I am in the process of rebedding some thru-hulls and seacocks and got the same, surprising advice from two unrelated people in the boatyard.
They both said that instead of bolting the flanged seacock in place, and then screwing in the thru-hull from the outside of the boat that I should instead insert the thru-hull (pushing it straight in) and then screw the flanged seacock onto it from the inside.
The reasoning behind this is that rotating the thru-hull will drag the sealant, which could create air pockets and lead to poor sealing. I would think that if you had a lot of sealant on there when you started that it would squish out any air pockets -- but they didn't seem convinced. Perhaps because the air pockets might form during the last little bit of tightening when most of the sealant has already been squished out.
After I thought about it for a bit, I decided I must be misunderstanding, because when tightening a flanged seacock it would have to stop at a very precise position for the flange to line up with the bolt holes in the backing plate. So I went back and asked for clarification. They reassured me that if you carefully dry-fit and mark everything that you can, in fact, hit the mark and get the bolt holes to line up. I am quite confident they use this method for flanged seacock installation and not some other situation (like a simple thru-hull with a quarter turn valve on it).
I then objected that it would be difficult to do a good job getting sealant under the flange if you are spinning the seacock around. But they said that if you did everything else right, it shouldn't leak there even if you had no sealant there. That gets into a second question I have about NPS threads and watertightness, but I will ask that in a different thread because it applies no matter which way you tighten things down and I don't want to try to tackle too much in one thread.
Has anyone else heard of this method? Is there any validity to it? I've seen Maine Sail's tutorials and in those he just tightens the thru-hull from the outside. I looked in Nigel Calder's Boatowner's Mechanical and Electrical Manual and it did not mention anything. I also tried searching the forums and Internet, but was not able to find this question. The fact that two people mentioned it makes me think that this idea must have some sort of origin. One of the people who mentioned it was a transient sailor from a thousand miles away, so it's not something that is local to this area.
I have no doubt that zillions of people have screwed in the thru-hulls from the outside and their boats have not sunk yet. But if there is real evidence that this other method has merit, I'd like to learn more.
They both said that instead of bolting the flanged seacock in place, and then screwing in the thru-hull from the outside of the boat that I should instead insert the thru-hull (pushing it straight in) and then screw the flanged seacock onto it from the inside.
The reasoning behind this is that rotating the thru-hull will drag the sealant, which could create air pockets and lead to poor sealing. I would think that if you had a lot of sealant on there when you started that it would squish out any air pockets -- but they didn't seem convinced. Perhaps because the air pockets might form during the last little bit of tightening when most of the sealant has already been squished out.
After I thought about it for a bit, I decided I must be misunderstanding, because when tightening a flanged seacock it would have to stop at a very precise position for the flange to line up with the bolt holes in the backing plate. So I went back and asked for clarification. They reassured me that if you carefully dry-fit and mark everything that you can, in fact, hit the mark and get the bolt holes to line up. I am quite confident they use this method for flanged seacock installation and not some other situation (like a simple thru-hull with a quarter turn valve on it).
I then objected that it would be difficult to do a good job getting sealant under the flange if you are spinning the seacock around. But they said that if you did everything else right, it shouldn't leak there even if you had no sealant there. That gets into a second question I have about NPS threads and watertightness, but I will ask that in a different thread because it applies no matter which way you tighten things down and I don't want to try to tackle too much in one thread.
Has anyone else heard of this method? Is there any validity to it? I've seen Maine Sail's tutorials and in those he just tightens the thru-hull from the outside. I looked in Nigel Calder's Boatowner's Mechanical and Electrical Manual and it did not mention anything. I also tried searching the forums and Internet, but was not able to find this question. The fact that two people mentioned it makes me think that this idea must have some sort of origin. One of the people who mentioned it was a transient sailor from a thousand miles away, so it's not something that is local to this area.
I have no doubt that zillions of people have screwed in the thru-hulls from the outside and their boats have not sunk yet. But if there is real evidence that this other method has merit, I'd like to learn more.
