# Which Prop for 1970 20HP Johnson Seahorse



## russ010 (Jul 6, 2010)

So... when it's just me in my 1546 Xpress with the 20hp johnson, my GPS Fishfinder puts me anywhere from 17-19mph.

When I put another person in the boat (weights ranging from 185-225), the top speed goes to about 10-12mph... is it just the person causing this much power loss? It sounds like it's not rev'd up to it's full RPM, but that could just be me


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## bassboy1 (Jul 6, 2010)

You need to get a tach to really make any changes, but to me, it sounds like the second person is weighing the boat down enough that the engine is overpropped for the load. Being overpropped, the engine doesn't have enough power to turn that much prop with that much load, and is lugging. A prop with a little less pitch will gain you the RPMs back, and possibly get you running a bit faster. A tinytach can be bought for around 40 bucks or so, and with that, you can determine how much of a prop change is needed to get the motor into the ideal operating range.


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## russ010 (Jul 6, 2010)

That's what I think the main cause is... before there was a bit smaller prop, then when I had the guy work on the motor, he put a bit bigger (looks to be anyway) prop on it. Before with the same person, there was still a lot of speed... but it's gone now.

I wish I knew what pitch prop he put back on, but I'm not sure what it is and he didn't write it down on the sheet I got from him. He just told me it was the replacement prop


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## crazymanme2 (Jul 6, 2010)

Why was a different prop put on or was that part of the motor work :?:


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## cajuncook1 (Jul 6, 2010)

crazymanme2 said:


> Why was a different prop put on or was that part of the motor work :?:




Was thinking the same thing! :wink:


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## huntinfool (Jul 6, 2010)

The numbers should be stamped on the prop. Go see what is on there and if you have the old prop, I would just switch it back.


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## Quackrstackr (Jul 6, 2010)

You won't really "see" a difference in pitch as being "bigger".

It may have more pitch as well as being a larger diameter if it looks physically larger.


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## Pruitt1222 (Jul 6, 2010)

Did you change the trim for the extra weight? I know on my little boat with just myself it runs 26mph on second trim lock. Add my dad I have to go to the last trim setting and only lose 2mph. Were as I lose 7 mph at the same trim setting for just myself with him aboard. Just a thought, I think BassBoy1 is right on. Sounds to me like you ain't got enough umph to get her up to rpms. I think the factory prop for those engines is a 9x10 with 9x9,9x10,9x11, and 9.5x11 fairly easy to come by.


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## russ010 (Jul 7, 2010)

He changed the prop because the one that was on there was the original and it was beat to hell.. sorry, should have been more clear as to why he did it.

I think he stepped up a size, maybe to a size 10?? I don't have the old prop anymore, but I'll check when I get home tonight to see if it's stamped on the current prop.

I changed the trim settings in all 4 places... the 2nd from the bottom is the best with just me and someone else in the boat... I tried all 4 settings out on the water that night with him in the boat. I did gain 2mph when I drove and moved him closer to the front

Pruitt.... I just realized you are in owensboro, ky - that is where my sister-in-law currently lives (her husband is from there)


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## russ010 (Jul 22, 2010)

I found some numbers on my prop (finally)... all they say are 12011. The prop is black, but where the numbers are, it's unpainted.

I keep looking and I've found 2 different props that I can use. A 9x9 and a 9x10.... but how do I figure out which to go with - especially when I don't know what is on there now.

I tried to measure from the diameter of the prop, and it' seems to be around 8.25". I'm almost positive this prop is bigger than the prop that was on there before (which I had no problems with, and the guy doesn't have anymore)


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## russ010 (Jul 22, 2010)

I think I just found the prop that is on there now!!! https://boatpropellers.iboats.com/J...29/20/?session_id=815112275&cart_id=027704256

It's got the same part number


SKU:#012011
Manufacturer: Michigan Wheel
Brand: Michigan Match
Material: Aluminum
Diameter: 9”
Pitch: 10”
Blades: 3
Rotation: Standard (Clockwise)


Should I get an OEM prop? or drop down to a 9 x 9


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## Quackrstackr (Jul 22, 2010)

If you aren't getting full rpm under load, I would drop back in pitch.

