Jet VS outboard power?

[imq707s]

I'm looking at getting a 19-21' tunnel hull like a liberator. I've seen a bunch of outboard powered boats, and jet pump boats with big chevy motors in them. What are the advantages and disadvantages of a jet pump as compared to a outboard motor? Can you really "fly" a jet boat since you still have to have the pump in the water? Thanks

[Rusrog]

With the O\B you get...

More fuel milage,
More performance
More interior room,
as well as less noise....

I see no comparison in the 2. O\B all the way.......

But that's just my opinion...

Russ Rogers
Ft Worth TX

[Techno]

Jets have potentially more acceleration, the pump is like a tranny and doesn't load the engine down at low rpms It can be wound up to the engines torque range.
Obs have to have low end torque to get the boat on plane. The jet doesn't.
Jets like all inboards have immensely heavy wieght packages. Engines about 700lbs and then the drive systems wieght about 200lbs?
The boat has to be built to hold these wieghts and torques so the hull is heavier. Even more poundage.
All this wieght does 2 negative things- the boat sits deeper in the water so has farther to rise to get out of it.
It has more mass to accelerate.
The jet has massive engine ponies to overcome this so massive fuel consumption. But the inboard can be built to extreme hp levels where the OB can't, its limited to roughly 400 hp.
The OB package wieghs in at 400 lbs total and is completely behind the boat. The old adage get the weight to the back- well the drive systems between Inboards and Outboards vastly change this.

The Inboard is a "car" motor so is easier for most motor heads to understand.
The OB is simpler but has things that are "Black science" to the motor head at first. But easy to learn. Most of the performance is built in the engine rather than an item that can be swapped out-cam.

Tunnels don't actually leave the water surface but any jet will have the water pick-up touching any way. I think the high speed ones have drop snoot? somthing like that.
OBs have a top speed limited by available power and hull design (to a point).
Jets are limited by the ability to scoop water to feed the pump, eventually this gets counter-productive so they are limited in their top speed. (somewhat low).

Jets are optimized and tuned for the operating requirements. Once set are not changed.

Obs have a huge advantage in they can be optimized for all requirements. The X-dimension the height of the propulsor can be changed, staticly(manually) or dynamicaly( hydraulic jack plate.) The props can be changed easily and quickly to change the use envelope. The OB can also be adjusted, tuned, horizontally for setback or wieght and thrust arm adjustments. This is like the jet boat in once set is hard to change. But this adjustment usually doesn't need to be changed. Prop hieght and prop style, size, and pitch can quickly change the low speed mid or high speed optimized zone.
A bass boat can be changed to a drag or top speed boat by changing the prop to the extreme end.

A twin engined OB will be nearly equal to a massive inboard engine-performance wise. The wieghts won't be. fuel consumption and cost doubles.
800lbs output ~600 hp twin OBs
900?lbs output ~1,000hp inboard. (plus hull wieght???) The jet may only have 600 hp but I pushed the engine.

OBs - the power head wieghs in at 200 lbs and can be taken off by hand-literaly! Easy to work on. Very little to rebuild when it is time to rebuild.
The inboard is buried in a boat and needs a high lift to remove.

2-cycle run at extreme use has a shorter life till rebuild than a 4-cycle. The 2-cycle has very little in the way of what is rebuilt though!

[Stoker100]

Check out my Laveycraft in hull's over 20'. It is FAST and has the reliability of a Big Block chevy. No "check the bore" for pin scratches every 50 hours!
It's got the rumble, it's got the speed, it's a tunnel.
one boat, one motor, 100 mph, any questions!

[Steven]

i have a 19 ft liberator ob. 200 merc. i like the boat and i have always had outboards. it is very sensitive to weight. i guess all boats are, but i think jets carry weight better(people). just my thoughts. steven

[jrumon]

I have had many many hot boats and it greatly depends on what you plan to do...top speed, skiing, crusing, investment costs, maintainance, where you run the boat, etc.

I have had several squirt (jet) boats...from stock power to an 8-71 supercharged 21' eliminator with all the trick pump mods....A massive investment ($80K)...super fun, accellerated like a banchee, drank gas like there was no tommorrow, 90+ MPH and loads for fun...mega attention getter, safe in shallow water areas. BIG MONEY for this "TOY" jet.

If you want SPEED...I would go outboard...faster, lighter, more fuel efficent, and you can buy up to a 300HP performance motor (Merc 300X or 2.5HP SS, etc.) for about $17K. If treated right (good gas and oil, proper break-in, proper warm-up, proper cool-down etc.) these motors will last for a long, long time...case in point, offshore runs them 7000-8500RPM for an entire race with seldom a problem. They are reliable and you can get hundreds of RACE hours before a freshining-up. My buddy has over 500 hours on his pair of Merc 2.5 offshores without any work other than plug changes...if you don't run them flat out all day (like racing), I bet they'll last for 1000+ hours without any work. When it does come time to freshen them up (provided you don't blow it up), they can be done for $2000-$4000 professionally per motor...Compare that to my 8-71 blower motor that needed valve springs, piston rings, and bearings every 100 hours (parts were $500, but labor would have been $2000-3000 if I had it done).

