Gear Box or Not

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Lwells
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Gear Box or Not

Post by Lwells »

I have a wide body 12 foot or so fiberglass boat that has a new rigging with a new 305 chevy small block that is stock and has poly on the bottom. I don't want to spend a lot of money on it for it is a second boat but I would like it to go some on dry if necessary so I don't have to worry about getting stuck somewhere. I hope to run it where I wouldn't take my 16ft. I"m hoping for advice concerning cheapest and best way to set it up so it will run dry pretty easy. It is setup for 3 people. If I need to run reduction drive I would prefer to go cheap as possible so I have no problem running belt drive if it would work for I don't or won't be constantly trying to see where it will go so however I go will probably last me forever where I'm sure cheaper wouldn't last some of you a day.LOL So, please tell me what will work as for prop also. Thanks in advance.

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Re: Gear Box or Not

Post by flcracker9 »

What prop is on it now? If it was a 350ci, I would suggest a 70" Q prop, and keep the rigging light and it would run the hill ok. Being a 305ci, I would venture to say a gear reduction of 2:1 and a 78" - 80" 2 blade would be needed at a minimum for it to perform anywhere near what you want it to do.
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GeeLeDouche
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Re: Gear Box or Not

Post by GeeLeDouche »

To push on dry ground, I would highly suggest getting a reduction. I think you can find old Kway belt reductions for less than 2K on occasion.
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kwanjangnihm
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Re: Gear Box or Not

Post by kwanjangnihm »

http://www.airboatgeardrives.com/1.html

I see these for sale used sometimes
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Re: Gear Box or Not

Post by Lwells »

I haven't been on here for a while but thanks for the info. It doesn't have a prop on it so I just wanted to get an Idea of how I would have to go with a stock 305 motor to have the power to get around dry if I needed or be able to run over weeds or grass or whatever in an emergency.

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Re: Gear Box or Not

Post by Striker543 »

Most likely you will need a gearbox to run dry ground. I had a direct drive sbc 350 that would run a little dry, but it was a light boat with slick bottom. It’s more likely than not that a direct drive 305 would not push a 12ft boat with poly on dry ground.

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Prototype
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Re: Gear Box or Not

Post by Prototype »

kwanjangnihm wrote:http://www.airboatgeardrives.com/1.html

I see these for sale used sometimes
Which one the 305 or 307? Both are anchors but just curious? Not that it applies to this post or anything of worst motor to try and build!

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Re: Gear Box or Not

Post by Seven3 »

I have owned probably a dozen 305 powered Monte Carlos and El Camino’s from the 80s...you are looking at 150 to 160 hp tops. My advice is to keep that boat as is so that it doesn’t become a money pit. You could put a box on it and it still might not even run dry. Might be better off putting that money towards a Lycoming 360.

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Barefootduck
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Re: Gear Box or Not

Post by Barefootduck »

Have a 12x7 beat up fiberglass hull that has a stock 305 with DD 72x36 woody stick. Only turns that prop 2300-2400 but still has what it takes to run some dry. Keep it light and don’t pretend it won’t get stuck fast if the land is sticky AT ALL. If it’s hard ground can run it easy but any softness or even tall grass it doesn’t like it. Granted I’m only turnin 2300-2400 so maybe with a prop more tunes for the 305 it might even do better. Just saying from my experience but I’m not saying it would do what you want but it will run dry if the conditions are right. Btw my boat is 2k total so that’s cheap! Lol I have a 350 waiting and looking for a new hull.
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Slidin Gator
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Re: Gear Box or Not

Post by Slidin Gator »

I did a little reshuffling of priorities.
Lwells wrote:I have a wide body 12 foot or so fiberglass boat that has a new rigging with a new 305 chevy small block that is stock and has poly on the bottom. I hope to run it where I wouldn't take my 16ft.
Lwells wrote:I don't want to spend a lot of money on it for it is a second boat but I would like it to go some on dry if necessary so I don't have to worry about getting stuck somewhere. I"m hoping for advice concerning cheapest and best way to set it up so it will run dry pretty easy.
I don't know what you got pushing the 16 footer, but just thinking it will outrun that 305. Take motor etc. off 16 footer and put it on the 12 foot hull. Viola, you got a boat that will run where you won't take the 16 footer.

Take that 305 direct drive and put it on the 16 footer. Viola, you got a 16 foot Lake Log that will become your second boat, use it for speck fishing and showing other old farts around the lake.

