R21EC Propellor

[Johnnieboats]

G'day everyone
Has anyone tried a different pitch prop to the factory standard?

 

[Equinox]

Yes, we just had a new prop installed with an increased pitch since we have added a bunch of extra weight to our boat. The result has been an average of 0.3 kts increase in speed for any given RPM. From what I understand, matching the prop to the boat depends on your typical/max workloads and is very intricate work. It required us to do some RPM / speed testing beforehand on a calm day.

 

[Here Be]

If the increased pitch resulted in an increase in speed of .3kts at any given RPM on aboat which has taken on board extra weight, why then should this prop be an option on all 21EC's as surely a boat with no extra weight wouls benefit by at least the same increase in speed ???

 

[Equinox]

Maybe it is a good idea to increase the pitch on all 21 ECs. However, Yanmar is pretty conservative with their prop configurations. If the prop is illsuited for the engine, it could be risky if the boat is loaded up with say six passengers and you are fighting a strong current. You want to make sure there is a safety margin that covers the maximum displacement load the boat will ever see.

It's all about how the engine is performing given the characteristics of your specific boat. For example, if my r21 sits lower in the water from a bunch of extra equipment, then it may take more RPM's to acheive the same speed as a vanilla/lightly loaded r21. In my case, it was slightly underpropped. I think Andrew is wise to work closely with the individual customer and Yanmar to get their buy-in.

 

[SlackwaterJack]

I would use extreme caution if wanting to experiment with different props for the R-21 (classic or ec).
Unless you have an EC that was the recipient of an incorrect prop from the factory (un-likely)or a previous owner(likely), the standard prop is sized within the boat's design requirements (classics are old enough that many may have been re-propped over the years).
If a boat is carrying excess weight (do not exceed the Coast Guard cert)...it may need the pitch reduced (not increased) to allow the engine to continue to reach max rpms under the increased load. The Classic is designed to achieve 8 knots and due to a re-design the EC is supposed to get 10 knots...neither will be exceeded by prop or engine change (within reason). I personally don't feel it is worth the cost or hassle for a 1/3 knot increase in speed. Travelling 30 miles (3 hours at full speed) to arrive 6 minutes ahead of someone else in a similar boat just doesn't seem worth it.
Problems with over pitching (or too much diameter)...engine may not be able to achieve rated rpm's, boat speed will be too fast at idle requiring constant use of neutral to slow down for slow speed control, overheating at higher rpm's, excessive prop-walk (esp. in reverse).

 

[rt11002003]

I discussed the prop with both Jeff and Andrew, about two years. I believe I was told they tried 22 different props before settling on the one used. 😎