The truth, Jet drive or Prop?

[teamgraphx]

I'm thinking of getting a new boat next year. I was at the boat store and the sales guy was telling me how great the new Yamaha AR230 is. It does have everthing I would want and more. I'm just not to sure of the performance of the Jet Drives. Right now I have a 96 Wellcraft excel 21SL cuddy with a 5.0 Penta and Cobra SX drive. I really love this boat I just need something a little bigger. I like to wakeboard and never have behind a jet boat. I would like to know the downsides of the jet boat and the ups of the props.



thanks
Wayne
teamgraphx@aol.com

 

[QC]

Re: The truth, Jet drive or Prop?

We debated this here recently and most of the standard rules of Jets have been rewritten in the last couple of years, and primarily by Yamaha. The test data on those boats is proving that efficiency is no longer the Achilles heel of jets and they will run a solid 50 MPH. Also twin drives, if operated properly, can be wonderful around docks etc. You cannot discount the safety and shallow water benefits either.

I have previously been somewhat of a jetboat detractor although I have piloted high powered jets and they are a whole bunch of fun . . . I think the latest 23 Yammies are making me a believer and would consider one now. I am not sure though about wakeboard performance as I have never seen the wake or spoken with anyone that has used one for this. You should go to Boatest dot com and search for the tests. Also, I believe Trailer Boats just ran one. Anything that can get over 3 MPG, and perform like these do, is a player in my book. BTW, I would buy a used one, as I don't believe the resale value is that strong as many still have reservations about jets. Good luck.

The downside of the props (V-drives) is low top speed and no way to get the prop out of the water. Upside is probably some handling characteristics and hmmmmm can't think of any more. Downside of the jets may be the noise of high RPM operation (10K max) and maybe a concern about sucking up ropes in the pump. I am not concerned about longevity at all . . .

Edit: BTW, you should delete your "add' as the mods won't like it . . .

 

[KCook]

Re: The truth, Jet drive or Prop?

The Yamaha 230 tested by Boating magazine didn't get such great gas mileage -

http://www.boatingabc.com/forums/ubbthreads.php/ubb/showflat/Number/233092/page/0/fpart/1

 

[Chris1956]

Re: The truth, Jet drive or Prop?

I was always under the impression that a jet drive would only be about 60% the efficiency of a prop. That is, a 60HP OB would seriously outperform a 60 jet OB on the same boat. If this has changed, I would like to see the test data.

Certainly a jet drive has advantages in shallow water, like an outboard or I/O has over a straight inboard.

 

[teamgraphx]

Re: The truth, Jet drive or Prop?

Thats great info, thanks.

 

[tommays]

Re: The truth, Jet drive or Prop?

They are powered buy "marinized" motorcycle motors which are good motors



BUT they need to turn very high RPM 7000 will get you 28MPH and WOT is 10500 RPM at 50 MPH


No matter how well its built that is a LOT of valves moveing at really high speed


Tommays

 

[ziggy]

Re: The truth, Jet drive or Prop?

i had one of them mr-1 engines in my pwc. only the 140hp one though. i agree. 10k seems fast and theres 4 valve per cyl. agreed. that's a lot of motion......had my valves checked at 200 hrs per service manaul. valves were in the middle of spec. it couldn't have been more perfect. i did nothing to my engine other than oil changes and proper reg. maint. that engine never let me down once. sold it at 238 hrs. still runnin like a top.....and ya just can't not like the simplicity of a jet drive. the impeller and brgs it rides on are the moving parts..... a few less parts than an i/o.....

as far as fuel consumption. i have no real gage for that other than i would ususally use 5 gal. of fuel in my pwc a day.....i use about the same in my L6, 5 gals. a day.....drive them about the same amount. lounged on the beach with the pwc. float around and lounge around on the speedboat...+ some cruisein around of course.......

 

[QC]

Re: The truth, Jet drive or Prop?

Well I double checked a couple of things after Kelly's comment on fuel. Boatest.com had a best of 3.74 MPG for the Yammie 230 HO, but they're saying 160 hp x 2 and I thought they were higher . . . oops 50 MPH max:

Yammie 230 test

This boat gets better fuel efficiency than my 23 footer with the same total hp (mine's a 6.2 320 Merc) but I'm faster (57 MPH)

I also checked for others and the SeaDoo 230 Wake with 415 total hp and a top speed of over 56 MPH got a best of 3.11 MPG:

SeaDoo 230 Wake test

The SeaDoo 230 Challenger didn't do as well with the same power plants, with 2.94 MPG best but a higher top speed of over 57 MPH

Challenger test

I also cheked on a 210 and it got over 4.10 MPG. . . So I think we're getting pretty close here.

I am not sure why we're worried about valves and stuff as if they were failing IMHO they wouldn't sell them. Yes there are exceptions like the OMC FICHT, but generally speaking everybody's stuff is pretty dern reliable these days. The SeaDoo comes with closed cooling, I thought that was interesting.

 

[dvan1901]

Re: The truth, Jet drive or Prop?

