Prop replacement / opinions
 

Hi, I posted this up in the prop forum but so far the only person with an opinion is an advertiser...so thought I would throw it out here where all the smart people are as well.

The Mirage 21P that came with my boat had a pretty hard life before I met her, and since I have no backup prop right now thought I would just upgrade and keep her for a spare.

Also I ran WOT on GPS for the first time last week and was disappointed to only see 42mph at 4200-4400 RPM, I would like to see a little more top end. I think I'm supposed to be seeing low-mid 50s at WOT, does that sound about right?

Should I just stick with the Mirage (or Mirage Plus) 21 and watch people wave as they go by me, or could someone offer opinion/advice on what I should snag for my new screw that might give me a little more top without completely sacrificing my hole shot? And is it really typical to top out at 42 in this boat in calm water at sea level with a full tank, three people and my dog on board?

Current prop is model 48-13702-21 on the inner hub, stamped 48 13702 A41 21P on the prop body.

Thanks!
Aaron

Re: Prop replacement / opinions
 

Need a few things 1st:

Boat length /model?
Engine/ drive package?

Off the cuff, your RPMs are too low, no matter what engine you have. Also you can't tell crap about what a boat is supposed to do even with a slightly damaged prop. Even slight damage can make a BIG difference. Go borrow a good prop if at all possible.

Re: Prop replacement / opinions
 

Activox,
Judging from another thread of yours, you must have a 242ss. I'll assume it has a 454/330 since most did.

I owned the very same boat some years ago. It also had a 21p Mirage Plus. Mine did about 52-53 at 4900 rpm. So, as Jaybird stated, you're rpms are way too low for WOT. The "SS" model 242 was never as fast as the "LS" model. The SS has more weight forward which makes them ride with more hull in the water.

Assuming you're WOT rpm reading is with the boat trimmed out, then there is definitely something wrong. Prop is not true to it's stamped pitch or the engine is tired.

I totally agree with Jaybird, find one of you're buddies with the same prop (they're very common) and borrow it. But, do keep in mind, max rpms is only attained with the boat trimmed out. If you've got the bow down, rpms will be low, like the numbers you're seeing. Of course, speed will be low also.

Re: Prop replacement / opinions
 

Just how does the 242SS have more forward weight than the 242LS?

Jon.

Re: Prop replacement / opinions
 

Hi Activox,

My 242 SS also came with a Mirage 21p when i bought her and was also very dissapointing showing a GPS top speed of 45mph. I fitted a new Mirage plus prop and the top speed went up to 53mph on the GPS.

That was great for a while, but now im thinking of fitting a 496HO next year. This should take her to low to mid sixties i hope.

Jon.

Re: Prop replacement / opinions
 

I ran Third's numbers in a prop speed calculator and it showed something like 18% slip. At 4200-4400, you should be running 46-48 mph. Full of fuel and people, prop not in great shape, trimmed in a bit, and your 42 mph doesn't sound out of line. You should be able to spin the props up more, but I believe the recommended WOT range on the 330's was only 4200 or 4400-4600.

Re: Prop replacement / opinions
 

The SS has a larger cockpit that extends forward. The deck of the boat is smaller and the cabin is smaller. The helm and passenger seats are farther forward in SS. All of this combines to make the hull "less light" in front than an LS.

With the same power, an LS will let more hull loose while trimming and therefore be considerably faster than an SS.

Re: Prop replacement / opinions
 

Maybe you're right Bill on the rpms. I really don't remember exactly what the engine turned but, the boat did hit low 50s.

Re: Prop replacement / opinions
 

I have a 242LS with the 454/350hp max rpm is about 4800 with a bravo 1 4 blade 22 pitch labbed, 54.5gps. You may want to try a hydromotive 4 blade also.

Many people who advertise here do know they are talking about, or they wouldn`t last long here.

Make sure you know your drive ratio very important.


good luck

Re: Prop replacement / opinions
 

Whoops, guess I shoulda posted the boat specs, not sure how that got by me. Yes, TB is right, 1989 242 SS with stock 7.4/330 Bravo One, 600 hours, very strong and clean block, purrs like a big fat kitty.

The prop on it right now is a Mirage 21P (not Mirage Plus) in fair shape, not good. One leading edge has an abrasion on it and the blades themselves are pretty rough, which is why I want to replace it with a primo screw and keep the tired one for emergency backup.

And indeed I have been fighting a trim issue with my controls which I think I have whipped now and hope to get it dialed in a bit more next time out, far as that goes, which should help a bit. But this prop needs to be replaced.

I know that prop discussions frequently enter Holy War status, I appreciate all the wisdom, experience, and enthusiasm that anyone might care to bring to bear on this.

Thanks!
Aaron

Re: Prop replacement / opinions
 

If your boat is already heavy in front I don't think the Hydro Quad IV will work very well, as it's a stern lifting prop. That would put even more hull in the water, slowing you down.

You'll need a "bow lifting" prop.

Re: Prop replacement / opinions
 

Russ ...check Thread in Props section ....Throttle UP and BBBlades seem to think the 311 should be running B1's "round ear" props ....

Re: Prop replacement / opinions
 

Anyone else with some more opinions on this topic? I also run an 89 242ss with stock 454/330hp, 370 hours turning a 21p mirage. I'm running 49.7 mph on gps with 4 people and 3/4 tank gas on calm water turning about 4300 rpm fully trimmed. this was the only time i had the gps, don't own it. Is this about all this boat will do?I'd like to see mid 50s, has anyone tried the 4 blade on this boat? i am considering one. Thanks to all of you for all of the info on here as well. This is my first I/O, coming from an 18ft baja with 150 evinrude on the back this boat is a bit different!

Re: Prop replacement / opinions
 

I had a '89 242SS, but the motor was tired and I had it rebuilt with a 30 over 454 (468?) and a very mild cam (est. 350-360HP). Using the stock prop, it would reach 53-54 MPH at WOT. I don't remember all the exact specs...

Re: Prop replacement / opinions
 

I had a 89 242LS with 454 mag 730+ hours. Came with a 21P mirage. Too many revs at WOT so I switched to a 22 pitch 4 blade. Top speed was 56 mph, cruised at 35-37mph. The boat seemed to run smoother in a chop and planed faster.

Re: Prop replacement / opinions
 

I have a 89 242 LS 454 Mag (365hp), 19 4 blade Merc Revolution. I see 55mph at 5000 rpm. I am looking for a 21 4 blade though if anyone has one.

Re: Prop replacement / opinions
 

I have an 87 242ss w/ 330/alpha 1.47 and Brett from bblades recomended the 19p rev 4. I got 51 mph gps out of it at 4650-4700 RPM. The drivability of the prop was great. It was real smooth, planed with ease, and made the boat feel light and nimble. This was also with the boat breaking up! I must have a bad wire because I heard spark jumping at idle. They are only on their second season, but it is a boat! I have to put wires, cap, and plugs in it and then retest. So far I am pleased...I will tune it up in the spring and see if I can get any more out of it.