Have a look at my Prop!

[Firefly625]

Well yesterday my Hardy came out the water. Having had a survey done I knew the prop was (according to the surveyor) probably only good for one more season....but I sort of hoped he was being over fussy..... turns out he wasn't!

IMO this must have an effect on performance...anyone like to tell me otherwise? Also any sort of balance will be thrown right out by now so this would cause more vibration than a nice shiny new one (not that I have noticed any).

So, anyone know of a good (& cheap!) prop supplier, if local to Solent all the better? My surveyor did mention someone in Dorset but I would need to call him to get the name again, I think he estimated a cost of around £350.... (I think that sounds a bit low, but hope he's right).

......but at least she's all out the water and in a nice spot to dry out over the winter. Has previously only left the water for a week a year for the last 5 years so surveyor recommended this year she stay out at least 2 months to dry out.

 

[sarabande]

a couple of points.

1 are four bladed props the norm for the Hardy (a really nice example , BTW) ?

2 couldn't see an anode on the shaft.


Pitting on the drive surface of the blades to that extent is going to create more cavitation zones. I reckon you need to look at a new one, possibly 3 blade configuration.

 

[Dave_Snelson]

When the prop was clean, was it "salmon pink"? If so, you need to have more (or more efficient) anodes. Lack of anodic protection on bronze props like yours means that the zinc is leeched out over time, leaving just the copper. That's why you see balanced anodes on shafts. The other option is that your prop suffers from "cavitation burns". Generally (but by no means always) these occur on the back of the blades. Take advice from a prop specialist like steel developments. They are reasonably prices as well.

 

[Firefly625]

a couple of points.

1 are four bladed props the norm for the Hardy (a really nice example , BTW) ?



2 couldn't see an anode on the shaft.



Pitting on the drive surface of the blades to that extent is going to create more cavitation zones. I reckon you need to look at a new one, possibly 3 blade configuration.

To answer your questions, firstly Yes, all Hardy Mariners are fitted with 4 blade props from new...(& thank you!)

and secondly Quite correct, instead of a prop anode the boat has shaft brushes on the propshaft which when I got the boat were badly adjusted, which AFAIK caused this extreme pitting to occur. Now adjusted correctly contact points fitting on the shaft correctly so hopefully will not happen again..... (unless anyone else has an opinion on this?)


Interesting, I guess confirms my thoughts.. but why would you suggest a 3 blade rather than 4..... ?

 

[jfm]

Yikes. Looks like corrosion, not cavitation. Definitely check the anode circuit - there is no shaft anode so the shaft needs to be grounded to the anode circuit. Is it? Test with continuity meter on outside of boat twixt prop and anode. Check rudder at same time

Once that wiring is fixed, you could get a new prop but it looks like there is loads of meat on it so you could, if so inclined, fill it with epoxy filler and fair it then paint it. A nice winter job at home?

Also worth emailing steel developments with those pics becuase their refurb prices are ver reasonable

I don't think you should leave it rough because I expect it will hit performance and fuel. Barnacles on props burn massive fuel so I'd guessd that your pitting will too

I'd tread very carefully if thinking of changing to a 3 blader. Hardy must have experimented and they know their stuff so they put the 4-er on there for a reason (I'm assuming it is original - it might not be but Hardy can tell you that). A 3er could slip too much and it's quite expensive to experiment at £350 a time...

 

[Firefly625]

When the prop was clean, was it "salmon pink"? If so, you need to have more (or more efficient) anodes. Lack of anodic protection on bronze props like yours means that the zinc is leeched out over time, leaving just the copper. That's why you see balanced anodes on shafts. The other option is that your prop suffers from "cavitation burns". Generally (but by no means always) these occur on the back of the blades. Take advice from a prop specialist like steel developments. They are reasonably prices as well.

see response above, basically shaft brushed were not touching prop shaft when I got the boat.... for how long this had been like this obviously I have no idea. Thanks for advice about Steel Developments, not that far from me... I will give them a call.

