Conference unifix::sailing

Flush thru hull fittings are designed to be flush with the outside of
the hull and do not relate what happens inside the hull. (OK, so I 
didn't read your note carefully the first time. You get some extra words 
of wisdom and knowledge. Ted Turner and I are both legends in our own 
minds.) The head of a flush thru hull is flat top and bottom and the
edge is beveled. Unless your hull has been molded with the proper
beveled recess, installing a flush thru hull is quite difficult (unless
you have a most expensive carbide bevel cutter tool and no, I don't know
who makes them). I know, I installed a flush thru hull for my knotlog. I 
should have had my head examined. The other kind of thru hull has a
flattish mushroom head and is easy to install. Drill the proper size
hole in the hull and pop it in. Of course, it sticks out 1/4 to 3/8 of
an inch, and that is a drag, especially if you race. If you don't or are
a cheap boat builder, why worry about a few hundredths of a knot? 

The thru hull is held in place one of two ways: easy and hard (of 
course). The easy way is to use a nut (with straight pipe threads by the 
way on US made fittings). You then screw whatever valve you choose onto 
the end of the thru hull. The hard way, but by far the best, is to use a 
flanged seacock. Drill the hole for the thru hull. Center the seacock 
over the hole and drill (usually) three bolt holes through the hull. 
Bolt the seacock to the hull with bronze bolts (assuming you don't have 
an aluminum hull). Then cut the thru hull to the right length and screw 
it into the seacock through the hole in the hull. Jabsco makes some nice 
flanged ball valve seacocks at not so nice prices. With the easy method 
when the bronze thru hull corrodes away or the plastic one breaks off,
water rushes in and you get to look frantically for the tapered soft
pine plugs you whittled one dull winter night. With the hard way you get
to wait until the seacock corrodes away before you etc. By then you've
most likely sold the boat. 

The flush Marelon thru hull is designed to be bolted to the hull as in 
the hard way, ie, no nut. I have seen pictures of a Marelon thru hull 
that looks like it has legs that allow it to be bolted to the hull with 
room under it for a nut on the thru hull. Hmmm. The other kind screws
onto the end of the thru hull which is clamped to the hull with a nut.
Disadvantage with the latter is that if you pull hard on a reluctant
seacock, you have quite a bit of leverage on the thru hull and there is
the possibility of breaking the stem, especially old bronze or plastic.
Also, plastic deforms under rather low loads, so you really can't screw
the nut or seacock onto the thru hull very tightly without stripping the
threads. 

Bedding compound. Do you ever want to remove the thru hull? If so, use 
something like BoatLife. It is OK and lasts a while. In my experience, 
though, it isn't very sticky and if there is any stress it doesn't hold 
(which is why our chainplates leak and why I am switching to Sikaflex 
241). For permanent installation, use Sikaflex 241 or 3M 5200. Very 
adhesive stuff. If a thru hull leaks, you either pump or haul out. 
Either is a pain, though pumping tends to build character and with 
embellishment makes good bar stories.

Plastic or bronze. As I recall PS came down firmly in the middle.
Plastic is OK for inshore (your sailing I imagine). If you insist on
being macho and going offshore, go bronze. After all, it is traditional.
I have the impression that the threads on the Marelon thru hulls,
seacocks, and tail pieces are not US standard pipe threads. Buy
everything you need from one source (West Marine, for example). I
suspect, in the absence of engineering data to the contrary, that the
plastic stuff isn't as strong, but it is strong enough. Yes, teflon tape
is fine for the thru hull to seacock and seacock to tailpiece joints.
Use lots. I do, and no leaks yet (that I'll admit to anyway). My snide
references to cheap boatbuilders aside, we have plastic thru hulls above
the waterline and bronze below. 

Dare I sign this?

    The Forespar catalog (free) has a good section on Marelon
    seacocks/thruhulls, etal. You can write to them at:
    Forespar
    2672 Dow Ave.
    Tustin, CA  92680
    
    Phone 714-838-9900
    
    They have two models of thru hulls, one with "feet", one without.
    I think the one with feet is designed to be through-bolted with
    a block between the seacock and the hull. The other is designed
    to be mounted on a block that is glassed to the inside of the hull.
    
