Any prop Gurus?

[JimmyG]

OK I have tried two different size Acme props and I am very happy with the numbers BUT can I get better or leave it alone is the question? And is 92% load enough? BTW this is full of fuel full water and 6 guys with fishing tackle
Cummins numbers 380 QSB

ACME 21 X 23 10/26/2014

RPM LOAD SPEED


600 1-ENGINE -3.3
600 -2 ENGINES 4.3


2000. 44 22kt
2100. 46. 23kt
2200. 49. 24.7kt
2300. 54. 25.9kt
2400. 61. 27.3kt 10.4 GPH
2500. 65. 28 kt
2600. 67. 28.9kt
2700. 71. 29.7kt
2800. 76. 30.5kt
2900. 79. 32kt
3000. 82. 34kt


ACME 21 X 24 11/16/2014

RPM LOAD THROTTLE FUEL SPEED

600 1-ENGINE 4.3
600 2-ENGINE 4.6

1700 47 46 6.1 17.5
1800 47 49 6.7 20.1
1900 49 54 7.3 21.5
2000 50 57 8.1 23.0
2100 50 61 9.1 24.7
2200 53 65 9.8 26.3
2300 57 69 10.4 27.3
2400 66 74 11.6 29.0
2500 69 78 12.3 29.9
2600 72 81 13.2 31.0
2700 75 85 13.9 32.2
2800 80 89 15.1 33.4
2900 84 94 16.2 34.4
3000 91 98 17.5 35.5
3050 92 100 18.8 36.0

[Navatech]

Not a prop guru but if you're fully loaded with water fuel and 6 guys you should reach full 100% load if properly propped... Maybe even go over it slightly... You're obviously still underpropped...

That's not necessarily a bad thing... Think of it as a built in safety margin... This way you're never going to overload the engines...

[Tony Meola]

Jimmy

Remember the famous UV saying: " the enemy of good is better."

The draw back will be that you will have trouble trolling for stripers, since at 4 knots on one engine is starting to get a little fast for them. You could always us JP's approach and have one set for offshore, and one set for trolling. I think JP runs one set in the spring and then goes over to another set once the stripers leave. Then he goes back in the fall.

Maybe he will jump in and comment.

[JimmyG]

Jimmy

Remember the famous UV saying: " the enemy of good is better."

The draw back will be that you will have trouble trolling for stripers, since at 4 knots on one engine is starting to get a little fast for them. You could always us JP's approach and have one set for offshore, and one set for trolling. I think JP runs one set in the spring and then goes over to another set once the stripers leave. Then he goes back in the fall.

Maybe he will jump in and comment.

LOL that saying has always stuck with me too and it did cross my mind, I also thought about the slow striper troll but I my home port is Cape May and we don't troll there its eeling in the rips or chunking the bay. If I wait I may own these props, now I can exchange them.....but " the enemy of good is better." what to do , what to do????

[Kevin]

You have big rudders right? Troll with one engine?
Mine hits 100% load at WOT.
Not a guru but I know that more cup is better than pitch (in most cases) if more forward speed is desired and you have the power.
Do search for a prop slip calculator and run your numbers with each set of props, see which one is better.
I suspect the 24's are better and you could add more cup to them and increase speed while reducing slip.
I could be off the reservation though!

[JimmyG]

BTW I was miss quoted the prop diameter on both props are 20" not 21"

[JimmyG]

You have big rudders right? Troll with one engine?
Mine hits 100% load at WOT.
Not a guru but I know that more cup is better than pitch (in most cases) if more forward speed is desired and you have the power.
Do search for a prop slip calculator and run your numbers with each set of props, see which one is better.
I suspect the 24's are better and you could add more cup to them and increase speed while reducing slip.
I could be off the reservation though!

Yes Kevin I do have the oversize rudders and for stripers I have to troll with one engine in gear 4.3 knots, I talked to the acme prop rep today and he suggested more cup he said nominal change at idle but will pick up speed and load at higher RPM but he does have a set of 20x26 with light cup i can try.

[CaptPatrick]

he does have a set of 20x26 with light cup i can try.

Don't think you'd like them... Might load your engine better, but it'll also kick your idle speed way past your wanted trolling speed. Pitch will increase speed, cup will increase load.

[JimmyG]

Thanks Capt Pat like I said I'm happy with what I have but the load was low I think I may try more cup. I really don't understand cup does it give you more speed or not?

