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post #1 of Old 04-14-2013 Thread Starter
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Tips for cutting hole for flush mount through-hull

Hey folks,
I'm replacing surface mount cockpit drains with some that will be flush mount, like a standard flush mount through-hull with the beveled edges. Does anyone have a suggestion on how to cut the proper recessed, beveled-edged hole, given that the is an existing hole there now? I'm not sure how to go about it.

Basically, this is no different than pulling a surface mount through-hull and replacing it with flush, it's just at it's on the cockpit sole instead of below the waterline. I'd think the same principles apply though. Any tips? Or suggestions for an article to read?
Thanks!
J

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Re: Tips for cutting hole for flush mount through-hull

Seen this?

http://www.goodoldboat.org/pdfs/Addi...inyourboat.pdf

The biggest issues you'll face is getting a properly beveled hole for the flange, and dealing with core materials if they are present in the area. Probably best to remove any coring a 1/2" or more around the hole, fill it to seal the core and then 'machine' the hole as required.

I'd have thought there was a specialty hole saw for just this purpose but I haven't been able to track one down yet... so it might be a job for a dremel or some such tool in the end...

Ron

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Re: Tips for cutting hole for flush mount through-hull

I've never tried this, but it seems to me that a trim router, template, and a chamfer bit would probably work (although you might run into clearance issues depending on how close the holes are to the sides of the cockpit.)


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Re: Tips for cutting hole for flush mount through-hull

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Originally Posted by PorFin View Post
I've never tried this, but it seems to me that a trim router, template, and a chamfer bit would probably work (although you might run into clearance issues depending on how close the holes are to the sides of the cockpit.)
A rotary zip cutter with a 1/4" shank will accept router bits and not need as much clearance as a standard router. Torquey little things, though, hang on tight.

Ron

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Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
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Re: Tips for cutting hole for flush mount through-hull

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Originally Posted by Faster View Post
Seen this?

http://www.goodoldboat.org/pdfs/Addi...inyourboat.pdf

The biggest issues you'll face is getting a properly beveled hole for the flange, and dealing with core materials if they are present in the area. Probably best to remove any coring a 1/2" or more around the hole, fill it to seal the core and then 'machine' the hole as required.

I'd have thought there was a specialty hole saw for just this purpose but I haven't been able to track one down yet... so it might be a job for a dremel or some such tool in the end...
Thanks Faster. I'll definitely deal with any coring in the area. Still not sure how I'd cut the beveled hole, since the cockpit wall is only about 1.25" from the edge of the current hole. I can see MAYBE doing it by hand with the Dremel, but it would all be guess work. More like art than engineering, which bugs me. If I mess it up, it will be plainly visible.


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Originally Posted by PorFin View Post
I've never tried this, but it seems to me that a trim router, template, and a chamfer bit would probably work (although you might run into clearance issues depending on how close the holes are to the sides of the cockpit.)
I think the cockpit wall might be the issue with a router. Not sure about the rotary zip that Faster mentions, but that sounds like a recipe for a big screw up (on my part).

Quote:
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A rotary zip cutter with a 1/4" shank will accept router bits and not need as much clearance as a standard router. Torquey little things, though, hang on tight.
Alternatively, I could go with a mushroom cap through-hull. The drain sits in a bit of a recessed spot, so most water would still drain. But a little would be standing around it in the recess. Not sure how I feel about that, but the install would sure be easier.

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Re: Tips for cutting hole for flush mount through-hull

My cockpit drain fittings are more like sink drains... a thin SS lip that doesn't sit very proud of the surface, rather than a standard throughhull.. maybe look for something like that.

http://www.alibaba.com/showroom/stai...pit-drain.html

Ron

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Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)

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Re: Tips for cutting hole for flush mount through-hull

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My cockpit drain fittings are more like sink drains... a thin SS lip that doesn't sit very proud of the surface, rather than a standard throughhull.. maybe look for something like that.
Well, you're dead on, Faster. I have those drains now. In fact, they ARE sink drains (2" bar sink drains). But all the attachments are pot metal, zinc, chromed brass, etc. All corroded originally and crumbling. I was planning to replace the corroded parts and put the sink drains back in. I found a few problems though:

1) It's logistically very difficult to get everything attached due to the bends in the hose (even with flexible hose). Long story, just trust me.

2) The hardware that screws on (all of which I had to replace because the original stuff had disintegrated) was very difficult to find. Although all plumbing/hardware stores carry these parts, the threads all vary. I had to buy 8 sets before I found 2 that matched what I have.

3) While installing one of these back in, one of those screw on nuts broke. Why? Because I put a wrench on it. That's pretty bad, and I'm not sure I want those parts to be the things that are supposed to keep our boat from sinking (our cockpit drains lead to hoses that connect to seacocks below the water line).

So after all that, I started to rethink the original drains and though about just switching to a real cockpit drain that was designed for this type of installation and isn't pot metal. Of course, there are problems there too.

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Re: Tips for cutting hole for flush mount through-hull

Faster, I took a look at some of these and a couple might even work. Do you have any idea where one can get access to these in the US without buying in bulk? I haven't seen these anywhere thus far in my search.

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Re: Tips for cutting hole for flush mount through-hull

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Faster, I took a look at some of these and a couple might even work. Do you have any idea where one can get access to these in the US without buying in bulk? I haven't seen these anywhere thus far in my search.
Sorry. I don't... If you're not in a hurry perhaps a local chandlery might chase them down for you. They look like nice fittings though... The one stated to be 316 maybe looks best. Chinese manufacture, though... buyer beware. You need 2, at $10-12 each even at the minimum of 10 that's not a load of cash and if they're any good I'd expect you could resell the remaining ones easily enough.

Ron

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".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)

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Re: Tips for cutting hole for flush mount through-hull

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... If you're not in a hurry perhaps a local chandlery might chase them down for you. They look like nice fittings though...
Unfortunately, we want to splash! I'll figure something out. Either buy another 8 more drains and find a part that fits, or buy new bar sink drains (still crappy parts, but at least I can find replacements), or bite the bullet and install something permanent. I really want to do the latter, just not sure of the "best" part.

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