Jet Boats vs Prop Drive

[czimpel]

I have just started boating this summer. I resurrected a 1997 Larson Flyer that had been very poorly cared for. The boat has a 4.3 Volvo I/O.

What I'm wondering, is why are I/O prop drives so much more prevalent than jet drive boats. It seems to me, at least here in MN, that a jet drive has much more ability to get into low water areas than a prop drive. Is there something with fuel economy, maintenance, ease of driving that makes prop drives preferred?

Thanks, Cory
Central MN

 

[Lion hunter]

Re: Jet Boats vs Prop Drive

jet drives are designed to run low water, they are great for rivers. But, they rob about 30% of your power. So a 90hp with jet wil only be a 60. Often when you see jets for sale they are listed as a 90/60 or a 60/45. They are pretty much a must have to run water 2' or less. Any deeper and I would take a prop any day. I have alot of freinds with salmon boats and almost all of them have a prop drive boat as well for lakes.

 

[tashasdaddy]

Re: Jet Boats vs Prop Drive

agree 100%, yamaha has the best jet rating. but is still highly inefficient.

 

[Sikiguya]

Re: Jet Boats vs Prop Drive

I know that I am outnumbered by prop guys like 100 to 1. But jet boats have come a long way in the last 10 years. It isn't like it was in the 90s. There are a lot of reason to consider a jet boat. The fact that there is no prop eases my mind as a parent. My kids were jumping off the back of my boat today and I didn't give it a thought. When you throttle down, the bow doesn't obscure your view like most prop boats. The trust is also instant...throws you back! No, it isn't fuel efficient like some of the 4 cylinder engines. But it isn't bad...plus the last I check, there are no hybrid boat out there!!! Do more investigation into the jet boats. There are a lot of pros and cons when you look at prop versus jet boats. Better yet..go for a test drive!!!

 

[H20Rat]

Re: Jet Boats vs Prop Drive

jet outboards are 30% inefficient. In my opinion those are VERY specialized engines and the people who need a jet outboard don't care about the cost, the engine serves its function.

Modern jets are substantially better, and at their optimum rpm/load they will get very close to a prop. (yeah, they will drop off ALOT on the low end though, so if you spend alot of time idling around a jet isn't great) The rpm load isn't linear like a prop, it takes some rpm to build up pressure in the pump, below that you are more or less just functioning like a inefficient prop drive.

Maintenance on a jet is dead simple easy, there are vastly fewer parts to break and no gears that need to shift. Depending on the manufacturer there may not be any gears at all. (mercury uses a vertical engine with a 90 degree bend, other manufacturers just use a driveshaft right off the engine)

You also don't have a water pump impeller that needs to be replaced, water pressure is just siphoned off the jet for that.

 

[Lone Duck]

Re: Jet Boats vs Prop Drive

jet outboards are 30% inefficient. In my opinion those are VERY specialized engines and the people who need a jet outboard don't care about the cost, the engine serves its function.

Modern jets are substantially better, and at their optimum rpm/load they will get very close to a prop. (yeah, they will drop off ALOT on the low end though, so if you spend alot of time idling around a jet isn't great) The rpm load isn't linear like a prop, it takes some rpm to build up pressure in the pump, below that you are more or less just functioning like a inefficient prop drive.

Maintenance on a jet is dead simple easy, there are vastly fewer parts to break and no gears that need to shift. Depending on the manufacturer there may not be any gears at all. (mercury uses a vertical engine with a 90 degree bend, other manufacturers just use a driveshaft right off the engine)

You also don't have a water pump impeller that needs to be replaced, water pressure is just siphoned off the jet for that.

merc O B jets DO have an impeller and I suspect all the others do also.

 

[mrdancer]

Re: Jet Boats vs Prop Drive

... They are pretty much a must have to run water 2' or less. Any deeper and I would take a prop any day. ...

