New Lower now its Cavitating

[50onRED]

I got a -2 Imco lower for my 27 daytona and tested it this weekend. This is suposed to be the correct lower for my boat. At some point a previous owner put a standard sportmaster lower on it which is 2" taller than this new imco unit. ive run into Two issues,
1: My time to get on plane is substantially longer, like uncomfortably long.
2: My tried and true 26p 4 blade Labbed Bravo prop is all the sudden cavitating when im trying to get on plane. I also have a 30p 5 blade that almost wouldnt plane out at all when it used to run just fine on my old lower. Both props cavitate and the 30p was taking every ounce of power I had just to get going a little. I managed to feather the throttle and get it flat but it took far too long.

HELP!

 

[HullofaTime]

What made you go -2? That sounds like the issue for the cavitation now.

Have you verified there is no reason the trim is not fully dropping now?

 

[RiverDave]

I got a -2 Imco lower for my 27 daytona and tested it this weekend. This is suposed to be the correct lower for my boat. At some point a previous owner put a standard sportmaster lower on it which is 2" taller than this new imco unit. ive run into Two issues,
1: My time to get on plane is substantially longer, like uncomfortably long.
2: My tried and true 26p 4 blade Labbed Bravo prop is all the sudden cavitating when im trying to get on plane. I also have a 30p 5 blade that almost wouldnt plane out at all when it used to run just fine on my old lower. Both props cavitate and the 30p was taking every ounce of power I had just to get going a little. I managed to feather the throttle and get it flat but it took far too long.

HELP!

I’d try a larger diameter prop first.. but I suspect you just figured out why the previous owner put a longer lower on it..

Maybe try a -1?

 

[ChrisV]

Can you add a spacer back to what it was and try it?

I would bring this to the lake.

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[Motoxxxloak]

This is interesting. I have a 26 Daytona (same bottom as you) and had a -1 on it before. It was decent but I was always trying to play with props and find the right prop, have multiple props for different occasions etc.

Went back to a standard XR lower and was honestly the best decision. I am sure it has something to do with the x-dimension. I use my 28p. It will prop up in half a second when its got 2 people, fuel and ice chests or a few seconds with 6 people and more ice chests....

Been thinking about going to a -2 but didnt want to deal with the issue you are having.

 

[GETBOATS]

The the closer to the waters surface with the propeller shaft the more likely you'll experience ventilation, larger blades, more rake, cupping can help. So I'd go down the road of props first. It should grab however when throttle is fist applied and then vent. Cavitation can lead to ventilation but I don't think that's what's happening.

BTW: cavitation is formation of vapour bubbles within a liquid at low-pressure regions that occur in places where the liquid has been accelerated to high velocities

this is evidenced by an actual wear pattern right where this low pressure occurs, behind a drain plug for instance. water actually boils and erodes metal.
happens on propeller blades as well.

 

[rrrr]

The the closer to the waters surface with the propeller shaft the more likely you'll experience ventilation, larger blades, more rake, cupping can help. So I'd go down the road of props first.

Changing to the Imco lower caused the ventilation. Why should he fool around with changing props? It seems obvious the -2" lower is the problem.

 

[GETBOATS]

I'm not a stern drive guy but the principles are the same, the higher the propeller shaft the more efficient the package is. Why not try to make it work, he might uncover the right combination, Ive never had a boat that didn't ventilate some coming on plane. That just told me height was close. If his plane is just a family boat, the bury the drive.

 

[Shlbyntro]

I'd start by playing with some larger prop setups. if you can't make it work to a satisfactory level, add a 1" spacer and start the prop testing over

 

[hallett21]

You can have hole shot or you can have efficient cruise/higher top speed. Can’t have both in an I/O.

 

[Fastdadtsmith]

Do you have a cavitation plate? We did the larger max machine tail on our -2 and it really helped

 

[rivermobster]

Changing to the Imco lower caused the ventilation. Why should he fool around with changing props? It seems obvious the -2" lower is the problem.

Maybe, maybe not.

I tell people this when they talk about building an engine...

It's like a symphony. Everything Has to work together! If you change just one thing, you have to alter everything related to it, as well, to keep Everything in tune.

So maybe the prop? Maybe different gears? Trim position? Cave plate position? Throttle position?

