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Author Topic:   What size prop for a 225 Johnson

heslmn15 posted 02-19-2003 10:29 PM ET (US)
I currently have a 19 pitch prop on my '95 225 Johnson. I have a 1996 21' Outrage and most of my time is in spent in the Pacific Ocean bottom fishing or running out for tuna. I am installing m120 sport tabs (Bennett) this coming weekend and I wanted to know if I should change my 3 bladed stainless steel prop. It seems to push the boat fine, but I was curious if I had the best thing available for this type of setup. I have heard of performance props build for saltwater use, but didn't want to throw my money away for something that I wouldn't really notice. I can get my boat up to about 52 MPH with 1 passenger and about 1/4 of a tank of gas on a flat lake. I don't think speed is a real problem. Could I get more speed by changing the pitch or would I not be able to get out of the hole if I went to a 21 pitch prop? If I went to a 17 pitch, would I lose a ton of top speed? Any suggestions would be appreciated.
jimh posted 02-19-2003 11:03 PM ET (US)
Questions about propeller dimensions are greatly enhanced if you provide the current dimension of your propeller and the engine crankcase speed that obtains at wide-open-throttle (WOT). Your measured boat speed at WOT is also needed.
In addition, please provide the weight of your boat and the lower unit gear ratio of the engine.
heslmn15 posted 02-20-2003 12:11 AM ET (US)
jimh-
I am not sure what the current dimension of the propeller and the engine crankcase speed is at wot. At wide open throttle my rpm's are at 5500 and that puts my top speed at 52 MPH. My boat weighs 2500 lbs. dry weight. I am not sure what my lower unit gear ration is. How can I find out? Sorry, but I haven't had very much exposure to working with engines, or have extensive knowledge of how to make them perform at their best. If you could explain to me how I could obtain the gear ratio of the lower unit I will do what I can to get that info. Thanks for your response and your valuable input to my questions.
jimp posted 02-20-2003 10:56 AM ET (US)
heslmn15 -
I am, correction, was running a stainless 15x17 on my 1990 Revenge 22 with a 225 Johnson (which now only exists in pieces). 5,600 RPM about 38 kts (about 44 mph).
Sal DiMercurio posted 02-20-2003 11:45 AM ET (US)

I believe your engine is rated at 6,000 rpms, max [ thats crank case speed ].
I really don't see any advantage of putting tabs on her, she should react very well to trimming her in to run flatter.
Being your only getting 5,500 rpms out of her with a very light load, I would certainly concider going to a Stiletto 14.25 x 17 to allow the engine to breath better.
Your 19 pitch is not allowing her to get to the recommended max 6,000 rpms, the 17 pitch will allow her to rev 5,900 rpms.
Now what happens when you put a pretty good load on her with the 19 pitch, she's going to drop way down to about 5,000 or less rpms.
Always prop the engine for the high end of the recommended rpm range, which in your case is, 6,000 rpms with a normal load as if you were going fishing with the usual people & a full tank of fuel, & the engine trimmed out as far as she can without blowing out.
You may not loose much at wot by going to a 17 P., as she will spin 400 more rpms, & the Stiletto will make her ride far higher out of the water then a run of the mill omc prop, unless it's a performance prop.
Still wondering why you feel she needs tabs.
I'm pretty close to where you live, [ bay area ] Pittsburg.
Sal
Bigshot posted 02-20-2003 01:26 PM ET (US)
My 20 hydr-sports runs about 5900 WOT with a 94 225 Johnson and runs about 53mph(t_top slows her down). If you are only getting 5500 I would step down to a 17" like Sal said. You can have yours taken down and save some money, should be like $75-100 to make it a 17 or 18".
Barry posted 02-20-2003 04:57 PM ET (US)
How high is your engine mounted?
Sal DiMercurio posted 02-21-2003 09:45 PM ET (US)
Bigshot, i'v found that removing pitch from a s/s prop dosen't always come out as it should, because they can only bend the edges of the blades & the pitch starts at the body.
