Replacement Prop For My 1997 Yamaha 20HP Tiller

[Sportdog]

Hi guys. Long time lurker, first time poster. I'm heading to Canada in the middle of June and want to purchase a new prop for my motor to either replace the stock one or as a back-up. The prop that is on the motor now is a 9 3/4 x 10 1/2F. The boat is a 14 foot Alumacraft V-14, a 68 inch beam Aluminum V-Bottom utility type boat. When I ran the boat (I just got it set up) there was plenty of speed with the following loading. Rear of boat, 29 series trolling battery, Endura 50#thrust Trolling motor, 3 gallons of gas, and my portly 240# of weight. In the front seat was my 100# grandson. I could not run the boat a WOT because of severe porpoising and it raised the front end significantly to get on plane and was slow to plane out. After it planed out the speed was impressive, even though I couldn't give it full power due to the porpoising issue. I'm looking for not only prop suggestions but any other advice on the issues stated. Thanks for any possible help with this. (Note: the motor has no tach or power trim. Test run was done with the motor angle trim pin in the second hole from the most lower position.) Please advise if more information is needed to help me find some answers. Again, Thank You.

 

[jestor68]

Re: Replacement Prop For My 1997 Yamaha 20HP Tiller

A Solas 9.9 X 10 ought to be a suitable replacement for your Yamaha prop.

A Doel Fin Hydrofoil Stabilizer should get it on plane in half the time and help to eliminate the tendency to "porpoise".

Or it might be a simple matter of adjusting the tilt pin setting in closer to the transom. You might try moving it in a hole at a time to find the setting that gets you on plane without excessive bow rise. Usually it will help to get the boat to ride more level and reduce the bow oscillation common with tiller controlled boats.

Here's a visual aid to show what I mean by trim angles.

 

[steelespike]

Re: Replacement Prop For My 1997 Yamaha 20HP Tiller

It would help to at least have your top speed by gps.If it was porpoising with 100 lbs in the front seat it is trimmed out too far or the hull has issues. Trim in/down a notch see what happens. If it still won't settle down you could buy or make some wedges so you can tuck it in more.You should put a straight edge on the bottom between the keels check for a bulge ahead of the transom.
Is the anti vent plate(just above the prop) about even with the bottom of the transom?
The 20 in the right setup could run 27 to 30 mph.

 

[Sportdog]

Re: Replacement Prop For My 1997 Yamaha 20HP Tiller

A Solas 9.9 X 10 ought to be a suitable replacement for your Yamaha prop.

View attachment 192462 A Doel Fin Hydrofoil Stabilizer should get it on plane in half the time and help to eliminate the tendency to "porpoise".

Or it might be a simple matter of adjusting the tilt pin setting in closer to the transom. You might try moving it in a hole at a time to find the setting that gets you on plane without excessive bow rise. Usually it will help to get the boat to ride more level and reduce the bow oscillation common with tiller controlled boats.

Here's a visual aid to show what I mean by trim angles. View attachment 192473 View attachment 192474

Great information and I sure appreciate it. I'm going to simulate the loading that I will have in Canada, more tackle and my 215# buddy in front instead of my lightweight grandson and then adjust the trim pin from there. I will post results in a few days when I can get to the lake. In the meantime I will check the transom height in relation to the motors anti vent plate and the bottom of the boat. Thanks to both of you gentlemen.