Imco sc lower causing ventilation
 

Just switched from scx upper/bravo xr lower to a scx upper/imco sc lower and having planing issues. Prop starts to ventilate at 3k right when boat wants to roll over. Used to plane without tabs, now even dropping tabs I’m struggling. Same props same everything. Anyone have any insight?

Different design cavitation plate ?

Nope. Literally the only change is the lower

Maybe try something like Max Machine works add on plates ? If they makem for those drives. Have had good reviews here and elsewhere.


https://cimg1.ibsrv.net/gimg/www.off...d471fc01c.jpeg

Think I figured out the problem. Now do I want to.chase it? The scx upper xr lower combo basically had a double cav plate. And the space between prop and plate were pretty tight. Now I have a big gap with just the upper cav plate. So chase it with a bigger diameter prop? Max machine wedge? Or scrap it and go back to a xr lower.

what happened to your other thread about this issue

Mixed terms here. Cavitation is the prop boiling water due to low pressure on the side of the blade causing loss efficiency and pitting of the prop. Ventilation is the props sucking in air from surfacing. Those plates on drives are ventilation plates but I guess people interchange the terms.

Changing your lower unit probably raised the X-Dimension of the prop shaft height and now you are surfacing the prop perhaps? Adding a spacer to drive the prop lower?

No still at 4.5"

Well I bought the max worx Batwing. See what happens. He is pretty sure it will do what I need. If that doesn't work, then I'll.have a new sc lower for sale lol.

Curious to see how that works out for you
Post results. Hope it works for you.

Will.do. Should.have mid week, test on Friday if weather is good.

Did you try what I suggested in the other thread you must of deleted, to remove the stud and nut thats sticking down below the bottom of the drive and replace it with an allen head so its flush with the bottom,

I didn't delete. But yes, I tried that. No difference. Called Brett@bblades, called Max, called Fred @imco. And the only person who had some positive input was Max. Fred was zero help, which pissed me off since I bought lower direct from imco. Spend $5k and get zero help with issues. Not cool.

sent you a pm

Thanks

well, took it out today. Same issues. The 28 bravo ran good once I got it on a plane but it took forever to get on a plane. To the point where it almost didn’t want to. Tried turning to port, and that did make the prop bite but then as soon as it bit it seem to spin out again. Tried slowing down to let my wake push me over that worked OK but still took forever to get on plane. my last try is this Max machine works plate. If that doesn’t work I’m about done. Just go back to the XR lower. once on plane it seems to act pretty good I’m getting 50 miles an hour at 3900

Well between changing stud to flush Allen head and adding the max machine batwing, all.is good again. Get on plane without tabs and runs like a champ.

Glad I could help.

You where nervous this wasn’t gonna’ fix the issue huh ? :wink :)

I’m having the same issues with my boat… went from bravos to imco scx/sc and now I boat won’t plane. What fixed your issues?

Max Machine Worx out of Havasu sells this cav plate. I haven't tried one myself.

https://cimg0.ibsrv.net/gimg/www.off...5e7a9acaa8.jpg

You missed post #17. :)

Need some more info, the sc lower std -1 -2 ? do you have the imco splash plate ? drive shower ?

Imco scx upper/sc lower. The lower is a -2. Have tried it as a -2 and with a 2 inch spacer. Have tried numerous props and come back with pretty much the same result. Boat had bravos on it before the switch over to imcos.