Skin Fittings Below Waterline - Best Practice?

[Scott79]

Guys,
I am in the process of installing/tidying up a Live Bait Tank pickup and Deckwash pickup using skin fittings, can you please confirm I am on the right track:

# 3/4 inch Stainless Skin Fittings, with Stainless Steel Taps;
# Drill the hole 6mm (?) larger than required;
# Apply Flowcoat to the freshly drilled holes (one coat or 2?);
# Liberally apply Marine Sikaflex inside hole and sparingly around flanges;
# Tighten allowing Sikaflex to ooze out;
# Install tap and pump using thread tape;
# Job's done.

Am I on the right track, or is there something else I should/shouldn't be doing?

Thanks,
Scott.

[Mike Delisser]

Sounds ok......why stainless?

[Rip it up]

Yep sounds good to me.
6mm larger? Hmm maybe not. Just a neat fit. Even if you have to file out a 25mm holsaw hole to make it 1mm oversize.
One coat of flowcoat will be fine. Just make sure that the flowcoat does not sag and leave a drip on the bottom edge. If the flowcoat is thicker or proud of the original hull then when you tighten the fitting it will crack off the edge.

Also it might pay to bevel the hole edges inside and out. You will get a better sika gasket that way.
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Get the idea?

Thread tape is a good idea. 6/7 wraps is needed. A smear of light grease wouldn't hurt to help with the binding effect of stainless threads.

Mineral turps for the sika clean up. And double glove before hand makes peeling off a messy glove halfway easier to continue work.




Damo's dodgy boat building factory.

[Scott79]

Sounds ok......why stainless?

Mainly aesthetics, don't see the point going for a plastic fitting which will fade etc when I can go for SS for a few extra bucks.
Scott.

[Scott79]

Yep sounds good to me.
6mm larger? Hmm maybe not. Just a neat fit. Even if you have to file out a 25mm holsaw hole to make it 1mm oversize.
One coat of flowcoat will be fine. Just make sure that the flowcoat does not sag and leave a drip on the bottom edge. If the flowcoat is thicker or proud of the original hull then when you tighten the fitting it will crack off the edge.

Also it might pay to bevel the hole edges inside and out. You will get a better sika gasket that way.
| |
\_/
_
/ \
| |

Get the idea?

Thread tape is a good idea. 6/7 wraps is needed. A smear of light grease wouldn't hurt to help with the binding effect of stainless threads.

Mineral turps for the sika clean up. And double glove before hand makes peeling off a messy glove halfway easier to continue work.




Damo's dodgy boat building factory.

Cheers mate, great info. Not sure if 1mm is going to be enough to allow a coat of flow coat and a smearing of sikaflex? I agree though, that 6mm may be a little excessive....
When you say bevel the edges of the hole, does that just mean take the edge off so that they don't meet at 90 degrees?

Top point about double the glove, will be doing that for sure.

Cheers,
Scott.

[docaster]

Marelon fittings are the go.
http://www.forespar.com/marelon-mari...plumbing.shtml
Better than stainless.

[Grand_Marlin]

G'day,

Cut a neat hole, definitely don't oversize it. A 3/4 skin fitting would be lucky to have a 6mm flange!!
Always use stainless, bronze or survey approved reinforced plastics like Marlon or True Design. Use the same material for the skin fitting, sea cock (valve) and hose tail.
Never use standard plastic fittings for thru hull underwater fittings. They can and do break...
Always double hose clamp hose fittings below water line.
Use a good quality hose like a sanitation hose, not the cheap flexible bilge hose.
No need to flow coat the holes. Use ample amounts of a sealant approved for immersion in salt water. Sikaflex 291 is my preference.
Clean up with a dry cloth, then Metho.

Cheers

Pete

[gofishin]

A 3/4" skin fitting is sized per 3/4 BSP thread, hence 26.4mm O/D or thereabouts.

So drill 1" hole and make ~0.5mm bigger all round with a bit of filing, 12" round bastard file should do it. Tight fit is good = max sealing surface to flanges = max sealing safety IMHO.

