18x8 with 450Hp LS3

Automotive powered airboat discussion.
OTL91
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18x8 with 450Hp LS3

Postby OTL91 » Sat Apr 13, 2019 9:26 am

Been reading around and doing as much research as possible. A lot of the advice for big boats seems to be when the LS platform was newer and unproven. Was wondering if a 18x8 boat with open layout, proper set up, and 450 HP LS3 would be sufficient or if I am needing to look at smaller boat/bigger engine. While I won't be running a ton of dry I want to be able to dry load/unload if situation requires, go over small levees/banks for when river comes out of banks flooding fields then recedes leaving trapped water or for when launching from around bridges without ramps. Normally hunt with 2-4 guys.

What is the price jump from an LS3 to an LSA?

Striker543
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Re: 18x8 with 450Hp LS3

Postby Striker543 » Sat Apr 13, 2019 10:10 am

That's not enough power for that size boat to go over a levee with just you in it, let alone 2-4 guys. You will need serious horsepower for that. If you're married to 450 hp, I would not go larger than a 14x8 boat.

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OneBFC
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Re: 18x8 with 450Hp LS3

Postby OneBFC » Sat Apr 13, 2019 12:23 pm

pretty much want to keep total running load at or under 6lbs per available 1hp if you want a capable machine.

Also, I haven't been impressed with the LSA when I see them on thrust test, I think you can do better with a properly built NA LS or big block.

Also, I think you should look at 650+ for a typical heavy 18x8 boat, but, just used the formula I gave above and match hp to your total load. You will br surprised how fast and high your power requirement will go as load goes up. At some point you run into the problem of diminishing returns on power with the prop diameter limitations on airboat. You simply can't put 800+ hp through a small diameter (84 to 88 inches) and get the same thrust per hp. Disc loading is such a mean physics barrier for airboat.

Anyway, good luck and remember, 6:1 ratio on weight to go. lower that ratio the better.

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-Russ
-----------------------------------
The only thing stopping you is FEAR
400+hp Ecotec, 12x7.6 DBDO, 80" 3B Maximus, 2.3 OX,85+mph, water = purely optional
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Debo75
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Re: 18x8 with 450Hp LS3

Postby Debo75 » Tue Apr 16, 2019 4:02 pm

Not a chance. I have a 20x8 with a sprayer setup, a hair under 600hp, and mine won't run across wet grass. Let alone load/unload, or run the hill.

Before I bought my boat I looked at a 16' with 750hp, and while it could run the hill with four people it was at full throttle to do it.

If I repower it will likely be a a 502ci or bigger Chevy, with fuel injection and twin turbos. And I will be redoing the rigging so the engine doesn't try to pass me when I punch it transitioning to dry land.

As you get bigger, the power required increased exponentially. That's why ants can carry 20 times their own weight, and elephants can't jump.
20'x8' GTO w/ MAS 509 BBC, 2.38:1 Stinger, 4 blade Power Plus.

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Slidin Gator
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Re: 18x8 with 450Hp LS3

Postby Slidin Gator » Tue Apr 16, 2019 11:55 pm

Debo75 wrote:Not a chance. I have a 20x8 with a sprayer setup, a hair under 600hp, and mine won't run across wet grass. Let alone load/unload, or run the hill.

That explains it as well as any. I run a 14x7, 1,800 lb boat, pushed by 260 Hp worth of Lycoming. I unload/load dry and run dry all day with a rider, 2 dogs and a fat dead hog. I only get nervous if I get near deep water. :stirpot:

It all depends on what you want to do with the rig. From what I see every swinging dick in Texas want's their 18 foot oyster basher with a 454, loaded with 6 people and the monster Yeti to run the marsh like a S. Florida 4 cylinder rig.

WTF

Not gonna "DO" more than 1 rider, add any more and ya don't get the full experience.
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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southern safaris
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Re: 18x8 with 450Hp LS3

Postby southern safaris » Wed Apr 17, 2019 7:36 am

Slidin Gator wrote:
Debo75 wrote:Not a chance. I have a 20x8 with a sprayer setup, a hair under 600hp, and mine won't run across wet grass. Let alone load/unload, or run the hill.

That explains it as well as any. I run a 14x7, 1,800 lb boat, pushed by 260 Hp worth of Lycoming. I unload/load dry and run dry all day with a rider, 2 dogs and a fat dead hog. I only get nervous if I get near deep water. :stirpot:

It all depends on what you want to do with the rig. From what I see every swinging dick in Texas want's their 18 foot oyster basher with a 454, loaded with 6 people and the monster Yeti to run the marsh like a S. Florida 4 cylinder rig.

