propellor ID on IL165Mercruiser from about 1978

[glastronomic]

Have a propellor on my boat (Savage Bluefin) that has the following indentification numbers;
48-66456A4 17P (itch)
Cannot find this proppellor in my catalogue, sadly
I would like to know which SS propellor to purchase.
Propellor on boat is old and has seen better days.
Plus the boat could do with a bigger prop as it jumps to max speed @ 4000rpm (27knots)
boat is 2.5ton, 21 feet, fibreglass cabin cruiser

also have a spare prop 48-79576A4 21P, could this be used?
Comes up in my Michacan wheel catalogue as an 13 3/4 Dia -21"P
Your help is much apreciated.

 

[Robbabob]

Re: propellor ID on IL165Mercruiser from about 1978

You say you reach max speed at 4000 rpm, when usually it's the rpm that dictates the max speed. Check out this link to provide a few more details that will assist in our efforts: http://forums.iboats.com/showthread.php?t=287818

Good luck!

 

[steelespike]

Re: propellor ID on IL165Mercruiser from about 1978

Your motor is rated for 4600 max rpm. I think your speed is prewtty good at about 30 mph.
But I think the tach is reading low.You may want to varify your tach I'm guessing it should read higher. A 5000 lb boats that jumps on plane should be running at max rpm or perhaps more.

 

[ziggy]

Re: propellor ID on IL165Mercruiser from about 1978

assuming ya got a IL6 cyl. engine. wot rpm is 3900-4300 (from service manual #3, pp. 1B-8). so your 17p prop is in the game imho. albeit a shade on the low side. imho. ya would be better if ya could achieve the high end of wot spec if possible. maybe rebuild your 17p prop so it's new and see what happens to rpm.

if ya got a IL4 cyl. engine. the spec. will be different. if this is what ya have. you'll have to let us know.... i guessing it's the 6cyl.engine. it appears to me that in '78 the 4 cyl. eng. start at 170 hp. you say ya got 165 hp.

i don't think either engine is gonna like the 21p ya got. to much prop for it. my boat is much lighter and 21p is too much for me. i can only barely reach wot spec. with a 21p.

 

[steelespike]

Re: propellor ID on IL165Mercruiser from about 1978

Pretty sure he has the 165 inline 6. Pretty common in older boats.
The the 170 4 cylinder is called a 470.In 78 4 cylinders it appears there is a 120,140 and 170.
Again a 5000 lb boat that jumps to full speed should be turning more rpm though history says the 165 doesn't rev too easily.

 

[glastronomic]

Re: propellor ID on IL165Mercruiser from about 1978

Pretty sure he has the 165 inline 6. Pretty common in older boats.
The the 170 4 cylinder is called a 470.In 78 4 cylinders it appears there is a 120,140 and 170.
Again a 5000 lb boat that jumps to full speed should be turning more rpm though history says the 165 doesn't rev too easily.

Sorry for the confussion, I have a 165HP mercruiser 1978ish ,

in this boat, 21 Ft, 6.4mtr long.

 

[fishrdan]

Re: propellor ID on IL165Mercruiser from about 1978

As suggested, make sure your tach is accurate as right now you are not reaching WOT RPM. If the tach is correct, going up in pitch is going to hurt performance, try the 21P and see how it works...

Is old 17P prop aluminum (didn't say)? If going from aluminum to SS of the same pitch, the SS prop will lower your RPM's, this isn't what you want. Just my gut reaction, but if going from a 17P aluminum turning 40000RPM WOT, I'd think you would need to go to a 15P SS prop.

steelspike, with that big ol' barge, shouldn't he be looking for a large diameter prop? IE: 15-16" dia instead of the more common 13-14" dia

 

[steelespike]

Re: propellor ID on IL165Mercruiser from about 1978

Usually as pitch goes down diameter goes up.The al 15" pitch run from 15" to 15 1/2 diameter.
While it is heavy it apparently planes easily.Usually they don't mess with diameter much unless the boat is something like a pontoon or a house boat.

 

[Jamie48]

Re: propellor ID on IL165Mercruiser from about 1978

First of all the numbers on your prop are the manufactors numbers ( mercruiser ) it is a 17 pitch prop. The 21 pitch prop will work but it will lower your engine rpms at wot and the boat will come on plane slower. In the shop manual the engine rpms @wot should be between
3800 and 4300 so you are in the ball park with that prop. Is that a cuped prop or a straight prop? If it is cuped you could go to a straight 17 p and raise your rpm slightly. An other thing you can do is to have a prop shop bend a prop to a 16 p to raise your rpms more so you are turning 4300@ wot. that is the max recomended speed by merc. All in all that is quite good for a 5000 lb boat, I had a 3100 lb boat with the 165 hp engine, I ran a 15 1/2" X 17P prop and I could pull 4300 rpms with just me in the boat. Good luck, the 165 hp engine is bullet proof and gives years of service, not fast but very dependable.
Jamie48

 

[glastronomic]

Re: propellor ID on IL165Mercruiser from about 1978

Specifications of "barge"
Long= 6.4mtr
Max Beam=2.44mtr
Deadrise =22 degrees
Hull weight=966KG
Weight on trailer=2300KG.
min Planing speed = +/-13knts.@2300rmp.
Is in top 10 of most wanted Australian Trailer boats in multiple publications here Down Under due to it's seaworthyness and build quality.
As I have the other propellor already for my IL6 2 stroke "tower of Power" smoker,

I will put other prop on and try it out if it fits and how it goes.

 

[fishrdan]

Re: propellor ID on IL165Mercruiser from about 1978

Mercury has a prop selector that can help get you into the ball park;

http://www.mercurymarine.com/propellers/prop-selector/#

I ran something that's close to your rig, 4000 RPM, 30MPH, and here's what the calculator spit out;

Black Max Features AL 3 16.0 14.0 RH 48-16438A45
Black Max Extra Cup AL 3 16.0 14.0 RH 48-16438CP1
Black Max Extra Cup AL 3 15.5 15.0 RH 48-78116CP1
Enertia SS 3 15.0 15.0 RH 48-898990A46
Enertia SS 3 14.7 16.0 RH 48-898992A46
Vengeance SS 3 14.5 15.0 RH 48-16312A46

The calculator doesn't go back too far (2000) so you have to play with it a bit, I used a 4.3L V6 Mercruiser and 1.65 ratio Alpha drive.