Size of thru hulls under head sink?

[Patches]

I've got a 1990 Mark 1.25, hull no 1016.   I purchased a new Racor 500fg filter to replace the original R220.  To mount it, because it is larger, it pretty much has to go where the old one is now.  Problem is I swapped out the original raw water strainer for a new Vetus and mounted it just under and next to the old Racor near the door.  I put it their because it is directly above the thru hull, and easy to clean out when it is clogged.  There is no way I'm going back to the old style strainer.  So I have to move the location of the Vetus strainer to accommodate the new Racor 500fg.

After looking at it for awhile, the cleanest solution appears to be to mount the Vetus strainer under the switch for the shower sump pump, and possibly put in a small access hatch there for cleaning it out. I could still see if there is plant life in the strainer basket in that location by opening the door, but might be easier to unscrew and empty through an access hatch.

To do this, it would be great to use the current thru hull for the head intake/shower sump discharge (the middle one) for the raw water strainer.  I can do this because I no longer have a marine toilet and holding tank.  I removed these in favor of a Dometic 975 MSD porta-potti short term, and an Airhead composting toilet longer term.  I also do not use the shower, but if I ever did I could move the discharge line to the current raw water intake thru hull. 

I would like to be able to plumb the middle thru hull as a "T", kind of like it is now but with new fittings, so I can remove a blockage at the intake with a long dowel by removing a cap on the top of the "T" (instead of the hose to the strainer).  I have to do this at least 4-5 times a season during the sunnier months when photosynthesis breeds all kinds of plant life in the water column.

Understanding well the need to replace all the thru hulls in this area, and after trying to find the answer in the forum archives, are all three thru hulls in this area (raw water intake, head intake/shower discharge, and head sink drain) the same size?

I want to make sure that if I move the raw water intake to the middle thru hull, there are no negative impacts to flow to the raw water strainer.  Anybody see issues here, or attempted something similar?

Many thanks in advance,

Patches

[Stu Jackson]

Many of us have "repurposed" our thru hull connections under the heads sink, primarily to switch the head intake (see 101 Topics).

I just looked at the manual and while it shows what is there, it shows no sizes for the thru hulls or the hoses.

Functionally, it would make no difference if you swapped the hoses; the thru hulls are all adjacent, so close they might be considered to be one location.  The main concern would be size.  What I suggest you do is remove the hoses from the thru hulls and see what size the thru hulls themselves are.  The head sink drain and toilet inlet are 1/2" hose, I don't know if the raw water intake to the engine is 1/2" or 5/8".  It is something easy for you to check.  I have a feeling (after 25 years) that the thru hulls are identical.

[waughoo]

My recollection from when my 1991 was out of the water about a year ago is that all three are the same size.  As Stu says, you could remove the hoses and check.  You could also put a caliper on each of the actual skin fitting threads to see if they are all the same.

[tvorgitch]

I read somewhere (can't recall right now) that the sink drain was 1" and the other two were 1/2". That seems to match the picture I took during my haul out of a 1993 C34.

This view from the port side, so the sink drain is the farthest port.

Hope this helps.

[Ron Hill]

Patches : I've done some screwing around under the head sink and here's what I've found. 

The raw water intake is probably a 1/2"  because the 5/8" hose to the RW pump fits easily over the 1/2" barbs and double clamp.  The head sink drain is probably a 3/4" or 7/8" thru hull because I was able to fit a 1" drain hose over the barbs and double clamp. No sure about the other thru hull - might be only 1/2"??  The shower intake is 5/8" hose, but do not know the output size from that pump!!

Hope this helps?  A few thoughts

[Noah]

I believe the original engine intake is 1/2 in. I replaced all three seacocks with 3/4 in. Marelon Series 93 with integral flanges. I used Buck Algonquin bronze tapered thru-hulls, as wasn't aware that Forespar made Marelon one with tapers to fit our hull until AFTER I installed the bronze ones.  Here is more info on my install.
https://c34.org/bbs/index.php/topic,11007.msg87002.html#msg87002

[tvorgitch]

Does anyone know why there are three thru hulls under the head sink?

My drain seacock handle broke off (fortunately in the closed) position and I was just going to but in an elbow and connect the drain in place of the shower sump as other have done since I've only used the shower once. In thinking about it, I may just put in a tee and connect the head input, sink drain and shower sump to the same seacock.

I would clean this all up at the next haul out, but I don't see any advantage to having three thru hulls in that location.

[Stu Jackson]

Does anyone know why there are three thru hulls under the head sink?

...................

OEM were three: engine raw water inlet;  shower sump to diaphragm pump outlet combined with head intake; head sink drain

The first makes sense to be on its own.

The second two make sense to combine because they are rarely used at the same time.

The third makes sense to drain the sink.

Many of us have revised the OEM to switch the head sink outlet to the head (toilet) inlet for a last freshwater flush of the day, leaving the shower sump outlet on its own.  I use the shower often, but can leave the thru hull for it closed most all of the time.

I think it makes sense.

If you don't have use for head intake (i.e., porta pottie and/or composting head) that's one you could eliminate.  The shower sump pump would operate properly connected to the sink drain because there is a check valve in the outlet of the sump.

Three down to two.  Doesn't sound like a huge improvement to me.

[Patches]

Thanks to all for your thoughts.  I'm headed down this morning to remove the old fittings for the head intake and shower discharge from the ball valve, and to do some preliminary layout.

Patches