Replacing Exhaust Pipes on Shamrock 20 Pilot House 1981

[Sailfree]

Planning to replace port and starboard exhaust hoses (rubber from engine to galvinized iron to rubber just forward of transom) with
3“ copper pipe from engine to transom on the port and starboard. Any thoughts?

 

[Mistress]

No reason to not be viable if you can get the right OD's.

Both of mine have been mostly rubber.

 

[Gary S]

It will be louder inside the boat and possibly outside as well.

 

[Ship]

3" copper has been done by others in the past. It's loud and expensive but the price of all things marine are high. Wire re-enforced rubber hose is quieter but pricey too. Many have used Venetube as well.

 

[Sailfree]

Turns out the exhaust transom portals measure 2 1/2” and are below the waterline. I’ll look at A1 rubber hose and Venetube. Thanks for your suggestions.

 

[fluke37]

Wire reinforced hose from manifolds to transom.

 

[pilarboat]

Copper is about the middle of the galvanic nobility scale and must be bonded or it will erode very quickly if in salt water. If you solder bonding tabs to each pipe it must be connected to the boat's bonding system or you will soon regret not doing so.

Regarding wire hose, keep in mind that steel wire inside the hose is another thing that can set up galvanic corrosion because of dissimilar metal in the manifold and wire. Just because the wire in the hose is covered with rubber this does not mean there can be a connection (grounding). This is prevented by using hose that has no wire where it connects to the manifold as it should not. have wire in that section of the hose. Ever notice that a SS hose clamp will erode on wire hose yet the wire in the hose is not touching the clamp, or so it may appear.

Although galvanic corrosion is a rather simple concept, many do not understand or realize what is going on until it is too late.

There is no way I would use copper exhaust, go fiberglass and wireless hose.

 

[Sailfree]

Thanks pilarboat, very interesting. This is not my first boat, but it’s my first powerboat. It’s clear I have a lot to learn to update this boat while maintaining it’s character. Reading the posts on this site really helps.

 

[Gary S]

I went this route using 3" hose, ski boat mufflers and tips. Would not do it again since it did not seem to quiet it as much as I had hoped. I was however going to go with this 3rd setup when I was going to put a 5.8 from a late model ski boat with single 4" exhaust,these boats being super quiet. I never had trouble with corrosion either since I hung it on davits

 

[Mistress]

Just my opinion, but some get too carried away with the concept of galvanic corrosion.

Galvanic Corrosion – SSINA

www.ssina.com

Requirements for Galvanic Corrosion:
In order for galvanic corrosion to occur, three elements are required.

1. Two metals with different corrosion potentials
2. Direct metal-to-metal electrical contact
3. A conductive electrolyte solution (e.g. water) must connect the two metals on a regular basis. The electrolyte solution creates a “conductive path”. This could occur when there is regular immersion, condensation, rain, fog exposure or other sources of moisture that dampen and connect the two metals.