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Raw Water Inlet Hose

May 12, 2020
33
Catalina 275 Sport 31 Quincy Bay
Does anyone know the inner diameter of the raw water inlet hose to the water pump assembly? Looking to start up the engine while on the hard and there are contradictory measurements on the internet. I'm seeing both 5/8" and 3/4" inner diameters.
 
May 12, 2020
33
Catalina 275 Sport 31 Quincy Bay
It's possible either could have been used(?) You may have to measure yours.
Yes, I can certainly measure. However, it's a 30 minute drive to the boat so I'm hoping to figure this out before I head over there next time. Thanks!
 
Jun 6, 2016
187
Catalina 275 Wilmette, IL
I'm not sure of the size of the surface area for the water intake, but could you use an outboard motor flusher, ie. cups? Either way, be careful about letting the water flow too much without the engine running as the water may work its way backwards through the exhaust and hydrolock the engine.
 
May 12, 2020
33
Catalina 275 Sport 31 Quincy Bay
I'm not sure of the size of the surface area for the water intake, but could you use an outboard motor flusher, ie. cups? Either way, be careful about letting the water flow too much without the engine running as the water may work its way backwards through the exhaust and hydrolock the engine.
Good point. That's why I was going to use an in-out bucket rather than muffs (or cups). Seems like the engine would only draw water when on this way, thus avoiding any potential for hydrolocking. Unless I'm missing something?
 

Ward H

.
Nov 7, 2011
3,097
Catalina 30 Mk II Barnegat, NJ
That’s what I do, use a 5 gallon bucket.
What engine?
My M25XP uses 1/2” if I recall correctly. Maybe 5/8” but definitely not 3/4”.
I’ll check my notes later today to confirm.
 
Mar 6, 2008
682
Catalina 1999 C36 MKII #1787 Coyote Point Marina, CA.
My M35B raw water pump uses 7/8" for intake of raw water. I am sure since I recently replaced it and it was hard to find.
 
May 12, 2020
33
Catalina 275 Sport 31 Quincy Bay
That’s what I do, use a 5 gallon bucket.
What engine?
My M25XP uses 1/2” if I recall correctly. Maybe 5/8” but definitely not 3/4”.
I’ll check my notes later today to confirm.
It's a Yanmar 2y15m.
 
Jun 6, 2016
187
Catalina 275 Wilmette, IL
If it was me, I'd probably just go the easy route and not muck around with the intake hose and use the muffs/cups assuming they can cover the holes correctly. I would have the hose run to a valve that would be on topside and then to the muffs so I could control on/off easily. Turn it on, wait a few seconds for the water to get to the impeller and start the engine. Check to make sure you have water coming out the exhaust. The motor is cooled with a closed system so it's not like the cooling is critical for a short run. If you did my temperature sensor pimp, you could keep at least keep track of the engine temperature. Worse situation with no water, you may tear apart your impeller.

Decades ago with my inboard skiboat, I just disconnected the cooling hose, inserted the water hose into the cooling hose and tightened the hose clamp onto the water hose and turn the water on. But on that boat the water would not back up the exhaust. I guess you could do the same as long as you have an on/off valve. You will get some leakage because of the threads on the end of the hose.

Bucket, muffs, direct all work, just pick the one that's best for you.
 
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Ward H

.
Nov 7, 2011
3,097
Catalina 30 Mk II Barnegat, NJ
@Souellette I confirmed my C30 with Universal diesel uses 5/8" hose.
Probably best to take the drive to measure the hose ID and length you need. I sure wouldn't risk using pressurized water for intake water.
Worse situation - Hydrolocking the engine.
 
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Feb 26, 2004
21,909
Catalina 34 224 Maple Bay, BC, Canada
Winterizing an Engine on the Hard (Thanks to Maine Sail) - NEVER connect a hose to your raw water pump inlet - NEVER!!!


Plus:

So buy both and bring 'em with you. What would you be out, $10?

My M25 uses 5/8" for raw water. 7/8" is between the manifold and the freshwater side, not the raw water.

Do you not have an engine manual for your boat? Is one here on this site?

Good luck.
 
May 12, 2020
33
Catalina 275 Sport 31 Quincy Bay
Winterizing an Engine on the Hard (Thanks to Maine Sail) - NEVER connect a hose to your raw water pump inlet - NEVER!!!


Plus:

So buy both and bring 'em with you. What would you be out, $10?

My M25 uses 5/8" for raw water. 7/8" is between the manifold and the freshwater side, not the raw water.

Do you not have an engine manual for your boat? Is one here on this site?

Good luck.
Thanks for chiming in Stu. Trust me, I won't be hooking the supply hose directly to the inlet. I have no interested in hydrolocking the engine. I've seen that video - it's excellent. Cheers.
 
May 12, 2020
33
Catalina 275 Sport 31 Quincy Bay
Confirming that the inlet hose to the water pump is 3/4” inner diameter. Ran the engine on the hard with an in/out bucket, as shown in the video shared in this thread. Worked great and was a breeze to set up.
 
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