Thanks to the Internet and some checking around we ran into TIO B.V. in Holland. They are Europe’s leading manufacturer of tailor-made silencers and related equipment and have developed a broad range of exhaust gas silencers designed to meet the requirements of every kind of application. They design and manufacture standard silencers for general purpose applications and custom models to suit your specific needs.  Their silencers are manufactured from carbon steel, corten steel or stainless steel and use reactive and absorptive principles or a combination of both, depending upon the application.

After plugging them like this, I figured, we are entitle to use their brief explanation on exhaust technology

Absorptive silencers
These silencers contain sound-absorbing materials and attenuate noise by converting the sound energy into heat. Absorptive silencers usually have relatively wideband noise reduction characteristics at middle and higher frequencies. Absorptive silencers are often used to attenuate the engine intake noise or supplement the performance of reactive silencers for the engine exhaust noise control.   Our current silencer is of this type. After all, it was just a fishing vessel.  They got the cheapest of all.

Reactive silencer
The reactive or chamber type silencer is designed with a series of expansion chambers connected with non-resonating tubes which reduce the gas flow sound power by creating a series of cross-sectional discontinuities that reflect the sound back towards the source. This type of silencer is generally more effective in the lower acoustical frequency ranges, and are most widely used to attenuate the exhaust noise of internal combustion engines.

Combination silencer
Some silencers combine both reactive and absorptive elements to extend the noise attenuation performance over a broader noise spectrum. Acoustical sections are added to the reactive type design. The addition of the acoustical sections provides improved acoustic performance in the higher frequency ranges.   That’s what we want!

Ours will be about 2.4 m. (8 ft.) high and 96 cm. diameter ( 3 ft.).  Of course you have to add the thermal and acoustic isolation material.  But , we have enough space up there.