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Old 04-26-2010, 03:46 PM   #1
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Thru- Hulls

Had a discussion with a friend of mine about NPTS vs NPT on Thru-hulls
He had a regular bronze mushroom head thru hull that he fitted a ball valve from Hme depot. It took a while but I convinced him that National Pipe thred*sraight is way different than National pipe thread tapered.* Do you have any of these on your boat?
SD
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Old 04-27-2010, 09:16 PM   #2
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RE: Thru- Hulls

Yes.

Some mfgrs, Perko, offer through hulls that have both. The very end threads are taper with the rest of the body being straight threads. Of course if you cut the thread shank, shorten it, you lose the tapered threads.
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Old 05-15-2010, 10:52 AM   #3
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RE: Thru- Hulls

I recently installed two through hulls above the waterline and the NPT vs NPS thing became a real issue. I believe it was Keith who sent me a link for the correct tail piece- which is still backordered. One TH is for a future blackwater tank vent- a larger more horizontal supply of air than I have now. Thanks Peggy. The other is a dedicated outlet for my Oh C*#^! bilge pump. This one is about 4" above the smaller primary pump. When I connected the mushroom to the NPT barb fitting I used a PVC coupler for a temporary connection BTW, I located a leak recently at the top of my port engine sea strainer, repaired this, and the bilge is dry again.
Obviously we are at the boat and is is raining frogs- thus the rambling.

Question:
When I used the wet/dry vac to vacuum the bilge out I ran across a small screw hole in the bilge floor near my primary bilge pump. Probably was used to mount a float at one time. While using the vacuum I noticed if I ran the attachment across the hole it would pull water through the hole. STINKY water!! Apparently this is like a false floor (in the center of the boat, above the keel) and below it are the remnants of years of spilled oil filters, fuel leaks, whatever.
I am considerering brilling an exploratory hole through the floor to vacuum and dispose of this old stinky water.
Rick, anybody?
Is my thinking correct?
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Old 05-15-2010, 07:07 PM   #4
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RE: Thru- Hulls

Steve,

I went through that in my boat. I cut out the false floor from bow to stern. From the top down it was a glass skin, bits of wood with resin poured over, saturated foam. The waterlogged foam stunk enough to make you gag. I removeal all the foam, filled the cavity with concrete and glassed it over. The smell we could never track down is gone! Good luck

Rob

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Old 05-15-2010, 10:51 PM   #5
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RE: Thru- Hulls

Rob,
I went ahead with a 1" spade bit and cut a hole through the false floor. It seems to be about 3/8" fiberglass with no core. Luckily the boat did not sink! Before I cut the 1" hole I drilled amuch smaller test hole and probed a shishkabob stick through and hit what I think is the top of the keel about 4" down. After the 1" hole was cut I used the wet/dry, a gallon at a time till about an hour ago. The water was not oily but it smelled pretty funky. The water level is now about 2" down, with plenty more to go. I will give it a look in the morning to see if the level is the same and possibly continue.
It seems that I keep fighting smells, think I have it, then a few weeks later back again. I hope this does it.
I bet adding concrete that low makes your ship very stable in rough weather.
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Old 05-16-2010, 07:05 PM   #6
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RE: Thru- Hulls

Steve,
I only added about 250# of concrete or less and don't notice a difference but it must help a little. After several test holes, I fired up the sawzall and went at it. I was on the hard at the time but did not cut out anything important. Was suprised at how easy it was to guide the saw. I did use a long blade which helped. I would like to post some pictures but they seem to be too big and my wife (help desk!) is on travel.

The section from the stuffing box aft had foam all around the shaft tube which I scraped away with all manner of impliments. I did not fill that area with concrete (thank God) because of a tiny leak we have been hunting for years. In April I dropped the rudder, pulled the shaft and pluged the hole in the keel with a plumbing test plug. Then modified a pressure test fitting (2"pvc vent) I made for plumbing when we built our house.This was attached to the stuffing box with a rubber coupler. The plan was to put 4# of air in it. A soon as the air went in we could hear it leaking. Soap bubbles foung the leak all the way aft on the bottom of the tube. No definite way to be assured I could clean it enough to reglass and that the repair would hold so I cut it out. My boat was built in Korea. I am sure it was built under a tree in some guys back yard. It always surveys well but there is a lot of weird stuff. The shaft tube looks like it was made by waxing then glassing a pipe. I guess it held up for 30 years so it can not be that bad. Anyway, I bought a new tube and the yard is glassing it in now. The measurements are more than I wanted to do. I will fill the "V" with something because I need to glass over the cavity so I can put the generator back in. No rush to do that as we have cruised the last three seasons without it and I want to be sure the leak is solved. Any suggestions as to what to use for filler? I suppose concrete would be fine as this tube is much better and should be good for at least 30 years,but......

Rob
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Old 05-16-2010, 08:23 PM   #7
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RE: Thru- Hulls

Great effort on finding your leak! I would love to see some pics when able.
I am not sure if I understand filling the V. I assume you are talking about the area below where the subfloor was? If so, how about putting a subfloor back in- possibly glassing in some starboard?
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Old 05-17-2010, 10:04 AM   #8
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RE: Thru- Hulls

I think you could glass over starboard.* But not to it. Nothing sticks to the stuff.

Better to use marine ply and glass or,*
I have heard of a company that makes fiberglass sheets in thickness up to like 1/2"

Also, if you know how to fiberglass there is a product called divinycell. *It is a PVC foam. Comes in sheets flat or grid scored, that would let you conform it to shape. Once it is glassed on both sides the stuff is pretty strong. almost as strong as glassed plywood without the weight.

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Old 05-17-2010, 10:25 AM   #9
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RE: Thru- Hulls

Rob,

When using cement what did you use to adhear the cement to the Glass if anything?

I worry about water between the two. I have considered filling my keel, but with my stuffing box dripping there is always some water below the engine in my keel.

Perhaps*this is not an issue but I have heard of issues with fiberglass in constant contact with water a sort of osmotic wicking of the water into the glass. not unlike blisters but from the inside.
*
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Old 05-17-2010, 07:13 PM   #10
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RE: Thru- Hulls

Steve,

The V is the area under the subfloor that was filled with foam. I was thinking of using a resin developed for re-coring outboard transoms but have to look into it more. I can glass over it fine but don't think I should leave it hollow.

SD,

I did not do anything other than grind it clean. In retrospect I guess I should have barrier coated. Time will tell. Now that the leak is solved (I hope) I may put another layer of glass over what I have with vinylester resin.

Rob
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