1988 242LS Speed Help
 

Well I just tested my boat out on the CT river this weekend and I showed 62mph at 5,000 RPM with a 21 pitch 3 blade mirage and a 454 with 428 dyno hp.

Any thoughts on the next prop to try? Any experiance with different props and this hull is greatly appreciated.

Thanks for the help.

Jed

PS I did search and my head is spinning!

62, is that gps or speedo? mirage or mirage plus?

as asked above is it a plus?? try a 21 plus, or 23, not real sure, my old 242 with the org 365hp mag ran 58mph turning 4900 on a 21 mirage plus, so it seems I'm missing something, that was on gps, I made it hit 59.8 once,

That speed was on the speedo, but I figured I could use it as a baseline for now and then when I get my gps I will know for sure.

I believe it is the plus, but I will check tomorrow.

What is the difference between the regular and the plus?

The prop I have was the one I bought the boat with, but it is alittle dinged and dented so I wanted to get a new one and upgrade at the same time.

Not sure what pitch or blade number to go with.

Thanks again for the help.

Jed

regular mirage is a flatter blade easier to spin, a plus is cupped. a boat that spins a regular 23 mirage usually goes back to a 21 when using a plus a plus.

now from past threads a 242 needs aboat 500 hp to break the mid 60's my twin makes 660 and I'm in the mid 60's. and there are a couple of guys with singles making over well over 5oo running just a click away from 70's.

23 Mirage should do the trick

A friend has a 242 with a warmed over HP 500 Dynoed at 535 hp gets 69.6 GPS with a labbed 24 Bravo.

I was thinking a 23 four blade bravo from my research.

How does eveyone think this will handle at lower speeds and holding the boat up?

Thanks everyone.

Jed

Bravo1 comes in even pitch numbers out of the box. I run a 22" it works well in my 242, stock 502.

add some wings and it will fly :)

Any final suggestions before I go and make a purchase?

I’m looking for a good mid range which will get me off plane as well as something to get my top speed up.

Thanks again guys.

Nothing?

try Kjo's idea

sorry it`s late but I also use a Bravo 1 22 pitch labbed a little and runs great I only have a 454/350 hp.

Im spinning a 26p bravo 1 4 blade at 5200 rpm . i need to gps the boat the speedo hits 60 then heads backwards . then again im running a 502 with a comp blower cam and a procharger pushing 7-7.5 lbs of boost

was out this weekend got 70.9 mph at 5000 rpm half a tank of fuel four people and a cooler . might has ben able to trim out a couple more mph but the wife was getting spooked so when i saw the 70 mark i called it good .

Thanks for all the help.

I believe my purchase is going to be a 24p Bravo 4 blade from what I have been hearing and what I have seen from people.

Hopefully I will like it.

Thanks,

Jed

Was that 428hp reading from your 454 on a boat style dyno or a car one ?
Meaning did you run your boat manifolds and all accesories
to get the reading? If not then your engine real hp might be more
like 380-390hp in the actual boat which would make your mph of
62mph pretty close to what it should be and not bad at all.
Just something else to consider

That was on the engine dyno with manifolds and only half the accessories.

These are the results after the new prop....

I changed from a 21p Mirage Plus three blade to a 22p Brave 1 four blade.

I found with the new prop I would need less RPMs to get the same speed as the original, however, coming on plane I found at around 3,000 RPM the prop would slip and rpms would shoot to 4,000 rpm and then slowly drop as the speed picked up and leveled. At around 3,000 RPM the speed was 35 mph but sometimes at the same RPM the boat would be at 25 mph where the prop seemed to be slipping alot. Not sure why but it seemed off. The other problem the stern seemed to be picking out of the water and the boat seemed less stable.

Any thoughts? Help me out everyone.

sounds like your may be trimmed up to much . maybe your trim sensors need adjusted . trimmed down may not be down as far as you think .

My thoughts exactly, but I checked it and when I power up to plane the drive is all the way down and I had it down most of the day because of the results I was having.

The increased speed at lower RPM was great, but coming out of the hole where the RPMS climb normal and they skip to 4,000 and then back down on the prop grabs was not right in my mind. Also the 3,000 RPM giving me 35 mph or 25 mph I didnt like. All around it felt like slipping everywhere and I was coving the steering wheel because the boat seems very unstead now when before it was a rock.

Any more thoughts or experiances with this.

This was also a test propr which the dealer gave me and instead of being one piece having metal spines that go onto the shaft like the mirage it had some plasic guts and then a piece that went in to hold onto the shaft. Again it seemed different to me.

Itr sounds like it is lifting the stern too much, I would stick with a 3 blade plus for best top end and handling, you will get more cruise with a 4 blade but less top end, you need a bow lifting prop in that hull, not a stern lifting prop...my opinion..

I agree it does feel like that. I do like the fast running at lower RPM so how can I get that? Should I try a 23p Mirage three blade?

MAybe but the higher pitch at lower rpm will take you out of peak power meaning slower speeds, I am going to bet that a 3 blad Mirage Plus 21P will be the best prop.

My thought was that i could over spin the 21 right now meaning I could go well over my redline if i wanted so I thought a taller pitched prop would backthe RPMs down to where I could not overprin the prop n the water.

Is this the wrong way to look at this?

Mercury prop selector keeps telling me to go with a revolution four blade 24 pitchI believe but honestly im worries abou the stern being to high again.

seems here in my area 4 blade bravos are favored . i can trim mine up pretty much as far as i want until i start getting chine walk around 74-75 mph and i never seem to blow through the prop at any rpm range . running a three blade on other boats i could alway trim up to the point it lost efficentcy. just my two cents

so here is the question, what is the slipping? i will be at idle in gear and then i will throttle up and the boat will grab nicely and then at around 3000 rpm the revs will jump to 4000 instantly (right before i plane) and catch and then the boat will speed up while the revs drop back down the 3000 and i will be cruising at 35. 0 trim and 0 tabs.
other times i will slow down and when I go to speed up alittle the boat will not gain speed unless i really get on it. it is alsmost as if there is a point where the hull sits a certain way it will get too much air in the water and it looses grip.

i dont know, somebody help. all i do know is the 21 feels like a pig to the 22 when it is running correctly.

What do you think is happening?

Any thoughts guys?

I have a 1990 242ls with a 650 h.p. 496 and I run a 27p plus three blade i'm running 75mph gps at @ 5200rpm I have had my boat act similar to what you have described but it was only when i was in a sharp turn with a fairly good wake I just assumed the outdrive just came out of the water if you find out any other info why this handeling problem occurs let me know. good luck with the prop.

I have a 1988 242 with the 454 mag and a weiand 177, basically a 525SC clone but with less HP. I run a
22" lab Bravo1 at 6' and experience the same issues. The Bravo1 is a stern raising prop so I don't run as much trim. I also have a 23 mirage lab that also slips on the bottom end but will allow me to run more trim at speed because it doesnt lift the stern as much. I have ran these props on 22 degree bottoms and never experienced this slippage.