Reply
 
Thread Tools Search this Thread Display Modes
 
Old 06-04-2019, 10:34 AM   #21
TF Site Team
 
Shrew's Avatar
 
City: Westerly, RI
Vessel Name: N/A
Vessel Model: 1999 Mainship 350 Trawler
Join Date: Jan 2014
Posts: 4,162
Quote:
Originally Posted by slowgoesit View Post
Although I appreciate the input, too many responders appear to be jumping to the conclusion that I am trying to save money. That was not the object of my post. I am interested in increasing RANGE and ENDURANCE in areas that may not be conducive to regular fuel stops. I believe in making decisions based on research and facts, not on "not invented here thinking". Hence my post to which I received some very good leads and thoughts for further research!
Technically, the only person who mentioned cost savings was me. Though technically it was more about the reduced duty cycle on the engine as a result of overloading.

Unclear what "Not envented here thinking" means.
Shrew is offline   Reply With Quote
Old 06-04-2019, 10:58 AM   #22
TF Site Team
 
slowgoesit's Avatar
 
City: MX, thru Canal to Bahamas
Vessel Name: Muirgen
Vessel Model: 50' Beebe Passagemaker
Join Date: May 2019
Posts: 3,400
Quote:
Originally Posted by Shrew View Post
Technically, the only person who mentioned cost savings was me. Though technically it was more about the reduced duty cycle on the engine as a result of overloading.

Unclear what "Not envented here thinking" means.

Shrew, I appreciate all the input I received, especially since people had to take time out of the schedules to read the posts, and respond to them. If we really wanted to save a substantial amount of $$, boat ownership would probably not be the wise choice for ANY of us! I'm just always trying to tweak things to my advantage, and the time for me to do that would be when we initially purchase a boat. Just trying to think out of the box.


By "Not invented here thinking" I was referring to a knee jerk reaction some people tend to have when confronted with anything new or out of their comfort zone.



Also the "Autoprop" was mentioned as a possibility. I am going to look into that as well. I'm curious about the overall efficiency in forward vs a fixed pitch prop. Efficiency in reverse doesn't really concern me that much as you are in reverse so little of the time.


Thanks again to all who contributed ideas!
slowgoesit is offline   Reply With Quote
Old 06-04-2019, 09:53 PM   #23
Senior Member
 
Jetstream's Avatar
 
City: Tasmania
Vessel Model: Old Town Loon
Join Date: Jul 2015
Posts: 218
Quote:
Originally Posted by twistedtree View Post
I’ll wager that 90% or more of your fuel savings were a result of slowing down from 7 Kts to 6 Kts

This is a very common misinterpretation of the fuel savings, or misattribution of the cause of the fuel savings.

Good thought but we did try that when we first got the boat. Did trials of fuel consumption from 800 RPM right up to 2800 RPM which was maximum cruise for our engines because we wanted to do some extended trips where fuel wasn't available.. It did save a little fuel and increase the range slightly at 6 knot but no where near as much as for single engine ops.
Jetstream is offline   Reply With Quote
Old 06-04-2019, 10:32 PM   #24
Guru
 
dhays's Avatar
 
City: Gig Harbor
Vessel Name: Kinship
Vessel Model: North Pacific 43
Join Date: May 2015
Posts: 9,046
Quote:
Originally Posted by DDW View Post
Take a look at the Autoprop. This is a 3 blade with true pitch, the blades are arranged to adjust their pitch by themselves, due to the offset in the pivot point. They will change their pitch with rpm or load. If you lock the shaft they will feather. For what you are trying to do they might be the solution.

I put an Autoprop on my last sailboat. It worked really well on a sailboat. In the PNW we spent a lot of time motorsailing. The self adjusting pitch was perfect with the variable propulsion from the sails.

There have been some that have complained that the Autoprop, since it always has a pitch that provides lots of load on the engine, can be hard on the engine at lower rpms. For me, it was great.
__________________
Regards,

Dave
SPOT page
dhays is offline   Reply With Quote
Old 06-04-2019, 11:06 PM   #25
DDW
Guru
 
City: San Francisco
Join Date: Apr 2018
Posts: 3,094
It looks like Autoprops are only available up to 23 1/4", so maybe not big enough.
DDW is offline   Reply With Quote
Old 06-05-2019, 06:55 AM   #26
Guru
 
OldDan1943's Avatar
 
City: Aventura FL
Vessel Name: Kinja
Vessel Model: American Tug 34 #116 2008
Join Date: Oct 2017
Posts: 10,595
Quote:
Originally Posted by Moby Nick View Post
Decades ago Sneckies (Scandinavian motor cruisers) similar to my Albin-25 appearing at left had feathering props instead of F/N/R transmissions. The control was mechanical, manipulated by a lever through the cockpit floor. Norwegian relatives of my wife's cruised all over Europe in such a vessel.
+1
__________________
Two days out the hospital after a week in the hospital because of a significant heart attack.
OldDan1943 is offline   Reply With Quote
Old 06-05-2019, 06:58 AM   #27
Guru
 
wkearney99's Avatar
 
City: Bethesda, MD
Vessel Name: Solstice
Vessel Model: Grand Banks 47 Eastbay FB
Join Date: Feb 2018
Posts: 2,164
Quote:
Originally Posted by slowgoesit View Post
By "Not invented here thinking" I was referring to a knee jerk reaction some people tend to have when confronted with anything new or out of their comfort zone.
Conversely it's just as bad a reaction on the part of newbies to think they're on a brand new trail, headed toward all sorts of magical solutions and discoveries.
__________________
-- Bill Kearney
2005 Eastbay 47 FB - Solstice, w/Highfield CL360 tender
wkearney99 is offline   Reply With Quote
Old 06-05-2019, 07:25 AM   #28
Guru
 
