Reply
 
Thread Tools Search this Thread Display Modes
 
Old 02-22-2020, 01:47 AM   #41
Guru
 
catalinajack's Avatar
 
City: Edgewater, MD
Vessel Name: Catalina Jack
Vessel Model: Defever 44
Join Date: Nov 2011
Posts: 2,435
Running a Ford Lehman constantly at 2,200 RPM would not be something I would do. I have never seen an owner posit they run their Lehmans at any more than 1,800 with most saying 1,600 to 1,700.
__________________
Advertisement

catalinajack is offline   Reply With Quote
Old 02-22-2020, 06:16 AM   #42
Guru
 
Cigatoo's Avatar
 
City: Narragansett Bay
Vessel Model: Grand Banks 36
Join Date: Sep 2016
Posts: 1,209
Quote:
Originally Posted by Al View Post
Well, you did find the information, so, out of forum curiosity, what did the die stamp say???
Plate said 2.0. Stamp was 1.47. Or maybe vise versa?
__________________

__________________
Charlie0
Cigatoo is offline   Reply With Quote
Old 02-22-2020, 03:04 PM   #43
Al
Guru
 
Al's Avatar
 
City: ketchikan, Alaska
Vessel Name: 'SLO'~BELLE
Vessel Model: 1978 Marben-27' Flybridge Trawler(extended to 30 feet) Pilothouse Pocket Cruiser[
Join Date: Apr 2012
Posts: 2,223
Quote:
Originally Posted by Cigatoo View Post
Plate said 2.0. Stamp was 1.47. Or maybe vise versa?
Thanks, from this branch of the wisdom tree, that is a big "Vise Versa" when posing the original question. If it is the 1:47, my guess is that the engine power is struggling with the ratio to turn faster than the wheel diameter/pitch will allow. I'd say you had a correct wheel on a wrong ratio.
The rated RPM of the engine is 2500 RPM and you are achieving only 2300 RPM, your by calculation about one inch in diameter to large, or two inches in pitch.
to obtain top RPM. or the 1:47 ratio is proving as stated, too much for the engine to turn a too large wheel.
I'd go with rslifkin: quote:

"If it's easy enough for you to switch props, I'd check for any markings on the spare to indicate size, then throw it on and see if the boat behaves better with it."
Al is offline   Reply With Quote
Old 02-22-2020, 03:18 PM   #44
Guru
 
kchace's Avatar
 
City: Brookline, NH
Vessel Name: Blue Heaven
Vessel Model: Albin 43 classic double cabin, twin 135 Lehmans
Join Date: Sep 2013
Posts: 2,054
Quote:
Originally Posted by catalinajack View Post
Running a Ford Lehman constantly at 2,200 RPM would not be something I would do. I have never seen an owner posit they run their Lehmans at any more than 1,800 with most saying 1,600 to 1,700.
Actually, there was someone posting on here maybe a year or 2 ago who said he ran WOT ALL the time!
kchace is offline   Reply With Quote
Old 02-22-2020, 03:25 PM   #45
Guru
 
kchace's Avatar
 
City: Brookline, NH
Vessel Name: Blue Heaven
Vessel Model: Albin 43 classic double cabin, twin 135 Lehmans
Join Date: Sep 2013
Posts: 2,054
Quote:
Originally Posted by Soo-Valley View Post
IMHO, what sounds off is you are only getting 7KN @ 2000 RPM with a more efficient 4 blade.
I can only compare to my GB and defer to others with same boat as yours.
With one engine down I was getting 7 knots @ 1600 with 2500 max under load.
Overpropped usually lowers the RPM to attain same speed.
I totally agree! The FIRST thing I thought when I read 2000 to get 7kts is that something isn't right. That's about 110hp (according to the HP graph) to move a 36' boat at *almost* hull speed??!! It doesn't make sense.

As a total guess, I would first check tach calibration, then check the transmission ratio, then check the prop pitch. Its possible this boat has an *underpitched* prop or had a transmission with a higher gear ratio swapped in AND the throttle stop (located INSIDE the throttle control on a FL135) does not allow actual full throttle.

Definitely need some investigation - it doesn't add up.

Edit - another correction - WOT throttle on a FL135 is 2600.

Ken
kchace is offline   Reply With Quote
Old 02-22-2020, 03:50 PM   #46
Senior Member
 
Sidclark's Avatar
 
City: myrtle beach
Vessel Name: Jubilee
Vessel Model: Marine Trader 36 Sundeck
Join Date: Jan 2018
Posts: 208
Quote:
Originally Posted by Island Cessna View Post
Search for tachometer in the App Store for your phone. If your smartphone has an LED flash you will find a free strobe tachometer app for it.
Now ya tell me.. I went and bought a Extech Photo tach 461895.

