pick apart my cooling system!

[sdj]

Firstly, apologies for yet another 'wet exhaust' thread, but would people critique my wet exhaust design?

Basically, it is lift muffler with low dip tube + lift trap + water separator. Requirements are a quiet exhaust at all times, hence the multiple mixing stages and the dual outlets.

I hope during cranking I can have the dip tube evacuate the lift muffler properly by using a smaller diameter outlet tube. For 90hp I wonder if 50mm from the muffler to the separator will be too small - this is a short vertical length of steel tube with the trap midway for extra lift safety. If not, then I'll have to take precautions during extended cranking, no deal breaker, just annoying.

What is the situation with making all these parts from mild steel and hot fip galv? Just make them from stainless plate and pipe?

Many thanks.

[skipperpete]

Hi SDJ
The important reference point for wet exhausts is the waterline relative to each component part so you need to add that to the sketch. 50mm diameter exhaust is probably too small for a 90hp engine, Yanmar specify 75 mm for that HP range but for your 90hp engine see what's recommended by the manufacturer.
Fiberglass is probably the best option for the aqualock and separator, maybe the pipework on the straight runs, even really good quality stainless steel seems to have a fairly short life in wet exhaust systems.
Silicone hose between the mixer elbow and the aqualock is a good idea too, it's very flexible and doesn't transmit vibration to the hull if the aqualock is rigidly mounted.

[sdj]

Thanks Pete.

The waterline is about the top of the engine, or about the top of the lift trap in tis sketch. I know I'm breaking cardinal rule number one, and I should really redesign the riser to use all the available vertical engine compartment space, and I may do that yet. Sailboats have low engines, and that's what that is.

The engine is non-turbo, so it is likely not especially concerned with backpressure from a short 2m run of undersize pipework.

I've never liked silicone hose - it has a nasty habit of popping out of places it really should be staying. I'm going to use a strong reinforced industrial hose, and put it in some location where it'll be right at home, vibration and torsion wise.

If I can make the lift muffler and the lift traps pump water with extended cranking, the system should be bulletproof.

The exhaust outlet at the top of the separator is almost the highest point on the yacht and it's a very long 5 meter trip for that hose around the back of the aft cabin to the waterline exit, so I can't see how seawater could approach it.

If the drain is valved shut for some reason it is inconsequential for the system, and also if the drain can't cope with the flow at full revs, it simply overflows out the transom as a spray.

It might be smart to use dual vacuum breaks, as if they malfunction it is game over. Even if I fix rule number one, there isn't much height to be gained.

Point taken with the fibreglass exhaust parts - everywhere I started looking at metal of any sort there was another gotcha... Fibreglass it is.

I'm really grateful for your engagement, thanks again!

[Compass790]

Not qualified to comment on your design re lift dia etc, but second skipper pete's idea to use GRP where possible.
Otherwise use ss but if u don't use tube rather better to use schedule 10 ss pipe you will get long life.
Galv pipe is not great in exhausts.
We have good use out of steam condensate flexible hose but only in an 8hp engine so not the heat load that you have.

[skipperpete]

The water separator idea is usually for generators on mid size superyachts, (no owner likes to be kept awake at anchor by a splooshing wet exhaust), but can be really useful to unload the residual water from the long run between transom and engine on sailboat main engines.
When you get this system in and running, at the very first shutdown it is wise to check the amount of raw water in the aqualock. If it's very high it's risky and if it's up to the mixer hose then the aqualock is way too small. The amount of drainback from the vent loop and the exhaust hose is often difficult to calculate.
I like the idea of "Bulletproof" I hope you achieve it.

[GordMay]

See also:
“Cool, Quiet, and Trouble Free Exhaust ” ~ by Jerry Powlas and Dave Gerr
Good Old Boat magazine: Volume 1, Number 2, September/October 1998.
➥ https://goodoldboat.com/cool-quiet-a...-free-exhaust/

[sdj]

Thanks guys.

Pete, good call on the size of the aqualock. I'm looking at two locations for the separator.
up at the highest point of the structure with the water exit straight down (maximum fall and extraction force) with gases out the transom, OR the whole unit near the transom area. So far I'm leaning toward the former.

Gord, Yes I think I should do the dry riser thing. The trouble is, the top of the engine compartment isn't comfortably far above the waterline, hence the staircase.