Prop boat to jet boat?

[Jimwhall]

I'm in the market for a new boat for my family. I'm looking at the 20 foot range and I've seen some Yamaha jet boats in my price range that look quite nice; but I've never had a jet boat.

How is it going from prop to jet? My kids like to ski and tube, is this do'able? The boat seems to have plenty of power (2 160 hp engines) but are the jets able to tow plus have a family in the boat?

Thank you for any input.

 

[Texasmark]

Only 2 things of which I am aware: 1. Had a friend suck up his ski rope in the impeller and had a bear of a time getting it out without putting the boat back on the trailer and trying there.
2. Pumps aren't all that efficient. In outboards, the 75 hp triple 2 stroke Merc is rated at 60 hp with the jet pump and the 4 cyl is similarly rated.....not remembering but I think it is listed at 100 vs 115 in prop or 115 rated 125 in prop, one or the other.
Going to guess the hole shot would be much slower especially pulling skis.

Since you are running the 75 hp for example and only getting 60 hp worth of thrust, you have a fuel consumption penalty there to consider also. Have no idea as to the normal maintenance schedule on pump impellers and all and no idea as to the difficulty in working that area, vs removing a nut and washer and off comes the standard propeller, sticking out in the open, readily accessible.

Good part is they work good in rocky waters as you see a lot of jets used in streams and rivers in advertisement literature.

 

[southkogs]

I've seen several of them towing on our lakes down here. They seem to have more wake boards and surfers behind 'em, so if water skiing is the goal make sure you see how big a wake they tend to throw. But from all indications, they'll tow for watersports.

 

[JimS123]

Only 2 things of which I am aware: 1. Had a friend suck up his ski rope in the impeller and had a bear of a time getting it out without putting the boat back on the trailer and trying there.

Suck up a line and more than likely you'll bend the shaft. The worst part is that it probably won't be noticeable, so you'll go along with no corrective action. Then later down the road you'll be in for some serious repairs.

 

[Pulse186]

How is it going from prop to jet? My kids like to ski and tube, is this do'able? The boat seems to have plenty of power (2 160 hp engines) but are the jets able to tow plus have a family in the boat?

For general family boating that is more than adequate. There are difference in the way the boat feels and you don't want to be sucking sand and whatnot into the jet but it will be a fun boat.

pulling kids on a tube is not the same as pulling a 200 pound experienced slalom skier.

 

[QBhoy]

I’ll admit first off... that I think these are silly things generally!
The sheer inefficiency of them is simply unreal. They are usually powered by jet ski small displacement engines. With sky high and screaming rpm. Some 3 cylinder from the BRP made and some 4 cylinder NA or supercharged versions of both.
Comparing to a prop powered boat...if we take an identical hull with an outdrive 300hp v8...and compare it to one with say the twin 160hp jets...despite having similar or more power...the difference in performance and fuel economy is nothing short of enormous. They are so inefficient it’s not real.
a couple of years ago there was a chap with a Seadoo 19/20ft jet boat here, powered by two 215hp supercharged jet engines. So he had 430hp on tap. It was far too tempting for me not to go up against it in my 18ft (certainly heavier) boat with single outdrive power. Mine will have around the 300ish or a little over Hp. 100-130hp less than him...
We were both sitting around 20mph next to each other. Both opened the throttles...the jet boat did leave me behind for about 20 seconds...but after that it was easily embarrassed. I sat
Next to him and the screaming engines at about 55 mph at its best...then left it looking silly. Likely used half the fuel he did too.
Have a look at the performance and fuel figures and compare them to a similar outdrive or outboard. The jet will lose out every time.
As for the argument “but you can run in much shallower water”. Usually utter none sense. If the intakes for these jets are anything less than about 3ft from the bottom...you’ll suck up sand and everything else through the impeller and wreck it and the wear rings in seconds.
also a total nightmare at slow speeds too, although I think yamaha have tried to address this with adding little skegs to the jet drive or similar. For me...long story short...don’t waste your time with them, unless you can stand the noise of screaming tiny engines doing 8000-10000 rpm and not going anywhere fast.

 

[Stinnett21]

But I wonder if the inefficiency isn't offset by lower maintenance costs vs sterndrive. Have to admit I'm envious, no gimbal bearings, yearly drive pulls, shift cables, ujoints, bellows, power trim issues. They sure are selling a lot of them.

