Don't Kill Your Engine!

[csleaver]

A smaller pitch propeller will maintain speed better with heavy loads and while surfing much better than a higher pitch propeller, but at the cost of fuel economy and top speed.  Extended cruising at 4000-4500 RPM should not be a problem, but running at 4500 to maximum RPM should only be done for short periods of time (perhaps just 5-10 minutes).  If the engine is being "lugged" and unable to even achieve the maximum RPM recommended range when loaded (regardless of the actual RPM the engine is running), then it is it is very hard on the engine and will likely cause premature failure. 

[CaptainMorgan]

On 7/8/2023 at 10:22 PM, csleaver said:

A smaller pitch propeller will maintain speed better with heavy loads and while surfing much better than a higher pitch propeller, but at the cost of fuel economy and top speed.  

i switched back to the 3077 (15.5" pitch) this weekend from the 2969 (17" pitch) -- and man, were you right!  i knew it was best for long-term engine health but was skeptical i'd notice the difference driving a surf session, but only a couple days between sessions made the change easy to identify.  Definitely a smoother launch and more stable speed control when fully ballasted for surfing.  yes i'll lose a couple mph top end but i don't make long-runs anyway.  

i'll keep the 2969 as my backup, sd it suits me just fine when i'm doing lots of half-ballast foiling or cruising/pulling tubes, but when its surf time, the 3077 is great for me. 

My general prop speculation is that my size boat with only Monsoon 409 can't quite push a 17" prop at the top end (if i had a newer boat with an M6, then i'd probably be fine).  The surf 'smoothness'//efficiency could also be related to the high cup on the 2969 compared to the highly rated 2805 (also 17" but lower cup).  if i were ordering a new A24 with M6, i think the 2805 would be my jam.