Another 500 DD

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DGroves
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Another 500 DD

Postby DGroves » Thu Sep 05, 2019 2:59 pm

New to airboats here. Picked up a 18x7.5, about 25 inch sides a while back for a new Bowfishing boat a while back and just now getting into getting the motor rebuilt and a new prop. I’m not sure of the make on the hull but it’s all 1/8 aluminum except the t-bars and some bracing under the front deck. Steel rigging/engine stand with poly on the bottom. We got it all ready to fish and the first night out it started spraying coolant out of the exhaust so I’m hoping it’s just a blown head gasket and nothing major. Right now it has a 78 inch wood prop that’s 11 inches wide. This is the first airboat I’ve ever been around and only been on one other and it was on a tour in florida. I’m wanting to stay dd mainly for the money and to use this boat to learn with and hopefully get a new boat in a couple years. I already have a good engine builder that’s been around 500s a good bit but I’m trying to figure out what prop to put on it. It was a dog in deeper water and where we fish we have a lot of it. We’re not going too crazy on the engine build, just a cam, new valve train, maybe new carb so nothing wild above factory hp. I don’t know the weight of the boat but it feels light and seems like the wood prop spins up fast and just makes a lot of noise before it goes to work. I know it’s been beat in the ground and all the threads kinda say different things about different boats but if any of you guys were in my shoes what prop would you go with and why? Main thing we want is good low-mid range push to run down fish.

Thanks

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Re: Another 500 DD

Postby One Eyed Gator » Thu Sep 05, 2019 3:59 pm

Welcome to the addiction

That is a big boat for a DD but a lot of mullet fisherman is the gulf ran big boats with caddys
I had a 15' x7-6 rivermaster with a 472 caddy bored .020 over and a few other upgrades always ran good
Well there are 3 main prop manufacturers
Sensenich
Whirlwind
Waterwalker

All 3 make a prop that work well on your boat. I would call all 3 and get a recommendation from them. Then do a little research on SA.
Most guys run 70, 72 ,74 or 76" 2 blade depending on the motor.

I would post a pic of the rigging setup - radiator needs to be close to the prop to keep it cool if you idle for long period of time.

Also the caddy thermostat is different then most there was a thread on here I think posted by deano about the caddy thermostat. A regular gm thermostat won't work. Caddy water pump has a bypass below where the stat sits.

I plugged the bypass with a freeze plug (put a 1/8" hole to let air out) and ran a gutted thermostat. boat ran 160-170 all the timeand it would idle at 600 as long as I needed it.

OEG

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Re: Another 500 DD

Postby DGroves » Thu Sep 05, 2019 4:36 pm

One Eyed Gator wrote:Welcome to the addiction

That is a big boat for a DD but a lot of mullet fisherman is the gulf ran big boats with caddys
I had a 15' x7-6 rivermaster with a 472 caddy bored .020 over and a few other upgrades always ran good
Well there are 3 main prop manufacturers
Sensenich
Whirlwind
Waterwalker

All 3 make a prop that work well on your boat. I would call all 3 and get a recommendation from them. Then do a little research on SA.
Most guys run 70, 72 ,74 or 76" 2 blade depending on the motor.

I would post a pic of the rigging setup - radiator needs to be close to the prop to keep it cool if you idle for long period of time.

Also the caddy thermostat is different then most there was a thread on here I think posted by deano about the caddy thermostat. A regular gm thermostat won't work. Caddy water pump has a bypass below where the stat sits.

I plugged the bypass with a freeze plug (put a 1/8" hole to let air out) and ran a gutted thermostat. boat ran 160-170 all the timeand it would idle at 600 as long as I needed it.

OEG



Yeah I know it’s kinda big for what it is, and I definitely don’t expect it to run like a 40k boat either. I believe there’s MAYBE 1.5-2 inches from the paddles to the radiator cause I was looking at the clearance there and thought dang I didn’t have much room to play with when I put a new one on. Before it blew the hg it would run on pretty good(don’t know what mph or rpm, it was before I fixed the gauges) but just took forever to get up on pad. Is 3000k rpm about the max when it comes to dd props? And I just changed the water pump out...I hate the way it mounts to that other plate but it is what it is. I’ll be sure to tell the engine guy about what you just said, I appreciate it!

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Deano
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Re: Another 500 DD

Postby Deano » Thu Sep 05, 2019 9:02 pm

That thermostat thread referenced above can be found here:
https://southernairboat.com/phpBB3/viewtopic.php?f=48&t=69615&p=675407
This is vital information to be aware of if you are going to be running a Caddy big block.

