3 or 4 blade

[Rellik546]

First time posting on iboats, have read alot of threads, and sticky notes. i just bought a 1988 wellcraft 170 classic with a 3.0l mercruiser with an alpha one outdrive. it currently has a quicksilver 1912p17 3 blade prop on it. the boat weighs 1950 dry. i have a few questions, first of all we mostly wakeboard, kneeboard and tube. the boat sits 8 and i would expect to normally have 6 or 7 people. I have not used the boat yet, so i donno know WOT at the moment. top end isnt a priority but would be nice to have some . so my questions are

1, 3 blade or 4 blade (for boarding and tubing) better pull/turning/holeshot? i also read that 4 blades arent recommended for i/o in the prop buying guide, why is that?

2, with my current prop what would be the top speed? 35-40mph? just a guess or if you have a similiar set up

3, and what would be a good pitch mainly for mpg/cruising?

I wished it wasnt winter so i could run the boat and give a WOT. i mostly care more about if a 3 blade or 4 blade is better for cruising/pulling a rider along with a full boat

 

[steelespike]

Re: 3 or 4 blade

Depending on the design of your boat speed would be expected to be around 40-45 lightly loaded with a prop about 21-23" pitch.This prop wouldn't likely work very well for skiing boarding etc.
I never heard of the 4 blade not reccomended for an I/O. It is very likely that with the load and activities you suggest that a 4 blade would work really well to improve hole shot,stay on plane with less throttle, handle better on plane and at the dock.Probably would be about a 17" pitch.
Your results with your present prop setup will tell us what you may need.
In the mean time weather permitting you might do a compression check,be sure the throttle opens all the way.

 

[Rellik546]

Re: 3 or 4 blade

Thanks steelespike. the boat currently has a 15 x 17 pitch 3 blade prop. im assuming that prop was probably used for 3 or 4 people in the boat, so if i have 6 to 8 people, i could probably keep the same pitch in a 4 blade prop because its a heavier load. for the same load you would decrease 1 degree in pitch switching from a 3 blade to a 4 blade. i was planning on doing a compression test. in the process of cleaning her out. the previous owner was meticulous with mechanical tuning, however lacked in keeping the boat clean so shes getting a good scrubbing to remove mildew, scum, and crap.

 

[steelespike]

Re: 3 or 4 blade

I would be interested to see how it performs with the 17 and a light load.

 

[Rellik546]

Re: 3 or 4 blade

you mean if it would exceed WOT? why would you be interested in how it would perform with a light load? i dont really plan on having a light load. unless i go fishing with my brother and my dad but i wouldnt be running wot, just putting around from shoreline to shoreline. (Connecticut river in MA)