[JP Dalik]

Pitch for pitch you overlap exactly with the old Chimera difference being we ran out of rpm at 2850

With the smaller wheels your a knot slower than the qsb305 up here. He is running 21" wheels on 1.75" shafts

Thought that boat was something like 21 24 or 25. Michigan dqx have worked the best even over the acme wheels, the acme wheels burned reel bad on the hub when you over square. Lots of lost blades

If your full full id look for 98-100% at full throttle, you wanted it to go fast so add the diameter and the pitch and load the engine. You can always pull the red knobs back.

And for bass we ran 3 blades on one engine for spooning at 3.2 kts

Good luck

[JimmyG]

Pitch for pitch you overlap exactly with the old Chimera difference being we ran out of rpm at 2850

With the smaller wheels your a knot slower than the qsb305 up here. He is running 21" wheels on 1.75" shafts

Thought that boat was something like 21 24 or 25. Michigan dqx have worked the best even over the acme wheels, the acme wheels burned reel bad on the hub when you over square. Lots of lost blades

If your full full id look for 98-100% at full throttle, you wanted it to go fast so add the diameter and the pitch and load the engine. You can always pull the red knobs back.

And for bass we ran 3 blades on one engine for spooning at 3.2 kts

Good luck

Thanks JP do you have any numbers?

[CaptPatrick]

Jimmy,

Think of cup this way: No cup, you're stroking the blanket with your fingers tips flat. Cup: you're gripping the blanket with in-curved finger tips. The more the cup, the more the grip. Increased cup has a similar action to increasing diameter. At 21" you've used all of your diameter safety margin, so increasing cup is the only way you can "increase" diameter to offset some of the out-of-square you have. Might try 21 X 23 with a #5 cup. That should be similar to a 22 X 23...

[bbtiller]

Stupid question: How does one determine/measure load? I have 6 BT Cummins.

[CaptPatrick]

Brad,

When fully loaded, your wide open throttle will give you full factory rated RPM...

[JimmyG]

Stupid question: How does one determine/measure load? I have 6 BT Cummins.

[Rocket]

Jimmy, if I am interpreting the data right, then why would you change anything? 3 Nautical miles per gallon at 20 Knots and 2.5 NMPG at 29 Knots, nearly 2 NMPG at WOT, hauling ass at 36 Knots! Wow really amazing numbers!

Gallon/Hr Kn/Hr NMPG
6.1 17.5 2.87
6.7 20.1 3.00
7.3 21.5 2.95
8.1 23 2.84
9.1 24.7 2.71
9.8 26.3 2.68
10.4 27.3 2.63
11.6 29 2.50
12.3 29.9 2.43
13.2 31 2.35
13.9 32.2 2.32
15.1 33.4 2.21
16.2 34.4 2.12
17.5 35.5 2.03
18.8 36 1.91

[Navatech]

Stupid question: How does one determine/measure load?

First, it's not a stupid question...

Second, there's several ways to determine the full load... It depends on your setup...

1) If you have the data from the manufacturer (for comparison) and you have pyrometers (exhaust temperature sensors) installed you can tell your load by the exhaust temperature...

2) If you have a digitally controlled/monitored engine the display will give you your load...

3) If you have neither of the above then there's the trial and error method... You should know the maximum RPM's for your engines... If you achieve the maximum RPM's at WOT you've reached 100% load... If you can't reach the maximum RPM's at WOT you're overloaded... If your maximum RPM's are higher at WOT then those specified by the manufacturer you're underloaded... This is HIGHLY dependent on you being properly propped...

[JimmyG]

Jimmy, if I am interpreting the data right, then why would you change anything? 3 Nautical miles per gallon at 20 Knots and 2.5 NMPG at 29 Knots, nearly 2 NMPG at WOT, hauling ass at 36 Knots! Wow really amazing numbers!

Gallon/Hr Kn/Hr NMPG
6.1 17.5 2.87
6.7 20.1 3.00
7.3 21.5 2.95
8.1 23 2.84
9.1 24.7 2.71
9.8 26.3 2.68
10.4 27.3 2.63
11.6 29 2.50
12.3 29.9 2.43
13.2 31 2.35
13.9 32.2 2.32
15.1 33.4 2.21
16.2 34.4 2.12
17.5 35.5 2.03
18.8 36 1.91

Well I guess I'm driven to get the best I can so if its 1 knot more and .5 Nmpg I'm going to try it, I know what I have and don't know what I don't know LOL

[JP Dalik]

Jimmy I know the top end numbers from the owner ( was passed in the old boat quite easily) and have driven the boat on one occasion. I am nearly positive that he is running a 21x25 dqx wheel with medium cup. The efficiency of this boat is ridiculous. For the extra horsepower you have (610vs760(you did say 380hp right?) you're numbers seem slow.....still efficient but not exponentially so compared to the lower hp version. Like Capt Pat said cup is merely an efficiency adder when your on plane...it adds load but at higher rpm as it pushes more water off the tips

Leads me to believe you can do better things with wheels, at the risk of needing trolling valves to fit your user needs.