That change should net you 200 rpm.


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## Whoopbass (Jul 22, 2010)

I think the stock prop for my 25 hp Evinrude is a 10 X 13. I have ran a 10 X 13 and a 10 X 11 on this motor and they seem to top out about the same speed but the 10 x 11 can handle heavier loads better. The 10 X 11 prop takes off faster and just feels better overall. The lighter the boat/load the higher the pitch you should get. 

Iboats has a 9.25 x 11 prop for your motor and that's the one I would go with. Kinda strange higher pitched props are not available for your motor. It seems like a 10 X 13 prop is standard for most small outboards.

https://boatpropellers.iboats.com/Johnson/20_HP_(1969-1973)_11.00-Pitch_Propellers/29/?rotation=Standard&session_id=423155545&cart_id=129658428


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## Quackrstackr (Jul 22, 2010)

If he's already overpropped, he sure doesn't want to add more pitch. :?


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## sturdi87 (Jul 22, 2010)

russ010 said:


> I think I just found the prop that is on there now!!! https://boatpropellers.iboats.com/J...29/20/?session_id=815112275&cart_id=027704256
> 
> It's got the same part number
> 
> ...



I recently went through the process of replacing a prop which included lots of research as I had virtually no experience prior to that. But I would agree with you, I would say that is the prop he put on for you as well. What I learned from my research the michigan match series of props are designed to be OEM replacements. What year is your motor? Keep in mind that the replacement may be bigger because the original had been beat up, filed down, beat up again, filed down again, who knows. So to answer your question to some degree from that he may have gotten you the closest thing to OEM he could find for you (so an OEM replacement may make absolutely no difference). What I learned from all the research and questions I asked when I was doing this is you really need a tach in order to even make a semi-educated guess at what changes you should make as far as pitch/diameter are concerned. Then when you throw in factors like cupping, rake, three or four blade, even blade thickness, etc. etc. etc. it just gets more complicated and difficult, especially without a tach. 

I personally would just be worried about laying too much money down on props on a 20hp, especially if its an older one, I know I have seen your thread more than a few times but I don't recall too much about your motor (I thought you were one of those electric only guys? glad to see you came over to the darkside though!). I'm assuming you have already bought one prop for it (i doubt the mechanic gave you that one for free, but if so I would like his number) and now you are talking about getting another one and the chances that it does no better or does worse seem higher than the chances it does better to me due to the complicated nature/unknown information. By the time you buy three or four props and get it exactly right you probably could have just bought a used 50 hp off craigslist. Good luck.


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## Whoopbass (Jul 22, 2010)

Yeah your right now that I read his first post better.
My 11 pitch prop looks larger then my 13 pitch prop. He said his original prop was smaller looking then the 11 pitch that is on it now so maybe his original prop was higher pitched. He said his motor can't push heavier loads now so that would make me think he needs a lower pitched prop.
Somewhat confusing.
Go back to your mechanic and see if he has any other props laying around that you can test since apparently he caused this mess.


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## russ010 (Jul 22, 2010)

Well... I'm going to get an OEM 9 x 9 prop and be done... If it does better or worse, so be it. This particular prop does fine with just me in it, top speed around 18-19mph (since I took another battery out to lessen weight). However, before when it was just me in it, it screamed and I never had any problems having another person in the boat with me.

If it turns out that I can get a few more RPMs (which is what I need at full throttle with someone in the boat with me) I think I'll be ok. Right now my motor just can't turn that prop with 2 people in it - and that's not right.

Thanks everybody for your input - always good to know I have smarter guys than me out there when it comes to motors.