I'v found while increasing pitch seems to work far better then reving it.
If he's running a standard omc prop, he may concider going to a stiletto, as the boat will ride far different for only $250 compared to $500 for an omc [ Bombardier ].
Sal
heslmn15 posted 02-22-2003 09:58 PM ET (US)
Barry-
After looking at my boat today, I saw that my boat motor is mounted on the lowest possible point on the mounting bracket. When I lower my engine, it will hit the ground if I try to lower it all the way down. Could this be some of the problem I am having with porpoising?
Sal DiMercurio posted 02-23-2003 11:53 AM ET (US)
You bet it is, but you can't tell if the engine is to low because the skeg hits the ground when all the way down.
Some towing vehicles are higher then others which causes the trailer to be higher at the front, thus your engine will drag on the ground.
Yes, you will be leaping around like a frog if your engine is mounted to low, better raise it a couple holes & you will see a world of difference.
Sal
Barry posted 02-23-2003 02:25 PM ET (US)
The anti-ventilation plate on the motor should not be lower then the bottom of the hull. Positioning the engine so that the anti-vent plate is 1 to 2" above the bottom of the hull usually provides the best performance.
If you crank your trailer jack all the way down, will that allow you to lower your engine all the way?
Raising the engine may increase your RPMs. As Sal said, it is usually best to have the engine positioned and propped so that it runs close to the rated maximum.
I have read about at least one other 21-Outrage owner that had problems with porpoising. If the engine is positioned correctly then installation of trim tabs or hydrofoil may resolve that problem.
How did your tab installation go? Did you do it yourself?
heslmn15 posted 02-23-2003 09:44 PM ET (US)
I will call the shop tomorrow to see if they can raise the mounting on my motor. The install of the bennett tabs was a little tougher than I had thought. It would of been easier if I would of picked a better place to put the hydrolic pump. I sometimes become my own worse enemy when doing projects like these. I can't finish the project until Friday. Hopefully it will work when it is all said and done.
Tim

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Author	Topic: What size prop for a 225 Johnson
heslmn15	posted 02-19-2003 10:29 PM ET (US) I currently have a 19 pitch prop on my '95 225 Johnson. I have a 1996 21' Outrage and most of my time is in spent in the Pacific Ocean bottom fishing or running out for tuna. I am installing m120 sport tabs (Bennett) this coming weekend and I wanted to know if I should change my 3 bladed stainless steel prop. It seems to push the boat fine, but I was curious if I had the best thing available for this type of setup. I have heard of performance props build for saltwater use, but didn't want to throw my money away for something that I wouldn't really notice. I can get my boat up to about 52 MPH with 1 passenger and about 1/4 of a tank of gas on a flat lake. I don't think speed is a real problem. Could I get more speed by changing the pitch or would I not be able to get out of the hole if I went to a 21 pitch prop? If I went to a 17 pitch, would I lose a ton of top speed? Any suggestions would be appreciated.
jimh	posted 02-19-2003 11:03 PM ET (US) Questions about propeller dimensions are greatly enhanced if you provide the current dimension of your propeller and the engine crankcase speed that obtains at wide-open-throttle (WOT). Your measured boat speed at WOT is also needed. In addition, please provide the weight of your boat and the lower unit gear ratio of the engine.
heslmn15	posted 02-20-2003 12:11 AM ET (US) jimh- I am not sure what the current dimension of the propeller and the engine crankcase speed is at wot. At wide open throttle my rpm's are at 5500 and that puts my top speed at 52 MPH. My boat weighs 2500 lbs. dry weight. I am not sure what my lower unit gear ration is. How can I find out? Sorry, but I haven't had very much exposure to working with engines, or have extensive knowledge of how to make them perform at their best. If you could explain to me how I could obtain the gear ratio of the lower unit I will do what I can to get that info. Thanks for your response and your valuable input to my questions.
jimp	posted 02-20-2003 10:56 AM ET (US) heslmn15 - I am, correction, was running a stainless 15x17 on my 1990 Revenge 22 with a 225 Johnson (which now only exists in pieces). 5,600 RPM about 38 kts (about 44 mph).
