Replacing a skin fitting - Advice please

rgsmg53

Member
Joined
1 Sep 2014
Messages
139
Location
Portishead
Firstly, I am fairly new to cruising yacht maintenance so please don't assume a great level of knowledge.

I'm having my elderly Fisher 30 lifted out on Friday in order to sort out a blocked cooling water inlet which I can't seem to unblock from inside whilst afloat. I'm expecting to replace the skin fitting, sea-cock and inlet strainer. Currently, my thoughts are to fit a plain through-hole skin fitting (the current one has a scoop which makes rodding-out from inside all but impossible) with a separate ball-valve sea cock screwed directly to the top of the skin fitting. I was then going to run a length of rubber hose to a Vetus-type plastic strainer (with the removable transparent plastic lid) so I could site the strainer in an easily accessible location. The skin fitting exits the hull in the engine compartment about 6 inches from the engine block.

Any advice on the following would be much appreciated:

1. Should I go for bronze, DZR brass or the new(ish) plastic (marelon?) skin fittings? There seems to be a good selection in the ASAP Supplies catalogue. any recommendatioons on make?

2. I assuming that whatever skin fitting material I use, I need to use the same material for the sea cock itself. Any thoughts?

3. I intend to reuse the existing hole in the hull (already reinforced on the inside) and to fit a flanged skin fitting with a back nut. Which sealant is best?

I don't have unlimited funds but I am prepared to spend a reasonable amount on good quality fittings in such a safety critical application.

Thanks in advance for any advice.

Richard
 

prv

Well-known member
Joined
29 Nov 2009
Messages
37,363
Location
Southampton
DZR brass will be fine, on a bed of Sikaflex 291.

If you need the valve handle to face in a particular direction, get another nut to tighten against it.

It makes a neater and slightly stronger job if you trim the skin fitting so that there isn't lots of surplus length between the nut on the inside of the hull and the valve (or the locking nut if using).

Expect to have to cut the old fitting out. You might be able to unscrew it, but that's a lucky bonus. So take cutting/grinding tools as well as your biggest spanners/stilsons/etc.

Pete
 

ctva

Well-known member
Joined
8 Apr 2007
Messages
4,601
I replaced our cooling water inlet with a Marelon one and three years on is still perfect. Several advantages; no electrolysis, integral seacock so bear that in mind when pricing it, I have it as a straight through with no strainer with no problems. It is an all in one unit to which I added a ply backing pad as I like belt and braces. Would I replace the others in the boat with the Marelon ones when needed, yes.

Relatively easy job.
 

Norman_E

Well-known member
Joined
15 Mar 2005
Messages
24,504
Location
East Sussex.
I fitted Tru Design through hulls and sea cocks throughout when I re-plumbed my boat last winter. I was not prepared to take a chance that locally bought bronze parts were actually not bronze at all or that DZR brass was actually what it claimed to be. I know I could have trusted some of the best known UK suppliers but with the boat in turkey a complete set of brass or bronze fittings would have been very heavy to take. The Tru Design fittings are good quality, and should have a lifespan equal to bronze.

I agree with Chris about fitting an engine inlet sea cock without an external strainer. Provided your internal strainer is directly above the inlet and higher than the static water line you can rod it through to get rid of any obstruction like a plastic bag.
 

Caer Urfa

Well-known member
Joined
28 Aug 2006
Messages
1,824
Location
Shropshire
Firstly, I am fairly new to cruising yacht maintenance so please don't assume a great level of knowledge.

Any advice on the following would be much appreciated:

1. Should I go for bronze, DZR brass or the new(ish) plastic (marelon?) skin fittings? There seems to be a good selection in the ASAP Supplies catalogue. any recommendatioons on make?

2. I assuming that whatever skin fitting material I use, I need to use the same material for the sea cock itself. Any thoughts?

3. I intend to reuse the existing hole in the hull (already reinforced on the inside) and to fit a flanged skin fitting with a back nut. Which sealant is best?

I don't have unlimited funds but I am prepared to spend a reasonable amount on good quality fittings in such a safety critical application.

Thanks in advance for any advice.

Richard

Hi Richard

1 100% go for DZR for any underwater fittings

2 As above

3 I would use translucent reinforced plastic hose so you can see any future blockage that might occur in the pipework, (I had seaweed) and just poked it all out, and use Sikaflex 291i for the skin fitting
inside and out of the fitting!

