Mobo's with side exit exhausts

[JOHNPEET]

Anybody out there with an aft cabin motor boat, mid ships mounted engines that is configured with the exhausts exiting directly from the engine bay/room through the side of the boat?

Would be interested to hear of any downsides or indeed upsides of this arrangement.

For me it would tick a lot of boxes for advantages.

John

 

[SimonA]

I have this on my boat. Advantage is much shorter run of exhaust pipe and easy to stick my head out and check water is coming out the exhaust. Disadvantages are the occasional smell blown into the cockpit and when in a lock or tied up the exhaust can sometimes be noisy, although in both those situations I usually am not running the engine for long.

 

[jfm]

Poster Silverdee has this. Perfectly ok.

If the exhausts are not underwater you might get noise, and if close to waterline you might get splashing, but that is true of stern exhausts as much as side exhausts

 

[burgundyben]

One of the Fairey Huntsman 31's in the London to Monaco race has this, its was very loud.

 

[Firefly625]

One of the Fairey Huntsman 31's in the London to Monaco race has this, its was very loud.

If distance running I bet they wore earplugs! but wonderful sound no doubt...

 

[MapisM]

Would be interested to hear of any downsides or indeed upsides of this arrangement.

Probably not something you're very interested in, since you're talking of an aft cabin boat...
But since you ask of ANY pros and cons, fast boats boats with straight transom exhausts are more prone to water reversion, for two reasons:
1) the transom "digs" deeper in the water when the boat falls from its planing asset, upon release of the throttle;
2) at the same time, the water flow creates a sort of reverse wave against the transom - similar to when reversing while maneuvering.
That's why in some of these boats you can find side exhausts.
But that's not so common actually, because on one hand it's a solution that makes the engine compartment layout more complicated, and otoh there are other ways to protect transom exhausts from water reversion.
Like rubber flaps on the exhaust tips, and/or internal steel butterfly valves - which you need with the straight/prop exhaust selectors anyway.

 

[david_bagshaw]

We have them, Were very concerned before purchase in 1990. After trials and for the next 24 years, love them. We had water line stern ones before, which were underwater underway. Present ones are at waterline stationary, but above when moving. Another advantage.
Not noisy with turbo charged engines, as turbo damps the exhaust pulses,.

only down side is can smoke or wet low freeboard alongsiders, or wash mud onto your self on down going locks occasionally.

good for low back pressure, low internal noise

 

[JOHNPEET]

Thanks to all for your replies.

Boxes ticked for me would be mainly the low back pressure but also - less tortuous route, doesn't use up space in the aft cabin, no problems with future access and cheaper initial installation.

Probably will be the way I will go.

Thanks,

John

 

[MapisM]

Boxes ticked for me would be mainly the low back pressure but also - less tortuous route

I see your point, but just to explain why I said the opposite with regard to the route (makes the engine compartment layout more complicated):
In performance boats, you have a separate straight exhausts for each cylinders bank.
Therefore, in the typical twin V8 engines installation (possibly staggered), it's much easier to route the exhausts of the internal banks straight to the transom, rather than to the sides.
I perfectly understand that in a more "normal" boat, with an aft cabin, and probably a couple of inline diesels, exactly the opposite is true.

 

[Latestarter1]

Thanks to all for your replies.

Boxes ticked for me would be mainly the low back pressure but also - less tortuous route, doesn't use up space in the aft cabin, no problems with future access and cheaper initial installation.

Probably will be the way I will go.

Thanks,


John

John,

I did ex Trinity House Nelson many years ago, we had room forward of engines but little aft, so exhaust was routed forwards over the engine, down into large Centek drum water lift then exit through side outlet which has downward sloping scoops. Centek mufflers sorted out the noise and engines were not smoky, owner still owns the boat today.

I did have some pictures will have a dig around.

 

[Designo]

Thanks to all for your replies.

Boxes ticked for me would be mainly the low back pressure but also - less tortuous route, doesn't use up space in the aft cabin, no problems with future access and cheaper initial installation.

Probably will be the way I will go.

Thanks,

John

I had side exhausts on a Moonen 85 and the only disadvantage was that the sides turned greyish on long hauls. A friend with a 46 m Feadship had them led to the stern and when they rusted through after some ten years, it was a hard job to replace them...

 

[MapisM]

Blimey, exhausts rusted to the point of being in need of replacement after ten years?
I'd have expected better than that from Feadship! :ambivalence:

 

[JOHNPEET]

John,

I did ex Trinity House Nelson many years ago, we had room forward of engines but little aft, so exhaust was routed forwards over the engine, down into large Centek drum water lift then exit through side outlet which has downward sloping scoops. Centek mufflers sorted out the noise and engines were not smoky, owner still owns the boat today.


I did have some pictures will have a dig around.

Would appreciate that. I'm in contact with Centekindustries on my project also

John

 

[MYStargazer]

Anybody out there with an aft cabin motor boat, mid ships mounted engines that is configured with the exhausts exiting directly from the engine bay/room through the side of the boat?

Would be interested to hear of any downsides or indeed upsides of this arrangement.

For me it would tick a lot of boxes for advantages.

John

I'm in the process of changing an aft-cabin Weymouth 32 from stern exhausts to side exhausts right now.