City: Italy
Vessel Name: Didi Mau
Vessel Model: Currently looking for next boat
Join Date: Jul 2015
Posts: 1,081
Looks odd

Quote:
Originally Posted by djmarchand View Post
You are kidding yourself if you think you will save significant fuel by shutting down one engine and feathering/braking the other one.


Take a look at the attached graph. The Alaskan based data was done by Bob Lowe and I know he reported it correctly. FWIW he didn't find significant difference between freewheeling and braking a fixed pitch prop.


David
I see the data, but still hard for me to believe a big,heavy, 50-foot OA can get 2.5 knots per gallon. My 0A 456 generally burns 5 gallons an hour at 8 knots, or 1.6 knots per gallon.

Wow!

Gordon
Gordon J is offline   Reply With Quote
Old 06-05-2019, 08:08 AM   #29
Valued Technical Contributor
 
DavidM's Avatar
 
City: Litchfield, Ct
Join Date: Aug 2012
Posts: 6,786
Quote:
Originally Posted by Gordon J View Post
I see the data, but still hard for me to believe a big,heavy, 50-foot OA can get 2.5 knots per gallon. My 0A 456 generally burns 5 gallons an hour at 8 knots, or 1.6 knots per gallon.

Wow!

Gordon

I agree and I suspect the Flowscans or whatever was used was poorly calibrated at low rpms. I just brought a boat up the coast about 300 NM and the Flowscans on the twin engines were within a gph of each other at 2,450 rpm and 27 gph total but at 1,300 rpm one said 2 gph and the other said 4. The high speed gph seemed about 10% high compared to fill to fill data but the low speed data was obviously off a lot.



So take the OA data with a grain of salt. The Alaskan data was done by Bob Lowe who ran a boat yard in the PNW. I had drinks with him once and saw his boat that was beautifully restored and and he was a very competent guy. His website gives much more data on this topic: Dreamer. This looks like it was rigorously done and Bob is the kind of guy who would do it right.


David
DavidM is offline   Reply With Quote
Old 06-05-2019, 08:53 AM   #30
Guru
 
catalinajack's Avatar
 
City: Edgewater, MD
Vessel Name: Catalina Jack
Vessel Model: Defever 44
Join Date: Nov 2011
Posts: 3,585
Quote:
Originally Posted by djmarchand View Post
You are kidding yourself if you think you will save significant fuel by shutting down one engine and feathering/braking the other one.


Take a look at the attached graph. The Alaskan based data was done by Bob Lowe and I know he reported it correctly. FWIW he didn't find significant difference between freewheeling and braking a fixed pitch prop.


David

Regarding there not be a significant difference between freewheeling and braking a fixed pitched prop, here is my anecdotal experience suggesting otherwise. Before leaving on the Great Loop last May I was fully aware that the cutlass bearings were very tight, so tight that it was extremely difficult with the boat out of the water to rotate the shafts even using the 25-inch props as a lever. Inside, using an 18-inch lever arm at the shaft coupling it was equally difficult. Still, the boat was that way when purchased five years earlier and we had no excessive vibration so off we went.



Fast forward to last January. In Pelican Cove at Cayo Costa in Florida, I managed to go aground in some sand exiting the cove at very low tide. No problem I thought, I'll just back off and retrace my course in-bound. I applied a fair amount of power, but too much as it turned out because I apparently exceeded the torque rating of my Drive Savers. The connecting bolts ripped out of the hard rubber and I was left with one-shaft propulsion. When I was able to get underway it was 40 miles on one engine to Fort Myers. Later, we had the boat hauled, eight cutless bearings replaced, the shafts trued, props reconditioned, and the engines aligned (in the water).


That's the background. Now for the anecdotal evidence. On the 40-mile run up to Forts Myers with the shaft not rotating keeping the boat on a straight course required TWENTY degrees of rudder. After the work was done, running on one engine required just four degrees of correction with the non-operating shaft happily spinning in the water AND I was able to use the autopilot. The transmissions are Borg Warner Velvet Drives which can be free-wheeled without damaging them. Before repair, on the one engine the fastest I could travel was barely 6 MPH at 1,600 RPM (Lehman 120). After repair, I got over 7 MPH at the same RPM.



Draw your own conclusions but, im my opinion, their is indeed a profound difference in running on one engine with a locked shaft versus a free-wheeling shaft. I do recognize that some brands of transmissions can be damaged if free-wheeled.


