RB190 on the water

[Ka'King]

Made this video this weekend at Table Rock:

[samck96]

What Prop are you running and do you have the Command Thrust lower unit?

[Ka'King]

What Prop are you running and do you have the Command Thrust lower unit?

I have a 20p LaserII at 3 1/8 below pad. I do not have the CT lower unit.

[samck96]

I have a 20p LaserII at 3 1/8 below pad. I do not have the CT lower unit.

Was that full speed/ WOT on this run? thanks

[Ka'King]

Was that full speed/ WOT on this run? thanks

Yup, that was about all she had. It's only got just over 4 hours on the motor...and I haven't played with engine height much. I don't believe it has much more, if any though.

[samck96]

I believe your RPMs were a little low. Well, compared to mine at least. I remember Don (or some other mechanic) from the 4 stroke page on BBC saying you want those up past 6k a little more. I've got the CT lower unit on my boat and I run a 20" PowerTech. It revved out at around 6250 at 48 ish mph. You may consider raising the motor some more or going down in pitch.

That is one sweet and spacious boat.

[samck96]

I believe your RPMs were a little low. Well, compared to mine at least. I remember Don (or some other mechanic) from the 4 stroke page on BBC saying you want those up past 6k a little more. I've got the CT lower unit on my boat and I run a 20" PowerTech. It revved out at around 6250 at 48 ish mph. You may consider raising the motor some more or going down in pitch.

That is one sweet and spacious boat.

I may have misspoken a little. You got up to 5900 rpm. That isn't out of spec, but there is definitely more to be had. The real issue I just realized is the amount of prop slip you've got on this setup as of now. 5900 rpm at 41.9 mph with a 20" prop and 2.07:1 gear case gives you 22% slip.

[Ka'King]

Thanks! What can I do about that slip? I’m sure I can come up some. I just got the water pressure sensor so I can keep an eye on that.

[n2ratfishin]

Gotta love the low fuel burn rate. Great music choice on the video.

[samck96]

Thanks! What can I do about that slip? I’m sure I can come up some. I just got the water pressure sensor so I can keep an eye on that.

Slip can be caused by a lot of things. Turbulent water/not enough setback, JP too high, not enough cup in the prop or different blade geometry. Id start with trying a 19" prop with a little more cup.

[quikcarl61]

I've got a 16' with the 4 stroke 115, 4" setback, 3rd hole from top. With a 17 pitch aluminum prop it runs right at 45 at 6000 rpm, I'm happy with that plus I can maintain plane at 2200 rpm

[flranger]

Spitfire x7 21p is the best prop I've found. 52.7 GPS @ 5850 RPMs (NMEA data). Trolling motor off. Light load.

[Ka'King]

I ended up trying a 17p Q4...huge change in acceleration and bumped top end by 4MPH to 45.9. This was with the same load as the video above. With summer heat and a normal load of another person, I expect the RPMs to come down a little.

h2o.png

[samck96]

That is much better. I hope you're still enjoying that rig!

[Surferboy120]

In the beginning of the video I saw the side view of the boat and motor. That motor with the silver paint for the lower unit should be the command thrust option if I am not mistaken. The non command thrust optioned boats are all black lower units. Am I missing something here? I have the same motor with command thrust option and looks identical to yours.