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Old 08-19-2016, 08:25 AM   #21
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Actually it is possible to quite accurately calculate the required prop for a boat. That said it also requires a lot more information that is generally available to anyone other than the boat's designer. Few, if any, prop shops will have the required information, so they use much more approximate methods.
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Old 08-19-2016, 08:50 AM   #22
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Hi Mr. Baker,

Thanks Mr.Baker.
Al


Not choosing to be argumentative, rather, unable to stand by with real life experience that includes so many of the topic related to what is 'Right' and what is 'Wrong'. the 'Gospel' is so many times open to interpretation I suppose.
All good my friend. This is what forums are all about. A civilized exchange of ideas. First off, I did quantify, somewhere, as does the article, that the main focus of this article is engines that are pumped up and running at high loads. Mr. Athens defines it as engines that produce 50-60hp per liter of engine displacement. BUT, there are some similarities and characteristics that do carry over. As far as your engine goes in your situation...just because it hasn't failed(yet) doesn't mean what you are doing is correct and not hurting your engine. You have no clue other than "it hasn't failed"...yet. It very well could be within healthy parameters that will give you thousands of hours of trouble free engine life. It might have cut your engine life from 30,000 hours to 15,000 hours....yet you won't know that either. But again, you have no clue and nothing that can monitor what is going on inside of your engine. THAT is the gist of that article. Your COOLANT temperature has absolutely nothing to do with how heavily loaded your engine is. It is simply stating that your cooling system is in good working order. SO the question is, how loaded is your engine??? And the answer is....you have no clue. I am not trying to be ugly here or argumentative. If you had an EGT gauge, that would be a start. BUT, do you know baseline numbers?? Can you compare it to how it used to be to how it is now? Nope. SO ultimately, you are the test pilot for that particular set up. One can purposely overprop a boat as long as they understand what is going on with the parameters of their engine. EGT, boost(turbocharged) and fuel flow tell you a lot about what is going on in your engine. If you had those instruments and then told us all what all of the parameters were as you changed everything.....THEN you would have an argument!!! Right now you are just hoping and praying!

PS...The 4236 is one of my favorite engines of all time!!!
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Old 08-19-2016, 08:55 AM   #23
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Actually it is possible to quite accurately calculate the required prop for a boat. That said it also requires a lot more information that is generally available to anyone other than the boat's designer. Few, if any, prop shops will have the required information, so they use much more approximate methods.
Just look at any prop calculator....there is a lot of grey area in every single one. Most even ask for hull shape....hahaha. We all know that is a black and white answer!!!!...
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Old 08-19-2016, 09:43 AM   #24
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Al, after a little coffee and a walk around the lake with my dog, there is another measure of work...and that is your boat's performance. You still don't have any prior baseline with your current rig, but if you are doing the same speed then likely the same amount of work is being done. It would be better if you had a baseline with the current rig but my argument really is more towards boats with planing hulls and squeezed engines. That Yanmar in my signature is a good example as are those Cummins. The 4LHA was 213CID...23CID LESS than your engine and putting out 3 times the horsepower. A full displacement boat running displacement speeds is not a highly loaded affair and therefore not as immediately subject to the scrutiny of an engine running close to the edge. But the parameters the OP stated are getting up there since he is fighting the bulge of being well past displacement speed. That is a very highly loaded regime! Especially since he ran the boat home at 1900 out of only a possible 2000RPMs!!!! Now THAT engine, I promise, would not last long if it was running there all the time. 10 knots on a PT40 with (only) 225 horsepower on hand is running that engine EXTREMELY hard. Are you with me here??? Are you feeling the vibe I am putting out here???

