Official Cummins 6cta 450C thread

Irie308 said:
Good info but that's what I'm not clear on. Not that I would, but from what I've read and you have posted here, I can run at full power for up to 2 hours? Also if my WOT is 2650, I can run at 2450 all day?
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To my knowledge, we can run our boats at 2400RPMs all day, assuming you're hitting 2650 or better at WOT. This way the engines are not overloaded. From personal experience, I run in the range of 2350-2400. This is where Inspiration seems to be happy. Anything lower and MPG ratio starts to be less attractive. Our model falls in a a category of "stern heavy" boats, dropping below 2300RPMs raises the bow too high and you're loosing efficiency. Being fully loaded and having heavy dinghy on the platform makes it even more noticeable. Giving her an extra 100 RPMs makes her level much better and you gain more speed as you burn through some fuel load.

Doing 16kts at 2100RPMs burning around 24GPH doesn't seem cost efficient to me. Not to mention that the angle of the bow is way off for normal conditions. At that point I rather do 9-9.5 kts at 1300RPMs burning 7GPH. On the other hand, 15.5-16kts is my speed in rough seas, this is where she seems to be most happy and no slamming.

I don't think we can compare EB to DB models, as EBs have different config and weight distribution, with the engines closer to the midship. No first hand experience, but I'd think that EBs could be a bit more leveled at slightly slower speed.
 
Alex F said:
To my knowledge, we can run our boats at 2400RPMs all day, assuming you're hitting 2650 or better at WOT. This way the engines are not overloaded. From personal experience, I run in the range of 2350-2400. This is where Inspiration seems to be happy. Anything lower and MPG ratio starts to be less attractive. Our model falls in a a category of "stern heavy" boats, dropping below 2300RPMs raises the bow too high and you're loosing efficiency. Being fully loaded and having heavy dinghy on the platform makes it even more noticeable. Giving her an extra 100 RPMs makes her level much better and you gain more speed as you burn through some fuel load.

Doing 16kts at 2100RPMs burning around 24GPH doesn't seem cost efficient to me. Not to mention that the angle of the bow is way off for normal conditions. At that point I rather do 9-9.5 kts at 1300RPMs burning 7GPH. On the other hand, 15.5-16kts is my speed in rough seas, this is where she seems to be most happy and no slamming.

I don't think we can compare EB to DB models, as EBs have different config and weight distribution, with the engines closer to the midship. No first hand experience, but I'd think that EBs could be a bit more leveled at slightly slower speed.
Click to expand...

Agree DB and EB aren't apples to apples. I have a 450 EB, and there is no noticeable bow angle change for me once I am on plane and have adjusted the trim tabs. I can do anywhere between 1900 RPM or WOT and it is roughly the same.

2400 RPM is 92% of rated power. Based on specs posted earlier, that is well above the 80% that is noted that we be at/under for continuous.
 
Alex F said:
To my knowledge, we can run our boats at 2400RPMs all day, assuming you're hitting 2650 or better at WOT. This way the engines are not overloaded. From personal experience, I run in the range of 2350-2400. This is where Inspiration seems to be happy. Anything lower and MPG ratio starts to be less attractive. Our model falls in a a category of "stern heavy" boats, dropping below 2300RPMs raises the bow too high and you're loosing efficiency. Being fully loaded and having heavy dinghy on the platform makes it even more noticeable. Giving her an extra 100 RPMs makes her level much better and you gain more speed as you burn through some fuel load.

Doing 16kts at 2100RPMs burning around 24GPH doesn't seem cost efficient to me. Not to mention that the angle of the bow is way off for normal conditions. At that point I rather do 9-9.5 kts at 1300RPMs burning 7GPH. On the other hand, 15.5-16kts is my speed in rough seas, this is where she seems to be most happy and no slamming.

I don't think we can compare EB to DB models, as EBs have different config and weight distribution, with the engines closer to the midship. No first hand experience, but I'd think that EBs could be a bit more leveled at slightly slower speed.
Click to expand...
Alex, that’s exactly what I’ve seen. Anything below 2200 and she’s very sluggish.Hydraulic platform and 450lb dinghy does contribute. 2300 in perfect conditions seems to be our sweet spot. 2400 is our hurry up and go range.
 
Forrestkk said:
...2400 RPM is 92% of rated power. Based on specs posted earlier, that is well above the 80% that is noted that we be at/under for continuous.
Click to expand...

When I got my boat and had a conversation with my Cummins tech on this, those were his words. As long as she's properly tuned to do 2650-2700 at WOT, she can safely run at 2400 all day. I know that for many people 2400 sounds too pushy, but my over 12yrs of owning her proves my mechanic's theory right. When I say "all day", the longest run on plane I had her for 12hrs with a quick fuel stop. Other than that, I've had tons of 8-10hrs runs.

The only point I'm making is answering the question of what's the "safe zone range". AFAIK, 10% is safe. The key part is properly tuned to the specs (and properly maintained, goes without saying...). In our case it's 2650-2700 WOT. If yours isn't making this WOT, don't push your luck.
 
Does anyone know part info for the transmission dipstick? Need to replace mine as its very loose. Afraid it will come flying out underway one day.
 
