Which prop is stock

[Thompsoncustom]

I was wondering if someone could tell me what prop comes stock on a 1990 Johnson 20hp J20CRESB.

I just bought the motor and the alum prop is destroyed so Ill be looking to put a prop on this thing. I see the way a lot of people do it is with a tach and the optimal rpm range but I don't have a prop at this point.

 

[Sea Rider]

Factory delivered prop probably is not opt for that combo, but it's a good start to go from there maximizing prop with a tach to suit your boating needs.

Happy Boating

 

[steelespike]

Your old prop may have the numbers near the base of the blades or under the prop nut.
Your prop selection would depend on the size,weight and typical load of your boat.

 

[Georgesalmon]

Now a days new motors don't even come with a "stock" prop. Each motor is propped to match the boat it is going on. Think about putting a 200hp motor on a lightweight aluminum boat or the same motor on a 25,000 pound barge. The boat prop might be a 23 pitch and the barge a 9 pitch. You need to look at what you had for a prop and start there. There are numbers on it somewhere as suggested above.

 

[Sea Rider]

Most engines in the small to medium size comes with a stock factory delivered prop, on larger ones a prop must be selected depending on the application, but very lucky that on first selected prop may match what you expect to accomplish. So a second prop selection is usually what you end with. That's if in pursuit to take all the ponies out of any given engine sitting on any given watercraft.

Happy Boating

 

[Thompsoncustom]

Thanks for the help so far guys, Prop that was on it is a 10x13 it was listed on the prop under the nut.

Well as far as plans go I'm looking for speed with this motor I have a 1965 6hp johnson for just getting around, boat is a 98 alumacraft and is only rated for a 20hp motor and 700 pounds of weight including all people, gear, and motor. This motor looks like the carb and intake manifold might need some upgrading to grab a little more power so the prop will probably need to be different when i'm all done with it anyways.

Anyone have a idea of the rpm range for this motor?

 

[Sea Rider]

You could buy same 13 pitch prop, but as that engine/prop has not been tached before won't know if it's a top performer at wot or not. It's always a great idea to tach stock delivered props from new, that way will know if opt to replace same when the original breaks or go +,- in pitch to maximize prop from there. Selecting second props by wild guessing method if stock has not been previously tached could end throwing money into the blue.

Probably hard to plane a large boat with just a 6 HP but can better its overall glide displacement speed and not lug the engine if liking going wot.

Happy Boating

 

[Thompsoncustom]

Bought the 20hp with the prop so messed up I wouldn't want to try and run it so never had a chance to get any rpm readings.

Ya can't plain with the 6 HP at all but its great for the shallow shallow wapsi if you dont mind a top speed of 7-10mph.

 

[steelespike]

As far as the 6hp goes buy or make a tiller extension so you can sit in the middle seat.We had a 12 ft steel boat with a 5 hp Gale it would pop on plane
with a 180 pounder in the middle seat.
Better than that check you tube , 2hp Jon boat.
Your 20 is rated 4500-5500. If your likely to haul a full load often I would start with a 12".
A healthy 20, light load, should run about 27-30 mph.

 

[Sea Rider]

In order to recommend a proper prop pitch, OP has not specified which lenght is the alumacraft. Factory delivered props perform very well on light to medium light applications. a 12 will move more weight, passengers much better than a 13, but if boating very lightly loaded engine will surely over rev and if liking going wot without a tach installed it's bad music for the engine.

Happy Boating