Summoning the Boatered Tech Panel, the best marine knowledge base I know of. Need opinions here. I will be tapping into steel about 18-24" above the waterline size 10-24 or 1/4-20. Machine screws will be 316 stainless. What compound would you use for bedding. In 20 years and hundreds of jobs later, only two have been in steel. I have used Sika 291 Polyurethane Bedding Sealant and Tef-Gel. Tef-Gel is about the best electrolyte barrier between two dissimilar metals (that I know of) but I question whether the contact there is of any issue. I am thinking better to use Sika or equivalent as a sealant/bedding. What would you use?
Fastening into steel hull
- Thread starter Rub Rails
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I would have no idea what to do, or the best way to do it, but this guy will... it's an exhaustive chronicle on the 5 year refit/restoration of a 46 Chris Craft Roamer, and an incredibly entertaining and informative read.
The information you seek is there, in his blog, and this is the link to his index page. You can probably just read the entries concerning the hull, and find what his recommendations were/are. Hope this helps!
http://1969chriscraftroamer46.wordpress.com/article-index/
The information you seek is there, in his blog, and this is the link to his index page. You can probably just read the entries concerning the hull, and find what his recommendations were/are. Hope this helps!
http://1969chriscraftroamer46.wordpress.com/article-index/
Tapping into steel hull??? Will you be drilling and tapping? What will you be holding up? How heavy? SS screws are not very strong. Get a screw of the size you wish to use and stick one end into a vice and grab the other end with a vice-grip and bend it. It'll likely break before 90* and if it doesn't, look at the outside bend. It'll be streaching and separating.
"Will you be drilling and tapping? What will you be holding up? How heavy?"
>Yes, I will be drilling and tapping and it will be a D bumper rail. There will be a screw every 6". I don't see strength of screw as an issue here. Though this will be only the third steel yacht I would guess I have driven at least 100k screws in my 20 years of doing this and can't recall a single failure except for a bow section in Hurricane Ivan which actually pulled out some chunks of a slate like composite core through the laminate. The screws (self tapping) didn't even break or strip through the hole.
Rythm, Thanks for that link. Perhaps I will find some pertinent info there.
>Yes, I will be drilling and tapping and it will be a D bumper rail. There will be a screw every 6". I don't see strength of screw as an issue here. Though this will be only the third steel yacht I would guess I have driven at least 100k screws in my 20 years of doing this and can't recall a single failure except for a bow section in Hurricane Ivan which actually pulled out some chunks of a slate like composite core through the laminate. The screws (self tapping) didn't even break or strip through the hole.
Rythm, Thanks for that link. Perhaps I will find some pertinent info there.
No expertise or even experience in this on steel hulls here, but FWIW, thinking slightly out of the box you describe....
If this is for rub rails, can you access the inside of the hull to use nylocks and threadlock?
If you could, you use an inert spacer tube (non-rigid plastic?) to help isolate 316 SS machine screws from the hull steel, perhaps with Tef-Gel in the spacer, plus a plastic washer inside next to the hull before the SS washer and nut go on?
This would take more labor with the needed helper. but avoid time spent tapping the hull threads if that's what you meant . And Sika or your preference to bed/seal the holes from the outside.
If this is for rub rails, can you access the inside of the hull to use nylocks and threadlock?
If you could, you use an inert spacer tube (non-rigid plastic?) to help isolate 316 SS machine screws from the hull steel, perhaps with Tef-Gel in the spacer, plus a plastic washer inside next to the hull before the SS washer and nut go on?
This would take more labor with the needed helper. but avoid time spent tapping the hull threads if that's what you meant . And Sika or your preference to bed/seal the holes from the outside.
That's why I asked what you will be holding up. Kinda makes a difference, huh!
Self tapping screws are hardened.
If all you're putting in is a rub rail, why do you need bedding compound.
100K screws...you should be the expert.
Self tapping screws are hardened.
If all you're putting in is a rub rail, why do you need bedding compound.
100K screws...you should be the expert.
Capt. Bill1
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I would use a thread locker. That way the screw is locked in and the threads are protected from corrosion.
Ha!!! Sandy, So how do you take my user name. I just got frustrated and punched the keyboard...but you couldn't tell [
]
I thought about sleeving the screws like you wrote but couldn't think of a product. Then thought about the high pressure plastic tubes made from HDPE. A little experimenting to set length and heat each end and it'll flare open when you put a screw and washer thru...just don't tighten down til the plastic hardens back up.
]I thought about sleeving the screws like you wrote but couldn't think of a product. Then thought about the high pressure plastic tubes made from HDPE. A little experimenting to set length and heat each end and it'll flare open when you put a screw and washer thru...just don't tighten down til the plastic hardens back up.
