Walleyehed, Dhadley, help on setup

[Rudy Brown]

On my 84 16ft bass boat, I finally got around to lifting the motor to the 4th(highest) hole. I didnt find to many R's between the 2nd and 3rd hole. (2nd 5k vs 3rd 5200) If the 4th hole is too high, what is my next step in getting the rpm's up? Prop now is OMC 13.25 X 19 SS. Should I really be looking at a turbo 13.25 X17 SS? And since I lost a little water pressure (still 20 psi @ wot) I'm assuming I'll lose more now in the 4th hole. How do I block off the upper hole and will the lower 3 be enough. Or at what PSI do I need to block off the hole/ safe to run at wot? Oh, one more, what causes the rooster tail on fast boats? The prop running on the surface of the water? Thanks.

 

[walleyehed]

Re: Walleyehed, Dhadley, help on setup

If you've lost some water pressure, it's time to plug the top hole on both sides..
The lower 3 is plenty. I drilled another hole below the fourth where the 1/8" drain hole is, then tapped and plugged the top 2 with allen head machine plugs.
If you shape the ports leading into the holes just right, it will increase pressure slightly.
As for a prop, in 13 spline I think you'll be looking at a Stiletto, from precision also...

 

[Dhadley]

Re: Walleyehed, Dhadley, help on setup

I'd have to believe that a 19" on a V4 90 and a 16' bass boat would be about right. Are we sure the motor is running OK? How about the tach -- are we sure it's accurate? What brand is it?

As for the rpm gains, I think 200 is pretty normal for going up 3/4". Keep us posted on your progress.

 

[walleyehed]

Re: Walleyehed, Dhadley, help on setup

I was going to mention the RPM rise, and I forgot about it when I posted...I've found 75-100RPM per hole is great, if you got 200 that's super. That 1 move was like dropping pitch 1" but increasing speed....efficiency going up.

 

[Rudy Brown]

Re: Walleyehed, Dhadley, help on setup

Ok, i'm back from testing. 4th hole on motor, planes nice and WOT= 5200rpms @ 42.7mph. WOT with trim= 5600rpms@ 39mph. :% What happened? Is the prop starting to blow out?(13 1/4 x 19 SS) As I'm trimming, I hear the motor reving just past 50% trim but the speed goes down. I had to place duct tape on the top water hole so not to lose pressure. WP started flucuating during the test runs, especially in the turns but never lower than 10psi. Flound out at dock the tape blew out and was flapping. Things I know: 1: thread and plug upper water hole. Whats my next step?? Thanks guys.

 

[Dhadley]

Re: Walleyehed, Dhadley, help on setup

It sounds like the 4th hole is slightly more height than that prop needs. Basic rule -- if you can use all the trim range, the prop can probably use more height. If you can use about 75% before the prop vents, that's about right (depending on hull type). If you're venting at 50% and losing water pressure, the motor needs to come down a hole. Don't forget, this is just a very general guideline, each boat / motor / prop combo is slightly different.

Now we have a couple of choices. Personally, I'd go down a hole and test. Compare that to the baseline, as you did before. Once the set up is maxed out for that prop then we might look at a prop with more technology.

Or you can leave the motor up and test another (better) prop. Naturally your plans with the water inlets is still a sound choice.