DPH props

[GrahamHR]

Well, it seems corrosion of these Nibral consumables is widespread. As standard, they are totally isolated from any anodes due to the outer prop being connected to the hub via a plastic bush. Is there any reason why a short bonding wire could connect the inner bush and the prop and provide protection ? There's plenty of room to do that.

 

[jimmy_the_builder]

I thought the problem with the dph props was not galvanic corrosion, but a combination of a bad alloy mix (now corrected) with cavitation corrosion.

(In fact, haven't we discussed this before...?)

 

[RogerRat]

I thought the problem with the dph props was not galvanic corrosion, but a combination of a bad alloy mix (now corrected) with cavitation corrosion.

(In fact, haven't we discussed this before...?)

Yes but always indirectly. Volvo tech suggest cavitation in most cases but I took my porous ones to Steel Developments. He was not complimentary but didn't want to be quoted so I wont. Bottom line is that they are not repairable due to the changes in the alloy properties. Put simply there is no welding rod compatible with a corroded prop.

A combination of Aluminium, Stainless and Phosphor bronze all down in the drive means that although the props are 'corrosion resistant' , they will, and do corrode. I was assured that any attempt to anode protect them is likely to cause more harm than leaving none. Princess have been replacing these props under warranty on certain V series boats for the the past five years. I'm pretty sure Volvo weren't too happy about it.

For DPH drive owners, they have to allow replacement cost into a service budget. Prop life varies from 1-5 years unfortunately.

RR

 

[GrahamHR]

Yes but always indirectly. Volvo tech suggest cavitation in most cases but I took my porous ones to Steel Developments. He was not complimentary but didn't want to be quoted so I wont. Bottom line is that they are not repairable due to the changes in the alloy properties. Put simply there is no welding rod compatible with a corroded prop.

A combination of Aluminium, Stainless and Phosphor bronze all down in the drive means that although the props are 'corrosion resistant' , they will, and do corrode. I was assured that any attempt to anode protect them is likely to cause more harm than leaving none. Princess have been replacing these props under warranty on certain V series boats for the the past five years. I'm pretty sure Volvo weren't too happy about it.

For DPH drive owners, they have to allow replacement cost into a service budget. Prop life varies from 1-5 years unfortunately.

RR

I know of a set of these props that sat in salt water for the first time for 5 months or so with less than 1 engine hour use. The blades were fine, the outer hub showed some surface "pinkness" and some pitting, so the start of corrosion; not related to cavitation I expect as they had hardly turned at all ! The inner hub, in direct contact with the shafts and in electrical contact with the drive anodes had no "pinkness" or pitting.

 

[jimmy_the_builder]

I wonder if we'll ever see aftermarket props for the DPH drives?

 

[GrahamHR]

I wonder if we'll ever see aftermarket props for the DPH drives?

I suspect not; Quicksilver introduced some for the DPS drive n 2011 ( 4/3 bladed like the DPH diesel ones. I think they were called the "Thunderbolt" series) They don't seem to be available any more; either because they were not cheap enough, or more likely in my opinion pressure was brought on them by VP (maybe!!!). Maybe they or their casting shop supply the original VP props ?

I saw some unfitted VP hubs for the DPS and the DPH props the other day. Completely incompatible due to diameter; the DPS prop hubs are much bigger diameter. I really do wonder, or actually I don't, why VP have both the DPH and DPR drives. Corrosion susceptible props and stainless props respectively, costing about the same. They use the same upper unit. Their market for replacement DPH props is a guaranteed income source !

In reality, all that is needed is a hub asembly that allows a pair of DPR props to be fitted to a DPH, assuming the DPR props do not have an excessively large hub diameter compared to the DPH.