What's the plate thickness of the steel hull you are attaching to? Even if the hull sides are 3/8" (heavy scantlings), that doesn't give you much to tap into. I don't think I have ever seen D rails attached to a steel hull with self tapping screws. Is the yacht classed? ABS or any of the recognized classification societies should have rules that you can use as a guide. D rails can take a lot of stress, why not weld the rails onto the steel hull?
If you drill and tap steel and thread a fastener into the threaded hole, I don't think there's anything you could put on the screw threads that would prevent metal to metal contact. It's going to rub off in at least one place. You could check it with an ohm meter after installation.
If possible, I would try through bolting with an insulating sleeve and washer.
If possible, I would try through bolting with an insulating sleeve and washer.
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If your in fresh water don't worry about it. If your in salt weld on studs and bolt to the studs. Google body shop equipment for stud welders.
Capt. Bill, are you referring to Locktite? If that will seal from corrosion that may be my choice.
Rails are flexible PVC and will go across the platform and up the sides about 15'. They will be fastened through 1" wide hollow stainless rub rail as a backing strip.
Keith, I am using machine screws. I've never used self tapping in my metal applications. I will check Feadships' classification for an idea on metal thickness. Good idea.
Rails are flexible PVC and will go across the platform and up the sides about 15'. They will be fastened through 1" wide hollow stainless rub rail as a backing strip.
Keith, I am using machine screws. I've never used self tapping in my metal applications. I will check Feadships' classification for an idea on metal thickness. Good idea.
Feadship is a consortium of builders, not a classification society. If the yacht is classed there should be current certificates, issued by a reputable classification society on display at the bridge. If classed you would have to go through plan review and approval prior to the commencement of the install and these issues would have been addressed. A UT machine will tell you the plate thickness or go old school and drill and measure.
I agree unless the hull side is thick enough to allow a lot of threads tapping is probably not the best idea. If the hull is 3/16" that only allows three threads of 1/4-20 screws.
Screws as clamps for strong adhesive might be an alternative to welding and all the problems that would cause. In that case you want adhesive, perhaps 5200, not bedding such as sika. Thread corrosion becomes less of a worry if the primary mount is adhesive.
Screws as clamps for strong adhesive might be an alternative to welding and all the problems that would cause. In that case you want adhesive, perhaps 5200, not bedding such as sika. Thread corrosion becomes less of a worry if the primary mount is adhesive.
Thread locker will not prevent metal to metal contact and subsequent electron flow in a hole with a threaded fastener. As you as you snug the bolt the thread locker will yield and get displaced.
For best results try and use a screw material closest to the hull material on the galvanic corrosion chart. It may not be 316L SS. If the screw is much more "active" the screw will dissolve, If the opposite is true, the hole in the hull will dissolve and enlarge itself.
Threads can be purchased in fine and extra fine pitch for thinner materials and better holding.
Ex: 1/4-28 and 1/4-32 respectively.
Interesting scenario and I am glad it is not me. I tend to over think this stuff
For best results try and use a screw material closest to the hull material on the galvanic corrosion chart. It may not be 316L SS. If the screw is much more "active" the screw will dissolve, If the opposite is true, the hole in the hull will dissolve and enlarge itself.
Threads can be purchased in fine and extra fine pitch for thinner materials and better holding.
Ex: 1/4-28 and 1/4-32 respectively.
Interesting scenario and I am glad it is not me. I tend to over think this stuff
Capt. Bill1
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According to Loctite, and what I've seen, it will.
"Mechanical fasteners cannot prevent corrosion. Loctite threadlockers seal your threads against moisture, protecting against corrosion and galling."
If getting totally displaced was an issue than I would think anything you put on the treads would not work.
Bill, right now that Locktite sealer sounds like the best product. I imagine it applies like Tef-Gel and maybe expands as it sets? Will read up on it. I have never had issues on the two steel boats I have done years ago, so I don't expect there is that much reaction between stainless and steel. Might be if below waterline. I assume Locktite will buffer some contact.
Well, I did exactly what you are planning about 13 years ago and the rub rail is still on the boat. I use 316SS machine screws on a 3/16 stell hull. The rub rails were a total of 84' and were 3" wide, applied directly to the hull. I used 5200 to glue the rail to the hull, then secured the screws. What I did differently was use epoxy in the holes and on the screws as a sealer/bedder. This was applied with a q-tip. I also used screws a tad larger than the holes. Since stainless is softer, they locked right in. No issues with rust, corosion or anything else over the years. Just lucky I guess