Stainless 316 elbows

[About Time]

Hi,

I need to replace my elbows on both my KAD300.
I can either do the cast iron original Volvos or try the SS 316 that is made by HDI marine USA.
Has anyone tried these ?… They are more expensive that the Volvos (should be as they are stainless steel) but I wonder why HDI gives only 2 years of warranty. I guess for stainless they should never require a replacement while the cast iron is due every 5-10 years.
Here is the product https://hdimarine.net/product/vg1/

Thanks for any guidance.

 

[Portofino]

It’s a two pronged attack the longevity.

You get some quite nasty acids , sulphuric as well as hydrochloride based from the products of diesel combustion that eat most metals ....... eventually.

So seawater can eat / corrode away the water jacket which should be cured with SS but the acid attack assault side remains there .
Could be even more so in any welds put on later or localised uneven cooling after casting which those look like .

 

[MapisM]

I guess for stainless they should never require a replacement while the cast iron is due every 5-10 years.

Something that on a boat never requires a replacement has still to be invented, I'm afraid.
In your boots, I'd go for cast iron, spend another 30 quid or so for a BodgeFlowTM , and waste the rest of the saving on booze. :encouragement:

 

[jrudge]

It’s a two pronged attack the longevity.

You get some quite nasty acids , sulphuric as well as hydrochloride based from the products of diesel combustion that eat most metals ....... eventually.

So seawater can eat / corrode away the water jacket which should be cured with SS but the acid attack assault side remains there .
Could be even more so in any welds put on later or localised uneven cooling after casting which those look like .

A nice fresh water flush will sort that Nasty sea water problem out ......

 

[MapisM]

LOL, I'm beginning to wonder for how long the poor PF will resist installing the BFTM himself.

Though in fairness, I would think that most of the chemical aggression to exhaust elbows happens while cruising, when obviously the BFTM is irrelevant.
But at risk of stirring up some objection from sub-atomic particles experts, to my simple mind leaving them sitting there unused after a good flush is still better than leaving all internals covered with salt...

 

[jrudge]

Markc recently had stainless exhaust bits made. Drop him a pm. U.K. based any might be cheaper. Remember shipping and import duty

 

[Portofino]

Starting to quiver a bit , I can see a use of BF tm in the exhausts / risers if left for extended periods diluting the nasty acids made from exhaust gas + sea water .

But I still believe in quality engineering in the first place and my Zincs for the engine coolers .

Hmm ?

 

[petem]

A nice fresh water flush will sort that Nasty sea water problem out ......

How do you do that on an outdrive boat?

Seems like a superior part to me and definitely worth considering if the boat is a keeper and the cost is marginal.

 

[MapisM]

How do you do that on an outdrive boat?

It depends, P.
I've seen some outdrive boats where the boatbuilder installed a strainer, downstream the leg raw water pickup and before the pump. I believe that is actually a rare setup, but if you would have strainers, the simpler way to tackle a BFTM installation is the one I made, as per pic in the other thread.

If you don't, you should intercept the raw water hose that somewhere inside the transom should go from the leg to the engine, cut it, and put in between a 3-ways valve that allows you to let either sea water (for normal operation) or the hose connector (for flushing) feed the engine pump.

Mind, I have no clue about how easy (or not) doing this can be on VP outdrives like yours.
I'm more familiar with Bravo outdrives, where it's a reasonably easy job - in sharp contrast with Alphas, where the pump is inside the leg, and I believe they can only be flushed with a muffler.
You could maybe pm VolvoPaul, who surely knows much better than myself, if he doesn't see this thread.

 

[petem]

It depends, P.
I've seen some outdrive boats where the boatbuilder installed a strainer, downstream the leg raw water pickup and before the pump. I believe that is actually a rare setup, but if you would have strainers, the simpler way to tackle a BFTM installation is the one I made, as per pic in the other thread.

If you don't, you should intercept the raw water hose that somewhere inside the transom should go from the leg to the engine, cut it, and put in between a 3-ways valve that allows you to let either sea water (for normal operation) or the hose connector (for flushing) feed the engine pump.

Mind, I have no clue about how easy (or not) doing this can be on VP outdrives like yours.
I'm more familiar with Bravo outdrives, where it's a reasonably easy job - in sharp contrast with Alphas, where the pump is inside the leg, and I believe they can only be flushed with a muffler.
You could maybe pm VolvoPaul, who surely knows much better than myself, if he doesn't see this thread.

