Engine Load Comparisons WOT vs Surfing

[dizzygti]

I wanted to continue the discussion about sustained engine rpms/speed while cruising so started a new thread (sorry about the Supra comparison thread!).   Boat in question is 2023 T250 with the M6.  4 adults aboard.   This is about engine health at speed, NOT about thermal management.   I'll explain in more detail later. 

First snapshots are cruising to our surfing finger.  Engine was fully warm as we idled out, got up to speed, waited 2 min at redline, ~34mph, took first picture (34.2 mph), waited 4 min, and took second picture (34.5mph).  Yes,  coolant,  trans, and both exhaust manifold temps are creeping, but still reasonable and no reason for concern.  The important thing to note is the load: 76%.

Edited March 15 by dizzygti

[dizzygti]

Then we got to the surf spot, loaded all ballast and PnP with starboard rear not quite full,  our normal setup.  While surfing,  11.4mph, snapshot taken and then another 6 minutes later.   Yes, temps are lower than cruising, but not drastically lower.   Again load is 74 and 76%.

[dizzygti]

So yes, under high rpms and high speed, there are thermal management concerns that should be monitored.   WOT and high engine rpms is no more "work" for the motor than surfing loaded though.    As an experiment, I had my two buddies (each 225ish) move to the bow while my wife was surfing.  Obviously this brought the bow down some,  and load decreased to 67%.

 

 

Edited March 15 by dizzygti

[dizzygti]

So can damage occur from high speed WOT cruising?   Sure, if your cat or trans or coolant temps creep up to the point of damage, you've just exceeded the cooling capacity of the system.   It doesn't mean it's "worse" for your engine life though, and the way you surf/board/load the boat can have an impact on that as well.    Less load means the engine isn't working as hard.   If the boat has the wrong prop or is underpowered or overloaded, that's a different situation where you again are exceeding capacity of the system.    As a former powertrain engineer, I don't see a problem with running high rpms for sustained periods if the fluid temps are controlled.    Your mileage may vary, and I'm not responsible for any damages that may result.   

[dizzygti]

And one more because the weather was awesome yesterday.   79°, water was 55°.    It's the start of the season, hang in there guys further north! 

[dshack]

Interesting stuff, thanks for posting. Maybe its because I've historically had to run a low pitch prop, but I suspect that 80% of the reason we collectively don't like cruising at or close to WOT is the engine sound....to the ear, it just sounds like its working way too hard when over 4500ish rpms.

[DRB10SEVEN]

This gets me all excited to beat on the 383 as soon as I can get on the water. 

I remember having a conversation with an old friend years ago because I had a Crownline 202 with a 350 and he was surprised that I would run pretty much wide open across the lake all the time going to and from the dock. He jokingly said "all my stuff breaks when I run it that hard" haha. I like the phrase "mechanically sympathetic". If you know what is happening mechanically in an engine/transmission/drivetrain on whatever it is you are running, you can really run things hard and still get lots of life and reliability out of it. Some people don't really understand what is going on (understandable, not everyone is a gearhead/nerd) and I think they can miss basic signs/noises/temps etc. that are a pre warning that you may be about to damage something, which in turn can cause them to keep pushing things past a safe limit and have things break more often. Just my own personal experience.

[dizzygti]

3 minutes ago, DRB10SEVEN said:

If you know what is happening mechanically in an engine/transmission/drivetrain on whatever it is you are running, you can really run things hard and still get lots of life and reliability out of it. Some people don't really understand what is going on (understandable, not everyone is a gearhead/nerd) and I think they can miss basic signs/noises/temps etc. that are a pre warning that you may be about to damage something, which in turn can cause them to keep pushing things past a safe limit and have things break more often. 

