What a difference a prop makes....!

[psycho]

Every day is a school day.....

I have been boating since I was knee high to a grasshopper, and have had numerous different boats over the years.

But, every boat that I have owned, have never had to change the prop. It has either had an ally or stainless prop fitted. Just left alone.

I got offered a stainless prop for my rib a while back, at a very good price, so thought why not? give it a go. Got told that I may notice a difference.

Holy crap, what a difference...... Going from ally to stainless is a HUGE difference, especially when you know how your boat normally handles. The hold it now has is brilliant.

[jwalker]

Originally Posted by psycho

Going from ally to stainless is a HUGE difference......

I don't doubt you have a big change in performance but it would be unwise to presume it's necessarily the change of material which is responsible for the improvement.

[psycho]

Spoke to my marine mechanic, and he says it is. The acceleration has improved, the hold it now has in turns, and no cavitation, is because the stainless is harder and has no flex like the ally has.

[paintman]

Does the ss prop have the same number of blades & is it of the same pitch as the ally prop that was on it?

[psycho]

yes and yes..

[paintman]

How do the WOT readings compare?

[beamishken]

Originally Posted by jwalker

I don't doubt you have a big change in performance but it would be unwise to presume it's necessarily the change of material which is responsible for the improvement.

You will notice that all high performance and race props are stainless
It's not purely the material but the fact it can be worked into better shape and blade profiles
You would expect a performance improvement going from ally to stainless
Think of it like your car having half worn under inflated budget tyres you wouldnt expect it to perform the same as if it were fitted with a good set of properly inflated Bridgestone/ continental Michelin etc

[psycho]

Not exactly sure mate, for a couple of reasons.

1. tacho is about as reliable as a Land Rover.....so dont look at it.

2. hardly ever use it flat out as it chine walks a bit, and missus prefers cruising at about 25 knots.

went out the other day, and it is still doing 32 - 36 knots, which is more than enough for us. Mainly used for diving, and or towing toys, and general family fun.

[psycho]

Originally Posted by beamishken

You will notice that all high performance and race props are stainless
It's not purely the material but the fact it can be worked into better shape and blade profiles
You would expect a performance improvement going from ally to stainless
Think of it like your car having half worn under inflated budget tyres you wouldnt expect it to perform the same as if it were fitted with a good set of properly inflated Bridgestone/ continental Michelin etc

+1...

The only thing that I can relate it to, a few years ago, after owning my VW T4, for a few years, then having it re-mapped, the difference was brilliant.

[jeepster]

The main reason stainless steel props give slightly better performance is because they have thinner blades than Aluminium props. Thinner blades produce less drag, hence they can provide a higher top speed. This is only possible because of the greater strength of S/S over Aluminium. But you will still get cavitation at the blade tips no matter what the prop is made from because all open bladed props produce cavitation. The two trade offs are price and weight...Weight is the enemy of speed and a stainless prop can be twice the weight of a Aluminium prop, negating it's advantages...The cost, often 2-3 times the price of an Aluminium prop, is also extremely expensive, which limits the sales and appeal of stainless props...Most prefer the price and performance compromise of using Aluminium props. One other thing to consider is the damage you can cause to your gearbox if your prop strikes something hard underwater...You might get a chunk taken out of an Aluminium prop in such a case, but your gearbox will suffer no damage...With a stainless prop though the prop is stronger and does not "give" so easily, transferring more energy from a collision to the gearbox, resulting in gearbox failure costing far more to repair than the price of a Aluminium prop.

[Last Tango]

There's even a difference to be had between one "brand" of stainless and another.
I've replaced a "Vengence" with a "Laser II" and found a big improvement in performance.
WOT was exactly the same but the acceleration with the vented "Laser II" and it's grip when trimmed well out is way better.

[ribber]

jeepster Best explanation given on this forum for a long time

[Pikey Dave]

Originally Posted by ribber

jeepster Best explanation given on this forum for a long time

If you think that's good, ask him for hints & advice on trailers[emoji6]

[jwalker]

Originally Posted by beamishken

It's not purely the material but the fact it can be worked into better shape and blade profiles

Exactly, that's why it is unwise to presume the increase in performance is the result of the change of material. It is more likely that it is the result of a change of blade characteristics.

You would expect a performance improvement going from ally to stainless...

One might, but it isn't a given.

[beamishken]

Originally Posted by jwalker

Exactly, that's why it is unwise to presume the increase in performance is the result of the change of material. It is more likely that it is the result of a change of blade characteristics.
One might, but it isn't a given.

Sorry but I disagree with that statement
Obviously if the blades were identical between an ally prop and a stainless prop you wouldn't see an improvement apart from the influence of the extra weight.
The fact remains a stainless prop correctly specified will always perform better than the best ally prop you will get for a given installation

Therefore is it unwise to assume a stainless prop will perform better?

Safe to assume if someone is going to the expense of buying a stainless prop they will ensure they get the correct one and will see an improvement

[jwalker]

Originally Posted by beamishken

Obviously if the blades were identical between an ally prop and a stainless prop you wouldn't see an improvement apart from the influence of the extra weight.

Exactly, that's my point. It's not the material, it's the prop characteristics which make the primary difference.

It is the case that some of the material sections of stainless props would be too week to replicate satisfactorily in aluminium alloy.
However, it is also the case that there is many stainless steel prop designs which are totally unsuitable for general boating use.

Safe to assume if someone is going to the expense of buying a stainless prop they will ensure they get the correct one and will see an improvement

You reckon!? There is plenty of folk who have been disappointed in their stainless prop selection.

There is also plenty of historical discussion about propeller selection on ribnet.

[jeffstevens763@g]

Steel developments told me to expect around 5% better performance from a SS prop over an Ali one for info.

[jonp]

Before those who have aluminium props rush out to buy new stainless props there are a heap of variables to consider.

Some makes of stainless and aluminium are both good and bad. The latest aluminium from Yamaha and solas are extremely good, to the point I know people who have gone back to aluminium on their commercial outboards. Outboards that spend much of the time in and out of gear have less pressure from aluminium and also tend to fare better from impact damage that often damages the prop and not the gearbox.

It's rare to fit a stainless of the same size and pitch of aluminium and maintain the same recomended max rpm. If you feel you have a poorly designed underperforming aluminium prop you will most likely need to drop down in pitch if changing over to stainless.

Here (Australia) most manufactures allow an exchange on props untill you get the exact right prop for your needs which makes life far more easier than buying lots of props. If you live close to an outboard dealer they will often allow you to take several props out for testing ( as I do ).