Wanted: C4 prop set

[LocoLoic]

Hi all,
Looking to move from B5 aluminimum props to a set of C4 stainless. Anyone got a set gathering dust they don't want?

Thanks in advance

 

[BruceK]

C4 are slightly less coarse than B5's. I have a set of B5's gathering dust for this reason. They were slightly over propping my engines imo. I'd say the difference is about 200 rpm in case you were unaware, they are not a direct replacement.

 

[LocoLoic]

Thanks - are you sure you don't mean the c4's are more coarse?

So, looking at the below, if I compare the Volvo AQ205, with the 2.30:1 ratio, I see B5's rated up to 37kts, and the C4's up toe 39kts.
http://www.pentamarine.co.th/pdf/propellers.pdf

I'm banking on the additional efficiencies of the stainless props minimizing the effects of the slightly longer pitch, so the boat will hopefully get up onto the plane just about as easily as before...

We shall see though. The stainless props will weigh a load more, so that might hinder initial hole shot, too... fingers crossed, it's all very minimal. Might have to find a way of lightening the boat otherwise!

 

[BruceK]

very sure. Regardless of what the pdf says I am talking from first hand experience. That's an old pdf and you wont find a current pdf quoting those figures. I can assure you the quoted speed is so bogus and relative to boat to be completely worthless. If that is what you are basing your expectations on you have an even chance of being disappointed. A C4 will give you a much better hole shot, that was my experience at least. But you would expect that.

 

[LocoLoic]

OK thanks. That makes it all the more complicated! So, the B5 figures in that document were actually pretty close for my boat. It used to have an AQ205 engine (now a vortec equivalent with 220HP), and I currently max out at around 36-37 kts on a good day with a clean hull. The main drive behind going stainless was to maintain a similar hole shot, but possibly drop a couple hundred RPM for cruising or gain a couple of knots top end.

My drive leg and prop selection were for my old engine, so with a more powerful engine, I figured going a fraction coarser would be reasonable, in addition to the efficiencies of stainless blades.

So, now I'm considering whether C5's would be the option to go for, or if that would be a rather expensive mistake to have to live with.... It would be useful to find an up to date comparison, i.e. same engine/boat/drive leg, but with different props... I'll have a look about!

 

[BruceK]

The speed issue is so boat dependant. For instance I can make max revs with C4 on my boat and according to the pdf I should be pushing ~30knts with B5 and ~40knts with C4. The reality is at my cruising revs I am pushing ~24knts with the C4 and ~27knts with the B5. The B5's actually felt better on my boat. A more planted feel if I could possibly use such a term, but the engines ran a bit hotter. The C4's by comparison feel a bit "thin" into what I can only describe as and please bear with me... as if the B5's were like driving on tarmac and C4's like driving on a good gravel road. ..... I know. It's the best way I can describe it though.