As to whether there is any fuel savings, my guess is perhaps some small amount but I don't run with just one engine now except in special situations and not to save fuel. For example, I ran on one engine when recently transiting the Dismal Swamp which pretty much requires speeds of four-to-five MPH. Keeping our boat at those speeds on two engines is quite annoying as it means operating at not much above idle speed which makes for annoying vibrations at times. Running on one engine the length of the river and canal made for a pleasant, quiet transit. I also ran on one engine going through Norfolk with its speed restrictions.


I think there are some folks who are convinced that running on one engine derives significant savings. I don't know that they are incorrect. I only know that I can't be bothered except in those special situations. One last note, I mentioned earlier that we had no vibrations before the repairs. Well, we just knew no different. We found significantly reduced vibration as perceived when standing on either side of our aft berth where the shafts exit the hull. The boat overall runs so much more smoothly now. We wish we had undertaken these repairs before on the Loop.


Oh, one last note on fuel consumption before and after the repairs. Before the repair we averaged 3.7 GPH. After we got down to 3.4 GPH. That is a huge difference over the course of a 6,000 mile trip. I calculate that I wasted four or five hundred dollars in fuel, perhaps more. Our boat weighs 56,000 pounds with a full load.
catalinajack is offline   Reply With Quote
Old 06-05-2019, 09:41 AM   #31
Technical Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,194
Second the above. A twin running on one will have asymmetric thrust and will need rudder to hold heading. Boat will be going a bit sideways in the water, along with a cocked rudder, neither of which is good for efficiency.

And the folding/feathering/etc props will not have the best blade shape for efficiency.

If you want maximum range, get a single engine. Carry tools and spares and it will be plenty reliable. Want more reliability? Get a single with a wing engine. Put a folding prop on the wing.
Ski in NC is offline   Reply With Quote
Old 06-05-2019, 10:16 AM   #32
DDW
Guru
 
City: San Francisco
Join Date: Apr 2018
Posts: 3,094
The drag of spinning vs. braked prop has been extensively tested by the sailboat crowd. The answer is "it depends". Number of blades, solidity ratio, drag on shaft, all have an effect. On a 4 blade high solidity powerboat prop, spinning might be better. A braked prop on a power twin has another effect, very disturbed flow over the rudder behind it, which might make half of the steering ineffective.
DDW is offline   Reply With Quote
Old 06-10-2019, 04:29 PM   #33
Veteran Member
 
City: Holland, Michigan
Vessel Name: Emerald Isle
Vessel Model: Nordic Tugs 32
Join Date: Jun 2017
Posts: 47
Cool

Quote:
Originally Posted by Jetstream View Post
We used to cruise on one engine when we need extra range and it made a significant difference. We went from 7 knots on two engines at 1200 RPM to 6 knots on one engine at 1200 RPM. Fuel flow from 12 LPH to 6.5 LPH.



The WOT for our engines was 3000 RPM so a load was not an issue at all and our transmissions did not require the engine to be running while free wheeling.


We used to alternate the engines about every 4 hours to keep the operating hours and wear the same. Did hundreds of hours like that.
I agree with Jetstream in that his numbers are about right and the logic behind it works. He goes from 1.7LPM at 7 kts to 1.1LPM at 6 kts. Sure, some of the gain is just due to the speed reduction, but certainly not all. It would be interesting if he had done the same thing, but adjust the speed of the working engine to maintain the same boatspeed. I don't have any data, but I'd be willing to bet that at those low speeds half the fuel consumed just keeps the engine spinning, with only half being used to propel the boat. That's the big reason to run on one engine, and a lot of people do it. However, there is no free lunch. The propulsion efficiency will drop when running on one engine. That is because the total effective prop area drops in half. The efficiency (reciprocal of slip) will be about 65% on two engines, but maybe more like 55% on one. So you gain a lot on engine efficiency, but lose propulsion efficiency. Sure, a feathering prop has less drag than a freewheeling prop, but its driving efficiency would be less. A complex tradeoff.
garycasey is offline   Reply With Quote
Old 06-11-2019, 11:07 AM   #34
Senior Member
 
City: port orchard, wa
Vessel Name: skybird
Vessel Model: skookum/one off
Join Date: Oct 2007
Posts: 143
...a feathering prop on a power boat? reason? you gonna add a mast too?...clyde
clyde is offline   Reply With Quote
Old 06-12-2019, 02:31 PM   #35
Senior Member
 
City: Hawaii
Join Date: Jul 2018
Posts: 275
When I checked into it 8 years ago the MAX prop for a 47' sailing cat was $2500 each whereas the fixed prop was about $500 each. Now I understand the MAX for the same boat is about four grand.

I'd like to put them on my 47 power cat for long-range cruising but I understand that to get the most efficiency your need to extend the rudders due to the distance between shafts on the cat.

I have a friend who shingle-engined a couple of trawlers from Hawaii to Seattle by taking one prop off and then putting on scuba gear and switching to other shaft enroute. He got unreally range on internal fuel.
ProMaritime 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 07:13 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012