Cruising RPM, Hrs, GPH, and longevity Tug and Cut diesels

[BB marine]

Bored with a tropical depression just north of my location with winds steady 20 mph gusting to 25, by Friday expected to gusty into low 30. My location is N27.5.2256. W78.1.1643. Very protected!

So to break the malaise, I looked back through my log and retrieved these numbers: engine hours 271, miles run 960, gallons of diesel 347. 100 hours on Mase 2.7 generator. This was just for the Bahamas trip, left Nov 7 2019, through Abacos, to George Town, Exuma, am now heading for Florida via the Abacos.

Would the number crunchers tell me if I’m doing okay? Or should I be more aware of additional numbers. :shock:

Not really worth crunching numbers. You are well under the 20%.

Sounds like a trip of a life time spending the winter in the Bahamas ! Have a safe trip back to Florida.

 

[ALICE J]

Thanks Brian, lots of wind, so patience, a good spear for the fish, lots of spares, tools and cash. But yes great way to float in place on a deserted Cay during the virus.

 

[SoCalSkers]

This is my first post in the forum, been a lurker here for quite some time and just recently purchased a 2014 C28 back in February. Been following this thread with great interest, as my numbers don't appear to be near ideal, but it's hard to tell without knowing the full history of the boat.

This is a D4 260, paint is at least three years old and probably a big source of the issues, but thought I'd throw these out there for advice.

Here's what I'm seeing so far:

Max RPM of 3150 (80/100 gallons of fuel, 4 adults on board)
196 degree max temp, but normally at 185 unless I'm full throttle for a few minutes
17.2 kt max speed
12.8 gal/hour burn at that speed

I've added a bit of weight since purchase, as I've added a 260 Takacat on the rear swim platform on davits, an additional house battery and we keep it pretty loaded with food and drink for overnights.

I'm planning to haul it out in the next month to do the paint and address some trim tab issues, was wondering if I should address the prop as well. From what I take from this and other threads I may be a bit over propped as well with the added weight.

Looking forward to spending a lot of time on the boat!!

Ryan

 

[SoCalSkers]

Sorry, forgot to add only 180 hours on the engine when I purchased it, now at 240.

Ryan

 

[BB marine]

I'm planning to haul it out in the next month to do the paint and address some trim tab issues, was wondering if I should address the prop as well. From what I take from this and other threads I may be a bit over propped as well with the added weight.

The earlier vintage C28's with the D4 260 were over propped.( I don't know about 2017 and newer) Most of the owners of 2014 to 2016 C28's that I have talked to or PM state that even during their PDI the engine never saw 3500 rpm. A new boat during the delivery process should turn at least Max rpm +3% Max(3500 rpm) + 3% (105 rpm) =3605. Personally I would want to see 3650 rpm. The reason is the boat is new and the owner has not had time to get all their gear onboard. So a good service technician when commissioning the boat and doing the PDI should raise a red flag at anything less. So what happens to the rpm as the boat starts to get loaded? Extra battery, cooler of drinks, refrigerator full of food 100 gallons of fuel, 30 gallons of water, dingy and outboard, grill..... and then add 2 extra passengers (4 total) and some scum on the bottom. The PDI approved 3450rpm now is 3200rpm , engine temperature runs 8 to 10 degrees warmer, exhaust temperature increases and the engine is running up a steep hill all the time and out of the Manufactures specifications 3500 +/- 100rpm. The C28 that was commissioned properly during the PDI propped at 3605 to 3650 is now running 3400 rpm borderline over propped but still in spec. The original prop installed on these boats was a 19 x 23 4 blade ACME. (This is a C28 with a generator) I was on board a C28 fully loaded for extended live aboard, with 12 volt portable freezer, 50 gallons water tank full (owner removed the 30 gallon tank that is advertised as a40 gallon tank) fuel, cooler, 5 group 31 Northstar batteries @75lbs each, Kayak and 4 passengers on board. Prop installed 19 X21 4 blade it cruised comfortably at 3100 rpm 14.5 kts and WOT was 3500rpm 19kts. The same boat with all extra living gear for extended cruising removed WOT 3650rpm 23kts. The only other change was 12x12 trim tabs were removed and 18 x12 trim tabs installed. The 19X23 original prop will be faster with a light boat but loading the engine outside Volvos specifications when used the way most people use the C28.

