Mercruiser prop help!

Howdy!

Got a new 4.3/MPI/Alpha setup in my old Zeta (19-cuddy/3000 lbs. empty).
Currently running the old alum/4-blade/18p that was on the 305/Chevy we pulled before the repower.

Still doing break-in but have briefly run her out to check speed/rpm @ WOT. GPS says -42 mph @ 4700 rpm.

Not bad but the Merc Marine test data with this engine on similar sized boats claims about 50 mph or better @ 4800 - 5000 rpm.

I'm also aware that my bottom (rather... the boat's bottom) desparately needs sanding and repainting.

My question stems from viewing the Merc test data on several boats tested with my engine using (Merc) SS-props. Seems to me that the 14 X 19p 3-blade Vengance is the way to go.

Can anyone recommend a better prop (considering max/speed/cruising/fuel-economy/occasional water-skiing) for the money? Michigan? Solas?

Thanks for your time and trouble!
Cheers.

Re: Mercruiser prop help!

Anybody home?

Since my original post above - which I see has received a 'whack' of replies -I have asked my mechanic for his opinion as to a new SS/prop for my boat.

He's suggesting a 3/blade/SS-17p vs. the current 4/blade/alum-18p that we're currently running.

I don't like to second-guess someone with his experiance yet I remain confused.

All test-data on the Mercury marine website on similar sized/powered boats as mine(new-boats mind you), indicates a 3/blade-19/pitch prop claiming top-ends of 50mph or better. I'm currently maxing out @ 42/mph.

In the meantime I'll try the Merc prop/selector again and see what it says.

Any HELP greatly appreciated!

Re: Mercruiser prop help!

You will definitely get more speed out of a three bladed propeller than you do out of the 4 blade. If your 4 blade is an 18 pitch, you could easily go with a 19 pitch 3 blade.

www "dot" propellerforum "dot" com

Re: Mercruiser prop help!

3 blade 19 pitch SS. stay away from a low profile (narrow blade) prop however as you will never get a cuddy cabin up on plane.

Re: Mercruiser prop help!

Thanks Guys!

MD... what do you mean by narrow blade?

If you were going to run a 3-blade SS, what specific prop (name: Vengence/Laser/Enertia etc.) would you be tempted to try?

Vented or not vented?

Thanks again.

Cheers,
Terry

Re: Mercruiser prop help!

I seem's to me your already a bit overpropped, that is if your turning 4700 rpm and no heavy load's. Walleyehed many time's talked of running a engine at the peak of it's rpm band when testing a prop. IF your 4.3 efi motor is like mine you have a rev limiter @ 5000 rpm, i stopped the prop selection process @ 4900 rpm with a full tank of gas and a 600 lb sand man.

With that said my engine was also very new and not fully broken in yet, today it is and i can now hit the rev limiter on a calm day, what i am saying there is probably another 100 or perhap's 200 rpm left in that motor when she losen's up

So with that said it seem's a 18 leaves you 200 rpm under, i am by no mean's well versed in prop's but you may want to post the type of 4 blade alum you have and perhap's someone will post in the know just how much cupping is present on the prop. The stilleto line is well cupped, the Bay Pro 11 line gave me crazy slip number's something like 3-4 % but when you adjust for cupping it became more realistc 8-10 % and that was done by adding 1 inch of pitch again per Walleyehed.

Looking back and doing some research i believe the results i recieved were from a number of circumstance's, One the Baypro series do create a lot of lift second was once that hull was up out of the water it caught a lot of air, additonal lift it's a 8' beam and only 18.6' long and when going 55 mph it's like a big wing and explain's why my wake goes straight out the back and how easy it is to go airborne just hitting a couple of 8-12" roller's......... RC is going to have some real fun with his boat, its the same boat and he put in a 300 hp 5.7 along with a 22 p 4 blade Stilletto, i can' wait for his first post explaining how he went airborne @ 60 just hitting someone's little wake..

Anyway's at 40- 50 hours id say a maybe a 3 blade 17 maybe a 18 if she really loosen's up (the motor that is) Stilletto's are a fine prop's i ran a 3 blade advantage and it was faster than the 4 blade ( 1mph) but it did not have enough lift to get the hull as high out of the water to get the additonal wind lift. If you boat is a cutty you have a lot more wind resistance going on there probably wont get as much lift with a 4 blade.... but ya never know until you try...

Re: Mercruiser prop help!

Howdy!

Thanks Gunner and rest of you cool-cats!

I figure I need to find a new/used prop to try out and see what happens.
I've been looking at SS/props on ebay, there's a 'whack' of em'...

...but, I should put that idea on hold for now till I know exactly what I want.

What's up with this Merc - 'try before you buy' thing?

Thanks again to all!

Cheers,
Terry

Re: Mercruiser prop help!

Howdy, me again.

Thought I'd (try to) post a coupla' links of the Merc 'test-data' I was mentioning earlier. I any of you guys have a minute to check it out -assuming the links work - you'll get an idea of where my confusion comes from with regards to finding the right prop for my boat.

http://northamerica.mercurymarine.com/_media/pdfs/bhb/sterndrives/4_3MPIAlpha_Stingray210C_1006.pdf

http://northamerica.mercurymarine.com/_media/pdfs/bhb/sterndrives/4.3MPI_ChrisCraftLaunch22_0806.pdf

http://northamerica.mercurymarine.com/_media/pdfs/bhb/sterndrives/4.3MPI_Godfrey195SD_0906.pdf

The Chris Craft (Launch 22) has a 'dry-weight' of over 4100/lbs.

I'm beginning to wonder about the accuracy of this data.

Opinions?

Cheers,
Terry

Re: Mercruiser prop help!

That boat is quite a bit larger and heavier than the boat i put a 4 blade and the same power plant. Recently a member here tried to put a 4 blade on a similar boat to your's and lost speed and no lift gain.

We used to have a pinned example in here and if i remeber right it WH recomended Solas Lexor or Mirage and Vengenace along with the Enteria. But before you do anything id break in the motor and clean your hull up a bit, only then will you get a true picture of your boat's potential. For now those chart's cannot determine what your boat will do, however you have posted a 4blade alum leaves you at 4700 rpm and that 200 shy, taking you to a 16 or 17 p SS four blade which will lose you speed or a 17 pitch 3 blade SS and if you want top speed perhaps a 18 p Enteria.

But id clean your hull up and and break in the motor before you jump....

Re: Mercruiser prop help!

Howdy!

Thanks Gunner!

I'm all over that hull. I'll post later after she's broken-in and let you know where I'm at.


Cheers,
Terry