Thru Hull Problem

[RoyS]

I purchased an Isotherm Refrigerator Conversion Kit during the great Defender Sale last week. The kit included a "Self Pumping" thru hull that replaces the galley sink drain with a larger thru-hull that incorporates the refrigeration lines, now sea water cooled. The problem is that the included thru-hull and ball valve have straight pipe threads which I cannot see any way to seal. The large thru-hull mushroom is 2-5/16" diameter with straight threads. This assembly reduces down to 1-1/4" straight threads. There is a 1-1/4" ball valve with straight threads and a hose barb for the 1-1/2" sink drain hose also with straight threads. Assembling this per the instructions results in what appears to me to be a very unseaworthy and sure to leak plumbing nightmare. Has anyone else solved this problem?

 

[Gunni]

Pipe sealant and about 10 threads deep you won’t have a leak or a problem. None of those fittings see any significant load.

 

[Ilanortho]

I purchased an Isotherm Refrigerator Conversion Kit during the great Defender Sale last week. The kit included a "Self Pumping" thru hull that replaces the galley sink drain with a larger thru-hull that incorporates the refrigeration lines, now sea water cooled. The problem is that the included thru-hull and ball valve have straight pipe threads which I cannot see any way to seal. The large thru-hull mushroom is 2-5/16" diameter with straight threads. This assembly reduces down to 1-1/4" straight threads. There is a 1-1/4" ball valve with straight threads and a hose barb for the 1-1/2" sink drain hose also with straight threads. Assembling this per the instructions results in what appears to me to be a very unseaworthy and sure to leak plumbing nightmare. Has anyone else solved this problem?

Sorry to be of no help, but I was thinking of refrigerating my ice box. I am curious and cannot find installation instructions on Defender's website. Would this be a good alternative to the above? I have a Hunter 34 and have read the posts about converting the icebox and was wondering if this is an easier alternative assuming of course cabinet modifications. I also hate the top loading ice box!
Thanks. Ilan

 

[Tom J]

Roy, you have presented a conundrum. You said you have "straight pipe threads". Pipe threads are tapered and seal with a bit of sealant as mentioned previously. Straight threads would need some kind of seal or gasket to be water tight.

 

[NYSail]

Speaking of threads...... sealant or tape? Which offers best results.

 

[dlochner]

Through hull threads are typically NPS, straight threads. Valves that attach to through hulls will have straight threads on one side and tapered on the other.

See for example here: Bronze NPT to NPS Flange Adaptor | GROCO

 

[RoyS]

Thank you for your comments. I asked a plumber friend about this issue and received an answer exactly the same as Tom J's above. The plumber stated that in USA the norm is tapered threads with sealant, but in Europe (it seems) the standard is straight threads with gaskets. The kit from Isotherm contains all straight threads and no gaskets. There is some mention of Silkaflex 291 for the thru-hull sealant but the rest is left to the buyer to discover for himself. When assembling these items dry there is no resistance or friction until the threads bottom out. I looked on line for a suitable gasket but I could not find anything specifically called out for these items. Suggestions?

 

[RoyS]

And NY Sail, my plumber friend uses both at the same time. He tapes then dopes the threads before assembling the joint.

 

[dlochner]

Groco recommends Teflon Tape, for example here: https://www.groco.net/media/file/file/i/b/ibv-fbv-tech-blltn.pdf They also note that some of their products have straight threads that transition into tapered threads. Could this be the case for your parts?

Seems like a call to Isotherm is in order.

 

[SG]

 

[jibes138]

Ball valves alone will not attach a thru hull. You need a nut to tighten it to a backing plate. Thru hulls have straight threads, sealant is applied to the flange and threads enough to fill the gap in the hull between the threads and hull. Why don't you install a true seacock while you are at it? If it necks down to 1 and 1/4 diameter why is it so large to begin with? Sounds like a 1 and 1/4 thru hull and seacock is what you want. Picture of your stuff would help to better understand. Read MaineSail's website on replacing thru hulls and valves before you do anything.

 

[Gunni]

Teflon or thread dope, your choice. Teflon offers easier disassembly if you need that.

 

[Gunni]

Ball valves alone will not attach a thru hull. You need a nut to tighten it to a backing plate. Thru hulls have straight threads, sealant is applied to the flange and threads enough to fill the gap in the hull between the threads and hull. Why don't you install a true seacock while you are at it?