 

[rosssavage]

IMHO don't go near Steel Developments -I asked them to repair a prop I had dinged and all they wanted to do was sell me a new one as "it was too badly damaged". T Norris' in Brentford managed to salvage and repair it for £130 inc vat (for a 21" x 24" three blade).

No link, just a disapointed and then happy customer respectively...

 

[Firefly625]

Yikes. Looks like corrosion, not cavitation. Definitely check the anode circuit - there is no shaft anode so the shaft needs to be grounded to the anode circuit. Is it? Test with continuity meter on outside of boat twixt prop and anode. Check rudder at same time

Once that wiring is fixed, you could get a new prop but it looks like there is loads of meat on it so you could, if so inclined, fill it with epoxy filler and fair it then paint it. A nice winter job at home?

Also worth emailing steel developments with those pics becuase their refurb prices are ver reasonable

I don't think you should leave it rough because I expect it will hit performance and fuel. Barnacles on props burn massive fuel so I'd guessd that your pitting will too

I'd tread very carefully if thinking of changing to a 3 blader. Hardy must have experimented and they know their stuff so they put the 4-er on there for a reason (I'm assuming it is original - it might not be but Hardy can tell you that). A 3er could slip too much and it's quite expensive to experiment at £350 a time...

Thanks for response jfm, certainly a galvanic issue, but I do hope that is now cured, but as you suggest as the boat is out of the water worth checking.

In fact some of the pitting is so bad there is not a huge amount of meat left on the prop, in fact the pitting has rather turned to craters.. The idea of changing away from the standard 4 blade prop to 3 blade to be honest is not something I would do unless Steel Developments or Hardy advised it. I am always of the opinion that there is a reason why a manufacturer opted for a certain prop size and number of blades, changing it may improve one aspect, but harm others.... I will replace like for like unless advised by experts.. But will probably still have a play with filling and painting as that does sound a nice winter job!

 

[Firefly625]

IMHO don't go near Steel Developments -I asked them to repair a prop I had dinged and all they wanted to do was sell me a new one as "it was too badly damaged". T Norris' in Brentford managed to salvage and repair it for £130 inc vat (for a 21" x 24" three blade).

No link, just a disapointed and then happy customer respectively...

Oh, thanks for the warning!

 

[omega2]

props

www.clementsmarine.co.uk. they have a branch down your way.

 

[Latestarter1]

Propeller problem

Looks real ugly

#1 Do you have shore-power?

#2 Do not even be tempted to fit shaft anodes. If I come across them other than on commercial vessels with deep reduction gears always knock them on survey.

#4 £350 for a new prop sounds about right, no point in messing with T Norris (good guys) or steel Developments, but they just flog other peoples props and you pick up the margin, far better to go straight to prop manufacturer, Clements are a decent bunch.

Do not get caught up in the 3 Vs 4 blade argument, the comment regarding 3 baldes and slip just goes to show how a little knowledge is dangerous, propellers NEED to slip in order to work!. Quite simply the fewer blades equalls better efficiency, however whist a three blade prop would give you slightly better top end, four blades are smoother with a tiny bit more urge at the bottom end, stick with what you have. Probably came from Clements in the first place.

 

[thefatlady]

Lack of anodic protection on bronze props like yours means that the zinc is leeched out over time, leaving just the copper.

That's true of brass, not bronze. Bronze is copper-tin, not copper-zinc and the tin does not leach out

 

[Firefly625]

Looks real ugly

#1 Do you have shore-power?

#2 Do not even be tempted to fit shaft anodes. If I come across them other than on commercial vessels with deep reduction gears always knock them on survey.

#4 £350 for a new prop sounds about right, no point in messing with T Norris (good guys) or steel Developments, but they just flog other peoples props and you pick up the margin, far better to go straight to prop manufacturer, Clements are a decent bunch.

