Jet vs. I/O

[pchansen]

First post. I've been looking at 2007-2008 Challenger 230 SE's. I've never owned a jet powered boat before- in fact I've never even ridden in one before. I like the lay out of the Sea-Doo's and Yamaha's, the safety and the perceived power. Of course I'll test drive anything I end up buying if possible but a few questions. I had a friend try to talk me out of jet drives because they would have a hard time pulling a large or heavy adult out of the water from a deep water start, they are very noisy (98db+ at full throttle) and create "very hard" water behind the boat. He described this as water being very turbulent and difficult to ski behind. He also mention atrocious fuel economy at throttle settings beyond 75% (as compared to a V-8 I/O).
What say you?

 

[timeman]

I have had only 1 jet drive,(Challenger 180,215 sc) previously had several different i/o from Bayliner and Rienell. Pulling a heavy skier out of a deep water start seemed equally difficult no matter the drive. Some were 4-6 bangers, the v-8's were heavier boats, extra engine power, was offset by size/weight of boat. Fuel econ and noise were also similar, slightly worse on my jet. Jets create a turbulent wake, flat but bumpy, prop boats cut more of a deep, even groove. Out-drives had maintenance issues,jet drives can suck up rocks/sticks, replacing wear rings...prop boats easier to maneuver at low speed, jet boats are roomier, have less draft ,no danger of harming someone in the water. Try them all out, get the one that fits and is most fun, the sport is expensive, I wouldn't make some differences in fuel econ. a biggie, though I hear Obama is offering big rebates on wind/solar powered boats soon, good luck pulling your 250 lb. brother in law up on a cloudy, calm day!

 

[feld1128]

When comparing outdrive boats test out the different power options a 19 ft bowrider will be underpowered by a six cylinder but really move with a 350 mag or big block. The other thing to look for is the duo prop setups that are available since they have much more torque and are ideal for pulling skiers. I have a big block 420 hp 6500 lb bowrider with the volvo pennta duo prop and it would pull the arms off a 250 lb guy at full throttle.

 

[RFoster130]

Of the cons you mentioned the only one i think is even true is the bad gas economy. But if you are shopping for a 23 ft boat,
fuel economy shouldnt be your worry.

 

[feld1128]

Please remove post.

 

[pchansen]

Thanks for the honest responses!

 

[davo]

I have a c180 255hp and will use 30lph going at 50-60 kph on average. A mate with a smaller boat and a 130hp outboard will go through the same gas, but won't go as fast!
I'd say a jet will go through 5-10percent more fuel than others for the horse power. I'll guarantee the service costs generally will be less though if looked after.
I can swing anyone towards a jet who I've had on board simply by showing a spin to them- sensational. Try them both out first.
Cheers and good luck

 

[parrothd]

Jet boats don't make great ski boats, any "good" skier can pull the boat side to side, but they're cheaper and are nicer in my opinion ..

Pulling a skier with a jet boat takes a lot more effort on the drivers part, harder to keep speed and you constantly have to adjust to keep the boat straight..

With my twin challenger 1800 I have no issues getting skiers up, unless I have the boat loaded with max persons and gear, the noise, gas are probably about the same as a I/O boat, if I had the money I'd get one of the nice ski boats, nautique, but the jet boat works fine for the average skier..

 

[parrothd]

Jet boats don't make great ski boats, any "good" skier can pull the boat side to side, but they're cheaper and are nicer in my opinion ..

Pulling a skier with a jet boat takes a lot more effort on the drivers part, harder to keep speed and you constantly have to adjust to keep the boat straight..

With my twin challenger 1800 I have no issues getting skiers up, unless I have the boat loaded with max persons and gear, the noise, gas are probably about the same as a I/O boat, if I had the money I'd get one of the nice ski boats, nautique, but the jet boat works fine for the average skier.

 

[WAJetboating]

I now own both kinds of boats - a Mercury powered Seadoo jet and a Tige v-drive true inboard - so I can give you solid answers from personal experience.