Most ALL of the European boats have ball valves with straight threads that attach directly to the thru hull. No reason you can’t do it with a Hunter. You are confusing thru-hull fittings and valve fittings. Totally different. There is no reason to turn this into a thru-hull replacement.

 

[NYSail]

Teflon or thread dope, your choice. Teflon offers easier disassembly if you need that.

Thanks...... that is what I used.

 

[dlochner]

Don't use teflon where there is high heat or on fuel lines. On fuel lines if a small piece of tape breaks loose it can clog filters and injectors. Use a good quality sealant that is appropriate for the liquid or gas.

 

[Terry Cox]

I was thinking of refrigerating my ice box.

Hi Ilan, refrigerating your ice box is a DIY project with basic tools. Our boat came with a 12V system that uses ambient air rather than sea water. Works quite well. Defender sells them in kit forms that comes with instructions.

You will need to find a location that is close to your current ice box for the small compressor/condenser. Defender site has the dimensions. Two copper tubes will run from the compressor/condenser to the evaporator located inside the box. Ours is mounted on the wall of the box and is the component that removes heat from the box. The evaporator is also used as the freezer section and normally will come in two sizes; large and small. We have the larger size, but the selection depends on the volume of your existing box.

We prefer the top loader version rather than side. Converting yours from top to side is another complicated matter better left to a separate thread. Unprepared to discuss here.

 

[SG]

Roy:

Beyond Gunni's observations on the thru-hull, valve and sealant above,

• Do you intend to have a readily serviceable strainer on the the raw water intake? (You should have one.)
• You need to consider how you'll winterize (Your coils need to be protected on the compressor.)
• I'm not familiar with the Hunter 33 except from some pics of the galley area. Are you putting the valve under the counter that separates the main cabin from the galley "U"; or are you putting it somewhere forward of that?

 

[jibes138]

Most ALL of the European boats have ball valves with straight threads that attach directly to the thru hull. No reason you can’t do it with a Hunter. You are confusing thru-hull fittings and valve fittings. Totally different. There is no reason to turn this into a thru-hull replacement.

A ball valve with straight threads that attaches directly to a thru hull is called a SEACOCK. A seacock has the advantage of a flange to spread the load of opening and closing the valve and holes to bolt it in place. If the OP is replacing a thru hull as described then MaineSail's article will show how to apply sealant correctly and proper backing plates. What is the discussion around a 2 and 5/16 necking down to 1 and 1/4 about? Is the OP referring to the flange diameter and the thread diameter or are the threads necking down? A picture is worth a thousand words give or take.

 

[jibes138]

Maybe this will help visualize what is being discussed. https://www.indelwebastomarine.com/...rine/Manuals/SP_Installation_Instructions.pdf
The thru hull is mounted with a nut then the ball valve goes on top where the threads are a smaller diameter. Instructions note to use Sikaflex 291 or equivalent sealant. I recommend following the instructions.

 

[JimInPB]

NPT is the most common pipe thread in the US. It is also known as black iron pipe thread. This is a tapered thread.
NPS is another American standard for a different pipe thread that is not common. This is not tapered.
The US National Pipe standards also have several other variants like dry seal, railing, etc.

BSP is a common pipe thread in Europe. It has straight threads with no taper. As with most British threads, the thread form itself is different from what we have here in the states. Fortunately, the pitch of the thread is usually the same as NPT, so I can often make a BSP female into NPT with a small amount of effort & a tap.

If you want to understand all the details of many different threads, then you can look them up in a book called the Machinery's Handbook, but it's a heavy read. http://allaboutmetallurgy.com/wp/wp-content/uploads/2016/12/Machinery_s_Handbook_29th_Edition.pdf

If you just want some basic info, you can take a quick gander in these few places -
https://www.ralstoninst.com/news/story/the-difference-between-npt-bspp-and-bspt-seals
https://www.usplastic.com/knowledgebase/article.aspx?contentkey=998
https://en.wikipedia.org/wiki/National_pipe_thread

I normally use tape on my NPT threads, unless it is for gas or fuel, then I use the appropriate dope. I know more than one guy who swears by using both tape & dope all the time for everything. There are different formulations of dope for different materials.

I seal my thru-hulls with 3M 5200 if I want a permanent seal. If I want something removable, I cut a gasket out of the appropriate thickness of a suitable rubber gasket material & coat it with Dow Corning 111. In some cases, an O-ring is also a good choice.