Duo-props

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pauln

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I have a boat fitted with twin AQAD41 engines and DP290 drives which is has just finished it's third season. When I lifted the boat last week for laying up I noticed pitting/corosion on the inner face of all three blades of the outer set of props on both drives. Apart from that the props have no damage. They were fine when the boat went in the water last March and the anodes are only about 50% wasted.
I'm guessing it is cavitation but what could suddenly cause it. I've done nothing different with the boat this year.
Anyone any ideas?
 
Aluminium or Stainless Steel?

If aluminium then too much flexing caused by too much power, known problem and only solution to switch to SS.

I have more info on this if required, PM me with an email or fax number.

Dom

I am boating again ;-)
 
Not sure what you mean by "inner face" of the props. Cavitation would cause pitting on the low pressure face of the prop blades, ie the front faces. The stress cracks that Dom refers to above would (I guess?) appear on the high pressure side, ie the aft-facing side
 
They actually start on the innerside where the hub meets the blade due to the props not being strong enuf in comaprison to the torque produced when you push it quickly to near WOT. Had the problem with mine. Volvo no go as in Aug 2000 they sent a letter to all dealers saying on these engines and gave a list of which AD41 is on, that SS must be fitted.

I have the actual info from Volvo on file. Only way to combat it is to go SS plus this will increase speed economy and reduce time to get on the plane making your boat more efficient.

Dom

I am boating again ;-)
 
Re: Dom, I dont understand

all ok, though I still dont know what "innerside" means in relation to a prop. Do you mean on the inside of the hub itself, I mean in the "bore" of the prop hub? So totally invisible unless you remove prop and look inside it..... that's not what Pauln is talking about I dont think.....
 
Re: \"stainless\" steel

stainless stel isn't stainless - it's more resitant to corrosion. Not sure if merely another(i'm guessing) 70 hours would cause pitting from cavitation? - more likely it is natural corosion of the things, the metal can be ground down to be like new.
 
Re: Dom, I dont understand

where the hub meets the blade, on the inner side i mean the side of the blade the water is most pressured.

Its a known fault and widely recognised, as I said before I have the Volvo fact sheet. The alu props cant take the power from the engine, have seen a set that have shattered.

Dom

I am boating again ;-)
 
Re: Dom, I dont understand

When I say inner, I mean the inner towards the drive as opposed to outer towards the prop locking nut.
I'm not sure how that relates to pressure though, ie which is high pressure face.
I also thought the Volvo proplem was with the KAD engines which are more powerful than mine and does it appear as cracks or pitting.

Thanks, Paul
 
Re: Dom, I dont understand

The main problem was with the KAD engines however it has been seen on the AD41s.

Check the hub where the blade joins it. If it is starting to break up slightly then this is the start of it.

When did you last get your props serviced and rebalanced? should be annually as aluminium props bend out of shape with constant use.



Dom

I am boating again ;-)
 
if tou have any pitting it is due to corrosion. are your anodes fitted corectly are they the correct ones i.e. fresh water anodes or sea .
if your anodes are not worn afte4r three seasons then they are not working maybe theyb have paint between them and the outdrive hope this helps
 
Hi Paul,

I have the same problem, my single duoprop props pit each year and each year I have them serviced and re-balanced. However my orginal props which have now done 3 seasons will need replacing before this seasons starts, so I feel three years of the same props is not too bad.

I see suggestions regarding must go to s/steel props which I agree are much better, however I understand you need more anodes as s/steel eats them quicker!

Regards,
RM.
 
Hi!

Sorry for breaking into the thread, but can you give me some more information on why a SS prop is better than aluminium? Also, you say that VP has since 2000 recommended SS props on some AD41 modells? Can you be more specific?

I've always heard a lot of people refering to that SS props are better than Alu props, but no one can tell me facts why its better.

On my boat (Sealine 365) i got 2 AD41A & DP-E sterndrives with (i suspect) ALU props. According to Sealine its shipped from factory with A5 props. Would I gain something on switching to SS props?

Best regards,

Kaj Lehtinen
Sweden

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Strongly reccomend electric anodes with ss props as well as double the anodes.

availalbe from Merc dealers...

<hr width=100% size=1><A target="_blank" HREF=http://www.boating-ads.co.uk> Boating Website</A>
 
Re:SS Props

Kaj

Welcome. You could do a search through the forum but, basically, the blades in SS are thinner and so more hydrodynamically efficient as well as being stronger so they can take more power and use before becoming damaged. The main benefit is in general efficiency and will usually pay for themselves through longer life alone anyway.

Anthony

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Re:SS Props

Triple ace had stainless steel props

13 years old same ones still serviceable

<hr width=100% size=1><A target="_blank" HREF=http://www.boating-ads.co.uk> Boating Website</A>
 
Re:SS Props

Hi!

Thanxs for the reply, do you or anyone else in the forum have any figure in percentage on how much better the fuel economy is with SS props? This so that I can have some sort of financial motivation to buy these expensive things....

I mean, are we talking 1-2% or 10-15% range?

Best regards,

Kaj Lehtinen

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