Rivets, Bolts or Screws?

[ndnoutlaw]

I have a 1448 Alumacraft. What is the best way to attach a foot controlled trolling motor bracket to the bow? Should I use rivets or screws?

 

[OldTinBoatGuy]

Had a similar concern and I've decided to go with stainless steel bolts. My Lone Star has a thin bow cap and I'm am planning on using a thick aluminum back plate with about a 50% bigger footprint than the trolling motor mounting plate on the underside and bolting it all together. I think it will be my best option and will allow for easier removal if necessary and an overall more sturdy mounting method. I love using rivets, but going with bolts for this one.

 

[Bob Landry]

Pop rivets are the boatbuilders fastener of choice because they are cheap, easy to use, and in most applications, hold up reasonably well. If I'm able to reach under what I'm fastening, my choice is always stainless machine screws with fender washers and nylon lock nuts. Sheet metal screws are the second choice, but they can work loose over time with vibration.

 

[Badbagger]

Bob Landry » 19 Aug 2013, 17:33[/url]"]Pop rivets are the boatbuilders fastener of choice because they are cheap, easy to use, and in most applications, hold up reasonably well. If I'm able to reach under what I'm fastening, my choice is always stainless machine screws with fender washers and nylon lock nuts. Sheet metal screws are the second choice, but they can work loose over time with vibration.

Bob hit the nail on the head. In EVERY case and if possible, ALWAYS use stainless machine screws. Do it once and do it right. End of story.

 

[harrywbrown]

Is there an issue with using stainless steel fasteners to attach to the aluminum hull? I plan to install cedar decking and need to attach the cedar planks to an aluminum substructure. However, I am concerned about using stainless steel fasteners for the simple reason that it may corrode the aluminum. Should I be concerned?

 

[DaleH]

Is there an issue with using stainless steel fasteners to attach to the aluminum hull?

If stainless steels (SS) are used in direct contact w/ aluminum; you will get galvanic corrosion due to dissimilar metals. This effect of galvanic corrosion is greatly increased on boats used in brackish or salt waters.

However, one can simply insulate the SS from the aluminum by putting nylon washers under the heads or nuts if the fastener, or heatshrink over the bolt body, or by applying a special grease like Tef-Gel. Between pieces of SS and aluminum I have also successfully used electrical or duct tape - anything to insulate one from the other.

FWIW, one can see this effect on aluminum body reels where SS screws hold the side plate onto the body. Especially in saltwater use, one of turns sees the paint on the reel 'bubbling' around these screw holes. What you're seeing is the effect of galvanic corrosion. I also once converted a Lund 18' Tyee from being a dual console to center console, and anywhere where a SS fastener was used to secure the aluminum, the aluminum was pitted around screw holes - window frames, panels, etc.

 

[turbotodd]

Rivnuts work well if the hole is blind.

 

[BigTerp]

Rivnuts work well if the hole is blind.

I used rivnuts for my driving lights and trolling motor mount. They work great!!

 

[putback]

I have some experience restoring aluminum campers, Airstream and Avion. You can have galvanic corrosion with alum and most any other metal. Stainless less than most but still a problem long term, your environment will determine how bad. Front and backing plates are usually needed on any load bearing attachments on sheet alum. Screws tend to loosen with vibration, pop rivets have low shear strength, alum buck rivets are the best. Stainless bolts work well but a dab of common auto undercoating around the hole in the alum will reduce corrosion issues. Tempro aluminum sealer or an equivalent is the only thing that will really adhere to alum & remain flexible, silicone is iffy on the best day. A thin layer of tempro on non alum backing plates tacked up before attachment goes a long way to avoid galvanic corrosion.