1988 242 LS Prop Blow Out
 

I currently have a 1988 242 LS with a 454 which was rebuilt and putting out around 430hp to the crank (confirmed on dyno). I am currently running a pretty beat up 21p Mirage which does perform well, however, being it came with the boat and was dinged up I purchased a new 21p Mirage Plus per many suggestions. This week I had an issue all day where the prop would start going well onto plane and right around 3200 RPM the prop would let go the RPMs would shoot to 4200 RPM and with a ton of work would come back down to normal levels. The prop was also imposible to go any slower than 30 MPH on plane. Has anyone experianced this issue? I had the same thing happened with a test four blade Bravo. One extra thing to note is my current 21p Mirage is a solid hub and all the other props have been the plasitc hub if that makes a difference.

Thanks for the help.

Jed

No ideas?

Maybe your engine coupler is bad and spinning under heavyier load. Is your drive all the way down (trimmed in)?

I thought the coupler but I have no rubber smell and it seems to be good with the other prop. This is with the drive all the way in and tabs down to help with the slower speed and no luck.

Do the new props you are trying have the vent plugs in them? Are you through prop exhaust?

Props do not have vent holes as an option and the exhaust is above the water line.

Is it possible going from a 21P to and 21P Plus could be causing this problem. Same with the 22 Bravo one I tested.

Should I try a simple 21P non plus or a 19P Plus? What is everyone else experiancing out there?

I would think a 23 would be better with that power

Call bblades

The 21 plus and bravo 22 should actually bite better than the regular mirage 21. The boat shouldn't have problems planing with any of those props. Definetly a strange problem

I agree extrememly odd. It grips well and then as soon as the bow begins the level off the RPMs fly up and stop and with alot of trim and tab play the RPMs will slowly come down. The old dinged up 21p bites all the time everytime through the whole RPM range at all spreads and any trim within the limit switch.

It just seems so odd to be happening with all different props. Besides being different blades, cups, and pitches all the test ones have the plastic hub insert versus a solid metal one. Would that make a difference?

Oreo,

on my 88 with stock 365mag motor I spun a 21 mirage plus, just wanted to put it out there, sounds as if something else is going on thou

What else could be the issue? I am doubtful of it being the coupler because I have no bruning smell ever and I had the Bravo 22 issue three years ago and went back to the 21p with no issues and no the 21p plus is acting the same as the Bravo 22. It acts just like if you had the drive trimmed up and tried to go on plane where it would initiall bite and then spin up to high RPMs. I would think possibly too much stern lift but that seems crazy because the drive is well below the lowest part of the transom. Very aggrivating. I will say when the 21p Plus did finally hook up the boat cruised very nicely, but I need the slow grip for those rough days where I cant be doing 45mph.

I think you should inspect the drive and prop on land, is the hub ok?

Everything appears to be good. No play in drive. Splines are squared on the ends not pointed on the shaft and coupler. Drive lube changed every season and when coming out never a burned smell or lack of fluid. Plastic hub is new and no spinning in the prop. Anythig else to check?

Thoughts on this......I had a guy at work ask me if I had a drive shower (which I do, the solid double tube) and he is swearing that the tips below the cavitation plate are causing the blow out. Anyone ever heard of this and could this be true. I will say the blades on the test props have been longer than the ones on my original. The thought process is that the initial water trying to push into the pickups and pushing water back into the tips of the prop causing the blow out?

Thoughts on the drive shower?

which side is it mounted on?

I think you answered your question...get a new solid hub 21" Mirage Plus.

It is a dual pickup mounted on both sides of the drive.