Engine suggestions

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TexRO
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Engine suggestions

Post by TexRO » Sat Oct 13, 2018 12:07 am

I am planning on having a 18 x 8 airboat built after hunting season is over, so I am currently gathering price information for the loan. I need to figure out what size engine I will need to push the boat loaded with 7 men and gear. I need the boat to run across dry ground with just me and gear. It is going to be a heavy high sided boat with decking back to the driver seat and 1/2" poly on the bottom. I am leaning towards a Chevy LS, LX, etc type engine, but I don't know what size or HP I should put on the boat. I don't want to be under powered, but I don't want to blow extra money unnecessarily on an over kill. I thought about the levitator, but it only produces 450hp, and I don't know if that will be enough hp to do what I want it to do. I have one shot at this and I don't want to make a mistake or regret my choice. I would really appreciate your suggestions.

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OneBFC
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Re: Engine suggestions

Post by OneBFC » Sat Oct 13, 2018 2:29 am

Well, this is both simple and complex.

Simple part is that the more weight you have the more power you need. Hard part is keeping weight down on big boats.

Keep your power to fully loaded weight to 4 to 5lbs per available hp and it should serve you well.

That said, a 5000lb boat isn't going to be as capable with a 1000hp engine as a 2000lb boat with a 400hp engine.

Take that to the bank as truth.

In reality the required power to weight ratio for a given weight isn't linear as weight increases due to the fact that no matter how much power you have, it still has to go through an 84 to 86 inch prop at most.

Big power through small props is very inefficient. You can't get around this not matter what your budget is. It's physics and it rather sucks for everyone.

So, number 1 thing in airboat design should be weight. Minimize weight before all without destroying strength at the same time.

I like to tell people that Airboats are the most complicated set of conflicting requirements and solutions you can think of next to space flight.


Anyway, good luck with your build and, seriously, concentrate on reduction of total weight. Your wallet will certainly stay fatter if you do and you will wear a smile in the end.

:salute: :old_glory:
-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
Life begins at 2 BAR, Just a good ole boy

SWAMPHUNTER45
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Re: Engine suggestions

Post by SWAMPHUNTER45 » Sat Oct 13, 2018 7:17 am

Big heavy boat I recommend big inch power.

Either a roller Cadillac by Branch or something in the Big Block Chevy stable from a builder like MAS.

Crate motors like BPE or GMF will not hold up.

Big wide blades and quite possibly a counter rotation drive if you want the best performance possible.

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Slidin Gator
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Re: Engine suggestions

Post by Slidin Gator » Sun Oct 14, 2018 7:39 pm

Do you really need such a big heavy boat, are you starting an air boat tour guide service or search and rescue or something? 2x 14 footers are a lot easier to make slide dry ground and more likely to get everyone home, 3 Guys on one, 4 on the other. Otherwise, the previous input is dead on, if you think it's overkill, it's not enough for what is described
TexRO wrote:It is going to be a heavy high sided boat with decking back to the driver seat and 1/2" poly on the bottom.
Forget about LS, LX etc., you need big inch and big RPM or big boost to make the power you are asking for.
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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digginfool
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Re: Engine suggestions

Post by digginfool » Mon Oct 15, 2018 11:32 am

I second the thought of staying away from crate engines as well as companies like Levitator or Marine Power (all they use is a crate engine and they don't hold up in the long run the way a purpose built engine will). You could get away with an LS if you went counter-rotator but by the time you buy the gearbox and two props, you're in at least $14,000.00 before you buy anything else (that's just for the gearbox and prop; no engine). Big inch is the way to go with a big heavy boat like what you're describing. Call MAS for a big block or Dave at Waterthunder if you're dead set on an LS (he builds the best LS engines).
“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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PAINKILLER
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Re: Engine suggestions

Post by PAINKILLER » Mon Oct 15, 2018 3:57 pm

I'm planning on building one 18x8 mostly for fishing with a big deck n lights 5to6 people I'm going 632bbc my 2cents
MATTHEW 25:35-45 LS 406 82 4bld WaterWalker falcon 2.68 ox box
LS 427 80 3 Bld WaterWalker Maximus 2.68 ox box :rebel:

TexRO
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Re: Engine suggestions

Post by TexRO » Sat Oct 27, 2018 6:17 pm

Thanks for the input, guys. Yes, the boat is going to be used for a bowfishing guide business. I need a big boat so I can fish 4 men comfortably; with 5 or 6 people on occasion. I need high sides so they don't sink the boat when they all decide to run to one side to watch their buddy fight a fish. The reason I mentioned an LS engine was because of the fuel efficiency you gain with fuel injection. A big carbureted engine will eat my profit up in short order, especially if the gas price stays at $2.65/gallon like it is in my area now. I also like the availability of parts since I will be maintaining and working on the engine myself.

