1989 Yamaha 150 hp max rpm is only 4400

[99yam40]

why would you think no load is being applied when you back the boat into the water still strapped to the trailer, crank up the motor,put into forward, and go WOT?

[Jason2tpa]

Well, now I think more about it I suppose you'd be throttling up against an immovable position, therefore it would theoretically be max load. But again, I've never seen one of these test props in use. When a propeller moves through the water it's pushing water. A test prop doesn't have blades, therefore it's not pushing water, more like spinning in water without load.

But I'm sure I'm missing something bc why else would they have these test props if they didn't produce accurate results. I'm just not sure how load fits into the equation. I think Rodbolt has posted about this in the past. He would know the answer.

[99yam40]

it will load up the motor to where it should hit a certain RPM at WOT

[Jason2tpa]

Gotcha. Do you know if these test props vary in pitch selection? For example, when I bought my boat/motor it has a 21" pitch and turns 4700 at WOT. Too low. If i go by the rule of thumb of 200 rpms for every 1" of pitch, then I'd put a 17" pitch on. But if these test props come in different pitches I would know for sure.

[99yam40]

different test props are set up for different motors.

they are for testing a motor to see if will get to the proper RPM at WOT nothing else.

if it can then the motor is running as it should
if it cannot they then the motor has a problem and needs to be fixed

[rodbolt17]

all the correct part numbered test wheel does is allow a tech to quickly determine if he is fighting a rigging/hull issue or an engine issue.

Yamaha did all the engineering.
test wheel does not provide thrust just load.

[Jason2tpa]

Ah ha, now I understand the test props functionality. Thanks for the clarification guys.