Or get a boat with a good prop (pocket) tunnel. I'm running a 26-foot aluminum flat-bottom with tunnel (115hp Merc) and with a specialized 3-blade tunnel prop I can run in six inches of water, and four inches of water in soft (sand or mud) bottom - the prop digs a little bit, since there is six inches of prop extending below the hull of the boat. The river I run has visibility of six inches or less, but any snags, sandbars, etc. within a foot of the surface make enough surface telltales to avoid them.

 

[DavidInWilmNC]

Re: Jet Boats vs Prop Drive

A jet boat that's NOT an outboard has another issue: the drive is always submerged in water. Marine growth can be a real problem with that. An outboard can (obviously) be tilted out of the water and an inboard is designed to stay in the water. I guess if one only trailers a boat or keeps it on a lift a jet could be nice. Are jet boats any more maneuverable at low speeds that a jet ski?

jet outboards are 30% inefficient. In my opinion those are VERY specialized engines and the people who need a jet outboard don't care about the cost, the engine serves its function.

Modern jets are substantially better, and at their optimum rpm/load they will get very close to a prop. (yeah, they will drop off ALOT on the low end though, so if you spend alot of time idling around a jet isn't great) The rpm load isn't linear like a prop, it takes some rpm to build up pressure in the pump, below that you are more or less just functioning like a inefficient prop drive.

Maintenance on a jet is dead simple easy, there are vastly fewer parts to break and no gears that need to shift. Depending on the manufacturer there may not be any gears at all. (mercury uses a vertical engine with a 90 degree bend, other manufacturers just use a driveshaft right off the engine)

You also don't have a water pump impeller that needs to be replaced, water pressure is just siphoned off the jet for that.

 

[Lion hunter]

Re: Jet Boats vs Prop Drive

Every boat and motor here has pros and cons. As far as inboards jets on v-hulls I have no experience. Outboard jets on river sleds are essential on the rivers where I live. People with these boats are running up to class III whitewater. You wont ding a prop here if you make a mistake, you'll lose it. And that can be very dangerous to lose a motor in those situations. No that you can't lose the jet, but they sit above the keel so it is less likely. Alot of the river sleds also run inboard jets and they work just as well for that purpose. All of my friends that have outboard jets do complain about their performance on open water. I also think it is important to look at the jet set up. River jets sit above the keel. As such they do not plane well and performance suffers on open water. If memory serves me inboard jets are set up much like a prop in relation to the keel and they plane very well. Each person is going to be different and have a favorite set-up that they run. The only answer is to try them all and get the one you like.

 

[H20Rat]

Re: Jet Boats vs Prop Drive

merc O B jets DO have an impeller and I suspect all the others do also.

yep, outboards do. inboard jet boats don't have impellers. (seadoo/sugar sand/yamaha, etc...) The original poster was talking about a jet inboard, not an outboard jet.

 

[H20Rat]

Re: Jet Boats vs Prop Drive

Are jet boats any more maneuverable at low speeds that a jet ski?

They are generally better than a jet ski and vastly better than a prop. Given some experience, you can do some incredible slow speed maneuvering. You can slide it straight sideways and parallel park, or pivot around the center of the boat. And you actually get brakes if you need to stop. In an emergency you can go from 50 mph to 0 in 2 or 3 boat lengths. (Granted, you will submarine the front end and will have to pump out water for awhile.)


(I've owned several jet boats and several props/IO's, as well as a couple jetskis, so i'm quite familiar with all of them)

 

[indy440]

Re: Jet Boats vs Prop Drive

I've had both prop driven boats and a jet drive boat, as well as jetskis.

They're just two different tools... for similar jobs...

For the lake I like to use, and the things I like to do, a jetdrive wins my vote. It all comes down to how you're going to use it... For me, the benefits of a jet out-weigh the cons.

They can be tricky at really low speeds, but once you get the hang of them they're actually very easy to maneuver and dock. There is just that learning curve to overcome.

