prop selection

[patrickj]

My prop is getting a little wore out from being grounded alot (we fish in shallow water alot) im thinking of replacing it but there are so many different props out the im lost when it comes to selecting a good one. Performance wise i just want one to give me better top end speed, i dont need hole shot or quick plane time. I have a 1987 force 85. any suggestions would be appreciated. also i see props designed for omc's/merc but you never see one that says force, how do i know which type to get.

 

[Frank Acampora]

Re: prop selection

There are so many variables and you don't give enough information: We know it is a 1987 Force 85 Hp engine, but that's all.

We really need to know at least the size boat, size of prop on the engine now, current RPM, and current top speed.

The only thing I can say right now is that if you are using an aluminum prop and switch to the same brand and size stainless, then you will experience about 400 RPM more and about 2 MPH higher top speed.

As far as brands, Michigan makes props that will fit the Force. If you look right here on iboats stores you will find Force props. Many Mercury props will also fit if the hub diameter is 4 inch (small gearcase). You do have the option of using open hub props (through the hub exhaust) or closed hub props.

The first four photos show open hub props, Ballistic stainless, Vortex aluminum, Michigan stainless with tailcone installed and again Ballistic. The last one shows the difference between a Chrysler closed hub stainless (bottom)and a Michigan open hub stainless (top)

 

[Frank Acampora]

Re: prop selection



Here is a different Chrysler closed hub aluminum. These props were made for Chrysler by Michigan. Then we have a blue aluminum Mercury test prop, a different view of the Chrysler prop installed with tailcone, and finally, an old school bronze solid hub Mercury racing prop. (look at the radical cup on the trailing edges of the blades))

So, your choices are not really limited although some props need to be modified slightly to correctly fit your engine. Note in the last answer, first photo, I showed the removed anode and the extra spacers needed to make the Ballistic prop fit.

 

[patrickj]

Re: prop selection

ok sorry... mines on a 17 foot cajun bassboat... right now my gps shows me running 38 mph with just me and my tackle in it. The prop thats on it is an aluminum one that i took off but cannot find the pitch size, i know it usualy says right around the hub but i dont see it anywhere...i know mine is an open hub, i guess ill try to take some pictures of it and post on here.

 

[Bondo]

Re: prop selection

that i took off but cannot find the pitch size, i know it usualy says right around the hub but i dont see it anywhere...

Ayuh,... Look under where the prop Nut goes...

 

[patrickj]

Re: prop selection

already looked there i even cleaned it with a brissle brush to make sure it wasnt covered up with carbon or something and i cant find it anywhere, This prop has 3 blades and at the back of each blade there is a bolt in the side of the prop and im not sure what its for. i dont know if that helps, i will get some pictures tonite if its light enough out and post them tomorrow

 

[jacoboregon]

Re: prop selection

Look on the blades for the size/pitch as well. That's where it's marked on my tohatsu prop.

 

[patrickj]

Re: prop selection

ok the only numbers i found on the prop where ssm 421 by michigan... so i emailed their customer support and they told me this.

Michigan Wheel P/N SSM-421 was manufactured from 1976 to 1982 as a 13" x 21" 3-Blade stainless steel propeller

I thought it was aluminum... apparently i was wrong. also my motor is a single exhaust. and as for rpms im running right now i have no clue... my tach shows 100 rpms idleing and 1200 full throttle... i believe it needs a new guage

 

[maverick974]

Re: prop selection

I just went thru this.
The 85 hp usually came from the factory with either a 17' or a 19' pitch prop. I'm no expert but 21 sounds a bit aggressive for an 85 hp engine.

 

[patrickj]

Re: prop selection

this is the prop that it came with when i bought it... i have no clue about sizes thats why im asking.

 

[jerryjerry05]

Re: prop selection

You can tell the difference betwen the alum and SS.
If it's SS and it's a 21p then you might be over propped.That's equivelent to a 23 alum.
You need a tach to be sure that you have the right stuff.
A 17 Cajun is light and fast. 38 with an 85 is really pretty good.
What RPM's at WOT??You post that and we can figure out the rest.
The tach has a dial on the back try turning the dial and see if it changes.J
They sell an item called a Tiny Tach.Works great!!!

 

[patrickj]

Re: prop selection

i will purchase a tach from the autoparts store and test it when i go out this weekend... I can get it to 38 and thats without me trimming it at all, my trim is having issues ive never tested it when the trim was working, im sure i could get a couple extra out of it with a working trim. but ill test this weekend

 

[jerryjerry05]

Re: prop selection

Working trim can add as much as 5 or more.