This.   As I mentioned in the other thread, the OEM I worked for ran engines for 400 hours at WOT/redline and 100 hours at peak torque rpms as a durability tests.   Now this was in a climate controlled chamber with a chiller on the coolant system.   All temperatures are monitored and the dyno would alarm out and stop the tests if anything exceeded threshold limits until a technician could figure out what was wrong.   The point is if temps are controlled, aka the cooling systems have enough capacity and are working properly, then being at WOT is not a concern.   

[UWSkier]

3 hours ago, DRB10SEVEN said:

This gets me all excited to beat on the 383 as soon as I can get on the water. 

I remember having a conversation with an old friend years ago because I had a Crownline 202 with a 350 and he was surprised that I would run pretty much wide open across the lake all the time going to and from the dock. He jokingly said "all my stuff breaks when I run it that hard" haha. I like the phrase "mechanically sympathetic". If you know what is happening mechanically in an engine/transmission/drivetrain on whatever it is you are running, you can really run things hard and still get lots of life and reliability out of it. Some people don't really understand what is going on (understandable, not everyone is a gearhead/nerd) and I think they can miss basic signs/noises/temps etc. that are a pre warning that you may be about to damage something, which in turn can cause them to keep pushing things past a safe limit and have things break more often. Just my own personal experience.

 

[justgary]

You are hitting redline at 53% throttle and your intake is below atmospheric pressure, so your engine load is only 76%.  I have no doubt that your engine is happy doing that, but it is definitely not near "WOT."  You obviously have your boat propped correctly for surfing.

For those of us with props that actually allow our engines to hit max RPM at WOT (with the throttle all the way open and the intake manifold at basically atmospheric pressure), engine load is indeed higher than 76% (more like 100%).  In this case it may actually be more stressful on the engine than a lower RPM.

[dizzygti]

2 hours ago, justgary said:

You are hitting redline at 53% throttle and your intake is below atmospheric pressure, so your engine load is only 76%.  I have no doubt that your engine is happy doing that, but it is definitely not near "WOT."  You obviously have your boat propped correctly for surfing.

For those of us with props that actually allow our engines to hit max RPM at WOT (with the throttle all the way open and the intake manifold at basically atmospheric pressure), engine load is indeed higher than 76% (more like 100%).  In this case it may actually be more stressful on the engine than a lower RPM.

Agreed, but I can't move the throttle any further open.    I can't make the engine spin any faster or the boat go any faster.   What are you calling "WOT"?   We're obviously dealing with fuel injection and DBW throttles, so there has to be a fuel cut, ignition cut, or throttle plate logic control that is limiting me from 100% actual throttle angle.   So in reality, we're in agreement.   For MY case, using the M6 in my boat at WOT/top speed for sustained periods with this prop (3077) isn't an issue if the cooling system is doing its job.   

If your boat/prop combination is at 100% load at WOT and redline, then you have the wrong prop for sustained high rpm cruising, and yes, are probably putting a lot more stress on your engine than I am on mine.   I think this is why most have this discomfort with being at WOT for long periods of time.  These new 2:1 transmission, DI engines with cam phasing and coil on plug (adjustable) ignition, 4 blade props, etc are all leaps and bounds ahead of where boats were 10 years ago.   

I think this also shows I will have no problem going up (numerically) in pitch and still have power to spare.   I am waffling on the 2805 vs 3087 and will decide after I put some lead in the boat first.   

Edited March 15 by dizzygti

[shawndoggy]

7 hours ago, dizzygti said:

This.   As I mentioned in the other thread, the OEM I worked for ran engines for 400 hours at WOT/redline and 100 hours at peak torque rpms as a durability tests.   Now this was in a climate controlled chamber with a chiller on the coolant system.   All temperatures are monitored and the dyno would alarm out and stop the tests if anything exceeded threshold limits until a technician could figure out what was wrong.   The point is if temps are controlled, aka the cooling systems have enough capacity and are working properly, then being at WOT is not a concern.   

Seems like about the same conditions as the sunburned guy with a few beers in him with the stereo blasting?

[justgary]

3 hours ago, dizzygti said:

What are you calling "WOT"?

