Gear Boxes

Automotive powered airboat discussion.
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joelb
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Gear Boxes

Post by joelb »

Q 1. using a car motor, caddie 500 stock, gear drive or belt ?
Q 2. what gear ratio ?
Q 3. two blade or 3 blade?
Q 4. what brand/manufacture do I need to look at?
my boat info 15ft glass, slick bottom, basic airboat.
looking for some input, boat runs good now but not a dry ground runner, thinking about the change so any advise would be
apricated. I welcome your suggestions, e-mail me at jbennett0213@gmail.com
SWAMPHUNTER45
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Re: Gear Boxes

Post by SWAMPHUNTER45 »

Joel if your going to run a Cadillac 425/472 or 500 on a drive you face limits in using a stock valve train.

If bone stock a 1.53 Rotator would give you a gain in usable power and if your careful and don't push the rpm a 1.77 range can work.

When you get beyond that you risk breaking the valve train.

If your having work done to a stock engine NEVER let some machine shop put heavy valve springs on your heads that is going to cause things to break for certain. When we put rpm to the Cadillacs we use a full shaft rocker system and upgrade the valves.
joelb
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Re: Gear Boxes

Post by joelb »

Thank you for info, guess more research is what I need to do before making decision on which way to go.
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kwanjangnihm
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Re: Gear Boxes

Post by kwanjangnihm »

joelb a few things to think about:
1. adding a gearbox will mean moving your rigging forward 12-14" and modifying the current setup.
2. cost of gearbox, new or used
3. cost of prop, new or used
4. gearbox - right hand rotation
5. belt drive - left hand rotation
He'll cut your throat, baby, stick you in the back, drive off in your Cadillac.
He's more trouble than you think, he'll kill your sugar, leave you in the drink.
joelb
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Re: Gear Boxes

Post by joelb »

Yes sir, have the room to move rigging, cost is always a factor, but we like our toys, knew a new prop was in order. Wasn't sure if I could add to what I use now, so car motor turns counter clockwise if standing at back of motor looing forward and clockwise if looking at water pump. so which one am I looking for gearbox or belt drive?
Thanks for the help.
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Slidin Gator
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Re: Gear Boxes

Post by Slidin Gator »

joelb wrote:
Thu Mar 04, 2021 2:06 pm
so car motor turns counter clockwise if standing at back of motor looking forward and clockwise if looking at water pump. so which one am I looking for gearbox or belt drive?
Thanks for the help.
Joel,

You ask a typical but great question. The following is in no way intended as a slight your way, just an opportunity to press a point.

All of the literature that you will find will refer to CW/CCW or Right/Left Hand rotation. It is all confusing as hell :scratch:

When flying a typical plane (engine in front) you are staring at the prop and that prop is spinning CW/Right hand. We put them same engines in our boats, just don't spend much time looking back to stare at them :blackeye:

To get the same perspective with a car motor, you gotta be pulled over on the side of the highway, hood open, steam pouring out, yelling at the wife to give the starter another try. Think about it, 10,000 ft on a clear day or broke down on I-10 in August, engine spins CW/Right hand in all cases, no confusion here. :stirpot: .

Now, throw that engine in an airboat, try and describe the prop rotation, it depends on your perspective: standing behind boat, in front of boat, scratching butt and looking over left shoulder :dontknow: Lot's of ambiguity for sure.

Airboats are registered and regulated as boats nautical terms would simplify :cheers:

I propose the following:
- Direct and Belt Drives are PORT Rotation (top of prop turns to PORT)
- Gear Drives are STBD Rotation

Isn't that simple?

Just throw in:
Direct and Belt Drives are STBD Torque side (the side that dips when you mash the gas)
Gear Drives are PORT Torque side.
I still think I-10 is the Mason Dixon line.
2013 Mike Stossel Boats, 13' x 7' deck over, IO-540, 74" NGQ less winglets.
joelb
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Re: Gear Boxes

Post by joelb »

So with your info, which I find very informative, If I buy a Belt drive I can keep the prop I am using now or I will have to buy another prop designed to operate with a gear drive.
All of this info makes my head spin, don't know if it is clock wise or counter clock wise, know it has something to do with my vertigo.
Do apricate your, hope you were able to get off I-10 ok.

JB
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nebraskaairboater
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Re: Gear Boxes

Post by nebraskaairboater »

Having done the Caddy direct drive converted to gear box then now with a big block chevy my suggestion is switch to a chevy small block or big block if you want the reduction. The money I spent in upgrades to my caddy valve train just to handle the rpm's I could have built a 383 stroker and would have been more economical for sure. Parts are easy to find and there are more good combo's of prop/gearbox available that will work to give you the performance you want. You are going to modify or start over on the rigging anyway. You will want a different prop regardless of if you go belt or gear and you will need a bigger cage for the larger diameter prop. A belt drive rotates the same direction as your direct drive and the gearbox is opposite. Price is the same for the props regardless of rotation. I ran a 2.12 rotator and 2 blade 80" S prop on my caddy. It worked good but I had the heavier valve springs, shaft rocker setup, cloyes timing set, different cam, aluminum intake, bigger carb. I strongly suggest you switch power plant to something with more available parts like the chevy. Just my opinion having gone through the process.
Dan Porter, Jr.
Fremont, NE
16 x 8 1971 Flat Bottom Fiberglass Hull / 496 Chevy/ 2.38:1 OX Drive / 80" 3-Blade Sensenich S
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Deano
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Re: Gear Boxes

