shifting RPM

[Trojan]

What is the safe shifting RPM for the hydrulic double clutch trans on a 6-71? What is the max RPM you can shift at?


BILL

 

[Genesis]

What gear?

Allison, believe it or not, claims you can shift at full power (!) (Yes, that really IS in their manual. I wouldn't do it, but they say it can be done!)

 

[Boatsb]

Many boats getting certified for passenger use need to be tested with a Full forward to Reverse shift at WOT for the CG. Its scarry to be the guy prepping the boat for this but I have done it about 6 times.

My dedination on the haghest safe speed to shift is simple.

Does it shift smoothly? If not slow down. props, reduction gears and other factors make this differant for each boat.

 

[egaito]

Many boats getting certified for passenger use need to be tested with a Full forward to Reverse shift at WOT for the CG. Its scarry to be the guy prepping the boat for this but I have done it about 6 times.

My dedination on the haghest safe speed to shift is simple.

Does it shift smoothly? If not slow down. props, reduction gears and other factors make this differant for each boat.

And how do they come up with the idea that ability to shife into gear at 2200 or more RPM is a safety feature?

The Velvet Drives in my old boat would supposedly grenade if you shifted above 1000, so I've always assumed this this was the case with Misty's MG's and with Sanctuary's Allisons....

Wow...the thought of it makes me cringe.

 

[Boatsb]

Never did this with a BW. Allisons and Twin disc only and believe me we were more afraid of tearing the mounts out of the stringers. They told me its a panic maneauver or sometimes necessary to avoid a collision. This is for boats larger boats with 50-100 passengers like the party boats for fishing and ferrys.

 

[MikeP]

Never thought about it but it does make sense for emergencies in passenger service. But I think I'll just take their word that the M20s can do it rather than testing them!

 

[Passages]

What is the safe shifting RPM for the hydrulic double clutch trans on a 6-71? What is the max RPM you can shift at?


BILL

I shifted at 800 a few times in tight docking situations but did not like the "thunk" as it went into gear. Personally, I'd set 850 as the absolute max with normal shifting between dead idle and 700.

 

[Angela]

If I'm asked to do that on Sanctuary when reinstating her certification, I'll decline to do so and just stick to the six pack plan while I'm in Miami. It's not worth the "what if" factor to me and I'm sure my insurance carrier won't see that as a viable claim, either. I won't need the certification in the BVIs. That's just too abusive for me, in my view.

 

[Boatsb]

I would check in advance with the local CG office to see what is required for your vessel. The US standards are more demanding.

 

[SKYCHENEY]

When you look at the design of the Allison gear, it makes sense that you could engage it at WOT without a catostrophic failure. In theory, the clutch should slip until the gear comes up to speed. I would, however, never intentionally try this. I would be concerned about the stress imparted to all of the components and you know the life of the clutch plates would be reduced. Now go try that on your new Volvo pod drive thingy.

 

[Genesis]

I had a guest grab my gear handles once and pull them to neutral while at cruise.

He did not pull them the rest of the way. I don't know what would have happened if he had, but I don't think it would be a good idea...... at all.

 

[Trojan]

I have the twin disc transmission. Model MG-506. The specs say Neutral to forward or reverse -under 80% governed engine rpm.
Shifting across Neutral - under 50% governed engine rpm.
So putting it into gear I can shift at 2120 rpm. Going forward to reverse I can only shift at 1325 rpm. That is based on WOT at 2650 rpm.. I wonder about that coast guard requirement. I was tolled that 700 rpm shifts would hurt the trans.


BILL

 

[egaito]

I had a guest grab my gear handles once and pull them to neutral while at cruise.

He did not pull them the rest of the way. I don't know what would have happened if he had, but I don't think it would be a good idea...... at all.

Yea, it sucks when you come home with one less guest than you left with...even if they did deserve it.

 

[Angela]

Yea, it sucks when you come home with one less guest than you left with...even if they did deserve it.

That really cracked me up!! LOL

Somehow, I think I can see that happening to a guest on Karl's boat if a guest ripped out his transmission...kind of like the woman who flushes a tampon down the head.

 

[luckydave215]

More like a woman who drops a tampon in a turbo.

 

[captwoodyb]

Interesting comments about the shifting WOT. I have been running a certified 53hatteras out of Baltimore for 20years. Recertified/inspected every 12months. Never been asked to do anything like that. I think my allissons would croak. I ususally shift below 800 even in emergency stop, something I have had to do on a few occassions.

 

[Trojan]

I have a friend that has a 38 Chris. His girlfriend was standing in the hatchway in the center of the boat while the boat was at WOT. They hit a wave. She lost her balance grabbed the gear shift to catch her balance. The trans shifted into neutral. The motor screamed. Then made a hell of a noise. The motors were the old Chrysler hemi type. The results was a motor that literally broke in half, the block, the cam, the crank, and the heads. What a mess. The trans was OK though.



BILL

 

[MikeP]

I could never understand why every gas-powered boat and anyone building a high performance street engine didn't include a rev limiter as part of the deal.

 

[egaito]

I could never understand why every gas-powered boat and anyone building a high performance street engine didn't include a rev limiter as part of the deal.

A lot of race engines in cars and boats have them. I think most of the offshore guys have them. It helps, but if you "stay in the rev limiter" it will still damage the engine, though not quite as catastrophically (spelling?).

 

[Genesis]

That's the nice thing about diesels. They're governed and don't mind running into the governor at all. When my guest pulled the gears out to neutral the only thing that happened was that the boat slowed down!