Hello. The FRP exhaust piping and some of the hosing on my 2001 32 is starting to fail, due to high temperatures before. Testing shows a max temp of 220F so I will be installing a Vetus mixer to help get rid of the hot spots.
I want to change the FRP out for silicone or rubber but how do I couple these hoses/elbows together?

Paul Bulk
Crown Prince
Brentwood Bay, BC
32-191

Hi Paul,
I strongly recommend further investigation into potential exhaust system issues. See both the attached articles (even though the NT 37 is a different model the type of exhaust elbow maybe the same) for some good info.
On my 2002 NT 37, shortly after buying her, I installed an exhaust hose temperature alarm. As it turned out, this probably saved me from a potentially really big problem. During our first summer, the alarm sounded. I carefully checked all engine temps using an IR temp gun, and found all to be well within expected range, except for a few spots on the exhaust hose. There were several spots reading way too hot (and these did not reach 220 degrees). Running that hot can cause the hose to delaminate leading to a possible full hose failure (resulting in exhaust gases and extremely hot salt water leaking into the boat). This is also the very first area where an overheat from almost any cause will first show up. So I highly recommend the installation of this type of alarm. The early alarm can save expensive engine damage, as relying on the regular factory alarm could be too late to avoid damage! The actual cause of my hose overheat was the fact that my exhaust elbow (that looked almost new on the outside, had developed interior perforations (resulting in INTERIOR leaks) that greatly reduced the effectiveness of the cooling spray pattern. This leak could have also allowed seawater to enter my turbo and maybe even my engine through the exhaust if I had not noticed the problem (due to the newly installed exhaust hose alarm)!! Water flow everywhere else was great. To be clear, this type of failure (in the worse case scenario) could result in the need for a new engine if the situation allowed seawater to enter the engine!! There would be no visible signs.
Also see sbmar.com (Seaboard Marine) under "Tony's Tips" to read up about "doomed to fail" exhaust systems. My exhaust elbow, like Kelly's (the author of the attached article regarding his NT 37) was a "doomed to fail" situation. Even these elbows made from stainless steel have an operating life and require replacement as ongoing maintenance, not to mention the "doomed to fail" setup. I used National Marine exhaust out of Marysville, Wash. to design and build a custom exhaust elbow for my boat and was very pleased with the result. The alarm I mentioned is inexpensive, and easy to install. Both Borel (the one I used) and Aqualarm sell models of this alarm. I also installed an Aqualarm water flow alarm between the sea strainer and the water pump to detect instantly any lack of water flow (that could be caused by forgetting to open the sea cock, some sort of external blockage like a plastic bag or seaweed, or a blocked cooler somewhere in the system). Again, not too expensive and very effective.
https://sentoa.org/maintenance_tips/wet_exhaust_37.html
https://sentoa.org/maintenance_tips/wet_exhaust.html
I hope this info proves helpful to you and other NT owners (of older boats). I found Kelly's article to be very, very helpful.
Best,
Tom Easterbrook
formerly Pilitak NT 37-068 (2002)
Nanaimo, BC

From: Paul Bulk via Sentoa sentoa@lists.sentoa.org
Sent: November 18, 2023 11:19 AM
To: sentoa@lists.sentoa.org sentoa@lists.sentoa.org
Cc: Paul Bulk crownprincenordic32@gmail.com
Subject: [Sentoa] Exhaust

Hello. The FRP exhaust piping and some of the hosing on my 2001 32 is starting to fail, due to high temperatures before. Testing shows a max temp of 220F so I will be installing a Vetus mixer to help get rid of the hot spots.
I want to change the FRP out for silicone or rubber but how do I couple these hoses/elbows together?

Paul Bulk
Crown Prince
Brentwood Bay, BC
32-191

Hi Paul,

This is Kelly B, the author of the other wet exhaust elbow article on SENTOA.  You’re definitely on the right track.  I second everything Cameron and Tom contributed, such valuable DIY experience and wisdom on this blog!

You asked: “For peace of mind I want to replace the FRP with rubber or silicone which has a much higher operating temperature. The issue is how do I connect up the rubber hoses and elbows . . . thinking of using a 5” OD piece of stainless pipe.”

Agree completely with your intent to upgrade to silicon for any hose, hump-hose couplings and elbows.  You certainly could connect it all with SS pipe but perhaps don’t give up on FRP yet as you’d likely risk the same foreshortened marine life with the SS pipe that you’ll have with your SS wet-exhaust elbow.  This marine exhaust RFP pipe is actually pretty tough stuff and would likely last the life of your boat if you can maximize your exhaust elbow mixing/cooling efficiency as you intend.

Learned a lot about FRP marine exhaust when we repaired our damaged wet-lift that had a cracked inlet elbow (originally delivered with over-tightened hose clamps).  I cut off the broken FRP 45 and took it to MJ Marine Exhaust in Ferndale WA (just across the BC border from Surrey, they fabricated all the original FRP exhaust components to NT for our boat).  Owner Maurilio made me a custom heavy-duty FRP 6” 45 with an oversized coupler-end I could slide onto the stub remaining on the wet-lift.  Most important part was he sent me home with a jar of the special hi-temp (and otherwise unobtainable) epoxy vinyl-ester resin fresh out of his production drum along with the requisite hardener.  Maurilio uses Hetron Fire Retardant 922 Epoxy Vinyl Ester Resin for his extensive catalog of FRP marine exhaust fabrications.  Hetron’s temp and chemical resistance rating on this resin is impressive.  Price from MJ was under $200 in 2016.  He would likely sell you any length of FRP pipe you might need.  Buy some for spares if you are concerned using FRP, easy enough to inspect and swap.