 

[QBhoy]

But I wonder if the inefficiency isn't offset by lower maintenance costs vs sterndrive. Have to admit I'm envious, no gimbal bearings, yearly drive pulls, shift cables, ujoints, bellows, power trim issues. They sure are selling a lot of them.

But you have frequent impeller damage and changes, wear rings too. intermediate shaft seal leaks and bearings to do. Serious fuel cost and certainly only a fraction of the life span on the engine. There are GM V6/v8 engines still in boats from the 70’s going strong. No way a 8000rpm 3 cylinder 200+ hp engine is lasting anything like that or close to it. They aren’t reliable in a 300kg jet ski for too long...imagine they’ll be less Hardy and long lasting pushing a 1500kg boat.
again. Just my thoughts.

 

[JimS123]

But you have frequent impeller damage and changes, wear rings too. intermediate shaft seal leaks and bearings to do. Serious fuel cost and certainly only a fraction of the life span on the engine. There are GM V6/v8 engines still in boats from the 70’s going strong. No way a 8000rpm 3 cylinder 200+ hp engine is lasting anything like that or close to it. They aren’t reliable in a 300kg jet ski for too long...imagine they’ll be less Hardy and long lasting pushing a 1500kg boat.
again. Just my thoughts.

If you act responsibly, impellers and wear rings shouldn't be a problem. They should last years and years.

Maybe PWCs shouldn't be talked about in the same topic. Jet skis are considerably cheaper than a boat, plus they usually are bought by younger people that don't have a clue about boating. As such, they are poorly maintained, run hard and put away wet. That's why a used 'ski is sometimes a poor investment. Now, for us old codgers that buy new and take care of our 'skis, please disregard my comments.

OTOH, buying a jet boat to me is really dumb. Sure, the fuel economy sucks the big one, maneuverability is awful and you don't dare go in shallow water. But the biggest drawback in my mind is the capital cost. For what a Yamaha twin engine runabout costs, you could buy a tricked out I/O bowrider and it would be bigger and better.

Remember that jets in runabouts started many years ago, and fell by the wayside after not too long. The current varieties were extensions of jet skis. Also remember that basically Yami is the only one left. Sea-Doo was one of the first out and they discontinued them a while ago.

Since we're talking about boats, as a previous owner of outboards, jet boats, jet skis and (the longest) an I/O, IMHO a current 4-stroke outboard is the only way to go. Faster, more fuel efficient, smoother, quieter, lower maintenance, run in very shallow water, superior maneuverability, etc, etc. No downside.

Everything has a time and a place. If I could only have 1 boat it would be an outboard.

 

[harringtondav]

This reply is based on opinion and observation, no facts. @QBhoy 's reply #6 mostly sums up my thoughts.

I don't know the engines pushing jet boats. But I know the engines pushing outdrive boats. Most are variants of proven automotive engines. Maximum power and speed around 4600 to 4800 rpm. Good low end torque for pulling up a load on the tow ropes. Higher rpms mean earlier engine wear out.

As mentioned above, efficiency is iffy on a jet drive, and deteriorates over time. Faster if you suck sand pulling off a beach or sandbar.

Maintenance costs? Depends on how you operate either drive, what you hit, what you suck up, or get tangled up in.

Outdrive or O/B drive maintenance is all external. ..again I've never dug into a jet drive, but I believe it's internal to the boat and requires more intrusive surgery.

Edit after more pondering the topic. In a prop driven boat you can tune your performance with a simple change of propeller pitch. ....not sure if this is so easy with a jet impeller.

 

[Stinnett21]

Agree on the outboard. If I could afford a switch I'd do it. Here soon, however, fuel tanks will be replaced by battery cells. It's coming quicker than we think. It seems this would further the demise of the inefficient jet drive. Amazing how quickly Volvo ditched Seven outboards focusing on sustainability.

