3 or 4?

Airboat propeller discussion.
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digginfool
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3 or 4?

Post by digginfool » Sun Feb 01, 2015 12:17 pm

I've put nearly 15 hours on my boat since getting it up and running again. The LSA performance is nearly identical to the old BBC, just a lot lighter. I don't use the trim tab anymore. Boat runs flat with no porpoise at all. I'm hitting same top end, burning the same amount of fuel, coming out of the hole about the same and boat is still a bulldozer in the heavy stuff. Currently, I'm running a 4 blade, 82" NGR at 5,100 at about the 2-1/2 mark with a 2.38 Stinger. I'm wondering if maybe that's too much prop. I've got a three blade Powershift hub but it was for an 80" setup. The hub is definitely smaller than my current hub, probably by 3/4" on each side. I'm thinking about trying the boat out with 3 blades but wondering if I will be able to put enough pitch to hold motor with 1 less blade and perhaps as much as 2" less diameter. What do you all think? What kind of change in performance should I expect, if any?
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HuntingBigun
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Re: 3 or 4?

Post by HuntingBigun » Sun Feb 01, 2015 12:42 pm

Brad had a 550 Thunder on old DB deckover when I meet him ran 3 blade WW it was a beast on the ground, but I try 3 blade NGR just use your hub and pitch them rule of thumb is 1 blade = 1 pitch mark so less diam but I try it heck you already got the hub.
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Re: 3 or 4?

Post by Joe » Sun Feb 01, 2015 2:17 pm

Damn,all that extra money for the Lsa and it's the same performance and fuel economy as your bbc? That sucks
Compromise is for those that cant get it done!!

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trailerdon
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Re: 3 or 4?

Post by trailerdon » Mon Feb 02, 2015 7:35 am

I would not say it sucks. Shaved hundreds of pounds and no longer needs a trim tab.

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Re: 3 or 4?

Post by Oilfield Trash » Mon Feb 02, 2015 7:54 am

What's your cruise rpm? I know there's a lot of variables there but on average what are you cruising at?

On my LSA I'm turning it right at 3k on cruise. RPM is pretty much speed matched at cruise (3,000 = 30mph). 4 blade 82" R and CH4 2.5 ratio. WO is around 5400. I have no idea what the pitch mark is, but the blades are each at 12.4 degree's.

I seen a few Hamant boats running 3 blades on their LSA set ups. I wouldn't mind driving one to see the difference.

I'd really like to port my intake for a little HP gain but being I've never done one, I'll probably try and find a place around Cocoa that can hook me up.

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Re: 3 or 4?

Post by DAGWOOD0520 » Tue Feb 03, 2015 2:33 pm

What was the difference in HP between the old and new engine, also what pitch mark and RPM did it turn with the BBC?

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Re: 3 or 4?

Post by farmboy » Tue Feb 03, 2015 3:26 pm

If it where me I'd try the 3-bld....
14ft JB Hull,Lycoming GSO480 w/water-meth injection,Sensenich 3-blade "R",ButtRaxx seats,B&S Trailer.

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Re: 3 or 4?

Post by SteveReid » Fri Feb 06, 2015 8:21 pm

I think I would try less pitch before changing if you're wanting to turn more RPM's. You will be turning that LS HP up soon anyway.

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Re: 3 or 4?

Post by digginfool » Fri Feb 06, 2015 8:44 pm

After looking at the prop again, I'm closer to the 2 mark than the 2-1/2. I know I had more pitch than this with the BBC. The mid-range seems to pull better than with the old prop but a little more sluggish out of the hole. I figure, what the heck. I've got the 3 blade hub, what do I have to lose? I'm going to ride all weekend and I'll keep my GPS with me so I can keep track of fuel consumption, max speed, cruise speed/RPM. Unfortunately, a GPS doesn't react to changes of speed quickly enough to measure acceleration so that will have to be seat of the pants. On Tuesday, I'm going to swap the hubs then ride on Wednesday to compare. I'll definitely post my results.
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Re: 3 or 4?

