Do I need a muffler

[GILow]

I am soon to replace my monstrous old 96 HP Nissan with a lovely little 50 HP Beta (Kubota)

Looking at the engine bay, I see that I’d get a huge amount of space back if I got rid of the enormous waterlock muffler.

Then I started to wonder, do I need a muffler? I’ve got nearly 20 feet of 90 mm rubber exhaust pipe from the engine bay to the outlet at the stern.

Anyone tried without a muffler at this sort of HP?

Matt

[Jim Cate]

Matt, we have no muffler and a shorter exhaust run. It is louder than some yachts, but not unpleasant to me (but I used to drive dragsters...).

Jim

[GILow]

Originally Posted by Jim Cate

Matt, we have no muffler and a shorter exhaust run. It is louder than some yachts, but not unpleasant to me (but I used to drive dragsters...).

Jim

Hmm.... yeah, that final disclaimer was relevant.

Arguably you now SAIL a dragster, but that’s a different discussion.

Still, that’s one in favour..

I’m not too worried about noise, since I don’t PLAN to motor much at all, I just wondered if there were any technical issues that would arise. One is that the exhaust may run a little hotter, since it currently has a big bath before it begins its journey aft.

[NYSail]

One purpose of the water lock is to substantially cool the exhaust gases prior to going down the rubber hose..... sure some highly qualified mechanics will chime in regarding back pressure on the engine as well. There are many new styles made up of different composites that don’t take up the room the old metal boxes use to.
I would not eliminate it.

Greg

[skipperpete]

Originally Posted by GILow

I am soon to replace my monstrous old 96 HP Nissan with a lovely little 50 HP Beta (Kubota)

Looking at the engine bay, I see that I’d get a huge amount of space back if I got rid of the enormous waterlock muffler.

Then I started to wonder, do I need a muffler? I’ve got nearly 20 feet of 90 mm rubber exhaust pipe from the engine bay to the outlet at the stern.

Anyone tried without a muffler at this sort of HP?

Matt

Depends on exactly how your exhaust is currently routed and how big your existing water pump">raw water pump is. One of the functions of a waterlock is to contain the residual raw water in the exhaust system at engine shutdown. With 20 feet of 90 mm hose it may be quite a lot and it needs a place to drain down into.

[jimbunyard]

Always thought the primary purpose was water containment and keeping the engine from flooding. 20 feet of 90 mm hose holds about ten gallons...

[GILow]

Ok. Very good point about water containment guys. Thank you.

It’s not a simple equation though. I mean yes, pi x r^2 x l is the pipe volume but the big question is what percentage is actually full of water when the engine is running?

Very small I should think, not that it eliminates your very good point. I shall think about this some more.

[GILow]

Originally Posted by NYSail

One purpose of the water lock is to substantially cool the exhaust gases prior to going down the rubber hose..... sure some highly qualified mechanics will chime in regarding back pressure on the engine as well. There are many new styles made up of different composites that don’t take up the room the old metal boxes use to.
I would not eliminate it.

Greg

Cooling was on my mind.

You’ve made a good point about the new ones being smaller too.

The current muffler is very, very quiet, but absolutely huge. And kind of wasted too, since there’s so much general engine clatter that the exhaust noise is unnoticeable in the racket.

[JPA Cate]

pi r not squR3e; pie are round.

[El Pinguino]

I think there is a reason the noise no longer bothers Jim.......

Westerlys were built with straight through exhausts... just a gooseneck at the transom... never bothered me..... neighbours? Not so happy.. Crew ditto..

Fitted a Vetus like this last year https://www.vetus.com/en/exhaust-sys...-5-litres.html

Bugger of a job shoehorning it in...

Crew happy... I can't tell the difference... dunno why....

[Steve Bean]

When I bought my boat (Samson C-Mist 32 ferro double-ender) I replaced the 10 horsepower Volvo and water-lift muffler with a 32HP Universal diesel, and no muffler. No problem, no noise complaint. Sea water is injected into the exhaust downstream of a riser and cools the exhaust abundantly.

[Jim Cate]

Matt, the raw water pump is more or less a constant displacement pump. It will push the same amount of water per rev whether or not you have a water lift thingy. I can't see that much of a cooling difference happens when you add the water lift.

Anyhow, theories aside, we have had no issues with our lift-less exhaust. There is an down pointing elbow at the exhaust manifold outlet, an injection point a few inches downstream, and then down to a flat run along the hull to the lazerette where there is a loop up to deck level and down again to a sea level exhaust pipe. As you know the boat has done a lot of miles, and experienced fairly harsh conditions over the past 30 years and nearly 6000 hours... and no issues with cooling, hose melting, backing up or were-sharks swimming up the pipe.

There is a low "growl" from the exhaust, louder than many boats, much quieter than any dry stack. An advantage for this is that on those rare occasions where we've lost coolant flow due to jelly fish or plastic bag ingestion, the exhaust note changes markedly and gives one a warning that something is agley.

On Insatiable II the exhaust port is slightly above sea level and the run of the hose to the stern is slightly below sea level. I dunno if this makes any difference... yours is likely deeper than mine.

Jim

[JPA Cate]

El Ping: fwiw, Jim's hearng is way better than mine. He hears rain drops on the deck.

You may be right, that he has some hearing loss, I think it is less than mine, but --appointment scheduled, but no quantification as yet.

Ann

[mvweebles]

Detailed article on wet exhaust design considerations from Steve D'Antonio. Might be interesting.

Whats not clear from your post is of size of exhaust is changing, and thereby size of lift muffler. Centek, a leading manufacturer of lift mufflers, makes several different sizes and configurations. My Perkins 4.236 (80 hp) has a 3-inch exhaust with a 12-inch round x 12-inch high lift muffler. Your 50 hp Beta may have an even smaller diameter exhaust and lift muffler so perhaps the conundrum is lessened.

https://stevedmarineconsulting...03/...s170-FINAL.pdf

[GILow]

Originally Posted by JPA Cate

pi r not squR3e; pie are round.

I now have a mild headache.