Reply
 
Thread Tools Search this Thread Display Modes
 
Old 10-10-2017, 09:37 AM   #41
Veteran Member
 
City: Langley BC
Vessel Name: Summer Wind
Vessel Model: Bayliner 4788
Join Date: Oct 2013
Posts: 96
I could believe that over propping is the cause if both engines ran 100 or so RPM below the governed speed. But these engines are shy by 500 RPM with a clean bottom, fuel tanks half full, water and holding tanks nearly empty and a 10' inflatable topsides. Carver engineers would not be dumb enough to OK that situation no matter what their marketing group wanted. Engine speed and fueling is controlled by ECM's and one is quite new. During sea trials the Volvo mechanic ran a heat gun all over the exhaust ,coolers, heads etc and found nothing alarming. It's a nice boat but I'n not going to buy it.
stanfromhell is offline   Reply With Quote
Old 10-10-2017, 09:59 AM   #42
TF Site Team/Forum Founder
 
Baker's Avatar
 
City: League City, Tx
Vessel Name: Floatsome & Jetsome
Vessel Model: Meridian 411
Join Date: Oct 2007
Posts: 7,147
Quote:
Originally Posted by stanfromhell View Post
I could believe that over propping is the cause if both engines ran 100 or so RPM below the governed speed. But these engines are shy by 500 RPM with a clean bottom, fuel tanks half full, water and holding tanks nearly empty and a 10' inflatable topsides. Carver engineers would not be dumb enough to OK that situation no matter what their marketing group wanted. Engine speed and fueling is controlled by ECM's and one is quite new. During sea trials the Volvo mechanic ran a heat gun all over the exhaust ,coolers, heads etc and found nothing alarming. It's a nice boat but I'n not going to buy it.
PLEASE PLEASE listen to what these people are saying. The Carver engineers do as they are told. My Carver left the factory with 23x27 props. I now have 23x25....IOW, lower pitch. If my props were "as they left the factory" I would be well overpropped. I am perfectly propped right now....about 100RPM over rated RPM. Carver is a large company. And all, and I mean ALL, large companies are driven by their marketing department. That marketing department wants to be able to post about a certain performance. That performance is gained when the boat is light and empty. Boats gain weight over time. That weight is in the MANY thousands of pounds. Also a fouled prop and a fouled hull. I will reiterate....LISTEN TO WHAT THESE PEOPLE ARE SAYING.

There used to be a guy on here that would not listen when the same argument was being made. He had the Cummins Guru, Tony Athens, telling him exactly what we are telling you. And his response is exactly your response. And guess what, he was replacing an engine within a year. Do not go chasing these ghosts down other rabbit holes. We have defined the rabbit and we have defined the hole.

The last 10-15 posts are excellent posts...especially PSNeeld's. When you set your "throttles" you are setting spring pressure on the governor. Flyweights help maintain that spring pressure. When the engine slows down, it is sensed by those flyweights as they "spring in" and that is connected to the rack which adds fuel to get the spring pressure and flyweights back in balance. That is basically how a mechanical diesel governor works....just to clarify terms being used like "requested rpm" and "sensed RPM". In a mechanical governor, it is all....wait for it....mechanical. No computers.
__________________
Prairie 29...Perkins 4236...Sold
Mainship Pilot 30...Yanmar 4LHA-STP...Sold
Carver 356...T-Cummins 330B...Sold
Meridian 411...T-Cummins 450C
Baker is online now   Reply With Quote
Old 10-10-2017, 01:19 PM   #43
TF Site Team/Forum Founder
 
Baker's Avatar
 
City: League City, Tx
Vessel Name: Floatsome & Jetsome
Vessel Model: Meridian 411
Join Date: Oct 2007
Posts: 7,147
I missed the part about you not buying the boat. Sorry about my overly dramatic post...������. But maybe someone will learn something. Overpropping a planing boat is never good.
__________________
Prairie 29...Perkins 4236...Sold
Mainship Pilot 30...Yanmar 4LHA-STP...Sold
Carver 356...T-Cummins 330B...Sold
Meridian 411...T-Cummins 450C
Baker is online now   Reply With Quote
Old 10-10-2017, 02:15 PM   #44
Guru
 
River Cruiser's Avatar
 
City: UMR MM283
Vessel Name: Northern Lights II
Vessel Model: Bayliner 3870
Join Date: Jan 2013
Posts: 1,357
Quote:
Originally Posted by sunchaser View Post
RC



I may be misreading what you said, but I'm not sure there is a direct correlation between RPM and fuel delivery. Even with a perfectly propped vessel. RPM and fuel consumption will independently vary dependent upon boat load, sea state and wind velocity.


