3 to 4 blade changeover on twin screw

[Benny67]

I've been thinking about swapping to 4 blade props on my 27ft Carver in hopes of getting it to plane out faster than it has been.

My thought is that 4 blade props would get the boat out of the water easier than a 3 blade and hopefully allow me to plane out easier than the boat does now.

I am running 14x19 props now and want to do the same but with 4 blade...actually the 4 blade would be 14.5 x19 my props on there now are old ones. I don't think they make the 14" anymore.

I am reaching WOT recommendations as per my manual now with this pitch and my top speed is somewhere in the ballpark of 27MPH. I usually cruise around 3600 rpm at 21-22 MPH. I can sacrifice 1 or 2 mph if need be if I could get the boat to plane out at 2700 rpm or so.

Thoughts?

 

[Sea Rider]

Wot achieved ? was while lightly, mdium or heavily loaded and inside min, middle or max wot rpm range with a 3 blade prop ?

Happy Boating

 

[Benny67]

WOT is as to be expected...boat runs as expected...no troubles. I just would like to get up on plane easier. It's a heavy boat for a 27 ft....Carver makes em thick and durable. probably around 6200 lbs dry.

My hope would to plane out faster than I am...and yes, I am using trim tabs, my bottom paint is fresh and no barnacles.

Im just wondering if it would be worth spending the extra cash to go to 4 blade props to get the boat to lift and plane out easier. I'm not concerned with top end. I rarely go over 20 mph. I have had the boat up to around 27mph and it had a bit more to give...I just don't like to run the engines hard. I am really smooth and easy on my boat and would like to achieve plane on less revs and less time.

 

[batman99]

I replaced factory 3-blade 19P aluminum with 4-blade aluminum props on my 16.5 ft bowrider. The 4-blade did create more stern lift on my boat's heavy weight rear. And, much faster to plane as well. For my boat, I went from 3-blade 19P to 4-blade 15P (for tubing / towing) and 4-blade 17P for long distance tours. For mixture of both usage conditions (and too lazy to change props), I'd use the 4-balde @ 17P. If going from 3-blade to 4-blade, many folks recommend lowering 1 P. And if going from normal 3-blade to cupped 4-blade, go down 1 P "more" as well. Thus, why I went down 2 Ps (from 3 to 4 blade - to obtain same WOT RPM range). Which 4-blade aluminum to get? Very hard question to answer - since one size doesn't fit all. If wondering, I like the Solars Amita-4 Aluminum props. They are low cost (compared to other brands) and low cost to replace - when one dings them up as well. For dual props, 1 prop should be left and other should be right rotation design. For me, I buy props from iboats.com store. Hope this helps in your research...

 

[Benny67]

Thanks for the input batman...I was actually going to buy the Solars 4 blades from Iboats...the price is definitely right.

Also,

My boat has both screws turning standard direction...I never heard of it before I bought this one but apparently it's not that rare. I am also wondering about the 4 blades affecting the steering torque.

I might wait it out till next season and give it a try.

 

[Sea Rider]

On previous posts OP has not said a word about wot rpm, that's the first thing one must know well in advance before venturing blindly guessing playing with props and pitches which is bad for the engine...

Happy Boating

 

[batman99]

Thanks for the input batman...I was actually going to buy the Solars 4 blades from Iboats...the price is definitely right.

Also,

My boat has both screws turning standard direction...I never heard of it before I bought this one but apparently it's not that rare. I am also wondering about the 4 blades affecting the steering torque.

I might wait it out till next season and give it a try.

For lots of good info on Prop performance (and opposite rotations), surf entire page @ http://www.iboats.com/basics/propeller_basics.html#left_handed

Always best to call iboats Sales folks to confirm your unique prop needs - before buying online.

Hope this helps as well....

 

[Benny67]

On previous posts OP has not said a word about wot rpm, that's the first thing one must know well in advance before venturing blindly guessing playing with props and pitches which is bad for the engine...

Happy Boating

Read post #3

I'm not guessing blindly....I have the stock propeller setup as per my manual right now...and the boat is meeting it's redline expectations and operating as expected.

It's a simple question of 3 to 4 blade changeover...

I am really looking for others who have ventured into the 3 to 4 blade changeover and their thoughts.

 

[Benny67]

For lots of good info on Prop performance (and opposite rotations), surf entire page @ http://www.iboats.com/basics/propeller_basics.html#left_handed

Always best to call iboats Sales folks to confirm your unique prop needs - before buying online.

Hope this helps as well....

Thanks...

The rule of thumb is drop 1 degree pitch if you are going from 3 to 4 blades..The real bummer of it is if it's not doing what you like you usually cannot return the prop.

After a bit more thought, I might actually switch my port drive to a CCW and see if it makes a difference in handling and getting up on plane. I have read that boats that do not have the opposing props handle much different than the ones that do. Meaning, docking and turning are much easier. My boat is the only one I have ever operated with twin screws so I have nothing to compare it to.

 

[jakedaawg]

For stern lift you would idealy want the starboard to be ccw i believe. Depending on what you have its not terribly difficult to couter rotate.