CM Setup

[digginfool]

There's been some interesting threads about props, motors and gearing on here lately. Currently, I'm still waiting to see what Marine Power is going to do about my motor. After reading some of these posts, I can't help but wonder if there isn't something better I can do for my setup, prop and gear-wise. 15 foot DB with oval tube aluminum rigging, seating for 7; heavy pig of a boat. Power is an LSA. I have both a 2.38 Stinger and a 2.5 Ballistic I can use, and an 82" 4 blade NGR. I bought the prop while I had a BBC on the boat and it turned it at just shy of the 3 mark with the 2.38. With the LSA, can barely turn it at the 2 mark with the 2.38 and about 2-1/2 with the 2.5, which is pretty disappointing since the LSA was supposed to be more torque and hp than the 8.1. In skinny water, I can cruise 2,800 - 3,000 RPM. Deep water pushes me up to 3,600 - 3,800 RPM with a normal load and heavily loaded not unusual to be 4,000 or a bit higher; boat will fall off plane much below 3,400 RPM even lightly loaded. Would I be better off with different gearing (2.68) or shedding a blade and going back to the 2.38? My understanding is the NGR likes RPM which is why I considered that route but wondering if more gear might be the answer to get better cruise performance. Would like to avoid having to buy a new prop; a hub would be expensive enough.

[CarMotorBarge]

Do you have the dyno sheet for the motor? What do you want to spin the motor at WOT? Do you want push or fuel mileage?

[digginfool]

Only have the generic Chevrolet dyno sheet. Motor makes over 500 lb-ft torque from 2,500 RPM, peaking at 556 lb-ft at 4,000. Peak hp at 5,800, which is 550. I've always had the motor pitched for 5,400 RPM at WOT with both gearboxes.

[flying fish]

3 blade 82" Maximus. Governed 5250 WOT with 2.3 ratio. JMO-

Wait, didn't you already have this setup and got rid of it?

Prop and gear suggestion coming from that same Dumbass from Kansas that tried to tell you how under-rated your 8.1 was in torque. Remember?? Amazing how that weak sister 8.1 just spanks that supercharged LS in prop swung.

I am serious about the combination suggested. Good luck.

You have too much prop with either choice of ratios you mention and engine you are repairing. Dropping back to a 3 blade on your current prop is not the answer either. Again, JMO-

[John Fenner]

Best I can suggest, go for a ride on Geralds boat!

[scottyroll]

For a boat that heavy and the fact that you usually have it full with family/passengers, I can't help but think a bigger hull may suit you better for displacing the weight. Any of the power combo's you have tried should fit the bill IMO when mated to an appropriate and tuned hull.

Seriously, you've changed just about everything else on the boat

Good Luck Man

[Tony480]

The boat is heavy..want to make it run better...shed weight!

[digginfool]

3 blade 82" Maximus. Governed 5250 WOT with 2.3 ratio. JMO-

Wait, didn't you already have this setup and got rid of it?

Prop and gear suggestion coming from that same Dumbass from Kansas that tried to tell you how under-rated your 8.1 was in torque. Remember?? Amazing how that weak sister 8.1 just spanks that supercharged LS in prop swung.

I am serious about the combination suggested. Good luck.

You have too much prop with either choice of ratios you mention and engine you are repairing. Dropping back to a 3 blade on your current prop is not the answer either. Again, JMO-

It was actually a 3 blade 80" Powershift. I did run that prop with the LSA for a month or so while my NGR blades were repaired and that was with the 2.38. Best way to describe the performance is 'woeful.' Loud and no push. But, yes, I did sell that prop almost a year ago. As far as shedding weight, probably the only way to get it on a diet would be to completely replace the rigging. Not gonna happen. I've dumped a ridiculous amount of money into this thing as it is. A gear ratio change, maybe a prop, but that's it. I'm totally spoiled by my sled and don't have any big ideas for my barge anymore. Just want to polish what I've got.

[flying fish]

Diggin

I hear Tony's boat is tuned Phenominal. Some guy from North Central Kansas tells me this.

Maybe you could bump into Tony and he help you tune your hull & rigging.

[John Fenner]

For a boat that heavy and the fact that you usually have it full with family/passengers, I can't help but think a bigger hull may suit you better for displacing the weight. Any of the power combo's you have tried should fit the bill IMO when mated to an appropriate and tuned hull.

Seriously, you've changed just about everything else on the boat

Good Luck Man

Spot on, the DB likely is rated at 7'6" wide but that is at the gunwale not the bottom, these boats don't displace weight as a true 7'6" bottom boat and fall off plane easily.