Your photos clearly show that the throttle is 53% open.  They also show that the manifold pressure is 11.3 PSI even though the atmospheric pressure is 14 PSI (as measured by your ECM at turn on).  Both of these suggest that you are not nearly at wide open throttle.

By the way, the atmospheric pressure at your location implies that you are boating at roughly 1,300 feet above sea level.

3 hours ago, dizzygti said:

If your boat/prop combination is at 100% load at WOT and redline, then you have the wrong prop for sustained high rpm cruising

Non-surfers tend to use the standard method for putting a prop on a boat: change the pitch until the engine gets to redline at WOT.  I do run my engine about 4,000 RPM for barefooting, and I also occasionally run it WOT, but usually only for a minute or so at a time.  Your "WOT" cruising is slower than my mid-range throttle cruising, so I don't generally think of WOT as cruising.

I think it is great that you have your boat propped correctly for its use.  Many people don't recognize the need to keep from lugging their engine and never actually check if they have the correct prop.  Larry at Indmar made an excellent post a few years back about it and suggested that everyone test their engine RPM at (true) WOT with their normal full load of people, gear, ballast, wake devices, etc.

As you have suggested, hitting the rev limiter with a lighter load in the boat is not hard on your engine.

 

[dizzygti]

2 hours ago, justgary said:

Your photos clearly show that the throttle is 53% open.  They also show that the manifold pressure is 11.3 PSI even though the atmospheric pressure is 14 PSI (as measured by your ECM at turn on).  Both of these suggest that you are not nearly at wide open throttle.

By the way, the atmospheric pressure at your location implies that you are boating at roughly 1,300 feet above sea level.

Non-surfers tend to use the standard method for putting a prop on a boat: change the pitch until the engine gets to redline at WOT.  I do run my engine about 4,000 RPM for barefooting, and I also occasionally run it WOT, but usually only for a minute or so at a time.  Your "WOT" cruising is slower than my mid-range throttle cruising, so I don't generally think of WOT as cruising.

I think it is great that you have your boat propped correctly for its use.  Many people don't recognize the need to keep from lugging their engine and never actually check if they have the correct prop.  Larry at Indmar made an excellent post a few years back about it and suggested that everyone test their engine RPM at (true) WOT with their normal full load of people, gear, ballast, wake devices, etc.

As you have suggested, hitting the rev limiter with a lighter load in the boat is not hard on your engine.

 

I understand everything you're saying,  I'm a mechanical engineer and gear head so this is all familiar.  I also play with turbo engines in toy cars so I understand manifold pressure vs atmospheric.   However, as I said, this "IS" WOT on my boat.   The accelerator pedal (lever) is as far forward as it will mechanically go.   The engine is limited to 5600 rpms.  Not sure what else to tell you.  

[Steve B.]

Wouldn't it be awesome to be a "tuner" today and be able to unleash these, maybe better put, to customize each one for our own use. So that you can safely achieve true WOT if requested. My guess is various pieces parts would break with more frequency, but, fun has it's prices !

Steve B.

[csleaver]

On DBW engines with an electric throttle body, there is a difference between throttle position and pedal position.  With a smaller pitch propeller, pedal position may be at 100% while the throttle position is at 51% when the engine runs at the maximum RPM.  Ideally, the engine should be able to run near maximum RPM when the pedal position and throttle position are near 100% at the altitude and with the loaded weight the boat will usually be operated.  This is not a always a realistic way to test surf boats due to the radical changes in weight they are subjected to during a typical day of operation. 

Some marine engine companies (like Pleasurecraft) will publish a WOT minimum full load RPM, WOT preferred RPM, WOT maximum RPM, and a maximum cruising RPM (E.G. the 6.2L DI CES recommends WOT min 5300 RPM, WOT preferred 5500 RPM, 5600 max RPM, and max cruise 4480 RPM).

A propeller that performs very well for surfing will perform poorly at cruise or WOT speeds, and a propeller that performs well at cruise and WOT will perform very poorly for surfing.

