Motor mounts, M-35 & M35 Cooling w/ Sherwood vs. Oberdorfer Pumps

[Stu Jackson]

It's not the pumping rate that is the question, it's how much flow does the engine need??
Yes the Sherwood (reportedly) pumps more (I haven't measured it and I question manufacturer's flow specs) BUT what does the engine require and is the additional volume simply "excess." (Not that excess is a bad thing.)

That's a very good explanation of the engineering analysis approach and is a perfect example of the way to look at it.

I doubt, from what I've posted earlier, that the flow differences are so much that the differences (reportedly true) would be apparent or meaningful to the engine, especially if the Oberdorfer meets the minimum flow rate for the engine and, of course, the associated HX.  It appears from the application of these pumps to that engine that they do.

I mention HXs to remind many who may not know that many of us were successful in keeping our M25 engines within specs by upping to a 3 inch HX from the OEM 2 inch model.  Just like Universal did with the M25XP and the 2 additional engine HP was not why they upped the size of the HX. The conclusion was always that the 2 inch HX was marginal for the engine load; it worked just fine when the HX was brand new, but age, use, salt deposits on inlet ports all contribute to reduced effectiveness and lack of heat exchange at WOT, which was the original M25 issue.

[Breakin Away]

I've been traveling and unable to respond. I'll try to clarify a few points:

I probably shouldn't have distracted this discussion by bringing up the "pump wars". But there are parallels here. I've spent my entire career in product development R&D, and I refuse to believe that companies just go and intentionally change their components to more expensive and inferior replacements. Adding more SKUs to the parts list is costly, and qualifying new suppliers is excruciating. So whether it's changing to a Sherwood raw water pump for the M35B or changing to totally different engine mounts for the B-series, these changes were certainly made for a reason, and I refuse to accept that the changes were done solely to produce an inferior, overpriced product.

I have searched all over for acceptable motor mounts and called multiple suppliers with no luck, so I'll probably just buy the Westerbeke mounts. I am not willing to custom modify something. If the modification doesn't work for some reason, I'll have ZERO support. And my motor runs smoothly with the current mounts, just like Jim Hardesty noted. I just need to go have another look to verify the sideways motion that the mechanic noted. I'll also double check the lock nuts on the studs to make sure nothing has loosened up. It's also possible the mounts were damaged in the underwater strike 2.5 years  ago that led to the prop, strut, and shaft needing replacement. The insurance surveyor was outstanding, but maybe he missed some damage to the mounts.

You're embellishing upon my words and that's not at all helpful.
I NEVER said Wb isolators are junk.

Junk was my word. I apologize for my sloppiness. However, you did use the word "crap" a couple of times, and said their defect rate is literally at least 25%. So while you're not making a direct accusation about this particular component, you are making an inference about Westerbeke's overall quality. And, more importantly, I still have heard from zero people who have successfully used Vetus mounts on an M35B, so I consider a custom mod of a Vetus mount to be more risk than I want to take. The project could consume my entire winter.

I've heard enough complaints about Westerbeke to know that they probably have some serious customer satisfaction issues. So I can't just ignore your concerns. Fortunately, I have not been personally burned on this yet, and Hansen Marine once backed me up on a Westerbeke issue that was partially my fault. That earns them another shot.

I've gone through my notes about the pump replacement, and I cannot find any data directly from Depco. My notes show that on 5/31/2018 Depco told me that the Sherwood pump puts out 25% more water at a given RPM, and that they do not recommend the Oberdorfer N202 for any engines over 30 horsepower. At some point I saw some graphical data, but I don't have it in my files. I probably saw it online, and not sure where.

It's not the pumping rate that is the question, it's how much flow does the engine need??

The M35B is 67% more powerful than the original M25, and the amount of heat that must be removed from the system is exactly proportional to the horsepower. I believe the M35B also idles and cruises at about 20-30% lower RPM) than the M25, so it is easy to understand that the M35B requires a larger pump cavity for more water throughput. At some point I held the replacement impellers for both pumps in my hands side-by-side, and it's very clear that the Sherwood has a significantly larger pump cavity than the Oberdorfer. Maybe you can get away with the smaller pump on an M35B in 45F water on the west coast or Great Lakes, but in the Chesapeake Bay in August you might bump up against the Oberdorfer's  more limited heat removal capacity. Maybe with a brand new heat exchanger it will work, but that heat exchanger won't be new forever. Maybe it will work fine in calm water, but I'd hate to have to motor into a 25 knot wind and punching through 3-4' chop and find out that the motor overheats under the strain.