Post by Deano »

Slidin Gator wrote:
Thu Mar 04, 2021 11:44 pm
....
I propose the following:
- Direct and Belt Drives are PORT Rotation (top of prop turns to PORT)
- Gear Drives are STBD Rotation
....
Everything Sliding Gator states in his post is factual, no doubt about that.
To further simplify the above proposition (for purposes of an airboat novice) to ease being on the same page as the rest
of the airboat world, and especially to understand the lingo used by prop manufacturers, it could be re-stated that:
- Direct Drives and Belt Drives use LEFT hand propellers (when viewed from behind the boat, as the top of prop turns left)
- Gear Drives use RIGHT hand propellers (when viewed from behind the boat, as the top of prop turns right)
Now with that possibly needless clarification out of the way, your next question is a good one and deserves an answer as well.

Direct Drive propellers are generally designed to run between 2700 and 3100 PROP rpms.
Depending on the ENGINE rpms and reduction ratio, it MAY be possible to use additional blade(s) to increase the needed engine loading.
In the case of your Big Block Cadillac, those odds are decreased more than dramatically (it is very highly unlikely).
For instance (using round numbers to simplify the example):
A SBC that will happily turn 6000 E.rpms could POSSIBLY use direct drive blades, if it were using no more than a 2.0 gear BELT drive.
For a BB Caddy to meet the same parameters would require a lottery win, a LARGE Masochistic streak AND a lot of constant Praying.
Even after having met those predefined needs, chances are pretty slim that it would exhibit any kind of longevity.
NOTE: This specifically references turning a constant 6K rpms, NOT using a gear box.

As such, your presumption that you would need another prop in ANY case is a justified and sound one.
This may initially sound like a bad thing, but it really isn't because if you find a hell of deal on a reduction you aren't held back by trying to humor the need for a preexisting prop. To share a reality that you may or may not be aware of at this point, there are more used props for sale than reduction units. This makes buying the reduction first, the more logical step (if you are NOT buying new). If your budget allows buying new, then this obviously lessens (or eliminates) the magnitude of your acquisition sequence.

On the other hand (if NOT buying new), if you were to find a hell of a deal on a prop first, you will be harder pressed to find a deal on a reduction of the correct type AND the gear ratio you need for that said prop. :idea:

JB, where are you located?

Related passive notes:
1 - I don't know what you're working with, but having done this in the past, my generic recommendation is to just build a new engine stand and then scab your existing rigging onto the front of it. Ultimately you would have to rebuild the back legs in any case (you'll need longer setback and lower height) and you may very well want to change the engine height to lessen the additional torque loading.
2 - If your current cage is built to the width of the hull, you may be able to reuse it, in spite of a bigger prop. The cage on the last 15' RiverMaster we did, would easily accommodate an 80" prop with no alterations. This may or may not be a concern in your case, but may be another consideration while you are running out the math on the front side.
3 - As Swamphunter eluded to, the valve train is where attention need be paid to turn more than stock rpms. IMO, that expense is commensurate with the intended rpms. Any decent non adjustable shaft rocker system will get you to 42-4600 rpms, if done correctly. If you intend to turn over 5000 then a top of the line adjustable is needed and could be up to 3 times the expense. I don't recommend this unless an entire engine build is also in the cards. Putting a high dollar valve train on an old engine is guaranteed to reveal the next weak link.
4 - 2 blades vs 3 blades. If two blades (of any type) will hold the engine back to the desired rpms, generally a third blade is not needed. Adding an additional blade (no matter the blade count) increases mass, weight and surface area which all contribute to parasitic drag that needs to be overcome before a net gain is thrust is realized. For those reasons, adding an additional blade can in fact be counter-productive. Whether this the case or not, is quite literally contingent on the gear ratio, the type of blades and the strength of the engine. Generally, if you don't NEED an additional blade, you don't want an additional blade.
"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."
- Carl Sagan
joelb
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Re: Gear Boxes

Post by joelb »

Deano , good info you have had I not have had this caddie rebuilt recently, would consider one of the big boy toys ( SBC's).
Guess I'll dance with the one I brought to the dance until I make the plunge into big boy world. Do apricate your help.
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Slidin Gator
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Re: Gear Boxes

Post by Slidin Gator »

Joel,

If your gonna stick with what you got, you need to :stirpot: these Caddy boys some more so they spill their secrets, cause it is way easier and cheaper to hot rod a direct drive caddy. It boils down to cam, carb and intake. Big plus, use the prop you already got, just more pitch :cheers:
I still think I-10 is the Mason Dixon line.
2013 Mike Stossel Boats, 13' x 7' deck over, IO-540, 74" NGQ less winglets.
SWAMPHUNTER45
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Re: Gear Boxes

Post by SWAMPHUNTER45 »

When your alone in the swamp that BIG GIRL will get you off !

2.55 OX and 4 big old S blades.....PUSH IT...PUSH IT REAL GOOD
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