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Drilling a hole for a USB port in the DC panel

Jun 25, 2004
Hunter 306 Pasadena MD
So my DC panel has 2 of the old cigarette lighter sockets for DC accessories, and I got this neat little dual USB port that I plan to swap in to replace one of the old sockets. Problem is, the old hole in the (metal) panel is 0.85", and the new hole needs to be around 1.18" (3cm). I want to redrill the hole without totally removing the panel from the boat, which would require undoing about 3500 different wires which are very nicely routed to the panel:
dc_panel.jpeg front_panel.jpeg back_panel.jpeg
As you can see: that's one heck of a lot of wiring, but I think they did a great job with it, so I'd prefer not to disturb most of it. The best idea I have so far: buy a 3cm hole saw and cut a hole in a bit of scrap plywood. Then clamp this to the back of the panel (3rd picture) as a guide, and drill from the back. Put something under it so I don't drill through the chart table. I'm guessing the panel is made of aluminum (painted black), but I suppose it could be steel. I hope not...

Anyway: if anyone has any better ideas, I'd be glad to hear them. Thanks in advance.
Jun 25, 2004
Hunter 306 Pasadena MD
Yea your plan sounds like it will work. I bought a USB adapter and just plug that in..... easy and works perfect.
I do have a plug-in USB adapter, but 2 things made me want to install the USB permanently. First, I do hear about problems with the cigarette lighter ports being used longer term, and second, our chart table opens on a side hinge, so if you try to open it with the USB adapter plugged in, it wants to break something. And it's a bit hard to remember it's plugged in.


Jul 25, 2013
Between Boats near Vancouver, BC
Yes, definitely a job for a step bit. It will make the tidiest hole. Or a die set, if you can find one the right size. But the step bit, though expensive, will be useful to you for the rest of your life.
Mar 20, 2016
Beneteau 351 WYC Whitby
Die mentioned above does the best job.I had 2 ,12v sockets. I left them and installed the usb in another space on the panel.
I purchased a 12v to 19v buck transformer off amazon for the one outlet . 19v is what a laptop takes & now allows me to power the computer off the batteries. Bought a wifi extender and POE powered it with 12v and cut the 120 v transformer wires off my wireless router and wired it to 12v,
I now have full wifi on the boat ,laptop, and with extender hook to the club when on a mooring . Our phones automatically hook to the wifi saving data
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Jun 25, 2004
Hunter 306 Pasadena MD
You can use a step bit like this one. Seadaddler suggested the same.
Ah, now that's just what I was looking for! Something I wouldn't have thought of myself, which really sounds like the right tool for the job. Thanks to all who replied! I always suspected I'd need a step bit some day, but had forgotten they existed :).

This does remind me of something I read here a while back, though, which really made me laugh. The responder said something like "Yeah, you could buy one of those, use it once, and then put it in your basement for your kids to throw away when you die, or you could borrow one from the auto parts store". Doesn't really apply here (it's just a drill bit), but... the thru-hull wrench I bought this past spring is one big hunk of metal that I'll probably never use again. Whenever I proudly show my daughter something I just bought, she says "Oh, more boat metal!" My basement is full of boat/car/lawnmower/plumbing metal...


Jun 4, 2009
Pearson 530 Admiralty Bay, Bequia SVG
Got a Dremmel tool? If not, they are cheap enough to buy and always useful. I've cut 1/2" SS shackles with mine before.
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Jun 25, 2004
Hunter 306 Pasadena MD
Got a Dremmel tool? If not, they are cheap enough to buy and always useful. I've cut 1/2" SS shackles with mine before.
I strongly suspect you're right, having read lots of people praising them. I guess I just haven't gotten around to it yet. Meanwhile: step bit is on the way...
Jul 7, 2004
Hunter 30T Cheney, KS
I like NYSail's adapter.
If you ever want to install USB recharging on the AC side, look at the combo AC / USB outlets at the big box stores. I bought one on Amazon . It charges pretty fast with a good USB cable
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Dec 19, 2006
Hunter 36 Punta Gorda
Harbor Freight has step down drill I have 4 complete set of drills but step down is your most go to.
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Oct 29, 2005
Hunter Marine 326 303 Singapore
My mantra is first do no harm. If the stock 12V socket is still working, just fit a dual USB Charger adaptor. Else fan it out to 4 usb port hub. That's what I did.
But if the stock socket is faulty, replace with a new single socket or a new panel mount usb port with 2 outlets. No cutting/drilling.
That's my take. Your mileage differs. Cheers!

Ken Y
May 17, 2004
Beneteau Oceanis 37 LE Havre de Grace
One consideration when adding USB outlets - Devices like cell phones are increasingly moving to USB-C chargers. You can get USB-A to USB-C cables, but they don’t provide the same fast charging advantages you can get with native USB-C. In the OP’s case you’ll still have one cigarette lighter socket, so you can still get a plug-in USB-C adapter. But in general I wouldn’t go replacing every 12V outlet with USB-A for fear of the lack of future-proofing.