As I sat here typing I was thinking about what you said about weight. Maybe a low side complete deck over would work. Any suggestions on that? Keep in mind that no matter how many times you tell customers not to load up one side, they still do it when they get excited.

Huffduf41
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Re: Engine suggestions

Post by Huffduf41 » Sun Oct 28, 2018 6:07 am

Looking forward to seeing your build, not looking forward to seeing the price though....ouch!

It will take some patience but I’ve seen a good number of used bowfishing boats pretty close to what you’re looking for come up for sale here and on Craigslist over the years. Good way to save $30k.

SWAMPHUNTER45
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Re: Engine suggestions

Post by SWAMPHUNTER45 » Sun Oct 28, 2018 3:52 pm

If power vs weight with a focus on fuel economy with a big boat "Cadillac" should be screaming in your head.

No platform can do that better with the advent of aftermarket EFI options. A Branch roller 542 or 555 mated to a 2.55 drive with 4 big monster blades is the Rx for that load. Shame ur not close to see one of these boats push a load. The 2 year warranty is nice also.

That would really be asking a lot from an LS platform. If you were to go that way I would strongly recommend looking at what WaterThunder has to offer.

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digginfool
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Re: Engine suggestions

Post by digginfool » Sun Oct 28, 2018 8:09 pm

SWAMPHUNTER45 wrote:If power vs weight with a focus on fuel economy with a big boat "Cadillac" should be screaming in your head.

No platform can do that better with the advent of aftermarket EFI options. A Branch roller 542 or 555 mated to a 2.55 drive with 4 big monster blades is the Rx for that load. Shame ur not close to see one of these boats push a load. The 2 year warranty is nice also.

That would really be asking a lot from an LS platform. If you were to go that way I would strongly recommend looking at what WaterThunder has to offer.
Definitely wouldn't discount Swamphunter's recommendations. Those Branch Caddies are beast.
“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

One Eyed Gator
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Re: Engine suggestions

Post by One Eyed Gator » Mon Oct 29, 2018 7:35 am

Big inch motor maybe the ticket but I would look at the hull design. If your not going the run a lot of nasty dry, I would make the hull a little wider. One the guides from gulf hammock has an 8'-6" wide deckover and I was surprised how much stable the 6" made the hull. It will also get on plane easier wide a wide bottom.

Just some thoughts and it not always just about the motor.

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Re: Engine suggestions

Post by bob_esper » Mon Oct 29, 2018 8:26 am

if you're guiding i'd strongly suggest a 20' boat. my 18/8 would get crowded in a hurry if i had 4 guys running around without a clue as to what they're doing. Typically builders only add like 1-1.5k per linear foot so the cost difference isn't huge. As long as you're not wanting to run up hills a LS will work for you.
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airduds
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Re: Engine suggestions

Post by airduds » Tue Oct 30, 2018 5:32 am

bob_esper wrote:if you're guiding i'd strongly suggest a 20' boat. my 18/8 would get crowded in a hurry if i had 4 guys running around without a clue as to what they're doing. Typically builders only add like 1-1.5k per linear foot so the cost difference isn't huge. As long as you're not wanting to run up hills a LS will work for you.
This. And on the rare (if ever) occasion the guys have to get out and push it will only add to their adventure, making their memories (and more importantly their stories), more exciting.
Hard times create strong men. Strong men create good times. Good times create weak men. Weak men create hard times.

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GeeLeDouche
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Re: Engine suggestions

Post by GeeLeDouche » Wed Oct 31, 2018 4:06 pm

Another vote for big block power. as much as you can afford, especially if you are making a living with the boat, so you will never have 2nd thoughts about "should I have gone bigger"...

