Opinions for Underwater Exhaust Deflectors

Deflectors have other names such as as cowlings, clamshells, and eductors. There are as many different designs as there are boat builders. Some builders turn the exhaust to the outboard side to avoid getting the exhaust into the props. I have seen some that are no more than a 3” lip around the exhaust penetration.
The ultimate purpose as is mentioned earlier on in this thread, is to reduce the backpressure and get the exhaust out the bottom of the boat. There are other factors that need to be considered. Is the diameter of the penetration, correct to the gas flow of the engine? Is the bypass properly sized? How deep is the penetration with respect to the loaded waterline? What is the vessel’s cruising speed?
Garry’s drawing is similar the basic design of what we would recommend if we were asked to include this as part of the design and fabrication of the exhaust system. Looking forward to additional feedback from others.

Hi,

Here is the Von Widmann Designs page in these unusual Exhaust Designs

http://www.vonwidmanndesigns.com/

The pictures and text are easier to follow than the pictures and text in this post so far.

The site says that amongst many others that DeAngelo are already clients so I am sure Jorge is already familiar with this concept and how it works.

comship, I believe you mentioned that all this jiggery-pokery beneath the hull would not add any drag.
From your photos, that long deflector would appear to be adding a not insubstantial amount of wetted surface which does add drag to a hull.

Hi,

This is not at all how it looks on the designers website, the exhaust comes out at the very aft edge of the transom.

The Dinghy Bailer that Gary posted the pic of actually works on very much the same principle as the exhausts on the website

Hi,

Comship- Do the exhausts come directly out the bottom of your boat or are they led to the aft edge of hull and transom?

Any chance of a photo of your yacht from the side showing where these pipes come out in your case?

Good Question. The Vonwidmann design is mostly used on sportfish boats where the exhaust exits near the transom. I think the original topic here was more towards what is used on larger yachts that have an underwater exhaust. Typically, the penetration is within the area of the engine room.

Hi,

Thanks for that.

That is what it looks like I just wanted confirmation.

Your system is actually nothing like the system shown on the Von Widmann design Website. The fact that you used this guy as an example of what you had and the photos were so different to his site drawings had me and I am sure a number of other people totally confused.

I have not personally seen anything remotely like what you have there. I would be interested to know how they actually work when you get your boat up and running.

Hi,

I am not familiar with this design of boat and doing a quick Googling see that the 2006 Models have 50hp more a side than the 2004 ones, this may explain why they go the same speed with the appendage shown in your photos hanging out the bottom.

Hi,

I am ony stating what I can read on sites that have tech details for these boats.

Here is a 2004 Model http://www.cnconnect.com/sales/yachtdetail.aspx?id=5150

Here is a 2006 Model
http://www.navis-yacht-charter.com/yacht_charter_greece_maiora_38_calma_III

Carl- Please delete these links if they break the rules of the forum.

Comship- If as you say the displacement varies significantly then the back pressure must also vary significantly. If the hulls are exactly the same and one displaces more than the other the heavier displacement one is going to be deeper in the water and have an increased backpressure.

This forum is anything but a closed shop for selected members. Your original post has been answered by more questions than the answers provided.

You got me confused initially by the terms you used them the pictures were not easy to follow.

"Edited to remove incorrect statement No offense intended"

Comship,
I also disagree with your statement in regards to this being a closed community that does not welcome new innovation and ideas. I shared K1W1's confusion, as I researched the Von Widmann exhaust systems in depth when I first learned about them. And, the system you were showing did not look anything at all to me what I had seen on the Von Widmann site.

Do you think the "strakes" solution you are using would be necessary in an aft engine room configuration such as using waterjets or Arneson drives?