Is this right?

[RICKEY]

I have recently met a friend who has the same boat as mine, which is a 53 motor yacht. Its powered by 8V71s natural. His is twin turbo, both the same year. He said that his boat will plane at 2200 RPM and do close to 18 knots. My Question is I'am not sure what degree pitch props I have but I know they are 4 blade. He says that I should be coming up on a plane at 2000 RPMs, is this true? Do I need to repower? The motors I have run very good and sound tight. I would like too hear any info on Hatteras and problems we have. I love my boat and want too do the best for it Thanks

 

[mike]

8v71 naturals are not turbo'd, hence the designation natural. So I am confused about his having turbos. To get 18 knots or more you'll need north of 500 hp, my bet is he is not achieving 18knots with 8v71n's, and maybe not with the turbo version either.

 

[MikeP]

IF it's the turbo, IF the bottom is clean, IF the seas are fairly flat and IF the boat has a fairly light fuel/water load, the figures pretty much correspond to what our 53MY does. Currently, with full fuel/water, other junk and the bottom fairly clean but with some grunge on it, the same RPM will produce about 15 knots. Last Saturday during a clean-out run she nudged slightly above 15 at WOT but it was a struggle! A Porsche 911, she's not!

I was trying to visualize how much fuel was dumping into those cylinders at WOT but my mind can't comprehend numbers that large!

 

[Nonchalant1]

Yes, your information sounds about right, but he's wrong about your boat planing at 2000 RPM. The 8V71TI's are 435 HP and will plane the boat between 2000 and 2200 RPM with 28X31 props. I believe the 8V71N's are 350HP so you may have different props to match the lower horsepower and the boat may not plane. Your props are very likely stamped on the hub ends with dia. and pitch. If you put higher pitch props on it, your engines may become overloaded. The turbo version will do a little over 18 knots with full fuel and gear. Maybe over 19 with nearly empty fuel tanks, water tanks, holding tanks, no waves and no dinghy, but nobody ever runs that way.

Like everything, it's a tradeoff. There are some advantages to "life in the slow lane" with naturals. You're more likely to go slow and get better fuel mileage, and naturals are more likely to run up to twice as long before needing rebuilds (for $10K-$15K per engine) and don't overheat as easily. At 9.1 knots (hull speed) you get better than 1 NM/gal. and you can do 12 knots all day, while at 16.5 knots planing cruise speed, a turbo boat gets about 0.5 NM/gal.

Doug Shuman
1978 53MY

 

[mike]

FWIW, my 53' MY with 350 hp naturals (8v71n's) are running 28x26 props, and 15 knots is about max.

 

[Capt K]

My 1965 50' motoryacht has 871n's supposedly with smaller injectors pushing 325HP. My props are 28 X 28. If you push her up to WOT she will plane and you can back her off to keep on plane 200-300 off the pins. I have gotten used to running her about 1500 which will average about 10knots. In Long Island Sound, the current really affects the speed but she's pretty steady in deeper waters.

Fuel and water aboard also make a difference but that is obviously controllable except in the "heart" of the season when a lot of longer cruising is going on. After 11 years of ownership, I've gotten to really love these naturals. They really will run on pretty much anything and are real forgiving as far a repriming goes for filter changes or "whoops" on figuring range.

Fuel economy improves greatly when you come down to 1400-1600 instead of 1800 (not that these burn much at any rpm).

I still say that the new engines are nice, but there's almost always a way to get the old iron home with a little bit of McGyver thinking and workmanship!

Boat safe, boat happy, drink at the dock (and often).

Capt K

 

[RICKEY]

Thanks for the info. Its always nice too hear from the east coast. Here in the san francisco bay we boat all year long and its beautiful. I will try again too get the boat up on a plane, but the more I hear about the problem We think its the props.

 

[Geoff58yf]

Ive got a 78 58yf here on the SF bay as well, 871-ti's. Shes a fully burdened beast since the run from FLA, inclu 300ft of 5/8ths chain in the forepeak incase the Hatt ride wasnt wet enough as is. Even with -tis, going down the front of a 15 footer at the Gate, I dont think we could hit 18k. We cruise at 1600rpm, 'bout 11knots. I cant recall, even on the pins, getting her up over the hump.

 

[SKYCHENEY]

My 53EDMY has 465hp 6v92's and I get about the same results. Same hull, about the same weight, a little more hp, but still only 15 knots cruise. I too, like to run her at 1300 and get 10 knots and 1NM/gal. My props are 28 x 28 and still a little over propped as I have a hard time getting over 2250 at WOT.

 

[Nonchalant1]

SKYCHENY,

Wow! 28 X 28 on a 465 hp boat is over propped? I thought that most of the 53MY's with 435 hp 8V71TI's ran 28 X 31's? Is your displacement weight 55,000 lbs. like the MY? (I think that's dry weight).

Doug

My 53EDMY has 465hp 6v92's and I get about the same results. Same hull, about the same weight, a little more hp, but still only 15 knots cruise. I too, like to run her at 1300 and get 10 knots and 1NM/gal. My props are 28 x 28 and still a little over propped as I have a hard time getting over 2250 at WOT.

 

[mike]

Sounds like it's time to have a Hatt meet here on SF bay. Per my earlier post I am running 8v71n's with 4 blade-28x26, fully loaded I can just make 15 knots going down hill when lightly loaded. One other point of note is that I lose about a knot due to my Naiad stabilizers.