[csleaver]

The most common complaint I have seen caused by high RPM cruising for extended periods of time is HEGO sensor or emissions alarms. 

[dizzygti]

33 minutes ago, csleaver said:

A propeller that performs very well for surfing will perform poorly at cruise or WOT speeds, and a propeller that performs well at cruise and WOT will perform very poorly for surfing.

This is basically in line with what I was getting at.   There is no rule for RPM as much as there is a lot of variables and anecdotal evidence of engine issues and rpms.  

[jjackkrash]

Ya, my manual (PMC) for the 5.3 and 6.2L DI engines says prop the boat so the WOT is in a range between 5300 and 5600, with 5500 "preferred."  It also says extended or "prolonged" operation at WOT is "abuse" that voids warranties.  "Cruising" RPMS are listed as 4000.  Im not an engineer.  Are you guys saying this is just BS?  

(Trying to understand)

 

 

[justgary]

1 hour ago, dizzygti said:

However, as I said, this "IS" WOT on my boat.   The accelerator pedal (lever) is as far forward as it will mechanically go.   The engine is limited to 5600 rpms.  Not sure what else to tell you. 

It is wide open pedal but not wide open throttle.  In fact you still have nearly half of your throttle left.  Your boat is set up the same as if it were a (modern) truck in first gear.  Yes, it will pull like crazy, just not very fast.  If you floor it, it will rev limit the same way your boat does.

Heck, put your boat in neutral and hit the throttle and tell us what the load is at 5,500 RPM.  The throttle plate will only be about 10% or so and the intake pressure will be maybe 1 PSI.

Again, I think you have your boat set up correctly.  I keep replying because you use the term wide open throttle, which is not the case.  I would hate to see somebody blow an engine because they read here that it is always ok to run at WOT for extended period.

[CaptainMorgan]

Maybe we need to see the same @dizzygti screenshot when ballast is fully loaded -- engine load and throttle position will both go up, and maybe it'll even read 100% and then everyone can be happy because pedal = throttle   

 

 

[granddaddy55]

biggest hurt you can put on a motor is running lower rpms surfing heavy ballasted loads (lugging).  higher rpms is better for heavy loads.  i run with only dry weight, ballast and lead (no passengers or batteries or equipment ) 11785 lbs.  i prefer having the rpms 36-4000 (speed 11.4) especially since the real load is more like 12,500-1300 with crew , gear and ice chests. doing this at 33-3600 is harder on the motor

[dizzygti]

On 3/16/2024 at 7:26 AM, CaptainMorgan said:

Maybe we need to see the same @dizzygti screenshot when ballast is fully loaded -- engine load and throttle position will both go up, and maybe it'll even read 100% and then everyone can be happy because pedal = throttle   

 

 

Fully loaded, as fast as it would go.   

Edited March 22 by dizzygti

[CaptainMorgan]

Interesting, I'm no expert but looks like you are still hitting rev limit with juice to spare.  A higher pitch prop is likely possible.

But more importantly I am stuck between admiration and jealousy that you got nearly 10 engine hours done in the last week and I havent even removed shrinkwrap

[dizzygti]

9 hours ago, CaptainMorgan said:

Interesting, I'm no expert but looks like you are still hitting rev limit with juice to spare.  A higher pitch prop is likely possible.

But more importantly I am stuck between admiration and jealousy that you got nearly 10 engine hours done in the last week and I havent even removed shrinkwrap

Yes, I'm not straining the motor at WOT (top speed with full load request,  not throttle plate = 100%) when fully loaded.   DBW means you can't sit at WOT bouncing off the limiter like @justgary wants to see.   However, yes, this does mean I can increase pitch no problem.

We got out two afternoons during the week and all day Saturday last week.   Last night was the first this week, but the weekend doesn't look great for weather.   

(I made wife turn off nav lights for this picture)

Edited March 22 by dizzygti