I have a waterthunder LS on my 16 foot Utah style boat and it pushes it wonderfully but I think a 20 foot boat to run dry with 7 people might be a tall order for any motor, even an LS.

Good luck!
16x8 Utah style hull With a Waterthunder motor W/ 2.3 CH3 reduction swinging a 3 blade 78" R.
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Re: Engine suggestions

Post by bob_esper » Wed Oct 31, 2018 4:32 pm

Good thing you don't have to run dry to Bowfish :) Lots of very stock 454s running around on 18/8 bowfishing boats, no NEED for 600+ hp
2017 18.5/8 Alumitech
408 LS
2.38 stinger with 79" 3 blade ex

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Slidin Gator
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Re: Engine suggestions

Post by Slidin Gator » Wed Oct 31, 2018 6:57 pm

Just to go the full round, I understand the need for a big boat here for sure. I don't think it matters if it is a high sided boat or a deck over, it's gonna be heavy (deck over probably being heavier). But Tex needs to clarify on this statement from the original post as it is pretty much the key to the right choice:
TexRO wrote:I need the boat to run across dry ground with just me and gear.
Is that really the goal, or do you need to haul the whole charter? With 5-6 fat a@@ (everything being big and all) Texans off the boat and standing in the mud, we are talking 1,000-1,500 of weight off the boat. So the rig all dressed for bowfishing is probably in the 3,500 lb range with driver?? To run dry the general rules of thumb lead to 500-600 Hp minimum. There are several recent threads on this board covering similar 18-20 foot boats with 454 motors making in the range of 390-425 Hp. None of the owners are happy with performance and are looking for significant improvement to run ground and rough trail.

Here are a couple threads to reference:
viewtopic.php?f=48&t=71377&hilit=454
viewtopic.php?f=2&t=71476&p=688598&hili ... ld#p688598

I think it is reasonable that a 600 Hp LS motor can push the boat and driver alone on dry ground. Maybe not a trail buster, we are talking about crossing some ground or leaving lunch island, but don't spend all day standing on it or that LS will die an early death. In the water, the LS can perform well with the load, particularly since a lot of the time is going to be spent bow fishing at an idle, where the LS will sip fuel, all good.

But, if you want it to push wherever you need to go with the full load of Texans, the equation changes to big block power. Swamp makes a good sell for the Cady. EFI in any event will help with fuel consumption regardless of platform.
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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Prototype
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Re: Engine suggestions

Post by Prototype » Wed Oct 31, 2018 9:52 pm

It sounds like your ignoring your local builder advice of a charter airboat for business and probably not insured or safety in place.

Maybe after hunting season it will work out for you to get a loan on a new business in the airboat world your new too?
Five guys rushing to one side to watch the catch kind of dictates some major helium balloons on your end.

Either way, I know your looking at 8-10 gallons an hour fuel burn for a healthy 18-20 footer

TexRO
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Re: Engine suggestions

Post by TexRO » Sat Sep 28, 2019 12:59 pm

I thought I would give an update to my original post. It turned out that having a boat built like I needed was WAY to expensive. For a very basic 20 foot boat with power to push it I was quoted prices from $60k - $80k. I started looking around and found a beautiful used 20x9 with a built 454 for half of what a new boat would have cost me. I can stop in sticky clay mud or soft sand with myself and 4 large men in the boat and it has no problem getting up and sliding again. It drinks some fuel, but paying for fuel is better than getting out to push. It is wide enough that stability is not an issue in deep water. 3 guys can lean over on one side in deep water without swamping it. It is a little harder to make turns because it bites into the water instead of sliding around, so I can't make a 180 degree turn at speed like I could with the smaller boat. To switch directions in the river I have to come off plane and turn at idle speed. It is not as much fun to drive as the smaller boat, but it sure is stable and roomy when loaded down with people and gear.

TexRO
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Re: Engine suggestions

Post by TexRO » Sat Sep 28, 2019 1:04 pm

I forgot to mention it has a 3 blade Whisper Tip 2 prop and the engine is putting out 600HP.

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Rick McC.
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Re: Engine suggestions

Post by Rick McC. » Sun Sep 29, 2019 10:40 pm

TexRO wrote:
Sat Sep 28, 2019 1:04 pm
I forgot to mention it has a 3 blade Whisper Tip 2 prop and the engine is putting out 600HP.
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