'59 Johnson QD-20

[Beefer]

I have a 1959 Johnson 10hp QD-20, and the prop is torn up beyond repair. From what I can find, the original prop was 8.25" D X 8" P. If I replace it with a 8.25d x 8.5p, would it work ok? How much rpm should I expect to lose with the extra .5"? Enough to be detrimental, or would it be negligible? I'm guessing I'd lose about 100rpm, but not sure if that is enough to be a problem for the motor. Thanks.

 

[steelespike]

Re: '59 Johnson QD-20

What size boat?What is the typical load?
How does it seem to perfprm?
59 brochure indicate 8 1/4 X 8 1/2.

 

[Beefer]

Re: '59 Johnson QD-20

What size boat?What is the typical load?
How does it seem to perfprm?
59 brochure indicate 8 1/4 X 8 1/2.

No idea yet. Have the motor, but haven't gotten a boat to put it on. I'm thinking of a 12-14' Jon Boat or the like. Helpful, I know.

 

[steelespike]

Re: '59 Johnson QD-20

Jon boats a good for sheltered areas if it gets rough a more standard utility will ride better.
Believe it or not the motor will do better on a larger size boat.The bigger the footprint the easier it gets up with a load.On a jon at least a 14/42 At least a "big" 14 footer for a more typical boat. There are 14s that are actually under 14 and kind of skinny you need a good full sized 14 or more.A nice bare bones 15 or 16 would work well.
We had a 18ft bare utility with an old 25 Gale it would plane with 6 adults. Our old 15ft Lonestar wouldn't even come close.Not only will the bigger boat plane better it will feel much roomier.

 

[Beefer]

Re: '59 Johnson QD-20

This is going to end up being a little something the wife and daughter can putt around the canal and well protected area outside our canal. Not looking for a primary boat, already have one of those.

Do you think the .5" more pitch will be a problem for the motor, or will it not really be an issue?

 

[steelespike]

Re: '59 Johnson QD-20

[Do you think the .5" more pitch will be a problem for the motor, or will it not really be an issue?[/QUOTE]
Again the 59 brochure lists the 81/4 X 8 1/2 as the standard prop.A healthy 10 hp can reach about 21 mph on a light reasonable fast boat with a light load.
Wife and daughter in a light boat it should be a typical load for the 10. 81/2 would generally have lower rpm
than an 8"Depending on the load. maybe 200 -300 ,a guess on my part.Small motors reacte more to pitch change than say a 25 or 30 hp.or more. The 8 inch may have been intended for a heavier boat or load.
Again if your looking for the boat to plane a 14 will generally do better than a 12 and if a jon I would shoot for at least a 42"

 

[Beefer]

Re: '59 Johnson QD-20

Great info. Thanks! The wife and daughter (11yo) combined weigh in at about 170lbs. No heavy load there. Now I just need to find the boat! LOL