THE BIG SUPPORT ARCH ON THE AFT - DRILL HOLES?

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BOAT
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THE BIG SUPPORT ARCH ON THE AFT - DRILL HOLES?

Post by BOAT » Tue Jul 16, 2019 10:42 am

aft mast support arch

WILL I COMPROMISE STRENGTH IF I DRILL A HOLE IN IT??

I suspect Tom Foolery the engineer with the computer formulas would know this one - I was CONSIDERING drilling a 1/4 inch hole in the mast support arch on the bottom side to run a wire for a new wind sensor.

Am I going to make the arch fail if I do that?

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Re: THE BIG SUPPORT ARCH ON THE AFT - DRILL HOLES?

Post by Tomfoolery » Tue Jul 16, 2019 2:26 pm

Depends where in the arch you put the hole. Got a sketch?

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Re: THE BIG SUPPORT ARCH ON THE AFT - DRILL HOLES?

Post by BOAT » Tue Jul 16, 2019 3:21 pm

in the horizontal part (the top) about midway between the center and the bend. should the hole be on the underside? or should it be on the back? I was avoiding the top so water can't get in.

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Re: THE BIG SUPPORT ARCH ON THE AFT - DRILL HOLES?

Post by kurz » Tue Jul 16, 2019 3:30 pm

remember the arch has 4 wholes where it is bolted to the boat. And even more there is the most stress... And the wholes go though both sides of the tube.

The whole that you will drill will just gon in 1 side of the tube.

I guess it will be no problem.

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Re: THE BIG SUPPORT ARCH ON THE AFT - DRILL HOLES?

Post by BOAT » Tue Jul 16, 2019 3:42 pm

I was just looking to run the wire for a new wind sensor inside the tube. I just don't know if it would be better to drill the hole in the bottom or the front or rear sides - only one hole.

i assume most the pressure up there on the top of the arch is downward from the mast crutch - so I thought a stress crack from a hole would be most likely if the hole were drilled on the top - but really - i do not know. I thought maybe all you engineer guys might have a better knowledge of such things. that arch is a bendy metal, not a rigid cracking kind, right?

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Re: THE BIG SUPPORT ARCH ON THE AFT - DRILL HOLES?

Post by Tomfoolery » Tue Jul 16, 2019 5:18 pm

Front or back is better than top or bottom for the loads and the location. That’s assuming primarily vertical load from the mast weight.

Bending stresses are maximum in the top and bottom of the tube, and theoretically zero in the front and back. Shear stress in that spot is maximum, but small in magnitude, so not a concern. It’s why you drill holes in the middle third of a floor joist, and not near the top or bottom.

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Re: THE BIG SUPPORT ARCH ON THE AFT - DRILL HOLES?

Post by BOAT » Tue Jul 16, 2019 5:41 pm

okay - i will pick a spot along the rear side - first i will look over some of the other arch pictures on the site and see where other people have drilled holes and see if they had any issues.

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