Skin fittings

[ninnes]

I am replacing the skin fittings on my 20 foot bilge keeler that is kept on the East coast. I have just removed the original 30 yr old skin fittings and gate valves (that were working OK) that drained the cockpit. Two questions and excuse the ignorance.
1. Do I need seacocks at all and if so why? I would have thought having fewer joints and parts would mean less chance of leaks, joints snapping and valves jamming. Why would I want to close a cockpit seacock?
2. Why use a wood backing pad on skin fittings? Surely tightening the internal locking nut directly onto the hull offers greater stability as the hull is solid GRP and a wooden backing pad has "give". Also the aim is not to tighten the skin fitting too much as the external mastic seal under the external fitting would be cut. Having no backing pad allows greater inspection of fitting integrity and any leak around the fitting is seen easier and can run off rather than seeping under/into a wood backing pad where it makes the GRP go soggy.
Your thoughts much appreciated. Many thanks

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[oldsaltoz]

G'day Ninnes,

[1] Depends on boat the design

[2] I have no timber backing on my seacocks, GRP hull, original fittings. However,
the hull has had extra glass added and it's feathered to avoid a hard spot / spread the loading.

I have added more openings and made them in the same manner, no problems,
you do need to make sure the seal area is flat, I fitted a neoprene washer
to provide a tight seal.

Also note that after drilling, the edges must be sealed with epoxy.

I hope this helps

Avagoodweekend Old Salt Oz /forums/images/icons/cool.gif

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[oldsaltoz]

G'day Ninnes,

[1] Depends on the boat design

[2] I have no timber backing on my seacocks, GRP hull, original fittings. However,
the hull has had extra glass added and it's feathered to avoid a hard spot / spread the loading.

I have added more openings and made them in the same manner, no problems,
you do need to make sure the seal area is flat, I fitted a neoprene washer
to provide a tight seal.

Also note that after drilling, the edges must be sealed with epoxy.

I hope this helps

Avagoodweekend Old Salt Oz /forums/images/icons/cool.gif

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[tillergirl]

The point about seacocks is what are you going to do when the pipe to the skin fitting hardens, cracks, splits or comes off. Do you really want to go to sea in a boat that has an opening below the waterline and no way of closing it off in the event of a problem occuring?

The backing pads are simply an issue of spreading the load. It doesn't really matter whether it's wood or GRP done like oldsaltoz says. The wood has worked ok for 30 years hasn't it? Although how much 'give' does it give - is it a bit soft aka rotten? Sure wood depending upon the variety will have a difference in its hardness but it obviously should not be soft.

I think you have to decide whether to get some small pieces of iroko, shape the back to the hull and then protect it after fitting with some kind of paint job or make up the faired 'swelling' that oldsaltoz says. You might think that the GRP is the easier solution but being a wood man myself I am curious as to how you shape that runny stuff - obviously it can be done but it will all want to run into the bottom of the bilge.

If you ever need a survey, you'll never pass without seacocks on a skin fitting belwo the water line - I have then above the waterline as well!

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[ninnes]

Thanks for your thoughts. Now to find the time to replace them.

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[tgalea]

Whilst on the subject.. maybe you can help.

I am replacing my depth instrument with the new nasa clipper version i just bought. The only problem i have is that my hull was drilled for the seafarer hull transducer and now nasa clipper have this transducer which requires such a small hole diameter.

Just so you can picture it.. i presume the new transducer would leave about 1mm eighter side.

Any suggestions ? Some locally have suggested i re-patch with GRP and re-drill. I was thinking of using some kind of backing on the inside as suggested on this thread .. just under the nut from the inside and fill the whole thing with silicon ?

Once again.. any suggestions would be appreciated.

Regards
Tyrone.


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[Jools_of_Top_Cat]

I would not do that, you are planning to trust your boat to silicon, and surely you really meant SIKAFLEX 292 or something similar, silicon is for the house.

If the boat is dry, chaffe hole out so the grp is thin at the edge of the hole and gradually gets thicker working out, maybe 5 inches from centre. Fix pad to outside of hull covering hole. Rebuild grp to fill hole, use maybe 10 sheets of glass. Use gel coat filler on outside once pad is removed. sand down filler till smooth.

Then fit new fitting, better if you can locate it somewhere new I would think.

My advice for what it is worth, do not skimp or try to cover up faults under the water line, it can only end in tears!

Good luck by the way. Remember to wear goggles and face mask when grinding sanding grp.

<hr width=100% size=1><font color=blue> Julian </font color=blue>

<A target="_blank" HREF=http://www.ukstaffords.com>http://www.ukstaffords.com</A>

 

[oldsaltoz]

G'day Tyrone,

If the new transducer will drop thru' the old hole and clear it, you must re-glass and re-drill: it's not a major job, but will take perhaps 3 0r 4 days to complete working less than 2 hrs a day.