Power: As long as you avoid the baby jetboats (the ones with a single jetski-style engine), you won't have any problem pulling up even large skiers. Any jetboat of 18+ foot length should have plenty of power. I had a ~250 pound guy behind us one day who insisted I needed to go to WOT immediately. I said no, and went a little soft the first time, but for the second run he absolutely insisted... and the force was so strong that it snapped the ski rope and darn near broke his wrist (swelled up to grapefruit size by the time he got back in the boat). His words: "I've never felt any boat pull so hard."

Fuel consumption: My jetboat averages 5 gallons per hour of actual engine operation in mixed use (wakeboarding, skiing, tubing, cruising). Basically one can of gas per hour. That means its 40 gallon tank is good for about eight hours of engine operation. My inboard is about the same, though in fairness it's at least 50% heavier and can legally carry twice as many people.

Skiing: My jetboat weighs about 3000 pounds with fuel, and it does indeed get tail-steered just a bit when I'm pulling a VERY aggressive skier who is cutting super hard. But it's really no problem, a light touch on the steering wheel easily compensates and I don't even think about it. It's like driving down the road, you automatically compensate for the slight directional variations caused by unevenness in the pavement. My inboard weighs ~4500 pounds and doesn't get tail-steered, though I'm not sure how much of that is due to weight vs. its rudder.

Maneuverability: That comment about prop boats being easier to steer at low speeds is (politely) totally wrong. NOTHING is more controllable than a jet. The ability to smoothly move the thrust reverser up/down lets you do virtually anything. I can spin our jetboat in its own length; try that with any other drive system. There's simply no contest.

Speed: Jetboat is the winner unless you're talking about a bass boat with a really big outboard engine. My jet will sustain 54 MPH. My inboard tops out at 40 MPH. If speed is important, get the jet. But remember, most people don't spend too much time at WOT. Almost all of our jet's time is spent between 20 MPH (boardsports) and 30 MPH (skiing). There's a fun factor in that top ~20 MPH but you probably won't spend much time there, so I'm not sure if that should be your deciding factor.

Maintenance: Jetdrives win, no question about it. Cheaper, simpler, easier to work on, the list goes on and on.

Noise: Varies greatly depending upon engine type. I've found the Rotax engines (especially the 2-strokes) to be the noisiest, and they really ARE noisy. I'd put my Mercury jetdrive about equal to a typical I/O; you can carry on a conversation at WOT but you'll raise your voice a little. My inboard's PCM V8 engine is whisper quiet; I've honestly forgotten the engine was idling a couple of times, and even at WOT it's far quieter than anything else.

Bottom line: Each category has its advantages (except perhaps I/O's, I truly don't know why someone would PREFER an I/O since it seems to have all of the disadvantages of every other drive type) and disadvantages. They can all pull skiers, tubes, boards, etc. If speed is paramount, go jet. If boarding is tops, get a v-drive. If skiing is all you'll ever do, get a direct drive inboard. And so forth.

Hope this helps!

 

[feld1128]

I agree with most points made but would like to add a litttle, I/O will have a speed advantage over the inboards since there is less drag and it can be trimmed for max speed. The other big advantage is it is far better in shallow water since you can raise it, this is very important to me since I boat in tidal waters and it can get shallow. My preference with big boats has been inboards since they stay in the water and corrosion can become a problem, I/O drives especially Mercury have a history with corrosion problems. You could always consider an outboard boat also simple to maintain self draining and easily trimmed up but noisy. Try them all before you commit.

 

[WAJetboating]

I/O will have a speed advantage over the inboards since there is less drag and it can be trimmed for max speed.

No argument about the trimming, but how do you figure less drag? The I/O has a huge lower end assembly hanging down in the water. The inboard has a short, narrow strut and a thin rudder.

As noted above, though, if speed is the goal both the I/O and the inboard lose out to the jetdrive.

The other big advantage is it is far better in shallow water since you can raise it, this is very important to me since I boat in tidal waters and it can get shallow.

Once again, the jetdrive is superior to all other options when in shallow water. That's why I said the I/O seems to combine all the worst features of every drive system... it's not really "best" for anything, though it can be made to work in most situations. But the same can be said of a jetdrive and it IS the best for shallow water, speed, maintenance, etc.