Being the conductor of a whole symphony, aint easy peasy.

 

[575cat]

inch spacer would be the cheapest to start with

 

[mattyc]

I got a -2 Imco lower for my 27 daytona and tested it this weekend. This is suposed to be the correct lower for my boat. At some point a previous owner put a standard sportmaster lower on it which is 2" taller than this new imco unit. ive run into Two issues,
1: My time to get on plane is substantially longer, like uncomfortably long.
2: My tried and true 26p 4 blade Labbed Bravo prop is all the sudden cavitating when im trying to get on plane. I also have a 30p 5 blade that almost wouldnt plane out at all when it used to run just fine on my old lower. Both props cavitate and the 30p was taking every ounce of power I had just to get going a little. I managed to feather the throttle and get it flat but it took far too long.

HELP!

I'm betting the 5 blade 30 is too much. Obviously the lower change is causing the cavitation problem. Option 1 is to go back to standard lower. Option 2 is to continue working with it to get it to work well, as long as you see benefit on the top end. That may be difficult with your driveability problem mentioned in your other thread. May need to get that sorted out first. Since you now have the -2, if it were me I would try some other props and maybe the whale tail deal. I have a couple of props I will lend you for testing that may suit you; a labbed b1 30p and a 4 blade cutting edge 27p with a good amount of cup that may help. Let me know, both props are in havasu, I think we'll be out next week and weekend

 

[RiverDave]

Can we start from the beginning here? What motor / HP is in the boat.. If you are running 90 mph and below you don't need any of this shit to begin with.. You are going to see zero to minimal gains, and it will just take longer to get on plane.

If you are running 90+ and are looking to capitalize on more top end, then I'd start heading down the -1 / -2 route and playing with props and can plates etc..


RD

 

[Bigbore500r]

I got a -2 Imco lower for my 27 daytona and tested it this weekend. This is suposed to be the correct lower for my boat. At some point a previous owner put a standard sportmaster lower on it which is 2" taller than this new imco unit. ive run into Two issues,
1: My time to get on plane is substantially longer, like uncomfortably long.
2: My tried and true 26p 4 blade Labbed Bravo prop is all the sudden cavitating when im trying to get on plane. I also have a 30p 5 blade that almost wouldnt plane out at all when it used to run just fine on my old lower. Both props cavitate and the 30p was taking every ounce of power I had just to get going a little. I managed to feather the throttle and get it flat but it took far too long.

HELP!

One thing to check - Is your X-dimension the same as other 27 daytona's that are successfully running a -2 IMCO ? Check a few other 27 daytonas and see.
You could also call eliminator and see if they can give you some info on what they came out of the factory with, and if there were any out there rigged at different dimensions.

The reason im asking, is because if you find it is rigged higher, that might explain why your boat doesn't run well with a -2 lower.

It would be nice to understand why the -2 doesn't work when it does for others. Just something to check, that doesn't cost $$$

 

[Bigbore500r]

Can we start from the beginning here? What motor / HP is in the boat.. If you are running 90 mph and below you don't need any of this shit to begin with.. You are going to see zero to minimal gains, and it will just take longer to get on plane.

If you are running 90+ and are looking to capitalize on more top end, then I'd start heading down the -1 / -2 route and playing with props and can plates etc..


RD

I remember when you played with a shorty lower on the Schiada.
That was no bueno

 

[50onRED]

One thing to check - Is your X-dimension the same as other 27 daytona's that are successfully running a -2 IMCO ? Check a few other 27 daytonas and see.
You could also call eliminator and see if they can give you some info on what they came out of the factory with, and if there were any out there rigged at different dimensions.

The reason im asking, is because if you find it is rigged higher, that might explain why your boat doesn't run well with a -2 lower.

It would be nice to understand why the -2 doesn't work when it does for others. Just something to check, that doesn't cost $$$

I did all the research long before I bought the lower. According to Eliminator my boat came with a -2 lower. I have reason to believe the previous owner blew it up and found a cheap sportmaster lower to throw on it. The x dimension is technically perfect for the boat.
I’m having the prop worked on a little which should give me less cavitation.

 

[50onRED]

What made you go -2? That sounds like the issue for the cavitation now.