Do not get caught up in the 3 Vs 4 blade argument, the comment regarding 3 baldes and slip just goes to show how a little knowledge is dangerous, propellers NEED to slip in order to work!. Quite simply the fewer blades equalls better efficiency, however whist a three blade prop would give you slightly better top end, four blades are smoother with a tiny bit more urge at the bottom end, stick with what you have. Probably came from Clements in the first place.

Thank you for some very sound advice. I do indeed have shore power. I was not tempted to fit shaft anodes, but interested to hear your aversion to them.... a load of boats are fitted with them..
I will just check who Hardy use to supply their props, but I seem to recall in the massive handbook file that came with the boat their being something from Clements. The boat is no lightweight so I guess 4 blades will give it the better urge to get it on the plane, top end speed I'm not really interested in, if I was I wouldn't have a Hardy!

 

[maverickofpoole]

I have used Propeller solutions for my prop repairs and supplies and found them very helpful
http://www.propellersolutions.co.uk/

If you do phone them ask for Tom who is a very knowledgeable chap

Martin

 

[VicS]

That should not happen to a prop made of the correct alloy even without anodes.

Common material for props is manganese bronze. It is normally resistant to corrosion in seawater but is in fact not a tin bronze but a zinc/copper alloy and technically therefore a brass, but containing manganese as one of the alloying elements. It can therefore suffer from dezincification but normally only as result of some other factor.

If the prop is just an ordinary brass alloy then dezincification is almost inevitable without an anode.


Two possibilities :

Not manganese bronze, just an ordinary brass therefore dezincified because the ande is not connected to the shaft.

That you are suffering from galvanic corrosion as a result of being connected to shorepower without having a galvanic isolator in the circuit. On reflection I am not so sure about that!​

I suggest if you now replace it:

You should if possible ensure that the replacement is manganese bronze (or something better such as nickel aluminium bronze).

Get the anode system sorted out. Vital if you have to fit anordinary brass prop.

Fit a galvanic isolator if you normally leave the boat with shorepower connected even if not actually in use.​

EDIT: A third possibility is that you have some horrible electrical fault that is leading to electrolysis!

 

[MapisM]

Quite simply the fewer blades equalls better efficiency

Mmm... this one sounds like an academic generalisation, if I just think of which props are fitted on many vessels where efficiency is a top priority.
But glad to stand corrected, if you care to explain why.

 

[Latestarter1]

Propellers etc etc

#1 Zincs on a boat should more correctly be termed "Sacrificial Anodes". Zinc is used because it has a higher voltage in the water so the current will be more inclined to flow from it than from your propeller. To complete the electrical circuit, the zincs must be connected to the items they are intended to protect. Usually this is no problem because the zinc is electrically connected to the shaft via shaft brushes (do not forget jumper cable on shaft half coupling) the and bolted right though to underwater housings. Non metal boats should usually have a copper bonding wire inside that connects all the underwater metal items together so they all share the protection from zinc anodes. Since engines use the metal frame as the negative battery connection and the engine is connected to the prop shaft, the engine and the negative side of your 12 volt system are also part of this bonding connection.

If other currents are allowed to get into this bonding circuit they can easily overpower the small voltage available from your zincs and defeat the protection you need. This is usually the most destructive form of electrolysis and you notice it because your zincs get eaten up very quickly trying to keep up. Under normal circumstances, zincs should last at least a year if they are working normally and much longer if you don't have any problems. If they are being "sacrificed" in a shorter period you need to find where the external current is getting in.

The most common source of this external current is the shore power connection, especially the ground lead. Pontoons are notorious for bad wiring and often the ground lead is not connected to ground, is connected to the neutral, is being used for carrying current to a mis-wired boat, and all other sorts of problems. So the ground lead should never be directly connected to the ground bonding system we talked about earlier. The purpose of the shore power ground lead is to provide a return path for current if there is a short circuit or power leakage from an appliance or the wiring on the boat. You don't want it to connect all the underwater items on your boat to the underwater items on all the other boats and the dock because now your zinc is trying to protect everyone else too.
Unfortunately it is not always possible to keep the circuits separate due to interconnections such as shore power chargers. There are a number of ways to separate the shore power ground from the boat's underwater bonding system. The preferable and safest way is to use a galvanic isolator to introduce a 1.2 volt insulator in the circuit. This is enough to isolate most galvanic voltages but it will still conduct electrical faults and keep the boat safe in the event of a ground fault in the wiring or in an appliance. The galvanic isolator must be rated for the size of your shore power circuit.

