Prop to Jet Drive

[hslobo]

I am currently running in OMC 4.3 IO With a Volvo Penta Out Drive on a 17’ Four Winn’s Freedom 180 bow rider. I’m thinking of selling it in switching to a Sea Doo jet boat. I’ve never driven a jet boat before and was wondering what the pros and cons might be making a switch from prop to Jet drive. Any information anyone has on Maneuverability and maintenance differences would be greatly appreciated

 

[cptbill]

A couple of my neighbors have small jet drive boats(14-17ft) and they love them only thing they had any problem with was remembering to use throttle to turn, they also say reverse is a little lackluster

 

[HT32BSX115]

remembering to use throttle to turn,

This is worth repeating since you can easily hurt or kill someone by "forgetting" it!

Also, even though no one should mention fuel economy when "speaking" boat......you'll burn more fuel doing performance dependent things like skiing, wake boarding etc.

You'll get poorer performance with the same HP in a similarly sized boat. (so you need more power)

At the same time, you'll never have to worry about banging a prop on the bottom again!

 

[JimS123]

Jet Pros:
* safer for swimmers (when engine is off) - no prop
* big wake looks cool

Jet Cons:
* poor maneuverability & docking
* poor backing up
* poor safety (when engine is on) - docking and running into other boats when you are inexperienced
* poor performance in weedy waters - constantly trying to free the impeller
* poor reliability in dirty water - plastic bags and debris (like after a rainstorm) will shut you down every time
* excessively expensive to purchase (e.g., compare an I/O of any make to a Yamaha)
* awful fuel economy.
* maintenance CAN be worse. An impeller & wear ring parts and labor is expensive. Even a shade tree mechanic can change a prop.

I've had them all - IMHO today the ONLY way to go is a 4-stroke EFI outboard. If your waterways are clean, not such a bad issue, but where I am floating weeds are rampant from mid - summer on.

Just my opinion. I realize that some think they are better than sliced bread.

 

[QBhoy]

They are good fun as an occasional toy...but only really that. Ridiculously poor in efficiency. I’d also add that the engine that’s likely in that is almost certainly the tiny 1.5l engine that is on the limit of insanity in terms of HP if it’s the supercharged variants of 255 or sometimes more HP. They have a hard time staying reliable pushing a 300kg jet ski...never mind a boat. The same HP from a propeller Archimedes conventionally set up would see far better efficiency and speed. You may tire of the noise too.

Good for a shot of. Would I have one for frequent days out and cruising ? Certainly not.

 

[Blind Date]

Only jet boat I'd EVER even think about buying. You couldn't give me a new Yamaha/SeaDoo jet drive boat. But.....It's matter of personal preference and you really need to drive one for yourself and see if it's for you.

 

[skibrain]

Here is a 2017 Boating magazine comparison of the 18’ Glastron offered with I/O, jet and outboard power. Pretty interesting stuff:

https://www.boatingmag.com/boat-engine-comparison/

 

[QBhoy]

Looks like they have the inboard engine details wrong there. Sure looks like a 4.5l merc mpi. Not a 4.3, haha.

 

[Texasmark]

3 comments. In outboards, my 90 Merc in jet was only rated at 75 HP.....translates to not all that fuel efficient....if it matters. Friend got ski rope sucked up into the impeller and had to put his boat on the trailer to get it out, where a prop wouldn't be a problem. If you boat around rocks, and in Lake Austin, Tx. there are HUGE rocks, a good idea.

 

[HT32BSX115]

Here is a 2017 Boating magazine comparison of the 18’ Glastron offered with I/O, jet and outboard power. Pretty interesting stuff:

https://www.boatingmag.com/boat-engine-comparison/

Interesting they did did an obvious "apples to oranges" comparison with the outboard!


Not sure how one can compare a 250hp jet to any 150hp outboard!!

The jet has a clear advantage in acceleration. We tested 0 to 25 mph "light" with one person on board and "heavy" with the equivalent of six 175-pound people on board. The jet simply lifts and leaves when the throttle is punched, blasting off with no bow rise. The outboard exhibits slight bow rise but is only about a second behind the jet to 25 mph. Bow rise blocked our view forward for a moment when the sterndrive accelerated, and with the heavy load the sterndrive was a slug, struggling to get on plane.

The GTS-180 max outboard HP rating is 150hp so a fair comparison is not possible.

The GTS-187 max HP is 250hp........... they used a 220hp Mercruiser I/O (not thinking 30hp would make a huge difference) but I think there might have been some operator skill involved since they mentioned the bow rise and a 19.3 second 0-25 time? .... judicious use of drive trim can minimize bow rise and increase acceleration.

I have a hard time believing a 19 second 0-25mph on any properly driven recreational boat! (maybe they meant 9 seconds)
If true, that boat is woefully under powered and/or over propped!

 

[skibrain]

Good catch on acceleration. Given the light/heavy comparison in each, 9 seconds would make more sense. The weight difference of +600# for I/O is typical and always striking. I could probably hunt down more engine specs, but it would be interesting to know the engine displacement for each drive.