I also would fit a standard DZR skin fitting ie not the scoop type, they are a pain in the arse as you have found as any blockage can not be cleared from the inside of the boat

Also all seacock connection pipework should have two jubilee clips per connection end

Yes the Vetus filter you propose will be fine and well worth the money. I have had one for 12 years and still good.

Yes shop around for prices but Never try to save money on skin fittings quality.
 

GrahamM376

New member
Joined
30 Oct 2010
Messages
5,526
Location
Swing mooring Faro
Another vote for no strainer on the skin fitting. Use either DZR, bronze or TruDesign composite - those can either be bedded in Sika or epoxied in.
 

Tim Good

Well-known member
Joined
26 Feb 2010
Messages
2,797
Location
Bristol
I didn't a few of mine recently.

1. Bronze would be good but mixing bronze with DZR is apparently ok. In fact I had to do that one a couple as sizing and availability dictated it. My seacocks are bonded to the Anode also but lets not open that can of worms.

2. See above. Generally don't mix.

3. Many people don't use the old wooden backing pads now and my hull was thick enough to do away with them and bolt straight to the hull after I cleaned the old hull and prepped the surfaces. If the reinforcement is solid and still there then keep it. Make sure the it is not rotten if it is wood.

Sealant - I used CT1 but Skiaflex 291 I think is fine and maybe 295 is OTT.

Removing the old fitting... You can either spend hours trying to unscrew it or just get wood bung, shove it in and then use a hole saw to gentle drill it out from the outside. Dead easy and very quick. In fact you can replace a skin fitting so quickly that you can do it in the slings and relaunch whilst it is still wet. I havent done it but I've seen people do it.
 

Tim Good

Well-known member
Joined
26 Feb 2010
Messages
2,797
Location
Bristol
DZR brass will be fine, on a bed of Sikaflex 291.

If you need the valve handle to face in a particular direction, get another nut to tighten against it.

It makes a neater and slightly stronger job if you trim the skin fitting so that there isn't lots of surplus length between the nut on the inside of the hull and the valve (or the locking nut if using).

Expect to have to cut the old fitting out. You might be able to unscrew it, but that's a lucky bonus. So take cutting/grinding tools as well as your biggest spanners/stilsons/etc.

+1 to all the above.
 

geem

Well-known member
Joined
27 Apr 2006
Messages
7,101
Location
Caribbean
I installed a Marelon skin fitting/seacock for my engine water intake. We fitted a strainer straight on top of the Marelon valve. The strainer is stainless steel and has a clear lid so you can see straight out of the boat through the open valve! You can watch the fish go by and see if there is anything blocking the inlet.
 

BabaYaga

Well-known member
Joined
19 Dec 2008
Messages
2,463
Location
Sweden
If you go for composite (Forespar/Tru design), be aware that the ID might be smaller than on a bronze/brass fitting of the same OD. Important for cooling water purposes.
In answer to question no 2: I have recently seen a study where a DZR skin fitting in combination with a composite valve and hose tail was suggested as the best approach, because of the higher resistance to external impacts (logs, ice) of the metal.
 

mattnj

Well-known member
Joined
26 Jul 2007
Messages
1,350
go for the Tru-Design plastic ones, I changed all 11 of mine last year, they are the way forward....ive done DZR and Tru-Design, I cant see any advantage of metal, but there is plenty of disadvantages.

Blob of Epoxy (West Six10) out of a gun, nip up, leave to set, done, never touch it again.
 

adwuk

Active member
Joined
10 Jun 2015
Messages
788
Location
Tarbert
I put in a new through-hull this year and was recommended 3M 4200 - apparently good sealant and adhesive, but does allow you to remove the fitting in the future without damaging underlying gelcoat or fibreglass.
 

Spi D

...
Joined
25 Jul 2011
Messages
2,253
Location
Denmark
The boat next to us is a single engine mobo with two seawater intakes. Apparently fitted so for use on inland waterways in Germany, but the setup is new to me.
 

Yngmar

Well-known member
Joined
6 Dec 2012
Messages
3,046
Location
Gone cruising
I'm about to do this as well and after much research decided on the Tru-Design ones. The hull is made of plastic, so might as well embrace it. The difference between the Forespar Marelon (or the very similar looking ASAP brand) and the Tru-Design is that Forespar has a flange with 3 holes and recommends sikaflexing a board inside the hull to screw those in. I didn't fancy that much, so the Tru-Design ones have a load bearing collar (ordered separately) that goes between the skin fitting and the ball valve. With that you can dangle two fat blokes from the far end of the ball valve (225 kg for 30s) and it won't break. Don't forget to order the right long tail pipe (hose barb, straight or elbow) and the plastic tools for the skin fitting and ball valve, which ought to save you some frustration and creative tool (ab)use. Read the fitting instructions for minimum hull thickness (if too thin, add backing).

