Best Prop for my '74 20'CC

[Ulf]

New Seacraft owner, '74 20'cc with a Merc 150 Blackmax.

Finally installed the GPS unit, topping out at 43/44 mph @ 5400 RPM. One person, light load, 1/2 fuel?

Does this sound right to you guys?

Running a stock Merc 14x19 s/s dog ear wheel.

Could I get more MPH with a different style prop?

Also think I can go up at least a bolt hole on the transom. My cavitation plate is below transom at nuetral/ negative trim. How are other boats set up with engine height ?

Just looking to make it as efficient as possible.

Thanks Guys

[gofastsandman]

Originally Posted by Ulf

New Seacraft owner, '74 20'cc with a Merc 150 Blackmax.

Finally installed the GPS unit, topping out at 43/44 mph @ 5400 RPM. One person, light load, 1/2 fuel?

Does this sound right to you guys?

Running a stock Merc 14x19 s/s dog ear wheel.

Could I get more MPH with a different style prop?

Also think I can go up at least a bolt hole on the transom. My cavitation plate is below transom at nuetral/ negative trim. How are other boats set up with engine height ?

Just looking to make it as efficient as possible.

Thanks Guys

Welcome, the nurse will see you shortly.

Move up 1 1/2 " above keel. Do a comp test on the Max. Do the annual service.

That should get the rpm and speed up a tad. Those numbers are about right.

A powertech, mirage+, bravo, enertia, or rev 4 are some props that are favored.

Google the#s on yours to see what you have.

Avoid e 10 at all cost. Use good oil and decarb. Check the steering arm for integrity.

Add location to your acct. so locals can share/swap/ trade pieces/parts and help/advice.

Cheers,
GFS

[Ulf]

Thanks for the reply.

I plan on raising motor in the next week or so.

But how am I supposed to stay away from E10? That shit is everywhere.

[WillyC]

I would google ethanol free gas stations in your area. Where I live there's a bulk/mixing plant that has it. Cost about a quarter more per gallon but well worth it.

[eggsuckindog]

17" Stilletto prop and raise the hell out it - I went 1 hole higher @ 21/2" above and it loves it. Incrediable performance - 7 to 11% slip readings. I used to have a Merc 19" also, thought I bought a new boat, honest.

[McGillicuddy]

Get a-c plate at least 1-1/2" above keel. PowerTech MQS3 14-1/2" x 17p

[Ulf]

What diameter for the Stilletto?

I have a Mach 14x16 four blade kicking around the garage, gonna throw it on and see what happens. As soon as I find those stupid rubber inserts for the hub.

Thanks for the input guys

[Ulf]

I just tied the Mach 4blade 14x19.

Ran like crapola overall.

Picked up another 200 rpm, up to 5600. Didn't really get much bite outta the hole.

Lost 3 mph on the top, and close to 5 mph on a cruise @ 3500 rpm. Went from 29/30 at 4000 to barely 24/25, and it didn't like staying there.

Overall just did some weird things.

So the stock Merc 3 blade 14x19 stainless goes back on.

My prop search continues. I'll have to find that stiletto that was being highly touted. Oh, and find some time to raise the motor up too.

[eggsuckindog]

Originally Posted by Ulf

What diameter for the Stilletto?

I have a Mach 14x16 four blade kicking around the garage, gonna throw it on and see what happens. As soon as I find those stupid rubber inserts for the hub.

Thanks for the input guys

I believe there all 14 1/4, they are very aggressive, similar to a Mirage+ so thats why I suggested you back down to 17 - it will take 300 off the rpm. They also like to be very high - agressive - I'm at 2 1/2" above and still can't break it lose even in a tight turn. Your perfect rpm is 5600 I believe and that should be right on. BTW they are reasonable for new props to 275 on the net, unless you can find one on ebay or craigs list - I found mine for 150

you don't need the plugs they really don't do anything past plane