And yes, I was an electric only guy for a long time - but that was before I got a bigger boat and started fishing bigger waters. I still have all of my trolling motors and fish electric only tourneys (except for one particular lake). I am going to get a bigger motor one day - but this seahorse is going to have to blow up before I do anything like that. I paid $350 for it and it serves it's purpose. The first prop I got was $100, and I can get the OEM one for the same price. But I won't be spending another $100 for it. I only saw 4 props that were available for this motor - and they were a 9x9, 9x10 in aluminum, and 9.25 x 9, 9.25 x 12 in stainless steel (https://www.dixiemarinesales.com/Propref.aspx).


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## bassboy1 (Jul 23, 2010)

> But I won't be spending another $100 for it.



Call around to some of the prop shops. Most have rebuilt props, from 45 and up. A prop for your engine should be at the minimum cost. I had to ship a 10 3/8 x 14 in from Nevada, as nobody locally had one, but the total bill, shipping and all, was 55 bucks - new Michigan wheel for this motor is 90+.


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## russ010 (Jul 23, 2010)

This is the one I ended up getting - 9 x 9 -- https://www.dixiemarinesales.com/detail.aspx?ID=1712.

If this doesn't fix me, then I'll have 2 props. I didn't want to go with another Michigan wheel, well I shouldn't worry about it, but that's what's on there now and I didn't want the same prop in a different pitch. I don't know if there's a difference between what I got and the Michigan Wheel - probably just price, but atleast I won't have the manufacturer to blame if I had the same problem.


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## sogafishin (Jul 26, 2010)

How did the new prop turn out?


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## russ010 (Jul 27, 2010)

I haven't gotten it yet - it should be here tomorrow (wednesday) and I'll try it out hopefully that night or Thursday before I leave for a week long military vacation....


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## Troutman3000 (Jul 27, 2010)

russ010 said:


> I haven't gotten it yet - it should be here tomorrow (wednesday) and I'll try it out hopefully that night or Thursday before I leave for a week long military vacation....



Where you headed to Russ?


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## russ010 (Jul 27, 2010)

back to my base in South Carolina.. we've got a mock mission going on. I haven't had a good trip in a looong time.... but I get to go to New Orleans for 10 days November (with only 2 days of work) for some dog and pony show about our equipment


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## Troutman3000 (Jul 27, 2010)

russ010 said:


> back to my base in South Carolina.. we've got a mock mission going on. I haven't had a good trip in a looong time.... but I get to go to New Orleans for 10 days November (with only 2 days of work) for some dog and pony show about our equipment




Nice - You should really enjoy that, too bad the ocaen is ruined down there.


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## russ010 (Jul 29, 2010)

I got the new prop in yesterday, but didn't have a chance to put it on or even take it out of the box... I'll do that tonight, but it will be a while before I get back on the water since I'll be doing military all next week.

But - for those of you looking for props, I just found this site. Wish I had seen it earlier last week when I ordered.

https://www.propcopropellers.com/


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## Pruitt1222 (Jul 29, 2010)

Thanks for the link, they are cheap. Don't wanna highjack or anything but what do you think light load is? like my boat loaded with myself is right at 700-800ish, You think that would be light load?


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## russ010 (Jul 30, 2010)

I don't know what they consider light load... but I know they told me I needed a heavy load (9 x 9) for my boat. 
I've got 3 batteries, about 100lbs of wood/accessories, 50lb trolling motor, me (185lbs), gas (40-50lbs), and the boat itself (320-350lbs) - this equals about 930-950lbs, and that 9x10 prop pushes me at a top speed of 18-19mph according to my fish finder GPS. When I get another person in the boat, the weight goes up another 200-250lbs - I guess that is what they consider a heavy load.

I'm going to get the prop put on tomorrow (I'm taking the boat to South Carolina with me), so I'll hopefully try it out tomorrow afternoon with another person in there with me to see how it does


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