sealing a new thru hull

[thomashoebus]

Over the last 5 years I had to change 4 of the 11 thru hulls on my boat. I did this between tides so there was never time to hand tighten and after 2 days tighten the bolt again with a spanner. Nevertheless it worked fine and there were never leaks.

Because all of the thru hulls really looked bad i took out the remaining 7 yesterday and today. Luckily because 2 just snapped of only when disconnecting the hoses, they were off course very unwilling due to the cold..

Tomorrow i will fit the new thru hulls. Now i read that most people advice to tighten the thru hulls in two times. Since i never did this before is this really necessary? I Always tighten them once, perhaps i was just Lucky before.

should i thighten just 1 time hard enough? Because thightening two times will set me back 2 days again. I'm also afraid that with the two times method there is a chance to break the seal again.

 

[pvb]

There's almost no water pressure on a skin fitting. Tightening once will be fine.

 

[rogerthebodger]

The reason to hand tighten then nip up after a day or 2 is to prevent all the sealant being squeezed out.

The skin fitting I fit have a recess under the head next to the thread so that it is impossible to squeeze out all of the sealant between the underside of the head and the hull.

If your skin fitting does not have this recess you could chamfer the hole so as to provide a gap for the sealant to be retained even with the fitting being fully tightened.

 

[Kwik Decision]

I fitted a new log impeller skin fitting a few years ago, using silicone sealant, and tightened it up fully first time. It weeped all season - very little when stationary as the water pressure is low, but you would get a pint or so in over a days sailing. Not the end of the world, but a pain none the less.
I changed it the following winter, and used the "do it most of the way, leave for a day, tighten" technique, and it has been leak free ever since.

 

[VicMallows]

For work between tides, I would never contemplate using silicone. I would always use polysulphide (Life-Caulk is polysulphide). Horrible messy stuff, but will set under water.

Edit: It doesn't 'set' ....it remains rubbery and removable. Not to be confused with polyurethane (Sikaflex) which makes removal a nightmare!

 

[Rossynant]

Tomorrow i will fit the new thru hulls. Now i read that most people advice to tighten the thru hulls in two times. Since i never did this before is this really necessary? I Always tighten them once, perhaps i was just Lucky before.

Depends on what sealant you are putting them.
Something like silicone rubber, not sticking - wait for it to set, then tighten, since this is a bit like rubber gasket, you want to compress it. This kind is not recommended under water anyway, but some use it...

Adhesive sealant, like polyurethane glue, sikaflex kind - set it once, any moving later will break the bond. But this is hard to disassemble.
Polysulfide rubber and such - similar, this is set once, but in case it leaks later on can be squeezed further.

 

[thomashoebus]

thans for the advice.

I used polyurethane glue and tightened once. All of the seven have no leaks.

 

[HermanD]

Only boaties have found out the stupid proces of this two stage sealing.
It is unnecessary.
1e With second time thighten you can just break the seal if the appendage twists.
2e You can put to much strain on the appendage.
The two stage sealing proces is never used only boaties.
It more important to chamfer the hole in the hull a little so there is room voor sealant
between the hull and the appendage. This gives a "O" ring effect with enough
thickness to have flexiblity in the sealant.
But do what you like an feel you happy with your method off sealing.

 

[curiousity]

Like HermanD, for years I have been counter sinking "soft" materials at bolt holes when fixing down deck fittings to get the "O" ring effect in the bedding sealant. Nipping up the nuts should it leak in the future seems to fix the problem.