...Just a note that our wiki has an Oberdorfer modified to fit their M35; this was before Oberdorfer wised up and modified the base to fit both engines.

Just because the Ob flange fits the M35B does not mean that it has sufficient pumping capacity to remove heat under stress conditions.

I have not heard of any complaints, certainly not the one you are projecting as a possibility.

Back in 2015 Mick Laver went through hell with his Oberdorfer experiment on his M35B, with problems exactly like I'm describing. He returned it to Depco for the Sherwood. Then he went through it again, repeating the same experiment with Ken. You guys seem to forget this. And Ron Hill also tries to remind you of this issue.

...However, I have to share with you the fact that this "flow rate" stuff has been around for years and makes little sense.

When dealing with heat removal capacity issues, "flow rate stuff" is the most critical design parameter. If a motor is 67% more powerful, it needs more water. The fact that the Oberdorfer N202 works OK on some M35B motors under certain conditions basically means that it's over-designed for the smaller motors, but for motors over 30 hp it is marginal, working adequately under ideal conditions but potentially not up to the task under high stress conditions.

And while it is true that a brand new, unfouled heat exchanger may overcome some deficiencies in pump design, heat exchangers don't always stay that way. In fact, there is a scenario where an infinitely sized heat exchanger cannot overcome an inadequately sized pump. Just do a heat balance around the motor, and you can see that there could be a situation where even with perfect heat transfer from the raw water side to the freshwater side (infinite heat exchanger capacity), the raw water heats up to 212F (because there isn't enough flowrate), and you're injecting steam into the exhaust elbow. The only way for the motor to expel its heat is through the water, so without enough water even a better heat exchanger may not help you.

This all makes perfect sense to me. As you get to higher power and heavier engines, you need a bigger pump - and bigger engine mounts.

[KWKloeber]

I believe that you're stating some conclusions as fact, based on incorrect or at least incomplete ?assumptions? (or maybe bad info.)

1. You're concluding that you would have a problem w/ an Ob. 

- You want hard data that a Vetus will work on a 35B, yet it's only an opinion that an Ob will be an issue on the chessie, not based on (hard data of) what flow a 35 needs.  Is it 100% of the Ob flow or 50% of the Ob flow? Yes an extra cylinder puts out more heat, that's a given.   

- You must have missed Mick's follow-up. With the problem resolved he moved back to the better-built bronze Ob pump. 

- You forgot that Randy in the Gulf has an Ob w/ no issue.

- You cited no data supporting that the Ob "works on some" "under certain conditions" and is "marginal" for over 30 HP.  Unsubstantiated conclusions -- where's the beef?

- Your comparison picks and chooses data.  The Ob is just fine on the XPB, and the 35B is 35% greater HP (not 67% as the M25.)  Yes, HP is higher but let's use relevant data for comparisons.  Note that the M25 originally had the 2" Hx, and the Sw did not fix that overheating issue.



2. Flow comparisons:

- I believe that the 25% number that's thrown all about the internet is bogus, and was originally supplied by Westerbeke (like they have no vested interest in exaggerating it) and has been perpetuated.  See the flow ratings below.   NOTE: The Sw curves show no relation to head so the rating is at zero (a head game that pump manufacturers play on us.)  The Ob is about 9.4 gpm, the Sw about 11 gpm.  That's 17% more flow, not 25%.



3. That Wb "moved" to the Sw pump. 

- You're unfamiliar with the history of pumps on Oshkosh and Wb engines.  Wb did not "move" to the Sw on the B engines, it has ALWAYS installed IT's OWN pump -- which Sherwood does not own, Wb owns it, and Sw cannot sell it except as a Wb part (and at Wb's price.)


I do hope that the damage caused your mount problem - at least then you'll be somewhat assured that replacing them won't lead to a premature failure.  But it's interesting that the mechanic feels they are not the proper rating.  Just based on published data I'd agree the rears should be heavier. 
Why not get Vetus' take/recommendation on that engine (regardless if you don't use them)?

BTW, Hansen is not the Wb dealer/distributor for the chessie area, so I am unsure how they backed up anything but otherwise must never sell in that region.  Regardless, the "crap" was referring to known defective parts and the 25% was a percentage of identical parts (one in four were bad) -- just to be clear -- in NO WAY am I implying that Wb has a 25% overall failure rate.  Words are very loose and so are the inferences drawn.  Just as you feel about the Vetus, I have no hard info whether the isolators are "just fine" (or not.)

[KWKloeber]

A few more points on loose facts leading to loose conclusions.