 

[tlkenyon]

While looping, racked up 685 hours and consumed 1,230 gal of fuel for an average of 1.795 gph and a cost of $3,685.59. Interesting.

TK

 

[Red Raven]

OK, I put my spare factory spec prop on the boat to get a baseline without the cup change.

Here is the new data.

1148 Engine Hours (Spring 2020) Factory spec prop 17x17 .105 cup
Slow Cruise: 2250rpm 7.4kts 2.8gph 176F
Fast Cruise: 3400rpm 14.5kts 7.8gph 187-189F
WOT: 3940rpm 19kts 10.7 192-198F 23TBPSI

Here is the previously reported data for reference.

1145 Engine Hours (Spring 2020) prop cup removed
Slow cruise: 2250rpm 7.0kts 2.5gph 174F 2.6TBpsi
Fast cruise: 3400rpm 11.8kts 6.6gph 183F 17TBpsi
WOT: 4160rpm 17.8kts 9.4gph 192F 22TBpsi

1130 Engine hours (Fall 2019)
Slow cruise: 2250rpm 7.3kts 2.8gph temp 178F
Fast cruise: 3400rpm 13kts 8gph temp 189F
WOT: 3850rpm 16.5kts 10gph temp 196F 23TBPSI

400 Engine hours (2016)
Slow cruise: 2250rpm 7.3kts 2.8gph 178F
Fast cruise: 3400rpm 14kts 8gph 183F
WOT: 4040rpm 19.6kts 10.7gph ?F

This new baseline for 2020 shows not all the WOT rpm increase in the last test was from the prop with the cup removed. The WOT is 90rpm higher than 2019 with the factory spec prop. More surprising is the speed was 2.5kts faster! The WOT is within 60rpm (3940 was the average reading, saw 3960 once) of rated engine WOT. The 19kts is nearly as good as ever (speeds are averaged from both directions to remove effects of current). It’s hard to say where the improvement came from for sure. I did extra effort on the bottom cleaning this year. I did remove some weight from the bow but the dinghy and dinghy motor were on the stern now in 2020 which wasn’t the case in the 2019 test. The WOT turbo pressure was so I’m not thinking the turbo cleaner made a difference. Perhaps the barnacle buster helped but seems unlikely given the continued temperature rise.

Still have a temperature issue. The temperature rise was slower than in 2019 so I think there was some improvement. I plan to do some more Barnacle Buster in the raw water system to see I can get any more improvement. I also with be checking for any air in the strainer. For now I’m sticking with this prop until I see the performance loaded up for a trip.

Curt

 

[BB marine]

I'm still waiting to get my prop back. I spoke with the prop shop last week they had finished checking the prop specs and stated it was exact to Acme original. Over 400 hrs of run time I was impressed with how well the prop is well held up. I spoke with them about your experience and said I only want a slight change enough to gain 100 rpm so that when I'm loaded down I stay at 4000 rpm or slightly above. he felt that .075 may be to much to remove he was going to do his own calculations. Looking at your numbers removing all the cup was to much. I'm not worried about loosing 1.2Kts at WOT but loosing 2.7kts at cruise is not a positive move. Based on your boost numbers the engine was not loaded at all with the cup change. That also shows in the engine temperature. These small displacement high Hp engines used in heavy semi displacement applications have a fine line of over propped and underpropped based on an extra few pounds. The difference in my boat full water, full fuel, dingy, motor, paddle board and extra supplies on board for cruising can be 4130rpm to 3950 throw some wind and waves into the equation and I'm below 3900 rpm. I hope to get the prop back this week and boat in the water next week. I'll post my results. I know I will see a slight decrease in speed now but hope the benefits are seen when I'm loaded for our trip to Florida.

 

[NorthernFocus]

...The information I took from his post is he is loaded heavy but also runs in the lower rpm range and burning average 2 gph which is operating at average 30% load. While not running at high rpm often I think there is still a benefit to prop adjustment....the WOT rpm determines" how steep the hill is that the engine is climbing" no matter what rpm the engine is running it is still climbing the hill"...

