94 Javelin 17 foot + F/S with 78 Evinrude 140. Best prop?

MaPaHa

Petty Officer 1st Class
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Jul 6, 2012
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I have a 94 Javelin 17 foot + fish and ski boat that I just installed a 1977 140hp Evinrude 140 V4 cross flow ?bubble back? motor on and I?m trying to get the right prop. This motor uses a 13 inch to 13.875 inch dia prop with 13 spline small hub. I have three props I?ve tried and still searching.

The first prop is one that I was running with this motor for several years on a 22 foot pontoon boat that is 13.5 dia and 13 pitch modified to about 14 pitch. It?s a 4 blade Power Tech RXB series stainless steel. Obviously it?s the wrong one but I already had it so I wanted to get a bench mark. It ran through the 5,500 rpm range very quickly. This blade has exhaust ports for better take off.

The second one I also have is a standard type OMC stainless steel 13.875 dia that I believe is a 15 pitch (no markings) with large blades. It runs past 5,500 rpm and hits 6,000 and would probably run higher if I let it. I only ran it there for a few seconds as it climbed through 5,700-5,800. This one is closer to what I need than the first 4 blade. This prop also has exhaust ports for better take off. I ran this one on the pontoon boat before I bought the Power Tech 4 blade.

The third one is a high rake 19 inch pitch stainless steel with the same 13.875 dia without exhaust ports. The boat would not even get out of the water and plane off. I went right back to the dock to swap back.

Ideally I would like to run a 4 blade because of the mid range skiing / tubing but right now I would just like to find an all around prop that will yield 5,300 ? 5,500 rpm with two people in the boat.

Should I look at a high rake prop like came factory with this boat or more of a standard rake? This boat had a 150 Johnson with a 24 Raker prop from the factory with exhaust ports. The Johnson had a 1.87:1 gear box and the 140 has a 2:1. The 140 hp is rated at the prop so I estimate about 125 hp real numbers today.

Most of the props I?ve seen for this motor are 13 inch. How much allowance should I make for the extra 7/8 inch of dia if I find a 13.875 dia?

I really thought the 19 raker x 13.875 with 125 hp and the 2:1 gear box would be just right based on the original 150 motor, 1.87:1 gear box and 24 raker prop.

Am I missing anything? Any suggestions?
 

steelespike

Supreme Mariner
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Apr 26, 2002
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19,069
Re: 94 Javelin 17 foot + F/S with 78 Evinrude 140. Best prop?

Unfortunately your rpm doesn't help much without a gps speed.
Its possible the tach is not accurate or the prop may have slip problems or be other than a 15' prop.
With your gps speed and your gear ratio and a confirmed prop size we can get some meaningful results.
Perhaps a prop shop can measure the suspected 15" prop.
Have you checked the area under the prop nut for numbers?
 

MaPaHa

Petty Officer 1st Class
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Jul 6, 2012
Messages
239
Re: 94 Javelin 17 foot + F/S with 78 Evinrude 140. Best prop?

Yes, the numbers in the area under the prop nut can't be read. I've got another prop to test run so I'll get better readings on speed and rpm's at different levels and re-post in a day or two when I can get on the water. Thanks
 

MaPaHa

Petty Officer 1st Class
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Jul 6, 2012
Messages
239
Re: 94 Javelin 17 foot + F/S with 78 Evinrude 140. Best prop?

I’m getting closer.
I took it back out today and ran the 13.875 x 21 Raker again and finally got it on plane with someone sitting on the front deck. (I had said this was a 19 but it's a 21) It ran 4,300 rpm and 42- 43 mph.

I came up with a 13 x 21 basic SS prop (non ported) and it ran the same rpm but not as fast, maybe 38. Still would not come out of the hole. I don’t understand why it bogged down like the Raker because it was 7/8 inch smaller diameter, way less rake and maybe half the cup. Anyway I learned something and got some more stats.

I also came up with a 13 x 19 basic SS prop (non ported) that was beat up a bit and it ran much better. It came out of the hole slow but ok, and it ran about 45 mph at 5,000 rpm wot. It’s much better but still a little tall. I'm going to keep it and have since cleaned up most of the buggered edges. I'm going to drill exhaust ports in it for a better hole shot and repost the final performance and numbers for this prop.

My motor is an Evinrude 140 with a 2:1 gear ratio which is rated at the prop that’s around 125 hp in today’s standard according to most folks.

I'm still baffled how the "basic" 13 inch x 21 SS prop ran the same (pulling wise) as the 13.875 x 21 w high rake and high cup. When you look at both of them side by side the raker has much more blade than the basic one. I did lose about 4-5 mph with the basic prop.
If anyone wants to make some comments about diameter, rake, cupping and blade area I'm all ears.
 
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82rude

Rear Admiral
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May 8, 2012
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4,082
Re: 94 Javelin 17 foot + F/S with 78 Evinrude 140. Best prop?

I see you've tried everything but the one id try.13x17p if you can find one to try.i like the plain old solas amita 4 blade for my rig as it seems to work great but all boats, motors,and applications are different so its just a suggestion.i see for your motor its a 12 3/4 x17 solas 4 blade.dont get too hung up on diameter its not to critical unless your varying a lot (plus 1 inch).in the prop section of the sales area of this forum they have a quicky theory area for props,dia,pitch,3vs 4 blade and s/s vs al.
 
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MaPaHa

Petty Officer 1st Class
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Jul 6, 2012
Messages
239
Re: 94 Javelin 17 foot + F/S with 78 Evinrude 140. Best prop?

I got the 19 pitch to work ok. I cleaned it up a bit more and the blades are pretty smooth and uniform. I drilled 5/16 exhaust ports in it following a pattern that's used on two other props I have. It jumps to around 4,000 rpm coming out of the hole and gets on plane pretty good. At WOT it runs 5,000 rpm with 450 pounds of people and a light boat load otherwise and about 5,200 with one person @ 200 lbs. With two people it ran 44 mph and I didn't get a speed with just one. The trim was adjusted to max speed per rpm without ventilating.

According to the tach, pitch and speed; this calculates to about 5% slippage. (5,000 rpm, 19 pitch and 44 mph)

I agree it wouldn’t hurt to drop back to a 17 pitch if the boat is used with a heavier load, but this one seems fair.
 
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