Alex F said:
When I got my boat and had a conversation with my Cummins tech on this, those were his words. As long as she's properly tuned to do 2650-2700 at WOT, she can safely run at 2400 all day. I know that for many people 2400 sounds too pushy, but my over 12yrs of owning her proves my mechanic's theory right. When I say "all day", the longest run on plane I had her for 12hrs with a quick fuel stop. Other than that, I've had tons of 8-10hrs runs.

The only point I'm making is answering the question of what's the "safe zone range". AFAIK, 10% is safe. The key part is properly tuned to the specs (and properly maintained, goes without saying...). In our case it's 2650-2700 WOT. If yours isn't making this WOT, don't push your luck.
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I don’t know you guys….. I run 2250 @ 26mph and 1.0mpg the boat is happy there….. wide open I run 2650rpm…. I would like to here real world mpg at 2400rpm
 
Irie308 said:
Does anyone know part info for the transmission dipstick? Need to replace mine as it’s very loose. Afraid it will come flying out underway one day.
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I just happen to be on the boat.
280-1 straight drive? If it’s the same as mine: part #3207301012 Hard to see in the picture, but that’s it
IMG_4674.jpeg
 
Blueone said:
I don’t know you guys….. I run 2250 @ 26mph and 1.0mpg the boat is happy there….. wide open I run 2650rpm…. I would like to here real world mpg at 2400rpm
Click to expand...

You're comparing apples to oranges when comparing 420/44DAs to 420/44DBs. DBs are much heavier with lot's more wind resistance. Historically, DAs were always a bit faster and a bit more efficient.

Rule of thumb for DBs 45-55'ers is 0.5 MPG. If my memory serves me right, more favorable I've seen 0.6-0.65MPG, when pushing her to high cruise numbers. Since mine are fully mechanical, I don't have SC to show instant numbers. But my manual math is usually ok.

The difference between 2200 and 2400 is about 4kts (2kts per each additional 100RPMs). Speed is obviously depending on the load and conditions. Starting off with full fuel, I see 20-22kts range. As I'm burning fuel, the speed goes up and I can be in 22-24kts range. This is all with clean bottom and clean gear.

In all fairness, any performance test depend on number of variable, where true load of the boat is one of the key parts. For this reason I don't use boattest numbers, as they're misleading, at least to me. How good are the numbers taken on super light vessel, barely any gear, low fuel and low water? From selling perspective those numbers are awesome. From real world "a family going on a 2 weeks trip cruising" perspective, those numbers are useless. We're talking about many thousands of pounds difference in weight.

My numbers are taken on as real as it gets (fully loaded vessel), which represents a true picture for a cruising family on most trips.

Quick disclaimer, between my hydraulic lift and my tender, I always have at least around 1100-1200LBs added all the way at the stern. This by default affects performance numbers. My heavy tender is always on during my tests.
 
No o-rings here either. So far those that say they have o-rings have EB’s don’t those have v-drives? Different trannys. Maybe zf started using o-rings on those before switching to the one size fits all approach, who knows…
 
Alex F said:
You're comparing apples to oranges when comparing 420/44DAs to 420/44DBs. DBs are much heavier with lot's more wind resistance. Historically, DAs were always a bit faster and a bit more efficient.

Rule of thumb for DBs 45-55'ers is 0.5 MPG. If my memory serves me right, more favorable I've seen 0.6-0.65MPG, when pushing her to high cruise numbers. Since mine are fully mechanical, I don't have SC to show instant numbers. But my manual math is usually ok.

The difference between 2200 and 2400 is about 4kts (2kts per each additional 100RPMs). Speed is obviously depending on the load and conditions. Starting off with full fuel, I see 20-22kts range. As I'm burning fuel, the speed goes up and I can be in 22-24kts range. This is all with clean bottom and clean gear.

In all fairness, any performance test depend on number of variable, where true load of the boat is one of the key parts. For this reason I don't use boattest numbers, as they're misleading, at least to me. How good are the numbers taken on super light vessel, barely any gear, low fuel and low water? From selling perspective those numbers are awesome. From real world "a family going on a 2 weeks trip cruising" perspective, those numbers are useless. We're talking about many thousands of pounds difference in weight.

My numbers are taken on as real as it gets (fully loaded vessel), which represents a true picture for a cruising family on most trips.

Quick disclaimer, between my hydraulic lift and my tender, I always have at least around 1100-1200LBs added all the way at the stern. This by default affects performance numbers. My heavy tender is always on during my tests.
Click to expand...

I certainly agree with all of that. I can get an extra 1.5mph and drop EGT 20 degrees by opening the front and rear glass on the bridge to let the “ wind blow through” lol
 
my3sons said:
No o-rings here either. So far those that say they have o-rings have EB’s don’t those have v-drives? Different trannys. Maybe zf started using o-rings on those before switching to the one size fits all approach, who knows…
Click to expand...

So, out on the boat today. V drives, I was wrong, no orings. Just channels.
 
Well there’s the o-rings… new and improved, plastic? With o-rings.
Pretty hefty price tag.
If those will work, I might try finding o-rings to fit in the groves of the original steel and rubber ones
 
my3sons said:
Well there’s the o-rings… new and improved, plastic? With o-rings.
Pretty hefty price tag.
If those will work, I might try finding o-rings to fit in the groves of the original steel and rubber ones
Click to expand...
I know quite pricey.
 
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