Exhaust thru hulls

[Swampyankee]

I'm repowering my S2 9.2a. Going from a Yanmar YSM12 (10hp) to a Westerbeke 20B Two (18hp.). The recommended exhaust hose size for the 20B is 2" so I'll have to replace the existing 1-1/2". That brings me to the exhaust thru hull, which appears to be a piece of 1-1/4" I.D. fiberglas tubing glassed through the hull. I'm wondering if I really have to replace that or just adapt the hose to it.
I wandered through the yard looking at other boats. It seems like the typical 30+ footer has a 1-1/4" to 1-1/2" thru hull. I'd assume most of these boats have at least a 15 - 20 hp motor - a couple I know have 18 or 20, since I spoke to the owners.

My question to my fellow S2 9.2 owners is, What size is your boat's motor, and what diameter is the exhaust thru-hull on your boat.

 

[Stu Jackson]

I wouldn't kludge something together like that. If the exhaust hose is 2 inch, put in a 2 inch thru hull for it. Then either remove and glass over the old one, or cap it inside the boat.

What other S2 owners may have is immaterial, 'cuz you may have a different engine than all the rest of them from your repower.

Good luck, sounds like a neat upgrade.

 

[FastOlson]

I wouldn't kludge something together like that. If the exhaust hose is 2 inch, put in a 2 inch thru hull for it. Then either remove and glass over the old one, or cap it inside the boat.

What other S2 owners may have is immaterial, 'cuz you may have a different engine than all the rest of them from your repower.

Good luck, sounds like a neat upgrade.

Agree with Stu completely.
Also, a couple of mechanics I know tell me that there are newer standards for diesel exhaust systems that do indeed call for much larger ID all the way thru the system than the boat builders were installing back in the 80's.

Perhaps no change in the hull is needed, except to enlarge the hole where the old fitting was. Different/larger waterlift muffler, too.

LB

 

[scottmcg]

I repowered last year with a Beta 25, also 2 inch exhaust. When researching the repower, I read at least a couple tales of woe (overheating / poor performance) from people who adapted their old smaller exhaust thruhulls when installing engines of 20hp or so (pretty close to yours..) Moving up to the recommended 2 inch fixed their problems. I too, would go with the manufacturer's specs.
For my install, I put a new 2 inch thru hull in. I looked like a bit of glass work to cut off, cap, or enlarge the old 1.5 inch fitting so I just ran the outlet for a new 1 inch electric bilge pump into an adapter and used the old fitting and thru hull for that (adapting UP is ok, just don't go DOWN in size). Just to be on the safe side, I made sure the loop went up to deck level and put an anti-siphon valve in.
Good luck with your project!

 

[garylinger]

I re-powered my 9.2C 2 years ago with a Beta-Marine that called for a 2" exhaust. I too wanted to avoid the work and expense but based on all of the feedback I changed to the 2" riser and thru-hull. All I did was use a hole cutting saw (like you would use for a doorknob hole in a door) and cut out the fiberglassed thru-hull and inserted a metal thru-hull. It worked out very well.

 

[Lorin Smith]

Tyr this, plug old hole with wood. using this plug to locate the center, use hole saw to enlarge existing hole. No need to re-locate this way. Then, glass in short section of fiberglass exhaust tube onto which your new 2" exhaust hose can connect. Clean, reliable, inexpensive.

 

[Stu Jackson]

There would be no need to add a fiberglass section to this very good description of how to do the work. I'd draw the center of the plug before you inserted it. Buy the right thru hull and attach the exhaust hose right to it. I also remember reading tips & tricks on using saws on fiberglass to avoid ripping gelcoat by running the saw backwards until it gets into the transom.

 

[Swampyankee]

An update on my re-powering project: The Westerbeke has the exhaust discharge from the port side of the engine, opposite of my old Yanmar. So I did the right thing (I usually do, I just have to consider all short cuts before choosing to "do it right") and I ran 2" exhaust hose to a nice stainless exhaust scupper I hole-sawed through the boot stripe on the port side, aft. I don't get as much rise in the exhaust hose as it did where it passed through the cockpit locker on starboard, but I still end up with a good amount over the minimum height above the through-hull and the waterline. BTW, 2 VERTICAL cylinders makes for much less shake and rattle than 1 HORIZONTAL cylinder! lol