[frank price]

I run Acme's also and love them, though on a 33 Sportfish with 330's. I agree with what's being said about adding a little more cup if you want a little more load/ speed but beware, Acme doesn't run the cup all the way across the back edge like other prop manufacturers so if the guy you take it to decides to extend the cup all the way across, according to the tech guys at Acme, it will ruin the performance of them.I'm going through this right now and it kind of pissed me off. According to Acme it's very important that whoever tweaks their props talks to them first.

[JimmyG]

I run Acme's also and love them, though on a 33 Sportfish with 330's. I agree with what's being said about adding a little more cup if you want a little more load/ speed but beware, Acme doesn't run the cup all the way across the back edge like other prop manufacturers so if the guy you take it to decides to extend the cup all the way across, according to the tech guys at Acme, it will ruin the performance of them.I'm going through this right now and it kind of pissed me off. According to Acme it's very important that whoever tweaks their props talks to them first.

Yes Frank, I'm aware I talked to Jim at Acme and Atlantis propeller is doing the work, everyone is on the same page

[Bob H.]

Jimmy, impressive numbers, Tony Athens likes to see 3100 for those engines, as you start to load up with gear you want to make sure you can still hit that max rpm. Will give you many years and long life expectancy. Speed and usable speed are two different animals, I went with trolling valves but rarely use them Im propped for 26 knot cruise and still can idle around the dock without pissing off too many harbor masters. I still get pulled over on a regular basis by my local guy, even when blow boats pass me in the channel. One harbor patrol lit em up an pulled me over and said "I just wanted to know what kind of boat this was" , my response, "31..Bertram..1966...Sir"..BH

[bob lico]

i have same numbers as yours with 2006 cummins recon 315hp .i slowed wot. down from 38 because docking at 12knots piss off a few people at my dock and a few harbor masters. the good new was a dramatic higher speed (27knt.)for maximum fuel economy.i have radical props and the blanks come from Ron Ellis in jacksonville FL.at 2950rpm i am way under prop but 33 to 34kts is all you want. you have a build in accident waiting to happen with those "flaps" on the transom .when you go down the back of a 5' or larger wave. even with tabs all the way in up position they will push the bow down into the trough.you must be bow proud to cruise at 22knt.to 23knt. in 5+ seas. .i have had 6 brothers drive my boat and have taken at least 20 brothers and girlfriends,wife`s to verify this.i done everything possible to roll the boat like wot.lock to lock turns into the side of a wave .the reverse chine digs in and rudders hold her into a 90degree turn. i have driven and tested a thousand boats and nothing handles like a perfectly balance 31 Bertram.

[Rocky]

Yeah I listened to you Bob about tabs possibly getting you into situations you don't need so I removed them plus it cleaned up that area of snags from lines. My Skipjack had more than one occasion were they cut my line, one was a 40lb Salmon decided to dart under - uhhhhh that was maddening!

[JP Dalik]

Bob
Tell the truth on your engines. How are you getting 2950 out of a 2850 mechanically governed engine. Dead rack and WOT Chimeras engines rated at 330hp were 2850. What did you do to the pump?

What wheel are you swinging , whose, what rake, what diameter, what pitch, what shaft size. Jimmy should be faster for horsepower than you

[bob lico]

JP you know the story, I have posted it many times and demonstrated it at every rendervous with 20 or more bertram owners . Engine is mounted as one piece with gears,shaft with shaft log in free air thru bottom cut out.engine gears are are1/2" off bilge,structs are shimmed then shaft log is epoxy into place at 12 degrees with 5" extension covering shaft.water From PSS seal keeps shaft log cool.then you have cockpit " clean cool air" accelerated through D pattern under gunwale into engine intake.4" hot pipe into 6" exhaust to 6"mini max mufflers and 6" all the way back to transom. 0 back pressure, pump is bench and customized ( captain patrick caught on to that when we all started up at same time to leave Greenport all boat smoke except "Phoenix"but a little tell tale fuel dribble out the exhaust ) captain question me !! Anyways next year one bass over 40 and I will go over your Bosch 7100 pumps.14 people on board full fuel on plane in 5 seconds 38 wot. 315 recon cummins .greenport rendezvous. what i fail to mention is the harbor master broke my balls (as usual) coming in harbor at 6knt+ on one engine.