 

[78 GT-150]

Re: Jet Boats vs Prop Drive

They are generally better than a jet ski and vastly better than a prop. Given some experience, you can do some incredible slow speed maneuvering. You can slide it straight sideways and parallel park, or pivot around the center of the boat. And you actually get brakes if you need to stop. In an emergency you can go from 50 mph to 0 in 2 or 3 boat lengths. (Granted, you will submarine the front end and will have to pump out water for awhile.)


(I've owned several jet boats and several props/IO's, as well as a couple jetskis, so i'm quite familiar with all of them)

Brakes?

 

[ziggy]

Re: Jet Boats vs Prop Drive

Brakes?

i come from jet skis, but my guess is he's referring to what i called the reverse bucket on my skis. since jets are usually direct drive, the impeller is always putting out fwd. thrust. the rev. bucket just drops down in ft. of the jet nozzle and deflects the water to the ft. of the boat, thus, reverse. if used at speed, like in dropping the bucket if ft. of the nozzle at speed, it'll act like a instant break, nose dive down. but it'll stop ya... this action was noted in my jetski/waverunner manuals as something not to do. the nose dive, the instant stop, stress on the bucket assy. were reasons i could think of to not do it. maybe real jetboats ya can do this safely with, i don't know..

 

[78 GT-150]

Re: Jet Boats vs Prop Drive

I knew about the reverse scoop, but I would never think to use it to stop... It doesn't really set down in the water very far.

 

[45Auto]

Re: Jet Boats vs Prop Drive

Given some experience, you can do some incredible slow speed maneuvering.

Maybe you could offer some kind of lessons or DVD or something on this incredible slow speed manuevering and put the Cobra Fin guys out of business ........

(Cobra Fin is making a killing selling fins for $160 to improve the low speed handling of jet boats)

http://www.cobrajetsteering.com/Testimonials/Testimonials.php

 

[bilmon]

Re: Jet Boats vs Prop Drive

Braking is done using reverse thrust,not from the drag of the bucket. The one on my 240 Merc powered Sugarsand is very beefy cast aluminum,I have no fear of using it at any speed.It is amazing how fast you can stop.Yes you can do incredible manuevers at low speed as for the Cobra Fin I understand it does work great but I think of it like training wheels,I don't see any need after some practice but to each his own.Had my jet since it was new in 03.Had OBs for 40 years before that, Not likely to ever switch back.

Bill

 

[czimpel]

Re: Jet Boats vs Prop Drive

Wow, amazing information. Thanks everyone for your comments so far. I am a fan of jet boats, I was just not sure why I can't find more of them out there for sale. Seems like I/O's are 100:1 to jets.

Thanks again, Cory

 

[H20Rat]

Re: Jet Boats vs Prop Drive

Braking is done using reverse thrust,not from the drag of the bucket. The one on my 240 Merc powered Sugarsand is very beefy cast aluminum,I have no fear of using it at any speed.It is amazing how fast you can stop.Yes you can do incredible manuevers at low speed as for the Cobra Fin I understand it does work great but I think of it like training wheels,I don't see any need after some practice but to each his own.Had my jet since it was new in 03.Had OBs for 40 years before that, Not likely to ever switch back.

Bill

Fins... yep, my thoughts exactly, they are training wheels for people who are having a hard time grasping how a jet works. Watch someone who knows what they are doing, they will EASILY out maneuver a prop boat.

as far as the brakes, on the mercs you CAN use it while moving, it is fairly safe to do and the boats are built for it. (yes, you use reverse thrust) My sugar sand has 2 bilge pumps for the cockpit area, and one bilge pump plus the jet suction pumps for the engine compartment. If you hit the brakes, it will dip the front end into the water and you end up sitting waist deep.

They are designed to have more then enough flotation between the outer hull and the inner sole, so you still have safe freeboard even full of water. The inner and outer areas are fairly sealed, very little water makes it into the engine area.


crappy video, but enough to give you an idea...

http://www.youtube.com/watch?v=npA_oB4xjsk