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Old 06-19-2016, 09:01 PM   #1
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Transom exhaust thru-hull: Bronze or fiberglass?

I have a 1978 Mainship with what appears to be a bronze thru-hull for the exhaust. It's 4" diameter and I'd like to replace it during the next haul-out.

It looks old and it's such a critical part I don't want to mess around. It looks like it's a straight flange with no angle. The bronze one from Buck Algonquin has a 16 degree angle and no flap. Vetus makes a resin-reinforced one with a flap, but bronze seems more trust-worthy. Does anyone have any experience with the Vetus exhaust through-hull?

Thanks,
RR
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Old 06-19-2016, 09:35 PM   #2
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I'm assuming you have 4" exhaust hose on the inside? If so, fiberglass in a piece of 4" fiberglass exhaust pipe. That will look a lot better and it's easy to add a rubber exhaust flap on the outside if you desire.

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Ted
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Old 06-19-2016, 10:38 PM   #3
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Wow - that looks really nice. Ideal to have no fasteners to worry about. I'm thinking in a new direction now.
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Old 06-20-2016, 06:18 AM   #4
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If you are concerned, take it off and inspect it. You may find it's OK. If you want to improve the look, paint the outside, but you can hardly see mine under the swim platform.
In bronze you can also find those outlets chrome plated. The + side of bronze is strength and lifespan, your current unit is almost 40 years old and I have never heard of one failing. The composite units should serve well as the will not corrode and are non conductive. Any of the uphill hose components will fail long before the outlet fitting regardless.

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Old 06-20-2016, 09:41 AM   #5
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Yep, just glass in a piece of FG pipe as OC did. You can get any angle you want.
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Old 06-20-2016, 11:40 AM   #6
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I might just be over concerned. If the bronze ones don't fail then I can just disassemble, clean, reaseal and use new bronze bolts when it's hauled next. But - that assumes they don't suffer from crevice corrosion or other nastiness. The current one looks tough - like if I backed into a dead-head piling it would be fine. I'm afraid the glass/resin ones could crack and with a hole that big it would go down fast. I've seen plenty of floating pilings in my area, some with huge, square-headed bolts sticking out.

I suppose a more realistic scenario is the dingy tied up over night with the outboard up. The outboard skeg finds it's way into the exhaust port and a few swells come by and crack it.

Somebody tell me I'm over-reacting - I'd like to use a piece of vernatone pipe or the glass/resin centek style.

Also, if I use the centek is 3M 5200 too permanent? It seems that plus 3/8" fiber-reinforced nylon bolts would be a totally composite construction.

Regarding the vernatone pipe, is there any concern about constant heating/cooling + the vibrations down the exhaust causing stress fractures? I don't spend much time checking out the e-hole on trawlers, but I seem to recall always seeing something bolted on. I think the all-glass look is super-clean and it's a great idea but do any manufacturers do that?

Thanks,
RR
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Old 06-20-2016, 01:16 PM   #7
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This is just one opinion: the existing fitting is almost 40 years old and to use your words: "The current one looks tough."
There are hundreds of these out there the same age (production numbers vary, but at least 800 on Mainships alone) and I have never heard of a failure.

That said vernatone and centek piping is pretty thin walled fiberglass tubing. I would not consider using 5200 to "glue it in." If you go down that road you need to glass the pipe into the transom, both sides with plenty of glass.

Both vernatone and centek piping are rated for exhaust. The temps of the water and the gases that far downhill is probably no hotter than 120f which is no big deal.

And again, if your MKI is anything like mine, the exhaust pipe is pretty well protected by the platform and the braces supporting it.

I think that on a '78 Mainship there are plenty of other things to worry about more than this exhaust fitting.

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I might just be over concerned. If the bronze ones don't fail then I can just disassemble, clean, reaseal and use new bronze bolts when it's hauled next. But - that assumes they don't suffer from crevice corrosion or other nastiness. The current one looks tough - like if I backed into a dead-head piling it would be fine. I'm afraid the glass/resin ones could crack and with a hole that big it would go down fast. I've seen plenty of floating pilings in my area, some with huge, square-headed bolts sticking out.

I suppose a more realistic scenario is the dingy tied up over night with the outboard up. The outboard skeg finds it's way into the exhaust port and a few swells come by and crack it.

Somebody tell me I'm over-reacting - I'd like to use a piece of vernatone pipe or the glass/resin centek style.

Also, if I use the centek is 3M 5200 too permanent? It seems that plus 3/8" fiber-reinforced nylon bolts would be a totally composite construction.

Regarding the vernatone pipe, is there any concern about constant heating/cooling + the vibrations down the exhaust causing stress fractures? I don't spend much time checking out the e-hole on trawlers, but I seem to recall always seeing something bolted on. I think the all-glass look is super-clean and it's a great idea but do any manufacturers do that?

Thanks,
RR
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Old 06-20-2016, 02:19 PM   #8
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Nothing like bronze... How long ago was the Bronze Age and we are still finding stuff. Your exhaust outlet should be good for 50 years or more. Can't say the same about stainless or plastics.
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Old 06-20-2016, 03:58 PM   #9
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Fiberglass tube has been used in exhaust systems and for exhaust flanges for more than 40 years. There is a high proportion of wound glass in it with a glass to resin ratio of probably close to 50:50 The the tube is very strong. You will not damage it. When you install it you will want to glass it in place with glass in the inside and the outside of the transom.
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Old 06-20-2016, 05:08 PM   #10
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Can't remember the last time I saw a new boat with a metal wet exhaust discharge.

Ted
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Old 06-21-2016, 12:43 PM   #11
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I still have the stainless thru hull that was oem on my Mainship.
It is in good shape and available if you want it.
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Old 06-21-2016, 01:15 PM   #12
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Is that the one you took out when you repowered with the racing Cummins?

LOL


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I still have the stainless thru hull that was oem on my Mainship.
It is in good shape and available if you want it.
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Old 06-21-2016, 02:01 PM   #13
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Good quality bronze should still be in real good shape.
May have to heat up parts in their threads to get them apart. Use some antiseize when putting back together, or some marine grease.

I have some through hulls in bronze from 1970, and like new shape.
My exhaust outlets are large copper pipe, and in great shape. they are caulked to the transom and painted. I have had all these parts apart to examine them in the last 10 years.
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Old 06-22-2016, 06:41 AM   #14
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All boats flex a bit , all exhausts change shape as they change temperature.

The bronze fitting with a bit of hose sounds like the easiest way to handle the movement.
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Old 06-22-2016, 06:58 AM   #15
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Quote:
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Is that the one you took out when you repowered with the racing Cummins?

LOL
Yes it is LOL.
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Old 06-23-2016, 06:56 AM   #16
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If the fiberglass tubes\thru hulls never failed, it would be difficult to find any to buy.
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Old 06-23-2016, 07:33 AM   #17
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If the fiberglass tubes\thru hulls never failed, it would be difficult to find any to buy.
They're everywhere because people are replacing the metal ones with them and are much more common in new construction.

Ted
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Old 06-23-2016, 12:44 PM   #18
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Depends on weather the exhaust is dry or wet. Dry exhaust can be very hot where as wet cooled with raw water is cool. I can not run the hot dry exhaust with out damaging the tube thru hull. The exhaust tube and the thru are connected with a hose. So depends on the exhaust temp.
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Old 06-25-2016, 07:58 AM   #19
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They're everywhere because people are replacing the metal ones with them and are much more common in new construction.

Ted
I wont be replacing my SS thru hull with a fiberglass one.
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