Masthead mounting plate - 6061 or HDPE

[ricksoth]

I have an approximate 1.5" wide flat mounting location at the top of my mast, and need to mount a Garmin wireless wind anemometer which has a plastic "mount" that has hole centers at 2.0" apart. See the attached images.

The semi-experienced, but not a full-time professional "rigger" that works at the marina where the boat resides is suggesting HDPE flat stock as a good material for this adapter. He had some that is 2.75" x 10" x 0.5" he gave me.

Since the Garmin mount is some type of 'plastic' also, maybe the adapter can also be 'plastic', or should I focus on 6061 plate aluminum of something like .25" thickness?

Using the free existing HDPE might be setup with SS backer nuts set flush in the HDPE holding the mount to it, and then 2 holes forward and behind the mount plate to attach the HDPE to the masthead. Basically raising the mount 1/2" above the existing masthead. This requires creating 4 threaded tapped holes in the masthead by the rigger.

The aluminum route seems more like an offset setup where one hole of the rear 2" wide holes will be exposed to the side of the masthead, and the other two holes will hold the mount and adapter to the masthead via the tapped threaded holes the rigger creates. Only 2 threaded holes need to be done by the rigger which is a plus I suppose for aluminum.

Thank you for reading this post and sharing your thoughts.

 

[dlochner]

First, the clevis pin for the forestay looks bent, should be replaced.

I don't think it matters much which material is used. ½" HDPE is probably overkill as is ¼" aluminum.

⅜" HDPE or 3/16" or ⅛" alumnimum should be adequate. Of course nothing wrong with using the thicker material if you have that and don't have the thinner stock. A couple of rivets to hold the plate to the mast head and a little 4200 will secure it. The 4200 probably won't work with the HDPE. Through bolt the bracket to the mounting plate using nyloc nuts and your good to go.

 

[jssailem]

What about shaping the piece of aluminum like the foot print of the Garmin base. Drill 4 holes in the aluminum plate tap one that is where the wing of the garmin base extends beyond the mast head. Drill and tap 3 holes in the mast head that will hold the plate to the mast head. Two of the holes will be in the same place as the garmin base.

This way there are 3 screws or bolts holding the plate to the mast head. And 3 that are holding the garmin base to the plate. The plate has a minimal extension off the mast head.

 

[Foswick]

First, the clevis pin for the forestay looks bent, should be replaced.

Not to sidetrack the discussion, but ... well-spotted!

I looked at these images for 5 minutes trying to see what you are seeing. I assumed you meant that you thought the pin was bent with an upward arc. Since I figured this was unlikely, and more likely just an optical illusion from the wear patterns, I dismissed that. Then, I drew a straight line across the bottom and ... sure enough ... it arcs upward.

 

[FastOlson]

If not metal, like good ol' Aluminum, I would opt for reinforced material like G10. My understanding is that cast resin products like HDPE can break or crack.

 

[ricksoth]

The "bent" clevis pin comments, is this the pin shown again with the arrow in my photo here? This is the holding the spinnaker halyard block only. The forestay is on a lower pin as you can see in the other image here.

Or am I missing something?

What about shaping the piece of aluminum like the foot print of the Garmin base. Drill 4 holes in the aluminum plate tap one that is where the wing of the garmin base extends beyond the mast head. Drill and tap 3 holes in the mast head that will hold the plate to the mast head. Two of the holes will be in the same place as the garmin base.

This way there are 3 screws or bolts holding the plate to the mast head. And 3 that are holding the garmin base to the plate. The plate has a minimal extension off the mast head.

 

[ricksoth]

Thanks to all about the base. I'm most comfortable with the aluminum option, and John, S/V Hadley's comment about how to fabricate it seems like a good plan.

 

[dlochner]

The "bent" clevis pin comments, is this the pin shown again with the arrow in my photo here? This is the holding the spinnaker halyard block only. The forestay is on a lower pin as you can see in the other image here.

Or am I missing something?

Yes that is the pin I mentioned. It is not as critical as a pin holding the forestay, but it still should be replaced. If the mast is down now, it will be much easier than if the mast is up. The pin is less than $10.

 

[ricksoth]

Thanks Dave. Mast is not down. When the rigger does the adaptor I will ask him to look at the pins. Thanks.