Thru hull fitting

[Bouba]

Hi everyone
My boat is on the hard and today I noticed that the underwater thru hull fitting for the water from the exhaust gas separator of the generator was almost blocked with rust.
I haven’t measured it yet but I think the pipe going onto the fitting is two inches (I will confirm that tomorrow)...
So first question...does that make it a two inch fitting or is there another metric involved.
Second...I would like to replace it with a composite plastic fitting...the hull is balsa cored...is it a two man job?
What sealant is used...how tight etc ...is there a definitive guide to teach me how?
Thank you

 

[colhel]

2" is 50.8mm

1 1/2" bsp thread is 47.8mm (outside diameter)

 

[Keith-i]

I fitted Tru-design plastic through hulls recently. It can be done fairly easily single handed but you need the little tool to poke down and prevent the outside bit turning whilst you tighten the nut internally. There are some good videos online.

 

[penfold]

Second...I would like to replace it with a composite plastic fitting...the hull is balsa cored...is it a two man job?

With an existing through hull the hole in the hull should be sealed by the builder, I'd be very surprised if the core is exposed.

 

[Bouba]

I fitted Tru-design plastic through hulls recently. It can be done fairly easily single handed but you need the little tool to poke down and prevent the outside bit turning whilst you tighten the nut internally. There are some good videos online.

My plan is also to use Trudesign...did you also use Trudesign seacocks ? Which sealant did you use ? How tight did you make all your fittings ?

 

[Bouba]

With an existing through hull the hole in the hull should be sealed by the builder, I'd be very surprised if the core is exposed.

The generator was added later...so the fitting is newer but perhaps to a different standard (although Beneteau aren’t renown for the quality of their fittings)...so a hole was cut for the fitting exposing some of the balsa core (round hole, rectangular pieces of balsa)

 

[Pinnacle]

When cutting a new hole in a balsa cored hull, it is best practice to drill the hole to the correct size for the new thru hull fitting all the way through the hull. The core should then be removed for at least 10mm from the original hole. The void in the core and at least part of the original hole should then be filled with epoxy (or something similar) and allowed to cure. The correct size hole can then be re-drilled through the now solid hull. This prevents both water ingress into the core and compression caused by overtightening of the thru hull fitting.

Hope this helps.

 

[Bouba]

When cutting a new hole in a balsa cored hull, it is best practice to drill the hole to the correct size for the new thru hull fitting all the way through the hull. The core should then be removed for at least 10mm from the original hole. The void in the core and at least part of the original hole should then be filled with epoxy (or something similar) and allowed to cure. The correct size hole can then be re-drilled through the now solid hull. This prevents both water ingress into the core and compression caused by overtightening of the thru hull fitting.

Hope this helps.

If I have understood that correctly...then it’s very clever But, in my situation, I am just replacing an existing fitting.

 

[Bouba]

Another question to all....
Is the rust that I found (and there was a lot of it) more likely to have come from the thru hull fitting or the seacock...or both?

 

[penfold]

The rust is most likely from the generator's water injection elbow, or possibly the exhaust separator if it was stainless steel but that's much less likely. I doubt it has anything to do with either the through hull or the seacock.

 

[Bouba]

The rust is most likely from the generator's water injection elbow, or possibly the exhaust separator if it was stainless steel but that's much less likely. I doubt it has anything to do with either the through hull or the seacock.

That is interesting!
I will try and investigate in the morning

 

[PaulRainbow]

If I have understood that correctly...then it’s very clever But, in my situation, I am just replacing an existing fitting.

Understood, but if the balsa core is visible you need to follow the advice in post #7

 

[petem]

Just pay someone to fix it. You don't sound like you know what you're doing and the consequences of messing it up are dire.

 

[Bouba]

Just pay someone to fix it. You don't sound like you know what you're doing and the consequences of messing it up are dire.

You sound like the wife...but she has faith in my abilities but knows the osteopathic bill will be many times greater than the marine engineer

 

[Bouba]

The rust is most likely from the generator's water injection elbow, or possibly the exhaust separator if it was stainless steel but that's much less likely. I doubt it has anything to do with either the through hull or the seacock.

I do remember that once during a service, the Onan engineer said if there is rust in the water pump the generator is toast

 

[Portofino]

Show us a pic of the “ rust “ .Also the inside of hull view of the seacock going through.

 

[Bouba]

Show us a pic of the “ rust “ .Also the inside of hull view of the seacock going through.

I could barely see inside the thru hull because it was such a bright day...and now I’ve cleaned out most of the corrosion and put WD40 through it...so there isn’t much left to photo

 

[LittleSister]

My plan is also to use Trudesign...

But, in my situation, I am just replacing an existing fitting.

Note that a Trudesign fitting's external diameter (i.e. the hole in the hull needed) will be larger than the standard metal fitting. (That's because the material isn't as strong as metal, and therefore the wall of the fitting needs to be a greater thickness.)

As per Penfold's post #10 above, I doubt rust staining is anything to do with the skin fitting, which will almost certainly be DZR brass and therefore not rust. Therefore you probably don't need to replace your skin fitting. (Unless it is showing signs of serious dezincification - which would show not as rust, but by it turning pink-ish, and the pink not just being on the surface (which can be tested by abrading the surface with fine emery cloth).

 

[Bouba]

Note that a Trudesign fitting's external diameter (i.e. the hole in the hull needed) will be larger than the standard metal fitting. (That's because the material isn't as strong as metal, and therefore the wall of the fitting needs to be a greater thickness.)

As per Penfold's post #10 above, I doubt rust staining is anything to do with the skin fitting, which will almost certainly be DZR brass and therefore not rust. Therefore you probably don't need to replace your skin fitting. (Unless it is showing signs of serious dezincification - which would show not as rust, but by it turning pink-ish, and the pink not just being on the surface (which can be tested by abrading the surface with fine emery cloth).

So do you also think the rust is coming from the generator?

 

[Bouba]

Here is my dilemma...the boat is out of the water now...but as soon as it’s back in the water the engineer is coming to service the engine and generator...if the problem is the thru hull fitting or seacock then I will have missed my chance to fix it before launch...and if the problem is the generator then I won’t know until after it’s back in the water