Delivery from Baltimore to N Shore LI- lessons learned

smitty477 · Jun 7, 2019

BDofMSP said:
Well if I haven't missed something, the PO ran the boat that way for 10 years since repower. Hard to imagine how the 11th summer is gonna be the deal killer.

That would depend a whole lot on how those 650 hours were previously run, whether or not the same props were in use the previous 650 hours, and what the current blow by test and other engine baselines set the current condition in.
This boat with healthy 370 engines and correct propping should be near 24 knts at WOT.
This post does not contain enough information to determine any reasonable conclusions on current condition of engines or anything about the props themselves. We cannot even confirm that the gage readings are correct at this point in time - so much of this is a best guess at this time.

smitty477 · Jun 7, 2019

smitty477 said:
That would depend a whole lot on how those 650 hours were previously run, whether or not the same props were in use the previous 650 hours, and what the current blow by test and other engine baselines set the current condition in.
This boat with healthy 370 engines and correct propping should be near 24 knts at WOT.
This post does not contain enough information to determine any reasonable conclusions on current condition of engines or anything about the props themselves. We cannot even confirm that the gage readings are correct at this point in time - so much of this is a best guess at this time.

Apologies....
I have gone back and reread this post as well as opening the listing and reading that.
It may or may not be a prop issue - a very poor move on my part to just assume that the boat and engines were in good to best shape as a result of my original reading.

After rereading the post and listing here are some new questions:
- Did the boat do 20 knots at cruise and 26 knots top speed at Seatrial?
- Did the boat ever do 20 knots cruise an d 26 knots top?
- Were the above speeds achieved with the same props as on the boat now?
- Are the trim tabs operational?
- Are the tachs know accurate? (mech survey)
- What were the gage readings at Seatrial?
- Did the mechanical survey include a blow by test? A high idle rpm check? A boost test? etc?
- Why were the aftercoolers etc just recently serviced?
- What other parts were recently replaced?
- On the trip home what did the hull/rpm do with extended tabs?
- What other mechanical maintenance records does the boat have?

These would allow you to see if the prop slips are/were in the ballpark for the boat...
- What are the prop specs? (D X P X # blades by material)
- What are the transmission ratio's

smitty477 · Jun 7, 2019

djmarchand said:
Smitty said:

""Can you use the boat the rest of the season? Yes, but keep it down to 2,450,"
Do not agree - by the end of the season that 2,450 rpm might be a firewalled number. I guarantee the rpm's will drop due to increasing loads adding heat and stress over the next weeks/months."

Smitty has a good point. I would use those engines at 2,450 only if the wot rpms stayed at 2,850. Presumably that high speed would keep some of the bottom slime off, but who knows what the bottom paint is like.

I think Larry will probably mostly use the boat at displacement speeds. 24-27 gph and $500+ fill ups was an eye opener. That is why we like slow trawlers, right!!!!

David

"I think Larry will probably mostly use the boat at displacement speeds. 24-27 gph and $500+ fill ups was an eye opener. That is why we like slow trawlers, right!!!!"

FWIW - our larger boats always used much less than those figures at the same cruising speeds in LI sound over maybe 25 seasons. If the boat is reasonably clean with tuned engines and well sized props I find the fuel use to be one of the lower costs of boat ownership. I do not know that hull form so comparisons will be somewhat inaccurate but these should have some value. We cruised 2 - 45' boats and one 47' boat (approx. 35,000#) mostly in Long Island sound
and the Hudson traveling at 15-17 knots for about 800-900 of our typical 1,000+ nm total season. These boats all had similar mechanical diesels - 6 cyl, 5.9L, turbo, aftercooled, and 3,000 rated rpm.
With a little rounding and a bit of nudging for ease of memory these are the typical fuel burns we would see over many seasons use:

6 kts - 3+ nmpg
8 kts - 2 nmpg
10 knts - 1 nmpg
16 knts - 0.92 - 0.95 nmpg
Towing a larger RIB at 16 knts - 0.90 nmpg

IMHO - We would hesitate to cruise the boat or those 5.9 engines at a 12+ gph rating. I would specifically avoid cruising the 5.9 engines at 12+ gph at 2,450 rpm.
Our expected fuel use at 16 knots and about 2,500 rpm was right about 17-18 gph between two engines or between 8-9 gph per engine.
If we were not going to travel at 6 knots then we would just about always move it up to 15-17 knts.

DavidM · Jun 7, 2019

The following is a little geeky, maybe a lot geeky, but I am a geeky kind of guy:

Larry's boat used 12 gph per engine to go 15 kts. This was the result of a fill to fill measurement.

