4 blade prop for 91 Bayliner Q: Aluminum or Stainless Steel?..

[malibu3105]

I have a 91 Bayliner Capri 2050. I have a 3 blade, but want to get a 4 blade for skiing and wakeboarding. I will be trying some samples from my local boat shop to get the max rpm range 4400 to 4800.

Couple questions, should I test for WOT Rpm's alone or with people? Or does it matter. Maybe alone I should try for 4,800 rpm so when loaded it will slow down.
2nd question is aluminum or stainless steel? And does it matter? Big price difference .

Thx, Frank

 

[flyingscott]

You prop for light load at the top of the rpm range which would be 4800 for you. That way when you load the boat up it stays in the recommended band. Stainless is better for skiing and tubing I would recommend looking at a high 5 prop probably the best holeshot prop there is. They also like to run deep in the water and they run smooth.

 

[malibu3105]

flyingscott, 5 blade would be pricey? is there a big difference from a 4 blade? And difference between SS and Alum?

 

[flyingscott]

Price depends mercury is the only one that makes the high 5 only stainless. Stainless is always more expensive if price is a big issue go 4 blade aluminum. Stainless is a better material for props less blade flex. If you have a mercruiser outdrive the dealer can help you with a prop and pricing.

 

[malibu3105]

Roger that. Well I prefer Stainless, but price between 4 blade and 5. I have been reading about High Five's. When I get a chance, I will get pricing from my dealer.

 

[SkiDad]

question is, did you get your motor running right ? if so, the main thing is to get your rpm up to the top of the range with a light load - you might want to get it just a tad over that if you don't run alone alot. If you are still only getting 3300 with your current prop you need to get that figured out first - unless there is just a crazy high pitch on it. I would think you want something like a 17p with your HP rating and a 2500 lb boat. It is nice if you can get some to try and don't be afraid of aluminum.

 

[malibu3105]

Answer is.... No, but working on it. Blown head gasket on both sides. So getting a valve job. Heads are at machine shop now getting done. Will be all nice and working well when it comes back. Also exhaust manifold was rotted out and pieces in the drive. Replacing those and risers, and getting it all serviced.
So repairs plus a full service. My shop guy says when I get back out to test my current prop, and we will go from there. He says I should now push 50mph at WOT. He says if I had 3,700 rpm that I should now get to 4,600 to 4,800 pretty easy.
I will get info on rpm and mph with current 3 blade, then go for the 4 blade. He is recommending a mercury 4 blade based on what I am doing. Some skiing, some cruising around.

 

[malibu3105]

Ok, update. Blown head gasket on both sides of block, exhaust headers rotted and leaving pieces in the drive, etc.
All fixed. Boat is ready to be picked up. Also the Tach was set to V8 so that was wrong. Full head service, valve job, tune-up and more.
Mechanic says the engine is kicking butt!! running awesome. So, I will go out with same 3 blade prop, hopping Saturday (even though rain in forecast) and get my new WOT Speed. I have a new Tach, new GPS Speedometer also. Drive was serviced also, new UJoints, etc. My Mech thinks I should be crowding or overtaking 50mph. so we shall see. My next post should be some results with my 3 blade. Also, my Mech has a 4 blade in mind. More to follow after my test drive !!

 

[predator240]

Frank, go to the mercury prop selector web site. put in your boat specs , be honest ! and they will give you a choice of propellers that will give you an idea of what prop will suit you the best, great web site, good luck,

 

[malibu3105]

Ok, boat done. Runs awesome. Purrs like a kitten on idle. Starts right up. So much better
Here are some prop results

Prop	RPM	Gear Ratio	Pitch	Slip	Speed	Trim Down
3 Blade	4,600	1.84	20	0.1552	40	75%
3 Blade	4,700	1.84	20	0.1525	41	70%
3 Blade	4,800	1.84	20	0.1904	40	70%
3 Blade	5,000	1.84	20	0.1839	42	70%
4 Blade	3,600	1.84	20	0.1364	32	90%
4 Blade	4,400	1.84	20	0.1645	40	50%
4 Blade	4,500	1.84	20	0.1148	41	50%
4 Blade	4,750	1.84	20	0.1205	43	50%
4 Blade	4,800	1.84	20	0.1094	44	60%
4 Blade	5,000	1.84	20	0.1645	43	45%

I am guessing at the Gear Ratio, but needed a consistent factor.
I am guessing, that for both props I need to go up pitch. The WOT is supposed to be 4,400 to 4,800 RPM.
I am guessing.... Over 4,500 or so I loose horse power so that is why I don't gain speed.
Open to suggestions.