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