yes another prop question....

[dexterlapua]

Hi all! i am new to iboats and new to forums all together.
Heres my question....I have a 97 rinker 18' open bow, its my first boat. the boat has a 4.3l lx merc alpha one. The boat came with an aluminum 3 blade 15x17 prop, i can only go half throttle before i reach 4800 rpmsand 30 mph. I used a friends 3 blade aluminum 14x19 pro and now about 3/4 throttle 4600rpms and 39 mph. I am considering a 4 blade aluminum 14x21 would this be a good choice or should i stick with three blades? Oh ya the boat always has 4 ppl and 15 galllons gas and planes off really fast with the 17 and 19 prop, top speed is not my goal i want to go around 45-48 mph and still pull a tube every once in a while

 

[steelespike]

Re: yes another prop question....

Is your speed by gps?
The safe way to prop a boat is to set it up so it reaches its recommended wot rpm.
That way if someone else runs the boat they won't over rev it.
running with too light a prop wastes gas and allows the motor to run at too much rpm in relation to speed increasing wear over time. Guessing your throttle setting doesn't give us any concrete indication to what prop maybe right.
The 4 blade 21 will lower your rpm yet maintain hole shot and ability to stay on plane at reduced throttle.
Without actual wot rpm with the 19 there isn't anyway to tell what prop you need.
If the 4 blade 21 over revs you'll need to be sure any operators know to be careful.

 

[dexterlapua]

Re: yes another prop question....

thank you for your reply, my speed has been verified by gps, both on my phone and a garmin. My rpms are from my tach that is on the boat i have never had it checked but being around cars all my life the engine sounds like its at 4500 when the tach says its at 4500. not saying that it may be off a little bit but it sounds really close. Why dont more people use 4 blade props it seems like the majority are using three blade? is there a big disadvantage i am not seeing?