For cutting out the old skin fitting I'm planning to use my trusty Dremel fibre cutting disc, sticking it straight into the fitting and cutting around the inside to remove the flange, then pulling the whole shebang into the hull. Sika 291i to seal the new fitting in.

Good luck! :)
 

Tim Good

Well-known member
Joined
26 Feb 2010
Messages
2,797
Location
Bristol
For cutting out the old skin fitting I'm planning to use my trusty Dremel fibre cutting disc, sticking it straight into the fitting and cutting around the inside to remove the flange, then pulling the whole shebang into the hull. Sika 291i to seal the new fitting in.

That'll work.

For some reason I decided against Tru-Design after a read something about their strength in comparison to bronze. It was shocking enough for me to think stick with what is a known quantity and bronze certainly is. If I had an aluminum hull I'd be all over Tru-Design though,.
 

prv

Well-known member
Joined
29 Nov 2009
Messages
37,363
Location
Southampton
The boat next to us is a single engine mobo with two seawater intakes. Apparently fitted so for use on inland waterways in Germany, but the setup is new to me.

I've seen pictures of such an arrangement on lifeboats; I don't know whether they all use it or only some.

The picture I saw was arranged so that the handle of the changeover valve blocked the lid of the "in use" strainer and exposed the other, thus ensuring that someone didn't accidentally open the wrong lid when hurrying to clean it out. I copied the idea for a couple of changeover fuel filter manifolds I made.

Pete
 

Yngmar

Well-known member
Joined
6 Dec 2012
Messages
3,046
Location
Gone cruising
For some reason I decided against Tru-Design after a read something about their strength in comparison to bronze. It was shocking enough for me to think stick with what is a known quantity and bronze certainly is. If I had an aluminum hull I'd be all over Tru-Design though,.

This is 115 kg dangling from a Tru-Design ball valve with skin fitting: https://youtu.be/zPVB06Vijkc?t=6m23s
That's without the optional load bearing collar they've now introduced (which brings it up to ABYC standards of 225kg): http://www.trudesignplastics.com/marine/products/70-load-bearing-collars

Yes, it deforms, but it doesn't break, whereas bronze won't deform until it suddenly snaps off.

However, I find all of this a bit silly, because I just can't imagine a situation where the seacocks, most of which live in a well protected place below a sink with nothing to fall around nearby could suddenly end up having to bear such loads. Mine (a mix of DZR and CW617N) are having to be replaced because of dezincification and because one is jammed (it was left open for a long time and a barnacle family must've moved in). I can imagine something hard hitting the hull from the outside, although in the unlikely situation where it would precisely smack into a skin fitting, any force sufficient to break the fitting would likely also pierce the GRP. Elastic deformation may even be a benefit in that case. So that leaves only corrosion/dezincification and in that department, plastic wins hands down. Oh, and in the cost department it is doing pretty okay too :)
 

lpdsn

New member
Joined
3 Apr 2009
Messages
5,467
Removing the old fitting... You can either spend hours trying to unscrew it or just get wood bung, shove it in and then use a hole saw to gentle drill it out from the outside. Dead easy and very quick. In fact you can replace a skin fitting so quickly that you can do it in the slings and relaunch whilst it is still wet. I havent done it but I've seen people do it.

No need for even that level of complexity. Use an angle-grinder to grind out around the fitting from the outside. Go carefully to avoid grinding into the fibre glass at all. When the neck is very thin and cut through in parts, lever off the flange with a screwdriver and pull the fitting in from the inside. Can easily be done in 20 or 30 mins. Saves a wooden bung and the greater risk of damaging the fibre glass with a hole cutter.

I've heard of this done in slings and the boat re-launched, but I prefer to give the Sikaflex a day or two before finally tightening up the fitting that last extra bit.

And goggles/mask are a good idea when grinding. I found the vibration of the grinder the most notable downside. Fine for one or two, but I wouldn't like to do it all day, five days a week.
 

rgsmg53

Member
Joined
1 Sep 2014
Messages
139
Location
Portishead
Thanks for all the advice. I like the thought of the composite materials (ie Forespar / Tru design) but as the inlet is within 6 inches of the engine I'm wondering what effect high temperatures will have. Both makes quote 80 C as max operating temp.
 
Top