WTF

Not gonna "DO" more than 1 rider, add any more and ya don't get the full experience.



I get calls for that boat you just explained almost everyday!!! And when i explain the kind of hp and set up it will take to run like they want i usually get some story of how a buddy has a 20x8 bowfishing rig with lights genset ,cooler,stripper pole etc.. pushed by a dd454 will run dry 4-5 guys yada yada... funny i never get to see the videos of them doing it , but they do it from what im told, oh and they want the boat to cost under 20k turnkey :roll: now to be fair i do get a few that understand what it'll take to get there but they are very few and far between

For the OP, i have a close friend that has a 18x8 fishing rig set up with a mas540 660hp 670ftlbs torque and we dry load unload on grass hop a few levees etc but mud and sand and it gets interesting quick , personally i dont have what it takes to give a heavy 18'er a rake shake !!! Guess im gonna have to stick to my little hunt boats but if you have deep enough pockets those big rigs can get it done if set up right , had a old geezer in a hanger one day we were sittin around cleaning our planes , told me if you have enough hp you could fly a brick so i guess that relative to boats too
Anthony Hughes
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SWAMPHUNTER45
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Re: 18x8 with 450Hp LS3

Postby SWAMPHUNTER45 » Wed Apr 17, 2019 8:20 am

Anything 16ft and up with weight takes BIG POWER and WIDE BLADES it is just the formula to move it in a way that an airboat was meant to move. When you cross into the heavy & raked 20ft mark you are talking about the need for a elite big inch car motor build.

That is big dollars BIG DOLLARS

Mossy Cypress
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Re: 18x8 with 450Hp LS3

Postby Mossy Cypress » Fri Apr 19, 2019 4:21 pm

Do you have any pics of the hull and setup?

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Re: 18x8 with 450Hp LS3

Postby Mossy Cypress » Sat Apr 20, 2019 12:56 pm

For what it's worth, my 16x8 with just over 500hp has no problems dry loading/unloading, and has no problems running dry or crossing any levees or pulling up on banks with a load. I guess it's all in the setup like they always say. Just curious how heavy these big boats are that cant run across wet grass, gotta be tanks, there is big tour boats around here that do what the O.P. described. Too many variables really to compare apples to apples with boat/setup/load/conditions. Lots of good posts here from people WAY more knowledgeable than myself, I'm just sharing my experience with my boat, hope it helps. To the O.P. Shorter hull,more power,less weight. JMO

Moritz
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Re: 18x8 with 450Hp LS3

Postby Moritz » Sun Apr 21, 2019 9:00 am

I have a GTO 8x16 with a 540 @740 hp and it will run dry with 5 people in it . I had a 600 hp 496 and it was ok but still a little under powered

. You are going to need at least 1000+ hp to make that 20ft run well> Drop back to an 18 and you can get by 830 +

Mossy Cypress
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Re: 18x8 with 450Hp LS3

Postby Mossy Cypress » Sun Apr 21, 2019 10:15 am

Moritz, do you have any pics of your 16x8 that the 600hp was on?

unforgiven11B
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Re: 18x8 with 450Hp LS3

Postby unforgiven11B » Sun Apr 21, 2019 9:05 pm

I have a 16x8 Diamondback SS rigging, pcm/levitator 6.0 MAYBE 365 hp ch3 2:1 3 blade k series. Runs dry all day with 3 people and all the stuff I carry. When I say I run dry I mean I go all over. Now there are limits I feel it getting sticky sometimes. If I was 425hp I could take it anywhere. Set up has more to do with it than most realize. A 800hp engine on a bad hull or set up and it won’t move on wet grass.

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GeeLeDouche
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Re: 18x8 with 450Hp LS3

Postby GeeLeDouche » Thu Apr 25, 2019 9:39 am

I have a 16x8 Utah style hull with a Waterthunder 550hp motor on it and it does surprisingly well. I go pretty much anywhere I want within reason. I don't think youll be running dry with 2-4 guys in a 16x8 with only 450.. but it might work well for what you want to do with it. just depends on your needs and your budget.
16x8 Utah style hull With a Waterthunder motor W/ 2.3 CH3 reduction swinging a 3 blade 78" R.
&
1648"M (& floatation pods) "Lowe" modified V Jon boat with a 31hp mudbuddy hyperdrive.

Aeon
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Re: 18x8 with 450Hp LS3

Postby Aeon » Mon Apr 29, 2019 10:34 am

17x8 hull with a 600hp ls3 2.55 ox and 3 blade jx. Runs dry and goes where i point it.

If you are getting a ls motor get it built right. They are easy to build over 550+hp.
17x8 Circle H powered by a TurnKey LS3, 2.55 ox box and 82" 3 blade JX


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