Have you verified there is no reason the trim is not fully dropping now?

Went with the -2 because it’s what my boat had on it from the factory.

 

[50onRED]

I’d try a larger diameter prop first.. but I suspect you just figured out why the previous owner put a longer lower on it..

Maybe try a -1?

I just dropped my prop off at Cutting Edge. Augie seems to think it needs more “cup” and might be a reason for the cavitation.

 

[50onRED]

The the closer to the waters surface with the propeller shaft the more likely you'll experience ventilation, larger blades, more rake, cupping can help. So I'd go down the road of props first. It should grab however when throttle is fist applied and then vent. Cavitation can lead to ventilation but I don't think that's what's happening.

BTW: cavitation is formation of vapour bubbles within a liquid at low-pressure regions that occur in places where the liquid has been accelerated to high velocities

this is evidenced by an actual wear pattern right where this low pressure occurs, behind a drain plug for instance. water actually boils and erodes metal.
happens on propeller blades as well.

Yeah my prop guy is working on one of my props right now to put some more cup into it.
What I’m feeling is, hard push at the beginning, then slipping that comes in and out. I have to feather the throttle to get it to settle down.

 

[50onRED]

I’ve got my labbed 26 at Cutting edge now for Augie to add more cup to it. Next up will be a 28 4 blade and see how she does. I love the way it handles once it’s on plane but I just need to find the right combo of prop and maybe a little larger cab plate to get her to settle down.

 

[ToMorrow44]

Do you have a cavitation plate? We did the larger max machine tail on our -2 and it really helped

I second this. I would try this cav plate first cuz it might fix your planing problem while keeping the top end of the -2. If this doesn’t fix it, then the prop is too high and you gotta space it down.

 

[50onRED]

It’s a 572 BBC NA making somewhere in the 7-750 range. The boat has done 93 at some point. But since I’ve owned it I couldn’t get it over 84. Tried multiple props, after the prop changes and no difference we started looking at the lower. After talking to Eliminator I was told my existing x dimension was 2” too low and they thought that was the reason different props weren’t making a difference. Basically the “prop engagement” was too high at speed.
Yeah it did great at low speeds but past 75 was a dog.

 

[50onRED]

I second this. I would try this cav plate first cuz it might fix your planing problem while keeping the top end of the -2. If this doesn’t fix it, then the prop is too high and you gotta space it down.

I have a small cav plate but looking into the MMW one for sure

 

[Joepump]

26 Daytona with a -2. I run a 27 5 blade and a 32 5 blade Cutting Edge. The 27 was when I had a N/A 540. Fully loaded boat , fuel, coolers, and 4 adults would plane in 4 seconds and topped out at 92 mph. Had Auggie make me a 32 because I now have a blown 572 (1200hp). When your boat is ready for testing, you’re more than welcome to try my 27. I’m in Elsinore.

 

[Motoxxxloak]

I’ve got my labbed 26 at Cutting edge now for Augie to add more cup to it. Next up will be a 28 4 blade and see how she does. I love the way it handles once it’s on plane but I just need to find the right combo of prop and maybe a little larger cab plate to get her to settle down.

He actually made me a brand new 28p when got my new drive. Told him what I wanted performance wise and I got it and then some, including great planing regardless of the situation.

I have a new MMW cav plate I’d let you try/sell problem is I don’t know when I’ll be back out to grab it for you.

 

[RiverDave]

I remember when you played with a shorty lower on the Schiada.
That was no bueno

Yep.. pretty much did everything bad after I put that on.. went back to a normal leg

 

[50onRED]

View attachment 1274593
26 Daytona with a -2. I run a 27 5 blade and a 32 5 blade Cutting Edge. The 27 was when I had a N/A 540. Fully loaded boat , fuel, coolers, and 4 adults would plane in 4 seconds and topped out at 92 mph. Had Auggie make me a 32 because I now have a blown 572 (1200hp). When your boat is ready for testing, you’re more than welcome to try my 27. I’m in Elsinore.

Augie is awesome. The 30 5 blade was a tester from him. He is re tuning my 26 4 blade now. He is going to get me a 28 4 blade to try. Maybe when I get the boat back from Pfaff I’ll pull it to Elsinore and throw your 27 on there.
How much power did your 540 make?