 

[SKYCHENEY]

Doug,

I may be wrong on prop size since I have not inspected them personally. I am going by the original Hatt manual and those props may have been changed. I am going to be pulling them this winter as I don't know when or if they have ever been tuned, so then I will know for sure. And yes, my displacement is about 58000.

 

[DLCameron2]

Sky:

I have 53 ED #760 which is one hull number away from yours. My engines are 6V-92TA 475HP rating. The props are scanned 28 X 30, at around 2150RPM I am doing 16kts on the GPS. Wide open is 2350RPM pushing 18.5kts. You have stabilizers and I do not however your numbers seem a little low. The original test reports from the 1983 intro of the EDH are available and have all the fuel curves etc. albeit for 8-71's, that is pretty close to the preformance I get.

Take care.

DC

 

[MikeP]

I've seen several posts re 53MYs at 10 knots getting 1NMPG. The best I ever got was .65NPG which corresponds almost exactly to the computer calculated figures for the boat weight and HP at this site: http://boatdiesel.com/index.cfm?CFIDC=APP1B

I'm trying to figure out the secret to getting that additional .35NMPG out of Brigadoon!

Are you guys SURE you are really getting 1NMPG at 10 knots? According to the calculator, the boat can''t do that until somewhere around 6 knots! Again, I've run the calculator at various speeds and it essentially duplicates what our 53 actually does.

Here is the page from the calculator; you can't access it unless you subscribe. I used 58000 as the displacement since the boat's listed 55000 is (I believe) "dry." Entering 55000 didn't change the figures anyway.

Hull Hull Form: DisplacementSlow Semi-DisplacementAverage Semi-DisplacementFast Semi-DisplacementSlow PlaningAverage PlaningFast PlaningPerformance Planing Total Displacement: lbslbskgsTonTonne Water Line Length: ftftm Engine(s) Number: 21234 Output: SAE hpMetric hpkW Maximum RPM: Cruising RPM: Transmission(s) Type: Straight DriveVee DriveOutdrive Ratio: :1 Propeller(s) Number of Blades: 234 Cupped Blades: NoYes Use Prop Diameter: inmm RESULTS MAX PERFORMANCE Available Power: 843.9 SAE hp ( 629.3 kW) @ 2350 RPM Max Speed: 18.7 kts Fuel: 51 US Gall/Hr (typical) CRUISING PERFORMANCE Cruising Power: 251 SAE hp ( 187.2 kW) @ 1500 RPM Cruising Speed: 10.2 kts Fuel: 15 US Gall/Hr (typical) RECOMMENDED PROPELLER Diameter: 28.5 in. Pitch: 25.4 in. Blades: 4 Cupped: No Transmission Ratio Acceptable ALTERNATIVE GEAR/PROP COMBINATIONS Gear Ratio Shaft RPM Dia. Pitch 1.2 1958 20 15 1.4 1679 22 18 1.6 1469 24 20 1.8 1306 26 23 2 1175 27 25 2.2 1068 29 28 2.4 979 30 30 2.6 904 32 33 2.8 839 33 36 3 783 35 38 3.2 734 36 41 3.4 691 37 43 All are acceptable - but the lighter the row color - the more efficient the prop at this boat speed.

 

[MikeP]

OOPS - in the preview the calculator looked like a calculator - in my post it just looks like text...

 

[SKYCHENEY]

Thanks Don, I'll check the props this winter.

Mike, Yes I do get 1Nm/gal at 10 knots. I can figure my fuel on a long trip almost exactly by using this figure. I just filled up and when I told the fuel dock that I would take 450-500 gallons based on my distance traveled, it took 476gallons. Maybe its the "fuel squeezer" 92's

 

[MikeP]

Well, the 92s are a newer design, I guess it's quite possible they are more efficient than the 8V71TIs. One thing I haven't looked at yet at all is the basic tune-up of the engines, including the state of the injectors and if they are the oem N-90's. They run well and start instantly so I have pretty much left them alone for this first season...

 

[Genesis]

No way on the efficiency - no significant difference between them and 71s.

I just installed Floscans. As soon as I get htem calibrated (which depends on fuel becoming available again around here!) I will post some ACCURATE flow rates at various RPMs and speeds for my 45C.

 

[MikeP]

That would be great. It will be interesting to see how that calculator, using your boat's pertinent data, compares with your actual results.

I installed floscans on my last boat (gas) and, as I posted here a while back, I found myself chasing optimum mileage instead of enjoying the boat. For that reason, (a touch of anal-ness is MY problem, not theirs) I decided I woulnd't put 'scans on another boat. I have been rethinking that a bit although I'm not sure I want to spend what looks to be close to 3 Gs for a pair of the diesel versions to see how much fuel I'm using.

I realize that there are other advantages - such as monitoring changes in engine performance but I have to admit in all immodesty that I don't really need them for that. But, being somewhat of a gadget freak as well as a Luddite - strange combination - I might consider them again.

I'll be very interested in your views after they are calibrated and operating to your satisfaction.

And, as a gadget freak, I HEARTILY recommend the Apple Ipod nano!
Admiral's comment when I ordered it: "Why do you need another Ipod?"
Admiral's comment when I received it: "It's too small, you'll just lose it!"
Admiral's comment when she fooled with it: "Order one for me!"

 

[Nonchalant1]

Mike,

I get about 1NM per gal at hull speed of 9.1 knots for a 1978 53MY with 8V71TI's. At hull speed, these 53MYs are just loafing. I'll see if I can verify it with my floscans, GPS two directions and a little spreadsheet.

Doug