trying to figure out what prop. I need

zell66

Petty Officer 1st Class
Joined
Jul 6, 2007
Messages
211
how do i know what prop. fits my outdrive?

I have a aq125 volvo 4cyl with a penta 270 outdrive.

do or can i use a 15 x 17 prop?
 

zell66

Petty Officer 1st Class
Joined
Jul 6, 2007
Messages
211
Re: propellers

Re: propellers

Also how can I tell what pitch is what I need? current prop has no readable numbers on prop.
 

zell66

Petty Officer 1st Class
Joined
Jul 6, 2007
Messages
211
trying to figure out what prop. I need

1) Performance issue you are trying to correct.

Nothiing realy just want a good crusing prop.

2) Current prop manufacturer, model, aluminum or stainless as a minimum.

Manufacturer unknown, model unknown, aluminum : yes

3) Current prop diameter and pitch (required).

15" RH curent pitch unknown

4) Wide open throttle RPM and speed with an average load.

If I remember correctly from last year i think it was around 4000

5) Engine/drive make, model, year, and HP

AQ125 Volvo 4cyl, 1983 or 1982, HP I believe is 120 or 125

6) Boat make model, year, length and weight

Bayliner Capri 195, 1982-83, 19' weight unknown

need to purchase a new prop and dont know what i need. Exp. 3 blade vs. 4 Blade, also can someone explain to this old man pitch of the prop.
 

jestor68

Commander
Joined
Jun 12, 2012
Messages
2,308
Re: propellers

Re: propellers

The prop size(dia X pitch) is stamped on the propeller hub. It is necessary to remove the prop nut to see the numbers.

To determine if you need a different size prop, you need to run the boat to see what WOT rpm the motor attains. The maximum rpm for that motor is 4800 rpm; the ideal rpm being 4500-4800. The gear ratio is 2.15:1.

While the prop is off, measure the length of the prop shaft to determine whether it is a "short shaft"(4.7") or a "long shaft"(5.4") lower unit; as that will determine what prop(s) fit on it.

If you are only getting 4000 rpm, you will need to lower pitch and/or diameter to get closer to 4800 rpm. This will improve the over all performance of the boat, including faster acceleration.

If you don't have one, you can go to the VP web site and search under "engine data base" to down load a owners manual for the AQ 125A/B. Parts manuals and repair manuals are available (to purchase).

The dry weight of your boat is 2200 lbs.
 

MH Hawker

Vice Admiral
Joined
Jul 13, 2011
Messages
5,516
Re: trying to figure out what prop. I need

Props are simple when in use but often very complicated to pick. the pitch is the angle of the blades and only part of it. In order to help you sort one out you need to know what the motor is turning at max RPM`s known as WOT and your real speed on a GPS unit boat and hull type, Or you can use the guess method at 100.00 a guess
 

jestor68

Commander
Joined
Jun 12, 2012
Messages
2,308
Re: trying to figure out what prop. I need

He has two threads going concerning the same issue.

Suggest we work on one or the other.
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: trying to figure out what prop. I need

You should find your prop size under the prop nut It is written diameter X pitch.
Probably better if you get us a fresh wot rpm and speed by gps.
Also would be good o know your gear ratio sometimes on a tag or stamped on the outdrive.
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
18,110
Re: propellers

Re: propellers

Very important on these smaller Volvos.
Use a Volvo made prop.
They might be more expensive but will outperform the aftermarkets.
I was asked to lok at a friends boat,said it wasn't performing the way it should.
I checked everything and found nothing.
As I was wrapping up my tools,I saw a new prop on the drive.Obvious an aftermarket.
I asked when did the trouble start?
Right after the prop change.
The old prop was on the ground next to the boat.
I cleaned up the edges and reinstalled it.
Problem solved.
Something about the smaller motors need the extra area on the blades???
They just operate better with original equipment.
 

zell66

Petty Officer 1st Class
Joined
Jul 6, 2007
Messages
211
Re: trying to figure out what prop. I need

First off thank you all for the advice,

I am sorry about the 2 posts could not figure out how to delete first one lol

My numbers on prop are worn to were no numbers are readable. I know I have a 15" dia. with it measures about 4 5/8" so I think it would be a short shaft.

With no numbers on my prop how does one determine what pitch the current prop is?
 

wire2

Lieutenant Commander
Joined
Jun 25, 2007
Messages
1,584
Re: trying to figure out what prop. I need

Place the prop on a flat surface and with an inclinometer, (or a cheap geometry set protractor) read what angle the main portion of a blade is. I just now checked an OMC 14? x 21+, it shows 32?. If yours is a steeper angle, it's more pitch, and vice versa. I believe the relationship will be linear, e.g. 10.5" pitch would be ~ 16?.
I'm sure there's a way to calculate the relationship with either geometry or trigonometry to arrive at a constant but I've been out of school way too long.
 
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