Installing Seacocks - Follow Up Info !!

[Ross]

Just a little more on this the taper for NPT threads

is 3/4 inch per foot. so on a 1 inch fitting the least diameter is 0.0625 smaller than the body diameter. that will reduce the pipe wall thickness by 0.03125 . Because of the taper the pipe size is not reduced outside the fitting. Mainesail, Do you suppose that the alternator might have struck the fitting more than on one occasion?

 

[Ross]

Just a little more on this the taper for NPT threads

is 3/4 inch per foot. so on a 1 inch fitting the least diameter is 0.0625 smaller than the body diameter. that will reduce the pipe wall thickness by 0.03125 . Because of the taper the pipe size is not reduced outside the fitting. Mainesail, Do you suppose that the alternator might have struck the fitting more than on one occasion?

 

[RAD]

Threading a die onto a thru hull? *o

I've spent a lot of time cutting and threading pipe in my career and I don't think you can get the die all the way to the end on such a short piece of nipple (thruhull with NPS) and the only way to hold the piece would be from the inside of the fitting soooo after all this goofing around go buy the right sea cock and call it a day.Great forum Maine Sail

 

[RAD]

Threading a die onto a thru hull? *o

I've spent a lot of time cutting and threading pipe in my career and I don't think you can get the die all the way to the end on such a short piece of nipple (thruhull with NPS) and the only way to hold the piece would be from the inside of the fitting soooo after all this goofing around go buy the right sea cock and call it a day.Great forum Maine Sail

 

[Maine Sail]

Ross

No the alternator never hit the fitting prior to the incident. I know this because the cutting board had always been stowed next to that shelf making a wall. Unfortunately the cutting board had cracked and was at home on my work bench being glued back together. It was a great place for the alternator as long as I left the cutting board there but as things go I never through about the alternator when I took the cutting board home to glue it. The alt would have hit the fitting near the top or hose barb, more leverage, as it slid off the shelf.

 

[Maine Sail]

Ross

No the alternator never hit the fitting prior to the incident. I know this because the cutting board had always been stowed next to that shelf making a wall. Unfortunately the cutting board had cracked and was at home on my work bench being glued back together. It was a great place for the alternator as long as I left the cutting board there but as things go I never through about the alternator when I took the cutting board home to glue it. The alt would have hit the fitting near the top or hose barb, more leverage, as it slid off the shelf.

 

[Ross]

If this discussion had not taken place

all of us would be less well informed than we are now. The only discussions /debates that are worthless are the ones that turn into opinion contests with no regard for proven facts and experience.we are all richer for the persistance of the members of this forum, especially Mainesail.Rad I quite agree with you about being able to use a pipe die on a short piece.

 

[Ross]

If this discussion had not taken place

all of us would be less well informed than we are now. The only discussions /debates that are worthless are the ones that turn into opinion contests with no regard for proven facts and experience.we are all richer for the persistance of the members of this forum, especially Mainesail.Rad I quite agree with you about being able to use a pipe die on a short piece.

 

[Ross]

Mainesail. this is the paragraph I was refering to:

I personally had an improperly installed through hull crack on me when a heavy item under the sink, a spare alternator, fell & hit the valve in rough weather. My boat did not sink, as it was just a small crack, and I found the problem in time, thank god for bilge alarms, but I could have lost it.

 

[Ross]

Mainesail. this is the paragraph I was refering to:

I personally had an improperly installed through hull crack on me when a heavy item under the sink, a spare alternator, fell & hit the valve in rough weather. My boat did not sink, as it was just a small crack, and I found the problem in time, thank god for bilge alarms, but I could have lost it.

 

[Maine Sail]

Ross..

It cracked right at the large nut that was holding the thru-hull to the backing plate. While not a large gaping crack it was "spraying water" which I was able to minimize, or at least re-direct the spray, with rigging tape and then electrical tape over that. I also dove over and stuck a wooden plug up into the through hull but found it very tough to actually "pound" it into place. When they hauled the boat the wooden plug was gone..?? The bilge pump was able to keep up for two days before I could get hauled. At the time I replaced this thru-hull with a Marelon seacock which I screwed to the semi rotted wood backing plate just to get back in the water. Not the right way to do it but I fixed it over the winter..Ross, I only bring this information so those who choose to read it and possibly learn an alternate approach. I obviously don't do this to start disagreement wars and do believe personally that mismatching threads is not necessarily the smartest or safest idea. I also try and bring all the evidence to support it and don't just shoot from the hip. Yes, I'm Mr. Overkill on, many things, but I don't feel it's overkill to use properly matched threads when installing something as important as a device that is supposed to keep water out of your boat. It's funny that the only person who claims to have re-threaded a thru-hull to NPT is a non-registered poster who has only ever had ONE post according to the search tool.. My guess is this "anonymous poster" is an actual member trying to justify and feel good about his or her own installation which they know to have mismatched threads? Perhaps I'm wrong, I've been wrong many times, and hopefully this poster will post a photo for us to show us just how they re-threaded a 6" long thru-hull fitting.Many of the folks defending this mismatching are the same ones touting large measures of safety in many other aspects of boating....

 

[Maine Sail]

Ross..