After a hundred upgrades over ten years on a similar setup, I can tell you without giving it ANY thought that
the SINGLE BIGGEST improvement ever made was going from the ol' woody to a two blade composite prop.

Realistically, the difference between the big three prop manufacturers will be less than 5%, so your preference and/or what you can find a deal on may very well be your best bet. You will find over time that difference is less than you will sacrifice by not having everything else set up correctly. The fact that you're talking about such a big boat (for a DD) will also compound the penalty to be paid for improper setup.

Diameter trumps pitch, so you ideally want as big a blade as you can effectively turn.
Obviously, this is contingent on how strong your engine is. A regular, healthy 500 should
swing at least a 72 or possibly a 74 inch prop in most cases.

IMO, even if it is fresh AND you could effectively turn it, a 76 would be to much of a good thing.
Remember that the noise you got from that woody was largely due to TIP SPEED.
Diameter is the parameter that allows you to keep that variable under control.
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
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Re: Another 500 DD

Postby DGroves » Fri Sep 06, 2019 2:01 pm

Deano wrote:That thermostat thread referenced above can be found here:
https://southernairboat.com/phpBB3/viewtopic.php?f=48&t=69615&p=675407
This is vital information to be aware of if you are going to be running a Caddy big block.

After a hundred upgrades over ten years on a similar setup, I can tell you without giving it ANY thought that
the SINGLE BIGGEST improvement ever made was going from the ol' woody to a two blade composite prop.

Realistically, the difference between the big three prop manufacturers will be less than 5%, so your preference and/or what you can find a deal on may very well be your best bet. You will find over time that difference is less than you will sacrifice by not having everything else set up correctly. The fact that you're talking about such a big boat (for a DD) will also compound the penalty to be paid for improper setup.

Diameter trumps pitch, so you ideally want as big a blade as you can effectively turn.
Obviously, this is contingent on how strong your engine is. A regular, healthy 500 should
swing at least a 72 or possibly a 74 inch prop in most cases.

IMO, even if it is fresh AND you could effectively turn it, a 76 would be to much of a good thing.
Remember that the noise you got from that woody was largely due to TIP SPEED.
Diameter is the parameter that allows you to keep that variable under control.



I’ve check out both Sensenich and Whirlwind and I’m seeing pretty similar numbers on both sides when it comes to the same prop from both companies. Their 2 blade 72 say around 2800 give or take and 3000 for the 3 blade in the same length and width. Why is that? I guess main thing is I just wanna do it once. And maybe I’m wrong it just seems like I’d be more in the power of the motor at 3000rpm than I would 2-300 rpm less. Are the composite props lighter than the wood?

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Re: Another 500 DD

Postby SWAMPHUNTER45 » Tue Sep 10, 2019 1:50 pm

Much lighter!

Hard to beat the Sensenich Q or NGQ on a DD Caddy for good all around performance.....just sayin :stirpot:

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Re: Another 500 DD

Postby Slidin Gator » Wed Sep 11, 2019 12:14 am

2 blade for sure. You are thinking right on rpm. Unless you have an exceptionally built caddy, it’s just coming in at 3k. Sesinich Q or Whisper tip are equally good choices. 72” is probably optimum. NGQ is for motors (AV) already making torque in the low 2k range. The NGQ drops off at the high end.

10-1/2” wide,2 blade turning as loud as you can stand is what you want.
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

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Re: Another 500 DD

Postby nebraskaairboater » Wed Sep 11, 2019 9:46 am

Caddy is a low rpm torque motor. I ran a 74" Q when I was DD and it ran really good. Ran dry OK on a 78 15' Panther Aluminum Hull with heavy rigging. (Dry in Nebraska anyway LOL)Good Timing chain set for reliability advanced 4*. There are some cams out there for DD application if you check around that might pick up some power. I set mine to turn 2750 ish WFO. The RPM listed usually are the safety (Warranty) limit for the prop. Optimal rpm varies for each application. They are adjustable so you can find what rpm works best for your boat and they style of boating you do.
Dan Porter, Jr.
Fremont, NE
16 x 8 1971 Flat Bottom Fiberglass Hull / 454 Chevy/ 2.38:1 OX Drive / 80" 3-Blade Sensenich S

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Re: Another 500 DD

Postby DGroves » Sat Sep 14, 2019 3:56 pm

nebraskaairboater wrote:Caddy is a low rpm torque motor. I ran a 74" Q when I was DD and it ran really good. Ran dry OK on a 78 15' Panther Aluminum Hull with heavy rigging. (Dry in Nebraska anyway LOL)Good Timing chain set for reliability advanced 4*. There are some cams out there for DD application if you check around that might pick up some power. I set mine to turn 2750 ish WFO. The RPM listed usually are the safety (Warranty) limit for the prop. Optimal rpm varies for each application. They are adjustable so you can find what rpm works best for your boat and they style of boating you do.