 

[Joepump]

Augie is awesome. The 30 5 blade was a tester from him. He is re tuning my 26 4 blade now. He is going to get me a 28 4 blade to try. Maybe when I get the boat back from Pfaff I’ll pull it to Elsinore and throw your 27 on there.
How much power did your 540 make?

700hp

 

[Dcb.blake]

My boat does the same thing. Went from a stock xr lower to imco -1 with the mmw whale tale and I have this issue. When getting on plane the boat drops the nose then I have to give a good amount of rpm’s for 10-15 or so seconds to get going fast enough to get fully on plane.

Either a spacer to get it back to original or maybe and extension box.


Gotta add too when I was playing with a smaller prop getting on plane was a lot harder. Took a lot longer time wise for the prop to grab. Band aid might be a bigger prop.

 

[RiverDave]

You guys do know that some cavitation getting on plane can be a good thing right?

If you are swinging a tall prop that the motor will pull when the boat is packing air.. in normal conditions it might not be able to roll it over on plane..

Most number six boats are running aerators to help break the prop loose to help get the motor rpm’s up and gently roll the boat over before the prop “hooks up”..

Almost all step bottom boats have some amount of aeration/cavitation coming on plane.. and the more aggressive you get with your x dimension it will affect it as well.

 

[farmo83]

I’ll recommend the most expensive fix as is common with boating. You can try putting an extension box on it.

A family friend had 26 daytona with a bow rider. He put on an extension box and a -2 at the same time and the boat planned out the same and picked up 9mph. How much of this was due to what piece I’ll defer to the other inmates to chime in on.

 

[02HoWaRd26]

Comparing the 4 blade 26p with the 5 blade 30p isn’t even fathomable. That 30p 5 blade is equivalent to a 32p 4 blade. That’s so much more prop to begin with.
Brian i really think you need to get the boat running right before trying to chase props and speed etc. you’re making so many changes all at once and then fighting three things at once.

Get it running good, then go out and see how it planes, we discussed in text that the planing will be totally different when you go up 2” regardless. I went through some of this on my boat and the boat was faster at -2 but all around i tried -1 and 0 a few times and frankly screw the extra 2-3mph I’m back to 0.
Also as RD said when you raise the lower typically you’ll find yourself running a larger diameter wheel. The 15.25” makes mine happy, the 14.75 my boat won’t barely plane unless i baby it for a while.

Get her running right then go play with her and see, a 15.25” x 28 will probably be your best prop, but a stock wheel not some oh it’s Labbed for this and that cause my boat was this and that. Find a stock wheel.

 

[Nanu/Nanu]

If you have a drive shower just try pulling it off.

My prop would "ventilate and break free" from like 2k-3k rpm then bite.

I took my shower off and it bites and doesn't"ventilate or break free"

In Tight turn arounds for skiers or having fun pulling tubes it bites all the way through.

Its a free experiment and you may find you like the results.

 

[Joe mama]

Had an experience with a new lower from imco stock length and that thing would have cavitation like mad. Didn’t matter what prop. Fred said a 5 blade would fix. That was just as bad. He told me something wrong with the boat. I said bravo no issue. Had them build the bravo and put it back on and it rolled over no problem. It was a Mach 26 and for some reason didn’t like that lower. Once on plane was great, I was over it lost to many weekends.

 

[50onRED]

Comparing the 4 blade 26p with the 5 blade 30p is t even fathomable. That’s 30p 5 blade is equivalent to a 32p 4 blade. That’s so much more prop to begin with.
Brian i really think you need to get the boat running right before trying to chase props and speed etc. you’re making so many changes all at once and then fighting three things at once.

Get it running good, then go out and see how it planes, we discussed in text that the planing will be totally different when you go up 2” regardless. I went through some of this on my boat and the boat was faster at -2 but all around i tried -1 and 0 a few times and frankly screw the extra 2-3mph I’m back to 0.
Also as RD said when you raise the lower typically you’ll find yourself running a larger diameter wheel. The 15.25” makes mine happy, the 14.75 my boat won’t barely plane unless i baby it for a while.

