Finally, after another boondoggle with the Sharrow prop, I got a preliminary prop test completed. After quickly replacing the prop torque fin with the flush fin, I put the prop back on, tightened the prop nut down, torqued to 40 ft-lb as spec'd by Suzuki, tweaked the nut to line up for the cotter pin.......and could not get the cotter pin through. Looking closer, the bottom of the slots on the castle/prop nut barely get past the hole in the shaft for the cotter pin. Unbelievable! I checked the prop barrel penetration into the cavity of the lower unit and it's perfect - could not possibly have a thinner thrust washer. After doing some online searching for a shorter prop nut spacer, I ran down to my Suzuki shop with prop and hardware and pics in hand, and it stumped their mechanic who has been doing this 30 years. He was unaware of a thinner prop nut spacer. That sent me home pissed, but determined to somehow get it right. More online research yielded nothing. So I began machining down the spacer and ultimately jigged it up on a right angle jig and cut 3/32" off on my chop saw (it's bronze so easy to cut), cleaned it up with a file, and also filed down the slots in the castle nut a bit. After a bit more fiddling everything fit together perfectly. With very little time before another major incoming storm, I took off for Whittier, an hour away, at 4:30pm. Needless to say the test is already inconclusive because I was unable to get back to the exact weight I was at when I tested the existing Solas prop, so I was probably 200-250 lb lighter.
I played around with engine trim to find the best trim at around 3000 rpm, but totally forgot to do the same for the trim tabs, and proceeded to get on with the test in the building twilight at 6:30pm. You can see in the results graph that, as typical with these props, there is improvement in the low to mid range rpms. In this case, at 3000 rpm, it was only about a 6.8% improvement in NMPG, pretty underwhelming. This graph is the average of my data going both out and back in the same fjord, to eliminate any effects of tidal current, which was minimal given it was low slack tide and there was no wind. With the test complete I started running back to port and realized I forgot to tweak the trim tabs, which always makes a noticeable difference for me. Short story is that at about 3000 rpm I was able to get 6.4% better NMPG than recorded during the test. So, with a lot of caveats, we can say this test shows 13.2% improvement in NMPG at the midrange, BUT, obviously, a proper test needs to be conducted with both props on the same body of water etc. The bottom line? If you are keen to order one for a standard GA, I'm only mildly enthusiastic to support you....for now. There's a good chance the improvement in efficiency/range is only about 7-12% here. I think it's fair to say it will not be up around 30% that I secretly pined for. Yes, it did run a bit smoother and quieter, and there was zero prop torque that I could feel. It's definitely a good prop, but I'm still unsure exactly how much better than my carefully selected standard prop. Another interesting point is that WOT was 5594 rpm, EXACT same as my Solas prop, so Sharrow nailed it there. I have a feeling they modeled the performance of my Solas prop with their design.
