Dufour Owners Association: new forum comment on Another one about Seacocks – with a new warning!

New comment from David Stanger

Unfortunately, I can't fit the ball valve straight onto the skin fitting – there simply isn't room. I have to have an elbow between the skin fitting & the ball valve. I am now planning to fit a female to female elbow with a "running nipple" to convert one of the female ends to male.


Original Post by David Stanger

Another one about Seacocks – with a new warning!

<p>Hi,  Sorry to add yet another topic on seacocks (administrator – pls feel free to move this to an existing topic if appropriate!). </p>
<p>Some years ago I had a seacock fail (cracked body) on my 2005 Dufour 385GL.  I did post on this site at the time, but long story short – the parts fitted were NOT DZR, confirmed by metallurgical analysis.  Dufour were approached, but responded in vague terms to the effect that they comply with the relevant standard (which only requires these parts to last for 5 years!).  At the time, I replaced all skin fittings, elbows, seacocks & hose tails with DZR.  Last season we started to have problems with some of the seacocks jamming open/half-open, & one getting very stiff to operate, so we recently lifted out. </p>
<p>There were signs of de-zincification on some of the fittings so I've bitten the bullet & have decided to try to fit TruDesign parts (if I can squeeze them in to the very tight space).  Between the skin fittings & seacocks, my boat has 45 degree elbows to bring the seacocks vertical.  These elbows are male to female threads. </p>
<p>The first problem is that TruDesign don't make 45 degree elbows, only 90 degree ones.  TruDesign have an excellent website & I found that you can happily mix their parts with bronze/DZR parts, so I thought I'd use bronze elbows. </p>
<p>This highlighted the second problem.  On inspection of the old parts, I realised that while the female thread is straight, the male thread is tapered.  As an engineer, I've always understood that you should never fit a tapered male thread into a straight female thread – it will lock up OK as you tighten it, but it will actually only be fully engaging on the last few threads.  It also means that you can't adjust the locked position to ensure alignment is correct for operating the seacock handle.  Researching the market, it appears that ALL bronze/DZR 45 & 90 degree elbows that we could find are like this!  One supplier confirmed this, stating that it was standard practice in the plumbing world to use tapered male threads in straight female threads!  However, they were also aware that you cannot use these in a below-waterline marine environment.  The only solution we've been able to find is to use female to female elbows, together with what is known in the plumbing world as a "running nipple" – essentially, a tube threaded along its full length (straight thread).  By screwing this into the elbow, this effectively gives you a male to female elbow with both male & female straight threads.</p>
<p>If you also have elbows between your skin fittings & seacocks, you might want to check this – a male tapered thread in a straight female thread, fitted below the waterline, does not meet the relevant regulatory standards, & more importantly presents a significant risk of leaking/flooding!</p>

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<p>Hi<br />I replaced most of my skin fittings and ball valves on my 45p, with countersunk Tru design product last season and will complete this season (left the hard ones where I need a helper!)<br />Tru-design do sell a male 120 degree hose tails with a BSP thread (not BSPT). I did buy them in NZ and took them to Greece<br />You need to fit the skin fitting, washer, nut, then valve, then 120degree hose tail. Take care to get the handles aligned for full free movement. The hose tail aspect came out pretty close to the brass ones I was replacing, that had the 30 degree elbow on the skin fitting.<br />If space is tight, as these are a little larger, assemble the hose tail onto the valve first, get thr handle aspect right and then have a mate fit the skin fitting… you on the inside, fit the washer, wind on the nut and your mate tightens the skin fitting onto the valve from the outside. I have done this before on a previous yacht and suspect will need to do again to finish my 45p. <br />For all skin fitting, I make a relatively thick epoxy glue and apply to the skin fitting a little less than hull thickness so the glue does not penetrate into the inside, then apply Sika 291 or 3m 5200 to the hull washer to be extra sure, I have fitted dozens this way and not had an issue.<br />Cheers</p>