Prop suggestion?

[JJJ]

I have a Cobalt 200 w/4.3 LX merc. in it. I only use the boat maybe 2 weeks a year to go to the Keys, so any speed data is by memory from last year.

I have tried the stock 13.75 X 21,
a Powertech (?) 4 blade stainless - maybe 20P,
a Solas 15.3 X 19 aluminum,
a Solas 15.3 X 21 alum.

The stock - bad hole shot, not enough lift - esp. bow.
The 4 blade - alright hole shot, not enough lift - in fact seemed to push bow down.
The Solas 19P - nice hole shot, almost perfect lift, rpms 4800 or so, mph 48 or so.
The Solas 21P - not bad holeshot or lift, rpms down to 4500 or mph still 48 or so.


Ok I like the Solas 19P, but it seems to be worn some and didn't carry the bow like it used to (last year). I am assuming I need a big blade prop similar to the Solas.

ONLY gripe on the Solas's is at cruise 25mph/3000 rpms or so, I get a vibration/noise - seems like prop blades flexing some due to loading. It could use a little more bite also to carry the bow under light throttle and rougher water.

Ok question IS, should I
A. have the 21P repitched - it is new
B. just get another 19P Solas - or repaired again
C. is there a different model prop that will give me the lift I need (mainly to just get the hull out of the water in rougher seas), but be stronger/more rigid than the Solas? (stainless, 4 blade, new Solas Rubex?

I think I need a big blade prop (not dia. but rather blade)for that, correct?

I know I didn't give all of the info needed, but my memory just isn't what it used to be

 

[JJJ]

Re: Prop suggestion?

No ideas, huh?

Anyone ever use a Stilleto 14.5 X 21P? comments?

 

[hwsiii]

Re: Prop suggestion?

JJJ, I don't know anything about the solas props, but I have never seen a major manufacturer have aluminum blade flex at 25 MPH to the point of creating problems and vibration. I don't believe it is possible, and if it is you would be able to tell from the thickness of the blade, it would have to be thin like a stainless blade and not an aluminum. My thoughts are you have probably hit something with the prop or worn it down in sand, vibration doesn't come from blades flexing at 25 MPH. That would also account for the prop noit being able to hold the bow up like it used to. I need to know the year of the boat and motor as well as the horsepower and gear ratio of the outdrive to be of any further help.

H

 

[JJJ]

Re: Prop suggestion?

Hi, it is an early 96 20' Cobalt with a 4.3 4bbl (non new vortec heads). The prop is worn slightly with one ear has very very minor damage. The vibration/noise seems to really be resonant - as I had the same prop but in a 15.3 X 21P on another time (brand new) and it was the worse. Also seems to be in a very narrow speed/rpm range.

Didn't notice it in fresh water, but I very seldom use the boat, esp. in fresh water.

I'm not so much worried about pitch, as the ability to lift the whole boat and carry the bow. If we are in rougher seas ( 5'-8') the ability to get the hull up and out of the water is a big big plus.

This Solas prop has BIG blades, which I think is why it works so well.

 

[JJJ]

Re: Prop suggestion?

Not sure on the gear ratio, and it is the Solas Amita prop. I know 96 was the mid year change for the 4.3 engine - early non-newer Vortec head, later had the new style Vortec head. I just don't know if the gear ratio also changed in 96.

I would love to get closer to 30 mph at 3000 rpms, the hull really likes the higher speeds but the fuel tank doesn't

Oh and to be honest, I very seldom do WOT, mostly cruising - even on calm seas.