    I probably have the above wrong and will dig out the catalog over
    the weekend and report back here on Monday.
    
    I'm planning to eventually replace most of my thru hulls with Marelon
    with one heat-related exception. I'm of the impression that plastic
    would stiffen up if subjected to heat so the engine exhaust will be
    bronzed. Is my assumption about the heating effect correct.
    
    Jamestown Distributors (800-423-0030 for orders or a catalog) carries
    Marelon fittings also. 
    
    Toodles...
    

    I second Alans recommendations.  I used the Marlin (sp?) seacocks
    on our 25.  They were an improvement over the gate valves the
    manufacturer put in.  I suspect the plastic thru hull could fracture
    very easily under stress (forcing the valve, dropping something
    on it etc) but the 25' manufacturer had the good sense to at least
    put in bronze thru hulls (which mated up perfectly to the plastic
    valve).   Our current boat has nothing but bronze thruout - and
    I have peace of mind (and some plugs).
    
    Walt

    
    Re .2
    
    I agree.  I would be wary using any plastic in an area subject to 
    high heat like engine exhaust.  I would also stay with bronze in
    an engine area or other space with a relatively high fire danger.
    A melted seacock would be no fun to deal with.
    
    BTW, the danger of melting is the prime reason the Coast Guard 
    will not accept plastic seacocks on commercial vessels.
    
    Steve
    

   FORESPAR SEACOCK INSTALLATIONS
                         |           | FLUSH MOUNTED SEACOCK
                         |   |   |   |     SCREWED ON TO STEM OF THRU HULL
                        _=============__   AND SCREWED TO GLASSED-IN BLOCK
                       /     |   |      \ <--- GLASSED-IN BLOCK
            __________/______|___|_______\_____________________
                             |   |                               <-----HULL
            _________________|___|_____________________________
                         \___|   |___/ 
         THRU        ____                     STANDOFF DESIGN
         BOLTED |    |
               \|/   |  SEACOCK BODY
                   __| 
                | |_______|    |_
                | |     __|____|__          THRU HULL NUT
               _| |____/__________\_______
              / | |       |    |          \   BACKING PLATE
         =======| |=======|    |===================================
                | |       |    |          HULL
        ========| |=======|    |===================================
                     \____|    |____/
                /|\
                 |

The flush mount seems to be the stonger installation. It would definitely
be easier to install. Thoughts?

Models for US market have "NP" thread. (What
is that, some sort of standard?  Models sold outside US have "B.S.P" thread.


Ed
    

    There are several different pipe thread standards. In the Fire service
    (I an a volunteer firefighter) we deal principally with IPT (Iron
    Pipe Thread) and National Standard which I thought was NS. Perhaps
    that is what NT stands for. In any case, there are a bunch of different
    pipe threads which have evolved over the years. What was the other
    one you mentioned BPT? I think that one is British Pipe Thread.
    In general, they are all incompatible. We use various adapters in
    the fire service. If you need to go from one to another, chack with
    your local fire dept or check the yellow pages for plumbing or fire
    protection supply dealers.
    
    Bill
        

    Thank god for this topic.Reply 273.1 has all the answers to my
    questions how to replace my engine seawater input seacock and the
    attached strainer.Well....almost,since I am a novice on this short of
    thing I still have a couple of questions.
    1.The bedding compount looks and feels like the regular house paint
    patty.Any guess what kind or brand it is.I would like to use the same
    thing since there wasn't any leakage and the bedding was soft even
    after 12 years.
    2.Altough the bedding was soft and moist when I took the seackock apart
    later from the exposure to air becamehard.How do I take any bedding
    compound from the plywood donut so it becomes smooth and ready for the
    new seackock.Should I use accetone?
    3.Is there any way that assures when cutting the tale pipe to the right
    lenth that the threads wont be screwd-up and cannot be screwed to the
    seackock.I have shortened screws that way and if they didn't work I
    throw them out and try another one.But I cannot experiment with an
    expensive tale pipe attached to an equal expensive strainer.
    Thanks in advance.....and I promise after the seackock thriller is
    solved I am going to ask you about the case of the uncooperative
    electic bilge pump.
    By the way I am changing the seacock because it is unworcable and ready 
    to go although no leaks.
    