You are correct, the amount of fuel delivered is controlled by the governor reacting to the load being applied. As the load increases fuel is increased, as the load decreases the fuel will decrease to maintain the set rpm. Being overloaded the fuel delivered and burned will increase combustion chamber and exhaust gas temperatures, not a good thing for long engine life. The problem when over propped goes all the way through the rpm range meaning more fuel is delivered at any rpm setting than would be required if correctly propped or loaded.
__________________
Ron on Northern Lights II
I don't like making plans for the day because the word "premeditated" gets thrown around in the courtroom.
River Cruiser is offline   Reply With Quote
Old 10-10-2017, 04:54 PM   #45
Guru
 
psneeld's Avatar
 
City: Ft Pierce
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 24,009
More words of wisdom from the marine engineer who covered diesel governing.

He responded to this sentence....

"“Being overloaded the fuel delivered and burned will increase combustion chamber and exhaust gas temperatures, not a good thing for long engine life. “

With this response.....

"The sky is not falling. Any increase in fuel flow will increase the exhaust temperature, that is why we monitor EGT, it is a good method to determine engine load. Stating that increased combustion chamber and exhaust gas temperatures are not a “good thing” without a whole lot of qualifying conditions is pure chicken little stuff.

Then this statement....

“The problem when over propped goes all the way through the rpm range meaning more fuel is delivered at any rpm setting than would be required if correctly propped or loaded.”

His thoughts.......

"The “problem” does not exist until the engine climbs above the maximum allowable EGT and that will only occur when the engine is asked to produce more power than it is capable of delivering to a propeller that is capable of absorbing much more.

It appears to me that the issue here is based on people looking at the rpm obtainable with a propeller that absorbs maximum power a little below the high idle speed. They seem to ignore the fact that their engine will run quite nicely at less than full power with a propeller that moves the boat further through the water at a given rpm. As long as that propeller does not absorb more than the power available per the power curve at a given rpm there is no overload condition. All you have is a lower powered propulsion system that lacks the “turn down ratio” of the ideal propeller curve. You lose the ability to move through the water slowly at idle in gear and you lose top speed and acceleration because you have effectively downrated your engine. Unless you adjust the fuel limiter and the throttle stop you risk an overload condition when moving the throttle to the stop while attempting to regain the performance you threw away by “overpropping.”"
psneeld is offline   Reply With Quote
Old 10-10-2017, 08:24 PM   #46
Guru
 
Fletcher500's Avatar
 
City: San Diego
Vessel Model: Helmsman 4304
Join Date: May 2016
Posts: 1,583
Good discussion, and a reminder regarding changing weights over time on a vessel and prop pitch.

We had a new planing boat that was sea trialed by the engine rep, the Broker, and myself, before they would hand me the keys, and put the engines under warranty.

We couldn't make the required RPM at WOT so we all went home. New props shipped in, tried it again, and the engine service rep who is representing the mother ship who made the engine in this case signed it off. Keys given to me at that point, and the warranty clock started.
Fletcher500 is offline   Reply With Quote
Old 10-11-2017, 08:04 PM   #47
Grand Vizier
 
Delfin's Avatar
 
Join Date: Jan 2010
Posts: 3,479
When I purchased Delfin, she was an empty hull with just a new CAT and genset. The CAT dealer came down to the vessel to do a delivery inspection underway at full load. He measured EGT, max rpm, etc. and signed off. I can well see the Carver folks doing the same thing to a vessel leaving their factory, and while not as light as Delfin, the brand new Carver would be quite a bit lighter than when in use by the owner. If you think about it, my CAT guy could only certify the engine "as is", since he had no idea what the final vessel weight might be.

Long story short, after adding a few tons of cabinetry and furnishings, Delfin probably weighed 15 tons more than when an empty hull and we were "over propped." No harm done since we never powered beyond around 35% of rated power but after flattening the props a couple of inches the engine runs EGT around 125 degrees lower, she doesn't run at 4 knots at idle and she seems "sweeter" at slightly higher rpm with no change I can measure in fuel consumption.

Point is, factory prop settings can easily be too aggressive since they match an empty boat. Whether they hurt anything depends on how the vessel has been run, but I would be very uncomfortable buying a planing hull that has run more than a few hours at WOT but reduced design rpms. Rhw OP is wise to pass, IMO.
__________________
Delfin
"Dad always thought laughter was the best medicine, which I guess is why several of us died of tuberculosis." - Jack Handy
Delfin is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Trawler Port Captains
Port Captains are TF volunteers who can serve as local guides or assist with local arrangements and information. Search below to locate Port Captains near your destination. To learn more about this program read here: TF Port Captain Program





All times are GMT -5. The time now is 07:42 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012