FF is a fan of overpropping on purpose. But he also gives caveats when he suggests it. Those being manufacturer prop and fuel curves with a way to monitor the work being done(ie EGT/pyro and fuel flow and boost of TCed). It is safe to assume that if your fuel flow and EGT are the same then the work being done(load on your engine) is the same....regardless of prop and RPM...but speed will likely be damn close to the same on the same hull since the same amount of work is being done.
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Old 08-19-2016, 11:37 AM   #25
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Just look at any prop calculator....there is a lot of grey area in every single one. Most even ask for hull shape....hahaha. We all know that is a black and white answer!!!!...
As I said, the simple prop calculators that most prop shops use are just that simplified. IF you have some information about the hull including general hull form (displacement, semi-displacement, planing, etc.), displacement, LWL, waterline beam, water plane area, wetted surface area, wetted surface roughness, prismatic coefficient, location of longitudinal center of gravity, depth of prop, aperture or not, number of engines, horsepower of engine(s), engine power curve, gear box ratio, type of prop (design, number of blades, disc area ratio, hub diameter, etc.), Torque and power function for the specific prop design, cross sectional area of the boat above the waterline for wind resistance calculation and a few other parameters that have slipped my mind now, you can calculate the prop quite adequately. No simple prop calculator that I am aware of includes this data. Given the data I list (and anything I forgot), you can calculate the required prop quite accurately.
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Old 08-19-2016, 11:43 AM   #26
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As I said, the simple prop calculators that most prop shops use are just that simplified. IF you have some information about the hull including general hull form (displacement, semi-displacement, planing, etc.), displacement, LWL, waterline beam, water plane area, wetted surface area, wetted surface roughness, prismatic coefficient, location of longitudinal center of gravity, depth of prop, aperture or not, number of engines, horsepower of engine(s), engine power curve, gear box ratio, type of prop (design, number of blades, disc area ratio, hub diameter, etc.), Torque and power function for the specific prop design, cross sectional area of the boat above the waterline for wind resistance calculation and a few other parameters that have slipped my mind now, you can calculate the prop quite adequately. No simple prop calculator that I am aware of includes this data. Given the data I list (and anything I forgot), you can calculate the required prop quite accurately.
I think taking the boat for a spin and seeing what it does in reality would be easier!!!
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Old 08-19-2016, 11:59 AM   #27
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Al
I am firmly in your camp. I also have a deliberately over-propped boat. This is also due to an change in engines. I went from a pair of Volvo TMD40s rated at 145hp to a pair of TAMD41s rated at 200 hp. I kept the same props, and at the same rpm, gained some fuel efficiency in addition to the extra hp. My cruising speed increased by 1 knot, to 8.2.
My mechanic, a Volvo specialist, who sold me the engines and supervised the installation, recommended over-propping, to gain further fuel efficiency and run quieter. I added 4" of pitch, bringing my cruise rpm from 2700 to 2100. The fuel efficiency gains were about 5%, on top of a 10% gain from the direct injection engines, part of which I gave up to cruise 1kn faster.
These engines are rated to top out at 3600 rpm, so my mechanic says they will last a lot longer now that I am running them slower.
If my mechanic said that in the last line as it relates to overpropping, I would get a new mechanic.
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Old 08-19-2016, 12:47 PM   #28
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Thank you all for your thoughts.



Another thought came to mind which I thought I'd pass along. Under no load, the RPM steadily increases with the increase in throttle. Under load, the RPM reaches 2000 with 10-15% of the throttle still remaining. The final 10-15% of the throttle movement has no effect on the RPM's.
We had similar issues when we sea trialed Ka-sea-ta we also have 6068 225hp Turbos were bad...
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Old 08-19-2016, 01:13 PM   #29
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Mr. Baker, Hummm, one would believe that there was a base line in our operation for two years prior to the engine change. During that time and then after,we noted what was and made the adjustments mentioned along the way determining changes.

Your repeated note on EGT and often read in forum posts, would seem more applicable to tubo driven engines over slower older NP engines such as the 4-236. This is a guess and I am going to review with my shop. It has not be the subject of conversation as we developed our solution although I am somewhat aware of the application and purpose.