That’s what I’m planning, just a cam, some headwork and the small stuff. I guess I’m more or less wanting to know how different it would run between say a 72-74 inch 2 blade vs a 72 inch 3 blade of the same model prop. What characteristics one would have vs the other cause it’s a bigger boat. The JM series Sensenich in particular

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Re: Another 500 DD

Postby SWAMPHUNTER45 » Sun Sep 15, 2019 8:39 am

In general terms what you should experience with a 500 is the 2 blade Q in most instances will be a strong contender for both speed, push and snap. Depending on you engines strength will dictate between 72 or 74. Blu ran a true 10:1 motor with slightly larger valves and a bit of mild porting. He had a custom cam, factory intake and 650 cfm Edelbrock carb. His ignition was an Accel HEI and his curve was done to match a direct drive application. This was a flat tappet engine that on a 13ft 6inch JW hull would run in the 60s and had no trouble pushing dry ground with 3 people in it. Bottom was done with SlickBottom. He would spin the 74 Q at 3,000 pitched near its 3 mark. A very versatile pairing of prop and power.

I personally ran a 76 NGQ on a 8.75:1 roller engine. It had decent response and pushed very well. Most 500's are not going to handle a 76 but rather a 72 would be the best option for the 90% of DD Caddys out there. Your snap is going to depend on your engines power, tune and cam choice. The NGQ is a little wider blade (12 inch) in the DD world think of it as a baby S blade. With the winglets they run up to 2850 safely.

My two other DD friends have run a 3 H blade configuration. The Sensenich H blades were narrower (8 inch) than the Q's (10.5 inch) and requires them to spin up making it a noisy ride. Not to the Warp drive level but fairly noisy. The one set up was on a bigger boat and I can't advise the cam but most likely it had more duration than needed. Excess duration favors higher rpm. The other paring is in a race boat / hunt boat sled with a highly modified engine with nitrous. It routinely sees excessive rpm and is a poor case study. That said it's fast.

Mr Branch has near 30 years of experience doing this and if you ask him what prop best matches your engine I am sure he could give you an answer that is accurate.

For the record his boat will have Q blades albeit it's a freak of nature being a 570 inch direct drive so it is gonna have 3 blades.

Hope this helps

Biggest thing is head prep or choosing the right head and matching the best cam. Stock intake with a spacer and super long tube headers help also.

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Re: Another 500 DD

Postby DGroves » Sun Sep 15, 2019 6:41 pm

SWAMPHUNTER45 wrote:In general terms what you should experience with a 500 is the 2 blade Q in most instances will be a strong contender for both speed, push and snap. Depending on you engines strength will dictate between 72 or 74. Blu ran a true 10:1 motor with slightly larger valves and a bit of mild porting. He had a custom cam, factory intake and 650 cfm Edelbrock carb. His ignition was an Accel HEI and his curve was done to match a direct drive application. This was a flat tappet engine that on a 13ft 6inch JW hull would run in the 60s and had no trouble pushing dry ground with 3 people in it. Bottom was done with SlickBottom. He would spin the 74 Q at 3,000 pitched near its 3 mark. A very versatile pairing of prop and power.

I personally ran a 76 NGQ on a 8.75:1 roller engine. It had decent response and pushed very well. Most 500's are not going to handle a 76 but rather a 72 would be the best option for the 90% of DD Caddys out there. Your snap is going to depend on your engines power, tune and cam choice. The NGQ is a little wider blade (12 inch) in the DD world think of it as a baby S blade. With the winglets they run up to 2850 safely.

My two other DD friends have run a 3 H blade configuration. The Sensenich H blades were narrower (8 inch) than the Q's (10.5 inch) and requires them to spin up making it a noisy ride. Not to the Warp drive level but fairly noisy. The one set up was on a bigger boat and I can't advise the cam but most likely it had more duration than needed. Excess duration favors higher rpm. The other paring is in a race boat / hunt boat sled with a highly modified engine with nitrous. It routinely sees excessive rpm and is a poor case study. That said it's fast.

Mr Branch has near 30 years of experience doing this and if you ask him what prop best matches your engine I am sure he could give you an answer that is accurate.

For the record his boat will have Q blades albeit it's a freak of nature being a 570 inch direct drive so it is gonna have 3 blades.

Hope this helps

Biggest thing is head prep or choosing the right head and matching the best cam. Stock intake with a spacer and super long tube headers help also.