This concept about "climbing the hill" sounds old school from when the only information that we had was a tachometer, coolant temperature, and oil pressure. The only way that "climbing the hill" makes any sense to me is if the operator is running the boat to those parameters with blinders on to everything else.

Just out of curiosity I compared the prop slip and performance numbers between my heavily loaded boat and the lightly loaded R25 test boat numbers published back in 2008. The slip curve from that original test clearly shows a hump between hull speed and running "on step". On my boat prop slip is nearly constant from just above hull speed to WOT and very closely matches the slip numbers from the test boat. I can't compare numbers with the "running on step" side of the curve because I can't get there with my boat with a cruising load. I'm running a 17x14+cup vs the test boat(presumably) 17x15+cup. My boat lives on a trailer and has never had bottom paint so fouling/coating condition is not an issue.

I guess what that's pointing out is that if you run heavily loaded you're running "up hill" regardless of chosen pitch.

 

[BB marine]

This concept about "climbing the hill" sounds old school from when the only information that we had was a tachometer, coolant temperature, and oil pressure. The only way that "climbing the hill" makes any sense to me is if the operator is running the boat to those parameters with blinders on to everything else.

It may be old school but it still stands in school today. The same gauge used 30 or 40 years ago for propping is still used today Tachometer! The first question an engine manufacture technician should ask when there is a performance issue or a engine failure is what is or "was" your WOT RPM? Does it match the manufactures Maximum rpm? The prop is the only gear you can "shift". If anything the "climbing the hill" that sounds old school is more important in todays small displacement diesels. Engines that are producing more than 70 hp per liter. A 2L diesel producing 150 hp you don't want to lug.

I guess what that's pointing out is that if you run heavily loaded you're running "up hill" regardless of chosen pitch.

Thats not true. The way it was explained to me years ago (Mercruiser Training Center) and still holds true today. I have serviced gas 2 and 4 stroke outboards, Gas and diesel inboards using this theory. Rated maximum rpm recommended by the manufacture puts the engine running on level ground. No down shifting required. Rpm drops 100 rpm the road has a slight incline but no downshifting required. 200 rpm drop road gets steeper time to down shift. At this point the engine is using the same amount or slightly more fuel at 3800 rpm than at 4000rpm. Drop the throttle back to 3000rpm the hill is still there, drop the throttle to 2000 rpm the hill is still there. Down shifting is only done by prop adjustments. This can be done by reduction in pitch, reduction in diameter, reduction of cup. Curt removed .105 of cup and gained 220 rpm, The WOT fuel burn dropped one 1 GPH, the complete rpm range showed a fuel burn decrease ,engine operating temperature dropped 6 degrees. The removal of .105 cup changed the roads slight incline to going down hill. Removing all the cup proved to be to much. I spoke with ACME props, the rep that I spoke with recommended removing .075 cup to gain 100 rpm. He said I could also drop 1" pitch and maintain the same cup .105 and gain 100 rpm. Bottom line in order to get off the hill operate the engine the way the engine manufacture designed it to operate. That is propped to achieve WOT recommended rpm. If you have your boat loaded down and it will only turn 3650 rpm and it is rated at 4000 rpm you are climbing a steep hill no matter what rpm you are operating the engine. That's not my opinion that is fact. The first parameter to start with is recommended WOT rpm.

The slip curve from that original test clearly shows a hump between hull speed and running "on step". On my boat prop slip is nearly constant from just above hull speed to WOT and very closely matches the slip numbers from the test boat.

That may be true but you are over propped so you need to increase the slip to get your rpm's up to rated speed. Yes your boat speed may drop slightly but you will be operating the engine to design. Its the price you pay if you want all the comforts of home! I know I do!

 

[NorthernFocus]

It may be old school but it still stands in school today. The same gauge used 30 or 40 years ago for propping is still used today Tachometer!...

And it is still valid today for setting up the boat. But it is archaic for operating it. As I thought you pointed out so well earlier in the thread with all the discussion about fuel burn 🙂

... The first question an engine manufacture technician should ask when there is a performance issue or a engine failure is what is or "was" your WOT RPM?...

