Larger Props For Efiency And Engine Life When Running Big Engines Slow

[Brian Degulis]

OK I spoke to a DD Aplication engineer acording to him all DD are designed to run at full rated power throughout the RPM range. That's full rated power not the proppler curve. So the cooling concerns are a non issue.

Brian

 

[Trojan]

GOOD LUCK!

Bill

 

[Pete]

I know, I know, I wrote that I would retire from this subject. So, I will do nothing but suggest that a discussion with Covington or J&T would probably be helpful as they did most of the marine application work on the Detroits that Hatteras used. BTW, back in the 80's I attended a Covington school in Greensboro, NC and remember seeing a trailer load of base engines being unloaded. At the time Covington had a small building doing nothing but marine conversions for Hatteras and a few others. They did the cooling systems, along with turbo selection, injectors, exhaust manifolds, etc.. Talk about easy breakin, when an engine was completed, they took it over to the dyno, warmed it up for maybe a couple of minutes and from then on it was WOT. A real show for DD fans.

Pete

 

[luckydave215]

What we need is one of these in our size.

http://www.autoprop.com/autoprop/international/index.html

I installed one on my last sailboat (38ft, slippery racing hull design, 14,000 pounds, 27 horse Yanmar) and the improvement was dramatic. The boat went from 5.5 knots@3000 rpm to 7 knots@ 1800. Fuel consumption was so small that I went 5 years on 12 gallons, and ran the boat almost every weekend (sailing most of the time of course)
Drag when sailing was reduced 85% because the prop feathers. That would be useful for running on one engine.
The cool thing about this prop design is that its a "constant angle of attack" design, not a "constant speed" design like we're used to on the airplanes we fly. When you apply 10 horsepower to the shaft, the prop pitches to absorb 10 horsepower, and so on. The faster the water is flowing through the prop, the higher the pitch. They work exactly the same in reverse as forward, a real plus for sailboats that don't usually back down worth a crap.
It takes some getting used to approaching the marina, as the boat doesn't slow down when you pull the throttle to idle, the prop pitches up and still pushes the boat with the available power at that engine speed instead of dragging the boat down to "idle speed"
In 10 years of regular use, I had no issues or maintanance different from a fixed pitch prop.
These have been fitted to trawlers with good results, but I don't think they make one in a 1000 horsepower size yet....

 

[Brian Degulis]

I know, I know, I wrote that I would retire from this subject. So, I will do nothing but suggest that a discussion with Covington or J&T would probably be helpful as they did most of the marine application work on the Detroits that Hatteras used. BTW, back in the 80's I attended a Covington school in Greensboro, NC and remember seeing a trailer load of base engines being unloaded. At the time Covington had a small building doing nothing but marine conversions for Hatteras and a few others. They did the cooling systems, along with turbo selection, injectors, exhaust manifolds, etc.. Talk about easy breakin, when an engine was completed, they took it over to the dyno, warmed it up for maybe a couple of minutes and from then on it was WOT. A real show for DD fans.

Pete

What's being overlooked is that the engine is rated to do what the maufacturer says it can. If you look at the power curves it's telling you that the engine is capable of producing X HP @ X RPM. The propeler curve is showing you what is actually being produced with a typical prop it has nothing to do with the engine and it's cooling systems capacity. So acording to DD if you stay within the HP ratings at various RPMs then you cooling system will handle it. In my case I'm not theorizing I've already done it and can tell you it works at the de rated WOT I'm running cooler than the OEM WOT.

As I said when this came up it's a good observation and it's good to kick things around but it's no very productive to invent problems that don't exist and this is getting to that point.

Brian

Brian

 

[Boss Lady]

I don't think everyone read your posts thoroughly, or have followed prior threads where this was discussed, before you actually did it.

 

[krush]

As I said when this came up it's a good observation and it's good to kick things around but it's no very productive to invent problems that don't exist and this is getting to that point.

Brian

Brian, it's an online forum--internet engineers are just part of being in this territory!

 

[Brian Degulis]

Brian, it's an online forum--internet engineers are just part of being in this territory!

I understand that and people throwing around ideas is the purpose of a forum like this I'm not complaining just throwing out my thoughts as well. Did you ever get into a discussion with someone maybe about politics and the person says look (I know I will never convince you and you will never convince me) I walk away from people like that. I can always be convinced and if you manage to do that then I'm the lucky one I gained something from the experience. People that cannot be convinced are usually pretty easy to spot because they present there ideas as facts. They don't start with I think or this is the way I see it they put it up as if it's fact and they never come back and say OK you convinced me they just don't respond when there idea is proven wrong. I often wonder if they change there minds and just don't say that or if they go on believing the wrong thing? These forums are as much a study of human nature as they are about boats.

