In addition to your advice, another rule of thumb I have used is:
The boat should be able to reach theoretical hull speed in flat water with a
clean bottom with about 80% of maximum RPM assuming there is enough clearance
between the prop tip and any portion of the hull or rudder so that there is no
cavitation.
My 36 XL/kcb hits hull speed (~7.2 knots) in the above conditions at about 3200
RPM on my Beta 28--with maximum RPM about 3600-3800.
As expected, moving the throttle to full max RPM in these conditions doesn't
change the boat speed.
You may want to discuss this with the Maxprop technicians--or a knowledgeable
propeller expert--if increasing the pitch incrementally doesn't get you to hull
speed.
The interplay between the engine RPM, transmission ratio, prop diameter and
pitch is complex but usually solved by the manufacturer or the 1st
owner--thereafter only minor tweaks are required.
After I went with the Gori folding 2 blade prop from AB-Marine, I had to change
to a different transmission because the propeller required a different
transmission ratio than the original Beta transmission.
FWIW
Charlie NelsonWater Phantom1995 C&C 36 XL/kcb
On Wednesday, August 20, 2025 at 06:32:15 PM EDT, Doug Mountjoy via
CnC-List <[email protected]> wrote:
What is your RPM at full throttle? Is the engine able to hit max RPM? The prop
is adjusted correctly when you are just barely able to reach max RPM. At least
that is what I've been told.
Douglas Mountjoy
1988 C&C Landfall 39
sv Rebecca Leah
On Wed, Aug 20, 2025, 13:10 rockland bazemore via CnC-List
<[email protected]> wrote:
Wondering what setups you all have with this configuration.
We have a newer 16" Maxprop (I never measured) with recently adjusted to 14º
pitch based on Rob's 37+ setup. He does a lot closer to hull speed.
When we left for our trip in Annapolis we could do 5.2kn. The bottom was
cleaned about 3 weeks prior. I changed the pitch to 14º in Block Is. Couple
weeks later and now we only do 4.2kn in slack water. The bottom doesn't seem to
be THAT bad. The prop and shaft are very clean.I'm wondering now if its
possible transmission slipping? The ATF oil smells fine.
Gear ratio 2.14 Prop shaft 1-1/8"
Ideas?
--
Rockland BazemoreS/V Blue PearlC&C 37/40+Annapolis, MDYour contributions help
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it active. Please help by making a small contribution using PayPal at:
https://www.paypal.com/paypalme/stumurray All contributions are greatly
appreciated. Your contributions help pay the fees associated with this list and help to keep
it active. Please help by making a small contribution using PayPal at:
https://www.paypal.com/paypalme/stumurray All contributions are greatly
appreciated.
