Chris Craft Constellation 500s
- Thread starter Pete37
- Start date
The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
If you have answers, please help by responding to the unanswered posts.
- Joined
- Aug 29, 2012
- Messages
- 2,678
- Location
- Good Ol' US of A!
- Vessel Name
- Pau Hana
- Vessel Make
- 1989 PT52 Overseas Yachtfisher
Is this a questions or statement?
BTW- welcome!
BTW- welcome!
Hi Janet,
Had a bad computer breakdown and have been offline for a while. Looking for something that looks like a Chris Craft forum but not sure I've found it.
The latest topic on the Boat US Forum is freewheeling which means running with one engine on and the other off.
Turns out this saves about half the fuel with a loss of only about 1.3 knots in speed. Our test boat has gone from 0.75 nmpg at 10.5 knots to more than 1.5 nmpg at 9.2 knots. We're even getting some reports of 1.85 nmpg. A huge cost saving.
This is a trick that can be done with just about any twin engine boat so it probably applies to other boat brands.
I'm going to try to transition the discussion to this forum.
Pete37
Had a bad computer breakdown and have been offline for a while. Looking for something that looks like a Chris Craft forum but not sure I've found it.
The latest topic on the Boat US Forum is freewheeling which means running with one engine on and the other off.
Turns out this saves about half the fuel with a loss of only about 1.3 knots in speed. Our test boat has gone from 0.75 nmpg at 10.5 knots to more than 1.5 nmpg at 9.2 knots. We're even getting some reports of 1.85 nmpg. A huge cost saving.
This is a trick that can be done with just about any twin engine boat so it probably applies to other boat brands.
I'm going to try to transition the discussion to this forum.
Pete37
Last edited:
ranger58sb
Guru
You've probably visited the related issues, but FWIW some marine gears might not like freewheeling... since they're not being lubricated when the engine is off. (Happens our gears are fine, at slow trolling speeds, according to the manufacturer.. but I didn't ask them about higher speeds like yours.)
Another issue is maybe about dripless shaft seals. You probably don't have those, but newer boats might be adversely affected under freewheeling there, too.
Just thoughts... useful to check with manufacturers, etc. for real factoids.
-Chris
Hi Chris,
Yes, we are aware of the lubrication problems. TwinDisc says we need to run the tranny 5 minutes in neutral for every 8 hours to keep them lubricated. That's not much of a problem. Our typical cruising speeds in this mode are 9 to 10 knots. Fast for a classic trawler but not a problem for the trannys. TwinDisc knows what speeds we are operating at and has no problem with them. Most Connies use the old MG5909 trannys which don't have dripless shaft seals.
I used to keep my boat on the South River a long time ago. Nice river. We keep our Connie at Piney Narrows Yacht Haven on Kent Island now under a covered slip. Covered slips are the greatest invention since sliced bread.
So far we haven't found any problems with free wheeling and everyone is loving the nearly 50% reduction in fuel consumption. Can't recommend it for all trannys though; we only know about TwinDisc trannys.
Pete37
Yes, we are aware of the lubrication problems. TwinDisc says we need to run the tranny 5 minutes in neutral for every 8 hours to keep them lubricated. That's not much of a problem. Our typical cruising speeds in this mode are 9 to 10 knots. Fast for a classic trawler but not a problem for the trannys. TwinDisc knows what speeds we are operating at and has no problem with them. Most Connies use the old MG5909 trannys which don't have dripless shaft seals.
I used to keep my boat on the South River a long time ago. Nice river. We keep our Connie at Piney Narrows Yacht Haven on Kent Island now under a covered slip. Covered slips are the greatest invention since sliced bread.
So far we haven't found any problems with free wheeling and everyone is loving the nearly 50% reduction in fuel consumption. Can't recommend it for all trannys though; we only know about TwinDisc trannys.
Pete37
knotheadcharters
Senior Member
- Joined
- Jan 31, 2011
- Messages
- 338
- Vessel Name
- Amar la Vida
- Vessel Make
- 1989 Carver Californian 48' MY
FWIW for what it's worth
ranger58sb
Guru
Yep, figured you had it all sorted. (And sometimes forums posts are also aimed at future readers.)