And why do they ask this? First because it's their get out of jail free card because 90 percent of boats out there(inclusive of outboards) are just running the prop that came with it regardless of fit. Secondly it's because the instructions they give for operating their engines are for the general public with little/no knowledge of operating the equipment. Tell them to watch one thing which they can understand, the tach. Forget about all the other wiz bang instrumentation we now have like gph burn and/or engine load.

But in the context of our engines in these boats what does the tachometer guidance really tell us? For example, the notes on the data sheet for the QSD 2.0 state:

... Intended for use in variable load applications where full power is limited to one hour out of every eight hours of operation. Reduced power must be at or below 400 rpm of the maximum rated rpm...

This statement is only valid in the context of the actual prop curve matching the theoretical/design curve(IOW the prop perfectly matched to WOT rpm). Which it never will(exactly) due to changes in weight, sea conditions, etc. It's possible to follow this guidance and run with the throttle at the firewall all day long as long as I'm below 3600 rpm. And then when the turbo burns up get grilled by the shop technician about my WOT rpm 😉

But if the note is taken in context with the theoretical prop/fuel burn curve what this guidance is really saying is that the engine should not be run continuously above about 70 percent load (6.1 gph@3600rpm/9.0 gph@4000rpm). Whether over propped, under propped, head wind, etc, rpm should be adjusted to keep the engine at/below 70 percent load.

...If anything the "climbing the hill" that sounds old school is more important in todays small displacement diesels. Engines that are producing more than 70 hp per liter. A 2L diesel producing 150 hp you don't want to lug.

Presumably by "lug" you mean to load the engine at low rpm. That may seem intuitive but regardless of engine size/weight we still get the benefit of a diesel torque curve. As long as it is operated below its continuous duty rating(in my case 70 percent load) the engine does not suffer and running at lower rpm has the benefit of producing less wear. Within reason. If low rpm loading is extreme then cooling can become an issue as the oil, coolant, and raw water pumps all move fluid proportional to engine speed. But in the context of a pleasure boat engine I doubt this is a practical concern.

...The way it was explained to me years ago (Mercruiser Training Center) ...

I wondered where that terminology came from. OK let's just agree that we're looking at life through a different key hole. The only time my boat has ever been up a hill was on the trailer and the prop made little difference 😉

...you are over propped so you need to increase the slip to get your rpm's up to rated speed. Yes your boat speed may drop slightly but you will be operating the engine to design...

Reducing pitch should reduce slip. But I get you drift and it has nothing to do with whether I operate the engine to design. Per above I operate to the engine design load and rpm/boat speed fall where they may. Changing the wheel to improve performance has little to do with extracting power from the engine and everything to do with matching blade pitch to boat speed thereby efficiently turning that power into motion. Which unfortunately is a different answer for each hull design, typical loading condition, etc.

All that said I do need a flatter wheel. Since I operate 90 percent of the time at 25 percent load it never rises to the top of the to-do list. But it would be nice to be able to troll a little slower. As I'm currently set up the only way I can catch salmon is to troll in a circle to slow the baits down 😳

 

[BB marine]

And it is still valid today for setting up the boat. But it is archaic for operating it. As I thought you pointed out so well earlier in the thread with all the discussion about fuel burn

Two different discussions. The tach is used for propping. Manufacture says 4K you use the Tach to confirm you are capable of turning 4K. Fuel burn mentioned before in the discussion is a gauge for operating the engine. I want the boat/engine combination as normally loaded to turn max rpm + 3% above. The 3% is for your statement

