Hi Roger,
Yes, you should use a thrust washer, just place it on the shaft followed by your locking nut, do this so it just backs up to the washer. use a little Locktite on the thread and screw the prop on, again till it touches the nut, now tighten the nut down onto the prop. This will give just a little free movement of the washer.
If you do not have an oiling tube fitted to the prop shaft remember to fill the tube with oil before fitting the prop.
Cheers – Ken