 

[skibrain]

Duh, the article includes that info:

3.0-liter inline-4 Mercury 150 FourStroke outboard
4.3 MPIC Mercruiser 220 hp i/o
1.5-liter, Rotax 4TEC (supercharged) 250 hp

 

[H20Rat]

Jet Cons:
* poor maneuverability & docking
* poor backing up
* poor safety (when engine is on) - docking and running into other boats when you are inexperienced
* poor performance in weedy waters - constantly trying to free the impeller

Having owned a bunch of different jet (and prop boats), I can fairly definitely say my jet boats were FAR, FAR more maneuverable than a single screw prop boat. I could pivot 360 in place, or walk it straight sideways. Neither of those are even remotely possible on a single screw.

My favorite thing to do in front of the local river restaurant was to idle straight into the middle of a double slip (20 feet wide, boat was 18 feet long), stop, pivot 180 to face out, and then walk the boat straight sideways and tie up. Love to see a single screw boat do that!

Lots of people equate jet boats with the old big block, berkeley pump boats of yesteryear. Modern jet boats (seadoo/yamaha/sugar sand) are a whole different craft.

The problem is inexperienced pilots, not the equipment.

 

[QBhoy]

Duh, the article includes that info:

3.0-liter inline-4 Mercury 150 FourStroke outboard
4.3 MPIC Mercruiser 220 hp i/o
1.5-liter, Rotax 4TEC (supercharged) 250 hp

Weird how they mention a 4.3 mpi...but the picture is clearly not that engine.

 

[JimS123]

Weird how they mention a 4.3 mpi...but the picture is clearly not that engine.

That's an excellent magazine. I've been a subscriber for 40+ years. I trust the data and writeup, but as anyone who reads knows, mistakes are often published. I suspect the photographer missed taking the engine photo, so they just published a file photo, knowing that few would know the difference.

 

[QBhoy]

That's an excellent magazine. I've been a subscriber for 40+ years. I trust the data and writeup, but as anyone who reads knows, mistakes are often published. I suspect the photographer missed taking the engine photo, so they just published a file photo, knowing that few would know the difference.

Agree but it’s more likely to be a 4.5 mpi featured maybe. They don’t make the 4.3 mpi now.
kind of brings the question...what was it they actually used ? If it was the 4.5...I don’t think there is a 220 hp variant. Maybe only 200 or 250. Maybe one less powerful again ? Few questions there perhaps.

 

[porscheguy]

This test is about as close as you’ll get to a true comparison. Jet drives are notoriously inefficient. That’s not to say they don’t have their uses. On something like a wave runner, it’s the ideal solution. On boats where underwater obstacles are a big concern the jet drive may be the best option but it’s shortcomings will show.

The 150hp outboard is a fair comparison to the other two engines. The jet has the most power, but also the most inefficient drive system. The i/o makes a lot of power as well, and it has a drive comparable to the outboard. But it’s downside is that it places 1/2 ton of cast iron on the transom. The outboard makes the least power. It has the most efficient drive. It’s half the weight of the i/o but heavier than the jet.

You’ll also note that the two prop boats were a bit stunted in comparison to the jet. The jet used a variable pitch stainless impeller. The prop boats both used basic mercury aluminum props, and I suspect the i/o boat was a bit overpropped, but we won’t know because they didn’t publish rpm at top speed. I would bet that if both were equipped with the enertia (19p) they would have both cracked 50mph.

I read the test and think that the bulk of engine development dollars from mercury and Yamaha have gone into outboards over the past 20 years or so and this test proves it. And for people who moan about outboards cluttering up the transom, hand them a fuel bill or let them change a starter.

 

[JimS123]

This test is about as close as you’ll get to a true comparison.
I read the test and think that the bulk of engine development dollars from mercury and Yamaha have gone into outboards over the past 20 years or so and this test proves it. And for people who moan about outboards cluttering up the transom, hand them a fuel bill or let them change a starter.

I had a single engine jet and it sucked big time. I understand the twin Yamis are quite reliable and have better performance, but the capital cost to me is prohibitive.

We had an I/O for 35 years and although we liked it, the maintenance was an issue and a lot of cockpit room was taken up by the engine.

Our second boat has always been a 2-stroke outboard and they have always given us good service. But now, the 4-strokes have changed the whole game. Currently own 2 mercs - a 60 and a 150, both fuel injected, quiet, fuel efficient and the maintenance is not even worth talking about. Winterizing - yeah, 20 minutes.

No more gimble bearings, u-joints, sucking out oil, draining water, and I don't even want to talk about bellows.....LOL.

I realize beauty is in the eyes of the beholder, but that huge Merc on the back of my SeaRay just looks cool!. And the compartment where the engine would have been is almost big enough to install a head.

 

[Sprig]

I could give a ton of pro’s and con’s, mostly con’s. But before doing so I’d want to know what you primarily use your boat for and the reasons you are considering switching to a jet drive.