Looking at the Cummins data sheet for this engine, 12 gph is 225 hp. If it were propped correctly I believe 225 hp would be fine for long term cruising use. Tony Athens advised me personally to that effect when I was considering buying a boat with a Cummins 6BTA. That is 38 hp per liter and is just under Tony's magic 40 hp per liter max for continuous duty.

In its over propped state 225 hp is certainly high, because it is making that 225 hp at a lower rpm than Cummins specifies in its data sheet. Making the same hp at a lower rpm means the torque is higher so the engine stress is higher.

But recreational boat engines are made for having fun and if going 15 kts for a few dozen hours over the summer makes it more fun, well ok. It will result in a little bit less engine life, but as pointed out by a PP it is probably no worse than the previous 10 years since its repower.

Actually I think installing exhaust gas temp or low r/w flow alarms is more urgent than repropping. The current prop situation isn't by itself going to blow the engine but an undetected overheating situation could.

How about fuel economy. Well 24 gph total at 15 kts is .625 NM/gallon, pretty high.

Running at 10 kts and below should be even better for this boat. Fuel economy will be better at 10, much better at 8 and the engine will be happy at either speed. My SWAG is about 1 NM/gal at 10 kts and maybe 1.5 at 8 kts. That is where Larry reported he plans to run the boat until he corrects the prop pitch.

David

smitty477 · Jun 7, 2019

djmarchand said:
The following is a little geeky, maybe a lot geeky, but I am a geeky kind of guy:

Larry's boat used 12 gph per engine to go 15 kts. This was the result of a fill to fill measurement.

Looking at the Cummins data sheet for this engine, 12 gph is 225 hp. If it were propped correctly I believe 225 hp would be fine for long term cruising use. Tony Athens advised me personally to that effect when I was considering buying a boat with a Cummins 6BTA. That is 38 hp per liter and is just under Tony's magic 40 hp per liter max for continuous duty.

In its over propped state 225 hp is certainly high, because it is making that 225 hp at a lower rpm than Cummins specifies in its data sheet. Making the same hp at a lower rpm means the torque is higher so the engine stress is higher.

But recreational boat engines are made for fun and if going 15 kts for a few dozen hours over the summer makes it more fun, well ok. It will result in a little bit less engine life, but as pointed out by a PP it is probably no worse than the previous 10 years since its repower.

How about fuel economy. Well 24 gph total at 15 kts is .625 NM/gallon, pretty high.

Running at 10 kts and below should be even better for this boat. Fuel economy will be better at 10, much better at 8 and the engine will be happy at either speed. My SWAG is about 1 NM/gal at 10 kts and maybe 1.5 at 8 kts. That is where Larry reported he plans to run the boat until he corrects the prop pitch.

David

"In its over propped state 225 hp is certainly high, because it is making that 225 hp at a lower rpm than Cummins specifies in its data sheet. Making the same hp at a lower rpm means the torque is higher so the engine stress is higher."
And the EGT is over the limit with unknown pyro accuracy, boost is high - lower rpm HP extraction is always a tight edge to walk.

"But recreational boat engines are made for fun and if going 15 kts for a few dozen hours over the summer makes it more fun, well ok."
My experience with the 6B has led me to conclude that utilizing these engines over the edge will lead to failures in the hundreds of hours and not thousands. There are at least 3 persons on this site that have replaced there 6B's due to these reasons and many more I have been in touch with over the years at other sites - they have sent me similar rpm, speed , boost and EGT data with some just above these readings having dire consequences.

"It will result in a little bit less engine life, but as pointed out by a PP it is probably no worse than the previous 10 years since its repower."
Please advise these details about the previous 10 yrs / 650 hours:
- were they run with the same props?
- are the tachs know accurate?
- did they achieve the posted 26 knts WOT?
- did the engines cruise at 20 kts?
- was the boat ever run on plane?
- what # hrs was the boat run on plane?

I know almost nothing about this boat and these engines at this time so it is very hard to agree or disagree with anything.

smitty477 · Jun 7, 2019

djmarchand said:
The following is a little geeky, maybe a lot geeky, but I am a geeky kind of guy:

Larry's boat used 12 gph per engine to go 15 kts. This was the result of a fill to fill measurement.

Looking at the Cummins data sheet for this engine, 12 gph is 225 hp. If it were propped correctly I believe 225 hp would be fine for long term cruising use. Tony Athens advised me personally to that effect when I was considering buying a boat with a Cummins 6BTA. That is 38 hp per liter and is just under Tony's magic 40 hp per liter max for continuous duty.