I'm doing this to free-up aft cabin space, but I also like that I'll be able to check at a glace that cooling water is still being discharged. The fully-enclosed cabin means that smoke will not be much of problem (I'm also switching from Ford Dorset to Cummins so there'll be less smoke anyway).

Here's a submerged exhaust system on another aft-cabin Weymouth 32:



I don't like avoidable holes in the hull at or under the waterline, so ours will exit well above.

Keeping things simple, I've bought some 4" stainless outlets with integral non-return flaps, which will have surge tubes - or be connected together to make a North Sea exhaust system, with engines discharging into the connecting tube.

This website is full of useful info http://www.sbmar.com/

 

[Imperial One]

All Atlantic Motoryachts are fitted with external exhausts and as you say it does make for a huge amount of additional room in the aft cabin. We never had any issues with any of the many we built at all BUT another boat manufacturer with external exhausts did suffer one small issue....crushing!
On the Atlantic's the exhaust box fabrication had an internal X bracing fitted in them made of marine grade Stainless. This was to avoid them getting crushed when the boat is in a sling during lift out or coming alongside too heavily. I once had a yard refuse to lift the boat as they had done a similar looking craft the week before and the exhaust boxes had crushed, when I agreed to be responsible for any damage they lifted her and were amazed that here was no damage done.
It is a simple enough thing to strengthen them before fitting and I would advise you to do so even though, in theory, the lifting points will be forward of their exit from the engine room anyway.
Hope this helps.

 

[JOHNPEET]

I'm in the process of changing an aft-cabin Weymouth 32 from stern exhausts to side exhausts right now.

I'm doing this to free-up aft cabin space, but I also like that I'll be able to check at a glace that cooling water is still being discharged. The fully-enclosed cabin means that smoke will not be much of problem (I'm also switching from Ford Dorset to Cummins so there'll be less smoke anyway).

Here's a submerged exhaust system on another aft-cabin Weymouth 32:

View attachment 41116View attachment 41117View attachment 41118View attachment 41119

I don't like avoidable holes in the hull at or under the waterline, so ours will exit well above.

Keeping things simple, I've bought some 4" stainless outlets with integral non-return flaps, which will have surge tubes - or be connected together to make a North Sea exhaust system, with engines discharging into the connecting tube.

This website is full of useful info http://www.sbmar.com/

The main advantage for me is the much lower exhaust back pressure. The other points such as cheaper initial installation, easier to inspect in the future and zero impact into the space of the aft cabin also come as a distinct advantage.
The appendage shown on the Weymouth in the photos just looks like it's waiting to come into contact with some underwater object!

I have a steel hull so will be welding my chosen fittings of stainless steel, direct to the hull and coating it (internally as well) all with the same epoxy as the rest of the hull. I will achieve a flush finish also above the waterline.

I've seen the North Sea arrangement, but unfortunately it's not an option for me as my generator sits directly in the location where the cross tube would sit.

I agree re the Seaboard Marine website - lots of good info on there under the "Tony's tips" pages.

 

[JOHNPEET]

All Atlantic Motoryachts are fitted with external exhausts and as you say it does make for a huge amount of additional room in the aft cabin. We never had any issues with any of the many we built at all BUT another boat manufacturer with external exhausts did suffer one small issue....crushing!
On the Atlantic's the exhaust box fabrication had an internal X bracing fitted in them made of marine grade Stainless. This was to avoid them getting crushed when the boat is in a sling during lift out or coming alongside too heavily. I once had a yard refuse to lift the boat as they had done a similar looking craft the week before and the exhaust boxes had crushed, when I agreed to be responsible for any damage they lifted her and were amazed that here was no damage done.
It is a simple enough thing to strengthen them before fitting and I would advise you to do so even though, in theory, the lifting points will be forward of their exit from the engine room anyway.
Hope this helps.

I wasn't really thinking about external exhaust as you describe them, just simply exhausts discharging sideways from the engine room. The external exhausts you describe sounds like a neat concept but doesn't tick the very low back pressure box that I need to achieve with my old type Perkins T 6.354s

 

[Latestarter1]

I wasn't really thinking about external exhaust as you describe them, just simply exhausts discharging sideways from the engine room. The external exhausts you describe sounds like a neat concept but doesn't tick the very low back pressure box that I need to achieve with my old type Perkins T 6.354s

Perkins installation guidelines were pretty much the industry standard of 3 inches of Hg, you need to have pretty nasty tortuous system to be on that threshold.

 

[MYStargazer]

I have a steel hull so will be welding my chosen fittings of stainless steel, direct to the hull and coating it (internally as well) all with the same epoxy as the rest of the hull. I will achieve a flush finish also above the waterline.

The outlets I've found (after much looking) are by Corsa - they are highly polished and I think are intended for flashy US skiboats. They take a 4" flexible exhaust hose. The pipe meets the exterior flange at 45 degress, with a pleasing oval exterior shape. But they're in storage, and I can't find a picture of them online...

Agreed re sticky-out submerged diffusers-cum-outlets. I've never seen these on any other boats.

 

[MapisM]

I can't find a picture of them online...

Are you possibly talking of those labeled as "unique style" in their GIF banner below?
Excellent choice anyway, over the pond Corsa exhausts are widely used also in very high performance boats, not just skiboats.