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  #1   IP: 99.231.137.223
Old 01-21-2019, 06:03 PM
Bratina Bratina is offline
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RPM in reverse - how much is enough?

Like many posters here, I've been at a point where reverse in my A4-powered Grampian 30 is low to non-existent.

I adjusted the reversing gear (one flat of the nut) towards the end of the season last year and it helped a little, although thrust in reverse remains extremely weak. I'm going to install an Indigo 3-blade prop over the winter, which many forum members have noted is more effective than a 2-blade. It's worth a shot, my boat is on the hard, and the cost is relatively low.

For no rational reason I baby my engine - I cringe when my RPMs climb over 2K, and cruise at between 1600 - 1800 (which nets me around 5kt - plenty for my short stint to get off the dock and out to Lake Ontario). I've read at length people noting that you have to 'really gun it' to get decent thrust backwards, but it's never quantified in terms of actual RPM.

So my question is twofold: what is 'gunning it' in reverse? I usually get to 2-2.2K RPM in reverse and, again irrationally, get scared. Likely part of my problem with the 'brakes'.

Second: a lot of forum members note that it's better for the engine to run at a higher RPM. Should I be scared cruising at 2,000 - 2,200 rpm or higher? Is it true that it's easier on the engine? If temperature and oil pressures are nominal, is it any more risky to run at 2,200 rpm vs. 1,800 rpm? It seems counterintuitive (and I should get a vacuum gauge...).
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  #2   IP: 173.17.89.29
Old 01-22-2019, 12:21 AM
sailhog sailhog is offline
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Ahoy, Bratina! Others will chime in here, but here's an introductory two cents... The reverse gear on the A-4, I believe, is geared down a third to the forward gear.

Standby for more commentary...
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Old 01-22-2019, 11:11 PM
Sam Sam is offline
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I'll chime in a bit. Having an older heavy displacement boat, 1966 Morgan 34, with a 3/4 keel somewhat similar to the Grampian you just can not expect make much headway in reverse. The reverse "prop thrust " is hitting the very nearby keel. Reverse "gunning" the throttle stops the boat nicely and the prop walk gets me next to the dock but getting out, especially against the wind is difficult.
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  #4   IP: 24.152.132.140
Old 01-23-2019, 12:34 AM
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ndutton ndutton is offline
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A technique I learned with my previous full keel boat was to give her a burst of power in reverse to get her moving, then take her out of gear and let her coast. Steering is much more responsive without the prop turning.
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  #5   IP: 192.186.122.174
Old 01-23-2019, 09:40 AM
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Quote:
Originally Posted by ndutton View Post
A technique I learned with my previous full keel boat was to give her a burst of power in reverse to get her moving, then take her out of gear and let her coast. Steering is much more responsive without the prop turning.
Exactly what I have to do, and turn to starboard to get facing the right way in the marina channel. brief bursts with the tiller hard to port. The key for my situation is brief busts - say 3-5 sec.... coast... burst....coast...

now, add some wind coming from starboard...
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Last edited by GregH; 01-23-2019 at 09:40 AM. Reason: speeling etroshus
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Old 01-23-2019, 10:08 AM
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sastanley sastanley is offline
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The reversing gear really screams when you rev it up to 2,000+ RPM, and I think until you are used to the noise, it scares people.

Also, newer users to the A4 may not realize they need to lean on the gear lever to hold pressure on the reversing band to keep the prop shaft fully engaged.
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  #7   IP: 24.152.132.140
Old 01-23-2019, 10:21 PM
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I knew a guy 45 years ago who had a downwind slip in Newport Harbor and no engine, a real handful coming and going. On his way in he would drop a stern hook and use it as a brake, left it there when he was done. Leaving next time he would warp out using the hook and retrieve it when he was clear.

And we complain about prop walk!!
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  #8   IP: 32.211.28.40
Old 01-23-2019, 11:13 PM
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I modified the reverse cam on my transmission to put a flat on it - at full reverse, the roller would come up on the flat and stay there. Personally, I liked the change. No more worry about holding the lever in reverse.
Of course, you have to have your linkage adjusted properly. Forward should just shift things into forward, and reverse was as far as the linkage in the transmission would allow. Side benefit of this was that is gave me a nice wide neutral band. Key is to have a shifter that gives adequate throw.
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  #9   IP: 179.50.222.56
Old 01-24-2019, 08:49 AM
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Quote:
Originally Posted by ndutton View Post
I knew a guy 45 years ago who had a downwind slip in Newport Harbor and no engine, a real handful coming and going. On his way in he would drop a stern hook and use it as a brake, left it there when he was done. Leaving next time he would warp out using the hook and retrieve it when he was clear.

And we complain about prop walk!!
This fellow could spend months in the summer, trying to get out of the Chesapeake.

Bill
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  #10   IP: 142.112.13.103
Old 01-28-2019, 11:49 AM
Bratina Bratina is offline
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Thanks for the replies everyone, super helpful as always.

I'm comfortable with the operation of the engine (e.g. the lack of detente in reverse, the reduction gear etc), and combating prop walk.

What I'm still not too sure of is how much is too much, and whether I risk damaging the engine at a higher RPM.

1. What RPM do you use in reverse (maximum and average)?
2. Is it better for the engine to cruise (forwards) at e.g. 2,200 RPM vs. 1,700 rpm?

I know these things will vary by engine / boat / conditions / prop / hull type etc, but I'm trying to get a feel for how far I can go.
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  #11   IP: 76.7.141.172
Old 01-28-2019, 12:05 PM
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Marian Claire Marian Claire is offline
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I think following thru with your plan to install a vacuum gauge, as mentioned in post #1, will give you the answer. I believe it is one # that can be compared to other boats despite different set ups.
Dan
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