Went down to the dock today and the Waccamaw is still up. Maybe a couple more days until I can get down to the boat.
__________________
USCG 100 Ton Captain Near Coastal
ASA Certified Instructor
Yacht Broker
Sidclark is offline   Reply With Quote
Old 02-22-2020, 04:00 PM   #47
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,114
I keep hearing copy reading like this in the last post. “I read 2000 to get 7kts”.

Sounds so much like the rpm produces 7 knots. So often people are implying that some rpm (engine speed) is the motive reason a boat achieves a certian speed. It’s the power that one would “get” 7 knots from. Nobodies propped the same. And what rpm varies a lot just w that one variable.
__________________
Eric

North Western Washington State USA
Nomad Willy is offline   Reply With Quote
Old 02-22-2020, 04:13 PM   #48
Senior Member
 
Sidclark's Avatar
 
City: myrtle beach
Vessel Name: Jubilee
Vessel Model: Marine Trader 36 Sundeck
Join Date: Jan 2018
Posts: 208
Quote:
Originally Posted by kchace View Post
I totally agree! The FIRST thing I thought when I read 2000 to get 7kts is that something isn't right. That's about 110hp (according to the HP graph) to move a 36' boat at *almost* hull speed??!! It doesn't make sense.

As a total guess, I would first check tach calibration, then check the transmission ratio, then check the prop pitch. Its possible this boat has an *underpitched* prop or had a transmission with a higher gear ratio swapped in AND the throttle stop (located INSIDE the throttle control on a FL135) does not allow actual full throttle.

Definitely need some investigation - it doesn't add up.

Edit - another correction - WOT throttle on a FL135 is 2600.

Ken
I put in an email to the PO to see if he has any info to shed some light here. I'm not real sure he used the boat that much. Most of his ownership seemed to be renovating the whole boat to liveaboard and cruise. I do know the boat has done the Loop at least once. In what configuration I don't know. It's getting more and more curious as I read all the posts here.

As soon as I get the tach and take the boat up and down the river I'll fill in the blanks....
__________________
USCG 100 Ton Captain Near Coastal
ASA Certified Instructor
Yacht Broker
Sidclark is offline   Reply With Quote
Old 02-22-2020, 09:04 PM   #49
Al
Guru
 
Al's Avatar
 
City: ketchikan, Alaska
Vessel Name: 'SLO'~BELLE
Vessel Model: 1978 Marben-27' Flybridge Trawler(extended to 30 feet) Pilothouse Pocket Cruiser[
Join Date: Apr 2012
Posts: 2,223
Quote:
Originally Posted by Sidclark View Post
I put in an email to the PO to see if he has any info to shed some light here. I'm not real sure he used the boat that much. Most of his ownership seemed to be renovating the whole boat to liveaboard and cruise. I do know the boat has done the Loop at least once. In what configuration I don't know. It's getting more and more curious as I read all the posts here.

As soon as I get the tach and take the boat up and down the river I'll fill in the blanks....
Thanks Sidclark- There will be several of us "Over Propped" guys who will be really interested in the end result of your situation.
Al is offline   Reply With Quote
Old 02-27-2020, 05:06 PM   #50
Senior Member
 
Sidclark's Avatar
 
City: myrtle beach
Vessel Name: Jubilee
Vessel Model: Marine Trader 36 Sundeck
Join Date: Jan 2018
Posts: 208
Ok, back with a few more pieces of information. According to the photo tach I'm running 20rpm low. I checked at 600, 1000 and 2000rpm. No load. The no load rpm reached 2900. I just bumped it up there for a couple of seconds. I couldn't bear to hold it there any longer. In my mind this can't be good for the engine. Tell me if I'm wrong. I didn't get a chance to check actual shaft rpm, but the gear ratio stamped on the transmission is 2.10-1.

I heard back form the PO and he sent me a chart on his fuel burn and rpm. His summary is:
"Average Consumption:2.19 GPH at 1800/1850rpm or 6.5-7.5 kts".
This includes generator use which he says wasn't much. This is based on using 956 gallons of fuel.