We're near the mouth of the River, easy access to the Bay... I know Piney Narrows, too, and learned much later that an uncle of mine used to keep his boat there long ago...
Cheers, -Chris
ranger58sb
Guru
Yeah, that's right next door to us... with deeper water. Looks like a nice enough place to me; on site services, etc.
-Chris
Miss Donna
Veteran Member
- Joined
- Nov 3, 2013
- Messages
- 52
- Location
- USA
- Vessel Name
- Miss Donna
- Vessel Make
- Chris craft constellation
Hello Pete, and all members.
I am the skipper of Miss Donna, the test boat for freewheeling.
After freewheeling for 180 miles I topped off with 160 gallons. Giving me 1.125 mpg. 1400 rpm getting me 9knt's. I was hoping for better, however I am traveling on the ten tom with barges to pass, locks to navigate and of course varying depths and currents. Which is nice to have the option to fire up the other engine underway. Dormant tranny stays cool around 102 degrees. The only reason it is that warm is from ambient temps from the engine from occasionally running it. Also I ran from my saddle tanks that do not receive the unused fuel.
Keep in mind I am doing this to conserve fuel and also keep the engine running at recommended temps.
Does anybody have any idea how much fuel is returned? I would imagine a true mpg test would be running from the stern tanks which receive the unused fuel.
I am the skipper of Miss Donna, the test boat for freewheeling.
After freewheeling for 180 miles I topped off with 160 gallons. Giving me 1.125 mpg. 1400 rpm getting me 9knt's. I was hoping for better, however I am traveling on the ten tom with barges to pass, locks to navigate and of course varying depths and currents. Which is nice to have the option to fire up the other engine underway. Dormant tranny stays cool around 102 degrees. The only reason it is that warm is from ambient temps from the engine from occasionally running it. Also I ran from my saddle tanks that do not receive the unused fuel.
Keep in mind I am doing this to conserve fuel and also keep the engine running at recommended temps.
Does anybody have any idea how much fuel is returned? I would imagine a true mpg test would be running from the stern tanks which receive the unused fuel.
FF
Guru
- Joined
- Oct 12, 2007
- Messages
- 22,552
Giving me 1.125 mpg. 1400 rpm getting me 9knt's.
Knots is very unusual inland , most waterways are measured statute miles.
Either way you will find dropping to 7K may double (or better) your KPG or MPG.
We ran the loop at 7 and got almost 3 mpg.50 ft also.
Slow works if you need or like to run cheaply.
Knots is very unusual inland , most waterways are measured statute miles.
Either way you will find dropping to 7K may double (or better) your KPG or MPG.
We ran the loop at 7 and got almost 3 mpg.50 ft also.
Slow works if you need or like to run cheaply.
Miss Donna
Veteran Member
- Joined
- Nov 3, 2013
- Messages
- 52
- Location
- USA
- Vessel Name
- Miss Donna
- Vessel Make
- Chris craft constellation
Hello FF, the reason I started freewheeling was becouse I have detroit 6v92's.
They need to be run at 185 degrees, can't do that unless I run at 1400 rpm hence I am only running one at a time.
They need to be run at 185 degrees, can't do that unless I run at 1400 rpm hence I am only running one at a time.
ranger58sb
Guru
Maybe we need to find y'all your own builder's forum so you can discuss all of this!!!...I will be working on it!
Aside from the obvious CC-specific stuff... I would think "freewheeling" in the sense used here is maybe applicable to a wide range of boat/engine/gear brands...
-Chris
- Joined
- Oct 1, 2007
- Messages
- 7,331
- Location
- Texas
- Vessel Name
- Floatsome & Jetsome
- Vessel Make
- Meridian 411
timjet
Guru
- Joined
- Apr 9, 2009
- Messages
- 1,920
Running single engine on a twin has been discussed thoroughly before on this forum. Do a search going back 2-3 years and you'll find a lot of info and opinions on this. Provided you can get past the dripless seals and free wheeling tranny problems there is an easy way to determine if single engine operation is cost effect from a fuel stand point.