Brian

 

[Pete]

OK, this time I will really retire from this thread. In departing, let me just mention a few facts. First, Hatteras used Covington conversions in over 95% of their boats back when 2 cycle engines were installed. DD did not do the cooling system, injector selection, turbo selection, heat exchanger selection, raw water pump selection, etc,etc. Covington did. All that DD is saying is "setup and operate our base engine within our spec. and you will be OK". Covington marinized these engines to drive a boat along the propeller curve. That is why they can crank the horsepower up on engines and have them hold together pretty good. Do what ever makes you sleep at night, but the fact is DD can not speak to the application details of a Covington Marinized engine, only Covington can.

Krush and Brian, I know you are not referring to me with your "internet engineers" comments, as I am a real one complete with the diploma saved with my other important papers. But, it doesn't take a engineering degree to understand what I have written above, just common sense. But then, common sense is often not very common.

Pete

 

[Trojan]

If you want to run that way that is fine with me and I agree you can run that way. My contention are five. One I think the props are to small and one could even do better with bigger props, less pitch. I know money is a big factor, props are not free. Two, Detroit's cooling systems have always been marginal on cooling on the upper RPM range. Especially in the sun belt. Running on the top end leaves no room for contamination of the system. If you over heat at all, you must reduce RPMs to such a slow rpm to recover that you will have very little forward motion to get you home. But, as long as you are not making any Atlantic crossings. I guess you will be OK. Three, you are not going to out run any storms or ruff seas and a following sea could really raise hell. Four, docking or turning around in a crowded marina could be a bear. Five, If I wanted to save fuel money and run blowboat speeds I would have purchase one. In a few months of running from now tell us how you like it. Maybe you got something going. As always it's just my opinion. I hope it works for you. In this day and age we need to experiment more. As said before, Good Luck.


BILL

 

[krush]

Krush and Brian, I know you are not referring to me with your "internet engineers" comments, as I am a real one complete with the diploma saved with my other important papers. But, it doesn't take a engineering degree to understand what I have written above, just common sense. But then, common sense is often not very common.

Pete

Pete, I won't speak for Brian (but I bet he thinks like me), but I agree with you 100% and you most likely already know that--just reassuring.

My comment was just a generalization to ALL internet forums (and real life)...apply it as you see fit .

Brian, I still find it funny that you catch so much flak from people. I guess they are clueless to the fact that what you did (derating an engine, changing prop) is done everyday in the commercial sector, right?

 

[Brian Degulis]

Pete If Covington used the prop consumption curve to size the cooling system I would think they would have an obligation to provide you with a power curve that shows that. They are a Detroit Diesel dealer I don't think they would have gotten aproval from Detroit the manufacturer who has to warranty it to do that. If covinton's cooling systems with whatever diffrences they may have is capable of cooling the engine at the max rating it should be able to cool the engine throught the rpm range at the engines rating. If it truly can't I would think they would open themselves up to an awfull lot of liability. Your an engineer with a degree would you design it that way?

Bill I agree more diam and less pitch would work better that decision was based on economics. As far as running at the top of the scale I'm not. At 10.5 kts cruise I'm capable of producing 350 HP and only using 150 HP. My new de rated WOT is 525 HP @ 1600. So I need 300HP to cruise and I've got 1050 HP available hardly running at the top of the scale. In addition when I run @ 1600 RPM I'm running cooler than I did at the OEM 2300 RPM. As far as out running weather sure I can't plane anymore I can Only do 14kts instead of 18kts that's one of the negatives. As far as maneuvering in harbors if your reffering to a little to much power at idle your right another negative. Those are simply decisions you make based on how you use your boat. If you want to go fast this obviously isn't for you. But if your one of the many people that run there boat at or near displacment speed. Doing this will make you run smoother and quieter use less fuel and run your engine in a much more favorable condition that should greatly extend life.

Brian

 

[bobk]

Very interesting thread to me. I am currently trying to figure out what props to use on my 48MY. Most of my running is done at 10kts. I have to turn 1500rpm to acheive 10kts. I would like to acheive 10kts at 1000 rpm and have the eng. temps at 180. I am now running 26x21x4bl props with 1.5:1 Allisons. 6v92's rated at 425hp.
Chris

Chris, did you ever do anything with your props? I have 26X22 four blade in my 48MY (same engines as yours), Walter has 26X23 four blades in his but probably his 6V92's are rated higher than ours. I'm thinking of increasing pitch for better performance at 8-9 knots. Interestingly the Hatt Owners manual for my 48MY calls for 6X23 four blade. At 1000 rpm I reach 7.8-8 knots. The test report on the boat showed 8.3 knots at 1000 rpm, but the test boat was not stabilized like mine, so I expect some loss.

Bob

 

[krush]

Thread back from the dead? This is one of the best threads on this site LOL

 

[REBrueckner]

BobK, Chris
Interesting that your newer 48 MY has 1.5:1 transmissions and approximately 26 x 22 props.

My older 1972 48 YF has 8V71TI's at 435 HP, close to your 425, but I have 2:1, maybe 1.91 to 1, I forget right now, and I am propped with 28 x 32 four bladed props, no cup. I turn up only 2150RPM instead of 2300 WOT.

