Replace plastic log through-hull fitting?

[Avocet]

It's the standard black plastic NASA threaded through-hull fitting for the log impeller. It's been in there for the best part of 15 years. There is no sign of any leakage and it's not in a place susceptible to knocks, but is subject to a bit of bilge water from the inside. The boat has been out of the water for the best part of 8 years and I hope to go back in this season. I can't remember what it was bedded with, but it would have been whatever was recommended at the time.

Do I replace it? Do these things have a "service life"?

 

[thalassa]

Unless subjected to impact, the supposed lifespan is that of the plastic it is made of. There are no electronics inside, just a 'Reed' contact: a small glass tube with a magnetic contact under vacuum. Make sure the rotating vane is in good order. The Nasa vanes sometimes lose one or both ceramic cylindric magnets from the vane. They van be replaced with new ones from Ebay (or perhaps Maplin).

 

[Rigger Mortice]

I think OP was asking about the life expectancy of the through-hull fitting, not the log itself.

It's a good question. I've got the same plastic through-hull and, whilst it has caused no problems, I do feel a little uncomfortable at the thought of a thin bit of plastic below the waterline

 

[RogerMayne]

It's the standard black plastic NASA threaded through-hull fitting for the log impeller. It's been in there for the best part of 15 years. There is no sign of any leakage and it's not in a place susceptible to knocks, but is subject to a bit of bilge water from the inside. The boat has been out of the water for the best part of 8 years and I hope to go back in this season. I can't remember what it was bedded with, but it would have been whatever was recommended at the time.

Do I replace it? Do these things have a "service life"?

They are very weak, I used to have one on my boat and when I had a close look at it ,it had sheared about a third around the flange. I think they are supposed to be fiberglassed in from the inside of the hull. Mine was held in with sikaflex or something similar. I took it out and fiberglassed over the hole, then use the plotter for speed. Don't think they are worth the risk personally, depends how interested you are in your speed through the water?

 

[sailorman]

They are very weak, I used to have one on my boat and when I had a close look at it ,it had sheared about a third around the flange. I think they are supposed to be fiberglassed in from the inside of the hull. Mine was held in with sikaflex or something similar. I took it out and fiberglassed over the hole, then use the plotter for speed. Don't think they are worth the risk personally, depends how interested you are in your speed through the water?

boat spd gives you tidal flow when measured against gps so give extra saftey for landfall

 

[pvb]

Do I replace it? Do these things have a "service life"?

As Nasa products aren't renowned for their durability, I'd certainly replace it. Fit the new one using silicone sealant - don't use Sikaflex or similar mastics, as they can damage the plastic, causing premature failure.
.

 

[Solly]

NASA recommend that the fitting should be glassed in on the inside. There were cases of them shearing off on the inside if they were fitted with the wrong sealant some years ago. I think there was a metal replacement available

 

[Avocet]

Thanks All,

I think I might ask NASA the question. I'll post back if I get a response.

 

[Swanrad2]

They are very weak, I used to have one on my boat and when I had a close look at it ,it had sheared about a third around the flange. I think they are supposed to be fiberglassed in from the inside of the hull. Mine was held in with sikaflex or something similar. I took it out and fiberglassed over the hole, then use the plotter for speed. Don't think they are worth the risk personally, depends how interested you are in your speed through the water?

Exactly the same fault with mine. I will be glassing the replacement in.

 

[Avocet]

No reply from NASA when I e-mailed them. I phoned today and was assured that there was no need to replace them as a matter of routine, they weren't "service" items and "would last indefinitely"....

...but I might glass mine in just in case...!