Fiberglass Exhaust Elbows

[Wind River]

My wet exhaust system uses 3" hard exhaust hose which doesn't bend well at all. Where it comes out of the exhaust manifold it drops down into the bilge below the water line and traverses to the other side (about 12") and up to a loop above the heeled water line. From there it goes back down to the bilge and out to the stern where it exits.

Anywhere it makes a turn (90 degree) there is what appears to be a galvanized elbow with threaded nipples to clamp the hose onto. These galvanized elbows appear to be well beyond their service life. Not leaking, but heavily rusted.

I have seen 3" fiberglass elbows for sale and wonder what the forum thinks of using these to replace the galvanized elbows in a wet exhaust system?
I also like that the fiberglass elbows have more of a sweeping turn that the abrupt 90 degree turn of the galvanized elbow. Any problems with these?


Also, where the exhaust exits there is a bronze through hull that is 2.5" (smaller than the hose) with a 2.5" bronze gate valve and a fabricated elbow (this is leaking). I would like to replace the fabricated 90 degree elbow with standard elbow fittings. I can find bronze elbows but only brass nipples in 2.5" to connect them. I am going to reuse the gate valve for the time being (I know the downfalls of gate valves). What would be better, using the bronze - brass set up or a bronze - stainless (304) combination? I realize neither is ideal but a common material for all just doesn't seem to be available.

The picture with the red elbow and rudder arm is what I am replacing and the other is what I would like to change to.

[model 10]

I am using 2 fiberglass elbows in our system. I have checked them out carefully after a water pump failure and they look fine.
What is with that gate valve?

[Cheechako]

I see no problem with your plan. They make a sweep elbow in smaller size I know, which is a bigger smooth bend. Not sure in 3".
I used 45 degree fiberglass ells on a 3" system once. No issues.

[SVTatia]

I think that by replacing the elbows you'll may even gain some engine HP.

If you have the room above the exit, check the use of a Vetus goose neck.

vetus - Abgas-Schwanenhälse Typ LT ab 98,90 € | SVB Spezialversand für Yacht- und Bootszubehör GmbH

It will eliminate one elbow and the gate valve. I am not sure what is the purpose of the gate valve with an exit above the waterline...

[Ambler]

I have a fibreglass water lift muffler made to my requirements from a specialist company in Sydney Aus. So fibreglass elbows are good to use, just make sure the wall thickness is good enough to handle the clamping pressure.
You need to check the condition of the exhaust hose, ensure it hasn't gone too hard where it is clamped. Use a sealant like Stag jointing paste. Use better quality stainless clamps with a wider band and bolt. If you cant find these, double clamp everything.
I would recommend replacing either or all three fittings, the through hull skin fitting, valve and barb so all are the same material, either all stainless or all bronze. Gate valves should be pulled down, cleaned and lubricated while your at it.

[Wind River]

Gaining hp or fuel economy would be a nice bonus if it did. Coming from an automotive background, I was thinking along that line myself.

The gate valve I guess is there simply to be able to plug a hole in the boat. Every other through hull, above or below the water line, has a valve or seacock attached to it. I don't see why this one should be any different, although I can't ever see a reason for closing it unless the engine was out of commission. There is a rubber flapper that covers the hole on the outside which probably keeps a following sea from being pushed into the exhaust.

There is no room at all to come vertical off the through hull as the platform for the aft berth almost sit's right on top of it.

How about the dis-similar metals issue with brass, bronze or stainless?

[Ambler]

Originally Posted by Wind River

How about the dis-similar metals issue with brass, bronze or stainless?

Google "marine metal corrosion"
Great info on minimising future problems where dissimilar metals are put together in the marine environment. There are a few informative PDF 's worth downloading.

Whilst I note your exhaust outlet is above the WL, it has salt water passing through it.

Personally my skin fittings are stainless above WL (looks nicer) and Bronze below WL.

Good call having valves fitted to all skin fittings above and below WL. I have closed my exhaust ball valve in a gale to stop the following seas from back pressuring the exhaust.
Cheers

[Wind River]

Originally Posted by Ambler

I have a fibreglass water lift muffler made to my requirements from a specialist company in Sydney Aus. So fibreglass elbows are good to use, just make sure the wall thickness is good enough to handle the clamping pressure.

The clamping area is really what I was concerned with so I will check some different manufacturers and see if there is one that is thicker than the other.

You need to check the condition of the exhaust hose, ensure it hasn't gone too hard where it is clamped. Use a sealant like Stag jointing paste. Use better quality stainless clamps with a wider band and bolt. If you cant find these, double clamp everything.

Exhaust hose will all be replaced so no worries there.

I would recommend replacing either or all three fittings, the through hull skin fitting, valve and barb so all are the same material, either all stainless or all bronze. Gate valves should be pulled down, cleaned and lubricated while your at it. [/QUOTE]

I would love to use all bronze fittings as the through hull and gate valve are bronze. Unless someone has a source for 2.5" bronze pipe nipples I would have to change to all stainless. I have priced stainless ball valves at around $369 USD and would rather stay with the gate valve for that prices. So would the brass / bronze combo be any worse than what appear's to be galvanized steel and bronze. I haven't tried to remove the fabricated elbow from the gate valve yet. I guess when I do that it might dictate what I have to replace when I find they have destroyed one another.
Gate valve has been service and operates well

[Cheechako]

Rethinking.... I t hink either is fine. I doubt a heavy, ungrounded fitting will fail in your boat lifetime. SS has a good history with bronze, but is very susceptible to hot water corrosion... so not sure it's any better.

[Ambler]

Try

http://www.go2marine.com/category/13...html?view=item

Might be an option here as the hose tail barb is part of the elbow see part number 32541 down the page on above link

[40 South]

Fibreglass is fine in wet exhaust. About 1/2 of my 8" exhaust is fibreglass the other 1/2 is stainless steel & rubber bellows.

[Terra Nova]

First of all, forget about using brass anywhere.

Try to do the whole run using only hose. If you must add a f'glass elbow, use a 45*, if possible. Use as few as possible.

Eliminate all traps in the hose run. It should from the engine directly to the waterlift muffler, then to its highest point, reasonably close to to the muffler, and then slope continuously downward from there.

Use only non-pierced, heavy duty, all-stainless, doubled hose clamps, the bolted ones, preferred.

[Wind River]

Ambler - Thanks for the link. I got my mind kind of stuck on making the same set up as I showed in my second picture and didn't think to look for that large of a hose barb. I will still need to address the different sizes between the fittings and the hose. (2.5" valve and fittings to 3" hose.) Maybe a straight 3"x2.5" fiberglass adapter.

Tera Nova - This exhaust does not have any muffler. I guess the trap that is right after the engine must do something to reduce noise because it really is not that noisy. With the position of the engine and the hull design there is no way to slope the exhaust downward away from the engine.

Thanks to everyone for their input. I think I have pretty good idea the direction I will go.

[Emmalina]

If you want to get adventurous make your own ! I have been making them for years.. Once you get a mould knocked up you make an inner skin then just keep adding woven roving to required OD sand it all smooth and away you go... Then you can do the same with a muffler if you want .. Every time I have a stainless or galvanized part go I try to replace with epoxy glass where ever possible :-)

[forsailbyowner]

Too bad your so far off. Dons salvage here in st pete has a big selection of bronze plumbing. They do have a website dunno if someone would go out and grab what your looking for. Ive found every fitting ive needed from his tables and bins.