Thru hulls vs thru leg back pressure test

[45Auto]

Re: Thru hulls vs thru leg back pressure test

Interesting test, TilliamWe - thanks for the link!

http://www.trailerboats.com/images/e...9_Mufflers.pdf

It strikes me as funny that going to straight pipes they went from 48.1 to 49.3 MPH, then when they started adding restrictions (tips) they went up to 50.6 MPH ?????

Be interesting to see some MPH vs Time curves on the Midrange acceleration also.

 

[abj87]

Re: Thru hulls vs thru leg back pressure test

To me the water in the exhaust of a boat provides the perfect muffling/sound enhancement.

try telling that to EVERYONE that can hear you for a 2 miles away. Tell your self what ever you want but your still annoying to others.
I love sailing around on my boat and hearing jackasses like you come blowing by me at 90db.

 

[JHuck]

Re: Thru hulls vs thru leg back pressure test

I'll be honest, if the switchable exhaust hadn't come on my boat when I bought it used, I wouldn't have dropped the extra cash to have it installed later. Now, I do like to open it up from time to time for the heck of it. Usually it's on a day when the lake is jammed and there is ZERO chance of finding tranquility anywhere.

I have noticed that while cruising through idle zones other boaters have actually commented how good the boat sounds. I have found that I would much rather hear a healthy V8 idle by vs 3 different boats play loud crappy music right next to me. At least the V8 moves on, the jackasses with poor taste in music don't.

 

[MikDee]

Re: Thru hulls vs thru leg back pressure test

I wonder if there would be any performance advantage with running both, thru-hull, & thru-prop exhaust, at the same time? Considering that thru-prop gives the extra advantage of vacuum pulling out part of the wet mixture.

That's the Fallacy that Mercruiser tried to perpetrate for years. That doesn't happen, sorry. At least not enough to outperform open exhaust.

You took me out of context TilliamWe, anyway, I'm sure there is a certain amout of advantage to thru-prop exhaust on it's own, but I'm with you, I never said that it can outperform open exhaust, but I tend to think using both at the same time, may be even more of an advantage

My old 20' SeaRay bowrider was pretty mellow with the 305/228hp and 2 foot of 3" rubber exhaust hose, plus a couple of stainless tips with flappers.

 

[TilliamWe]

Re: Thru hulls vs thru leg back pressure test

try telling that to EVERYONE that can hear you for a 2 miles away. Tell your self what ever you want but your still annoying to others.
I love sailing around on my boat and hearing jackasses like you come blowing by me at 90db.

Well, I don't have open exhaust on my boat. So I'll come by you at 85 decibels. While you are waiting for the wind to pick up. Or as you are firing up that smoke and oil belching, environment destroying 2 stroke engine that you NEED to get back to port.
See, I make assholish assumptions, too!

 

[JHuck]

Re: Thru hulls vs thru leg back pressure test

When I wrote my first post on this topic, I wondered if the thread would take a heated turn because of the way similar posts have gone. To each their own.

Now, back to the original idea...having read that more than one forum poster has seen zero mph improvement on GPS leads me to think that if there is a difference, it's negligible. In the end, that's what matters vs fractions of a PSI difference in back-pressure.

 

[cannonford57]

Re: Thru hulls vs thru leg back pressure test

everybody!!!!!!!!!!! breathe..................... gonna be a beautiful day tomorrow here in the south......how bout ya'll

 

[wca_tim]

Re: Thru hulls vs thru leg back pressure test

I'm not sure I buy that a mile an hour or so is really that reproducibly measurable. Think about it... you pick up more than that when going from flat water to a little light chop...

 

[45Auto]

Re: Thru hulls vs thru leg back pressure test

I'm not sure I buy that a mile an hour or so is really that reproducibly measurable. Think about it... you pick up more than that when going from flat water to a little light chop...

I was thinking the same thing about the small differences in top speed and 0-30 MPH times, Tim. On the other hand, I also found the HUGE differences in 30-50 MPH times (almost 50% difference????) to be really questionable. Never timed any boats 30-50 to see how repeatable it was, but I don't believe exhaust tips could repeatably make as big a difference as the test showed without making a HUGE difference (10-15 MPH maybe?) in top end also.

I've mentioned the drive heat thing a couple of ties and no one seems to say a word about it... I know that heat is a big enemy on overpowerd drives, and that people claim a big difference with drive showers, but why then don't we worry aobut running ALL of the exhaust gasses throughthe outdrive... Surely when runing flat out for a good bit that contributes as much heat as anything to the drive? (unless the water is cool enough that it drops the temp to below oil degredation temps... but wait, we let the water drain on the bottom part... I have a feeling that the heat capacity of the water as well as the heat of vaporization is the reason that it's not a problem

I'm assuming that the exhaust gases are substantially less than 212 degrees by the time they hit the outdrive (hopefully no steam in your exhaust). My guess is that the outdrive normally runs hotter than 212, since a common problem on Bravos without coolers is salt and calcium deposits baked onto the drives, caused when they come off cruise and drop back into the water hot, boiling the water away and leaving the salt and calcium.

Merc also recommends an exhaust tube as opposed to an exhaust bellows with a big block, that probably helps some also with the drive cooling issue.

Can't help any to have the hot exhaust running through them though, so I would expect the thru-hulls to help at least a little in that respect.

 

[Tail_Gunner]

Re: Thru hulls vs thru leg back pressure test

Good read alway's fun to see it from different angles. I still believe you cannot get and good gains in thru the hull exhasut. Heres a pic of the water turbulence inside of a wet system.

Now all that water being shot around i dont see how it couldnt slow down the exhasut velocity...Any hoo stickly a opinion..

 

[Friscoboater]

Re: Thru hulls vs thru leg back pressure test

I have heard some boats that sound great with a through hull and others that just sound raspy. On my lake everyone and their dog has a loud boat, and i personally love it. Now I am a gear head, so hearing those boats makes me grin. Our lake also has ZERO noise restrictions, so all the BIG boats come here and run it out. I am rebuilding my V8 this winter and I am thinking of a through hull also. I think I am going to use muffs though to try and tune the sound. How cool would it be to have a flowmaster sound... huh?