Homemade Boat Exhaust

[waldo271]

Boat exhaust
Hello everyone,
This is my first post here so I apologize if my terminology isn?t correct or I?m posting in the wrong place .
So, I have a 96 Wellcraft 2150SS 21? with a 5.7 mercruiser engine and an alpha one gen II drive. It?s my first boat so I?m trying to learn as much as I can about it. I got this boat about 6 months ago and it was running perfectly except it was leaking water into the bilge area so I thought I should change the bellows but that didn?t stop the leak. So, in the last 2 days I took out the drive and the engine and I plan to drop it in water today to see were the leak is. I checked the engine and the transom seals and found no leaks.

Now, since I had my engine out, I started thinking of adding a new exhaust to it. What I plan to do is this:
- Remove the Y pip and close off where it connects to the transom.
- Fabricate a new 4 inch stainless steel pip that goes to the side of the boat. Pointing slightly down and backwards and above water level.
- And obviously, cut through both sides of the boat.

Question is, would my plan cause any problems? For example closing off where the Y pip connects to the transom? I plan to close it off with a stainless steel piece that is shaped and cut exactly like the Y pip bottom.
Is there any electrical work done?
Adding an external exhaust, does it harm the engine?

Thank you very much in advance.
cheers

 

[DuckHunterJon]

Re: Homemade Boat Exhaust

Will you be adding mufflers to the exhaust? If not, what is the point of doing this. You'll anger more people than you impress. Money would be better spent on outfitting the boat than modifying the exhaust. JMO of course.

 

['78 Crusader]

Re: Homemade Boat Exhaust

I'm not real clear on what you already have. Is your exhaust currently going through the propellor hub?

I have "Through Transom" exhaust on my boat....and your motor should be fine with the exhaust going through the transom....or sides.

I know the newer Chapperals have thier exhaust ported out the sides of their boats.....nice setup.

 

[Chris1956]

Re: Homemade Boat Exhaust

That modification is fine, however, it will not increase performance at all. Thru the prop exhaust is just as efficient as thru-hull exhaust, just a whole lot quieter.

Why not just make the pipes a dummy setup, for the appearance, and keep the stock setup. A lot of folks who live on the water will like you better.

There is a boat that comes by my waterfront house a couple of times each weekend. It has thru hull exhaust and is so loud everything vibrates and all activities must come to a halt until it passes, as you can hardly think with all the noise. Don't join that club...

 

[waldo271]

Re: Homemade Boat Exhaust

What I have right now is through the prop but I wanna convert to make it come out of the sides. I know it's going to be louder but
that's the thing, I want it louder. I take the boat to a beach close by and trust me people will not mind the loud exhaust. I've seen many boats with side exhausts and they sound amazing.

 

[sublauxation]

Re: Homemade Boat Exhaust

I'm getting a headache just thinking about it.

 

[waldo271]

Re: Homemade Boat Exhaust

Oh and I don't think it is supposed to be setup with a muffler because I've seen the Corsa captain call exhaust and it doesn't come with a muffler.

So you guys don't think it will cause any damage to close off the opening in the transom where the Y pip connect to?

 

[QC]

Re: Homemade Boat Exhaust

I happen to boat at a place where thru hull exhaust is the norm, not the opposite. I completely understand those that don't like it, but some places it is just fine. Let's help the guy with his question. If people run from his boat screaming bloody murder, then so be it, but I am guessing his location is one like Lake Havasu where thru transom doesn't cause a blink.

You can go with or without muffler tips. A softened thru hull sounds pretty sweet too

 

[shrew]

Re: Homemade Boat Exhaust

Trust me, you're wrong.

With that said, you do realise you will have to build an double chambered exhaust so it can pump cooling water though it, right?

IMHO it would be more accurate to state that if you boat on a small inland lake or river where most if not all of the local boats do not have through hull exhaust, then people could potentially be mildly annoyed. However ALL inboards have thruhull exhaust. If you boat in an area with larger boats with inboards they will have through hull exhaust and people wouldn't even bat an eye.

