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Old 14-06-2016, 13:33   #1
vjm
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Dumb question aboout drilling into hull

I have to install a new seacock, but not a new throughull on my boat. The old tapered plug seacock had the key strippedd off the plug and the screws were stripped. Efforts to get that fixed in a machine shop fell flat, so I ordered a new Spartan tapered plug seacock to put on.

In taking off the old seacock, I noticed that it was only held in place by screwing onto the throughull and adhesive. No bolts.

I would like to install the new seacock by screwing it on the throughull, adhesive (Sikaflex 291 unless someone has a better option), AND BOLTS.

Here is my question: this is under the sink, and the hull curves downward pretty sharply. How do I drill at 90 degrees to the hull in this situation? It seems like drill guides really only work on flat surfaces.

I know this a super basic question, but I am stumped and really need some enlightenment. I don't want to screw this up, since it is safety related.

Thank you so much!
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Old 14-06-2016, 13:50   #2
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Re: Dumb question aboout drilling into hull

I don't get the "bolts" idea. Any chance you mean set screws? If so, you might drill and tap some holes before you screw it on. If not an angle drill will help.
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Old 14-06-2016, 13:55   #3
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Re: Dumb question aboout drilling into hull

What do you think is going to occur? The seacock isn't going to back itself off. I've used teflon tape on the threads and it's held for years. I need a wrench to remove my through hulls. I removed on this year that I needed mechanical leverage to start unscrewing.
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Old 14-06-2016, 14:19   #4
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Re: Dumb question aboout drilling into hull

I would recommed replacing the thruhull at the same time as the seacock. Typically you build a backing plate that "flattens" that section of the hull interior so that the seacock can be bolted securely. Best reference is:

Seacock Backing Plates / Alternate Method / No Through Bolts Photo Gallery by Compass Marine How To at pbase.com
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Old 14-06-2016, 14:22   #5
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Re: Dumb question aboout drilling into hull

Guy: sorry, I should have said machine screws. The idea is that the correct installation for the Spartans involves drilling two holes through the hull, countersinking at both ends, inserting the machine screws do that the heads are on the exterior hull, those go through the seacock backing plate, and are secured with nuts. Then you fill in and over the exerior and repaint the antifouling in those spots. Hope that helps.

Shrew: I hear ya. All my seacocks are installed like that, and they have been in place since 1977 with no issues. All the sources I can find say that that is an installation that was done for cost saving, and is not safe or correct. Believe me, I would much rather just stick the thing on and move on with life.

If anyone else shares Shrew's opinion that the machine screws are overkill and adhesive + screwing onto the throughull is safe and sufficient, please let me know. It would certainly make things easier.

pcmm: I think I have memorized the Compass Marine site at this point, but I was looking for just that part of it and couldnj't find it, so thank you so much!

The issue with installing an additional backing plate is that I am not replacing the throughull at the same time (mine is fine, they are expensive, that is even more work and yard time than replacing the seacock), and the throughull is already cut to length. So if I drop a backing plate on there then 1) itis goingon area of the hull that is already built up, and 2) there won't be enough threads available to tie the throughull and the seacock together. If I wanted to do that, I would have to chisel out the existing fiberglass to make room, then fiberglass in a backing plate. Seems kind of redundant. That's why I am going with the "screw on, adhesive, bolts from the exterior" method.

If anyone has any suggestions or agrees with pcmm that I should also replace the throughull, I am interested to hear it.
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Old 14-06-2016, 14:32   #6
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Re: Dumb question aboout drilling into hull

In today's world the screws to bolt the seacock to the hull are probably overkill. I always disliked drilling 3 holes in close proximity to a large diameter hole in the hull. But that's probably worrying about nothing. Bolting seacocks started with wood hulls.
You do want the seacock base to fit well to the hull (or adaptor plate), to avoid any pressure on the mushroom fitting's threads if you have to apply some pressure on the seacock.
I too would replace the mushroom/thru hull fitting as long as you are going that far. Does the Spartan seacock have a good wide flange?
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Old 14-06-2016, 14:41   #7
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Re: Dumb question aboout drilling into hull