There is another forum dedicated to these boats and it has a TON of information. I have a 19' Larson and am looking to replace it with one of the SX 230's. A couple things to me were; no prop, manuverable (twin engines), easier to maintain. With these, there is the engine and the impeller. They have cleanouts for the impellers and about all you have to worry about is sucking something (ropes for example) into them, but they have a screen you can put over it. There is no outdrive so doing maintenance is easier, no drive to pull off, no gimbal bearings, no bellows, etc. Think of all the moving parts in an i/o, you don't have all that with a jet drive. Now, the jet drives don't handle well at low speeds and if you are used to an i/o I understand it handles differently and takes some getting used to. There is a guy that sells some fins you put on the drives and it makes it handle a lot better at the low end and gives it more stability.

 

[Texasmark]

Re: The truth, Jet drive or Prop?

I have a recent Merc Service Manual and they rate the 90 hp 3 cyl at 65 with the jet drive; the 4 cyl 115 is rated 80. Since you are feeding the same powerhead, there is your (most of your) loss. Also, usually the jet (pump) has to be maintained at higher rpm's to get the thrust necessary to compete with a propeller. Jet race boats have been around for years and everyone I ever heard was screaming, unless it was docking.

I don't know how prop hp is rated. I know they use dyno's to test the hp (at least on tractors) at the PTO shaft, but I don't know the method used for marine engines. If it is the twisting moment on the prop shaft, then the efficiency of the propeller comes into play. You have to hook to it somehow and sliding a coupler on the spline of the propshaft seems to be a good way to do it. Since the jet is a water pump rather than a propeller, I would guess that you are in for more loss there.

As far as sucking in ropes, I only saw one boat do that and it was years ago, before the advent of polyethylene rope that floats. So unless you just drive right over it I don't see sucking ropes as a problem.

I would think that jets are much safer for skiing as there is no exposed prop blades to mame the swimmer.

Mark

 

[ziggy]

Re: The truth, Jet drive or Prop?

As far as sucking in ropes, I only saw one boat do that and it was years ago, before the advent of polyethylene rope that floats.

i've seen it a few times with pwc myself. ya don't want to suck up a line with a jet. the polypropalene line melts and streches, then cools hard all wrapped up in the impeller. they're a drag to get them out.....baseball hats do the same thing. the bill is plastic and melts......

 

[tmh]

Re: The truth, Jet drive or Prop?

I saw the Yamaha Jet boats (21' and 23') at a show and loved them. The best of that size at the show for layout.

I've read pros and cons on several forums, most of the cons coming from non-owners. Many think these are like the jet boats from years ago that were really just big jetskis and fun to bomb around on, but not like a real boat. of course, these ARE nice bowrider boats.

However, I still wonder about one thing - no trim control. With my I/O boat, I adjust the cruising trim for a nice ride based on conditions. If it was a fixed angle then some days would be good, some not so good. I just wonder if/how there is any way to get the bow up or down more with the jet drive boats. Maybe there is, i just haven't heard it.

Other than that, I'd be very inclined to have them at the top of my list next time I'm in the market for a boat.

The is, however, one

 

[QC]

Re: The truth, Jet drive or Prop?

They run a lot of big block jets where I boat, more 10 -20 years ago, but you still see them. Waaaaaay different than what, until recently, I considered nothing more than a toy boat. Anyway . . . here is a pic of one throwing a "rooster" from a device called a place diverter or a jetavator. It is effectively a power trim mechanism that will allow you to get the bow up.

BTW, what is there for trim on a Vdrive or Direct drive? Yes I know about the trim tab thing they use to build a bigger wake, but that is not trim . . . You could use Bennett's on these jet boats too if you set them up for high speed with the bow up, you could trim them down with the tabs.

 

[eeboater]

Re: The truth, Jet drive or Prop?

If you want more info about the Yami's I highly reccomend the Yamaha Jet Boaters forum: http://www.yamahajetboaters.com

 

[dvan1901]

Re: The truth, Jet drive or Prop?

If you want more info about the Yami's I highly reccomend the Yamaha Jet Boaters forum: http://www.yamahajetboaters.com

That is a great forum, and is the one I was referencing earlier. As for trimming; some on that forum have put both manual tabs and Smart Tabs on their boats so you could check into that.

 

[Texasmark]

Re: The truth, Jet drive or Prop?

Yeah QC that's what I was referring to.

On a jet, efficiency or not, if I were fishing a river, like the rocky things of the NW, USA I wouldn't have anything else.

Mark

 

[sprdty]

Re: The truth, Jet drive or Prop?

i am going to assume that these are considered to be inshore use only, as for example a pontoon boat.
even though i know of a few that have taken a pontoon 10 miles offshore.

has anyone tested these jet drives offshore in 2 to 5ft choppy swells?

as with any type of boat there are limits - but there are those who will go to the edge just to see if they can go offshore & if they have a good trip will go again.

i think i will stick to a dual purpose boat with a prop - big enough to go offshore but yet can also be used in rivers & lakes.

unless i win the lottery then ill get one.