FYI on silicon exhaust components. Turns out the parts generally available from marine suppliers like Fisheries, Defender, etc turn out to be particularly expensive as they generally only stock stuff with a US Coast Guard certification logo.  Found the ones without that for a whole lot le$$ through industrial sources like www.mfcp.com here in Seattle.  Pretty much what all the commercial fish boats around here use.  Contact me if you want more details.

Good luck Paul!

Kind regards,

Kelly Britz, SANDPIPER, NT37-042 Edmonds/Seattle

From: Paul Bulk via Sentoa sentoa@lists.sentoa.org
Sent: Saturday, November 18, 2023 11:19 AM
To: sentoa@lists.sentoa.org sentoa@lists.sentoa.org
Cc: Paul Bulk crownprincenordic32@gmail.com
Subject: [Sentoa] Exhaust

Hello. The FRP exhaust piping and some of the hosing on my 2001 32 is starting to fail, due to high temperatures before. Testing shows a max temp of 220F so I will be installing a Vetus mixer to help get rid of the hot spots.
I want to change the FRP out for silicone or rubber but how do I couple these hoses/elbows together?

Paul Bulk
Crown Prince
Brentwood Bay, BC
32-191

From: Paul Bulk via Sentoa sentoa@lists.sentoa.org
Sent: Saturday, November 18, 2023 11:19 AM
To: sentoa@lists.sentoa.org sentoa@lists.sentoa.org
Cc: Paul Bulk crownprincenordic32@gmail.com
Subject: [Sentoa] Exhaust

Hello. The FRP exhaust piping and some of the hosing on my 2001 32 is starting to fail, due to high temperatures before. Testing shows a max temp of 220F so I will be installing a Vetus mixer to help get rid of the hot spots.
I want to change the FRP out for silicone or rubber but how do I couple these hoses/elbows together?

Paul Bulk
Crown Prince
Brentwood Bay, BC
32-191

This is an update to my 2016 SS dry-riser/insulated exhaust-elbow article in SENTOA’s Maintenance section with a bit of extra soap-box. We replaced our stock wet-elbow with an insulated dry-riser elbow at 8K engine hours.  This past winter at 12K hrs (+4K hrs) we had to replace the corroded SS double-walled RW mixing “shower-head” portion of that replacement elbow.  We have a Cummins but this posting applies to every NT regardless of what engine you have because you have a wet-exhaust elbow.

The original project objective in 2016 was to replace Cummins’ double-wall stock exhaust elbow that, according to boatdiesel.com, had contributed to the ruin of a fair number of 6B’s in other boats.  On our early NT37, engine placement puts the turbo right at the boat’s waterline.  Additionally, with our NT’s draft, Cummins would likely say they believe their stock wet-exhaust elbow was probably installed too ‘flat’ (not angled ‘downward’ enough) to achieve an optimal underwater exhaust layout (NT subsequently upgraded exhaust elbows on Cummins with newer boats).

We replaced our stock wet-exhaust elbow with a custom fabricated insulated ‘dry-riser’ type of wet-exhaust elbow.  This got us 8” more freeboard/height from possible backwash from the wet-lift up the exhaust system in rough seas, and relocated the RW mixing shower-head section farther downstream so that any raw-water leakage from corrosion to that SS RW-mixer portion would be far less likely to get back up into the turbo and ruin the engine.

I had added an R&R visual inspection of our replacement elbow with our 1K engine hour maintenance intervals.  With this most recent one, even with the thick encrustation of carbon, I noticed what looked to be pitting in the SS so I thoroughly wire brushed the inside of the double-wall mixer section.  The SS pitting was pretty extensive.  Hydro-testing the elbow to statically pressurize that double wall section identified dozens of tiny pin holes penetrating the inner SS wall starting to allow RW into the exhaust stream ahead of the all-important exhaust cooling shower.  Largest hole was maybe only .010-015”, so they were remarkably hard to see deep up in the pipe especially with the exhaust carbon layer.  The other end of the elbow that bolts to the turbo with the dry-riser portion and flange (only exposed to the exhaust stream, not RW) was OK.

National Marine Exhaust in Marysville, WA made our replacement dry-riser elbow in 2016 for $1400 including the insulation blanket.  Now in 2023, I had JNL Welding (custom SS marine exhaust fabricator for Seattle’s fishing fleet) fabricate a new heavier walled SS shower-head section which owner-Jason then welded to NME’s original riser-flange portion for under $1K.

Soap box: regardless of what engine you run on your NT, and whether you still have a stock wet-exhaust mixing elbow like ours or whether NT delivered your boat with a better one - even though these wet-exhaust mixing elbows have no moving parts - solely due to the harsh environment in which they run all wet-exhaust elbows are CONSUMABLE parts and they need to be monitored.

Running exclusively in fresh water might put this reality off but probably not forever.  I would strongly suggest adding inspection of your wet-exhaust elbows with every 1K engine service.  And this doesn't just effect your main engine, your diesel gen-set has a wet-exhaust mixing elbow too and it's operating in the exact same harsh RW-exhaust environment.

If you think I’m exaggerating here, take a look at the rusty chunk of scrap that used to be a Yanmar with only 675 hours on a Ranger 25 that was recently donated to the Marine Tech program at Skagit Valley College here in WA.  They didn't get to root-cause so it may not have been the fault of a failed wet-exhaust elbow but I'd bet a fair bit that it and that Ranger’s entire “flat” wet exhaust system are certainly implicated in this tragic engine failure.  Will be most interesting to see in their future episodes what they do to avoid it happening again with the re-power.

https://www.youtube.com/watch?v=Yy-EO-a5zWA

Respectfully,

Kelly Britz, SANDPIPER, NT37-042 Edmonds/Seattle