Your allering to the discussion being directed more towards high speed application of planning/SD hulls and the concequences of both weight and prop have an immediate effect offsets those of our more displacement style hull/power/wheel package.

Yet in fear of a anticipated 'Manyboat' response to our continued calling of our hull a FD hull, the factors and concerns you have mentioned confirm our results that our hull form is more FD than SD. As such, we will continue in a total 'Ducky' world of boating bliss!!

Al-Ketchikan 27'Marben pocket CRUISER
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Old 08-19-2016, 01:32 PM   #30
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We had similar issues when we sea trialed Ka-sea-ta we also have 6068 225hp Turbos were bad...

Usually when turbos go bad there is black smoke due to the lack of boost and over fueling. Was that not the case?
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Old 08-19-2016, 02:17 PM   #31
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Usually when turbos go bad there is black smoke due to the lack of boost and over fueling. Was that not the case?
I think because the turbos don't significantly boost the Hp over the NA motors the fuel flow is not that great of difference...
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Old 08-20-2016, 10:01 AM   #32
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Baker- I got your message and skimmed through this. Lots of words and I admit I have not digested every argument.

Regarding the OP's boat, a few things stand out. Running 9kts at 1900 at 5gph on a 30k 40ft boat is pushing it well past hull speed. With max available hp of 225 that thing is not going to plane or semi plane. Any additional hp beyond 1900 is simply going dig more hole and make more wake.

It looks like it is overpropped. Might be intentional by some PO. No problem running this way, but not too good if you try to push it past say 1700.

You could change the prop to get to 2600 but there really is not any benefit to doing this. Due to the boat, anything above 8kts is a no-go zone and rather pointless to prop for operation there.

Keep the same prop and don't try to cheat hull speed and the engine will be fine.

I have sea trialed many trawlers that are intentionally overpropped. I make a note of it, make sure the buyer understands what it means regarding operation, and that is it. If engine is otherwise healthy, no big deal.

In the op's case, one thing that seems a little off is that with a max of 2000, the flowscan is reading 5gph at 1900. That is about 90hp. I would expect it to be higher than that. And would expect black smoke at 2000.

Might be worth putting a boost gauge on. Boost will be pretty low there, but should be some, maybe 5psi. It won't go to spec if engine can't get to 2600, but it should show some.

If engine is running fine, I would not spend a lot of time and money chasing that last 600rpm. It is not practical to run over 1700, why do battle to get there.
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Old 09-15-2016, 01:08 PM   #33
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Hi Tengee,

My Pacific Trawler 40, hull #37, is equipped with the John Deere 6076AFM30, specified by John Deere at 300 hp at 2400 RPM. Interesting that they were probably delivered within months of each other, but with different engines from JD??? Although I haven't weighed my boat, I do not doubt it weighs within a few hundred pounds of yours, as mine also includes 65 gal of water and 65 gal of fuel in the swim step.

My transmission is a Twin-Disc, with a ratio of 2:1. Interesting that yours is 2.45:1, which complicates things a bit. In addition, mine is specified at 2400 WOT at no-load, versus your 2600. Some performance results of MY hull, which carries a 25" x 23" five-blade prop, are as follows:

1200 RPM=7.1 knots
1600=9
1800=9.3
2000=10
2200=11
2400=11.8

In my personal opinion, propellor calculators cannot be expected to provide an exact match to hull/engine combinations. They simply get you in the ballpark. Your existing propellor is close, but (again, in my opinion) apears to be over-pitched. As reducing propellor diameter is a one-way street, it would be my suggestion to de-pitch your prop two inches, and try again.

Yes, you can live with an over-pitched prop. Many operators do so, but you run the risk of overfueling the engine at WOT, and having to explain to your next owner (and providing some cash at sale to correct the situation) why the engine will not achieve WOT of 2600 RPM. And yes, anything over about 7.5 knots is in excess of hull speed on our hulls, but so what? For what it's worth, my fuel burn at 1600 RPM is 4.2 gph. That's low enough for me. Still gives my about 800 nm range, not including reserve.