It seems to me there are really only two serious options for non-outboard boats: Inboard or jetdrive. An I/O doesn't seem to have a place that it exclusively "shines", a place where it can't be bested by one of the other two.

 

[feld1128]

You are advocating for the jet boat and I have no problem with that it has advantages no doubt but when you get into bigger applications the jet cannot compete for example my 28 ft bowrider weighs 6500 lbs dry, 90 gals of fuel and 25 gals of fresh water etc you are past jetboats and your choice is inboard or I/O. In my case I need to raise the drive so I/O it is. We are looking at this from two different views with different needs. The only thing I disagree with is the drag between I/O and straight inboard the I/O when on plane has less drag since the lower unit is contoured and when trimmed up there is not much in the water. The inboard always has the strut, shaft, rudder and prop in the water. This is why Formula for instance uses I/O's in their SS application vs. the inboards they use in their express cruisers. Manny of the inboard applications are also v drives which are less efficient than straight drives. Great debate while it is 20 degrees outside.

 

[RFoster130]

The other big advantage is it is far better in shallow water

Yeah I am gonna have to totally disagree. I have had my boat in spots less than 24 inches deep.

 

[feld1128]

We were comparing I/O's and inboards....

 

[WAJetboating]

You are advocating for the jet boat and I have no problem with that it has advantages no doubt but when you get into bigger applications the jet cannot compete for example my 28 ft bowrider weighs 6500 lbs dry, 90 gals of fuel and 25 gals of fresh water etc you are past jetboats and your choice is inboard or I/O.

Or a bigger jetdrive. Some ocean-going tugboats are jet powered, for example, and I guarantee they weigh more and have more power than your bowrider! {grin}

Another example is cable-laying ships - the ones that lay cables on the ocean floor. Those are commonly jetdrives now, because of the extreme accuracy of placement jets make possible (back to my thrust reverser comment above). Like a prop-driven airplane, they set the engine to a constant optimum RPM and vary the thrust by feathering the prop (airplane) or varying the thrust reverser (jetdrive). This gives them an extremely fine degree of control. BTW, the jetdrive can also rotate 360 degrees on those cable-layers so they can thrust in any direction to hold themselves on course while paying out the cable.

Cable-layers are BIG ships that weigh a LOT, and the spools of ocean-qualified cable they carry add a lot more to that weight.

Yet another example is cruise ships. I was on the Sapphire Princess a couple of years ago, going through the fjordlands at the southern tip of New Zealand's south island. It turned around in its own length at one point (this is a 1000 foot long ship!) so I asked about the ship's propulsion systems. For maneuvers like that, they have jetdrives in the bow and stern that punch entirely through the hull from one side to the other. Doors open up and they can push the boat SIDEWAYS for tight docking in the absence of tugboats, rotate it either direction, etc.

So there's really no limit to how big you can get a jetdrive. Whether it's optimal for the application... that's another question!

Great debate while it is 20 degrees outside.

Agreed! If we can't be on the water, at least we can talk about it!

 

[feld1128]

Then my question is why has the pleasure boat industry not embraced jet drives across the board specifically larger pleasure boats? In the 25 ft to 50 ft range there are very few jet drives with some exeptions like Hinkley and a few other manufacturers of down east style boats. The trend now is away from traditional inboards to pod drives like the Volvo penta pod drives and the zeus drives from mercury/ cummins. They are in essence a lower drive from an I/O underneath the boat facing forward with duo prop technology, which is btw derived from large vessels like cruise ships.

 

[WAJetboating]

Then my question is why has the pleasure boat industry not embraced jet drives across the board specifically larger pleasure boats? In the 25 ft to 50 ft range there are very few jet drives with some exeptions like Hinkley and a few other manufacturers of down east style boats.

Good question. There must be a reason. All I was trying to say was that there isn't any strict limit on the power available from a marine jetdrive. I'm sure there are other considerations besides just power.