Post by digginfool » Sat Feb 07, 2015 3:16 pm

WTF?!?! I take my boat out today, launch and start to pull away from the landing. I go to accelerate, get up to about 2,000 RPM and boat starts shaking like mad. I immediately turn off the engine and walk back to see if there is something obvious going on. Nothing wrapped in prop, blades all feel tight, nothing shakes, so I try it again. Same thing; 2,000 RPM and boat feels like it's going to shake apart. Idle back to trailer, can't run it up high enough to power load so I have to crank it on, filling my boots in the process. :banghead: :banghead: Take boat back to house. Check for loose bolts; everything fine. Check box mounting bolts; all good. Start to check that blades still pitched correctly. Check first blade, rotate prop to check second blade. It's good. Step off stool to rotate prop and notice water streaming down bottom blade. How does this happen? I used my boat last Saturday night and everything was fine all night long. Washed boat on Sunday, put in warehouse Monday, pulled out this morning. It's been sitting high and dry, out of the weather ever since I put it back together. Only water it's seen is when I've washed the boat. I've owned this prop for a year and the boat has sat out in summer monsoons, endured countless washings and never once had water in the blades. Sent the prop to Sensenich for Duracoat and put nearly 15 hours on prop with no issues. Suddenly, I have water in the blade. I'M NOT BLAMING SENSENICH SO DON'T EVEN START WITH ME!! :angry5: How do I fix this or do I have to send the blade back?
“When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that glorifies it” - Bastiat

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Re: 3 or 4?

Post by Scarecrow » Sat Feb 07, 2015 3:57 pm

Diggin, I might be wrong but I thought they were plugging the props now to stop water intrusion. :scratch: :rebel:

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Re: 3 or 4?

Post by digginfool » Sat Feb 07, 2015 4:03 pm

I turned the prop blade by blade. Three of the four drained out water. Total amount of water probably wasn't much more than a few tablespoons, certainly not even a quarter cup. But, I suppose at the end of a blade spinning around 1,000 RPM, it's enough to cause quite an imbalance. Still feels like a bit of vibration remains but don't know if that is due to water in the blades or just oscillation due to sitting on the trailer. Gave each blade about 5 minutes each, along with rocking back and forth, to drain whatever was inside. Sure is a disappointment. Hopefully, somebody from Sensenich can weigh in and advise a proper course of action.
“When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that glorifies it” - Bastiat

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Re: 3 or 4?

Post by SteveReid » Sat Feb 07, 2015 7:00 pm

That sucks!! They are nice people, Rich and I was over there last week and they rebalanced his. If you had the time I would take them up there because the guy came up front and explained everything and had his ready the following day. Very nice people.

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Re: 3 or 4?

Post by wildcard » Sat Feb 07, 2015 8:10 pm

carma.thats what you get for bad mouthing me :stirpot: :violent1: :rebel:

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Re: 3 or 4?

Post by aherr520 » Sat Feb 07, 2015 8:28 pm

digginfool wrote:I turned the prop blade by blade. Three of the four drained out water. Total amount of water probably wasn't much more than a few tablespoons, certainly not even a quarter cup. But, I suppose at the end of a blade spinning around 1,000 RPM, it's enough to cause quite an imbalance. Still feels like a bit of vibration remains but don't know if that is due to water in the blades or just oscillation due to sitting on the trailer. Gave each blade about 5 minutes each, along with rocking back and forth, to drain whatever was inside. Sure is a disappointment. Hopefully, somebody from Sensenich can weigh in and advise a proper course of action.
that's what happened to mine sensenich told me to drill a small hole to drain it, I need to send them back and have them resealed
aaof member

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Re: 3 or 4?

Post by Tony480 » Sat Feb 07, 2015 9:17 pm

They make new caps for the ends that fix that issue...send them back

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Re: 3 or 4?

Post by digginfool » Sun Feb 08, 2015 9:16 am

They had my blades when they announced that. It looked like new end caps already when I took them out of the box.
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Re: 3 or 4?