 

[QBhoy]

Agree with the above. Without being smart, I’m not too badly placed to offer an opinion on it. I’ve had a few jet skis and boats over the years. I had a ski with these very engines. The Yamaha 160hp engines are the excellent MR1 units. Derived from the motor bike R1. But at 10200 rpm rated. I don’t want them in a boat for sure.
In reply to the responsible use and impeller and wear ring lasting for years...that can be true...but only takes a second or two for sand or pebbles to make mince meat of them both in shallow water. Suppose I was demonstrating that the idea that they have an advantage over a sterndrive in shallow water, isn’t really true at all. The only guys who have use for them, I can think of...are guys with aluminium hulls and running in rapids, rocks and skinny water. Some guys get a kick out of that. But also are constantly pulling the jet pump for maintenance to do so.

 

[JimS123]

Here soon, however, fuel tanks will be replaced by battery cells. It's coming quicker than we think.

I disagree wholeheartedly. If it comes to that we'll all be running 14 foot tinnies.

My buddy has (had) a Jap widdle compact all electric vehicle. When he gave me a ride in it I was surprised because it ran so nice. Then he told me with the batteries it weight over FIVE THOUSAND pounds. Later in the year he hit a deer and that little collision totaled the vehicle....but that's yet another story post.

Cars have rolling wheels and the drive train can be geared such that you can generate a lot of power. Sure, weight matters, but it can be overcome.

OTOH boats suffer badly as weight is increased. No positive displacement tires, but rather a prop that "slips" when put it to any resistance.

I won't see an electric 40 mph runabout in MY lifetime. But hopefully there will still be a few gallons of gasoline left so I can run my old woodie with its 25 HP OB.

 

[QBhoy]

I disagree wholeheartedly. If it comes to that we'll all be running 14 foot tinnies.

My buddy has (had) a Jap widdle compact all electric vehicle. When he gave me a ride in it I was surprised because it ran so nice. Then he told me with the batteries it weight over FIVE THOUSAND pounds. Later in the year he hit a deer and that little collision totaled the vehicle....but that's yet another story post.

Cars have rolling wheels and the drive train can be geared such that you can generate a lot of power. Sure, weight matters, but it can be overcome.

OTOH boats suffer badly as weight is increased. No positive displacement tires, but rather a prop that "slips" when put it to any resistance.

I won't see an electric 40 mph runabout in MY lifetime. But hopefully there will still be a few gallons of gasoline left so I can run my old woodie with its 25 HP OB.

Totally agree. Decades away from it even being close to being sensible, if it even is.
Im all for innovation and progress, but for me, boating is about pleasure and relaxing. About the experience and stimulation of the senses.
I spend my working week running wind farms and being sensible...I need a V8 experience or at least something that won’t run out of power and performance at the weekend...or have the ability just to put more fuel in to continue.
I don’t want my pleasure limited by the amperage of a battery !

 

[harringtondav]

I disagree wholeheartedly. If it comes to that we'll all be running 14 foot tinnies.

For sure. The available fossil petrol is in the ground and fading fast. Pleasure uses of it will fade just as fast. My new gas powered pleasure craft boat will be here this summer. I'm not sure which will die first: Me, or my ability to afford to keep it fueled up.

I cringed when I hard a news blurb touting new developments in EV battery tech. "400 mile range, and acceleration 0-60 mph in three seconds". ... erm, that should be "or" acceleration 0-60...etc. Energy in a gas tank or EV battery is what it is. How long it lasts depends on how you use it.

 

[QBhoy]

For sure. The available fossil petrol is in the ground and fading fast. Pleasure uses of it will fade just as fast. My new gas powered pleasure craft boat will be here this summer. I'm not sure which will die first: Me, or my ability to afford to keep it fueled up.

I cringed when I hard a news blurb touting new developments in EV battery tech. "400 mile range, and acceleration 0-60 mph in three seconds". ... erm, that should be "or" acceleration 0-60...etc. Energy in a gas tank or EV battery is what it is. How long it lasts depends on how you use it.

Totally get you. And no doubt things have progressed hugely here in Europe with cars and charging etc. But here on the west coast of Scotland around the god kissed scenery...there isn’t going to be scope for electric waterside charging anytime soon.