Thanks, P all sounds a bit too complex (aka recipe for a disaster) on a shared boat with partners that are even more clueless than myself!

 

[Bandit]

On a Sunseeker with Volvo Penta D12 engines that we looked after it had stainless steel Halyard water injection bends.

They lasted 5 to 7 years max before both sides being replaced, we did that job twice the boat at 13 years old is on its 3rd set of water injection bends.

My cast iron Volvo Penta ones lasted 13 years.

I agree with Itama exhaust systems and exhaust gas acids do not make stainless steel a supply and forget item, or the answer to all of your problems.

 

[MapisM]

Thanks, P all sounds a bit too complex (aka recipe for a disaster) on a shared boat with partners that are even more clueless than myself!

Actually, once everything is arranged properly, I wouldn't call the BFTM a complex system.
I mean, handling a radar or a chartplotter is by far more complex, for instance.

Yours is a good point though, because mistakes can be expensive: running the engines with seacocks closed is obviously as much dangerous with the BFTM as it is in a plain vanilla installation without it.
But with the latter, most folks just leave the seacocks open and forget them, so in this sense life is easier.

Btw, we are only talking of engines: nowadays, I've got no less than six BFTM implementations in my boat: 2 + 2 for engines and shaft seals, 1 for genset, and 1 for a/c...! As I'm writing, I've only got seawater around, rather than anywhere inside my boat (A/C aside, which is running)!

 

[About Time]

Hi,

Thanks a lot for all the guidance/ information. Great forum.

I guess I will just go for the cast iron VP original elbows and consider these as replacement parts... boating has never been for free (sadly though).

Anyway I have one last question in reference to the nasty seawater in the cooling system....

Zincs are on the outdrives and protection is great ….but the heat exchanger does NOT have any zincs. I have always found this very strange. Please see this picture of the heat exchanger on the VP KAD 300:

http://www.marinepartseurope.com/sv/volvo-penta-sprangskiss-7738870-26-4923.aspx

I wonder if the heat exchanger is made of special metal so it can withstand the nasty salt ? ….And if so - Why is the elbows not made of same metal then - Do I overlook something ?

 

[Bandit]

The water in the heat exchanger is below boiling point of the mix so about 85 to 95 celsius.

When the water mixes with the exhaust gas, the exhaust gas is probably at bout 500 celsius and the exhaust gas has lots of nasty acids and stuff in it.

 

[MapisM]

The water in the heat exchanger is below boiling point of the mix so about 85 to 95 celsius.

Zincs (if any) are bound to be placed on the raw water section of the HE.
And that surely can't go anywhere near those temperatures!

The rule of thumb I was given for checking a proper sea water circulation is that it shouldn't get more than 10 or 12 degrees warmer than at the intake, when checked after it has done its job of cooling everything but the final exhaust section.

 

[Bandit]

Agreed I was thinking Coolant, when i check tempeature on sterngland which is raw water cooled using water that has already cooled the engine normally about 25C.

However the diesel combustion gas remains exceptionally hot 500c or more when it meets the water in the injection elbow.

 

[About Time]

Yeap … I understand that you cannot use zincs at the iron cast knees due to the extreme temperatures… but why is it that VP does not have zincs anywhere on the heat exchanger when they have zincs mounted on their outdrives…. The heat exchanger is like 80-90 degree I should think and the salt water should still cause a lot of damage to the metal... or not ?

 

[MapisM]

'Course it does - don't ask me how I know. :ambivalence:
Not because of the temperature, though: as already mentioned, unless you are cruising in tropical waters, you're very unlikely to ever see more than 40 deg or so on the salt water side of the HE.

 

[BruceK]

How do you do that on an outdrive boat?

Seems like a superior part to me and definitely worth considering if the boat is a keeper and the cost is marginal.

The same way you put in antifreeze over the winter months. Take the raw water feed off the raw water pump, connect a hose to it and to a bucket (or fresh water feed in this case) start the engine and wait till the bucket drains.

However 5 year longevity to a £200 quid part doesn't make sense. I'd rather be doing it to flush the various coolers out. In the end I dont really bother but stick to annual maintenance and put in antifreeze over the winter months