While that statement may be true in your area, it is not the case in most areas.

 

[H20Rat]

Re: Homemade Boat Exhaust

IMHO it would be more accurate to state that if you boat on a small inland lake or river where most if not all of the local boats do not have through hull exhaust, then people could potentially be mildly annoyed. However ALL inboards have thruhull exhaust. .

The issue isn't thru-hull vs prop, its muffler vs no muffler. The inboards I wake behind are very, very quiet, but they also have good mufflers on them.

I've never seen dyno data to back it up, but its been rumored thru hull actually hurts performance vs thru-prop. The vacuum of the water passing through does an amazing job at sucking out the exhaust gases. Also, if you run a vented prop, you are taking advantage of the exhaust to give your prop a 2 speed transmission.

 

[Maclin]

Re: Homemade Boat Exhaust

When you go to the ramps or other places that are not the norm regarding thru-hulls then that is where the Captain's Call is a good idea.

One thing about it, everyone will know the answer to "Where's Waldo?"......

 

[Philster]

Re: Homemade Boat Exhaust

No need for stainless at all. Use fiberglass piping for marine wet exhausts, which absorbs enough sound to keep it from being obnoxious. It will sound deep, rich and sporty, but no one will want to murder you (well, not because of the exhaust). On the boat? She's a little harsh. Away from the boat? Just sounds sporty, throaty. Will link a video to mine ASAP.

.

 

[shrew]

Re: Homemade Boat Exhaust

The issue isn't thru-hull vs prop, its muffler vs no muffler. The inboards I wake behind are very, very quiet, but they also have good mufflers on them.

I've never seen dyno data to back it up, but its been rumored thru hull actually hurts performance vs thru-prop. The vacuum of the water passing through does an amazing job at sucking out the exhaust gases. Also, if you run a vented prop, you are taking advantage of the exhaust to give your prop a 2 speed transmission.

If you could show me that in the discussion above I'd appreciate as clearly I have overlooked it. I see that DuckHunter john asked if it was going to be muffled or not. However I see no other mention or discussion of it. I do see discussion on noise differences, but I am sure that I'm simply overlooking the muffled vs. unmuffled point in the discussion.

 

[Philster]

Re: Homemade Boat Exhaust

Okay, here is 502 cubic inches of through-hull exhaust with 470 HP. This is fully open, 4" fiberglass pipe. The only time it is metal is the exhaust tips, which point straight down.

Is this obnoxious on my Scarab*? http://www.youtube.com/watch?v=EpvM3c3dNa8

As to the tech bits,:

It is very easy to build a custom exhaust for a boat. The pieces are easy to work with. Ensure a proper downward angle to prevent water from being sucked back on the exhaust stroke, and you can exit it anywhere you please (more or less). I'd look at a production boat with the thru-hull exhaust and measure the slope if you don't know it.

Is is more dangerous for an engine to have an above waterline exhaust, because the drop/slope is less drastic, which means there is an increased chance that water can be sucked back into the engine. Many cams create a slight overlap during the exhaust cycle, which can pull water back into the engine. This is almost never a problem, but it can be if you modify the exhaust and don't create an acceptable slope OR if you decide to play with the cams/timing, you could create a problem, because more aggressive cams increase the risk. Since you are already interested in changing your boat, it's not out of the question that you might want to hot rod it someday, thus this advice.

Fiberglass exhaust tubing comes in various sizes, bends, etc. You clamp it up using two clamps at every joint. Here are some pics of an exhaust with bends. You can just use reinforced rubber exhaust for wet exhaust mixed with fiberglass elbows. It sounds less hot rodded than all metal/stainless pipes . Jamestown distributors has many of the parts.