Operate your boat with both engines running at whatever speed you want to compare, but likely just below displacement speed. Note the GPS speed and engine rpm. Now operate single engine at the same rpm as before and note the GPS speed after the boat is trimmed for the single engine. If the GPS speed single engine is more that half the speed with both engines running then there is a fuel saving running single engine.
At about 7.5 kts my boat drops only about 1.5 kt on one engine.
Operate your boat with both engines running at whatever speed you want to compare, but likely just below displacement speed. Note the GPS speed and engine rpm. Now operate single engine at the same rpm as before and note the GPS speed after the boat is trimmed for the single engine. If the GPS speed single engine is more that half the speed with both engines running then there is a fuel saving running single engine.
At about 7.5 kts my boat drops only about 1.5 kt on one engine.
Miss Donna
Veteran Member
- Joined
- Nov 3, 2013
- Messages
- 52
- Location
- USA
- Vessel Name
- Miss Donna
- Vessel Make
- Chris craft constellation
I apologize if I brought this up in the wrong area. Obviously new to site. Give a guy a break.
- Joined
- Oct 1, 2007
- Messages
- 7,331
- Location
- Texas
- Vessel Name
- Floatsome & Jetsome
- Vessel Make
- Meridian 411
Hey, I wasn't chastising per se....but with forums, in general, you want to put topics where they belong so people know where to look for them. It also allows more related searches and traffic to provide you the information you are looking for....IOW, people do not come to the "Welcome Mat" to find out about fuel saved by running a twin on one engine!!! If you put that in the powerplant section, then more people are likely to find it and reply to it....make sense?....
CPseudonym
Moderator Emeritus
A forum to discuss the maintenance and repair of Chris Craft Constellation 500 and related motoryachts
You'll notice you are currently in the Chris Craft section
It's a little thin content wise right now so invite your friends and enjoy
Miss Donna
Veteran Member
- Joined
- Nov 3, 2013
- Messages
- 52
- Location
- USA
- Vessel Name
- Miss Donna
- Vessel Make
- Chris craft constellation
Nice pic CPseudonym.
Hi All,
Pat: Glad to see that you managed to find our new forum on this site and post a message. Unfortunately the Boat US forum is getting less and less reliable. I think we need to transfer our posts to this forum. Sorry to hear that your latest nmpg figures were less than expected but suspect it had something to do with the way the fuel consumption was measured. I’ll try to explain the nmpg you should get.
A Connie running at 1400 rpm on both engines gets 10.5 knots and burns 14 gph. That comes from running at that speed for several years plus the Detroit Diesel engine performance curves. So the specific fuel consumption is 10.5/14.0 = 0.76 nmpg. When running on one engine the speed drops to 9.2 knots and the fuel consumption drops to half of the two engine fuel consumption or 7.0 gph. This makes the specific fuel consumption 9.2/7.0 = 1.31 nmpg. That’s a (1.31-0.76) = 0.55 nmpg saving or a 42% saving over the twin engine fuel consumption.
A few posts ago you thought you were getting 1.85 nmpg so the 1.125. nmpg you think you’re getting now must be a great disappointment.
Your latest data gives a specific fuel consumption of (180.0/1.15)/160.0 = (156.5/160.0) = 0.978 nmpg at 9.0 knots which is only 0.978/1.31 = 74.7% of the nmpg you would expect. But I assume that you estimated the fuel consumption based on the fuel gauge readings. My experience is that you can only read them to an accuracy of about 5 gallons and the saddle tanks are tapered top-to-bottom which throws the reading off a bit more. So I don’t think you can really trust the gauge readings to better than 10 gallons. So you might have only burned only 150 gallons which would make the specific fuel consumption (156.5/150.0) = 1.04 nmpg.
That’s still only about 79.4% of what you should expect but it is (1.04/1.125) = 92.4% of what you think you actually got. Either way it’s not what you should expect so there still must be a factor we haven’t accounted for. But an 8% error in this type of measurement isn’t bad. We’ll have to wait for further data to really nail this number down. Expect the answer to be somewhere near 1.31 nmpg.
