prop expectations

I am currently running a 3 blade rh prop on my single engine 30 foot boat. I managed to find asecond hand 4 blade prop for a good price that should work OK. My questions are, what things should I expect going from a rh to a lh prop, and generally speaking, will the 4 blade give better cruising performance thanthe 3 blade?

 

My questions are, what things should I expect going from a rh to a lh prop, and generally speaking, will the 4 blade give better cruising performance than the 3 blade?

Only a few marine trannys can be operated in reverse on a long term basis.

If your prop is the correct one for the boat the 4 blade may be smoother , but slow the boat a few percent , and increase fuel burn a few percent.

Its called induced drag , and is the reason the By plane and Try plane are in museums.

 

Tranny is a zf 220 a , full power in reverse or forward (apparently), I was wondering more about the differences in driving the boat between the 2. Obviously parking will be different and I guess it will walk the other way when backing in.
Has anyone done the rh to lh swap before?

 

A lot more information is needed for reasonable answers, but some general guidelines can be offered. A 4 blade prop generally will be slower off the line and a slight lose at the top end, compared to a similar 3 blade. Often blade cup can compensate for the hole shot, which will also help in turns to a degree.

Assuming you are now running an engine that runs in reverse of the previous engine, the new rotation will have no impact on the boat's performance. Yes, she will prop walk to the other side now, but this should be logical. If you're attempting to run this trans in reverse, you should contact ZF as I suspect as Fred mentioned, you'll find though you do get 100% thrust in reverse, it's not rated for continuous duty this way. All this statement (100% reverse thrust) means is, the reverse gearing isn't reduced, like it is on other transmissions.

 

Thanks for bugger all. As a 23 year diesel fitter, I have seen my share of jobs where more research could have been done. I have also done all the research on the mechanical side of what im proposing, thats not what im asking about so please stop answering questions im not asking . It has come from Tony at Seaboard Marine, and the ZF repair manual that the trans can run at the same torque and ratio in either direction.

 

There is very little difference in performance between 3 and 4 bladed props, if they are designed for the same condition. There will be a slight pitch difference to get the same performance, but assuming the other variables are the same, no noticeable differences in performance.

I don't understand Fred's comment about induced drag, which is basically lift squared over aspect ratio. Given equal total lift divided over 4 blades vs 3, with higher aspect ratio "wings", the induced drag of a four blade prop is less. There is higher parasitic drag with four blades, but for equal thrust and with equal blade area, efficiency should be equal.

 

There will be reduced vibration and generally, smoother running gear with a 4 blade.