Trojan Boat Forum

Should one replace the original muffers in a '77 F32? Do they evntually fail? I have no idea how they are made and whether or not mine are still effective.

Also, does any one have knowledge of wrapping exhaust pipes to reduce noise?

Thanks,
Dave

DAVIDLOFLAND wrote:
Also, does any one have knowledge of wrapping exhaust pipes to reduce noise?

Thanks,
Dave

I have a big Vernatone muffler on my single 350 which I wrapped in sound insulation. The sound reduction however was minimal. What did help allot was changing the way the muffler was supported. It used to hang from brackets that were attached to the under side of the cockpit floor, which caused sound/vibration to resonate thru the cockpit area. Instead I made a couple of stanchions for the muffler out of marine plywood and epoxied them to the bottom of the hull. Now the muffler sits in these like a cradle and cockpit noise is greatly reduced.

Hope this helps

I don't believe wrapping the exhaust would help much . The main time exhausts are wrapped is on dry sections for heat ( like a dry riser or dry turbo ). However this bring up a good question . Is your exhaust the correct size for your new engines ? Diesels flow more air and cooling water so you want to make sure its right . The cooling water also helps quiet the exhaust .

Looking at the drawing of the engine the exhaust outlet is 102 mm almost exactly 4" . Is that correct ? If so you would want to have 4" exhaust unless yanmar specs say other wise . Centect call for 5 to 6" But I believe they consider 2 cycle diesel in there specs and they flow a lot more .

FWIW my outlet is 6" and exhaust is 6" to and though the muffler but change to 5" after the muffler .

Some key points , Check the specs ,Bigger is ok ,avoid sharp bends .

4" is the correct exhaust diamater for the engines, which is existing on the boat. I am just wondering if the original mufflers could be worn out and should they be replaced whil I have everythin apart, or would replacement be a waste of money.

Interesting point regarding diesels drawing more air. I had heard that in the past, so I asked my Yanmar dealer/mechanic if it was OK to block off the existing vents on either side of the salon and rely on air from the rear vents only. He said that would be fine as the new engines (2.993 l / 183 ci) would actually draw less air than the old 350 Chevy's (5.7 l / 350 ci), even after factoring in the turbocharge.

David , I would rethink about blocking off the front vents , for several reasons . First is the amount of air need for the engines . Yes the are smaller CID then the old , But the HP is about the same so would you expect the amount of air to be less ? Second air flow in the engine room helps keeping engine room temps down . ( may not be a big issue in a cooler area like yours )

Yanmar should have a spec for minimum vent size total . I have seen charts on this but can't find any now will keep looking .

I did find this by Tony Athens "Good "rule of thumb" that will satisfy all of the engine manufacturers needs/specs---------50 sq inches of "open area" per 100HP....." I have seen others say 1/3 o 1/2 sq in per hp .
interesting read
http://boatdiesel.com/Forums/index.cfm? ... rch=2&SR=1

http://boatdiesel.com/Forums/index.cfm? ... ch=2&SR=41

Good info. Thanks PF.

I'll consult with my installer before I block off anything. I want adequate ventilation of course, but don't want all the moisture and salt spary. We run in rough seas on a regular basis and I have witnessed the water the passive forward side vents bring in.

Nobody has spoken up about old mufflers/silencers and if they go bad. Does anyone know what's inside them?

David , Not sure what the Trojan mufflers where made of , Mine are glass but not OEM . I mainly run into 3 types of materials use in mufflers steel/case plastic and fiberglass . I don't think you would have steel ,if you do dump it . That leaves glass and plastic . These can hold up well and last a long time . But can be damaged by heat , like when pump impeller goes out or a plugged up riser . I also have seen the baffles in side them broken lose from a back fire . Just reglassed the baffles back in one last year . This was a very large on about 3.5' tall 2' round 10" inlet and outlet . Cause was backfire .

Don't know if this helps or makes it more confusing

Mine are either plasic or fiberglass. Just looking at them I'm thinking plastic. Attached is an old picture that shows the end of one.

I would guess glass . Look close at it if its glass then you maybe able to see the fibers . http://www.centekindustries.com/vernatoneround.html

I've seen one of these blow due to a backfire. Appeared to be fiberglass. Nothing much to them at all.

Can't speak for anybody else but every muffler with a blown baffle that I've come across has been pretty obvious because of the rattle the loose baffle makes banging around inside while the engine is running. If the port size is enough for the repower spec, and the units are glass not metal, I'd leave them unless you have reason to suspect there is an internal problem.

As mentioned before, it's critical that the elbow height above the water line meets minimum requirements. As an extra precaution, you could add exhaust flaps on the exhaust outlets at the transom to minimize backflow under the right conditions.

I had an issue where one engine was considerably louder than the other. I replaced the fiberglass muffler to no avail...still just as loud.(was easy to find the exact replacement on line) What I realized and it is stated early in this topic, it is all in the how the water sits in the muffler to baffle the noise. I tipped the muffler up a tiny bit and wallah...the engine quieted right down. At the same time, I also treated my heat exchanges with salt away...amazing stuff! It cleared any and all blockages out and forced even more water in. My f32 is so quiet at the dock, you can hardly hear it run other than the water running out of it.