OEM mast wall thickness?

[Patches]

Somewhat new to riveting.  Removed the old Forespar steaming/deck light combo which was on the boat and failing.  Was attached using aluminum rivets.  New/replacement Forespar light holes do not match up, so drilled new 3/16" holes while up the mast.

Right rivets depend on mast wall thickness (grip range).  Thought I would ask the very experienced crew here if, offhand, you know the mast wall thickness so I go up with the proper rivets.

Thanks in advance!

Patches

[Gregory M]

Not quite sure for exact thickness, it's around 1/8"(plus maybe).When I did mine I used SS long rivets, as short ones where too short.
Hope that helps.

[Admiral_Swellson]

I just changed mine the other day as well, put LED bulbs in it too. It was on there with 4 screws and while it was a very tight fit getting the new Forespar fixture's holes to align with the old ones I managed it. I also added a stainless cage around it by drilling and tapping for three more screws. 

https://www.catalinadirect.com/shop-by-boat/catalina-380390/electrical/navigation-lights/steaming-amp-halogen-deck-light-mast-guard/

https://www.amazon.com/gp/product/B000XBF91G/  (Catalina Direct didn't have the correct replacement for mine so got it on Amazon)

[Ron Hill]

Patches : I did mine a couple of times.  Believe that I used 1/8" medium length!!

Try one and if it doesn't bite drill it out and use the 1/8" long ! When I pulled the mast I had a number of old drilled out pop rivets on the mast step!!!

A thought

[waughoo]

I did my mast light with a new dedicated LED fixture from marine beam.  I used large stainless rivets (i think they were 7/16 long).  To get those to "pop" i had to get a bolt cutter like rivet gun.  The hand squeeze one could not get enough purchase to pop them.  I believe I ended up with the harbor freight one.  Not my first choice for sources, but it seemed pretty nicely built.

[Ron Hill]

Alex : 7/16"  -  WOW why such a big pop rivets for the anchor/steaming light? 

I've learned to stay away from the 7/16" Stainless POP rivets, unless I have King Kong on board to make them pop!!  On the mast I've always used 1/8" Aluminum rivets!!

A few thoughts

[waughoo]

By the time you place it through the fixture with a washer and if the hole doesnt get drilled straight, i found 7/16 to be the right choice.  Otherwise the mushroom wont be behind the inside of the mast, but rather inside the hole drilled and thus not as strong of a bite.

[Noah]

Interesting technique, Alex. I have never used a washer with a pop rivet.

[waughoo]

I only used it at the plastic mounting tabs of the mast light.  It seemed like a good idea.

[Jon W]

Using a properly sized washer helps avoid damaging the softer plastic. Another option is a wide flange blind/pop rivet.

[Jim Hardesty]

This thread has turned to replacing the steaming/deck light so thought I'd pass along, may be confess, the fix I did a couple of seasons ago.  Found a black plastic part on my deck, determined it was the bottom of the deck light.  Went up the mast and put that part back in place noticed the plastic of the light was well worn from tacking.  So I used Gorilla duct tape over the deck light, a single layer, nice and neat.  Was up the mast this spring to replace a flag halyard block and inspect, Gorilla tape is still good, will last this season.  I consider this a good fix, will replace the light next time the mast is down.  For me Gorilla taping is much preferable to drilling, fitting and wiring from a bosuns chair.  But then I'm a senior citizen.
Gorilla tape is a good thing.
Jim

[Patches]

Thanks to all who responded! Exactly what makes this forum such a valuable, and helpful, place.

I planned on using the aluminum washers with the new aluminum rivets.  The was the old setup and appears to have worked for for 30+ years.  The old Forespar mounting bracket was aluminum and, as noted by Robert and Jon, the replacement light bracket is some kind of plastic.  So I think the washers are a good idea, and thanks to Alex for explaining the reason for the longer rivets.

Didn't think to use stainless rivets because of future corrosion, and I think the aluminum rivets are plenty strong for the application.  I also purchased the Forespar protective cage and, like Robert, am planning to drill and tap the holes for attaching that.

Love the Gorilla tape idea.

Patches

[Ron Hill]

Guys : Years ago I found (West Marine?) a slightly bent Forespar deck/steaming light like the OEM one installed on the mast.  I straightened it out and swap them out when one has a problem!  Both are metal.  A small dab of caulk works great to make sure the cap stays on the steaming portion of the combo. 

The aluminum rivets work just fine.

a thought

[waughoo]

Just because of the shift in conversation, I figured I'd drop a link to my LED mast light.  Im really happy with it.

https://store.marinebeam.com/led-masthead-foredeck-combination-light/

I also bought a set of their stainless nav lights:

https://store.marinebeam.com/stainless-steel-led-navigation-lamps-uscg-ip67/

The mast light is on, but I'm still building the new mounting plates for the new Nav lights.  They are bigger than the originals.

[Phil Spicer]

  Just got home from a 2 week trip so this is a little late.
Years ago I cut 3/4" off the mast because I only had one or two threads holding the turnbuckles together when we set the mast each year. Cut mast shorter to try to make it easier to pin the rigging and have more threads in the turnbuckles. Just measured the piece I cutoff ( 1988, Tall rig) Front is .200" + .001 -.000, sides are .175" +/- .005. Back is same as sides,
including the slot for sail slugs. This is a Mark I, don't know about Mark 1.5 or Mark II.