#2 Shaft mountded sacrificial anodes are a complete nonsense on most pleasure vessels. Why do so many vessels have them, because the people who fit them know little about the fundamentals of marine engineering. If stern gear is protected as in note #1 at best shaft anode serves no purpose. However fitting a shaft anode can have many undesirable side effects.
(A) Any propeller must have “clean” water ahead of it if it is to be efficient. A lump of scrap bolted to the shaft certainly does a good job of spoiling chances of getting a nice flow of clean undisturbed water for the prop to get its teeth into.

(B) If shaft anode starts to deplete then the situation becomes even more unhappy, as the depletion is never equal all the way around, now not only creating even more “dirty” water for the propeller to eat. Now compounded by the imbalance of this ugly piece of scrap. Say 3,000 rpm engine 2:1 box, shaft spinning at 1,500 rpm. Builder elected to have four blade prop for optimum smoothness, defeated by lump of unbalanced metal on our nice sweet drive line.

(C) Finally have you ever seen the effect of a shaft anode letting go, dependant on reduction ratio and rated engine speed, they can cause structural damage to the hull when they come adrift.

#3 I did not want to get into a blade number discussion as not actually relevant to this post however;
The most efficient propeller has one blade as it has no other blades ahead disturbing the water flow. However from a practical perspective as much use as one legged sailor as ass kicking party.

Without rambling on forever on the subject, three bladed propellers are generally proven to have the best compromise between balance blade area and efficiency.
Propellers with four or even more blades are useful for two reasons. First more blades create more total blade area for a given diameter. Nasty modern and relatively inefficient hull designs with tunnels need to absorb a lot of power for a given diameter. However you cannot ignore the fact that four or more blades scramble each other’s water flow, fact.

The second persuasive reason to use four or more blades is to reduce vibration, every time the propeller passes the strut or under the hull they cause a change in pressure (or suction). Consider this; the blades of a three bladed propeller passing under the stern 3,000 times a minute equals 50 Hz. The four blade propeller still at 1,000 rpm would change this to 4,000 times a second or 66Hz the smoother the feel and less likely to cause hull resonance.
Starting to ramble now as I feel blade loading, blade tip clearance etc etc coming on. But will call it a day here.

As a final aside looking at the pictures of the effected propeller blades i would suggest prop started life as a good quality Nibral casting.

 

[burgundyben]

http://www.hamblepropellers.com/2404/frames.php

I've had good service from Hamble Props.

 

[MapisM]

I did not want to get into a blade number discussion as not actually relevant to this post...
...
Without rambling on forever on the subject, three bladed propellers are generally proven to have the best compromise between balance blade area and efficiency.

Hang on, it was something you said that made me curious, hence my simple question.
With apologies if it was the "academic generalisation" that sounded offensive, it wasn't meant to.
But I totally missed the point where we started "rambling forever"!
Anyhow, thanks for your explanations. I'm still missing the reason why I've never seen a 3 blades prop on any of the most efficiency-oriented vessels I've seen, ranging from oceanic full displacement trawlers to 150mph air entrapment machines. But never mind, I won't surely loose my sleep over it.

 

[Latestarter1]

Rambling

No t'was me that was at risk of rambling nobody else.

Displacement trawler whith large block coefficient is different case altogether. Very high speed vessels with supercavitating propellers also different case. This is why it is a very complex subject that I was unwilling to risk hijacking the thread

Think pure, say modified deep V Ray Hunt Fairy hull as PURE, planes at lower speeds with less power than modern compromise designs, tunnels, horrible.

Ask Burgundyben about pure hull forms from Hunt/Burnard and Levy.