Jet boat loses 30% efficiency or worse, true??: talk me into still getting a jetboat!

[Enduro900]

I was told by several boating friends that the reason they all went with props over jets is that the prop boats are always much faster than the jet boats for the same engine size/rating.

I know the jet boat can get a bit less fuel efficiency,5% to 15% it seems depending on what source you look at, etc...

What surprised me was the claim that the prop boats will always go faster overall than the jet boat.

I appreciate all the replies in this thread as well to help disabuse me of this notion.

I’ve been told the same thing, BUT when I look at the boat test videos, all the 23’-24ft boats with 300hp-350hp all seem to be in the 49mph-53mph, which is also the range the 240-242’s fall into.

So I personally have not found much difference.......

 

[Beachbummer]

I do think it takes less hp to get an outboard equiped boat to 50mph.

The drivetrain in inherently different, and the boats are well priced to overcome this limitation.

 

[djetok]

I’ve been told the same thing, BUT when I look at the boat test videos, all the 23’-24ft boats with 300hp-350hp all seem to be in the 49mph-53mph, which is also the range the 240-242’s fall into.

So I personally have not found much difference.......

Your mind screwing yourself. @OrangeTJ said it well. Also when he says the i/o takes up real estate. The jet you get awesome back deck. Maintenance is awesome. In my boat ownership, I spent 0 on the boat besides upgrades and maintenance. Maintenance includes oil change , spark plugs, and grease.

You also have awesome resale value compared to i/o s

 

[Canuckjetboater]

Last I/O in a bowrider I had was a Mercruiser 350 Magnum with a B lll prop. First, right off the top - that combination loses 50 Hp from the crank to the prop - then there is prop slippage to factor in. The acceleration of my 2020 SX195 with supercharged 1.8 will smoke any bowrider I have owned (except one with a 390 HP 383) and will hit 50 MPH almost any day at 2.9 - 3.0 MPG. I could could have bought a lot of different engine configurations for what I paid for the Yamaha but I was GLAD to lose the outdrive with its initial cost, yearly cost of maintenance, increased danger to people on transom or swimming at the stern and increased draft. No thank you to stern drives. As for outboards - yes, more efficient for acceleration but I bought the Yamaha for the swim platform layout not to have an outboard hanging off the back!

 

[Canuckjetboater]

EDIT as I had bad info:

I was TOLD that a jet boat is 30% less efficient in HP usage or rather applying the HP of the engine into moving the boat.

The claim was with the same HP engine the jet boat gets 30% less 'power' than the same HP rated engine in a prop boat. So for a jet boat to match a 175 HP prop boat the jet boat would need a 250HP engine.

IF it is true that the jet boat engine design is less efficient for horsepower, why still get a jet boat?

How can I talk myself into the jet boat, I love the safety and everything else about them, but that MPG and HP loss.... that hurts if it is true

@JoshCanSwim ......my friend has a 21 foot Sting Ray with a 5.0L MPI with a top speed of 44mph. I owned a 2011 22 foot bow rider with a Mercruiser 350 Magnum it would just hit 50 mph with the through hulls opened-up. My 2020 yamaha SX195 hits 52.4 MPh (GPS) on a cooler day (70F) and will hit 50 MPH on a normal summer day (85F). FWIW using my 350 Mag as an example: it lost 50HP right off the top from crank to prop, then there was prop slippage. None of the aforementioned boats could touch my SX195 for acceleration, safety, ease/cost of maintenance or swim platform room. Yes, the I/Os were a bit quieter but the SX195 is quieter than many outboard-driven boats I have been on.

 

[JWExperience]

I’ve heard the 30% rule applied to jet outboards like these:
View attachment 127558
In typical human fashion they take that and apply it to ALL jet boats (which would include PWC’s, they don’t run outboards you notice).

This is dead on. I had an uncle do a jet mod to his outboard evinrude about 25 years ago and that was the problem exactly. A jet bolted onto that outboard lost efficiency/power and that idea continued to get passed on over time even though it was no longer applicable. I don’t beleive my boat is as efficient as the same size boat with comparable power but it’s not the same apples to apples comparison with bolting a jet onto an outboard.

 

[WestMIJet]

I’ve heard the 30% rule applied to jet outboards like these:
View attachment 127558
In typical human fashion they take that and apply it to ALL jet boats (which would include PWC’s, they don’t run outboards you notice).

I think the outboard is the best comparison. I own an outboard jet and a 242. My outboard jet is a 115/80. It’s a 115 hp outboard motor but with a jet pump you get 80 hp at the pump. All outboards are sized like this.

