What is Silent Thunder?
 

Vague title, I know. But I was hoping someone could explain exactly what the silent thunder exhaust platform is.

I just bought a 292 and having a quieter exhaust has really been a change. I can actually hear people and listen to music.

But how does the system work and what kind of maintenance does it require?

Does it just force the exhaust under water or or what?

It is a swim platform where the exhaust is run through like a muffler. Between the water and the baffles inside it silence the thunder of those bad 502s. Leave it alone and enjoy. Just watch for possible cracks in the fiberglass.

the platform has a "bowl" for lack of a better term where the exhaust water/sound dumps into this small space then the over flow water is pushed out by the force of incoming water. Once on plane and running the water doesn't accumulate as much and is somewhat louder but the exhaust still passes through that space, quieting it a bit. You shouldn't need to do anything to it unless damage occurs, then inspect for water entering the structure of the boat/platform.


think of poop: Doesn't smell so bad if dropped under 3 inches of water but if left out on a bed of leaves it becomes much more powerful :eekdrop:

Not to swipe your thread, but I noticed a couple very small hairline cracks in my ST box this year. Its by the handle on the same side as the ladder. is there a fix for it? I've been trying to only keep a person or two on it at a time... Thanks,

I have some small stress cracks on the platform it does flex, but at 25 years old I can`t complain.

I'm actually enjoying the quieter boat! I just wanted to make sure I didn't need to drain the platform or something when it comes out of the water..

Think of farting in a bathtub.....just that your engines are now doing it. :D :D

I loved ours when we had it!!

Do the older boxes have the plugs in the bottom? If so you can remove them and the box holds less water and becomes a bit louder I believe.

Beats me but I would be interested in knowing the answer to this..

Where would the plugs be? I'm headed over to do some weekday boating, I'll take a peek and see if I can find them..

Would you leave the plugs out all the time?

Yes there are plugs under the swim platform. I removed mine and it did seem a little louder (2000 312)

Yep, on either side near te edge. I left mine out as well..... and then took a 2" holesaw and made the holes bigger. Just to make it a little bit louder. :D

Interesting........but I've never farted before. :D :D

So on plane, there wouldn't be any water in the box?

This is really going to sound stupid, but its got wet exhaust, right? So the box is filled with the water thats coming out of the exhaust, not from just being in the water and filling up.. So opening the plugs wouldn't completely drain it, it would just keep the water from getting too "deep" inside the box and less sound absorption..

Correct. Instead of drilling larger holes in the bottom of the platform, I cut out the baffles which are about 4"-5" inside the exhaust tips. I used a sawzall with a long blade and it took all of about 5 minutes. A little louder, but nowhere near thru-hull.

When you're on plane, the faster you run the higher the exhaust pressure. This effectively "blows" the accumulated water out of the platform. The exhaust still has to force itself under the baffles but since the baffles are no longer submerged, you get less back pressure and louder exhaust. It really is an ingenious design that quiets the engines around the docks but results in no appreciable loss of exhaust flow at speed. It was (is) a patented Formula design. Very cool!

The later models, Fastechs, initially used a somewhat modified Silent Thunder design. Essentially the same except that the "box" was really just a panel under the platform that rattled and cracked. It was just too wimpy. The earlier models with the full ST platform were much better but still susceptible to exhaust leakage and rot of the embedded wood in the platform.

http://img818.imageshack.us/img818/3028/alsidjfo9.jpg

Is this what you're talking about? It looks like the plugs have already been pulled out of mine.

Yep. A regular transom type rubber plug (for a smaller boat) can be inserted in there if you want to try it.

Silent thunder
 

is when you eat a pot of fresh baked beans then you go to bed and you pass gas vary quietly and pull the covers over the old ladys head...

Just run the Silent Thunder as is. Leave it alone.
The design works great with no real issues.
Opening up the baffles makes it a little louder, but you get ZERO prrformance gains. Unless you are running BIG power through it, the ST can handle everything you can dish out.
The ST is cooled by wet exhaust and does not have much water in it once on plane. If you listen real close you can hear the difference when the water that filled the ST at idle, drains and starts blowing out the back unrestricted.
I cut holes in an older ST on a 272 and it made the rubber flappers vibrate and sound like crap at idle around the docks. The extra exhaust flow really screwed it up.

LMFAO! Thats one way of putting it!

The center port flapper is stuck in the open position. Are these that crucial on this setup?