[JP Dalik]

Bob

You can still come for a ride and catch your 40 in the spring, but unless you can raise hell out of a 3196 CAT you'll be hard pressed to find a Bosch 7100 on the new boat.

[bob lico]

Yep forgot your in the big leagues now.cat 3196 out of my realm .this is photo from rendenvou with Harry babb doing the piolting he took it up to 38 with 14 on board and full tank. Don't want to go on and on with this but I wanted jimmy to PM. Me before engine installation or go back on posts. Boat should be around 40 but that is 90 percent in the installation ,props are just icing on the cake, BTW ,My advice on props ONLY apples to diesel power in excess of 500 pounds of torque.i desigh wheels to utilize this torque on over 300 hp cat,cummins diesels that normally spin there "wheels" and waste energy with the normal props and trim tabs.

[bob lico]

Cannot get photo bucket to come up onIPad

[bob lico]

ok on my office computer. the wise Captain whom caught the phoenix or i should say recognize something strange coming out exhaust instead of smoke a trickle of fuel indicating a detroit garbage truck motor or a tricked out cummins.

[bob lico]

[bob lico]

[bob lico]

The last photo is at wot.. Notice only 5' of boat is in the water!the boat is slightly bow proud. And entirely out of water.exhaust is shooting water 5' from transom this is maximum speed a 31' Bertram should ride at.wheels are Ron Ellis,3 blade 22" cut down to 21",raked 5 degrees,pitch is varible starting at 24" and cup is radical ( actually the entire blade is cupped right down to hub.)about 97 percent efficient.don`t forget we are not using conventional drive plates with springs .i have Vulkan direct drive .no pussyfooted around when you put it in gear there is not slipped and slide it grabs instantly 100 percent.

[JimmyG]

Bob, I am going to change tabs to smaller ones, I can't do with out them all together I use them to stabilize boat and for fishing in the Delaware bay short steep chop. As far as props I am going to try 20 x 26 Acme 4 blades with a light cup (offered to me at no cost to try) but I think i'll probably end up with what I have with more cup. Speed is not my major concern I want a fast dependable boat that I can fish and troll White Marlin with natural baits @ 5-6.5 knts 70 -120 miles offshore. I did move fuel tank and bulkhead back 3" and the boat rides so much better then my last 31, don't know if it was that or the extra weight of these iron engines.

[bob lico]

Jimmy I have been preaching for eight years it is all about weight aft. Of main bulk head. Moving a 1100 lbs of engine back three inches is tremendous (taking a eight pound anchor and 20' of chain out of anchor locker and put in rear cockpit area is also a move in right direction (law of levers) moving 20 pounds 30' ,it all adds up.there are so many "free" horsepower feature that. I could go on and on like fuel raccors are close to bilge in cockpit and fuel lines are 5/8" direct to fuel block.fuel (45 centane)is always as cool as possible .at that speed fuel economy left a lot to be desired so I changed to straight 23 1/2 pitch , Ron Ellis ,3 blade,21",4degree rake and full cup .new spec. 331/2 wot but max fuel economy at 2350 rpm and 27 knots..short chop you get up on top at 24 knots ( no tabs) there is no boat around that can stay with it in those 3 to 4' chop 25 knot winds.i also pilot a 36' see Vee with triple 275 varado's .no way in hell that boat or the 32' regulator with twin 300 yamaha can maintain that speed in those awful conditions.chances are you will be in chop with 2 to 3' waves but there is always a 6' out there and that's the problem the tabs will catch on the down side of wave at that speed and catapult you out the front window on bridge as bow hits and goes under next wave.you have a built 14 or more degrees in those shaft constantly pushing that bow down the faster you go the worst it gets .having tabs is like throwing a cement block to a drowning man in your situation (1800 lbs of torque). The key to having 380hp cummins is to back off the throttle to bottom of torque curve (1900-2000) and mantain bow proud 28/29 knt. At maximum fuel economy and ride the top of the waves at 20 to 45 degrees off the bow.i believe 26" pitch is a mistake you need that boat to go 5 /6 mph on one engine at idle to troll for bill fish/ tuna any more and you will shoot yourself in the foot with quest for top speed.Yes I have trolling valves but you just cannot slow the boat down with wild props .and don't ever attemp to menever with them.