When we compare many of the boats above to our boats using mph or mpg we have to remember not all factors are equal. Hull shape, weight, gear reduction all kinds of things factor in which don’t make it comparable. I think 20-30% efficiency is straight motor output at the prop or pump.

 

[TheArk]

When we compare many of the boats above to our boats using mph or mpg we have to remember not all factors are equal. Hull shape, weight, gear reduction all kinds of things factor in which don’t make it comparable. I think 20-30% efficiency is straight motor output at the prop or pump.

Boating Mag did a comparison between outboard, sterndrive, and jet on the same platform/hull (Glastron GTS):

Boat Engine Comparison

Outboard, sterndrive and jet drive go head-to-head. Find out which performs better, and which best suits your boating needs.

www.boatingmag.com

Take it with a grain of salt ... comparing hulls purpose built for each power platform is probably better ... but even in their quantitative data, you can clearly conclude that choice of jet vs sterndrive vs outboard comes down to what your priorities are and what compromises you're willing to make.

 

[biglar155]

I was told by several boating friends that the reason they all went with props over jets is that the prop boats are always much faster than the jet boats for the same engine size/rating.

I know the jet boat can get a bit less fuel efficiency,5% to 15% it seems depending on what source you look at, etc...

What surprised me was the claim that the prop boats will always go faster overall than the jet boat.

I appreciate all the replies in this thread as well to help disabuse me of this notion.

Not to pick on you, but whenever we get into this conversation about how much "faster" a boat is I always wonder exactly where it is we're going in such a hurry. Isn't the whole point of boating supposed to be the journey?

The vast majority of boaters I talk to are driving their boats counter-clockwise in lakes that take them roughly a minute and thirty seconds to cross.

I launch up in Oshkosh and have the entire Butte des Morts chain, the Fox and Wolf rivers, and Lake Winnebago to play on. I can put a hundred miles on my boat in a day of cruising. I've never "needed" to go that fast.

My boat cruises beautifully at 6k-7k RPM. This usually has me around 25 - 30 mph. It just "feels" like a nice speed in this boat.

50 on a boat is not like 50 in a car. You have to remember that in a car at 50 you have a reasonable expectation of a clear, defined path ahead and that traffic signs and signals will alert you to reasons to slow down. On a boat, you need to be watching for traffic and water conditions (waves, wakes, logs, flotsam and jetsam) so there's a lot more to think about - this means things happen a faster than you expect. If you collide with something at 50, it's going to be a very bad day for everyone and everything involved.

Just trying to keep the perspective that the family cruiser shouldn't be chosen on whether or not it's going to win a race across the lake with someone you'll never see again.

 

[Zizzou 192]

Boating Mag did a comparison between outboard, sterndrive, and jet on the same platform/hull (Glastron GTS):

Boat Engine Comparison

Outboard, sterndrive and jet drive go head-to-head. Find out which performs better, and which best suits your boating needs.

www.boatingmag.com

Take it with a grain of salt ... comparing hulls purpose built for each power platform is probably better ... but even in their quantitative data, you can clearly conclude that choice of jet vs sterndrive vs outboard comes down to what your priorities are and what compromises you're willing to make.

Read this article awhile back. Best article I have seen showing what compromises lead to what traits In a small bowrider.

The changes made in the hulls between the three boats to suit the needs of the three power plants say it all.

Their resulting data after the hull optimizations clearly shows the general strengths of each kind of boat.

 

[IvanRZB]

When we bought our boat the sales guy made a similar comment about a propeller being more efficient than a jet--we were trying to decide between the Yamaha and a more expensive boat with an outboard, so I chalked it up to "things salespeople throw out there to drive a sale".

I was TOLD that a jet boat is 30% less efficient in HP usage or rather applying the HP of the engine into moving the boat.

I don't have much to add to what's already been said, other than to say this is not something that should swing your buying decision on its own... engine is just one piece--an important one, sure, but one of many.

IF it is true that the jet boat engine design is less efficient for horsepower, why still get a jet boat?

How can I talk myself into the jet boat, I love the safety and everything else about them, but that MPG and HP loss.... that hurts if it is true

I think you answered your own question you get a jet boat for "the safety and everything else about them" that you love, all the reasons you've decided this is a boat that works for you. Let's say the efficiency claim is true, is 30% of less than 3MPG really going to keep you up at night thinking you've bought the "wrong" boat?

 

[Daren and Heather]

I can’t speak to the MPG differences if any but a jet boat will out accelerate a comparable prop boat off the line. A comparable prop driven boat will have a higher top speed.

