prop / jackplate questions

[Waco]

I have a 15.5' blazer bass boat, with a 70hp OB. I have not owned it very long (3 months) so i cant answer "historical questions" about it. My problem is getting the boat to run WOT at the desired RPM range which is 5500. There is a manual 6" jackplate installed. When i bought the boat, he had a 17"p prop on it, and the cavitation plate about 3.5 inches above bottom of the boat. With this setup, and ONLY me in the boat, i can reach 5500 RPMs using the trim, but cavitation (ventalation?) becomes a problem. Yesterday i was on the lake and did some tests. I removed the 17p prop, and put on a 15p prop. I couldn't get the boat over 3500rpms without cavitating. I came back in and lowered the motor/jackplate about 1.5 inches. With the 15p installed, and the motor lowered, i could only get 5100rpms out of the motor, and the nose of the boat wanted to dig in the water, making the ride fairly rough and wet.

The original prop is a 14p which i am currently having rebuilt. I think my simplest solution is to remove the jackplate, put the 14p on, and set the motor down where the cavitation plate and bottom of the boat are fairly square. I need some suggestions from you guys, i am taking my family fishing for a week in the near future.


thanks for reading, sorry for the long post.


-craig

 

[Esox]

Re: prop / jackplate questions

What kind of prop is the 17p? Certain styles of props will run at higher engine heights than others. Also, do you have power trim?​

 

[studlymandingo]

Re: prop / jackplate questions

I would use the jack plate, if you get it set up properly it should make the boat perform better than without.​

 

[Waco]

Re: prop / jackplate questions

the 17p is SS and cupped, but I don't recall the name..i know it's not a popular namebrand, or i would have remembered it. The 15p is aluminum.

I went out last night and moved the motor to the lowest hole, and set the jackplate down as far as it would go, and i still have right at 1 inch difference between AV plate and the bottom of the boat.

i do have power trim, and a trim gauge.

 

[t.martin]

Re: prop / jackplate questions

Sounds way to low to me. I have never seen a bass boat with motor on bottom hole and jackplate all the way down. I guess it depends on what you are looking for ; speed, holeshot, or fuel economy. Blazers are made for speed. fastbass.com is a good site for your boat setup.