Prop Question

[fishnski14]

Would anyone happen to know of a 4 blade 21 pitch propeller that would fit a 1985 force 125?

 

[alldodge]

Would anyone happen to know of a 4 blade 21 pitch propeller that would fit a 1985 force 125?

:welcome: to iboats

Here is just one place I found
at propline dot come

Guess the question I would have is why 4 blades?
For every blade added to a prop you get more lift but you also get more drag

 

[SkiDad]

the Michigan wheel vortex 4 will fit but I think it only goes up to 19 pitch. you have to take your anode off and also remove the plastic ring from the prop. And the thrust washer in the hub kit is not a complete match but it will work. 21 is a lot of prop for a Force - is your boat really light ? most of us run 17 or 19 pitch. Even 15 is not that uncommon. You want to make sure your RPM is 5000-5500 or you have too much prop.

 

[achris]

Merc do a series, the Spitfire... Up to 23"...

https://www.mercurymarine.com/en/us/...ries/spitfire/

 

[Jiggz]

Just wondering what kind and size of prop you have on it right now. 21P 3 blade is about the max these Force 125's can handle for a very light or small boat and when using 4 bladed props it is recommended to use the next lower pitch due to the added drag.

 

[fishnski14]

I have a 16ft King Fisher. The motor had a 13x15 and I was maxing out the rpm on a 6k tach. I then tried a 13X19. The 13X19 did decease the rpm but once the boat would plane out and get up to speed the rpm would max out. I have a Solas 4 blade 21 pitch but now having difficulty finding the correct spacers.

 

[SkiDad]

what GPS speed are you hitting - I'm betting you don't have a 20 pole tach hooked up - Force has it's own deal for tach and a regular tach will read wrong - I can see you pegging it with a 15 but not a 19

 

[Jiggz]

As Mitzysman mentioned, you need to validate your tach with your speedo or even better with a GPS. With a wrong tach or faulty tach, you can easily max out RPM despite the boat speed being only in the 20's MPH.

 

[fishnski14]

You guys are awesome, thanks for all the information. .

I have not got a GPS speed as of yet, I was more concerned with assuring I'm in the right rpm range to prevent damaging the engine. If I had to guess the speed I would say 45- 48 mph easily at half way between 3/4 and full throttle.

I have used the original tach and a tach in the same year model...the tach are running very close with in 200 rpm.. the motor pegged both. The engine came off a bay liner Capri which is a lot larger than my boat.

 

[fishnski14]

what GPS speed are you hitting - I'm betting you don't have a 20 pole tach hooked up - Force has it's own deal for tach and a regular tach will read wrong - I can see you pegging it with a 15 but not a 19

I used the tach that came with the motor I used all the gages that was with the boat originally. I thought this would be the best in the event something did not act according

 

[jerryjerry05]

The 125 can peg a 19p on a real small boat.
A 21p SS might bring it down.
The 21ss is about a 23 aluminum.

 

[SkiDad]

this 19p prop will fit if you are looking for stainless - the price is a little high but it's a direct fit (will need the black plastic aft flare or brass spacer) http://www.ebay.com/itm/MICHIGAN-ST..._Accessories_Gear&hash=item2c8efc65b7&vxp=mtr

here is a 21p (black aft spacer won't work but the brass spacer will work) http://www.ebay.com/itm/MICHIGAN-WH..._Accessories_Gear&hash=item3f3e26df4d&vxp=mtr

 

[fishnski14]

The 125 can peg a 19p on a real small boat.
A 21p SS might bring it down.
The 21ss is about a 23 aluminum.

I wasn't aware that a stainless steel prop will would make such a difference. I wouldn't mind getting a SD but around here an aluminum would be a better decision.

I would rather buy another prop then have a lower unit replaced the SS pro isn't as forgiving.

 

[fishnski14]

this 19p prop will fit if you are looking for stainless - the price is a little high but it's a direct fit (will need the black plastic aft flare or brass spacer) http://www.ebay.com/itm/MICHIGAN-ST..._Accessories_Gear&hash=item2c8efc65b7&vxp=mtr

here is a 21p (black aft spacer won't work but the brass spacer will work) http://www.ebay.com/itm/MICHIGAN-WH..._Accessories_Gear&hash=item3f3e26df4d&vxp=mtr

Hey thanks for the links. I'm going to save them to my watch list.

 

[achris]

...I would rather buy another prop then have a lower unit replaced the SS pro isn't as forgiving.

This statement/belief is a urban myth. I have no idea where it started or who started it, but it's bollocks!

It matters little as to the material of the propeller as to the extent of damage to the internals of a gearcase on submerged impact.... I have seen gearcases completely destroyed, and it didn't matter, SS or ali. I have also seen SS prop blades folded over like a piece of paper, and the gears and shaft completely unscathed.

The material of the propeller has as much to do with the damaged sustained by a gearcase as a tea-leaf knows the history of the East-India company.

So, will everybody who reads this please STOP perpetuating this myth about SS props and gearcase damage...

Chris........

 

[jerryjerry05]

Your opinion? Or fact?

 

[achris]

Your opinion? Or fact?

Fact, borne out over more than 20 years in the boat fixing business.... I have seen stainless props screwed up like bits of paper, expected the internals to be much the same, but with not a thing wrong. Seem the same with ali props (a lot) too... Seen plenty of ali props with barely a mark on then, but the drive shaft sheared. That was a common one for the older Mercruisers with the 'O' ring groove on the top of the drive shaft... Once they changed to the ungrooved shaft, see a lot less sheared shafts, but the prop on has no bearing on how much damage will occur inside the drive.... That is an indisputable fact...

Chris.....

 

[fishnski14]

This statement/belief is a urban myth. I have no idea where it started or who started it, but it's bollocks!

It matters little as to the material of the propeller as to the extent of damage to the internals of a gearcase on submerged impact.... I have seen gearcases completely destroyed, and it didn't matter, SS or ali. I have also seen SS prop blades folded over like a piece of paper, and the gears and shaft completely unscathed.

The material of the propeller has as much to do with the damaged sustained by a gearcase as a tea-leaf knows the history of the East-India company.

So, will everybody who reads this please STOP perpetuating this myth about SS props and gearcase damage...

Chris........

From a generalized standpoint it would seem that SS props would be less forgiving than aluminum. Aluminum is generally more softer ferrous metal compared to SS, but I do not have the experience to make that argument so I am going to take your advise. I was able to find the necessary adapters to put the blade on but haven't had a chance to put it in the water...and if the rpm's are still too high I have no idea what to do next.

 

[Jiggz]

I hate doing this, but FYI Aluminum is NOT a ferrous metal.

 

[fishnski14]

I hate doing this, but FYI Aluminum is NOT a ferrous metal.

it's OK.. that's what I get for not proof reading. Lol

what would you do if after a 4 blade 21 pitch and the rpm's are still to high.