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Thread: Thru Hull Fitting Advice
03-03-2013, 12:09 PM #1
Thru Hull Fitting Advice
I have a few questions about buying thru hull fittings for the boat and installing them. I did take a quick look to make sure that I'm not replicating another thread but there is so much info on here that I'm sure I am.
First off is there a thread that walks you through the process of drilling into the bottom of the boat and sealing the holes with 3M glue. I would really like a picture by picture walk through because honestly I am really nervous about adding these into the bottom of a perfectly good waterproof boat. I am adding 4 Johnson reversible pumps and ripping out all the 3/4 inch line for the fill and empty but the part I'm most nervous about is the drilling through the bottom of the boat part.
1. Do you use a regular hole saw, if so what size for a 1 inch fitting.
2. Should I be buying 1 inch or 1 1/8 fittings? If 1 1/8 what size hole saw do I need?
3. I understand that you run the hole saw in reverse first but there is always a certain amount of wobble in the hole saws is that going to be an issue? Do they make a diamond type hole saw and would that be better?
4. I am planning on leaving the vents 3/4 inch, does anyone know if I need a 90 degree fitting for any of these. I also wanted to know if the smaller diameter flange fittings would work for this or if I need to get the wider flange. is this area usually scuffed up underneath the fittings.
5. Also planning on putting the check valves in there to suck the bags flat. Any reason I shouldn't do this?
6. Getting back to the bottom of the boat, How much glue do you use and do you need to buy the lock-nut with the screw in it?
7. I had this done for me on the last boat I owned and it cost me 200.00 for 1 fitting, I am not prepared to pay that again, Is there someone in the forum that lives close to me (Cumming GA) that has done this before on their boat, that would like to work for BEER?
8. Anything else that I really need to look out for when doing this? I understand that you need to smooth out the hole with a dremil tool or sand paper after the hole is drilled, but any other gotcha's would be greatly appreciated.
03-03-2013, 12:57 PM #2Senior Member
- Join Date
- Sep 2005
- Claytor Lake, VA
Check this post out.
http://www.moomba.com/msgboard/showt...rill+hole+hull2005 Mobius LSV
03-03-2013, 03:34 PM #3
1) Yes, standard hole saw.
2) when you say fittings, do you need the thru-hull? There really isnt a big selection of 1.125" thru-hulls and ball-valves. 1" is more then plenty to feed a couple of pumps, depending on your particular setup. There is no real measurable flow advantage using 1.125" hose over 1". Its not worth the cost difference IMO. Some fittings you will use will be a 1" barbed fitting and some will be a 1.125" like the W746 and W743 Fly High female quick-connects. I would rather heat up and stretch over 1" hose, then try to crimp down 1.125" hose on a 1" barbed fitting. My suggestion would be to purchase the thru-hulls first, then measure their OD and go with the hole saw that best fits.
3) If your hole saw wobbles, you need a new saw bit or drill. Its well worth getting a quality bit from Home Depot or a Lowes as opposed to a $5 kit from harbor freight with 20 bits and a single arbor.
4) if you are going with tall sacs, the 90* vent thru-hull turned up can help reduce passive draining through the vent line. If your hole saw is a good match to the thru-hull, then a large flange is not needed. Scuffing the area is not needed IMO, but striping it of any wax, etc, before applying the sealant is best.
5) no reason not to in most cases.
6) I uses a bead of sealant around the hole on bilge side, after cleaning first, then a bead on the flange before installing. Once you get a little sealer squeezed up into the threads of the nut as its seats, the sealant will cure and it will not come loose.
just dont drill blind. Know where the bits going before you cut that hole. I like to use a tiny bit for a pilot hole first. Then I can see where it came through to make sure im not going to be on a trailer bunk or something. If all looks good, then proceed with the hole saw.
03-03-2013, 08:16 PM #4
Thanks guys for the info, Anyone ever tried to use one of the diamond type hole saws? Would one of those be preferred.
03-04-2013, 02:17 PM #5
1) Used a regular wood hole saw myself-went thru the floor with no issues at all
2) 1" fittings
3) had no wobble myself so not sure, but dont think it should
4) vent holes are able to take 1" fittings
5) yes on the check valves, makes the bags look like a raisin
6)a nice wide beam of silicone, locking nut not used on mine or from the factory, when you tighten the nut the excess silicone comes out
7)plan to be in Georgia middle of July, will work for cold beer, always willing to help out
never sanded the hole edges or used a dremil, to this day the hole I drilled does not leakHey, Its Moomba time
13 Mobius LSV
08 Mobius LSV-sold
03 Mobius LSV-sold
life is about finding the balance between being a responsible adult and staying young at heart
03-04-2013, 07:49 PM #6
I appreciate the offer to come and help, maybe just cold beer and skiing instead of working when you come through. The reason I drought up the sand paper or dremal is to bevel the edge of the hole so that it doesn't crack the gel coat. Maybe I'm confusing the process for installing a tower vs a thru hull fitting.
I think I might have it I just need to grow a pair and start drilling into the bottom of a perfectly good boat. Has anyone ever used a larger thru hull fitting and ran 2 pumps off of it? I would think going to like an 1 1/4 thru hull would be able to handle the flow requirements of 2 Johnson reversible pumps.
03-04-2013, 09:00 PM #7
Thru Hull Fitting Advice
Me & E will come and drink some beers & start drillin holes in your boat. My Dad's got an ultimate set of tools.
2015 Supra SG
03-04-2013, 09:08 PM #8
Use painters tape from the outside on the gel coat to prevent chipping, it usually gets covered up.A Day at the Lake...Priceless
A Day in Powder...Endless
2012 Möbius XLV~ Loaded & Exiled
2007 Outback V ~ sold
03-06-2013, 01:59 AM #9
Don't notice this mentioned yet. I drilled a pilot hole from the top down. Then went under the boat and drilled up into it with the hole saw. This method allowed me to double triple check placement with the small hole before committing to the big hole. If I was off a little I could move in any direction just a little and go again as long as the pilot hole stayed within the diameter of where the hole saw was going to go.
Never had to, but liked having that option in the back of my mind as I was mustering up the courage to pull the trigger.I do all my own stunts
2001 MobiusV - Slightly Modified...
03-06-2013, 09:31 AM #10
That's what I did too and taped over the gel coat to avoid chipping. Drilled up from the bottom using the pilot.My Mom said I'm not allowed to get wet!
2000 Outback LS (sold)