Pete37
Pat: Glad to see that you managed to find our new forum on this site and post a message. Unfortunately the Boat US forum is getting less and less reliable. I think we need to transfer our posts to this forum. Sorry to hear that your latest nmpg figures were less than expected but suspect it had something to do with the way the fuel consumption was measured. I’ll try to explain the nmpg you should get.
A Connie running at 1400 rpm on both engines gets 10.5 knots and burns 14 gph. That comes from running at that speed for several years plus the Detroit Diesel engine performance curves. So the specific fuel consumption is 10.5/14.0 = 0.76 nmpg. When running on one engine the speed drops to 9.2 knots and the fuel consumption drops to half of the two engine fuel consumption or 7.0 gph. This makes the specific fuel consumption 9.2/7.0 = 1.31 nmpg. That’s a (1.31-0.76) = 0.55 nmpg saving or a 42% saving over the twin engine fuel consumption.
A few posts ago you thought you were getting 1.85 nmpg so the 1.125. nmpg you think you’re getting now must be a great disappointment.
Your latest data gives a specific fuel consumption of (180.0/1.15)/160.0 = (156.5/160.0) = 0.978 nmpg at 9.0 knots which is only 0.978/1.31 = 74.7% of the nmpg you would expect. But I assume that you estimated the fuel consumption based on the fuel gauge readings. My experience is that you can only read them to an accuracy of about 5 gallons and the saddle tanks are tapered top-to-bottom which throws the reading off a bit more. So I don’t think you can really trust the gauge readings to better than 10 gallons. So you might have only burned only 150 gallons which would make the specific fuel consumption (156.5/150.0) = 1.04 nmpg.
That’s still only about 79.4% of what you should expect but it is (1.04/1.125) = 92.4% of what you think you actually got. Either way it’s not what you should expect so there still must be a factor we haven’t accounted for. But an 8% error in this type of measurement isn’t bad. We’ll have to wait for further data to really nail this number down. Expect the answer to be somewhere near 1.31 nmpg.
Pete37
Miss Donna
Veteran Member
- Joined
- Nov 3, 2013
- Messages
- 52
- Location
- USA
- Vessel Name
- Miss Donna
- Vessel Make
- Chris craft constellation
Hello Pete, glad we caught up. I started with full saddle tanks and then topped them off. Definitely room for error. Plus the factor of fuel returning to a different tank. Non the less, we leave Demopolis Al on early Wednesday morning and will run on both to make 10 knots so we can reach a decent anchorage. It will be nice to let "The Ladies" run.
Miss Donna
Veteran Member
- Joined
- Nov 3, 2013
- Messages
- 52
- Location
- USA
- Vessel Name
- Miss Donna
- Vessel Make
- Chris craft constellation
Lets not forget the buoyancy of salt water compared to mud.
Hi CPSeudonyn,
I have an address list of about 200 Connie owners. This forum running under the Boat US Manfacturing Forums ran for seven years, had 2000 posts and nearly a half million reads. We also have a 2.5 gigabyte Connie Owners Library on DVD which documents what we have learned about Connie in the past seven years. When I have notified the Connie owners about this new forum by mail this site should get a lot thicker.
Pete37
I have an address list of about 200 Connie owners. This forum running under the Boat US Manfacturing Forums ran for seven years, had 2000 posts and nearly a half million reads. We also have a 2.5 gigabyte Connie Owners Library on DVD which documents what we have learned about Connie in the past seven years. When I have notified the Connie owners about this new forum by mail this site should get a lot thicker.
Pete37
Miss Donna
Veteran Member
- Joined
- Nov 3, 2013
- Messages
- 52
- Location
- USA
- Vessel Name
- Miss Donna
- Vessel Make
- Chris craft constellation
I would sure like to get my hands on one of those dvd's.
- Joined
- Oct 1, 2007
- Messages
- 7,331
- Location
- Texas
- Vessel Name
- Floatsome & Jetsome
- Vessel Make
- Meridian 411
You'll notice you are currently in the Chris Craft section
It's a little thin content wise right now so invite your friends and enjoy
WOOOOHOOOOOO!!!!!! Great job Craig!!!!