Which it never will(exactly) due to changes in weight, sea conditions, etc. I

Now that I know it is propped correctly I use fuel burn to monitor the engine load. I set the engine at a specific rpm say 3400 rpm at 3400 rpm I burn 8.7 GPH just over 70% load. When I get into rougher seas and wind I will see an increase in fuel usage sometimes as high as 9.5 gph just under 80% load the engine is still turning 3400 rpm. If I see the fuel burn continue to climb to 10 gph just under 85% its time to back the throttle down. I know based on the way the boat/engine is propped its working hard at those moments but still propped per manufacture. The issue comes in when the boat manufacturer markets a product to do a specific speed and props it on the edge. The dealer delivers it, the boat owner loads it, and goes on his/her merry way. That same boat owner goes through the same conditions sea's and wind. He's over propped, running in disturbed water, doesn't back down because he doesn't know to. Something goes wrong, dealer has PDI, Manufacture has PDI, boat owner doesn't realize he has been running over propped and the turbo is shot or head gasket is blown. Get out of jail card comes out " you have been operating the engine out of specifications. They know to because they can pull that information from the ECU. It's unfortunate that this happens. I know it does. You have no idea how many outboards, stern drives and inboards I changed props on in the 80's and 90's during or slightly after delivery. I can't put a number on how many 2 stroke outboards I rebuilt because they were over propped and took out a piston. How many Mercrusier 454 and 5.7L had tulip valves from being over propped. There is plenty of information that is readily available to educate the boat owners that cares. I would hope that even this thread has at least sparked some interest even if one doesn't agree with it they are at least thinking about the subject as they read it.

This statement is only valid in the context of the actual prop curve matching the theoretical/design curve(IOW the prop perfectly matched to WOT rpm). Which it never will(exactly) due to changes in weight, sea conditions, etc.

Bottom line is it can be if the boat owner makes sure it is propped per manufacture +3%. I agree more boat owners don't follow this mostly because they don't know or don't care or don't want to compromise speed 1kt +/-. Let the next owner worry about it!

I wondered where that terminology came from. OK let's just agree that we're looking at life through a different key hole. The only time my boat has ever been up a hill was on the trailer and the prop made little difference

Your right but fortunately for your truck engine has a multi gear transmission that could downshift so it wasn't lugged down pulling the boat and trailer up the hill :shock:

https://pubs.volvopenta.com/ProdDocs/Ho ... ang=en-US/
This shows Volvo's GPH specs at given rpm.

There are all kinds of opinions about this. You know mine right or wrong!

 

[ALICE J]

Thanks Brian for tying rpm, load, fuel burn, and prop into an understanding package. It takes a village of TugNuts to keep our boats afloat. I cross the Gulf Stream tomorrow and will log the numbers and see where Alice J sits. :geek:

 

[NorthernFocus]

...I can't put a number on how many 2 stroke outboards I rebuilt because they were over propped and took out a piston. How many Mercrusier 454 and 5.7L had tulip valves from being over propped....

"Props don't kill engines people do". - Confuseus, 2020

 

[BB marine]

Hi Brian,

Based on my experience you may want to consider removing less than .075 to get 110rpm considering I got 310 rpm by removing .105. The other work done on my boat could be at play though and the cup vs. rpm may not be linear.

Thanks for your feedback and good luck!

Curt

I launched the boat last weekend. Unfortunately Lake Michigan is not the perfect place to get good performance numbers. We waited three days to get sea's under 4'. The prop shop Air Marine made a .035 adjustment to the .105 cup. with the final cup reading of .070. He said that should yield me 100 rpm based on the numbers I gave him. Sunday was the calmest day 2' to 4's with 3'swells. A bit rough to get good numbers. I had 80 gallons of fuel in main tank and 7 gallons in 20 gallon aux tank. Water tank 100% full, waste tank empty, Gala F270 dingy with gear in it 80 lbs mounted to swim platform, 6hp Suzuki, normal gear for a weekend of boating. I would say 200 lbs less weight than long term cruising.

Max rpm 4100 rpm average was 4050 and the lowest I saw was 4000. My speed was down but I believe the sea's had a bit to do with that 17.5 kts max but I stuffed the bow in a wave while I was at that speed. It was to rough to get good readings. I believe Air marine hit the mark. Last year I would be seeing 3940 to 3880 rpm in similar sea's. I was able to cruise at 3450 rpm 13kts 8.7 to 9.2 gph average 75% load in the sea conditions. In similar sea conditions last year I was at 9.5 to 10 gph 3450 rpm. Boost numbers all matched previous numbers.

I'm amazed that .035 reduction in cup made that difference. I told Jerry at Air marine that Todd from Acme said to remove .070. He said he ran calculations and the prop efficiency would have be reduced too much. I'm going to say he was spot on with 100 rpm increase and .035 reduction. I will post flat water numbers when I can. Hopefully the lake will settle down one of these weekends so I can post a good comparison.

