R-21 Performance

[Kamalani]

Andrew - I am wondering if you have generated any speed data for the 21. I am finding that w.o.t. yields about 3200 rpm and a resulting speed on GPS of just under 9 kts. (three persons onboard will be a definite factor.) However, is there a reason that YM-30 engine would be set to restrict throttle to 3200? Alex.

 

[Andrew Custis]

Another good question. Every engine that is put into a boat has a restriction or governed rpm that is allowed. Maximum output for RPM on the 30hp is 3600. When I test run them, I run them at 3575. We have tried many different props for this boat and the one we use is by far the best. 3200 is still in the range of the max rpm on that engine. It is rated 3200-3600 rpm. Make a long story short it is the prop that determines what RPM you will get out of the engine.

 

[rustednail]

I was wondering the same thing about the RPM. In the first few hours I would only max out around 3200 to 3250 with just me and my wife on board. The GPS would report around 9.5 knots (corrected for currents). Now I have about 16 hours on the tachometer and am maxing out on RPM around 3400 to 3450. Perhaps as the engine "breaks" in the RPM will increase a little more.

As for speed, one thing I have noticed When cruising in shallow water, my speed seems to be less then when crusing in deeper water. With a depth of around 4 to 5 feet I seem to go slower then when in water over 12 feet.

If the weather clears up this weekend I might get a chance to get a better average for deep water vs shallow water speeds.