# Jet drive flats boat



## DuckNut (Apr 3, 2009)

Driving north bound on I-75 this morning I saw a flats boat without a motor. Then I noticed the black nozzle coming out of the back of the transom and sure enough - the very first flats boat powered by an inboard jet drive system I have ever seen.

Very cool to whoever owns this boat.


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## firecat1981 (Nov 27, 2007)

I've seen a few of them, including one gheenoe. I often wonder why jet drives, inboard or outboard, aren't more popular on the flats here.


PS I just realized this was my 2000th post


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## Swamp (Jul 12, 2010)

It is my understanding that jet drives are very inefficient, so you drop 5-10hp in thrust.  I also suspect that it's like a 4 wheel drive truck, you still get stuck, you just get stuck worse.    Not knocking them, hey do have their place.  Didn't Brett run one years ago? Maybe he will pipe in.

Swamp


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## Brett (Jul 16, 2008)

Somebody say my name? 

previous post...

http://www.microskiff.com/cgi-bin/yabb2/YaBB.pl?num=1232027473


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## Guest (May 10, 2011)

There seems to be a few types of "jet Drives" out there.

Tohatsu makes a 35hp jet from their 50hp. I'm not sure how how these newer styles differ from the older style except that I think Mel put one of these on an SUV 17 and it sucked up floating grass and stuff.


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## firecat1981 (Nov 27, 2007)

Brett, correct me if I'm wrong, but aren't the newer factory jet drive motors rated at the discharge, like how a normal outboard is rated at the prop?
I seem to remember that when I was looking at them the merc 20hp jet had a 25hp powerhead. That being said I know you lose efficency from the power head to the output, but would a 20hp jet run as fast as a 20hp prop?

I've toyed with the idea of canabalizing a jetski in the future too


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## Brett (Jul 16, 2008)

New jet outboards are rated at the nozzle,
but look at the engine specs and you'll see the power loss.
As a comparison, I had the 35 hp OMC jet (50 hp block) on a 18' flat bottom jon,
in a straight up drag race, a 13' Whaler with a true 35 hp propped outboard walked away from me.
Hulls weighed about the same, about the same load.

But I could cut corners and run over sand bars
and we ended up at the same fishing spot at almost the same time..


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## firecat1981 (Nov 27, 2007)

Hmm I wonder if someone could find a comparisson chart between a prop and jet on a similar boat


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## Brett (Jul 16, 2008)

Don't need a comparison chart. Basic physics will answer the question.
1) A 25 hp propeller outboard weighs less than a 25 hp jet outboard.
2) Propeller is more efficient at providing thrust than an impeller.
3) Propeller obtains more bite as it is in cleaner water.
The jet is operating in the top 2 inches of the water column
and so is ingesting highly aerated water and has to compress it
in order to provide thrust. Major friction/power loss there.


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## fsae99 (Apr 8, 2010)

DuckNut said there was no motor so that means it was a sport jet and they loose a lot less HP (10-20%) at the nozzle than OB jets (20-35%). This is due to the fact that OB jet turn the water 90 degrees as well as spin it around 360 degrees. A sport jet picks up the water and pressurizes it and exhausts in the same plane.

Jets do not work well in where vegetation comes up to the surface and with out the proper grate are prone to sucking up rocks and shells. In shallow water you may not get the obstruction out. They do make what is called a stomp grate, it has extra "bars" to prevent things from entering the impeller and every other bar can be lowered by stomping on a pedal. 

Brett, most OB jets are used on hulls not specifically designed for jets, they pass aerated water to the pump. riveted aluminum hulls being some of the worst. Most sport jets are used on hulls designed for this purpose. Mainly they have what is called a delta pad that water with minimal aeration to the intake. Think of the dreaded PWC these accelerate very hard.

I would almost bet what DuckNut saw was a Proline flats boat. They came with 90 HP sport jets. I was really considering one of these but the deck lay out sucks. Also the hull shape under the deck make it very hard to customize to something I wanted. So I ended up with the sea squirt which I become more and more impressed with the dryness, drift, and handling every time out.


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## DuckNut (Apr 3, 2009)

Alright you JOKERS is Carolina Jim the only one who actually read my post?  I did not see an outboard with the jet foot hanging on it - it was a full fledged flats boat with a center console and poling platform.  It was shaped as a traditional flats boat (ie: action craft).  As CJ pointed out it may have been a Proline but I was not able to see the name on it because I was driving in heavy traffic and quite honestly I didn't even look as I had to rub my eyes in disbelief.

These new jets are not the same as the older versions.



> Jets do not work well in where vegetation comes up to the surface


CJ look at Phantom jet boats and specifically their military version as these things are everywhere up north and these things do not stop for anything.  At a huge wildlife refuge I visit I watched a DNR officer slam into a levee at what looked to be about 30mph and slide right over it and then nailed the gas again and continued on his intended chase.  I have sat in my boat chatting with wildlife officers in very heavy vegitation and they have no issues. Unbelievable what people have dreamed up.


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## fsae99 (Apr 8, 2010)

DN, Not dreamed up. Not working well in heavy vegetation that grows to the surface is personal experience in the Albemarle and Currituck sound where I grew up. The damn Hydrila there would choke out these jets if you were any thing less than full plane. I've pulled several grates to pull hydrilla wrapped in the impeller that it just would not cut. I'm not sure why it would not chop it up, you could pull the hydrilla apart by hand.

