1973 Aquasport 19-6 prop question

[John G]

I've got a 1973 Aquasport 19-6 that is currently in the water with a 1994 Yamaha 85 outboard. I purchased it a few week ago and the plan is to run it for the summer and then tear it apart over the winter.  It has a stainless prop with some dings and I can't find any size markings on it.  I'm getting some shaking/vibration at low throttle, so I'm thinking I'd like to replace it with a new aluminum prop. Does anyone have the same boat with similar outboard that can give me an idea of prop size/pitch? The tachometer isn't working (on the repair list) so I have no idea if the current prop is running the correct rpms.  Thanks.

[boatnamesue]

Dialing in prop/pitch can’t be done without a functioning tach.  And before you spend the time and money on tearing down that motor I’d highly suggest replacing it with more HP.  You will experience significant hull performance issues with an 85hp hung on a 19’6.  Sluggish would be an understatement.

[wingnut]

If you're just looking for a decent/cheap starting point so you can safely run your motor this summer, the prop wizard for Turning Point would not be a bad place to start. Maybe lean towards a little more pitch so you don't fry your motor with unknown high RPMs. But to do it right you definitely need a tach.

Ditto on the power on your 19'6. I have an 85 two stroke on my 170, and I'd say it's on the smaller end of perfect. 19-6 is a lot more boat though.

However, with the right prop, you may be able to happily cruise around in the low 20s; if that's good enough for you and you don't want to repower, then run with it and get out on the water!

[John G]

Dialing in prop/pitch can’t be done without a functioning tach.  And before you spend the time and money on tearing down that motor I’d highly suggest replacing it with more HP.  You will experience significant hull performance issues with an 85hp hung on a 19’6.  Sluggish would be an understatement.

I'm actually tearing the boat apart, not the motor.  Sorry - I wasn't clear on that. I've got the transom and floor to do. The motor runs great and I'll deal with it for now.  A HP upgrade may be in the future, but right now the selection for decent, used motors is very limited.  I'm hoping to get the tach working again this weekend. I've got some wire chasing to do!

[John G]

If you're just looking for a decent/cheap starting point so you can safely run your motor this summer, the prop wizard for Turning Point would not be a bad place to start. Maybe lean towards a little more pitch so you don't fry your motor with unknown high RPMs. But to do it right you definitely need a tach.

Ditto on the power on your 19'6. I have an 85 two stroke on my 170, and I'd say it's on the smaller end of perfect. 19-6 is a lot more boat though.

However, with the right prop, you may be able to happily cruise around in the low 20s; if that's good enough for you and you don't want to repower, then run with it and get out on the water!

That's exactly what I'm looking to do.  I don't mind spending a few bucks on a prop to eliminate the vibration and get me through the summer.  I just can't figure out why I can't find the specs on the existing stainless prop.  At least that would be a starting point.  As "boatnamedsue" mentioned - I need to get the tach working.

[Tampa Bay Mike]

Try taking the prop off and looking on the inside. My stock Suzuki prop didn't have any markings on the outside, they were stamped on by the hub.

[wingnut]

There is a way to measure the pitch, but it's kind of a pain. It involves a bit of trigonometry; you have to pull the prop, place it on a sheet of paper, and put a point at the center of rotation. Then use a compass to draw an arc that goes through the fattest point of a blade. You then take a vertical measurement at the leading and trailing edge, find the arc length between the two points, and solve for how many inches the blade would "climb" in a full rotation. Google "how to calculate prop pitch" for a description with diagrams. I've done it before and it's actually very accurate if done correctly (I too had a prop with ZERO markings on it, inside or out).

Here is the prop wizard that might give you a baseline:
https://turningpointpropellers.com/PROPWIZARD/index.html?tan=

Just plug in all of your boat/motor/weight info and it'll give you options.