MSD Vent fitting

[Roy 845]

Hello all, In the next few weeks I'll be installing an MSD Potty in my O'Day 22 just forward of the Port Bulkhead and I plan on putting a deck fitting for pump out but I am wondering where the vent line goes. I'm figuring that I need to install a Marelon fitting in the Hull with I think it's a 5/8" or 3/4" hose. The questions are does this sound right? If so I'm locating the vent how far above the waterline? I just don't want to wind up doing anything stupid and I only want to do it once.
Thanks to all!

 

[py26129]

OK, I'll bite. On the boats I have owned, the vent fitting has been as high up as possible. Both of them were located just below the rub rail.

Matt

 

[Peggie Hall HeadMistress]

The standard size is 5/8"...installed on the hull. How high depends on how far you heel. A little splashing and/or a short dunking won't matter, but it does need to be high enough not to stay submerged on a long tack.
Install an open "bulkhead" fitting--one you can stick your finger into--instead of a "vent" fitting. It'll allow more air exchange, which helps to prevent odor.

 

[Ron20324]

I think you'd want one of the white mushroom thru-hulls. Maybe better UV resistance? That's what I have.

 

[Peggie Hall HeadMistress]

Any material except nylon will do. UV turns nylon into powder.

 

[AaronD]

How high depends on how far you heel...

@Peggie Hall HeadMistress : (Doing a similar MSD on my Catalina 22). Is there any advantage to bringing the vent up to the cabin side? I could go below the rub rail (and just below the pump out I'll put on the side deck), or on side of the cabin side, forward of the windows. The latter would mean another couple bends in the vent hose, but would presumably get splashed less frequently. It's possible the rub rail might be submerged at some point, but shouldn't stay that way for very long - I don't push her that hard, and it's not efficient to sail that far over anyway.

 

[py26129]

Not trying toimpersonate Peggie but I would not run the vent up to the Cabin side. If you ever overflow the tank you'll have a mess on your deck. In your shoes, I'd pick just under the rub rail.

Matt

 

[Peggie Hall HeadMistress]

Matt, you did a fine job of impersonating me--good advice!

 

[AaronD]

Not trying toimpersonate Peggie but I would not run the vent up to the Cabin side. If you ever overflow the tank you'll have a mess on your deck. In your shoes, I'd pick just under the rub rail.

Matt

Good point. Thanks!

 

[Pat]

On our 272 LE the vent is just below the deck on the head side (starboard) side of the boat...the location is just above the shelf in the head/locker...maybe an inch above the interior port shelf behind the head....this makes removal of the hose very easy, i.e. to facilitate removal of the hose from the back of the vent in case something is clogged...which is not so seldom....We have had to learn from Peggie that the exterior vents can become clogged due to insects/wasps, spiders, etc....the above installation makes it very easy to remove any clogs that may affect the hose which runs to the top of the holding tank.simply loosen the hose clamp attachment to the vent.....Its all a very slick system other than the insect clogs.....Pat....

 

[Peggie Hall HeadMistress]

We have had to learn from Peggie that the exterior vents can become clogged due to insects/wasps, spiders, etc....the above installation makes it very easy to remove any clogs that may affect the hose which runs to the top of the holding tank.simply loosen the hose clamp attachment to the vent.....Its all a very slick system other than the insect clogs.....Pat....

It would be easier to replace the vent thru-hull with an open "bulkhead" thru-hull (the kind you can stick your finger into). That will let you prevent future vent blockages by sticking a hose nozzle up against the thru-hull and backflushing the vent line every time you wash the boat.

 

[Sunbird22358]

@Peggie Hall HeadMistress : (Doing a similar MSD on my Catalina 22). Is there any advantage to bringing the vent up to the cabin side? I could go below the rub rail (and just below the pump out I'll put on the side deck), or on side of the cabin side, forward of the windows. The latter would mean another couple bends in the vent hose, but would presumably get splashed less frequently. It's possible the rub rail might be submerged at some point, but shouldn't stay that way for very long - I don't push her that hard, and it's not efficient to sail that far over anyway.

From personal experience with our old CAL 21, you want the vent fitting (we just used a standard mushroom thru-hull, 5/8") just below the rubrail on the hull side. We originally had one on the cabin side wit ha 90deg bend (a bilge-pump outlet) and we had trouble getting fresh air into the tank. Moved to the hull side (at Peggy's suggestion) and had immediate rush of air coming in through the hole as soon as I removed the hole-saw, just the wind moving past the boat forced air into the hose! Great reduction in odor! Those 2 bends in the hose needed to mount on cabin side reduce airflow tremendously.

 

[FasterHorses]

It would be easier to replace the vent thru-hull with an open "bulkhead" thru-hull (the kind you can stick your finger into). That will let you prevent future vent blockages by sticking a hose nozzle up against the thru-hull and backflushing the vent line every time you wash the boat.

Where would I find such a thru hull?

 

[Peggie Hall HeadMistress]

Any marine store. It’s a common thru-hull used for bilge pumps and a lot of other above-waterline drains...available in almost every size. You,ll be looking for a 5/8”.

 

[FasterHorses]

Is this what you speak of?

 

[Peggie Hall HeadMistress]

Yup....that's it.