Modified:
Just watched the video on Phantom website even that big 200 sport jet was slowing rapidly in that hydrila before they cut away. That video with the weeds looks very much like the stuff I dealt with. 

Also, I was really talking about the 90 and 120 sportjets that I have a lot of experience with and came as standard and option on the prolines.

I will say this even when choked with weeds it will still move and I was never left stranded. Just would not produce enough thrust to get on plane.


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## Brett (Jul 16, 2008)

> is Carolina Jim the only one who actually read my post?


Well yeah...we read it...doesn't mean we were gonna stay on topic though... ;D

Note the section you posted under...General Discussion!

Nowhere does it say Specific Discussion... [smiley=happy.gif]

I never did like coloring inside the lines...or playing by the rules...


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## firecat1981 (Nov 27, 2007)

> Alright you JOKERS is Carolina Jim the only one who actually read my post? I did not see an outboard with the jet foot hanging on it - it was a full fledged flats boat with a center console and poling platform.


Ok this was my fault cause I mentioned outboard jets. However my original comment when I said I've seen several jet powered flats boat I meant inboards. Including the gheenoe that one guy canabalized a jet ski for.

So to derail this a bit more, Jim you obviously have a lot of experience with this stuff and Brett you gave a good explaination, but I'm still slightly lost. Outside of the weight increase, which on a small motor isn't much, why would a 20hp prop motor, rated at the prop, be that much faster then a 20hp jet rated at the nozzle? Both are pushing out 20hp of energy?


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## wrobil (Apr 19, 2011)

many years ago I was a fishing guide in AK and we ran lots of jets. 

The pros
1) can run some very skinny water
2) with the right hull you can almost throttle steer with a little movement of the tiller


The cons
1) If you suck in weeds you have some work in front of you
2) If you suck in a bunch of gravel it will increase the distance between the impeller and the boot which lessens your efficiency and speed greatly.
3) Must grease the pump religiously or else
4) Not fast. 

These are just my thoughts and.02 so take it for what it is. Personally I would only recommend them for rivers and not for lakes or oceans due to lack of speed, power and potential weed issues.


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## fsae99 (Apr 8, 2010)

FC,
If you could get 20HP for the same weight and you feed good water to the pump should not be any difference. HP is just work/time.


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## Brett (Jul 16, 2008)

Horsepower may be the same, but friction loss and compression of flow are different.
Much more wetted surface on the interior of the pump means more friction,
whether outboard or inboard, and aerated water affects thrust.
The weight and speed of the water being pushed out the jet nozzle determines thrust.
Any time aerated water is being pushed through, a jet/pump loses thrust,
where a prop is buried below the surface, where aeration is not as big a factor.
Prop is just a more efficient method of propulsion.

FC, when using a hose, ever notice how air bubbles in the line
jerk the nozzle around until all the air is forced out.
A jet pump does the same thing in a chop.
The flow of water to the impeller is inconsistent, so the thrust is also.
You can feel the loss of "push" when running a light chop with a jet.
The prop driven hull fares much better in a chop,
as the blades are so much further below the bottom of the hull.


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## Mike_Poczik (Jan 24, 2010)

I wonder if that is the Hobie Jet Skiff I saw on the St. Johns at the mouth of the Wekiva 2 weeks ago. Nice lookin skiff.


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## cutrunner (Jun 8, 2010)

I am currently redoing a hobie skiff, just not a jet one, outboard style. Really cool little skiff


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## Mike_Poczik (Jan 24, 2010)

> I am currently redoing a hobie skiff, just not a jet one, outboard style. Really cool little skiff


Thats why it really caught my eye. really nice lines on that one for sure.


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## firecat1981 (Nov 27, 2007)

Kinda what I was thinking Jim. I understand the facts of friction loss (I mean that is what I do, got a state certification for it too ), but all things being equal they should push near the same. Compairing a jet that's tucked high in a tunnel to a prop down in the water isn't really apples to apples in my mind. Now if you ran a jet at the same level as a prop shaft, or if you jacked a prop way up into a tunnel then I think things would work out differently.


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## DuckNut (Apr 3, 2009)

As I said before, these are not the pump of yesterday

http://www.youtube.com/user/PhantomMILPRO?blend=9&ob=5#p/a/u/2/FVYn4FIGqcU

http://sj-x.com/


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## beyondhelp (Nov 6, 2008)

> As I said before, these are not the pump of yesterday
> 
> http://www.youtube.com/user/PhantomMILPRO?blend=9&ob=5#p/a/u/2/FVYn4FIGqcU
> 
> http://sj-x.com/



Sure wish I could hear the engine noise in the first video. I absolutely hate the hydrilla after battling it only two times. (lake O and the Loxahatchee river) 

I always wanted to do the jet in a jon conversion just to see what it would be like.


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## jlowens2968 (Jul 28, 2010)

> Driving north bound on I-75 this morning I saw a flats boat without a motor.  Then I noticed the black nozzle coming out of the back of the transom and sure enough - the very first flats boat powered by an inboard jet drive system I have ever seen.
> 
> Very cool to whoever owns this boat.


Could have been a Pro or Hobie as mentioned earlier.  Shipoke also made a couple of 15's with inboard jets in the late 90's...got some nice staples in my head at the Englewood ER back then from being thrown out of one of them.


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