I spoke with an engineer from Volvo Tait Guilherme about max rpm for continuous operation. He calculated @ 4050 rpm 3450 to 3500 would be a recommended max for continuous operation. Which is his conservative opinion, slightly lower than the Volvo manual-10% of max rpm.

 

[Red Raven]

Hi Brian,

Nice! It looks like you hit the optimal tune for your load conditions. This is very good information as I plan to retune my original prop to add some cup back. I think I will likely go for a similar cup on that prop that you did.

In the mean time it appears I have finally solved my temperature problem. I rigged up a circulating raw water flushing system based on Glen Wagners instructions posted here on Tugnuts as follows:

http://www.tugnuts.com/viewtopic.php?f=5&t=7353&p=52109&hilit=Rydlyme+flush#p52109

I used Barnacle Buster instead of RydLyme because it was available locally. Immediately after my test run, it showed no difference in temperature climb but we just finished a two week trip during which the temperature held steady at 185F at 3400. Delayed effect I guess? The stock prop I have on the boat right now is getting 3850 WOT fully loaded for that two week trip with two persons, half fuel and water, and dinghy and motor on the swim step. I’m good with this for now but since I have the other spare prop it makes sense to to tune it to be more optimal. I will then put it on the boat at a future date.

I have met Tait on several occasions and discussed these performance questions as well as other questions. Great guy!

Curt

 

[ALICE J]

Hi Brian, I returned from the Bahamas, departing Freeport, Grand Bahama; and logged the numbers that were referenced in this thread. Not sure how to critically interpret since this was a oneway crossing with the vagarities of wind, current, and waves.
Speed Wind RPM GPH Turbo Load Temp Oil Pressure 4BY180 Yanmar 2011 R27
7.0 7 E 2000 1.7 3 56 193 49
7.5 7 E 2070 2.2 4 64 194 43
6-8 4 E 2550 3.2 8 73 196 50 counter-current affected by winds
7WSW 2820 4.4 12 74 199 51
7.3 5 S 2910 4.6 13 78 199 51
11-13 5 S 3850 9.9 24 100 204 70
11-13 5 S 3910 9.9 24 100 204 79 trim tabs applied
8 5 S 3000 5.1 15 78 200 53
13.8-14.2 6S 3890 9.6 24 100 204 xx
9.2 6 S 3160 5.8 18 78 201 55
the course was about 300 degrees the last two hours was about 291 degrees.
seas were port quarter one to two feet, but smooth out in the center of the stream, but built to 2-3 on the western side
My interpretation is that the turbo is working fine, the prop appears to be tuned, perhaps detune to increase top RPM? Temp is good although I did not hold the RPM at WOW for more than a minute or so. Miles run 1237, hours on engine 369, but maybe 30 hours were for charging batteries @ 1000-1200 RPM. I have noticed that the mouse fur is showing many water stain streaks in forward cabin and cave, along with what appears soot stains around bulkheads on the mouse fur. Replaced the windlass with new as to old one groaned and lost speed, regreased, but still had issues, i do carry and use 100 ft of 5/16 chain, 35lb Manson Supreme anchor and the galvanizing has worn off the chain, will replace in the fall.

 

[BB marine]

Hi Brian, I returned from the Bahamas, departing Freeport, Grand Bahama; and logged the numbers that were referenced in this thread. Not sure how to critically interpret since this was a oneway crossing with the vagarities of wind, current, and waves.
Speed Wind RPM GPH Turbo Load Temp Oil Pressure 4BY180 Yanmar 2011 R27