Take the edges off but don't like the sound of big bevels because that means smaller sealing face against flanges, but that's just my opinion (no disrespect Damo).

Weave the hole saw a bit and you will reduce your filing, but you will need to be careful with this.

Can you drill from both sides? Once you get the pilot thru/before you take the saw right thru, ring it from the inside so you don't blow out chunks of flow coat when coming thru, or vice versa with gel coat.

Oh, it's glass I presume and not timber or timber core?
Cheers
Brendon

Oh yes, and what Pete said

PS. You can save filing with a mini drum/roll sanding bit on your battery drill. Will make short work of the ream job.

Pack the skin fitting thread with 291, for the penetration thickness, before inserting.

[fisho64]

as said, dont need to go bigger unless maybe its not solid glass but a wood/foam core maybe?

Double hose clamp everything below the waterline with the screws opposite sides and dont use the perforated type hose clamps.
Find the stamped thread type (both made by Tridon and others).
The perforated hose clamps are somewhat notorious for breaking without warning.

[scottar]

Just watch what you use to prepare and clean up with. Alcohol base solvents can interfere with the curing of many of the polyeurethane based sealants. If you do use metho to clean the area before application, give it plenty of time to evaporate away before applying the sealant. Tooling off with metho will make the surface of the sika stay a bit tacky.

[Scott79]

Thanks guys, great info. Will tackle it in coming days. Am surprised that the recommendation does not require resin/flowcoat as a sealant for the timber first - although I am aware of the quality of Sika I thought flowcoat would have been a must.

I can easily access both sides Brendon, no trouble at all.

Am definitely gaining a better appreciation for clearances required!

Regards,
Scott.

[gofishin]

...as a sealant for the timber first ...

Well that changes everything!

More explanation required, what timber, and where? I assume through the hull in the bilge area, or where???

...I thought flowcoat would have been a must...

Flowcoat is not a real good sealer of timber by a long shot. Plenty of better products Scott.

But yes, if timber is involved, it should be sealed very well (and allowed to cure) before application Sika & fitting.
Cheers

[Spaniard_King]

A 3/4" skin fitting is sized per 3/4 BSP thread, hence 26.4mm O/D or thereabouts.

So drill 1" hole and make ~0.5mm bigger all round with a bit of filing, 12" round bastard file should do it. Tight fit is good = max sealing surface to flanges = max sealing safety IMHO.

Take the edges off but don't like the sound of big bevels because that means smaller sealing face against flanges, but that's just my opinion (no disrespect Damo).

Weave the hole saw a bit and you will reduce your filing, but you will need to be careful with this.

Can you drill from both sides? Once you get the pilot thru/before you take the saw right thru, ring it from the inside so you don't blow out chunks of flow coat when coming thru, or vice versa with gel coat.

Oh, it's glass I presume and not timber or timber core?
Cheers
Brendon

Oh yes, and what Pete said

PS. You can save filing with a mini drum/roll sanding bit on your battery drill. Will make short work of the ream job.

Pack the skin fitting thread with 291, for the penetration thickness, before inserting.

Not entirely true.

A 3/4 skin fitting is generally sized to take a 3/4 Hose... buy a 3/4 stallion skin fitting and try and make that formula of yours work?

[fisho64]

its got a timber core in the hull bottom, just curious as to what sort of hull as many/most are solid glass in the bottom?

Hole size? a "3/4" skin fitting" which takes a 3/4" hose-the nut wouldnt fit over it if the hole was the same size as the lump end so is always going to be bigger than 3/4" in a conventional type skin fitting.

http://www.arnoldsboatshop.com.au/ac...5450b/dp/10770
http://www.ebay.com.au/itm/Through-hull-3-4-Bsp-Skin-fitting-316-Stainless-Steel-Polished-outer-face-/111441233811?_trksid=p2054897.l5664

What is a Stallion fitting? Ive googled it but comes up with nothing?

[scottar]

Not unusual for manufacturers to glass in timber pads to allow bilge pumps and float switches to be screwed down. Also not unusual for these to be totally rotted out.