Get her running right then go play with her and see, a 15.25” x 28 will probably be your best prop, but a stock wheel not some oh it’s Labbed for this and that cause my boat was this and that. Find a stock wheel.

I’m IMPATIENT PETER! Ha!
I hear you loud and clear. At this point I know the 26 runs good and the boat is at Pfaff/Baca now to get it ironed out. When I had the 26 on it she was getting on plane, but it took twice as long as before. When I say twice as long I mean it took 6 seconds instead of 3.
At speed I could definitely feel the new lower. I really like how it handles. And I think the 30 I had on it was a 15.25 because it comes within 1/4 inch of my cav plate.
What cav plate do you run currently?

 

[50onRED]

You guys do know that some cavitation getting on plane can be a good thing right?

If you are swinging a tall prop that the motor will pull when the boat is packing air.. in normal conditions it might not be able to roll it over on plane..

Most number six boats are running aerators to help break the prop loose to help get the motor rpm’s up and gently roll the boat over before the prop “hooks up”..

Almost all step bottom boats have some amount of aeration/cavitation coming on plane.. and the more aggressive you get with your x dimension it will affect it as well.

Yeah and maybe I’m just being more sensitive than I should be. It’s one of those situations where the boat broke and now I’m being overly sensitive of every single thing out of sheer anxiety.
I actually love the way the new lower handles at speed and I think I just need to get used to it again. It’s definitely breaking loose at different rpm’s when attempting to plane. It did the same thing a little before but now is more pronounced. Again I might just be being a sensitive pussy…

 

[ToMorrow44]

I’ll recommend the most expensive fix as is common with boating. You can try putting an extension box on it.

A family friend had 26 daytona with a bow rider. He put on an extension box and a -2 at the same time and the boat planned out the same and picked up 9mph. How much of this was due to what piece I’ll defer to the other inmates to chime in on.

This is a good example of exactly how an extension box is supposed to work. Putting an extension box on “effectively” lowers the x dimension (its doesn’t actually lower it, but the boat will act like it) so you need to go up 2” with a ex box. Then you get the best of both worlds, better planing and higher top speed because of less drag.

This might help with the OPs boat, but like you said, expensive endeavor.

 

[Joe mama]

Yeah and maybe I’m just being more sensitive than I should be. It’s one of those situations where the boat broke and now I’m being overly sensitive of every single thing out of sheer anxiety.
I actually love the way the new lower handles at speed and I think I just need to get used to it again. It’s definitely breaking loose at different rpm’s when attempting to plane. It did the same thing a little before but now is more pronounced. Again I might just be being a sensitive pussy…

I wasn’t sensitive when I had my buddy and his wife in the back seat, but when I was turning 4K trying to plane, I told his wife to move to the front so the nose would drop. Talk about sensitive. Lol

 

[02HoWaRd26]

Had an experience with a new lower from imco stock length and that thing would have cavitation like mad. Didn’t matter what prop. Fred said a 5 blade would fix. That was just as bad. He told me something wrong with the boat. I said bravo no issue. Had them build the bravo and put it back on and it rolled over no problem. It was a Mach 26 and for some reason didn’t like that lower. Once on plane was great, I was over it lost to many weekends.

My F26 same thing. It still isn’t happy with the SC lower, compared to the BXr lower but I’ve learned to compromise. Hell Tony straight told me from the start, leave the XR, did i listen ?? nope.

 

[02HoWaRd26]

I’m IMPATIENT PETER! Ha!
I hear you loud and clear. At this point I know the 26 runs good and the boat is at Pfaff/Baca now to get it ironed out. When I had the 26 on it she was getting on plane, but it took twice as long as before. When I say twice as long I mean it took 6 seconds instead of 3.
At speed I could definitely feel the new lower. I really like how it handles. And I think the 30 I had on it was a 15.25 because it comes within 1/4 inch of my cav plate.
What cav plate do you run currently?

The -2 lower really shouldn’t be anything at all until you get into the mid 80’s low 90’s before you’ll ever see the difference in the two for drag.

1/4” from cav plate that may be more like a 15.5+. A 15.25 and mine was all of 1/2”+ maybe more like 5/8-3/4”

I swap back and forth from the factory IMCO cav plate and the MMW plate. All around the MMW is better but i like playing with shit, but mines dialed.