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Author Topic:   18 Outrage 115 OMC, What prop?
Tim Ehlers posted 07-19-2004 06:05 PM ET (US)   Profile for Tim Ehlers   Send Email to Tim Ehlers  
Hi all, We have gone from a 1972 16 ft Katama to a 1985 18 ft Outrage with a 1999 115 hp Johnson Ocean Pro.

What size and model propeller do you prop experts suggest? It currently has the 14-1/2 inch diameter by 19 inch pitch stainless steel prop that originally came off the previous old 150 hp Johnson that the new (in 1999) engine replaced.

I really have very little power boating experience. The Katama had a 120 hp Tohatsu with a 17p prop. It was underpropped (probably good for a beginner like me) and really accelerated. I originally felt the Outrage was underpowered, but after taking it out for four times, I think the boat will be fine for our family needs.

The engine is up two holes and the propeller breaks free in tight turns unless trimmed all the way in. I only had a gps on it when we test drove it. It got about 37 mph at around 5400 rpm max. I originally thought it had a 17 inch pitch prop because of these numbers and relating them to my old Katama, but the prop hub on the Outrage says 14.5x19.

As of late I have read a lot about what power you guys like on the 18 Outrage. A lot of proponents going for the top rated hp at 150, but a lot who are happier at the 115 hp range I am at. I have not read what propeller you 115 hp range guys are at. What do you suggest?

Also, the manual does not give me the gear ratio this 1999 115 hp Johnson has. Does anyone know? I do know that the prop has a 4-1/2 inch diameter hub as compared to the old Tohatsu 120 with a 4 inch hub.

As always your advice is appreciated. Three years ago when we got the Katama I learned about this site and have read it fervently. We could not be happier that by chance we picked an old Whaler as our first boat.

Also thanks to Mike Gephart for the parts sheets he faxed for the 18 Outrage a few weeks ago. The boat needs a few things, but overall it is a keeper. Tim

kamie posted 07-19-2004 11:01 PM ET (US)     Profile for kamie  Send Email to kamie     

With the current prop on there and lightly loaded what is the engine RPM's at WOT?

Peter posted 07-20-2004 07:21 AM ET (US)     Profile for Peter  Send Email to Peter     
I believe the 25 inch shaft version of the Johnson 115 runs 2.25:1 gears in the gearcase so a 19 inch pitch should be about right. Your calculated slip is a bit on the high side and makes me wonder whether your motor is mounted too high for the particular propeller you are running. Is there a model number stamped on the hub of the propeller?
Tim Ehlers posted 07-20-2004 09:43 AM ET (US)     Profile for Tim Ehlers  Send Email to Tim Ehlers     
Thx for the gear ratio. The 120 Tohatsu had 2:1 and an aluminum 17p prop. The 2.25:1 ratio on the Johnson explains the similar performance although a bit less due to more slip. Because of the trim sensitivity and blow out in turns coupled with what seems to be a low percent efficiency at wot I think the engine is too high for this propeller.

The back of the hub has these markings: 14.5 x 19 389924 and the letter M in a tilted square border. The outside is marked with the numbers 5174

WOT, trimmed out with two adults, two kids and half tank of gas is around 5300 to 5400 RPM.

So what size, type and manufacturer of prop are you guys with similar engines on an 18 Outrage running?

Peter posted 07-20-2004 10:32 AM ET (US)     Profile for Peter  Send Email to Peter     
You have an OMC SST II. My experience with this style is that it doesn't run shallow very well and there is a sharp transition between good traction and a blow out. If you are going to run two holes up, an OMC Raker 14 1/2 x 18 is a better propeller for that situation. If you drop down to one hole up, the SST should work OK.

I used to run a 14 1/4 x 21 Raker on the 18 Outrage with a Johnson 150 mounted two holes up.

elaelap posted 07-20-2004 08:31 PM ET (US)     Profile for elaelap  Send Email to elaelap     
Tim, with your permission I'll tag along with a similar question about propping a 115:

I have a 13" diameter 19" pitch '19-K' Yamaha black steel prop on my '04 Yamaha 115 four stroke. The prop came off the '88 Yamaha 115 two stroke which came with my boat and was part of the trade for my new motor. My '88 Outrage 18 hits 41 mph/GPS on a calm lake at 5800 rpm WOT, one hole up.

I'd like to hit 6000 turns wide open and I'm thinking of trying a stainless 17" pitch prop...think that would do the trick, guys? And I've recently heard about a very good deal on Stiletto props...are they what I'm after?


Abalonehunter posted 07-20-2004 11:13 PM ET (US)     Profile for Abalonehunter  Send Email to Abalonehunter     
My brother and I were skeptical about Tony's 115 on an 18 Outrage but after riding on it with 4 on board, plenty of gear and a full tank of gas I can very comfortably conclude that in our SF Bay Area waters, Bodega Bay specifically you don't need to go any faster and the 115 yamie got up plenty fast to move out of the way. Tony, haven't got a chance to say thanks again, been gone for a bit but the ride was great, no fish really to speak of then (don't want to hear about the last couple of weeks) but a very pleasant day on the water with you and the boys. I'll be off for 5 weeks come August maybe we'll see you out and about.


Peter posted 07-21-2004 07:41 AM ET (US)     Profile for Peter  Send Email to Peter     
Tony, a 17P propeller is likely to put you over 6000 RPM, probably in the neighborhood of 6200 to 6300. In my opinion, you are running the right propeller for your situation.
Tim Ehlers posted 07-21-2004 09:28 AM ET (US)     Profile for Tim Ehlers  Send Email to Tim Ehlers     
Peter thx for the info. Tony, tag along. The more info the better. What gear ratio do you have? My max rpm is 5500 per manual and if Peter is right 2.25:1 gears mean a higher pitch prop if I am to get near 40 mph if possible.

Doesn't the size and weight of a boat kind of determine what diameter propeller it needs? How come Tony is at 13 inches and I am at 14-1/2 inches? Same HP. Different brand engines? I remember reading on another thread, by Sal I believe, that bigger boats demand larger diameter props. I would think that larger engines in general would also use larger diameter props. I was surprised that my 115 Johnson was swinging a 14-1/2. Any more insight on this would be appreciated. Tim

Peter posted 07-21-2004 10:32 AM ET (US)     Profile for Peter  Send Email to Peter     
You can try turning a smaller diameter 19P propeller. The V4 propellers were usually in the 13 to 14 inch diameter range. You will gain some RPM by doing that.
Peter posted 07-21-2004 10:33 AM ET (US)     Profile for Peter  Send Email to Peter     
You can try turning a smaller diameter 19P propeller. The V4 propellers were usually in the 13 to 14 inch diameter range. You will gain some RPM by doing that.
elaelap posted 07-21-2004 10:38 AM ET (US)     Profile for elaelap  Send Email to elaelap     
Thanks for the ride, Tim. My motor's gear ratio is 2.15 (28/13).

Peter's probably right--the boat is doing fine as it is; no complaints at all. My last boat, a Katama with a 50 hp Yamaha 4/s High Thrust, topped out right on the button at 6000 rpm, and I've been told by the dealership mechanics that Yamahas like being propped to achieve the highest turns without exceeding redline. I'll probably leave it alone, but I do have an opportunity to pick up a Stiletto prop at a very good price, and couldn't resist wondering...


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