Safe Shifting RPM

[Kevin Henderson]

I've been reading up and also practicing honing my mad docking skills  
In a book that I've been referencing (7 steps to boat docking) it talks about preset RPM's to safely shift from Neutral/Forward/Reverse at a safe RPM with the engine idling.  
Is there a known RPM range where one can shift with the engine idling without damaging the transmission?
The idea is to make all maneuvers without throttle (all in idle) and only using rudder and shifting.  But to get the maximum bite in the water with the prop perhaps the "dead low" idle speed does not provide the sufficient thrust needed.  
Any thoughts? or am I just loony?.. (don't answer that last question)  

[Stu Jackson]

Kevin, the answer is in the transmission manual.  IIRC it's up to a max of 1200 rpm.  Many of us run idle anywhere from 800 (rumble, rumble sounds like a tank and shivers) up to 1100 (sometimes seems racy).  I think all of us, at one time or another, have shifted mistakenly when the rpms were higher and the transmissions have survived.  

I've learned that that the "trick" is to find, on YOUR boat, the "delicate balance" between comfortable engine rpms in idle forward and neutral and the "clunk" of the transmission.  Always shift "assertively" so the lever down below gets thrown completely.

As Ken Juul mentioned in a related topic, once you're in your own fairway it should be easy to find "your" comfortable idle speed and just shift in and out of forward as you turn into your slip.  Assuming you're comin' in bow first.

If you need reverse, best bet is to get there in idle and then just goose it a bit.  As you know, it'll bring your stern to port.

Havin' fun yet?  

PS  -  All this depends on your engine and transmission.  RTFM.    They're in the manuals section in the C34 Tech wiki, although I just read what we have and it's not in there!!!  

May be in the Service manual.  Or just a note in the engine manual.  I know I've seen it somewhere.

[Ron Hill]

Kevin : Not to sure what your M25XP Operators Manual says, but the M25XPB/M35 manual states the following:

"NOTE : Too low an idle speed will produce a chattering noise from the transmission gear and damper plate.  In such cases the idle speed should be increased."

Having had about 22 years experience with your engine and transmission until it was replaced at 5000hrs, the best shifting speed that I have found is about 1200 rpm
That RPM allows the transmission to shift nicely, and with a 3 bladed prop will still influence the change of boat direction.  You can always add throttle or shift to neutral if needed.

If you get the engine rpm too high (much over 1500rpm) the shifter does not want to go out of gear - easily. The higher shifting rpm is also MUCH tougher is on the damper plate!! (the damper plate takes up the shock from the transmission of going instantly in the opposite direction)

Again, you need to check your tach rpm against a laser tack to find the REAL engine rpm and then adjust accordingly.

A few thoughts from someone that has shifted over 5000hrs worth!!  

[Les Luzar]

On my M25XP low idle is 800 RPM and the engine chugs and thumps at that RPM, but continues to run, so when I shift gears I drop the throttle to 800, then shift, and immediately inrease the RPM to 1000. My engine sounds much better at 1,000 RPM in idle when going slow. I also watch my speed, and switch from neutral to in gear as needed to maintain about 1.5 knots heading into my upwind slip. This works for me. When in gear I adjust my RPM between 1,000 and 1,200 as needed depending on my target speed.

[Ralph Masters]

From the "Shop Manual:  The HBW permits direct reversing at full engine speed, for example, in emergency cases." 
But in normaly day to day use I would recomend droping RPM to idle, shifting, then coming back up on speed.

Ralph