Anyone running 19 or 21 pitch on Force 85?

[capri1600]

Anyone running 19 or 21 pitch on Force 85? I have this engine on a 1972 Glastron GT-150 with 17 pitch and it hole shots and jumps on plane like you would not believe on a 3 blade stainless prop. It's GPS'ing at right about 40mph and the engine sounds happy but I think I'm a little under propped and I don't have faith in my tach. So, is anyone running 19 or 21 pitch on the 85 and if so, on what hull? I think a GT-150 of that era was originally well under 600 pounds. I read somewhere that a runabout style hull of under 1200 pounds was a good candidate for 19 pitch. I only mention 21 pitch because I'm sginificantly lighter than that.

Marty

 

[Frank Acampora]

Re: Anyone running 19 or 21 pitch on Force 85?

Yeah, Marty. I run a 19 pitch on a 90 Chrysler on a 15 foot V153. She turns 5000 and does 45MPH. You should be able to use a 19 pitch on your GT 150 and still get 5000 RPM since the GT is shorter and lighter than the V153. 21 pitch just might be too much for a stock 85. You may need to play with engine height, HOWEVER, the transom on the GT is 21 inches versus the 20 on my V153 so be careful. a 1/2 inch higher might be all you can get. Play around a bit: I would expect a couple of MPH MORE out of the GT versus the V153--say 45-47 MPH.

My GT 150 has yet to see the water, probably won't for another year at least, but it is going to get a Chrysler 140 with a nice 21 or 23 pitch cleaver or maybe that beautiful 25 pitch two blade Mercury bronze racing prop.
Which, by the way: If your Force is earlier than 94, why don't you get a Chrysler 12 X 19 SS cleaver prop. They boost performance remarkably well. Check with Franz over at franzmarine@aol.com.

In either case, stay with stainless

First photo is my 1971 V153 with a 105 on the back. It does 45 just like the 90 does except the hole shot is much faster. Second picture is the BEFORE of my recently acquired GT 150 and the last shot is over the transom of my V153 with the Chrysler 90 pumping away at 45 MPH.

 

[my1stboat1]

Re: Anyone running 19 or 21 pitch on Force 85?

hey capri, If you decide to go with a 19 pitch i will be ready to buy your 17 stainless if your looking for a sale... let me know

 

[capri1600]

Re: Anyone running 19 or 21 pitch on Force 85?

Where should I look for a 19 pitch Chrsyler that'll fit my Force? I watch eBay constantly and do open searches in the Internet once in a while. I know I can buy a new aluminum 19 pitch from Michigan Wheel and I may have to start there. Thats what I did with the 17. I have an alomost brand new aluminum 17 pitch on the shlef as a backup after I fell upon this gorgeous 17 pitch in stainless that I'm using now.

 

[jerryjerry05]

Re: Anyone running 19 or 21 pitch on Force 85?

Before you spend $$ Get a tach that you can trust.
Then go for a ride and see what you run.Just switching to a different pitch might be ok but you might be overpropped.
It could and probably will hurt the gas mileage.
I have a 21 with twin 85's stock 17p.I wanted MORE!!!! So I got a pair of 19's and got the speed(3-4mph) and the poor economyabout 20-25% more.
I switched back and resold the 19's.
The 17 stainless is the same as a 19 aluminum.J

 

[Frank Acampora]

Re: Anyone running 19 or 21 pitch on Force 85?

Check your private messages.

 

[capri1600]

Re: Anyone running 19 or 21 pitch on Force 85?

I was able to get some runs in this evening using a tach I trust and GPS. With 17 pitch I was seeing 38mph at about almost 6000rpm. I can either use this prop to get a great hole shot and then throttle back to get down below 5500rpm or go to 19" pitch. Any thoughts?

 

[jason32038]

Re: Anyone running 19 or 21 pitch on Force 85?

I have an 84 15ft capri bowrider with an 86' 85hp force and it came with a 19p prop. It's was a screamer until the bottom piston failed. It doesnt have a tach yet and I didnt have the speedo hooked up but it felt like I was atleast hitting 45.

 

[capri1600]

Re: Anyone running 19 or 21 pitch on Force 85?

I'm running a full blade 17 pitch stainless prop on a Glastron GT-150 with this engine. If I find one similar in a 19 pitch I think I'll try it but the engine sounds happy and I'm not running around at full throttle so I dont think I'll hurt it as is but I wouldn't a little more travel speed.

Marty

 

[Frank Acampora]

Re: Anyone running 19 or 21 pitch on Force 85?

38 MPH is just too slow for that boat and engine combination!

I would be embarassed running that cute, classy little hull at that speed. James Bond wouldn't be caught dead going that slow. LOL (But he had a "Rude" 135)

6000 won't hurt the engine but you can't go fast without pitch. So, if you consistantly run 6000 at WOT with the 17 pitch, you really need to step up to a 19 pitch prop. That will drop RPM to about 5600 and the speed may rise a couple of MPH. Of course, you still need to use a stainless prop--aluminum will be slower.

Right now with the 17 pitch, your theoretical top speed is 43 MPH. If you step up to 19 pitch and drop to 5600 RPM your theoretical speed will be 45 MPH. This has the assumption that based on current RPM the lower unit is a 2 to 1 ratio and prop slip is 10%.