Sal DiMercurio	posted 02-20-2003 11:45 AM ET (US) I believe your engine is rated at 6,000 rpms, max [ thats crank case speed ]. I really don't see any advantage of putting tabs on her, she should react very well to trimming her in to run flatter. Being your only getting 5,500 rpms out of her with a very light load, I would certainly concider going to a Stiletto 14.25 x 17 to allow the engine to breath better. Your 19 pitch is not allowing her to get to the recommended max 6,000 rpms, the 17 pitch will allow her to rev 5,900 rpms. Now what happens when you put a pretty good load on her with the 19 pitch, she's going to drop way down to about 5,000 or less rpms. Always prop the engine for the high end of the recommended rpm range, which in your case is, 6,000 rpms with a normal load as if you were going fishing with the usual people & a full tank of fuel, & the engine trimmed out as far as she can without blowing out. You may not loose much at wot by going to a 17 P., as she will spin 400 more rpms, & the Stiletto will make her ride far higher out of the water then a run of the mill omc prop, unless it's a performance prop. Still wondering why you feel she needs tabs. I'm pretty close to where you live, [ bay area ] Pittsburg. Sal
Bigshot	posted 02-20-2003 01:26 PM ET (US) My 20 hydr-sports runs about 5900 WOT with a 94 225 Johnson and runs about 53mph(t_top slows her down). If you are only getting 5500 I would step down to a 17" like Sal said. You can have yours taken down and save some money, should be like $75-100 to make it a 17 or 18".
Barry	posted 02-20-2003 04:57 PM ET (US) How high is your engine mounted?
Sal DiMercurio	posted 02-21-2003 09:45 PM ET (US) Bigshot, i'v found that removing pitch from a s/s prop dosen't always come out as it should, because they can only bend the edges of the blades & the pitch starts at the body. I'v found while increasing pitch seems to work far better then reving it. If he's running a standard omc prop, he may concider going to a stiletto, as the boat will ride far different for only $250 compared to $500 for an omc [ Bombardier ]. Sal
heslmn15	posted 02-22-2003 09:58 PM ET (US) Barry- After looking at my boat today, I saw that my boat motor is mounted on the lowest possible point on the mounting bracket. When I lower my engine, it will hit the ground if I try to lower it all the way down. Could this be some of the problem I am having with porpoising?
Sal DiMercurio	posted 02-23-2003 11:53 AM ET (US) You bet it is, but you can't tell if the engine is to low because the skeg hits the ground when all the way down. Some towing vehicles are higher then others which causes the trailer to be higher at the front, thus your engine will drag on the ground. Yes, you will be leaping around like a frog if your engine is mounted to low, better raise it a couple holes & you will see a world of difference. Sal
Barry	posted 02-23-2003 02:25 PM ET (US) The anti-ventilation plate on the motor should not be lower then the bottom of the hull. Positioning the engine so that the anti-vent plate is 1 to 2" above the bottom of the hull usually provides the best performance. If you crank your trailer jack all the way down, will that allow you to lower your engine all the way? Raising the engine may increase your RPMs. As Sal said, it is usually best to have the engine positioned and propped so that it runs close to the rated maximum. I have read about at least one other 21-Outrage owner that had problems with porpoising. If the engine is positioned correctly then installation of trim tabs or hydrofoil may resolve that problem. How did your tab installation go? Did you do it yourself?
heslmn15	posted 02-23-2003 09:44 PM ET (US) I will call the shop tomorrow to see if they can raise the mounting on my motor. The install of the bennett tabs was a little tougher than I had thought. It would of been easier if I would of picked a better place to put the hydrolic pump. I sometimes become my own worse enemy when doing projects like these. I can't finish the project until Friday. Hopefully it will work when it is all said and done. Tim