Just the way I think.
I still think I-10 is the Mason Dixon line.
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Lwells
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Re: Gear Box or Not

Post by Lwells »

Ok, Some interesting information but why do I still lean toward some kind of gear drive that will allow that stock 305 to blow alot of air without working it to death and making it run dry easily. I just hoped I could do this and not have to bring my 540 HP small block down here out of my 2wheel drive street sleeper S10 Blazer and go to one of my 454 engines to get it back going for I would never put that 305 in it. I'm afraid to use one of my 454's because of weight and I wanted to stick with what I got and stay light but you guys got me wondering now. I just thought for sure that even a low hp 305 would be able to turn a prop with a gearbox high enough to go pretty strong but maybe I don't understand how deep I got to get in my pocket on a gearbox/prop setup.

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Re: Gear Box or Not

Post by Striker543 »

To push a 12 ft boat well with a car engine I think 300hp with a gearbox is probably the base line. Yes you can make a water boat with a lot less hp than that, but what you’re describing is not a water boat. If I were building it I would either put a 300-400 car engine and gearbox on it or a 6 cylinder aircraft engine (a 4 cylinder would work if you kept it super light).

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Deano
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Re: Gear Box or Not

Post by Deano »

You have a good option in left field that you had not shared prior to your last post.
Unfortunately, the Laws of Physics don't play favorites or accommodate good intentions. EVER.
A 454 DD will always be the better monetary option to a weak, baby small block and a gear box (and associated blade set).
Before you become overly concerned with weight, realize that Pontoon Outlaw runs a 507 Cadillac AND a gearbox on a 12' hull.
You should be able to do the same without the box.
Lwells wrote:Ok, Some interesting information but why do I still lean toward some kind of gear drive that will allow that stock 305 to blow alot of air without working it to death and making it run dry easily.
Your thought process seems to imply that you are misinformed, and think that a gear reduction will allow you to make more horse power.
It will NOT. It will allow you to leverage the little bit of torque that you are making, but this is NOT a horse power increase.
To be blunt, the realistic fact of the matter is that a 305 is 'weak sister' compared to the other engines routinely used to accomplish the task you envision in your minds eye. You will move more air with a gearbox, but the lesser the HP involved, the larger are the deleterious effects involved with adding that extra weight. If you are short of the power to push your rig dry, adding the weight of a gearbox is actually going to compound your problem, not alleviate it.
Lwells wrote:I just hoped I could do this and not have to bring my 540 HP small block down here out of my 2wheel drive street sleeper S10 Blazer and go to one of my 454 engines to get it back going for I would never put that 305 in it.
Here you seem to understand the 'weak sister' potential of this engine (although be it in a different application).
Why would you think different rules apply to a boat application than to an automotive one?
Consider if you will, that you would 'never put that 305 in it' while it has 3 or 4 gears to be used to it's advantage, and yet you seem to think that 1 gear could address the same weakness in a boating application. Consider beyond that, you only get to pick one gear for your reduction. You still have a direct drive application (transmission wise), you have only changed the ratio to not remain 1:1.
Lwells wrote: I'm afraid to use one of my 454's because of weight and I wanted to stick with what I got and stay light but you guys got me wondering now.
This is good because you are coming around to realistic view of what will work like you'd expect and what won't. Staying light is always a good thing, BUT you still need to have the available power at hand to perform the task you are attempting. In the end you will find that the 454, on that hull will allow you to do what you are wanting to do. Is there a weight penalty for the 454? YES, but given the extra power, it is a penalty that could be worked around. The penalty of insufficient power with the 305 would be MUCH more expensive to work around because you not only would need a box and a prop to go with it, but then the 305 would need new forged guts because making power with a small CID will require big RPMs. Not an inexpensive endeavor, going that route.
The 454 would happily chug around at 3k rpm all day, in spite of the fact it was a little heavier.
Lwells wrote:I just thought for sure that even a low hp 305 would be able to turn a prop with a gearbox high enough to go pretty strong but maybe I don't understand how deep I got to get in my pocket on a gearbox/prop setup.
Here, you have used 'low hp 305' and 'go pretty strong' in the same sentence. :scratch:
Equate this to your Blazer analogy and statement (which are spot on, imo). Reconcile.
As far as your pocket depth goes, see prior analogy. :wink:
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Lwells
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Re: Gear Box or Not