Looks like you had a good trip and a decent arrival trip to the US. I envy your explorations in you R27 Tug. Your numbers are interesting. You have a lot of equipment onboard. I remember meeting you at the Rendezvous SWF 2 years ago. You are set up to cruise. Your numbers are spot on maybe slightly over propped but with all your equipment just 100 rpm off rated rpm is not bad.Your temperatures seem slightly higher than I would expect. It is interesting that the Trim tabs reduce load but make no difference in speed performance. You probably would see a speed difference after a few minutes of power pushing the boat. I see your temp numbers climb quickly. This seems to be a theme with the Ranger/Cutwaters. I believe this to be the marginal water flow do to the 1" thru hull combined with a few years of saltwater use. The water flow is marginal at best then the slightest build up of deposits reduces the flow more. I have not experienced this yet (fresh water use). The difference in temperature from 2250 rpm to 4050 rpm with a clean after cooler, clean reverse gear cooler and clean heat exchanger is 178 F to 193 F = 15 F. With additional flow these numbers could be cut in half. With reduced flow( build-up of deposits) the numbers seem to increase by 10 F or higher. The link that Curt posted. Will be my go to once a year when we are in salt water. I removed my raw water flush for the head so I have a port with a ball valve installed. I can attach a dock side fresh water hose to the strainer for an easy fresh water flush which I will do periodically but will also do a raw water cleaning seasonally to stay on top of it. Thanks for adding to the information. Knowing the engine performance numbers and hours of run time gives information of what to expect positive and negative. So far the only questionable number is temperature and max rpm of most of the information posted on this thread. Two components to watch to help maintain longevity.

 

[BB marine]

6/19/20 finally a decent day on Lake Michigan for a Sea trial with adjusted propeller cup. C26 standard prop 17 x 17, 1.25, 105 cup. Adjustment made .035 reduction to cup. Prop spec 17 X 17, 1.25, .070 cup.

2230 rpm 2.6 gph 7.6 kts 8.7 mph 178 F (new)
2250 rpm 2.8 gph 7kts 8 mph 178 F (original)

3220 rpm 7.2 gph 11 kts 12.8 mph 179 F (new)
3250 rpm 7.8 gph 11kts 12.8 mph 180 F original

3420 rpm 8.2 gph 12.7 kts 14.5 mph 181 F (new)
3400 rpm 8.7 gph 12.2 kts 14mph 183 F (original)

3550 rpm 9.1 gph 14kts 16 mph 183 F ( new )
3600 rpm 10 gph 14.3kts 16.5 mph 185 F (original)

4120 rpm 12 gph 18.7 kts 21 mph 190 F (new)
4130 rpm 12 gph 19.1 kts 22 mph 193 F (original)

The numbers are close and the change is not significant. The differences are this. The original numbers were documented in 2018 log book. The original data was without dingy and outboard on board, before battery change out ( original batteries weight (3) 46lbs and (1) 49lbs = 187 lbs) Northstar group 27 AGM 67 lbs x 4 = 268lbs. Water and fuel unknown on board. I did not record in 2018.

2019 trip to North Channel and Georgian Bay is when I noticed a change in my numbers from 2018. My WOT was 3980 high to 3880 low rpm after filling the fuel tank and full tank of water. My WOT speed was 17kts (average). My new numbers were trying to simulate the Georgian Bay trip. Tender on board, outboard, full fuel and water, cooler (beer)refrigerator loaded, all tools on board, dinghy 3 gallon gas tank full in box. The only equipment missing was the paddle board (55lbs).

I did find a note from my Drop fin sea-trial in 2017.

Second sea trial was the RIB and outboard removed. We had 2 adults full water, 63 gallons of fuel . 3200 rpm 12 kts 6.8 GPH Bow down and a real solid ride in the water. 2250 RPM 7.5 KTS 2.8 GPH bow down full tab . WOT 4130 full tab 20.5 kts +/- 12GPH bow down. (The boat was lighter, I didn't have all the extra stuff installed. RPM was the same but 1.4 kts slower a year later 2018 data numbers. )

My conclusion is with all the added equipment over the last 4 years I have taken a boat that was propped correctly from the factory to a boat that is over propped marginally. And a slight prop adjustment to the tune of $75.00 for reducing the propeller cup by .035 brought the engine /boat back to Volvo specifications. I lost almost 2 kts in speed from 2017 season to 2020 because of added equipment and 250 rpm. I now recovered the rpm but the speed is not coming back at least the way we plan on cruising.

I will monitor the change this season and during tour trip this fall to evaluate if it was worth while . Right now I am going to say it was.

 

[FWTMD]

Brian, this is nothing new to you. Its just another guy expressing your point of view in his own way. I thought others might enjoy the read and perhaps extend the life of their engine.

https://www.sbmar.com/articles/engine-l ... e-loading/