Help with prop

[davis74]

Looking for help choosing a prop for my 1971 19-1 that I just purchased. It has a 115 yamaha 2 stroke. The prop that is on there now is a 13x19 aluminum. The motor is turning over 6000 rpm according to the aftermarket dial style tach ( not yamaha digital) Not sure if I need more pitch or a new tach. Any thoughts

[John Jones]

You need some confidence in your tach somehow before you start changing props.

[GoneFission]

Are you doing 50 MPH?  That would be about the speed for over 6000 RPM with a 19 pitch prop...   Check your tach settings and make sure they are set correctly - not all tachs work with all motors.

[MarshMarlowe196]

Hmmm... I just put a new Suzuki  140hp on my 19-6 Aquasport.  What is a 19-1?  Is that the same boat?  I think you'd be hard pressed getting a 19-6 to do more than around 40mph given the hull design w/o hanging at least a 200hp outboard.  

When I first got my motor, it had a 19" pitch and would scream at over 6000RPMs to break 40mph.  Well, blessing in disguise, I chewed up the 19" prop pretty good at a boat ramp, and had a 21" prop laying around and switched to that one (out of necessity...).  Now I can cruise at 30mph doing a little over 4000rpms and about 42-43mph @ 5800rpms.  I think the 21" is perfect for the boat, but a 20.5 or 20 would work well, I suspect

[davis74]

Thanks for the help. I think a 21 will be right for me also. I am running a 19 and going over 6000. I'm having problems with the GPS that came with the boat so I have not been able to get a speed. The 19-1 was only built until 1972 (i think). Here are a few pics from the night I brought her home. One more question I dont seem to be getting much bow rise when I trim the motor up. I feel the boat would ride better with the bow a little higher. Most of the boats I drive are larger but the bow seems to rise more on those when I trim the engines up. Could it be because of the flat bottom that engine trim does not affect it so much or just because the boat is small?

[GoneFission]

Some boats are more sensitive to trim than others.  It has to do with the length versus width of wetted surface.  A boat with a wide and short wetted area will be much more sensitive to trim than one with a long, narrow wetted area.  I think your (and most) Aquasport has the latter - a fairly long and narrow wetted area at plane than some other boats.  That will mean that the bow rises less with "out" trim than a boat with a wide, short wetted area.  

Another contributing factor is the "depth" of the prop compared to the surface.  Think of the prop as a lever - the longer the lever - the more effect.  A prop 24" under the surface will have a bigger lever effect than one 12" under the surface.  Your boat has a semi-V hull, and if the motor is mounted right, the prop is only about 16" or so below the surface.  Not much lever there, and trim is less effective than on a deep-V boat with a prop that is 25" below the surface.  Of course, that other boat can't get into skinny water like your boat, either!

Hope this helps - see ya on the water!

[davis74]

Thanks for the info that makes sense. Badonquasport196  is the 21 pitch stainless or aluminum?

[MarshMarlowe196]

Stainless.  Anyone want a chewed up 19" pitch prop that fits a suzuki/johnson?  Its repairable... come on... :)