6000 rpm divided by 2 equals 3000. 3000 times 17 inches divided by 1056 and multiplied by .90 equals 43MPH

1056 is a constant and is the product of 12 (inches per foot) times 88 (feet per second at 60 MPH) When divided into the product of lower unit (Prop) RPM times prop pitch in inches it gives a direct (theoretical) top speed MPH result. Then factor in the prop slip.

Using your GPS result of 38 MPH, your prop slip is at 22% which is too high. Going up to the 19 pitch may result in a lower prop slip and a greater gain than the difference in theoretical-- that is, you may see closer to 45 MPH than the calculated (39-40 MPH) would indicate.

 

[jerryjerry05]

Re: Anyone running 19 or 21 pitch on Force 85?

If your running a 17SS at 6000 Then you can move up to a 19SS or a 21 aluminum.
Some dealers have extra props laying around. Ask around the service local department.
Tell them what your doing and they might loan you one till you buy a new one.J

 

[capri1600]

Re: Anyone running 19 or 21 pitch on Force 85?

Well, I didnt want to say so but I was thinking the same thing Frank. Thanks for the well thought out reply. I'm expecting 43 when I find that 19" stainless prop. We have a prop shop right here in town that is pretty well known, Delta Propeller in Cleves, Ohio. They get stuff in all the time that becomes available 2nd hand. If I'm patient something will come up. I have an aviation background so I understand your prop slip calculations and theory. It's fun comparing the math to real world. Sometimes there is a surprise.

 

[Frank Acampora]

Re: Anyone running 19 or 21 pitch on Force 85?

Ask them to be on the lookout for a Chrysler 12 X 19 stainless Cleaver. It will be expensive, but worth it. You may also want to try a Ballistic--see my post on aftermarket props. Ballistic is fully cupped and bow lifting. You may be able to raise the engine and also use full out trim with this prop. This means you will get the hull up out of the waterand riding "loose" I have not yet tried my ballistic so I can't tell you if it will actually do what I said.--unfortunately that will need to wait until next spring.

Here is my 90 on a 14 foot flat bottom. It goes 55 MPH with a Chrysler 21 pitch stainless cleaver prop...Will try to post a photo of it at speed.

 

[capri1600]

Re: Anyone running 19 or 21 pitch on Force 85?

You dont know expensive until you buy a prop for an inboard hydroplane. 2nd hand the good stuff starts at about $600. I run a 10 X 16 3 blade cleaver direct drive at 6500rpm on my APBA hydroplane.

 

[anple]

Re: Anyone running 19 or 21 pitch on Force 85?

Hello,
My recent purchased boat is 17' with 120 Force and 21p prop, I found on Craigslist 2 props for sale: 15p, and 19p, can someone tell me if which one will make my boat go faster? The blades of the 19p seem to be larger than 21p's, and the blades of the 15p seem to be the same with the 21's. Many thanks in advance!

 

[Frank Acampora]

Re: Anyone running 19 or 21 pitch on Force 85?

There you go, capri! It took me a while but I finally found the photo. This is the 14 footer with the 90 swinging a 12 X 21 cleaver at 5500 RPM and 55 MPH. Notice how the trim is all the way out? That's because the cleaver is fully cupped along the trailing edge and can hold the water at that setting. Notice how much of the hull is in the air? that's how you want the GT 150 to ride.

anple: It really depends upon how well the engine is running now. If the 21 pitch is letting the engine turn up around 5000-5500 RPM, then the 19 pitch will be slower. In any case, the 15 pitch will give less speed and is too low a pitch for your application.

 

[capri1600]

Re: Anyone running 19 or 21 pitch on Force 85?

I just found a nice looking 19 pitch 3 blade stainless prop on eBay. Hopefully this weekend I'll be able to make some runs and see how it changes things.

Marty
http://www.martyhammersmith

 

[my1stboat1]

Re: Anyone running 19 or 21 pitch on Force 85?

capri do u want to sell ur 17

 

[capri1600]

Re: Anyone running 19 or 21 pitch on Force 85?

capri do u want to sell ur 17

Not yet. The 19 isn't even here yet. Once it proves itself, then yes.

Marty
http://www.martyhammersmith.com

 

[anple]

Re: Anyone running 19 or 21 pitch on Force 85?

Thank you, Admiral Frank!

My 1997 Force 120 does only 50mph on WOT 5250 RPM with 21p aluminum prop. My boat is Maxum 17'. Any ideas how to make it runs faster? Thanks - Anthony.

There you go, capri! It took me a while but I finally found the photo. This is the 14 footer with the 90 swinging a 12 X 21 cleaver at 5500 RPM and 55 MPH. Notice how the trim is all the way out? That's because the cleaver is fully cupped along the trailing edge and can hold the water at that setting. Notice how much of the hull is in the air? that's how you want the GT 150 to ride.

anple: It really depends upon how well the engine is running now. If the 21 pitch is letting the engine turn up around 5000-5500 RPM, then the 19 pitch will be slower. In any case, the 15 pitch will give less speed and is too low a pitch for your application.