Safety wise there is no comparison, any boat can kill you but at least a jet boat won’t leave you or anyone one hit by it in pieces. Finally, not to be penis but if you are worried about the cost of gas when it comes to which $40k+ boat to buy are you really in the market for such a boat?

When is comes to boating costs, recurring and non recurring, gas is on my list but is not very high on it. For example insurance costs me $750 per year, the luxury tax is currently about $250 per year, my upgrade and repair costs im too afraid to calculate. 87 octane fuel is around $3 per gallon or $150 per 50 gallon tank. Two weeks ago it took me nearly three days of boating and tubing to burn through one tank of fuel which was a good thing since fuel on the water that weekend was priced at $5.25 per gallon. My camping and RV fees were 5 times my fuel cost. Still worth every penny from my perspective. When I’m on my death bed I will not regret spending money on boat fuel but I think I would regret not spending it and not having the experiences that come with boating with friends and family.

Hey Ronnie, I don't know if it's cheaper because I'm in Minnesota, but our boat insurance is really good and only $330/yr for our brand new boat. Insurance company is called Chubb Insurance, they specialize in marine insurance.

 

[Canuckjetboater]

Hey Ronnie, I don't know if it's cheaper because I'm in Minnesota, but our boat insurance is really good and only $330/yr for our brand new boat. Insurance company is called Chubb Insurance, they specialize in marine insurance.

@Daren and Heather .....really good point I couldn't believe how reasonable my insurance cost was with a jet boat. At most 70% of cost of a friend's similarly priced stern drive. Didn't say anything but in an unrelated conversation with the insurance agent he said bet you liked the cost of the insurance for your jet boat. I said, yeah I thought you made a mistake. Ha Ha

 

[212s]

Someone show me how to get 3mpg out of my 212x!!!

My 212s hits an indicated 9.0gph at optimal cruising speeds of about 27mph around 5300rpm, which works out to 3.0mpg exactly. That's the best I've seen with just the two of us and our regular cooler and gear with fairly calm conditions and 50% fuel. We spread out the weight of gear so it's not too bow heavy which cuts efficiency and speeds. My old stern drive managed about the same efficiency based on fuel consumption at the pumps. Newer stern drives will be a bit better, but not by much. Outboards tend to be the most efficient I think. Jets are less efficient at higher speeds though, but we go WOT about once per outing on average.

But we didn't buy a boat to be economical on fuel, we bought it for the fun. If you want high fuel economy, buy a motorcycle instead.

 

[212s]

Yup it pays to shop around for companies that deal with marine insurance. Our house and vehicles are with one company, but they couldn't get close to marine insurance companies for cost and coverage.

 

[Zizzou 192]

My 212s hits an indicated 9.0gph at optimal cruising speeds of about 27mph around 5300rpm, which works out to 3.0mpg exactly. That's the best I've seen with just the two of us and our regular cooler and gear with fairly calm conditions and 50% fuel. We spread out the weight of gear so it's not too bow heavy which cuts efficiency and speeds. My old stern drive managed about the same efficiency based on fuel consumption at the pumps. Newer stern drives will be a bit better, but not by much. Outboards tend to be the most efficient I think. Jets are less efficient at higher speeds though, but we go WOT about once per outing on average.

But we didn't buy a boat to be economical on fuel, we bought it for the fun. If you want high fuel economy, buy a motorcycle instead.

I heard that sailboats were more efficient than jet drives. Is this true???

I also heard that cruise ships ride smoother than waverunners from a different website. Can this be true as well? Maybe I should start a new thread on this.

 

[212s]

I heard that sailboats were more efficient than jet drives. Is this true???

No, that's propaganda from the green earth society. Sailboats use entire tractor trailer loads of sail fuel to make them work - very inefficient!
Just check the facts yourself.

 

[Bogus]

The Best thing about ourboard engines, you can take proppelers and engines out from the water while you are moored. Aand you have less metal corrosion

 

[Beachbummer]

And simpler drivetrain than I/O as you don't have to redirect thrust sideways with a fixed position engine.

 

[YamFSH210]

This discussion has made my day , Boat efficiency , LMAO , Noting efficient about boat ownership. Count the number of times used vs the yearly cost and you will not buy a boat at all. The cost of Fun and Relaxation is not measurable .

The best thing about the Yamaha jet boat is the rear seating areas , 23 foot boat seems more like a 28 when compared to a boat with an outboard taking up 2-3 feet on the back.