Exhaust Diameter

[Paul Meyer]

I will be changing the exhaust on my Catalina 27 before next season. It currently has a 6hp Petter diesel inboard with 30 year old, 1 9/16 inch inside diameter exhaust hose. The hose started leaking late last summer and the transom through-hull bedding compound was almost gone and also leaking. I’ve removed the through-hull and the hose and will be replacing both.Next season will likely be the last season with this engine. I hope to replace it with a used Universal M12 or M18 or possibly a Yanmar 2GM20F or similar.The early Universal diesels apparently had 1 1/4 inch exhausts right up to the 24 hp engine. I am not sure about the more recent M series. The Yanmar 2GM20F apparently has a 2 inch exhaust outlet. I want to build an exhaust system that will work with my 6hp but be optimal when I move to a bigger engine. Besides replacing the exhaust hose and through-hull, I also want to add a waterlift muffler.Based on my research to date, I think a 2 inch exhaust system would be best if I want to have the option to go to a 2GM type engine. My plan is to go with the larger 2 gallon Vetus waterlift muffler. Is a 2 inch exhaust best in this situation? Would that large an exhaust, with waterlift muffler, also work with my 6hp until I am able to install a bigger engine? Or is a two inch exhaust overkill with my potential future 16 hp diesel?Thank you in advance for sharing your experience and opinions. Also, if anyone has an engine that I might be interested in (either working or a rebuild candidate), I would love to hear from you.Paul Meyeralgonquin23@yahoo.ca

 

[jim]

length of run?

I'm not a diesel expert but 2" sounds way overkill on that small of an engine unless the run is very long... like more than the length of the boat in this case. I upgraded a 40 hp to 2" from 1.5" a while back.I think 1.5" will even be more than you need.

 

[Pat McCartin]

Paul,

2" is the way to go, the Yanmar and all the current Universals and Westerbekes use a 2" exhaust port. It's over kill for the Petter but with your repower in mind I'd go for it.Pat McCartinInland Marine DieselBuford, Gaimd_ga@hotmail.com

 

[Paul Meyer]

Answer

Thank you Pat for your definative reply. I'll be using 2 inch hose.Anybody have any comments re: plastic vs stainless steel vs bronze exhaust through-hulls?Also, I'll be routing my exhaust hose around some pretty good bends to get it high enough to minimize the risk of engine flooding. Anybody have any experience to suggest a particular brand of hard wall exhaust hose that is more flexible than other brands?Thanks in advance,Paul

 

[Pat McCartin]

Hose...

Paul,Use a waterlock muffler as cloes to the engine as posible. I like the Vernalift over the Vetus. Trident Rubber makes a corrugated 2" hose that has an incredibly small bend radius. I use this hose more than any other. I'd go plastic/Marelon on the thru hull. Exhaust temps won't be an issue at the end of the system and the synthetic materials mean no maintainance. Pat McCartinInland Marine DieselBuford, gaimd_ga@hotmail.com