3 Prop comparison with data

[fishfearme]

Background: past fall the 4.25 lower unit had a gear let go. For 15 years I've been running a 3 blade SS quicksilver 13x18P 1/4 hole vented prop. Boat is used for skiing and fishing. From my perspective, that was a great setup, nice holeshot and top end (bump 48mph @5500). Based on Merc XR4 manual, rpm should be 5000 -5500.

I picked up a lower leg off a mid 90's 200hp, 4.5" lower with 2:1 gear - and the prop hunt began.

Friend and I went out tonight ad tried out three props as detailed below:


Observation:
Turning point Max rpm was difficult. Did not have a cliff in the trim, but I also was not going beyond 5800 RPM either - it did not blow out. The QS 3B and 4B both cavitated about 100 RPM above the RPM noted. Merc prop slip calculator is 11% for the 19P, 19% for the 21P

To stay withing the 5 -5.5K RPM band, I think I'll enlarge the QS 4B vents to 5/16 and acquire a 14x23P 3blade vented for trial.

Does having a (near) knife edge help in performance? The QS 3B had an edge, not sharp, but not square like the al props which were both new. i realize the SS can have a thinner blade than the Al props.

Thought/comments from experience?
Am I far off in my thinking?
Will going to 23 only increase slip? Next time, I'll catch the RPM at a lower speed, say 40mph.

thank you in advance

[Magcat 62]

A mid 90 200 are 1.87 gearing not 2.1

[fishfearme]

2:1 spinning the driveshaft and counting the prop turns.

In addition, the replacement lower is 3/4in longer. Moved the engine up 3/4 and will try again.

[ssv1761982]

If you are skiing I would prop it to run closer to 6k. Try a quicksilver stainless 19 or even drop to a 17 for skiing and tubing.