                       HAPPY NEW YEAR
    

    re: .7
    
    Two suggestions......  
    
    Don't use a solvent on the old gunk it may attack the glue in the
    plywood.  Make new backing plates if you can.  If you can't then
    attack old gunk with sharp tools (whatever you have) and a small
    amount of heat.  Use an electric powered heat gun [sparingly].
    
    When cutting threads (any threads) always put the nut on the piece
    you are cutting.  That way when the cut is complete you just back
    off the nut (over your new end) and this chases out any burrs that
    are in the end.

    The suggestion of first putting on the nut is excellent, but only works
    for machine threads. If you are cutting pipe threads, this option may
    not be available.
    
    Ross Faneuf

Avoid cutting the threads, if you can! If you must cut the threads, use the
nut (preferably two nuts, one each side) as a saw guide for your hacksaw, to
get a perpendicular cut. After backing out the inner nut, you can further
dress the edge with a file to get rid of the sharp edges left by the hacksaw.

--RS

re .8:

Hmmmm, I've never heard of any common solvents dissolving the glue in
plywood. Anyway, be sure that the plywood backing plate (assuming that 
there is a backing plate) isn't rotted or delaminated. Obviously, if it 
is, it should be replaced. In any case, I'd recommend giving the backing 
plates two or three coats of epoxy (especially the inside of the hole) 
to prevent water absorption and rot in the future.

    On a related note, I have seven Taiwanese seacocks, all bronze and rubber 
    copies of the cocks made by Groco. The plugs are rubber-coated
    bronze. I've heard some horror stories about early versions of
    these counterfeits -- some contained zinc and ultimately turned to
    oxide dust at inopportune moments.  I recently took these apart to 
    clean and examine them, and, though 10 years old, they appear to be in 
    excellent condition.  
    
    What I don't know is the appropriate lubricant.  I am getting radically 
    conflicting advice.  The previous owner used Armor-All -- that vinyl 
    conditioner people use on car roofs.  I think it's mostly silicone and
    it really doesn't coat them very well and freezes pretty quickly this
    time of year. 
    
    The other day, I examined some real Groco valves in a marine supply outlet 
    and they had a brown grease on them.  When I asked the owner of the 
    establishement, he said Groco made a "special" grease for their rubber
    valves, but he didn't carry it because he had so little call for it.  He 
    suggested Vaseline.  Someone else said Vaseline would definitely degrade 
    rubber.  I got tired of equivocating, so I went through all the publications
    I had but was unable to find Groco's address or number.  
    Does anyone have it or know where I can find it?     
                                                     

    Try water pump grease.  It will not affect rubber, it does not wash
    away, it is readily available.  Suitable for all moving rubber parts
    like impellers, toilet pumps, and seacocks.  Worked for us.
    
    Brian

    Sounds like what I'm looking for.  I glanced through the Boat/US catalogue,
    but it wasn't listed.  Is it something a hardware store would carry, and if
    so, is that what they would call it?  Do you remember any brand names?  
    Thanks.
    
    Brian

    Try an auto parts store or plumbing supply house.  Spag's is almost
    certain to have it.  It is not marine specific.  It goes by the generic
    name of water pump grease.  I am sure several manufacturers make it. 
    The can we had on our boat was several years old and I believe it was
    Castrol.  Of course the boat came from the U.K. so it it stands to
    reason the grease came from there also.  We used this to lubricate our
    all bronze seacocks, the head, the water pump impeller, fry eggs
    ;-)....
    
    Brian

    
    Oilzum makes what your looking for, go to a good automotive
    store, they will have it.  i have already bought some.
    
    Need a lot???
    
    JIm.