[SWAMPHUNTER45]

Sounds like you finally need to break down and try a big inch Cadillac instead of the new stuff Diggin.....lol

[JLACOUR]

Can you post a pic of your boat? I have a 16x8 DB deckover with an lsa and absolutely love it.

[CarMotorBarge]

Everybody is hating on the fool. So I think we need to get back to basics to better understand this problem. Here is a couple of items to consider:

1. Need to remember what the 1, 2, and 3 marks on the Sensenich hub mean. The 2 mark identifies the pitch at which the prop is the most efficient at transferring HSP to thrust while you are "stuck". Anything above 3 means you are slapping too much air and anything below 1 means you aren't biting enough air. Again this is while you are "stuck". So trying to create more thrust by adding more pitch past the 2 mark while you are "stuck" isn't particularly effective. You are better off adding more prop speed and keeping the pitch close to 2.

2. This is where it starts getting a little interesting. When you are moving, dynamic thrust takes over and you need more pitch to maintain the efficiency of the prop to convert HSP to thrust. This is why planes have variable pitch props and this concept has been demonstrated by the Water Walker Concept boat. As you get faster (MPH), you need more pitch to maintain this efficiency. That is why it appears that boats run better with more pitch.

3. More prop diameter creates more thrust as long as you can put enough pitch in the prop. The larger disc area generates more thrust. However, the increased prop diameter causes you to give up snap. This is why you see all of the race boats with smaller props. They are trading thrust for snap when racing 400 feet. More prop diameter also lowers your top end speed (MPH). This is because there is less pitch and more blade area to cause wind resistance.

4. Wide and super wide blades make more static thrust when you are "stuck" than skinny blades. The skinny blades shine at higher speeds (MPH) and create less vibration.

5. A 4 blade prop will tighten the thrust curve and produce thrust sooner than a 3 blade prop. So an engine running 5000 RPMs with a 4 blade prop will make more thrust than the same engine running 5000 RPMs with a 3 blade prop (I am assuming the same gear ratio and the pitch in each prop is reasonable). The same is true when comparing a 3 blade and 2 blade. The 3 blade prop will produce thrust sooner than a 2 blade prop.

6. HSP is what determines how much prop you can turn and an engine will turn the maximum amount of prop where the maximum HSP is made. You don't even need to look at the torque curve. All the torque curve tells you is how much the prop will accelerate. Torque isn't useful until you know how much torque over distance and time (BTW this is HSP). Assuming the dyno sheet you provided is accurate, your engine will turn the most prop at 5800 RPMs.

So to address your specific combo. The NGR is a great prop. Honestly any wide or super wide prop from any manufacturer is a great prop for a barge. You want a 4 blade because it will produce thrust sooner. The 3 blade is better for barge racing. A 4 blade NGR blade does really good turning it at 2100 to 2200 prop RPMs at WOT. You get a compromise between fuel mileage and good thrust. I do not think you have too much prop. With the 2.55 ratio at 5400 RPMs, you are turning the prop at 2100 RPMs and you are still pitched at 2.5. I personally like to be pitched at 2.5 to 3 because it gives you a good compromise between static thrust when you are "stuck" and dynamic thrust.

I would pick a 2.68 ratio. This is because at 2100 prop RPMs, the engine will be at 5600 RPMs and at 2200 prop RPMs, the engine will be at 5900 RPMs. This is right around where the 4 blade NGR likes to be. Also with the 2.68 ratio, you could change pitch and vary the WOT engine RPMs any where from 4800 to 5800. This gives you a lot of flexibility for getting better fuel mileage, making more thrust, or a compromise between the two.

So here is a couple of cheap things to look at. Have you verified that your tach is reading correctly. Most people don't realize how much error is in a tach even new from the factory. Have you experimented with adding more pitch to the prop and reducing WOT RPMs? This will lower your cruise RPM and improve fuel mileage. However, you give up some dry running ability. Do you have any jacks in the boat? Have you experimented with them? More flat bottom will help you plane better, but you want a little round for running the hill. Also what size of cage wire do you have? Less wire reduces air resistance and gets more air to the prop. Ultimately everything is about trade offs.

Also I do agree with John that a sled would out perform that old DB hull. It is only money and you can't take it with you.

[Tony480]

Pitch marks don't mean shit..use a protractor. I ran a 4 nlade and when they were all set the same with a protractor 2 blades were on 1.5 and two blades were on 3. I never ran a 4 blades ngr..but have ran the 82" 4 blade r and with 14.5° degrees at the tip it would turn 5800 and an 82" 3 blade ngr with 18.5 ° at the tip ot turns 5900

[John Fenner]

Airboat performance is 70% hull and 30% powerplant, I and my mentor have proved this by outrunning a hunt boat with a well built PE-60, you can have a worn engine on a good hull, destroy a big engine on a schitt hull.
Not cutting bad on any manufactures but it has been proven!!!!