There's no data citec to support the statement (conclusion) that the pump flow is "marginal" for the 35B.

The water flow is not "THE most critical design parameter" it's ONE parameter.  Just as a scenario can be conjured up where an infinite Hx with too little flow is a fail, also a scenario with infinite water flow and too small a Hx can be conjured up and also be a fail. Picking' n choosin' to support a pre determined conclusion.

The cruise RPM on the XPB and 35B are identical, and so the flow isn't reduced on the larger engine.
And, yes the idle is 800-1000 compared to 1000 - 1200, but it's irrelevant.
At idle the coolant generally doesn't get hot enough to open the TStat.  In other words on the original early M25s (that had the water heater in line with the Hx) they couldn't make hot potable water at idle, only under load.  Possibly the 35 will open the TStat but still it's not the significant/critical condition.

[Breakin Away]

I'll say a few words about my decision logic. I come from a Six Sigma engineering background. For long-life durable items, my default position ("null hypothesis") is always going to be to follow the manufacturer's recommendation unless 1) the recommended part is discontinued or manufacturer out of business, forcing me to another alternative or 2) I have compelling evidence (95% certainty) that an alternative is better (superior performance, or equal performance at significantly lower cost). That does not always have to be "hard data". It can be user experience (which still appears to be zero in the case of using modified Vetus mounts on an M35B), controlled experiments (where Mick Laver's experience suggests that the Oberdorfer may be insufficient in certain non-ideal conditions), or solid engineering calculations backed by well-known engineering theory (a 35 hp M35B generates 67% more heat than the original 21 hp M25). The threshold of 95% certainty is a high bar, but IMO it is appropriate for critical components like engine mounts and cooling pumps. Plus MBMC.

Regarding engineering considerations, recognize that a heat exchanger does not provide cooling - it just transfers heat between the heat source (engine horsepower) and the heat sink (raw water). The water comes in at sea temperature (which can be very different in different places), and goes out significantly warmer, and hopefully below boiling temperature. The heat exchanger merely transfers the engine's heat from the freshwater side to the raw water. So with a smaller pump and a bigger/better heat exchanger, your thermostat may say the engine temperature is fine, but the raw water that then goes into the exhaust elbow will always be warmer. This is an irrefutable fact, since the only place for the heat to go is into the raw water. And this hotter water can lead to other issues, like precipitation of more minerals in the exhaust elbow (leading to clogging), faster degradation of rubber hoses due to higher temperatures, greater thermal expansion/contraction of muffler, muffler mounts, and other components, etc. Yes, this is speculative and not a "conclusion", but it is irrefutable that lower water flow with higher horsepower (energy) will lead to hotter water.

I still am not ready to buy into your anti-Westerbeke bias, where every recommendation they make is based on some sinister motive of self interest, and a failure of one out of four parts turns into a conclusion of "literally at least 25%". Maybe someday I'll get burned and come around to your way of thinking.

I acknowledge that there's an element of self-interest in everyone's recommendations, including yours and Westerbeke's. That's human nature, and not sinister. Interestingly, Depco might be the least biased of anyone, since they'll sell or refurbish either pump. (They rebuilt my Sherwood for only $87.99 in 2018, since it was only one seal that was worn out.) And Depco says the flowrate of the Oberdorfer is insufficient for any motors over 30 hp. Somewhere inside Westerbeke/Universal, there is/was an engineer who did the calculations and testing that determined that the Sherwood pump was the best choice for the M35B/M40B/M50B motors. They probably tested under some abuse conditions, and allowed for reasonable safety margins in making an engineering decision, and took into account the experience and feedback of their customer base. This is purely speculative on my part, but that's how companies that have been around awhile generally work. I'll trust the judgment of that hypothetical engineer until I have compelling evidence that he was wrong. And I have yet to see any hard evidence that Depco's "upper limit" for the Ob pump of 30 hp is unreasonable.

Thanks for posting the chart. I'm not sure why you were asking me to post it if you had that already. Your arrows make it clear that you are not considering the possibility that the larger motors turn at a little slower RPM, which might get it closer to 25% difference. But regardless, every pump will have a limit for how much energy it can remove, and I choose to follow the 30 hp recommended limit of the Ob pump.

Speaking of incorrect assumptions, you seem to think that I live on my boat and that Hansen is violating their Westerbeke agreement. I have no reliable way to receive shipments at my boat, so parts are shipped to my home in Pennsylvania, which is why I am in Hansen's territory.

[Jon W]

Good thing the discussion is about cooling, because this conversation is getting hot. 