 

[dsw222]

Here's an interesting read. Its not exactly what you're looking for, but its a good comparison of jet vs prop boats by a good source (popular mechanics)

http://www.popularmechanics.com/outdoors/recreation/boating/1276876

 

[WAJetboating]

Here's an interesting read. Its not exactly what you're looking for, but its a good comparison of jet vs prop boats by a good source (popular mechanics)

Unfortunately, that article:

1) Is 11 years old.

2) Only discusses jetboats that have two jetski engines. As just one example, just a year later (in 2000) Seadoo started offering Mercury V6 engines that solve many of the problems this article attributes to twin jetboats (fuel consumption, excessive noise in general, excessive high frequency noise, excessive RPM's, etc.).

3) Attributes control problems to jetboats that are not present in later designs due to changes in the way the console controls were improved.

...and so forth. Basically, in the mid to late 90's jetski makers realized they could expand their market by wrapping a larger hull around their existing drivetrains. These early jetboats were hardly worthy of the name "boat". But the manufacturers learned, and got better, and the boats and engines improved. It's hardly valid to base a buying decision today on a review of technology that is over a decade in the past.

Just my $0.02....

 

[dsw222]

Unfortunately, that article:

1) Is 11 years old.

2) Only discusses jetboats that have two jetski engines. As just one example, just a year later (in 2000) Seadoo started offering Mercury V6 engines that solve many of the problems this article attributes to twin jetboats (fuel consumption, excessive noise in general, excessive high frequency noise, excessive RPM's, etc.).

3) Attributes control problems to jetboats that are not present in later designs due to changes in the way the console controls were improved.

...and so forth. Basically, in the mid to late 90's jetski makers realized they could expand their market by wrapping a larger hull around their existing drivetrains. These early jetboats were hardly worthy of the name "boat". But the manufacturers learned, and got better, and the boats and engines improved. It's hardly valid to base a buying decision today on a review of technology that is over a decade in the past.

Just my $0.02....

Guess I should have posted that somewhere else. I know its not related because first and foremost, he's looking at 4stroke which is vastly different from the 2stroke rotax in general. But i have the same boat they reviewed in there, and thought some other people would like to read it

 

[WAJetboating]

Guess I should have posted that somewhere else. I know its not related because first and foremost, he's looking at 4stroke which is vastly different from the 2stroke rotax in general. But i have the same boat they reviewed in there, and thought some other people would like to read it

No, I'm glad you posted it, but it needs to be read with the above limitations in mind. More data is always good.

 

[feld1128]

Even though the article is 11 years old and the boats have developed to a great degree I think some of it still holds true, seaworthiness is not a strong point of the pleasure jet boats that are available today. I boat in big water at times and travel long distance which I would not do in a jet boat, I need a good amount of freeboard a descent deadrise to keep everyone safe when the weather picks up.

 

[WAJetboating]

Even though the article is 11 years old and the boats have developed to a great degree I think some of it still holds true, seaworthiness is not a strong point of the pleasure jet boats that are available today. I boat in big water at times and travel long distance which I would not do in a jet boat, I need a good amount of freeboard a descent deadrise to keep everyone safe when the weather picks up.

I totally agree. But now you're talking more about boat design, not the choice of propulsion system. I would be perfectly content to venture onto big water in a jetdriven boat - if the hull, deck, etc. were designed for big water. Sub-25 foot boats of any type aren't truly "big water" boats, no matter how they're powered.

 

[davo]

Jet drive boats not seaworthy as compared to others. HMMM.

I believe they're no worse/better than comparable sized boats from other manufacturers who utilize other propulsion types. Personally I don't care what pushes the boat along, going out in anything smaller than a 28' cruiser in big chop is asking for it. Not to mention who would like to pleasure boat in these conditions.
I have a few rellies who question/put down my boat with how it would handle really rough conditions. My response is ' why would I go out in crap conditions'. That usually shuts them up. Most pleasure boaties go out in mostly fine conditions so their less experienced passengers don't get the crap scared out of them. Yes the weather can change, but this is usually more a problem with poor planning, or not understanding the weather & forecasts very well.