If you like safe boating (shallow waters), no prop to worry about, fun for the "kids" skiing, great accelleration, don't mind the fuel consumption, and are happy with that 65-70 MPH top end, I'd go jet in a heart beat. If you seek that high speed stuff 75+, I would put my money in outboards in a light hull, or an I/O on bigger/heaver applications. My current boat a is a 23' Warlock offshore with an HP500 set-up and a Mrecury Bravo outdrive...It will see 85 MPH in two foot chop like your driving down the freeway in your convertible. Outboards like light, low-friction hulls (tunnels and cats)...The big V8 I/O's will push heavier "V" bottoms well with enought power ($$$$$). jrumon@yahoo.com

:cool:

[heath brinkley]

I agree with rusrog, and though I'm not certain I've heard jets rob about 30% of your horsepower. one more thing if your wanting to go fast try fueling a high performance big block anything at 5 to 8000 rpms all day. I know I can't afford it.

[jrumon]

Heath, Your correct, jets will typically draw more power and that number increases the harder you push them...hence its takes big power to push a jet with any speed in mind. I currently have a 23' Warlock offshore running a 500+ big block (MPH in the mid 80's). At "cruising speeds", this thing is supprisingly fuel efficent so to speak....My boats weighs in at around 3200 lbs, and I would need a healthy pair of outboards to get the same performance out of this deep "V" hull. Going back to my Vegas XT with the outboard, the whole deal weighted about 1200 lbs, but I count even think of running that boat out in big water....It's the price I pay to boat in the great lakes! If I was buying something new, it would be OUTBOARD POWERED! :rolleyes:

[Capt.Insane-o]

I going to have to argue that one. And there is no way a 2.5 Hi perf will make 1000 hrs short of divine intervention.

[Stv Euro]

My dad and I have both. They are similar in that they float on water thats about it. The jet has a 468 Olds Mondello motor with a Berkely pump. The boat has had a ton of work done to it and will run around 70. With a jet it seems that you will get a lot of looks at idle while you are shaking the water. Don't get me wrong I love jets but if you want to fly down the lake at 100 plus a HIGH PERFORMANCE ob is the way to go. Notice I said HP OB not a stock 5800-6100 rpm motor. I am talking a 7800 plus rpm all ball bearing motor.

The gas thing: I don't know if I have a jet that is good on gas or do I have a ob that loves it?!? My big block jet can run all day on 24 gals of 93octain. My 2.5 merc runs about 2 hours on 28 gals of 93octain.

Out of the hole jets are very strong. Jets also carry weight better. But don't be shocked if you see a ob blow a jet of the lake out of the hole. My dad can be in the jet and I will be in the STV and when we kick them off at a stand still I will stay beside him and then I will be gone. Then we will switch boats and the same thing the power and speed runs out with the jet. BUT the fun thing by now you will have a ton of boats around you because the jet is so loud everyone comes over to watch.

It's a blast!!!

Good luck and the main thing get what is best for you. Ride in a jet and an ob. You may like the ride of one better than the other. They both have a very different ride.

[GeorgeI]

There is another possibility that just became available, you can choose an outboard waterjet with a 275 hp GM V-8 or a 150 hp International diesel and get the advantage of having the weight in the right place and having the waterjet propulsion. The product is the JetPac outboard waterjet and it is at website http://www.jetpac.us if you want more information.

[signpro]

I have owned them both, including a few I/O's, My STV is the first outboard that I have had, beign able to change props between a low pitch drag prop and a higher pitch top-end prop is a great assset, I just recently installed a Nitrox nitrous kit, and really like it, with a 24 pitch yamaha copy drag prop, it is faster on the bottom end than any of the jets I have had, the only thing I do not like about to outboard, is that lack of any good idle noise, nothing sounds like a roller cam big block, but that 2-cycle sounds pretty good at 8,500 rpm too!! take a ride in both, I had never ridden in a STV, and just asked for a ride, I am sure that there is a board member near you that is willing to take you for a ride.

Just my thoughts

CHRIS

[KC462]

Its a case of horses for courses.

I crew chief a '79 Mantra Jet Vee with 540 ci of alcohol injected Chevy spinning a Berkeley. We race it in the River Racer class in the SDBA/CSDBA/IHBA in Oklahoma, Kansas, Arkansas, and Texas. Best pass to date is a 11.37 at 93 mph at the Marble Falls Lake Fest. Not too far from running Stock Eliminator. The boat is a lake hull, not a 300 pound race hull. Therefore the engine needs to make about 750hp to get the heavy old thing out of the hole. This thing sucks as a lake boat, as it only carries 3.5 gallons of alcohol and the Enderle will drink it up in about 90 seconds of WOT running. However, it does not get beat out of the hole by any prop driven boat we race against. We never played catch up to any prop boat in the 9.00 second class this last weekend at the Smokin' on the Cove ET drags, even against some hard charging outboards. This is all great if you plan on just racing the boat. Even with a forged 4340 stroker crank, Eagle H-beam rods, J&E 13.5:1 forged aluminum slugs, and a blueprinted 502 Chevy Block it was cheaper to build than it would have been to purchase a stock 300 Merc or equivalent. You can get a jet boat to run big speed numbers, Ray Wahler's Edge Stealth can run in the 140s on a 1000 foot course, but he has a professionally built blown race engine on board and it would cost more than a speed comparable outboard.

If you are looking for a comfortable boat to run up and down the lake then an outboard offers the most versatile performance. All you really give up is the extreme down low accleration that a properly setup jet can deliver. The outboard will always offer up higher top speeds, better top end acceleration, and more passenger comfort than any 130db open header V8 jetboat. The jet boat just isn't as efficient as the prop at high speeds.

So, what do you plan on doing with it?