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Old 02-12-2020, 14:17   #1
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Thickness of horizontal plate at masthead.

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?

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Old 02-12-2020, 15:50   #2
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Re: Thickness of horizontal plate at masthead.

I never have seen one to thin to tap.
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Old 03-12-2020, 07:10   #3
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Re: Thickness of horizontal plate at masthead.

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.
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Old 03-12-2020, 07:37   #4
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Re: Thickness of horizontal plate at masthead.

Quote:
Originally Posted by Thumbs Up View Post
I never have seen one to thin to tap.
Quote:
Originally Posted by tkeithlu View Post
... 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'.
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Old 03-12-2020, 07:53   #5
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Re: Thickness of horizontal plate at masthead.

Hi Connemara, do you have a picture of your masthead as it is currently?
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Old 03-12-2020, 10:18   #6
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Re: Thickness of horizontal plate at masthead.

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.
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Old 03-12-2020, 12:06   #7
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Re: Thickness of horizontal plate at masthead.

Pilot holes, self taping screws and don't worry about it.
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Old 03-12-2020, 14:11   #8
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Re: Thickness of horizontal plate at masthead.

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.

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Old 03-12-2020, 14:23   #9
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Re: Thickness of horizontal plate at masthead.

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,

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Old 04-12-2020, 08:18   #10
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Re: Thickness of horizontal plate at masthead.

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.

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