Whats my next step?

[tgell001]

I have a StingRay 180RX with a 3.0L 135HP engine with a Volvo SX outdrive. I have been getting serious about wakeboarding (not really serious but enjoying it a lot and progressing). I have a 6ft insanity pylon that works great and I'm currently making enough wake with the right trim to get 4-5ft of air. I just bought and got in the mail two 350lbs LaunchPad ballast bags and I have cleaverly placed them with one in the bow and one infront of the bench. I havn't tried this set up yet but I will be testing it this weekend. I know I am pushing the HP and weight limit with my measly 135hp but I think it can be done since I get up effortlessly with 4 normal sized guys in the boat. But, my question is whats my next move? Prop? Hydrofoil? or trim tabs?

I currently have a 21p 3 blade that isn't too shabby but i'm looking at a michigan wheel 4blade 18p.... good idea?

Or, should I go with a hydrofoil or trim tabs?

Anyone have any experience with trying to do the best with what they got?

 

[stimps]

Re: Whats my next step?

A five blade prop is a real big improvement. I also looked at the michigan wheel 4 blade but was lucky to get a mercury high five second hand. Trim tabs do not promote a good wake shape so not really a great addition for what you are trying to achieve. Not tried the hydrofoil on an I/O but never heard much positive about them either. Lots of boats wakeboard in same area as myself and use just a tower and prop change with 3.0 engines.

 

[tgell001]

Re: Whats my next step?

I'm just afraid with the 5 blade that i'll lose all my top end. I really want to be able to jump out of the water with 700lbs of ballast and a few friends yet still be able to break 40mph. Which is reasonable since i can do 49mph with just me and my girlfriend and a half a tank of gas. Also, my concern with a 5 blade is the rotational weight will bog down my no torque having 4-banger.

Also, how much difference do the degrees of pitch really make? like would 18 do the trick of should I go more like 17 or 16? And is over reving a problem if i stay moderate with my pitch selection?

 

[skibrain]

Re: Whats my next step?

a. Knowing what your RPM at WOT is one of the first questions you will get asked, so you should check that next time you are out.

b. What is the your current prop made of? Aluminum? Stainless steel? Original equipment with the Volvo outdrive?

c. A GPS speed is preferable for accurate info. Speedos are notoriously off.

d. Know what your recommended engine max rpm is. You don't want to over rev when you prop down...and you will likely be able to do that at WOT. If you are the driver and know that or can instruct others to keep an eye on it, not as much of a problem.

Assuming you go up to same rpm with each prop. but stay with the same type of prop, the math on comparing pitch in theory is what I have below (prop pitch is defined as the distance the prop would travel through the water in one rotation if there was no slip). 21" pitch will go further (faster) in one rotation than an 18" will.

18"/21" = 85.7% 85.7% x 49 mph = 41.9 mph @ XXXX rpm
17"/21" = 80.8% 80.9% x 49 mph = 39.6 mph "
16"/21" = 76.1% 76.1% x 49 mph = 37.3 mph "

If you post this question in the prop section of the website, someone will have more insight into the additional info involved with adding number of blades, or changing prop material.

 

[stimps]

Re: Whats my next step?

I'm just afraid with the 5 blade that i'll lose all my top end. I really want to be able to jump out of the water with 700lbs of ballast and a few friends yet still be able to break 40mph. Which is reasonable since i can do 49mph with just me and my girlfriend and a half a tank of gas. Also, my concern with a 5 blade is the rotational weight will bog down my no torque having 4-banger.

Also, how much difference do the degrees of pitch really make? like would 18 do the trick of should I go more like 17 or 16? And is over reving a problem if i stay moderate with my pitch selection?

I went to same pitch on five blade as I had on the three blade and have almost identical if not identical top speed suprisingly. The difference is the extra bite out of the hole and holding in turns. Pretty sure the diameter is smaller which probably counteracts the increased blades. The rotational weight has no difference, compared to the effort (power) that goes through trying to turn the prop in water the weight is nothing. It's a bit like changing one steel on your car to one ally, nothing it would notice. With the data below I would think a 19 or 21 pitch four or five blade would be a half decent bet which I have two friends using one of each on there 3.0 (Don't know gear ratios).

 

[tgell001]

Re: Whats my next step?

Turns out my neighbor owns a prop shop here locally and over a few beers came to the conclusion that a 4 blade mercury 18p prop for 140 w/ the hub kit is going to be the way to go and if i dont like it i'll try something else free of charge. So, its nice to know people!

also, have anyone out there done a good job shaping their wake on a I/O of similar size? and if so how'd you distribute the ballasts?