Marine Heat exchanger vs. Regular plate Heat exchaner

[Noes]

Hi there
I am looking to build a heat exchanger onto my VP 4,3 to save it from the rough nature of saltwater. The marine exhanger models are mighty expensive, so my dad and i got to thinking why wouldn't you just use a regular stainless plate heat exchanger.
Can anyone tell me why the marine models are so much more expensive, og why a regular exchanger could not be used as long as it cools enough?

On another note, does anybody know exactly how much cooling power an exchanger needs to have for a V6 225 Hp engine.
If a regular plate exchanger ain't good enough, i'll maybe just have to calculate and weld one up from stainless pipes?

 

[Maclin]

Welcome aboard!

It looks like you are thinking about doing this with a new engine, as you are suspecting that your current block is cracked. With a used engine that has been run a while in the brack, it is not recommended to close cool it due to preexisting corrosion and recirculating all that around in the engines cooling jackets and other components. If you are thinking about an automotive used block that would work as it has been in the closed environment anyway.

The closed cooling kits are expensive, but they come with all the fittings and connections and all the accompanying hardware to install, and ensure a working warrantable system.

Just saying, it is not just a fabrication exercise for a heat exchanger.

Also, there are systems like Salt-Away I think is the name, that can be used after a run in the salt,. Less expensive that adding closed cooling, and just a bit more hassle when putting away.

Good luck, hope you get it sorted

 

[alldodge]

Stainless does not have the same heat transfer capabilities as copper and brass.

See if Scott Danforth can assist

 

[tpenfield]

I think by the time you have messed around trying to save money with heat exchanger alternatives, you may as well bought the heat exchanger/closed cooling system for your engine.

 

[Scott Danforth]

plate and frame heat exchangers work well.... when you have about 100 plates. the problem with plate and frame heat exchangers is you need to have good sea-strainers. something not found on the small motors we deal with. if you dont, you will be unstacking plates to take care of fouling. with passages only 1-2 mm in size, they foul easy.

shell and tube heat exchangers use big tubes compared to the small passages in a plate and frame. typical 4" x 20 shell and tube that you would find in a 4.3 installation would have a bit over 300 tubes in it. there are simple end caps to allow clean out on a regular basis

if you think shell and tube heat exchangers are expensive, wait until you look into titanium plate heat exchangers. stainless isnt recommended on marine for a variety of reasons, however it can be done.

for a 4.3, your looking at about a 4" plate stack with each plate being about 8 x 20" you have to watch the restriction as if you add too much restriction to the sea water side, you stop flow.

personally, I would simply spend the $1000 for a complete kit and go boating. however you will need to have a pristine block and heads.

adding a HX to a boat that has been in salt water is a no-go

 

[Noes]

Hi guys
Thanks for the replays. Sounds like you have some good experience in this area.
Unfortunately in Denmark, you don't really get a system for this engine for less than 2400 bucks, which is a bit steep for a boat that actually work really well. (except for a little leaking water into the engine) You really can't tell from listening to the engine.
First of all i want to tell you that i love tinkering with things like this, doing calculations, fabrication and fitting.
Second - i believe i have all the tools i need to make exactly what i want - cnc water jet, tig welders, welding certificats, loads of steel, etc. (all general shop tools plus a few)

I know that stainless steal isn't a good heat transfer material compared to copper, brass, alu etc.
However why does it not work well with saltwater? I know a lot of industrial HX Tube and shell are made from stainless.
Plate Exchangers should be good if you just make sure the water is "clean" (filtered), it would just need and occasional cleaning right. Install sensors to monitor flow rate and temps, and setting the immediate values as default. then the sensor will show an alarm at a given defined diviation right, and the system would need a check. I know this sounds expensive, but i really isn't that expensive, when you can do all the coding yourself.

I am looking to take the top's off the engine to check up the condition, then absolutely cleaning the water channels which should make it okay to put a freshwater system on the boat right?

 

[Scott Danforth]

I used to design marine heat exchangers. The same ones on Mercruiser, Volvo, Ilmore, Indmar, Westerbeke, Kohler, Cummins, Cat, John Deere, etc. I can tell you that you are simultaneously over-complicating it as well as under estimating it.

No one uses flow sensors, and most do not have any temp senders

If your motor is not brand new, adding a heat exchanger is going to be wasted effort. The block is already scaled on the water jackets and it cant be cleaned.

Plate heat exchangers are generally not used because the average boat does not have filtration. So rocks, dirt, small fish, plant material, etc will plug it. On large yachts where the motors have plate and frame geat exchangers, there are sea strainers and centrifugal filters that get cleaned every time the motors are run. Even then, the heat exchanger needs to be disassembled and cleaned.

Shell and tube are more forgiving for the average boater, hence the reason they are used. In addition to the heat exchanger, there is the expansion tank, and deareation tank. This can be one and the same.

I dont care if you have a million dollars worth of material and 5 million worth of lasers, cnc equipment and welding equipment. If you dont have the experience designing and building heat exchangers, it is still thousnads of dollars cheaper to buy it. I do have access to all of the above and I still buy my heat exchangers from Alfa Laval - Champ as i cant make it cheaper than I can buy it.

As for the cost. If you buy from the US, and pay shipping and the customs fees, your in it for $1500 total. Plenty of marine companies in Denmark, many of which make shell and tube heat exchangers for the aftermarket

However unless your motor is new, you still get no warranty, and the installation will still fail