I am not having luck uploading pictures from photobucket, but it is the S701 by Spartan and it does have a decent flange.
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Old 14-06-2016, 14:44   #8
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Re: Dumb question aboout drilling into hull

Quote:
Originally Posted by vjm View Post
I am not having luck uploading pictures from photobucket, but it is the S701 by Spartan and it does have a decent flange.
You don't need to use Photobucket on this forum. Just place the pic in your computer and download straight from there by cliking on "advanced"
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Old 14-06-2016, 14:48   #9
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Re: Dumb question aboout drilling into hull

Hopefully this works.
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Old 14-06-2016, 18:35   #10
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Re: Dumb question aboout drilling into hull

The hull is probably not very thick so drilling the holes exactly vertical shouldn't be an issue. If you go to all the trouble to drill the mounting holes use a fiberglass or Starboard backing plate. Through bolting the seacock is probably not necessary unless it's somewhere that it might get stepped on or something heavy fall against it.
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Old 14-06-2016, 19:11   #11
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Re: Dumb question aboout drilling into hull

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The hull is probably not very thick so drilling the holes exactly vertical shouldn't be an issue. If you go to all the trouble to drill the mounting holes use a fiberglass or Starboard backing plate. Through bolting the seacock is probably not necessary unless it's somewhere that it might get stepped on or something heavy fall against it.
The hull is 1-1.5" thick right there. If I don't change out the throughull, in order to put in a backing plate, I would need to grind out the extra fiberglass that was laid up originally under the seacock (it's like a pad under the seacock), and the adhere the plate. It seems a little weird to me to grind out fiberglass to replace it exactly with fiberglass. Right?

That is sort of why I am defaulting to machine screws through the hull. It's the only other thing I can think of besides replacing a perfectly good throughull or grinding out only to replace the fiberglass with a backing plate.

Maybe I am overthinking this. I'm just concerned because this is a major safety area. It is also a small seacock- 1/2". Do you think that installing the bolts lends very little strength and dependability in this scenario, compared with Teflon tape and something like Boatlife caulk?
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Old 15-06-2016, 09:27   #12
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Re: Dumb question aboout drilling into hull

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Originally Posted by vjm View Post
The hull is 1-1.5" thick right there. If I don't change out the throughull, in order to put in a backing plate, I would need to grind out the extra fiberglass that was laid up originally under the seacock (it's like a pad under the seacock), and the adhere the plate. It seems a little weird to me to grind out fiberglass to replace it exactly with fiberglass. Right?

That is sort of why I am defaulting to machine screws through the hull. It's the only other thing I can think of besides replacing a perfectly good throughull or grinding out only to replace the fiberglass with a backing plate.

Maybe I am overthinking this. I'm just concerned because this is a major safety area. It is also a small seacock- 1/2". Do you think that installing the bolts lends very little strength and dependability in this scenario, compared with Teflon tape and something like Boatlife caulk?
You just need a flat surface, you could grind the slight curve flat.

In a reversal of my earlier post saying you don't really need the screws... I had one thought: In today's world I am less convinced when I buy something "bronze" that it really is bronze or possibly might be some sort of brass or mix of the two. The screws provide insurance that the Mushroom fitting will not snap off and sink the boat. If you look at the thickness of a mushroom fitting at the root of the threads to the Inside diameter... there's very little material there.
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Old 15-06-2016, 09:36   #13
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Re: Dumb question aboout drilling into hull

If the hull is that thick I would level the extra fiberglass with thickened epoxy and tap holes from the inside for machine screws that do not go through the hull. If the hull is 1" to 1 1/2" thick I would tap 1/2" deep or so. You will need a bottoming tap.
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Old 15-06-2016, 09:59   #14
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Re: Dumb question aboout drilling into hull

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If the hull is that thick I would level the extra fiberglass with thickened epoxy and tap holes from the inside for machine screws that do not go through the hull. If the hull is 1" to 1 1/2" thick I would tap 1/2" deep or so. You will need a bottoming tap.
Not a bad idea at all...
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Old 15-06-2016, 10:02   #15
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Re: Dumb question aboout drilling into hull

Is this seacock likely to be hit with anything like stored items, or loose items that could hit it if things really got rough?
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