Seasloth - Before you go out and buy anything I hope you will read and consider the following information.
Sailorchic and Hopcar are spot on in identifying the plastic material used in the components that are concerning you, and like them, my first reaction was suggest that you immediately replace the PVC and nylon with bronze. But then I reread your post and took a second look at the picture. It was only then that I realized that you might have an equally important second problem that you need to be addressed. My concern is, that by simply replacing the plastic for bronze, you will have lulled yourself into thinking you've addressed the full problem.
An additional and equally critical issue that you should concern you is the inadequacy of your cockpit and deck drainage system.
1. If I understood you correctly, ALL your cockpit and deck drains go trough this one seacock. This is woefully inadequate for even the smallest cruising sailboat. Are you sure there isn't another sister seacock that services on the other side of the boat, or any scuppers that discharge above the waterline? My Shannon 28 had two 1 1/2" forward cockpit drains with seacocks and two 1 1/4" rear above the waterline aft drains. All the deck drains were above the water
2. If this is the only discharge point then you do have a serious second problem, discharge potential. It's potentially as serious as the first, but, sadly, not as easily corrected.
3. There is no ABYC standard for tail pieces or components coming off a seacock, none. However, it is generally accepted that a material like PVC and nylon are a serious liability when used below the water
line and surveyors frown on it's use. The ABYC theory I guess is if the seacock is working you can at least shut it off, even if the tailpiece is broken. Let's say it's not a theory I subscribe.
Here are a few options for your consideration.
A. Leave well enough alone, I'm not an advocate of the "I've never had a problem" approach to solving potential problems, but the bronze solution (not an inexpensive one and doesn't solve the second issue) may lull you into not addressing the the larger issue. Also, as you said all of your boats seacocks have PVC fittings.
If it were my boat I'd take a deep breath, get out the check book, get it up on the hard
as soon as possible and check every seacock, thru-hull. hose, and system, then come up with a plan to address the plumbing
issues and implement it.
B. If you want to keep it in the water for the short term, you can address the plastic issue, especially the age and strength issues by buying
new and better plastic components. Sadly, there has been very little consistency in the marine
plastic plumbing fitting world, as your picture suggests.
Ocean Link in RI (they're on the internet) has a fairly complete line of plastic plumbing fittings that exceed the ABYC material tensile strength and flexural modulus standards for seacocks and thru-hulls. I know of no other company that has this complete a line of fittings that both meet the ABYC standard and are capable of addressing your needs.
This isn't a product I'd normally recommend for below the waterline, it would at least give you a higher level of short term security
, especially with regard to strength and age. More importantly it would also keep you thinking that you needed to address the longer term issues.
C. Go with the all bronze solution. Before you do that, make sure your seacock is functional. I'm guessing, but I believe you have a Groco 1 1/2 FBV series flanged seacock, the white plastic handle cover suggests that's the case. Groco recalled some of these valves not to long ago. If the seacock is smaller than 1 1/2" then your drainage problem is worst than I thought.
The other thing that caught my eye and prompted this long response was the 1 1/2" to 2"coupler/reducer (the reverse bell shaped object that sits atop the seacock.) My guess it's bronze but the nipple fitting that attaches the seacock to the reducer may well be brass, and depending on the environment
and length of time in use may be more tender
than the plastic.
If the coupler/reducer and seacock are in good shape you'll need a 1 1/2" nipple, a 2" nipple, a 2" tee, a 2" barbed fitting, a 2" to 1 1/4" bushing reducer, a 1 1/4" to 1" bushing reducer and a 1" barbed adaptor (I haven't been able to find a 2" to 1" coupler/reducer). These will cost close to the $150.
The best source of these parts
is, I believe, Hamilton Marine. I don't know of any marine supplier that has a better selection of bronze plumbing products. If anyone has any better sources of a better and complete lines of either plastic or bronze plumbing components, please mention them. These are the best I've found.
The fittings on top of the seacock utilize NPT threads. The only NPS threads are the thru-hull and lower seacock threads.
I'll leave the seacock tree issue for some else to bring up.
Hope this is of some help.