[Deano]

CMB, Everybody ain't hatin' on diggin'. . .

You just missed the beginning of the three year old ongoing saga.
http://www.southernairboat.com/phpBB3/v ... 48&t=55035

It's interesting to note that along the way he documented that the later, higher HP engine would not turn the same given prop at the same pitch setting as the earlier, lesser HP big block.

It almost looks as though the torque produced by the earlier engine may have been relevant.

[John Fenner]

Not one bit of hate on my part, but if that LSA was on a real boat, it would be a total different story!!

[Deano]

For what it's worth John, I agree with you whole heartedly.

That boat with that load is trying to act like a displacement hull, and consequently requires an inordinate amount of power. Given the load he totes, he would be better off with a bigger and wider hull.

[John Fenner]

Like I said, he needs to take Mr Geralds boat for a ride, total different story, 34.5 MPH at 2200 engine RPM on an un trimmed and over pitched packaged boat.
Mr Gerald can attest!!!

[digginfool]

Like I said, he needs to take Mr Geralds boat for a ride, total different story, 34.5 MPH at 2200 engine RPM on an un trimmed and over pitched packaged boat.
Mr Gerald can attest!!!

I would if he wasn't working all weekend, every weekend. Tony, point taken as far as the marks are not for pitching the prop and are there only for a reference. I use a digital gauge for pitching my prop. I level the trailer so that the bottom of the boat is at zero (I know, I should be using the motor but there are no flat spots on the motor. Besides, it's more important that all four blades are pitched the same), next, I measure 4 inches in from the tip on each blade and mark with an erasable marker, then adjust each blade at the same point of rotation. Not that it's relevant (since I don't know if the blades are referenced to perfectly vertical), but using this system, I can put about 11-1/2 degrees in using the 2.5 box. That being said, I do believe you are running quite a bit more HP than I am.

I know my hull is not as good as the hulls DB makes today and the extra weight of the oval tube rigging isn't helping. I'm just wondering if it would make enough difference changing the gear ratio and be able to add more pitch, not to mention take some of the load off the engine, to be worthwhile. One other thing that is on my mind is if the LSA was running on 7 cylinders from day one and that's why it never performed better than the 8.1. The 8.1 was supposedly 465 HP and 500 TQ while the LSA is supposedly 550 HP and 556 TQ. I would have thought that it would have been a very noticeable difference, especially after losing over 200 lbs by dumping that cast iron anchor for the all aluminum engine.

[John Fenner]

Hmm, 7 cyl LSA, was a noticeable difference in the FWC techs boat too, does that boat have polymer?

[Dirtman]

Diggin, there seems to be a consensus that you have too much weight and that it will be hard to get the performance you want without some major changes such as a new gear ratio. Have you given any thought to a new hull to switch your rigging over to? You have at least one gearbox that won't fit your needs, and a marketable used hull. If one of the boxes you currently have would be a good fit with a hull better suited for the weight you have all it might take is a trip to a hull builder to get some precise measurements and get a 16x8 built to get more bottom. I realize that there might be some fitment issues with the cage being a little narrower but I believe that could be addressed. I know this sounds like a n expensive option but when you consider that you would have some pieces to sell off to cut the total expense and have something in the end you would be happy with. Just a thought

[406 JAMIE]

its simple just build a bbc and put it back on the boat it worked before with no issues.and there u go use 1 of those gearboxs u have and bbc u would be wayyyyy more happier and send that LSA back where it came from.because ur trying to sound like ur some NASA guy with ur boat trying to fix it.and i had a old 98 DB with bbc 414ci 500hp on 87 pump gas 7-11 best and run all day with a load in it on dry so quit trying to bring NASA in to help u out ur not building the SHUTTLE.jmo y all be safe.

[SWAMPHUNTER45]

I am anxious to hear how Marine Power treats this defect and how the matter is resolved.

You would think they would have you return your engine for an autopsy and send out a "new" replacement engine or refund your purchase and part ways.

That LSA is fancy stuff but for me simple big inch torque works best pushing a heavy load.

[406 JAMIE]

I am anxious to hear how Marine Power treats this defect and how the matter is resolved.

You would think they would have you return your engine for an autopsy and send out a "new" replacement engine or refund your purchase and part ways.

That LSA is fancy stuff but for me simple big inch torque works best pushing a heavy load.

ty sir X2.what u spent DF u could of got a merlin/dart alumn bbc 632ci shed weight and keep ur low rpm TRQ and run a nice set of h- beam alumn rods and alumn topend ur wright ABOUT the same weight as cast iron sbc.just get ur $$$$ money back and go back to BBC set up save in long run.jmo y all besafe