In its over propped state 225 hp is certainly high, because it is making that 225 hp at a lower rpm than Cummins specifies in its data sheet. Making the same hp at a lower rpm means the torque is higher so the engine stress is higher.

But recreational boat engines are made for having fun and if going 15 kts for a few dozen hours over the summer makes it more fun, well ok. It will result in a little bit less engine life, but as pointed out by a PP it is probably no worse than the previous 10 years since its repower.

Actually I think installing exhaust gas temp or low r/w flow alarms is more urgent than repropping. The current prop situation isn't by itself going to blow the engine but an undetected overheating situation could.

How about fuel economy. Well 24 gph total at 15 kts is .625 NM/gallon, pretty high.

Running at 10 kts and below should be even better for this boat. Fuel economy will be better at 10, much better at 8 and the engine will be happy at either speed. My SWAG is about 1 NM/gal at 10 kts and maybe 1.5 at 8 kts. That is where Larry reported he plans to run the boat until he corrects the prop pitch.

David

"Actually I think installing exhaust gas temp or low r/w flow alarms is more urgent than repropping. The current prop situation isn't by itself going to blow the engine but an undetected overheating situation could."

If we knew the pyros were installed with the tips correctly, if we knew they were reading immediately after the turbine , if we knew they were accurate we would know he is now on the edge at 2,450 (actually a bit over).
Since we all know that there are many ways this will only get worse over the next weeks and months there is no real margin IF anyone should advance the throttles.
Temp differences between the post turbine location where I am guessing these senders are located and the actual internal engine temps will be in excess of 350 degrees. I have seen cummins 6b's that have these post turbine temps rise near 1,000 have issues quickly - so knowing whether the gage is accurate or not when currently already at or over 900 is a focus.

smitty477 · Jun 7, 2019

djmarchand said:
The following is a little geeky, maybe a lot geeky, but I am a geeky kind of guy:

Larry's boat used 12 gph per engine to go 15 kts. This was the result of a fill to fill measurement.

Looking at the Cummins data sheet for this engine, 12 gph is 225 hp. If it were propped correctly I believe 225 hp would be fine for long term cruising use. Tony Athens advised me personally to that effect when I was considering buying a boat with a Cummins 6BTA. That is 38 hp per liter and is just under Tony's magic 40 hp per liter max for continuous duty.

In its over propped state 225 hp is certainly high, because it is making that 225 hp at a lower rpm than Cummins specifies in its data sheet. Making the same hp at a lower rpm means the torque is higher so the engine stress is higher.

But recreational boat engines are made for having fun and if going 15 kts for a few dozen hours over the summer makes it more fun, well ok. It will result in a little bit less engine life, but as pointed out by a PP it is probably no worse than the previous 10 years since its repower.

Actually I think installing exhaust gas temp or low r/w flow alarms is more urgent than repropping. The current prop situation isn't by itself going to blow the engine but an undetected overheating situation could.

How about fuel economy. Well 24 gph total at 15 kts is .625 NM/gallon, pretty high.

Running at 10 kts and below should be even better for this boat. Fuel economy will be better at 10, much better at 8 and the engine will be happy at either speed. My SWAG is about 1 NM/gal at 10 kts and maybe 1.5 at 8 kts. That is where Larry reported he plans to run the boat until he corrects the prop pitch.

David

"Tony Athens advised me personally to that effect when I was considering buying a boat with a Cummins 6BTA. That is 38 hp per liter and is just under Tony's magic 40 hp per liter max for continuous duty."

It has been a while but I had spoken to Tony often in the past and agree with everything he has done with and about the Cummins 6b.
If you take the above quote and add this to it:
"as long as the engines are propped so as to always achieve rated WOT rpm + 3-5%"
Then I agree.
Leaving out that part of his 'rule' is not a good idea as it skirts the key method to avoid the problems with running near those limits.

DavidM · Jun 7, 2019

Interesting conversation and I think we have scared Larry off of ever running those engines again in their current over propped state at 2,450 rpm.

David

smitty477 · Jun 7, 2019

djmarchand said:
Interesting conversation and I think we have scared Larry off of ever running those engines again in their current over propped state at 2,450 rpm.

David

I no longer can say the boat is over propped , I do not know enough…..
Knowledge can reduce and/or correct problems and fears.
Do we know any of the important specs about that boat and the engines that are posted above?

Delivery from Baltimore to N Shore LI- lessons learned

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DavidM

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DavidM

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