[Ron Hill]

Guys :  Kens' statement  -"It's not the pumping rate that is the question, it's how much flow does the engine need??
Yes the Sherwood (reportedly) pumps more (I haven't measured it and I question manufacturer's flow specs) BUT what does the engine require and is the additional volume simply "excess." (Not that excess is a bad thing.)"

Water temperature enters the equation somewhere? and "excess water" just might be just where??  The raw water temperature greatly varies between the Bahamas and norther Maine!!

The Sherwood pump (I found) is a bit more difficult to rebuild and the "C" clip that holds the compression in place was made of bronze!!  I found that salt/brackish raw water slowly ate away at the bronze "C" clip just like - Jabsco found out with their bronze "C" at the bottom of their head pump. 
I change that clip to SS and had eliminated that problem!!   I passed that info back to DEPCO, but don't know if they use it or not?

A few thoughts

[Breakin Away]

Here are some engineering calculations that will go to Ron's questions about "excess" and impact of seawater temperature. There are some assumptions here, but I think they're reasonable. Here are the equations:

• Select a cruising speed of 2500 RPM. I selected this value so we don't have to interpolate Ken's pump performance curves. You could pick 2200 RPM or some other value, but you'd get essentially the same result because both heat generation and pump flowrate would go down roughly in proportion.

• The Westerbeke power curve shows that at 2500 RPM the M35B delivers 31 hp (mechanical) = 79,000 BTU/hr mechanical energy output (see attachment)

The diesel power cycle delivers about 30-40% thermal efficiency (higher than Otto cycle, but obviously lower than Carnot cycle). I'll use the more optimistic value of 40%:
• Heat generated = 79,000 / 40% = 198,000 BTU/hour

• Assume water comes in at 90°F (mid-summer in mid-Atlantic) and exits at 120°F (can't be much higher than this because there will be insufficient ΔT across the HX to keep the antifreeze at 160°F): Net ΔT= 120-90 = 30°F
• Heat capacity of seawater = 4.0 J/g°F = 0.95 BTU/lb-°F (slightly lower than pure water. Note that the BTU was originally defined as a value of 1.000 for pure water)
• Density of seawater = 8.7 lb/gal

• Required seawater flowrate = 198,000 BTU/hr ÷ [(0.95 BTU/lb-°F)*(30°F)*(8.7 lb/gal)] = 800 gal/hr = 13.3 gal/min

If you look at Ken's pump performance curves, you will see that it is plausible that the Oberdorfer might not keep up in warm climates, and the Sherwood pump does a little better because of its larger cavity size. This calculation assumes that all heat escapes in the seawater. There is also some heat that escapes in hot exhaust gas, so my estimate is admittedly conservative. But you can't just assume that the Oberdorfer will work with everyone's M35B in every situation just because it works great with a smaller motor or with someone's M35B under more ideal circumstances.

[EDIT: This is a simplified example that makes an assumption about the heat exchanger (exit temperature of 120°F). A full model would include data on the heat exchanger's shell-and-tube design, including the surface area of the tubes, their heat transfer coefficients in the new and fouled states, number of passes (2-pass, 3-pass, 4-pass). With that information, you could set the exit temperature as a variable and solve for it at different pumping rates and determine whether you're able to maintain the antifreeze coolant at 160°F. That additional detail could lead to a higher or lower flow rate requirement, depending on how good the heat exchanger is, and how warm/cold the seawater is. There is, however, a theoretical pump capacity that is so low that no heat exchanger can help, and that is the pump rate where the seawater rises to 160°F (equal to the desired temp for the antifreeze coolant). At that point, no extra surface area will help you.]

[KWKloeber]

The Sherwood pump (I found) is a bit more difficult to rebuild and the "C" clip that holds the compression in place was made of bronze!!  I found that salt/brackish raw water slowly ate away at the bronze "C" clip just like - Jabsco found out with their bronze "C" at the bottom of their head pump. 
I change that clip to SS and had eliminated that problem!!   I passed that info back to DEPCO, but don't know if they use it or not?

A few thoughts

Ron

Why not pass your idea directly to Sherwood??
My suspicion is that Depco uses "genuine" parts.

Gee, I wonder why Sherwood doesn't smarten up and realize that bronze, not iron, pump bodies are the higher standard?????

[KWKloeber]

Good thing the discussion is about cooling, because this conversation is getting hot. 

Jon

Just wait till it morphs into wax vs. polyglow. That will be more entertaining because that's an even higher level of personal opinion and conjecture, zero fact.   

[KeelsonGraham]

Good thing the discussion is about cooling, because this conversation is getting hot. 