It cracked right at the large nut that was holding the thru-hull to the backing plate. While not a large gaping crack it was "spraying water" which I was able to minimize, or at least re-direct the spray, with rigging tape and then electrical tape over that. I also dove over and stuck a wooden plug up into the through hull but found it very tough to actually "pound" it into place. When they hauled the boat the wooden plug was gone..?? The bilge pump was able to keep up for two days before I could get hauled. At the time I replaced this thru-hull with a Marelon seacock which I screwed to the semi rotted wood backing plate just to get back in the water. Not the right way to do it but I fixed it over the winter..Ross, I only bring this information so those who choose to read it and possibly learn an alternate approach. I obviously don't do this to start disagreement wars and do believe personally that mismatching threads is not necessarily the smartest or safest idea. I also try and bring all the evidence to support it and don't just shoot from the hip. Yes, I'm Mr. Overkill on, many things, but I don't feel it's overkill to use properly matched threads when installing something as important as a device that is supposed to keep water out of your boat. It's funny that the only person who claims to have re-threaded a thru-hull to NPT is a non-registered poster who has only ever had ONE post according to the search tool.. My guess is this "anonymous poster" is an actual member trying to justify and feel good about his or her own installation which they know to have mismatched threads? Perhaps I'm wrong, I've been wrong many times, and hopefully this poster will post a photo for us to show us just how they re-threaded a 6" long thru-hull fitting.Many of the folks defending this mismatching are the same ones touting large measures of safety in many other aspects of boating....

 

[Tom S]

Mainesail That 500lbs is a static measurement

A 60 lb alternator rolling off a shelf on a hard tack can create a decent dynamic force . Combine that with metal to metal and I could image it. But you are right , one would have though that it could have taken that hit.You explain that this particular Thru-Hull had a large nut on the backing plate holding the thru-hull down. So that means you didn't have a flanged seacock on this particular thru-hull and only a ball-valve spun on ?

 

[Tom S]

Mainesail That 500lbs is a static measurement

A 60 lb alternator rolling off a shelf on a hard tack can create a decent dynamic force . Combine that with metal to metal and I could image it. But you are right , one would have though that it could have taken that hit.You explain that this particular Thru-Hull had a large nut on the backing plate holding the thru-hull down. So that means you didn't have a flanged seacock on this particular thru-hull and only a ball-valve spun on ?

 

[Ross]

Mainesail, That failure could only be prevented with a proper seacock

. There is in the material testing business an impact test that uses a pivoted hammer so that it is very repeatable. It is used for many purposes including notch sensitivity. A threaded rod is by definition notched so the fact that the thru hull broke where it did and when it did is not too suprizing. I have had car radiator hose burst and served it with bailing twine and gotten it tight enough the limp into the next town.Keep up the good work. I can't think of a way to hold a thru hull fitting in a lathe to chase new threads .

 

[Ross]

Mainesail, That failure could only be prevented with a proper seacock

. There is in the material testing business an impact test that uses a pivoted hammer so that it is very repeatable. It is used for many purposes including notch sensitivity. A threaded rod is by definition notched so the fact that the thru hull broke where it did and when it did is not too suprizing. I have had car radiator hose burst and served it with bailing twine and gotten it tight enough the limp into the next town.Keep up the good work. I can't think of a way to hold a thru hull fitting in a lathe to chase new threads .

 

[sailaway78]

Lots of good posts

This has been a really interesting thread. I am impressed with Main Sail's attention to detail, and the quality of the photos. And as always, Ross's seemingly unlimited knowledge when facts and figures are concerned. For example I have probably ran several thousand feet of both black and galvanized pipe over the years. But I never ever considered learning how much taper there was on the threads. Anyone besides Ross have this little tidbit of info stored away somewhere. Lots of good thoughts and suggestions on here. I am always impressed with the knowledge of those on this board.

 

[sailaway78]

Lots of good posts

This has been a really interesting thread. I am impressed with Main Sail's attention to detail, and the quality of the photos. And as always, Ross's seemingly unlimited knowledge when facts and figures are concerned. For example I have probably ran several thousand feet of both black and galvanized pipe over the years. But I never ever considered learning how much taper there was on the threads. Anyone besides Ross have this little tidbit of info stored away somewhere. Lots of good thoughts and suggestions on here. I am always impressed with the knowledge of those on this board.

 

[Maine Sail]

Tom..

Tom,Quote;" A 60 lb alternator rolling off a shelf on a hard tack can create a decent dynamic force . Combine that with metal to metal and I could image it. But you are right , one would have though that it could have taken that hit. You explain that this particular Thru-Hull had a large nut on the backing plate holding the thru-hull down. So that means you didn't have a flanged seacock on this particular thru-hull and only a ball-valve spun on ?"That particular alternator weighed 12 lbs as I later sold it when I sold that boat so I do know the shipping weight as I offered to pay the shipping. It was actually wrapped in packing plastic with silica packets to keep it dry.You are correct this was NOT a proper seacock and I learned my lesson. I now only use proper seacocks.

 

[Maine Sail]

Tom..

Tom,Quote;" A 60 lb alternator rolling off a shelf on a hard tack can create a decent dynamic force . Combine that with metal to metal and I could image it. But you are right , one would have though that it could have taken that hit. You explain that this particular Thru-Hull had a large nut on the backing plate holding the thru-hull down. So that means you didn't have a flanged seacock on this particular thru-hull and only a ball-valve spun on ?"That particular alternator weighed 12 lbs as I later sold it when I sold that boat so I do know the shipping weight as I offered to pay the shipping. It was actually wrapped in packing plastic with silica packets to keep it dry.You are correct this was NOT a proper seacock and I learned my lesson. I now only use proper seacocks.