Through hulls in steel boats

[tpierce]

I have a 40 year old steel hulled houseboat. I want to add a through hull for marine air, and relocate a through hull for sanitary discharge from the Type 1 MSD I'm installing. Can anyone offer me guidelines as far as what type of material to use and proper install-sealing methods?

[Thunderhead19]

I prefer Marlon fittings bedded with Sikaflex caulking.

[capefearboat]

We make 3/8" donut shaped doubler plates which have stainless studs welded from the back to the plate. The plate is then welded to the inside of the hull on both the outer and inner rims. Then we fit the mushroom head from the outside. We use a gasket on both.

[safewalrus]

It's the gasket that matters! seperates the fitting from the hull material so make it good and oversize to ensure whatever the fitting is made of it does NOT come in contact with the metal of the hull (if your using a screwed fitting tape the fitting where it goes through the hull PTFE is as good as anything, but will no doubt get someone moaning). Don't use plastic fittings they shear very easily and yer shoes get wet!!

[tpierce]

Thanks for the replies. My boat is always in fresh water- Ohio River, so I don't have the corrosion problems common in saltwater. I'm using bronze fittings. So, if I understand, I'll bore a slightly oversized hole, make a gasket to isolate the fitting from the hull on the outside. Then use a backing block of dense plastic or wood on the inside, seal the gasket and fitting inside and out with 3M 5200, and tighten fitting with large nut on the inside.( I have the threaded pipe fittings-bronze) I also have bronze seacocks to install on both through-hulls.

[safewalrus]

Don't you believe it 'tpeice' your in water you'll get corrosion problems! maybe not as bad but you'll STILL get them!

Generally your about right but don't forget the gasket where the steel hull hits the fitting - all of it, a lot forget that thickness of hull and put a lovely gasket around the fitting on the flat; I've done it myself - there again your anodes should grab all the 'nasty' stuff (especially in fresh) but why take a chance! Reakon you'll be OK but it needs checking ocasionally! Old adage for boats ANYWHERE - if it can go wrong it will! As long as you check and maintain you got no problems, forget that or can't be bothered and you'll get kicked!!

[Thunderhead19]

NEVER USE PLASTIC THRU-HULLS they arent coast guard approved. That's why I use Marelon ones. They can take one helluva smack and not break. That's not to say that metal ones aren't tougher still. I have nothing against bronze fittings. But when using metal fittings in a houseboat situation, you may be required to electrically bond all metal components (I don't know what the regs are like for you guys) enhancing corrosion problems. There's two schools of thought on this. "I make my sacrificial anodes work hard" or "I lessen corrosion by making sure that the sacrificial action takes place over as great a surface area as possible"...I guess there's a third option of "I electronically manipulate the corrosion on my boat" but I don't have that kind of money......

[tpierce]

Thanks everyone for the advice. I will gasket, seal and isolate appropriately.

[safewalrus]

Or the fourth one Thunderhead - I chuck it all in a bucket, and chuckit! Don't have problems with "through hulls!" Buckets are coastguard approved, chucking it ain't but only if your caught! Can't have anything that is not 'coastguard' approved can we?

[Thunderhead19]

I worked on a fuel dock one summer. I remember distinctly a Seiner coming in for diesel fuel. She was riding high in the water because she had no load. I tied her up and it was just then that someone pulled the plug in the galley sink. This would ordinarily have not been a big deal, but she was high enough in the water that the through-hull spewd out onto my nice clean dock. It looked like vomit and smelled worse. I consider it fortunate that they didn't tie up on the other side, because I noticed some "Brown Floaters" after they left.

[globaldude]

Originally Posted by Thunderhead19

I worked on a fuel dock one summer. I remember distinctly a Seiner coming in for diesel fuel. She was riding high in the water because she had no load. I tied her up and it was just then that someone pulled the plug in the galley sink. This would ordinarily have not been a big deal, but she was high enough in the water that the through-hull spewd out onto my nice clean dock. It looked like vomit and smelled worse. I consider it fortunate that they didn't tie up on the other side, because I noticed some "Brown Floaters" after they left.

Do I recall some derogatory comments you made regarding " blow boats " & or their inconsiderate & ignorant skippers , whilst you toiled at said fuel dock ?

Did they ever leave you any "brown floaters " ? [ I know, I know, you were just sh** stirring eh boy ! ]