Maximum RPM and Cruising Speed, Single engine MS 400

[Newtrawlerowner]

I know this subject has probably been discussed previously, but I am getting ready to do a run and wanted to ask what you single engine guys are getting on maximum rpm and maximum SOG.


I'm running a Cat 3126.


I know props can make a difference and I don't have that information to share yet, but am curious.




The next time I'm on my boat I'll note what mine is and report back as well.



Thanks in advance

 

[Bacchus]

My MS 34HT is a single Yanmar 370HP 6LYA-STP and here is the info for mine as a comparison
The Yanmar spec list max output @ 3300 RPM
AT WOT, clean hull and minimum loading other than full fuel I get just about 20 MPH in calm seas.

My prop is a Fly Torgue 26 R 20 Tip Cupped with 2" shaft / bore

See attached
Also Steve Cyrs website Stella Blue is the best resource I have seen for MS 400's
Stella Blue was my inspiration to start my Bacchus website
https://scyr.org/stellablue/index.php

 

[DavidM]

As noted by Bacchus above, all things having to do with the MS 400 can be found on owner Steven Cyr’s website:

https://scyr.org/stellablue/index.html

Except for the engine. His is a Yanmar 370 as are most. But ratio your Cat’s wot hp to his 370 and adjust the wot speed accordingly and you will be pretty close. As he notes, that boat and engine need to stay in the 8 kt range as it will barely plane at wot and any rpm in the 2,800 rpm range (for the Yanmar) will be trying to climb over the bow wave and will lug/stress the engine.

And BTW, you want speed through the water not SOG. SOG is influenced directly by the speed of the current + or -.

David

 

[Shrew]

When I look up the specs on a Car 3126, I finding:

Max RPM: 2800
Max Cruise: 2400
(Anecdotal) often Suggested 'sweet spot': 2200-2300

 

[Newtrawlerowner]

My MS 34HT is a single Yanmar 370HP 6LYA-STP and here is the info for mine as a comparison
The Yanmar spec list max output @ 3300 RPM
AT WOT, clean hull and minimum loading other than full fuel I get just about 20 MPH in calm seas.

My prop is a Fly Torgue 26 R 20 Tip Cupped with 2" shaft / bore

See attached
Also Steve Cyrs website Stella Blue is the best resource I have seen for MS 400's
Stella Blue was my inspiration to start my Bacchus website
https://scyr.org/stellablue/index.php

Thank you Bacchus

 

[Newtrawlerowner]

As noted by Bacchus above, all things having to do with the MS 400 can be found on owner Steven Cyr’s website:

https://scyr.org/stellablue/index.html

Except for the engine. His is a Yanmar 370 as are most. But ratio your Cat’s wot hp to his 370 and adjust the wot speed accordingly and you will be pretty close. As he notes, that boat and engine need to stay in the 8 kt range as it will barely plane at wot and any rpm in the 2,800 rpm range (for the Yanmar) will be trying to climb over the bow wave and will lug/stress the engine.

And BTW, you want speed through the water not SOG. SOG is influenced directly by the speed of the current + or -.




David

I just installed a TriData instrument to measure speed through water. I'm anxious to see what that says as well. But yes that needs to be considered.


I am also experiencing the max speed at about 8-8.5 knots.



Thank you for the reply.

 

[DavidM]

I am also experiencing the max speed at about 8-8.5 knots.

That is pretty slow. But Cat made the 3126 in many hp versions. What is yours?

David

 

[Newtrawlerowner]

That is pretty slow. But Cat made the 3126 in many hp versions. What is yours?

David

The horsepower for the Cat 3125TA is 385 hp.
I will be back on board in 2 weeks and will run again at full throttle to confirm what I said previously, both RPM and SOG. I should have my Speed through water instrument repaired by then and will report back that as well.


Thanks for your reply

 

[DavidM]

That is too slow. Others are reporting 12-13 kts and you are getting 8.5 at wot. Something is very wrong.

What is your rpm at wot and 8.5 kts? Your throttle may not be opening all the way. Check your wot in neutral (won’t hurt anything unlike a gasser. Your diesel is governed), you should hit about 2,900 rpm.

If so then maybe the bottom and prop are severely fouled.

You need to fix this.

David

 

[danderer]

Years ago I chartered one with a 380 Cummins. 12 knots was the top end.

