rivets or screws?

Discussion in 'Boatbuilding' started by muskieslime, Aug 7, 2006.

  1. muskieslime
    Joined: Aug 2006
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    muskieslime New Member

    I'm restoring an old Terry bass boat and had to replace the wood in the transom. I split the top half of the boat off by drilling out about a million rivets around the rub rail. My Question is should I re-rivet the thing back together or use srews to replace the rivets? I have seen some boats with screws. This one has a metal or aluminum strip inside the bottom half that the rivets went through that should hold screws fine. Any input would be apriceated
     
  2. safewalrus
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    safewalrus Ancient Marriner

    Small bolts sound better, with a 'lump' at each end. :) The trouble with 'srews' tends to be that tis' only held on by the thread - great in new firm material not so clever using older stuff of questionable hold or into old holes - so either small bolts or rivets. There again can you get to the damn things, could cause a problem with rivets, bolts might be easier, screws only need to be got at from one side and with a modern battery screwdriver!!! However your the guy on the ground, as it were, i.e. doing the job so it's up to you to decide! Quite frankly if you ain't decided something this fundamental, have you 'bitten off more than you can chew?':confused:
     
  3. stonebreaker
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    stonebreaker Senior Member

    How often are you planning on taking it back apart?
     
  4. Toot
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    Toot Senior Member

    I dunno. It's one thing to do a repair/replace job for refurbishing. It's a whole other ball of wax when you start thinking about "improving" a design. I don't blame somebody for wanting guidance before making such an alteration.

    Of course, then again, what do I know? If I were refurbishing this boat, I would most certainly be in over my head. ;)


    For whatever it's worth, if I were on my own in making this decision, I would probably do a pull test to ensure that you have comparable strength with the screws. Screws will not be as strong as the rivets, but if you have enough space to use a closer spacing on the screws without severely limiting the sheer strength of the wood, then you may be able to use additional screws to make up the difference in strength. In other words, you don't want the wood to crack between two screw or rivet holes... so if the rivets are already very close together, you can abandon the idea of using extra screws to make up for the lessened strength because using extra screws will make the distance between the holes less and that can lead to a sheer failure. However, if you have enough space between the rivet holes, this may be viable. Of course, some of this also has to do with the orientation of the fibers on the wood (unless it's plywood, which it probably is). If you're talking about something other than plywood, you will also be limited in that the strength of the wood between holes will be less if those holes are parallel to the grain... And one final consideration is the size of the head and tail of the rivet. Is there any chance that the rivets are subjected to any loads in tension? I hope not. It shouldn't be designed that way, at least... but if there's a huge head and tail on the rivet then that might be the case... and that would be another strike against replacing them with screws. But this is all from my knowledge of structures though.. it has nothing to do with boats. ;)
     
  5. Frosty

    Frosty Previous Member

    I assume when you say rivet you mean the pop rivet inserted with a gun. some times when drilling these out the drill can slip off course and enlarge the hole so as to make a screw unusable. You could end up with half of each.

    I would go with small bolts with washers and lock nuts. Even enlarge the hole slightly to 6mm or 1/4. You could probably use a few less than a million too.!!!!
     
  6. Toot
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    Toot Senior Member

    Generally speaking, I don't like bolts being used in wood for structural members. The lack mechanical lock with the wood will allow some flex and may cause the bolts to loosen over time as the washers rub against the wood. The nuts may not move, but the wood can compress silghtly.

    In aviation, when using wood (not that that's very common these days... lol) we will over drill a hole, insert a dowel, plane it down, and then drill and screw into it.

    When you said rivets, I was hoping he was referring to some sort of fastener that doesn't put pressure on the wood. The problem with pop rivets or traditional rivets in wood is that they pinch the wood, breaking the fibers, weakening the structure. Screws, with appropriate-sized pilot holes are the best way to go, so long as you can use enough of them without worrying about sheering between the screws.
     
  7. SamSam
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    SamSam Senior Member

    Toot, it's a fiberglass boat. Slime, rivets are faster and cheaper. Were They still working well when you took the boat apart? Screws won't pull the two pieces together good unless you drill two different size holes, one big enough in the outer piece for the screw to fit through and a smaller one on the inner piece for the screw to thread into. Either will work. You might have a problem with stainless screws and the metal strip on the inside of the boat being dissimialar (sp?) and corroding. Sam
     
  8. van stoneman
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    van stoneman fiberglass shop manager

    the most simple answer for you i believe is pop rivets they lasted awhile already Just rember nothing last for ever anyway.
    but seriously Ive been building & tooling fiberglass bass boats for 26 yrs if that makes any differance
     
  9. Toot
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    Toot Senior Member

    Well now I'm *really* confused.


    I wouldn't use screws into fiberglass unless it has a wood core, or if I were screwing all the way through the FG. However, if I were screwing all the way through the fiberglass, I would absolutely use a speed nut to secure it. Screws are abrasive. They will scratch along the edge of the hole in the fiberglass as the piece flexes. The hole will enlarge and eventually the screws will be worthless unless you are using something with a bit of a backing plate, such as a tinnerman nut or "u-type" speed nut.
     
  10. van stoneman
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    van stoneman fiberglass shop manager

    there is a material that is used for screw retention its called trevera core.
    It is wet out heavily with resin then applied to the inside of the hull.
    it works very well in most cases. but in the rivets or screws issue I would go with the rivets because its so much faster and less trouble and still holds really good if done right.
     

  11. Frosty

    Frosty Previous Member

    I think what your supposed to do is put the deck into its proper position, then screw it any old how, just to close the gap. Glass it on the inside. Take the screws out again. Finished.

    Thats how they( manufactures) fitted the fly bridge to my boat. When I am out in roughish seas I often sit up there thinking about it.
     
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