If you are new to fibreglassing I would be happy to send you some information / tips. Use epoxy resin for this underwater work.

Hope this helps

Andavagoodweekend Old Salt Oz.../forums/images/icons/cool.gif

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[qsiv]

While your at it - tie a softwood bung of the correct size by each fitting, so that should the worst happen you are fully prepared. It's a requirement for race boats - but good practice for all.

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[PuffTheMagicDragon]

I did something similar on Cyano some years back. The old transducer was the kind where the stem is very slender compared to the actual head - approx. 16mm if I am not mistaken. The new one had a thin flange to the head and quite a thick body / stem, around 40mm from memory.
I opened out the existing hole, removing all traces of goo. I then fastened the plastic top of an aerosol can to a piece of plywood, applied release wax, and propped it into the hole from the outside. Fibreglass was applied from the inside using the plastic top as a male mould (this was conveniently slightly larger in diameter than the transducer stem) A flange cut previously out of 12mm marine ply was incorporated into the layup.
Upon removal of the outside plug I was left with a nicely moulded opening of the right size, complete with a backing pad.
It is not clear where you have the 1mm clearance that you mention. However, do remember that a transducer should be free to vibrate independently of the hull; you need some clearance for the mastic. I used Life Calk (black) which is suitable for continuous immersion in sea water and which remains flexible.
Fair Winds!

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[tgalea]

Hi Wally,

Thanks for the info. I'm gonna need some more help on this one. Ok, so is Lifeseal no good for the depth transducer ? .. it's a below the waterline transparent silicon sold locally maybe you've heard of it.

Regarding the stem tickness; the older one was thicker whilst the new one is about let's say 1.75 to 2 mm thinner in diameter (the stem i mean). Let's put it this way the head of the transducer covers the hole, quite limited but actually covers it.

What do you think ?

Thanks once again
Tyrone.


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[tgalea]

Good day you too.

Ok i'll look forward to any fibreglass tips you may have for me.

No, the transducer dosen't fall through; in the sense that the actual head of this thing is wider than the hold and covers the hole; it's the stem which is about 2mm less in diameter than the older one. Whilst the head is lets say 2 mm wider than the hole.

My worry is about the approx 2mm play due to the hole being wider than the stem.

What do you think ?

Thanks
Tyrone.




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[vyv_cox]

My opinion is that it doesn't matter a bit. If the flange of the fitting doesn't come through the hole, and doesn't expose a part of it if the fitting is moved as far as possible to one side, there is little to worry about. You're only trying to seal a head of water of a couple of feet maximum and it takes very little to do that. You could put a washer of sheet plastic under the transducer flange if it looks like it would help but otherwise use fill the gap with the appropriate grade of mastic, as suggested Boatlife is good, or of course Sikaflex, and I don't believe you will ever have any problems.

Just to illustrate how it's easy to exaggerate these problems. My first boat had been owned by a "botcher" of the highest order. One redundant underwater plastic skin fitting had been blocked off by hammering a piece of broomstick into it. Nothing else. It never leaked.

I had always suffered a weep of water into the bilge and it annoyed me. To investigate, I started grinding back a strange lump in the moulding in the general area of the weep. After taking off about 1/2 inch of gelcoat I began to wonder when I would hit the reinforcement. I never did! A large hole that had previously been occupied by a drive leg had been filled by slapping a tray full of gel coat over it. No glass reinforcement, GRP, or anything. The hole was about a foot by 8 inches and straight sided, no attempt at fairing it. Other than the small weep it was OK and had probably been there for at least 5 years.

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[PuffTheMagicDragon]

Hi Tyrone,
As Vyv has said, you're only sealing out a couple of feet of head (probably less on a Snapdragon). My transducer is an all-plastic affair and I doubt the plastic flange was wider than 3mm. If yours is similar, just remember not to go "overboard" when tightening the nut on the inside.
Ar far as the goo is concerned, I get mine from Michael down at Gauci Borda's, Msida. Yours might be from the same supplier for all I know; I don't know about Gozo. The clearance of 1mm all round is quite normal.
This is hydrodynamics and not aerodynamics ;>)
If you need anything, feel free to call me. I live at San Gwann and CYANO lives on pontoon 'B'.
Fair Winds


<hr width=100% size=1>Wally

 

[richardandtracy]

I have an alternative solution for someone [who knows someone?] with access to a metal lathe. You'd be surprised how many there are.

Take a lump of Bronze, steel or stainless and machine it into a boss that'll take the new transducer while still going through the old hole. Then fix to the boat. Any competent machinist will take no more than an hour to make it. No fussing with GRP, and it can be done at any time of year.

Regards

Richard.

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