I'm beginning to think some current had to be in play with my 7 kts at 2000rpm. Sometime next week I'm going to run up and down the river to get more useful rpm/kts numbers. I'll photo tach the shaft rpm and recheck WOT also. I do question his statement that he went from 6.5 kts to 7.5 kts with only an increase of 50 rpm. Thoughts on that?
__________________
USCG 100 Ton Captain Near Coastal
ASA Certified Instructor
Yacht Broker
Sidclark is offline   Reply With Quote
Old 02-27-2020, 05:49 PM   #51
Guru
 
City: Clearwater, Florida USA
Vessel Name: Seas the Bay
Vessel Model: 1981 42' Hardin Europa
Join Date: Aug 2016
Posts: 1,459
I think the way I'd read the PO's statement a little differently. My read is that he typically cruised at 1800-1850 rpms and, depending upon the seas, he'd typically see 6.5-7kts in that RPM range.

We also don't know how that speed was observed, e.g. relative to water? Relative to ground? By GPS? Relative to course? By paddle wheel? Etc. So, there are a lot of variables in play beyond tach calibration.

"20rpms low" isn't low at all. That is totally well within tolerances.

The something in play could have been sea conditions. Or the mechanism of observing speed. Or the type of speed measured. Or, maybe tolerances changed over time and the tachs need, or needed, an adjustment, etc.
gkesden is offline   Reply With Quote
Old 02-27-2020, 05:58 PM   #52
Guru
 
Soo-Valley's Avatar
 
City: Gulf Islands, BC Canada
Vessel Name: Soo Valley
Vessel Model: Grand Banks 36
Join Date: Jul 2019
Posts: 2,532
measured by GPS I have seen large drops and increase in speed over ground.
20 rpm off is negligible.2850 no load and 2600 under load for 135.
The 7KN at 2000 may have had opposing current.
look forward to your up/down average report
__________________
SteveK AKA Soo Valley
You only need one working engine. That is why I have two.
Soo-Valley is offline   Reply With Quote
Old 02-27-2020, 07:52 PM   #53
Guru
 
Cigatoo's Avatar
 
City: Narragansett Bay
Vessel Model: Grand Banks 36
Join Date: Sep 2016
Posts: 1,209
“1800/1850rpm or 6.5-7.5 kts”
That is what my GB 36 with a 135 turns. With slack current I am at about 7.5 knots at 1800 RPM. Which is just a touch below hull speed. I consider that about right.
__________________
Charlie0
Cigatoo is offline   Reply With Quote
Old 02-27-2020, 08:40 PM   #54
Senior Member
 
Jmarsh203's Avatar
 
City: All over
Vessel Name: Chapter II
Vessel Model: 1972 42 foot Alloy Mfg
Join Date: Sep 2019
Posts: 179
If you look at a hp to rpm curve for any given engine it will tell you the maximum hp that engine will make at that given rpm, now if the engine is spinning at lets just use 1500 rpm and say the graph says it can make 55 hp at that rpm that will be the maximum hp that that engine is capable of making at given rpm. , now if you ask the engine to do something like spin a bigger propeller and that prop requires more than 55 hp to spin it you will be overloading your engine and it WILL damage your engine in the long run for lots of reasons I just don’t feel like explaining. Now the inverse is not true on a Diesel engine if you are spinning the prop at 1500 rpm and the propeller only requires say 20 hp to spin the prop at that rpm the engine will only be producing 20hp, maybe slightly more just from parasitic loss
Jmarsh203 is offline   Reply With Quote
Old 02-27-2020, 08:43 PM   #55
Guru
 
BandB's Avatar
 
City: Fort Lauderdale. Florida, USA
Join Date: Jan 2014
Posts: 20,279
Quote:
Originally Posted by Sidclark View Post
Ok, back with a few more pieces of information. According to the photo tach I'm running 20rpm low. I checked at 600, 1000 and 2000rpm. No load. The no load rpm reached 2900. I just bumped it up there for a couple of seconds. I couldn't bear to hold it there any longer. In my mind this can't be good for the engine. Tell me if I'm wrong. I didn't get a chance to check actual shaft rpm, but the gear ratio stamped on the transmission is 2.10-1.

I heard back form the PO and he sent me a chart on his fuel burn and rpm. His summary is:
"Average Consumption:2.19 GPH at 1800/1850rpm or 6.5-7.5 kts".
This includes generator use which he says wasn't much. This is based on using 956 gallons of fuel.