*Ignore the gauges. I was in the middle of rerunning wires for GPS and new Livorsi speedo. That was over 4000 RPMs and about 55 MPH. ..



.

 

['78 Crusader]

Re: Homemade Boat Exhaust

Man, I can't believe you guys are giving the OP so much opinion instead of helping him out. If the OP did some research in more friendly forums to this kind of modification, he might actually find an answer to his problem.

To prevent water from backing up into his motor though the exhaust, the OP simply should install a set of "logs and snails".

Here are some websites that are more friendly towards people who want to do this type of modification.

http://www.forum.jetboatperformance.biz/

Www.performanceboats.com

Www.texashotboats.com

Www.socaljetboats.com

And I have several more websites if the OP wants them.

Sheesh!!

 

[smokeonthewater]

Re: Homemade Boat Exhaust

what he is asking about is illegal in most states.... anyone who modifies a boat for the sole purpose of making more noise and forcing the public to endure it likely has thick enough skin to take a little criticism.... The stuff above is VERY mild compared to what many of the other boaters will say as he passes......

 

['78 Crusader]

Re: Homemade Boat Exhaust

what he is asking about is illegal in most states.... anyone who modifies a boat for the sole purpose of making more noise and forcing the public to endure it likely has thick enough skin to take a little criticism.... The stuff above is VERY mild compared to what many of the other boaters will say as he passes......

Prove that it's illegal to modify the exhaust on the boat!! I'm calling your bluff on this one.

 

[smokeonthewater]

Re: Homemade Boat Exhaust

Prove that it's illegal to modify the exhaust on the boat!! I'm calling your bluff on this one.

I don't bluff
I have certainly not checked all states, but for example... my boat is registered in Ohio and here is the law in ohio: http://ohiodnr.com/watercraft/opsguide/ohiovr2/tabid/2752/Default.aspx

This is the section about exhaust

"Exhaust Muffler Required
(ORC 1547.31)
Every powercraft shall be equipped with a muffler or muffler system that is in good working order, in constant operation and effectively installed to prevent excessive or unusual noise.

No person shall operate or give permission to operate a powercraft in a manner to exceed the following noise levels:

90 decibels on the "A" scale in a stationary sound level test prescribed by SAE J2005. (Measured from one meter with engine at low idle speed when at dock or tied to another boat.)
75 decibels on the "A" scale measured as specified by SAE J1970. (Measured from shoreline with boat in any level of operation.)


No person shall remove, alter or modify a muffler in a way that prevents compliance with this section. No person shall operate or allow to be operated a powercraft with an altered muffler or muffler cutout or in a manner that bypasses or reduces the effectiveness of any muffler system."

 

[smokeonthewater]

Re: Homemade Boat Exhaust

a little more research yielded this: http://questtechnologies.com/Assets/Documents/BoatNoiseRegs.pdf

There is a chart listing which states restrict exhaust modifications and which ones have noise restrictions... I can not guarantee that it is up to date tho so If you are hell bent on a loud boat (please no) I'd suggest using it as a starting point and checking with your state agency before doing modifications....

looks like 31 states outlaw loud pipes.... Looks like Texas isn't one of em..... yet

EDIT: just realized that was from information collected in 2000.... I suspect that list has grown in the last decade.

 

[tswiczko]

Re: Homemade Boat Exhaust

https://www.facebook.com/video/video.php?v=1215995408938Can you do it?

yup, anything is possible.

Is(would) it be loud?

yup. I have thru hull exhaust on a 5.7 mercruiser, and it is loud, to other people, I don't notice because it is pointed away from me and I am moving.

Should you do it?

It's up to you. You would probably spend less, or have less work restoring your old through prop exhaust.

As for a do it yourself thru hull is up to you. If you do go thru hull you might want to look into getting a kit for the application instead of doing it yourself and fabricating what you think will work.

if this link works for you at about 26 sec. in I went from about 22 knots to WOT. about 42 knots(about 25mph to 47 mph)