Post by Lwells »

Thanks Deano and I get where your coming from to a certain extent and I'm gradually learning more and more on these airboat but what is confusing to me is how the old timers ran around in the swamps and ran dry, in mud,etc, and so on and they never had a tenth the Hp or technology we have or did those guys stay out for days trying to get back home due to getting stuck all the time. I dont want to climb over the dike nor do I want to run dry for miles, I just don't want to go exploring and get in a situation I can't get out of and my rigging already has this 305 mounted and it is a brand new Chevy vocational school engine(obsolete) and I thought it could possibly get me out of a possible disaster if it was set up right. I know its under powered but I also wondered if it would stand nitrous in an emergency situation. I figured if I threw information out there then maybe with everyones thoughts or experiences I could make this work and keep it cheap and go like the old timers did. Of course I realize that the old timers of todays generation is me and I grew up in HORSE POWER HEAVEN of the 60's, 70's but the guys before me were airboat guru's who got around without all the fancy stuff. Lol

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Re: Gear Box or Not

Post by SWAMPHUNTER45 »

Old timers didnt run barges...lol

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Re: Gear Box or Not

Post by Striker543 »

SWAMPHUNTER45 wrote:Old timers didnt run barges...lol
And they ran light boats with aircraft engines, which is old technology that will do what you’re asking.

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Re: Gear Box or Not

Post by OneBFC »

Striker543 wrote:
SWAMPHUNTER45 wrote:Old timers didnt run barges...lol
And they ran light boats with aircraft engines, which is old technology that will do what you’re asking.
Formula for success never changes. 6lbs of boat to 1hp and you will have an adequate performance experience. move that to 4lbs per 1hp and it's a do all machine. The more you trend to less weight the better in most use cases for airboats.

There are exceptions of course.

what type of engine you use to achieve the required power is not important from a "will it go" perspective.
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Re: Gear Box or Not

Post by Lwells »

SWAMPHUNTER45 wrote:Old timers didnt run barges...lol
I didn't think a 12 Ft fiberglass with 2 seats was considered a barge but then what do I know and that's why I'm asking questions. I do see where the aircraft engine would make a difference , in probably weight and hp.

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Re: Gear Box or Not

Post by Lwells »

OneBFC wrote:
Striker543 wrote:
SWAMPHUNTER45 wrote:Old timers didnt run barges...lol
And they ran light boats with aircraft engines, which is old technology that will do what you’re asking.
Formula for success never changes. 6lbs of boat to 1hp and you will have an adequate performance experience. move that to 4lbs per 1hp and it's a do all machine. The more you trend to less weight the better in most use cases for airboats.

There are exceptions of course.

what type of engine you use to achieve the required power is not important from a "will it go" perspective.
Thanks, now that is understandable and makes sense.

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dodobird
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Re: Gear Box or Not

Post by dodobird »

305 with 2 to 1 belt 72" powersh^t ha prop would run ground till poly got hot it would stop in its tracks put a 330 350 n 78 whirlwind prop goes anywhere now
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Re: Gear Box or Not

Post by Lwells »

Thanks dodobird;Your boat looks lot like mine other than my rigging sets lot lower as far as seat setup. I'll start looking for drive setup and prop.

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Re: Gear Box or Not

Post by dodobird »

Lwells wrote:Thanks dodobird;Your boat looks lot like mine other than my rigging sets lot lower as far as seat setup. I'll start looking for drive setup and prop.
If u keep the 305 n put reduction on it just make sure to get a 78" prop or so imo

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Re: Gear Box or Not

Post by Lwells »

Dodobird;Do you have any kind of spray system on your boat to wet the ground in front under you

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Re: Gear Box or Not

Post by dodobird »

Lwells wrote:Dodobird;Do you have any kind of spray system on your boat to wet the ground in front under you
No sir this is an old boat I sold it few years back my buddy has it now but once I put the 330hp 350 n the 78" prop didnt need any sprayer

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Re: Gear Box or Not

Post by daxxe »

Striker543 wrote:Most likely you will need a gearbox to run dry ground. I had a direct drive sbc 350 that would run a little dry, but it was a light boat with slick bottom. It’s more likely than not that a direct drive 305 would not push a 12ft boat with poly on dry ground.
Really sounds it is way better to have a gearbox.

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