 

[Texasmark]

Agree with the above. Without being smart, I’m not too badly placed to offer an opinion on it. I’ve had a few jet skis and boats over the years. I had a ski with these very engines. The Yamaha 160hp engines are the excellent MR1 units. Derived from the motor bike R1. But at 10200 rpm rated. I don’t want them in a boat for sure.
In reply to the responsible use and impeller and wear ring lasting for years...that can be true...but only takes a second or two for sand or pebbles to make mince meat of them both in shallow water. Suppose I was demonstrating that the idea that they have an advantage over a sterndrive in shallow water, isn’t really true at all. The only guys who have use for them, I can think of...are guys with aluminium hulls and running in rapids, rocks and skinny water. Some guys get a kick out of that. But also are constantly pulling the jet pump for maintenance to do so.

That is the synopsis of my reply, a Mercury OB commercial, in a Merc OB catalog with a 75/60 hp Jet on an aluminum boat, specially designed for the Pacific NW, on a river full of rocks.

 

[H20Rat]

As for the argument “but you can run in much shallower water”. Usually utter none sense. If the intakes for these jets are anything less than about 3ft from the bottom...you’ll suck up sand and everything else through the impeller and wreck it and the wear rings in seconds.
also a total nightmare at slow speeds too, although I think yamaha have tried to address this with adding little skegs to the jet drive or similar. For me...long story short...don’t waste your time with them, unless you can stand the noise of screaming tiny engines doing 8000-10000 rpm and not going anywhere fast.

I've owned about 6 jet boats, and 5 prop boats.

Yes, you can run in MUCH shallower water. Whoever tells you can't has never owned a jet. (have you?) I would frequently take my jet on the Missouri in 3 to 4 inches of water. Yes, you can't start or stop, and if you touch down, you are getting the shovel out. (yes, i carried a shovel!) I owned that boat for 7 years, never had to touch the wear ring. (and even then, that is a quick and easy replacement) From a dead stop, I needed maybe about 18 inches of water if I hit the gas. A little less if I idled up slowly.

Handling? I could EASILY outhandle any single screw boat out there. My favorite thing to do at a nearby dock was to go straight into the double floating dock, stop, pivot in place, and then walk the boat straight sideways and tie up. Easy to do if you are experienced with a jet, simply impossible to do with a single screw boat. Again, people who say they handle poorly haven't spent enough time behind the wheel.

My last jet boat was 17.5 feet, 175 v6 merc, and would do about 55 on a good day. My current boat is 18.5 feet, merc 4.3l i/o, and does about 43 mph. Granted, HUGE different in weight, but still a comparison.

 

[H20Rat]

Going to guess the hole shot would be much slower especially pulling skis.

All things being equal, jets are MUCH faster off the holeshot. The RPM of an engine connected to a jet drive doesn't vary with load. IE, if you tie a jet boat to a pier and hit the gas, it will hit the same RPM as with 1 person flat out. Do the same with a prop boat and you might be at half your normal WOT rpm. That is important when you think about the horsepower curve of your engine, the jet connected engine is putting WAY more power into the water immediately instead of having to get moving.

The other trick pulling skiers is to make sure they jet wash hits their skies. Pops them up instantly!

 

[JimS123]

I've owned about 6 jet boats, and 5 prop boats.

Yes, you can run in MUCH shallower water. Whoever tells you can't has never owned a jet. (have you?) I would frequently take my jet on the Missouri in 3 to 4 inches of water. Yes, you can't start or stop, and if you touch down, you are getting the shovel out. (yes, i carried a shovel!) I owned that boat for 7 years, never had to touch the wear ring. (and even then, that is a quick and easy replacement) From a dead stop, I needed maybe about 18 inches of water if I hit the gas. A little less if I idled up slowly.

Handling? I could EASILY outhandle any single screw boat out there. My favorite thing to do at a nearby dock was to go straight into the double floating dock, stop, pivot in place, and then walk the boat straight sideways and tie up. Easy to do if you are experienced with a jet, simply impossible to do with a single screw boat. Again, people who say they handle poorly haven't spent enough time behind the wheel.

My last jet boat was 17.5 feet, 175 v6 merc, and would do about 55 on a good day. My current boat is 18.5 feet, merc 4.3l i/o, and does about 43 mph. Granted, HUGE different in weight, but still a comparison.

Yup, don't touch down. Aye, there's the rub.

I would ask, since you owned 6, how many needed repairs before you got one that was trouble-free?

Second question, why do own an I/O now? Why not another jet?