Props

[Janky]

Just trying to stir up some conversation... Our 20' Chaparral came with a 15x16 and a 14.5x18 backup in the engine compartment (both 4 blade). I was surprised the top speed as configured was a little slow at around 40mph. Did a little googling and it appears that smaller pitch and bigger diameter would give better acceleration and lower top speed. I suppose that's good for wakeboarding.

The 15" prop is a bit worn and I like to run our the boat once a month instead of winterizing, so I went ahead and swapped to the backup.
Whatcha all think?

I'm guessing it will be a little slower to plane, but a higher top speed.
The one thing I'm curious about is how different the ride will be at wakeboard speed. The Chappy rides bow quite high at wakeboard speeds. I wish I could change it but I doubt the prop will make much difference.

 

[Denny]

You can change the boats attitude with trim tabs, it will ride like a totally different boat.

 

[Janky]

Thanks @Denny . I actually installed some 'automatic' (compression spring activated) trim tabs that do settle the bow down a bit. Unfortunately, they also create a bunch of turbulence in the wake, which I really don't want. I took them off but the mounting hardware is still there. Now that I have the perfect pass, I might give them a shot again.

 

[Denny]

What kind of turbulences do you have, do you have them mounted correctly?

 

[Janky]

Good question. I followed the instructions and tried to align them perfectly with the bottom edge of the stern.
See attached. Look at the bottom edge of the attached with file with_tabs3.JPG and you'll see they kick up some water and make the wake a little choppier, in my opinion. See "without4.JPG" to compare what the wake looks like with the trim tabs off.

 

[Denny]

What you are seeing is normal when using trim tabs. When they are parallel to the bottom there will be no center hump. The further down they are deployed, the bigger the hump, because they are no longer in parallel with the bottom, and are now creating drag trying to lift the stern of the boat.
I have Bennett tabs, and are adjustable to my needs.
The video and photo were taken with the tabs fully deployed at about 18-20mph.

 

[Denny]

 

[Janky]

Thanks @Denny I'll put them back on and try changing the setting. I believe I have 5 settings and only tried one or two of them.

 

[Denny]

How much tab you will need is determined by many factors, speed, wind, current, waves, weight and how it is displaced in the boat, and towing people on toys.
Are yours determined by speed or are they fixed, with a pin position?
I noticed that they seem to be close to the center of the boat, is that how they said to mount them?
I know that adjustable tabs are expensive. They give you the ability to fine tune your tabs individually to your specific needs at the time.