Post by Scarecrow » Sun Feb 08, 2015 9:33 am

Maybe they put water in them before plugging them. :lol: :rebel:

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Re: 3 or 4?

Post by digginfool » Thu Feb 12, 2015 5:26 pm

The great 3 blade experiment failed before it ever launched. Swapped out the hubs today. First pull, set at about the 3-1/2 mark (all relative with the Powershift hub since it has about a 1/8" gap). Got to 3,000 RPM and didn't like the vibrations I was feeling. Shut down, re-pitched, made sure gap on the hub was same all around and tried again. At this mark, blades had a lot of pitch and it showed as the engine only turned up to 4,200 RPM. Took it down to around the 2-1/4 mark and tried again. Again, got to 3,000 RPM and vibrations set in. Shut down, re-pitch, made sure the gap was right and tried again. Got up to around 4,500 RPM, still had plenty of throttle left, no mad vibrations but it kind of hit me; this three blade set-up is noisy and definitely some harmonics that I only felt when I had the Powershift blades before. I shut the engine off and put it back in the warehouse. I don't even care to find out how it will run with the 3 blade. I'm spoiled by the smoothness of the 4 blade prop. So, now I either live with the performance I have or go to a different gear ratio. I've noticed most people running LS motors are using either a 2.55 or 2.68 ratio (I'm running a 2.38 Stinger). Need some input. Thanks!
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Re: 3 or 4?

Post by DynaMarine » Thu Feb 12, 2015 6:32 pm

I'm a fan of the 2.55 with the LSA as well as 2.68 and 4-blade.
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Re: 3 or 4?

Post by digginfool » Fri Feb 13, 2015 3:29 pm

MILSAR wrote:I'm a fan of the 2.55 with the LSA as well as 2.68 and 4-blade.
I appreciate the response, Shane. How will the higher ratio affect overall performance? By my calculations, the change will add around 90 lb-ft of peak torque and would require about 365 RPM to match same prop speed that I have at 5,100 RPM with the 2.38. But, I guess the better question is, are you trying to keep prop speed the same or engine speed the same? How much more pitch would you be able to add? Would the higher ratio result in a higher cruise RPM or would the additional pitch keep engine speed same or lower? What about fuel consumption? I know that's a lot of questions but a new box is a lot of money so want to make sure I'm spending wisely. I could just as easily add $3,500.00 in engine work and possibly achieve a better result (although I know my current box is worth at least $2,000.00 so I would really only have $1,500.00 total outlay).
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Re: 3 or 4?

Post by flying fish » Fri Feb 13, 2015 5:04 pm

Try a new 3 blade Sirius 82". Govern 5100 Static. JMO-
All the way from Kansas.
Show him what it will do with the 2.3 Plum :-)
15' DB - 6.2 LSA - 4 blade 82" R - 2.52 CH-4

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Re: 3 or 4?

Post by flying fish » Fri Feb 13, 2015 5:10 pm

Or, go 2.68 and a 3 Blade 82" S.
Design her to run strong as hell on the ground and water is not necessary. Then, you got a strong boat. Again, JMO-
15' DB - 6.2 LSA - 4 blade 82" R - 2.52 CH-4

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Re: 3 or 4?

Post by DynaMarine » Fri Feb 13, 2015 7:05 pm

Now we're talking Chris. 2.88/2.9 gearbox with 3-blade 82" Superwide. Pitch it on 2 3/4 to 3 and turn it 5600rpm WOT on the water.
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Re: 3 or 4?

Post by digginfool » Fri Feb 13, 2015 11:35 pm

MILSAR wrote:Now we're talking Chris. 2.88/2.9 gearbox with 3-blade 82" Superwide. Pitch it on 2 3/4 to 3 and turn it 5600rpm WOT on the water.
I don't know, guys. The smoothness of a 4 blade vs. a 3 blade? Plus, running a 3 blade takes so much pitch, more prop noise, and the harmonics a 3 blade creates (IMHO)? I don't know. It seems you could spend $10K just trying to figure it out. :?
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