 

[Cold Duck]

I have the MS350 with the single 3126 350hp. That's probably as close to your MS400 as you can get. Cruise speed depends what you want to accomplish. On purchase I cruised Santa Barbara to Sacramento Delta at 2000rpm, gave me about 8kts. Now that I am in the Delta most of my cruising is 1600-1800rpm depending on whether I am towing a dink or not. Relatively short distances, 20-30miles so cruising slow doesn't take much longer to get places. If I cruise "down bay", 60 mile run, I will do 2000rpm. If you want to burn more fuel to go a little faster, that's the trade off. You have to trade fuel for speed, it's that simple. At 1800-2000rpm I can get around 2.1-2.3mpg which works for me.

 

[C lectric]

I'll add one comment about check your tachometer for accuracy by going to either Ebay or Amazon and getting a handheld phototach for between $20 - $30. THey are accurate
to between 2 to 3 rpm. Often far better than the typical dash tachs installed.

If the tach reading are not decent then your testing will goofy.

 

[Bacchus]

That is pretty slow. But Cat made the 3126 in many hp versions. What is yours?

David

Agree
My MS with a Glendining control has a "Troll" mode that cuts the throttle response basically in half. If yours is similar, Worth checking to make sure it's not in troll mode.

If WOT RPM is correct worth confirming prop specs to make sure someone didn't under prop intentionally?

 

[High Wire]

8 knots with a 3126? Somethings really wrong. I can get 8.5 with my Perkins 135! Do you have trim tabs and where do you set them? Love to know your running angle too.

 

[Newtrawlerowner]

I'll add one comment about check your tachometer for accuracy by going to either Ebay or Amazon and getting a handheld phototach for between $20 - $30. THey are accurate
to between 2 to 3 rpm. Often far better than the typical dash tachs installed.

If the tach reading are not decent then your testing will goofy.

This is a great idea. I did have had both tachs calibrated by different companies (a new tach I bought was repaired under warranty by Faria) and they both read the same. But confirming actual is best. Thank You.

 

[Nomad Willy]

Cruise speed is not about rpm. It’s about engine load.

Relatively small rpm changes can result in relatively large changes in engine load. Too many variables boat to boat. Since most everybody's variables are different rpm comparisons are relatively meaningless. Using a percentage of rpm down from max rpm works fairly well as does EGT. But rpm varies not only by engine size but various engine design features like turbos, # of cylinders and piston speed .. ect.

But loading of engine and prop has most to do w prop loading via rpm, blade design, # of blades and even hull or keel design effecting water inflow turbulence and water inflow speeds.

But just posting rpm variations promotes easy conversations but overlooks too much to have much to take to the bank at the end of the day.

 

[Cold Duck]

8 knots with a 3126? Somethings really wrong. I can get 8.5 with my Perkins 135! Do you have trim tabs and where do you set them? Love to know your running angle too.

You are not looking at the figures. That's at 1800rpm, the engine hasn't even spun the turbo up yet. It's all about fuel burn vs speed. Just this weekend we were doing 8.5 at 1800. Just because I have 350hp available doesn't mean I want or need to use it but it's there if I need it. Some people want to run more WOT, nothing wrong with that. I have a 26ft boat that will do 80mph. I don't need speed outta my MS350. Everyone uses their boat in different ways. This is just mine.

 

[Cold Duck]

Cruise speed is not about rpm. It’s about engine load.

Relatively small rpm changes can result in relatively large changes in engine load. Too many variables boat to boat. Since most everybody's variables are different rpm comparisons are relatively meaningless. Using a percentage of rpm down from max rpm works fairly well as does EGT. But rpm varies not only by engine size but various engine design features like turbos, # of cylinders and piston speed .. ect.

But loading of engine and prop has most to do w prop loading via rpm, blade design, # of blades and even hull or keel design effecting water inflow turbulence and water inflow speeds.

But just posting rpm variations promotes easy conversations but overlooks too much to have much to take to the bank at the end of the day.

THis is so true! My 40ft Newport trawler (wood 1970s version) had 2 400hp GMCs, run at 3000rpm we had 10kts@ 1 nm/gal. Can't compare to a 39ft MS with a single CAT turning 1800rpm getting 2.3mpg. This is why my figures with the CAT in almost the same vessel are more relevant than other engines and other boats. Have a friend with same boat as mine but the Volvo engine and we can't compare any numbers.