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Old 23-05-2022, 11:19   #1
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Flush thru-hulls flange/head size

Dear Forum,

Apologies in advance for this "long read".

Could you please kindly help me with this:

I've got my Catalina 42 1992 last November. Besides ...well... "everything else" I am replacing now all thru-hulls and valves.

Previously/originally these were all Forespar Marelon thru-hulls and valves except two bronze on holding tanks macerators outlets.

Without any intent to start another "Marelon vs. Bronze holy war" I'd would like to mention that:
1. All Marelon thru-hulls were in pretty good shape when I removed them.
2. A broken handle on one of the Marelon valves in a process of very careful "exercising" of it and a leak as an unpleasant "side-effect".
3. One valve completely broke in half on a very minor force applied while I was removing a hose. (Good for me that this happened while she was on the hard. Otherwise .... <your imagination goes here>...).
4. One Marelon of "93 series" looked good ... but had periodical minor leak on open/close.
5. Bronze valve (I removed one) looks very good. After some exercising/lubing works smoothly. From the inside looks good as well. I don't see any disturbing signs. Bronze thru-hull also looks not bad.

So basically Forespar / Marelon valves currently is not an option (or an option that I will consider as absolutely the last one). Except that one "93 series" valve which has two barbs and I need exactly the same. Part number is 931233 which is not available online and should be ordered directly.)

So without Forespar I have these two options left (all 3/4 except one 1-1/2) :
1. TruDesign valves/thru-hulls. For example TruDesign Ball Valve with load bearing collar
2. Groco bronze flanged with the backing plates;

Ordered both to try.

During "dry-fitting" I realized that I feel uncomfortable with TruDesign because that "load bearing collar" completely blocks any access to a thru-hull without complete removal of the valve. Not sure why I don't like this. Probably because of a hypothetical case of a leak between a thru-hull and a hull that I will not be able to temporary fix. Thru-hull's flange diameter is 1-2/3'' but Forespar 3/4 thru-hull fits OK. For now I don't consider TruDesign as an option for now.

With Croco valves I am having another problem: Catalina has the "flush thru-hulls". Only Forespar has thru-hulls with a flange/head of that size (please see the images).

Outer flange/head diameters for comparison:
- Forespar is 2.430(61.72mm)
- Groco is 2".

I feel not very comfortable with a smaller one but was unable to find a bronze flush or mushroom 3/4" thru-hull with the similar flange size as Forespar.

Technically Forespar thru-hull looks and feels like has the same NPS thread as Croco flanged valve NPS thread. Given that Groco flanged valve will be on a backing plate a smaller flange head should be OK.... r-r-r-ight ?

So my question is what should I do:
- Use a bronze thru-hull with a smaller flange?
- Use Marelon thru-hulls with a Groco bronze flanged valves?
- Other options ... ?

Any ideas/hints/thoughts/considerations are needed and appreciated.
Thank you.

P.S. Some other related thoughts. I ordered one backing plate from Groco and I didn't like it at all. This is an overpriced cut made of PVC panel that look similar to what I see in Home Depot. I honestly not sure how it will bond to an adhesive but have some doubts about any "epoxy-based" one.
Got these instead.

The images to compare how both tru-hulls fit.
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Old 24-05-2022, 01:57   #2
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Re: Flush thru-hulls flange/head size

Greetings and welcome aboard the CF, BourbonS.
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

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Old 25-05-2022, 12:29   #3
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Re: Flush thru-hulls flange/head size

Thank you!

Found this from Buck Algonquin with flange diameter 2-1/2".

Ordered to try. Will see.
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Old 25-05-2022, 12:45   #4
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Re: Flush thru-hulls flange/head size

Congrats on the sweet boat. I don’t think Hunter ever used a poor product deliberately. I replaced on ballcock on a Jeanneau cause these threads made me paranoid. I’d want to replace the flange with the factory spec in either material. I don’t think there is any question the bronze is the best material and the base they put in is sure secure.
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Old 25-05-2022, 13:11   #5
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Re: Flush thru-hulls flange/head size

One more question.

That "93 series" two-barbs seacock likely can be done differently using a regular flanged seacock and some "tee connector". But again, can't find any tee with NPT thread (except this one)

not sure whether this would be a right way to go or just get a new "93 series" and don't bother?
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head, hull, size

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