I'm beginning to think some current had to be in play with my 7 kts at 2000rpm. Sometime next week I'm going to run up and down the river to get more useful rpm/kts numbers. I'll photo tach the shaft rpm and recheck WOT also. I do question his statement that he went from 6.5 kts to 7.5 kts with only an increase of 50 rpm. Thoughts on that?
You're running 20 RPM low? Are you now saying at WOT you're running 2480 RPM? You said 2300 before. So, no load, you're running in neutral? Why? What are you learning by doing that?
BandB is offline   Reply With Quote
Old 02-27-2020, 08:45 PM   #56
Senior Member
 
Jmarsh203's Avatar
 
City: All over
Vessel Name: Chapter II
Vessel Model: 1972 42 foot Alloy Mfg
Join Date: Sep 2019
Posts: 179
And it will have a fuel burn reflecting that hp figure, or at least close enough to not matter. So all you are doing when overproping a boat is taking away your ability to produce the maximum hp that that engine is capable of producing at maximum rpm, and opening up the ability of damaging your engine in the long run from overloading and lugging your engine down from too large a propeller.
Jmarsh203 is offline   Reply With Quote
Old 02-27-2020, 08:50 PM   #57
Senior Member
 
Jmarsh203's Avatar
 
City: All over
Vessel Name: Chapter II
Vessel Model: 1972 42 foot Alloy Mfg
Join Date: Sep 2019
Posts: 179
There are also other advantages of using your full hp range even if it does not produce much more speed such as more control from having more flow velocity over your rudders while the inverse only takes away control.
Jmarsh203 is offline   Reply With Quote
Old 02-27-2020, 08:56 PM   #58
Senior Member
 
Jmarsh203's Avatar
 
City: All over
Vessel Name: Chapter II
Vessel Model: 1972 42 foot Alloy Mfg
Join Date: Sep 2019
Posts: 179
if You go ride 2 boats that are the same spec and one guy has proper wheels on her and the other is so over propped that she can only spin to say 1500rpm out of the rated 2500 the guy spinning the proper propeller WILL have more rudder response at any equivalent speed and it will be quite noticeable.
Jmarsh203 is offline   Reply With Quote
Old 02-27-2020, 09:00 PM   #59
Senior Member
 
Jmarsh203's Avatar
 
City: All over
Vessel Name: Chapter II
Vessel Model: 1972 42 foot Alloy Mfg
Join Date: Sep 2019
Posts: 179
There would be times when underpropping would be acceptable such as running High output/hp requirement hydraulic or pto driven accessories off of the engine full time. I can think of no reason that will truly stand up to scrutiny for over propping a boat since it will just damage the engine.
Jmarsh203 is offline   Reply With Quote
Old 02-27-2020, 09:16 PM   #60
Al
Guru
 
Al's Avatar
 
City: ketchikan, Alaska
Vessel Name: 'SLO'~BELLE
Vessel Model: 1978 Marben-27' Flybridge Trawler(extended to 30 feet) Pilothouse Pocket Cruiser[
Join Date: Apr 2012
Posts: 2,223
Quote:
Originally Posted by Sidclark View Post
Ok, back with a few more pieces of information. According to the photo tach I'm running 20rpm low. I checked at 600, 1000 and 2000rpm. No load. The no load rpm reached 2900. I just bumped it up there for a couple of seconds. I couldn't bear to hold it there any longer. In my mind this can't be good for the engine. Tell me if I'm wrong. I didn't get a chance to check actual shaft rpm, but the gear ratio stamped on the transmission is 2.10-1.

I heard back form the PO and he sent me a chart on his fuel burn and rpm. His summary is:
"Average Consumption:2.19 GPH at 1800/1850rpm or 6.5-7.5 kts".
This includes generator use which he says wasn't much. This is based on using 956 gallons of fuel.

I'm beginning to think some current had to be in play with my 7 kts at 2000rpm. Sometime next week I'm going to run up and down the river to get more useful rpm/kts numbers. I'll photo tach the shaft rpm and recheck WOT also. I do question his statement that he went from 6.5 kts to 7.5 kts with only an increase of 50 rpm. Thoughts on that?

Quote BandB:"You're running 20 RPM low? Are you now saying at WOT you're running 2480 RPM? You said 2300 before. So, no load, you're running in neutral? Why? What are you learning by doing that?"
Exactly!!!


"River??
" Nobody said River all throughout this thread til now. Surely currents have a large part in your predicament. Even running 'up and down' will be affected by the daily difference in 'river conditions', more so than tidal actions where tidal conditions are more predictable. Not sure even this thought can be interpreted as informative as I am not a 'river' student, just seems right to assume.
Corrections to the conclusion are welcome.
__________________

Al 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 05:10 AM.


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
×