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Cruise RPM - how close to WOT?


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I typically cruise ~5 miles to our best surf spot, and at a comfortable ~3500rpm (~20-22mph maybe) its a 15min trip.  Yesterday i sped up to 30mph briefly at the request of my 11yr old who then asked with a grin "Can we go that fast ALL the time?!?!"

i'm definitely being conservative, and rarely is saving the couple minutes gonna matter, but it did make me curious what other TMC members consider max cruise RPM?  No one cruises at WOT for 10+ min  do they?  Is the answer engine dependent? (i have a 2019  PCM 409)

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I'm guessing your normal surf RPMs with that motor is ~3800.  Whatever RPM you are willing to do surfing should be fine for cruising as well - the boat doesn't know the difference.  You WILL use more gas.  I would advise against WOT.  We need 2 speed transmissions  :)

409 is the 6.0 right?  I would switch to a speed prop if you mainly surf.  The speed prop will both drop RPMs while surfing and give you a better cruise speed.  The only time I think the speed prop is a negative is if you wakeboard heavy and have a big crew.  IMO.  

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For me and probably unrealistically, I worry about having an oiling failure and trashing the engine running at or near WOT. Boating on a river I also have to dodge trash from time to time and WOT sees the cost of repairs go up exponentially. For that reason and now even more so with gas prices, I have always tried to keep the rpm’s as low as possible to stay on plane for piece of mind and wallet. Fortunately, I can pretty much start what ever water sports we want to do from the the back of the trailer as I live off the beaten path. Meaning, I don’t have to go any distances at top speed. We do occasionally due cruises with the rest of our crew and keeping up with them was kind of unnerving at the upper rpm’s, 3800 -4000 rpm’s. On my M5 with a 15”, 2773 I stayed in the 3800 rpm range at 11.2 surfing or 21 mph which is our normal cruising speed. That is also the M5 torque sweet spot. Now that I am running the 16”, 3337 I have dropped my rpm’s to 3400 rpm across the board. Gained 5 mph on the cruising speed and dropped 450rpm surfing. The rpm drop also saw a decrease in cabin noise by @ 5db. It still doesn’t like to wakeboard with max MLS, pnp and wedge. No loss in my book though. 

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44 minutes ago, pauley71 said:

I'm guessing your normal surf RPMs with that motor is ~3800.  Whatever RPM you are willing to do surfing should be fine for cruising as well - the boat doesn't know the difference.  You WILL use more gas.  I would advise against WOT.  We need 2 speed transmissions  :)

409 is the 6.0 right?  I would switch to a speed prop if you mainly surf.  The speed prop will both drop RPMs while surfing and give you a better cruise speed.  The only time I think the speed prop is a negative is if you wakeboard heavy and have a big crew.  IMO.  

i have the 3077 (17 x 15.5in pitch, sea level), so my surf is probably 3500 ish regular, 3300 goofy.  Hence anything in that neighborhood seems conservative/comfortable for cruising but i can probably push it *some* as loafing along at 20mph for 15min to get home can feel slow (especially to kids after a few hrs on the water).  25mph "felt" like a big difference in progress and 30mph felt screaming...but haven't spent any significant/sustained time >4krpm before so thought i'd solicit input.

My mechanic recently came for a test-ride after fixing something and said he uses WOT once in a while as a diagnostic tool (for <5 sec) -- if its not reaching WOT then that can indicate something wrong that you do'nt see at idle in a shop environment.  But when he took it to ~35mph at 5500rpm, it was squirrely and engine was working HARD.

a while ago i thought about speed prop, as if we wakeboard its nothing serious.  From a 15.5 to a 17" pitch would add 2-3mph i suppose, but would be a long time before 100-200rpm decrease in surf rpm saves enough gas to offset the $800 prop purchase; hence cruising at higher rpm increase is the easier/cheaper answer but only if 4000-4500rpm is a 'no brainer' on the engine for 15min at a time. (note: may need to redo that payback calc now with $6 gas!)

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PopsA22

There is definitely a happy spot for that engine.  I have the same one.  Best engine RPM for cruising is 3500 RPM.  I recently switched props to allow faster speed at this RPM.  Original prop was 2249 and I changed to a 2277.  This allowed me to drop my RPM about 300 RPM at all speeds.  

EX. 2249 prop at 3500 RPM was 22 MPH.

2277 prop at 3500 RPM is now 25 MPH.  

I'm at sea level.  

 

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2 hours ago, CaptainMorgan said:

Yesterday i sped up to 30mph briefly at the request of my 11yr old who then asked with a grin "Can we go that fast ALL the time?!?!"

Time to trade the tub for a ski tug and get the 11 year old on a slalom or barefoot!

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In the Crusader Challenger series owner product technical specifications manual, the 6.0L/6.0L HO engines have a WOT operating RPM of 5400-5600, preferred WOT RPM of 5500, and a maximum cruising RPM of 4000.

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Mostly it's about fuel vs urgency.  In most boats they are most efficient just after they come on plane.  I find that's around 23mph or so.  Most of the time that's where you'll find me driving like a grandpa.  Now when I have a multi-mile run over smooth water then I'll start increasing or just like driving faster.  I don't push over 5000rpm for cruising to and from.

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i cruise at the lowest speed to plane or barely plane, with tabs snd a center plate deployed you can plane at 11.5-12 

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