Solas told me that they only recommend 4 blade above 150hp from memory

Iboats has a great section on prop selection etc

http://boatpropellers.iboats.com/?cm_mmc=Google_Main-_-Props%3AGoogle%3ASitelinks-_-1+Boat+Prop+Selection-_-NA&mkwid=s9qtOA6gV&crid=45449327899&mp_kw=iboat&mp_mt=e&pdv=c&gclid=CMT70LvqqMACFZcRvQod9C8Acw

....it's shiny and looks schmick!  Obviously stronger than ali, which means if you hit something there's more likely to be damage to not only the prop, but also the shaft/gearbox.

Conceivably, could have its advantages in shallow, sandy environments, where occasional (or more) contact with the sand would wear an ali prop more quickly than a ss one...of course your impeller wouldn't be too happy with this sort of treatment but!

Depends on what you are looking for in a prop.
A stainless is more rigid so will flex less under load but as said can cause more damage if you hit something.

A 3 or 4 blade can change the way a boat handles. I am currently looking at a 4 blade for my 140 Suzuki to give more lift on the back to get the boat up quicker when at trolling speeds after talking to Mick at Solas.

A 4 blade prop will give you greater fuel economy especially in the 4000 rev range,, but that's of no concern to my application. great on heavier boats but you will loose some top end speed.

 I found the standard Yamaha aluminum OME props are rather lacking in bottom end takeoff as well as top end speed. My current prop on my Yamaha F100 is actually a aftermarket prop from a mercury fitted to a Yamaha hub (same 19 pitch as OME I had). The larger lobe style of the prop made a noticeable difference bettering holeshot, topend and also lowering max RPM. Can't exactly explain it, but put it down to yamaha ali props being crap. I also rather an ali prop it's 1/4 of the price and is sacrificial than doing a gearbox.

 I took off the 19inch stainless for a 17inch Ali just in case I hit something 

Anyways Murphy's law I did hit something really hard last

Weekend off mindarie 400M straight out in 6m of water. Not only did I smash my prop but cracked a

Conrod put thru the block and destroyed a perfectly good 4 stroke with 690 hrs on the clock. Hence why the cover is for sale

When u are having a bad day u have a really bad day. 17 inch is perfect by the sounds of it

This subject relates back to my trade so I have a little knowledge on the subject, a quick read on the web and the operating characteristic of a marine prop are similar to those on an aircraft.

The power from the engine must be absorbed by the prop. So the bigger the engine, the more propelling surface is needed by the prop.

As a prop gets bigger in diameter (to absorb the power), the tip speed increases. The speed at the centre of the prop is slower than the tip. At some point for instance on an aircraft the tip speed exceeds the speed of sound and that area of the prop stops working. On a marine prop at some tip speed, the end of the prop cavitates, drag goes up efficiency drops off, and fuel usage increases and top end speed is lost, as per previous thread.

To reduce the diameter of the prop and to absorb the power more blades are added.

The next issue is the angle of attack, which is the angle between a line drawn from the leading edge of the prop to the trailing edge, and a line being the “RELATIVE” flow of the medium it’s working in. Apparently the best angle of attack is between 2-4 degrees.

But as the boat, aeroplane begins to move forward, the angle of the relative flow to the prop decreases. For a fixed pitch prop the pitch will only be at its most efficient at one speed. Either side of which the prop will be either over, or under pitched. So you have to decide what you want, initial acceleration (poor top end speed), fuel economy at cruising speed, or a high top end speed (poor initial acceleration).

Other things like less loading and other forces on the blades when the prop has multi blades, but there would be increased manufacturing costs.
I’ve tried to make it simple, there is loads on the net about this. Have a look at pictures of aircraft props at the beginning of ww2 when they were getting higher speeds,the fixed pitch props had massive angles on them. Must have needed really long runways to get airborne. To overcome this problem variable pitch props were invented.

At 5300-5800 the tip speed may be over the threshold and the water is boiling due to the negative pressures there and that's cavitation.
However there is another equation, if you are a mathematician and that is drag increases at the square of the speed. That's why at higher speeds a lot of power is needed to get any speed increase. So those transducers, outboard legs, and anything else, hull friction are not doing you any favours.