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Old 17-01-2012, 09:23   #1
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Dry Stack is Where It's At ... Conversion Thoughts ?

A while back, I posted a threat about whether to keep my little diesel engine or repower with a gas 350 on my 31' Trojan. After a lot of research, I've decided to keep the diesel. So, here's what's next:

DRY STACK CONVERSION!

The Isuzu C240 Diesel engine I have is currently set up for a keel cooler (engine, trans) and raw water cooling in the manifold only. In fact, the water enters the manifold right at the outbound end of it and essentially just cools the tip of the manifold before water and exhaust gases mix and go overboard.

The Setup

Since I have to install a keel cooler anyway, it would be easy to add a little extra capacity to keep the engine cool without raw water exhaust. Then, thru-hulls for water would be closed up. The current manifold is wrapped to keep heat to a minimum and I may be able to use it. Exhaust would be routed up through the floor in a 3 or 4" pipe with a truck muffler. That would be enclosed in 8" stove piping and boxed in. The stove piping would be vended so there should be plenty of engine room ventilation.

The Rationale
The entire setup for this dry exhaust never enters the cabin due to my boat's design - noise and heat should be at a minimum.
Exhaust gases are routed 7' up from the deck courtesy of the piping.
This setup in the end should be easier to maintain and last longer.
Less thru-hulls at the end of the conversion - always a good thing
Still able to keep my keel cooler and cabin heater + hot water setup.
It's different and therefore cool.
If I ever needed to repower, I could use a truck engine with minimal marinization.

So what do you think? Anything you would add?
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Old 17-01-2012, 21:39   #2
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Re: Dry Stack is where it's at ... Conversion Thoughts?

Do you presently run a Trans. cooler?
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Old 17-01-2012, 23:24   #3
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Re: Dry Stack is where it's at ... Conversion Thoughts?

Quote:
Originally Posted by 2DASEA View Post
Do you presently run a Trans. cooler?
yes, it's routed through the keel cooler.
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Old 18-01-2012, 09:06   #4
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Re: Dry Stack is Where It's At ... Conversion Thoughts ?

IMO, setting up a pleasure boat with a keel cooler and a dry stack may be different and cool, but it is complex and causes some problems that you may not have considered.

Nordhavn's have a very well engineered dry stack system that avoids many of the inherent problems that you mention: noise and heat. But diesel soot will cover the boat when idling any length of time. Not a problem for a commercial fishing boat, but a big nuisance for a pleasure boat.

Since your engine already has a raw water pump, how about setting it up for fresh water cooling. Buy a heat exchanger from Sendure or others and run the jacket coolant through the shell side. Route the raw water through the heat exchanger and then through the manifold and then to an exhaust injection elbow. Your biggest expense will probably be for a custom fabricated injection elbow. Seems like there is a PNW company that marinizes Isuzu's that you could check with.

I'll bet you will spend more for your keel cooled, dry stack system than for a raw water cooled fresh water system. And it will be quieter, your engine room will be cooler and no soot on deck.

David
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Old 18-01-2012, 10:11   #5
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Re: Dry Stack is Where It's At ... Conversion Thoughts ?

I considered a dry stack when doing my refit...but not for long.
Sounds like you have a plan to handle the heat and evacuating warm air out of the engine room (via the space between the exhaust pipe and the heat shield) This air will be hot so it will convect up....I'm thinking it wouldn't be usable for combustion air...will probably need another source for that...but the convection may be great in powering the circulation.
I'm not sure what to think about the soot issue...or if it really is an issue.
Can we see some pictures of your boat?
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Old 18-01-2012, 12:48   #6
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Re: Dry Stack is Where It's At ... Conversion Thoughts ?

Your plan seems well thought out and doable. I've always thought keel cooling to be a simpler and more reliable way to use coolant in an enclosed system, besides it sounds like a fun project. Many years ago I was skipper of a 73' landing craft with four 671 Detroit diesels, it was keel cooled and spent a lifetime running up on beaches with no aparent damage, kept the bottom clean too. The coolant ran inside the keel though, not through tubing attached to the bottom which has varying degrees of vulnerability. Your right its a cool way to cool. Keep us posted on your progress. Jesse
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Old 30-01-2012, 13:03   #7
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Re: Dry Stack is Where It's At ... Conversion Thoughts ?

Quote:
Originally Posted by James S View Post
I considered a dry stack when doing my refit...but not for long.
Sounds like you have a plan to handle the heat and evacuating warm air out of the engine room (via the space between the exhaust pipe and the heat shield) This air will be hot so it will convect up....I'm thinking it wouldn't be usable for combustion air...will probably need another source for that...but the convection may be great in powering the circulation.
I'm not sure what to think about the soot issue...or if it really is an issue.
Can we see some pictures of your boat?

I don't have great pictures of the boat, so here's an old catalog photo. the major difference being that mine has a fly bridge and won't be planing like that.

anyway ... design-wise:
The ER is vented through 4 independent vents on the side of the boat. I am relying on two additional pipes to carry hot air from the ER up the stack, so 3 pipes in all if you include exhaust. another option is to have one large vent pipe with a smaller exhaust pipe inside it. obviously the muffler will be encased in the stack and the appropriate heat shielding measures taken.

the engine is a diesel so i'm not sure what the limit is as far as intake air temp and combustion. i'm doing my best with the setup to keep the ER as cool as possible through ventilation but I could devise some sort of exterior ventilation system if needed. previously with this engine, the intake was only 24" from the engine and it ran fine - again only the manifold was raw water cooled and it's wrapped pretty good so my guess is this "new" setup won't be that much of an issue but I could be wrong.

any more thoughts?
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