Good thing this discussion is about M35 mounts. No thread hijacking here. Nothing to see, move on.

[Jon W]

The original post was about M35 mounts, but the rather tense discussion the past few days was about cooling. Maybe you should comment to the folks that hijacked it.

[Stu Jackson]

The original post was about M35 mounts, but the rather tense discussion the past few days was about cooling. Maybe you should comment to the folks that hijacked it.

I just "evolved" the OP title to reflect the thread divergence. 

[Breakin Away]

The original post was about M35 mounts, but the rather tense discussion the past few days was about cooling. Maybe you should comment to the folks that hijacked it.

I just "evolved" the OP title to reflect the thread divergence. 

Thanks, I think that's the most constructive way to deal with our (my) inappropriate thread drift.

Regarding the characterization of our discussion as "tense", I see it as a very useful exchange of information from all involved. Some of us have strong views, and may poke each other by calling our own claims "fact" and others' claims "assumptions", but I still value the expertise and input from our members, even in cases where our views differ.

Back to the original topic of motor mounts, I finally made it down to the boat today and ran the motor in the slip with my wife shifting gears while I was below observing. I have a lot to unpack from that, including viewing some videos and pictures in zoom mode. I'm too tired to do that now (after 4 hours of driving and mowing 3 acres of our property). I'll report more details sometime soon. But bottom line, I am very concerned that spending up to $1200 on new mounts (of any variety) may not fix the problem. I think the problem might be mis-alignment of the stuffing box and/or hose, and possibly exacerbated by too-soft PTFE packing that allows the shaft to contact the nut. I loosened the hose clamps and tried to loosen the hose from the shaft log, but it wouldn't budge under gentle torque, and I didn't want to torque it too much for fear of my tool ripping into the rubber (or other catastrophe) while the boat is in the water. I have all winter on the hard to address this problem, so I may explore other less costly alternatives before plunking down for new motor mounts. I may also get a second opinion from another mechanic before haulout (if I can find one who is available).

Solving this problem had been rather urgent, because this Friday I was going to start a 2-day trip (mostly motoring) through the C&D Canal to bring the boat for haulout near my home. But for a few different reasons, I've decided to haul out in Rock Hall this year, so I'll have the boat in the water for another few weeks and no longer need to motor for two days and risk damaging my shaft - I'll just motor long enough to get in/out of my slip over the next few weeks.

[KWKloeber]

• Required seawater flowrate = 198,000 BTU/hr ÷ [(0.95 BTU/lb-°F)*(30°F)*(8.7 lb/gal)] = 800 gal/hr = 13.3 gal/hr

Typo - 13.3 gpm.

it is plausible that the Oberdorfer cannot keep up in warm climates, and the Sherwood pump does.

Wrong.  The Sw produces 11 gpm (if the curve is even correct, which I question but will go with it for this.)  That is at ZERO head.  Add Hx backpressure and the analysis goes further to heck. 
I hadn't checked the assumptions or math/values and don't intend to.  There's theory and there's real-world. 
For the past 18 or so years I've been an OB dealer and have put 202M pumps on 4 cylinders (M4-30, M30, M35, M35B) including one on Soloman's and have not had ONE situation of not being able to adequately cool an engine.

Randy's has had ZERO problems with cooling, and I'd think his challenge is the same or more difficult than on the chessie.  Additionally, the 202M has been put on C36s with no reported issue (agreed, N does not equal 95% of 202M pump owners but there have been none reported that I know of.)  Witness that opposed to owners who have had snapped camshafts due to SW pump failures.   Zero known/reported for Ob pump owners.

Note that Wb wants owners of Sw pumps to inspect the pump EVERY TIME before starting the engine.  Do you (that is, "follow manufacturer recommendation" LOL )?

There's even more instances below of twisting what I had plainly written and/or putting words that I never said into my mouth, or drawing an incorrect conclusion from what I said re: both the pump and the mounts -- but I spend more time calling attention to/correcting them and the next post simply (intentionally?) creates more. 
I'm not participating in that never-ending game anymore.

I do have a suggestion though.  Instead of comparing the 35B to an M-25 (opposed to the XPB that also works excellently with the 202M pump) compare the 35B to the heat/power output of the Universal M-18, or even the M-12, or 5411.  It will produce an even stronger, yet just as irrelevant, comparison.

Hxs require maintenance, as do pumps, and not doing so hoping that a pump will substitute for that would (IMO) define rather poor seamanship.

Do post once dissecting the cause of the mount/shaft/stuffing issue.  Hopefully the mounts are not to blame.