Thickness of horizontal plate at masthead.

[Connemara]

Not sure if this is the right section, but ....

I am replacing my masthead wind transducer with the OpenWind device. That means I have to find a way to attach it to the plate that closes the top of the mast (there's probably a technical term for that but I dunno).

The device has an extender arm that could attach directly to the plate or there's a railmount attachment whose top section could itself be mounted to the plate, with the extender arm attached to that.

In either case, I am thinking I could simply tap a couple of holes, but I don't know thick the plate is. If it's too thin I'd be worried about losing the device in a stiff breeze.

Boat is a Mirage 27 sloop; the mast is about 26 feet. I don't know the mast maker.

I guess the other possibility is to take the plate off in some way (not sure how it's attached), drill up from underneath, and screw the extender arm on. Difficulty there is it has to come off after haulout and I'd be worried about losing the screws every time.

So, thoughts?

Connemara.

[Thumbs Up]

I never have seen one to thin to tap.

[tkeithlu]

Beautiful instrument. I wish I had one for my powered boat.

The transducer is light, and of minimal windage given the solar panel. I recommend you tap three holes, probably 10-32 or 4mm. Attach. Only get concerned if reasonable torquing (about 30 inch pounds) strips the threads.

[GordMay]

Originally Posted by Thumbs Up

I never have seen one to thin to tap.

Originally Posted by tkeithlu

... The transducer is light, and of minimal windage given the solar panel. I recommend you tap three holes, probably 10-32 or 4mm. Attach. Only get concerned if reasonable torquing (about 30 inch pounds) strips the threads.

I agree with both, earlier posts.
The OpenWind device indicates mounting by (2) m5 screws (drill 5.3mm) ≈ 10-32 (drill 13/64")
The length of engagement should be approximately 1 to 1.5 times nominal diameter. After that, there is no appreciable increase in strength.
It's called a masthead 'top plate'.

[Spot]

Hi Connemara, do you have a picture of your masthead as it is currently?

[Scubaseas]

Tapping would probably be fine. Three full threads will yield pretty much full strength. If the top plate is too thin (unlikely) and you do not have to regularly remove it use rivets (aluminum or tefgel or toplac coated stainless or monel) . If removal is required nutserts AKA rivnuts put in with Tefgel or toplac will work fine. Another option would be wellnuts.

[Cadence]

Pilot holes, self taping screws and don't worry about it.

[Apollo366]

The "Mast head plate" is know as the mast Truck, on modern boats it has a Crane (a portion of the truck that extends out foreward of the mast to receive the spinnaker halyard block. Even on a 26ft boat it should be 1/4" aluminum and able to receive a 10x32 tapped bolt to hold your wind sensor crane. A 10x32 bolt is 3/16 dia. so the 1/4' aluminum should do fine, self tapping screws should work just fine too, esp if the sensor & crane are lightweight.

Capt Wayne

[Apollo366]

I just looked up the Open Source instrument, it weighs 290 g or 10+oz, over 1/2 lb.
This is fairly heavy & very expensive, I would actually remove the truck & through bolt it in place, esp if the truck is <.25", 6.33mm thick or seems to be a soft type of alum.

Just me thoughts,

Capt Wayne

[Connemara]

Thanks to all for some good comments on my top plate or mast truck, whichever.

I am leaning toward tapping holes for the supplied M3 screws, but I might try to take the top plate/mast truck off to inspect it first. I have no idea how easy that is. FYI it does have a crane, Capt. Wayne.

Connemara

[Connemara]

Just to follow up, in case anyone was wondering what happened: I ended up using the existing wind instrument mounting, with some finagling.

The top plate was only about an eighth of an inch thick so when the manufacturers mounted the original SR Mariner instruments, they ran bolts through from the underside to match holes in the extender arm.

I got a small quarter-inch thick slab of aluminum, about 3" by 5", drilled holes on one end to match the existing mounting bolts, and tapped holes in the other end to match the Open Wind mount. A bit of a chore but relatively easy.

Connemara