Increasing pitch will increase your load at lower RPM as will cupping blades. I cruise about 11 knots at 1500 RPM and only about 500 degrees turbo temp, via infrared thermometer test, so I do not like to go lower cruise RPM.


I wonder why Hatteras changed the reduction drive for smaller props in your newer boats: engines,boat, or both...What's the rated RPM of your 6V92's?

 

[chris]

Chris, did you ever do anything with your props? I have 26X22 four blade in my 48MY (same engines as yours), Walter has 26X23 four blades in his but probably his 6V92's are rated higher than ours. I'm thinking of increasing pitch for better performance at 8-9 knots. Interestingly the Hatt Owners manual for my 48MY calls for 6X23 four blade. At 1000 rpm I reach 7.8-8 knots. The test report on the boat showed 8.3 knots at 1000 rpm, but the test boat was not stabilized like mine, so I expect some loss.

Bob

Bob
Still running my 26x23's. I am looking for a used pair of 29x29 or 30x30's. I want to try a used pair to see how the boat performs before spending $$$ on new.
My speed is the same as yours at 1000rpm. I also have Niads. My water temp runs just under 180. How about yours.
Chris

 

[chris]

BobK, Chris
Interesting that your newer 48 MY has 1.5:1 transmissions and approximately 26 x 22 props.

My older 1972 48 YF has 8V71TI's at 435 HP, close to your 425, but I have 2:1, maybe 19.1 to 1, I forget right now, and I am propped with 28 x 32 four bladed props, no cup. I turn up only 2150RPM instead of 2300 WOT.

Increasing pitch will increase your load at lower RPM as will cupping blades. I cruise about 11 knots at 1500 RPM and only about 500 degrees turbo temp, via infrared thermometer test, so I do not like to go lower cruise RPM.


I wonder why Hatteras changed the reduction drive for smaller props in your newer boats: engines,boat, or both...What's the rated RPM of your 6V92's?

Rob
I'm not sure why they changed gear ratios. I know the hulls on the 48my's are unique. More of a displacement hull. Maybe that had something to do with it.

Chris

 

[bobk]

Bob
Still running my 26x23's. I am looking for a used pair of 29x29 or 30x30's. I want to try a used pair to see how the boat performs before spending $$$ on new.
My speed is the same as yours at 1000rpm. I also have Niads. My water temp runs just under 180. How about yours.
Chris

Chris, your original post said you had 26X21 four blades that's why my interest. If indeed they are 26X23, that is the same as my owners manual and Walter's boat. Mine are clearly 26X22 but I believe there is a (small?) cup in the pair that is mounted on the boat. The spares are not cupped.

I run at 160-165F at 1000 rpm. It gets to 180F and holds at 1800 rpm and above regardless of the sea water temperature. That suggests a 180 thermostat, but why would your hold 180 at low rpm???? Any idea what the thermostat is? And does it maintain 180 at high rpm?

Anyway, any guidance guys? I'm going to pull the props because of a vibration and might as well make them more efficient if I can. I run strictly as a trawler for the economy, except to blow out the engine every day or so. And by the way, if I blow it every four hours, there is virtually no smoke, if I wait for 10 hours, I get a puff initially which trails off to nothing after 30-60 seconds, even before the temperature gets up. If for what ever reason twenty or so hours passes before blowing them out, it takes several minutes and the temps will have come up before it clears.

Bob

 

[chris]

Chris, your original post said you had 26X21 four blades that's why my interest. If indeed they are 26X23, that is the same as my owners manual and Walter's boat. Mine are clearly 26X22 but I believe there is a (small?) cup in the pair that is mounted on the boat. The spares are not cupped.

I run at 160-165F at 1000 rpm. It gets to 180F and holds at 1800 rpm and above regardless of the sea water temperature. That suggests a 180 thermostat, but why would your hold 180 at low rpm???? Any idea what the thermostat is? And does it maintain 180 at high rpm?

Anyway, any guidance guys? I'm going to pull the props because of a vibration and might as well make them more efficient if I can. I run strictly as a trawler for the economy, except to blow out the engine every day or so. And by the way, if I blow it every four hours, there is virtually no smoke, if I wait for 10 hours, I get a puff initially which trails off to nothing after 30-60 seconds, even before the temperature gets up. If for what ever reason twenty or so hours passes before blowing them out, it takes several minutes and the temps will have come up before it clears.

Bob

Bob
I am running 26x21's. My mistake.
I run just under 180 at 1000 rpm. At 1850 - 1900 it runs 185. Those temps are off manual gauges in the er. I very rarely run above 1000 rpm so I am happy with the temp.
I have a vibration in noticeable in my rear st rm. It is at higher rpms. The po of my boat had a vibration test done on the boat and it talks about a few different things that were causing it. One reccomendation they made was to stiffen the hull where the intermediate strut is bolted.
PM me your email address and I will scan and email you the test report. It is several pages .
Chris

 

[REBrueckner]

Have never heard of a Vibration Test....Is it a formal procedure and or test debvice??? can someone explain what's involved...how it's done....can it isolate different sources???