The fella that has it is supposed to let me know which 500 it is and then we’re gonna go from there when we find out. I’m not 100% positive on what rpms this 78 Woody was turning (rpm gauge didn’t work half the time) but to me it sounded and felt like it was gonna fly apart but I still had peddle left, I never held it wide open and even with it running like crap to me it still felt strong once it got on plane. I’m not worried about top speed long as it’ll cruise good. A lot of the water we fish is pretty dirty and with my kicker boat we’d be stuck in the mud or up on a sandbar before we knew it because we couldn’t tell how deep the water was. The guy I got the boat from said he had it stuck a time or two at the same place I was just talking about. Don’t know how he drove it or what he did to get stuck but I definitely don’t want that to happen by accident at 2am with no cell service. I’m still reading over threads on here. Wish I could run across someone’s that’s went from one of the 2 blades you speak of to the 72 whisper tip or 72 jm series 3 blade on a dd...most of what I can find are some of the older stuff like the h series and whatnot.

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Re: Another 500 DD

Postby SWAMPHUNTER45 » Sun Sep 15, 2019 9:26 pm

My bet is a 2 blade 72JW will be your best option and much like a Q/NGQ hybrid. When your ready to buy call Darrin at Sensenich my bet is he will concur.

You have to get an accurate tachometer it is a safety concern. When a prop fails it becomes a bomb and on a Caddy it can lead to the crank breaking and shizt flying everywhere. Wasn't but a month ago some folks over this way had a prop fail and needed some medical attention. Blu had one 20 years ago with an IVO prop dang near chopped the boat bottom out.

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Re: Another 500 DD

Postby DGroves » Sun Sep 15, 2019 11:35 pm

SWAMPHUNTER45 wrote:My bet is a 2 blade 72JW will be your best option and much like a Q/NGQ hybrid. When your ready to buy call Darrin at Sensenich my bet is he will concur.

You have to get an accurate tachometer it is a safety concern. When a prop fails it becomes a bomb and on a Caddy it can lead to the crank breaking and shizt flying everywhere. Wasn't but a month ago some folks over this way had a prop fail and needed some medical attention. Blu had one 20 years ago with an IVO prop dang near chopped the boat bottom out.



I’m going to, I couldn’t stand not knowing what it was turning that’s why I just took it easy and ran it just enough to stay on plane. I’ve read horror stories about them on here. What’s the 2nd number mean on the wood props? I’m gonna call him again tomorrow, I talked to him a couple weeks ago and he said what I’ve been hearing on here. Most people use the wide 2 blade but the few that do 3 have loved them too. I’ll get back on here in a week or two when I get the motor back on and let everyone know how it runs with whatever I decide to go with I appreciate it!

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Re: Another 500 DD

Postby SWAMPHUNTER45 » Mon Sep 16, 2019 12:06 am

Diameter and degree are the usual reference numbers embossed into a wood prop.

I would not hesitate one second if rigging out a DD Cadillac to go with the 2 blade if the boat was a ride boat.

The 2 blade adjustable works very well and are usually a value, saving the buyer $700 to $800 over a 3 blade prop and hub.

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Re: Another 500 DD

Postby One Eyed Gator » Mon Sep 16, 2019 9:26 am

Swamp, I believe when it comes to woody's (fixed pitch ) it is Diameter, bolt pattern and the pitch number which is how far the prop moves forward it 1 turn with no slippage if am not mistaken.

Remember props do bad thing when get close to the speed of sound so be careful just stating max rpm. They start to lose efficiency at approximately 90% of the the speed of sound (approximately 772 mph). 90% would be around 700mph @75 degrees. A 76 it prop at 3000 has a tip speed of 678mph at 75 degrees while the 72 has a tip speed 642mph.

What you will find is the each prop has a sweet spot, best push for your setup, which may take a bit of trial and error to find.

My motor was a high compression 472 with a few mods - I tried 6 different props- FAP72lxl38 wide blade, FAP74lxl36 wide blade, 70" Stump puller 2 bld, 72" Q 2 bld, 74" Q and 72" 3 Bld H (would make your ears bleed at at 2900 it was so load). 2 blds pushed better over broad RPM. H series was like a 2 stroke motorcycle narrow power band at the top, had great snap though. Best all round prop was the wood 72lxl38 motor turn 2900 and it pushed very well. Next was the stump puller and the 72" Q.

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Re: Another 500 DD

Postby Striker543 » Mon Sep 16, 2019 3:40 pm

I tried a lot of props when I had my direct drive 472. It was freshmen rebuilt to basically stock except for an MTS cam. I think the 2 blade 74” ngh (not ngq) pusher the best. I ended up running a 3 blade 72” ngh because it was smoother. You’ll lose snap, but I think you’ll find your best push is with the longest prop you can turn.


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