Hope you enjoy your new boat. Mine's a peach.

Regards,

Pete
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Old 09-15-2016, 02:08 PM   #34
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Thanks for the great reply, Pete. It is the type of response I was hoping for when I originally posted the thread. I did converse via email with another owner named Mike who reported that he owned hull #37. Is yours possibly hull #39?

Anyway, I am strongly leaning toward the prop being over-pitched. Once the boat is hauled this fall, I am going to have the prop inspected to qualify the exact diameter and pitch. Then look to determine the necessary adjustments. I realize the first adjustment may not give the exact results we're looking for but hopefully, we'll be closer to the specified RPM. I do not plan to live with the current situation, since I believe the engine should be run and achieve its designed specifications.

It is interesting that you have a larger engine and a 5-blade prop but are still getting results that are similar to what I believe we should achieve with our boat, with the correct prop that is. I did talk with the builder and he said that they put a few JD's into some of the boats but I didn't know they were different sizes. I guess they were still doing some experimenting with the power packages after adding the integral swim platform and extra tanks.

Our boat has the added fuel tank back aft (165 gal.) giving us a total of 600 gal. There is no water tank. We currently run the engine at 1,700 burning around 3-3.5 gal./hour doing around 8 knots. Gives us a decent range.

Thanks again for your response, Pete. We have really enjoyed our boat so far and look forward to many years of good cruising on her.

Jim
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Old 09-15-2016, 06:17 PM   #35
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Hi Jim,

Oops, yup, mine's hull #39. And FYI, I have my prop at the Prop Shop as we speak, and have asked them to note the EXACT pitch and diameter on the invoice. The info I previously provided (25" dia x 23" pitch) is marked on the hub, but who knows the actual numbers. Will find out soon, and update accordingly.

Not to hijack your thread, but interesting that you have a 165 gal fuel tank in the swimstep, vs my 65 gal fuel and 65 gal water, for a total of 465 gal of fuel and 265 gal water. My water tank in the swimstep feeds the manual head, which means I don't have to monkey with solenoids and backflow preventers on my ship's water system to provide safe fresh water flushes. In my install, the tanks are separated by about 36", which leaves a 2nd lazarette.

Looks like these boats were far from cookie-cutter boats, as I have yet to see two that are identical. Via the grape vine, it seems like the builder might have been a little TOO generous with buyer-requested mods, which may have contributed to the brand's demise. Too bad. There's some features on the Pacific Trawler that I very much value vs both the Nordic and American Trawler lines. Doubt I could afford a new one if Pacific Trawler were still in business, and glad I've got mine. Enjoy!

Regards,

Pete
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Old 09-16-2016, 06:47 AM   #36
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Thanks for the response, Pete. Interesting set up for the freshwater feed to the head. Should I ever run into problems with the aft tank and need to make a change, adding a water tank back there that would be exclusively for the head would be a good idea.

Before buying our boat, we looked very seriously at the Nordic and American Tugs. We were on several of them and came close to buying. However, we have actually found many features in the PT40 that we like much better than the other tugs. Granted she has only one stateroom but the extra room gained in the salon, galley and the up head makes her a much better boat for us. Being a more custom boat, I have found that the quality of build is actually equal to or better. Nice to hear you have similar feelings about your boat.

Jim
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Old 09-21-2016, 02:38 PM   #37
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Hi Jim,

Final numbers on my propellor, as it's back from the Prop Shop. Mine is 25" dia x 23.5" pitch, RH, 5-blade. Hope this info helps.

Regards,

Pete
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Old 09-22-2016, 06:24 AM   #38
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Hi Pete - Thanks for following up and sending the prop numbers. Very helpful. I will pass these dimensions off to the prop guy for comparison.

Jim
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