". Small discs of wood(hopefully the same as the planking) set in shellac, varnish or some thing similar. Then planed or sanded flush with the hull. I think it is advisable to orient the grain to match the plank if possible. I believe there is a drill bit available to make your own. Just as important is the proper tapering pilot hole. There are bits for this too. Pick up a copy of Wooden Boat magazine as it is a valuable resource and good place for sourcing out the things you need. Galvanized fastenings were popular in workboats or economy boats and provided a long service life but silicon bronze is best. Check with Kai Nui, he is one of the "wooden boat guys" here.
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Old 09-06-2007, 12:04   #8
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Oh yes - I have seen those wooden "bungs" they are usually used in cabinet making. As my boat will be painted with white gloss (above the water line) and anti fouling below, I dont suppose it matters whether I use a bung or the putty. I am calling it "putty" but that might not be the correct term - its called "marcun" in Turkish which is means "paste" or "putty" - they use the Marine marcun a lot to get a smooth finish before the painting. Do you use that where you are? What is it called in English ?

Also - I'd still be interested to know how you would locate and remove screws (or nails) when covered with a "bung" or other stuff after sanding flush and painting !

Thanks
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Old 09-06-2007, 12:43   #9
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The problem I see with some type of putty is it will fill up the screw head slot and make future removal difficult. Even when sanded smooth the bungs are easy to see and being held in by shellac or varnish they are easy to split out and remove if needed. Since you know where the frames are it's easy to sand of the paint in this area to find the fasteners. There are traditional putties used by the wooden boat crowd but epoxy mixed with various powders to give it fairing and easy sanding properties may be commonly used too. I have never heard of the putty method used to fill the screw holes in traditional wood construction. On the other hand my plywood epoxy trimaran has many places where fasterners were used to hold things together during construction and then covered with epoxy putty. They have never caused any problems. But epoxy ply is a monoquoc structure glued together and wooden boats are made up of many small pieces held together by fasteners all slightly independant of each other. The question is do you want to cause yourself or another owner potential future headaches by taking a quicker path now? It has been 25 years since I owned a wooden boat and that was a 20 foot C Scow so you should also check with Kai Nui. He may have some good insight on this.
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Old 09-06-2007, 12:45   #10
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Aloha Dave,

Kudos to Steve Rust for a very good, succinct description of refastening a wood hull. You'll find "plug cutters" widely available for making your own bungs, and as with most everything else in life, you get what you pay for... buy good quality ones. Same with the combo pilot hole/countersink bits.

My own preference is to use varnish to seat the bungs, and again I'd second Steve's advice to orient the grain of the bung parallel to the plank and try to use the same type of wood for the bungs as the planks.

Hang in... not a fun job, but very rewarding when done properly. You'll really appreciate it the next time you find yourself in truly rough weather!

All the best to you aikane.

John K.

P.S. I'd vote for silicon bronze or stainless as a second choice.
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Old 09-06-2007, 14:05   #11
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Silicon Bronze screws are the best easiest to come by. Monel is better, but very expensive and very rare to find. In fact, I have never seen a monel screw, so it is possible they are not made. Titanium is the tops, but expensive and still very limited in what is available.
SST is bad news in any external timber, even above the waterline. The timber starves the SST of oxygen and then if the timber gets damp, the acids and tanins inthe timber simply eat the screw away, leaving nothing put a thin plug of rust.
Hot dip galv is hmmm..OK above water line. I still don't like it. The galv protects the steel, but I have also found the galv corrodes to a white powder in most extreme cases. Trying to pull and old corroded galv nail is next to impossible.
Silicon Bronze screws are not cheap, but are probably the best most cost effective fastening still. They tend to be soft and easily broken by over tightening. They always break right at the edge of the thread and you are left with a head and the screw shank embeded deep in the wood. A correct hole size and a countersink is essential to correctly fastening them.
the wooden plug is used because of expansion and contraction of the timber. The plug moves at the same rate. A "putty" or epoxy filler doens't and will eventually let go around its edge. Wood remains tightly fixed. However, timber planking is thick and you have plenty of depth to play with. You can sink a screw in deep and have enough depth over the headto plug with a wooden plug. A ply hull does not have that depth. So hence why epoxy is often used. You will notice on ply hulls, that the heads of screws and nails start to show over time. This is as the ply expands and contracts. Which brings me to my last point on nails. Ring shank nails are the only nails that should be used. They grip like nothing (other than a screw). Wire nails are not used because they do not grip. With the movment of the timber, the nail eventually works loose. Ever seen a timber paneled fence after a couple of summers. The boards all have the nails sticking out.
If you can't buy Silicon Bronze screws where you are, I suggest you buy them on line and get them sent to you. Yeah I know it is expensive, but you need to do it right.
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Old 09-06-2007, 21:40   #12
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Hi Dave.
Are you having fun yet? As to the finding and locating the old nails. Once you scrape the old paint off they become easy to see. The nails will be sunk below the surface. By using a pincher type hammer puller with the jaws ground down to 1/8 inch you drive the puller over the filled hole and test until you have a hold of the nail head. Put a thin plate (I had used a stainless drywall trowel) under the foot of the puller( to prevent denting the wood) and pull out the nail. The putty plug will break up. As I said before I had read all the stuff on preferred screws when I redid the fishing boat but stainless 316 screws are not the same as 308 stainless and are used for marine applications. That job was done 25 years ago and last time I saw the boat it still looked great. Even with a proper pilot hole you will need a lot of torque to drive the screws. Beeswax on the screw helps. Wood plugs do the nicer job of filling the holes.
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Old 09-06-2007, 22:03   #13
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Thanks Alan for that extra info.

I have been Googling "Silicon Bronze screws" and notice that some suppliers go up to 3" length and some strop at only 1 1/4".

My planks are 1" thick.

What size screws (thickness no. and length) do you recommend and what size should the pilot drill be ?

Many thanks again.
Dave
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Old 09-06-2007, 22:49   #14
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Thats interesting Lancerbye "stainless 316 screws are not the same as 308 stainless "

Unfortunately they are not that suffisticated here. You only get krom screws ( which means some type of ss screw) or no-krom screws.

I will probably have to import them from UK.
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Old 09-06-2007, 23:31   #15
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Probably a 10g-12g x 2 1/4" - 2 1/2"
308 SST screws?? never heard of them. Sounds interesting.
There is a nifty little electronic device for finding nails and screws in timber. They are cheap (sell in NZ for $30) and simple to use. They will detect a screw or nail head buried in timber.
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