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Congrats Tim and Stabicraft! All I can say is business has got to get better or I gotta stop dreaming....

Tim, Barry thanks for the reply.

I’m sorry that Barry misunderstood what I posted, shown by his incorrect paraphrase of my post;
Barry: "The comment that the thrust in a water-jet is developed in the intake via ram is incorrect.”
That shows I’m not communicating very well!

I didn’t say or mean to imply the water-jet intake is where the thrust is developed. I’d hoped to convey the velocity gain aspect of the pump’s effectiveness at providing higher speed(s) was incremental and somewhat conditional on the velocity of travel and therefore intake volume flow. So I used the term ‘ramming water’ perhaps I should have said, really increase water flow instead of using the more colorful word ‘ramming’?

What I posted was;

“By the way, it's pretty important to note that the idea that Hamilton Jet pumps have much nozzle and there fore thrust gain is sort of misleading. The real effect of these pumps comes from ramming water up into the pump as the boat moves. The gain from the thrust of the pump duct/ or 'nozzle' is very small compared to the head/speed/ram. The Hamilton pump will get more and more effective the faster it goes, because you're using the boat's momentum to get more and more water at higher speeds into the intake. “

Poorly worded, but interesting to note that Barry posts a phrase very similar statement to mine?

Barry: “At high speed where water feed is enhanced by the forward boat speed, it helps a water-jet to go faster as the can develop higher pressure head in the nozzle.”

("water feed is enhanced" is essentially "ramming water into the pump" to me!)

Kevin: “The Hamilton pump will get more and more effective the faster it goes, because you're using the boat's momentum to get more and more water at higher speeds into the intake.”

Barry concludes with a statement: “Thrust equals "change in velocity on a given mass". Speed the water up to greater than boat speed..... the overall thrust goes up. Slow the water down in the system below boat speed, removes thrust.

I agree and didn't mean to imply otherwise, but a “given mass” is when the Hamilton pump boat stands still more or less fixed inlet flow. We have an “increasing mass” since in Barry’s words “where water feed is enhanced by the forward boat speed”. (italics mine) I was remarking about the increasing speed coming from “changing the velocity of an increasing mass”. I called this the ‘real effect’ and should have made it clearer, sorry mate.

I wasn’t attempting to say the force is expressed anywhere but the nozzle outlet, just that the nozzle outlet speed increase (IT IS MY UNDERSTANDING???) is most increased by the increase in mass which happens (only) at higher speeds and the associated higher flow rates in this design of pump. [Hence ‘ramming water’, not meant to imply compressibility as in a gas jet.]

If I understand correctly then Barry's new drive exhibits performance characteristics that are substantially different from its Hamilton 'ancestor'? So the range of performance of the new drives is much wider and much less prone to the limits associated with the Hamilton type pump? And since the Hamilton drive's limits are mostly experienced in lower speed the new drive is effective at low speeds as well as higher speeds????

A few questions about the drive physical elements: but they may not be for release at this time?
Does the drive have a bearing, on the aft end of the tail shaft, in the 'cone'?
Is that a lubricated roller or ball type steel element bearing or a water film 'cutlass' bearing type?
Do the two impeller/propeller's shape and radial (fluke) orientation act to 'counter weight' the other's eccentric side loads on the shaft(s) and on the fore (and aft) bearings?
In reverse; is the flow into the "flow chamber" from around the conic end element inside the illustrations?

thanks again for the information about your ingenious new drive system.

Cheers,
Kevin Morin

This messenger might want shot... Information overload.

Seriously though, I am posting this to help everyone out there looking for more information.

Contrapel is getting good coverage around the world but this site is one of the few that has active and thoughtful consideration for the concept. Contrapel, Stabicraft and I appreciate that immensely and I hope all you AABer's do too.

The Contrapel team is about start the long drive north to display the boat at the Auckland International Boat Show (it is a four day drive) so Barry though prudent to quickly reply to KMorin (Kevin).

Kevin, Barry appreciates your thoughts a lot. He commented to me how impressed he was with your process and obvious knowledge. What is below is again taken straight from an email from him. If there is incorrect intonation, please forgive it, it will be due to the nature of talking through a third wheel - me.

Kind regards and I hope this is of value to you all.
Tim

From Barry 20 September 2012.

I've clipped below a white-paper that I used to confirm what I discovering in practice, with the Contrapel system


This text was taken from Mechanics of Fluids, Second Edition, A C Walshaw (Professor Emeritus, University of Aston in Birmingham), D A Jobson (Formerly Assistant Professor of applied Mechanics Royal College, Greenwich) and sets out the precise differences between waterjets and other propulsors such as propellers.

“ The basic difference between the propeller and the jet, apart from their conversion efficiencies, is that the former exerts a thrust by imparting a small increase in velocity to a relatively large mass of fluid, whereas a jet generally discharges a much smaller mass flow at a much higher speed. The question arises as to which one of these is fundamentally more efficient in any given circumstances?

The answer to this was established by Rankine in 1865, and his theory was elaborated by R E Froude who, with his father W. Froude, laid the foundations of resistance and propulsion and, indeed, of much of naval architecture. According to the Rankine/Froude momentum theory the propulsive element is assumed to be replaced by a hypothetical actuator disc...and which is assumed to accelerate the fluid axially without rotation.

Although this may appear to be a very abstract concept it come much nearer to describing how a propeller acts than the more popular but erroneous notion that a propeller “screws” its way through a fluid. A cordless section through a propeller blade encounters an on-coming stream which it deflects in a fore and aft direction, so that the axial component of the fluid velocity is increased. The various helical motions which are imparted to the fluid are merely parasitic in so far as they represent a useless waste of energy.

Considering the motion relative to the actuator, fluid approaches it with a velocity U. If we concentrate on the fluid which is destined to pass through it, the stream will contract as the fluid accelerates to its final velocity, V, say.

If the rate of mass flow is m’, the force or thrust exerted is:

T = m’(V-U)

And the thrust power is:

P=TU

Hence the work output or useful work done in time(t) is:

W₀ = Pt = m’t U (V-U)

During this time the actuator has increased the velocity of a mass (m’t) from U to V, so that the work input Wί which has been used to increase the kinetic energy of the fluid is;

Wί = ⅟₂ (m’t) (V²-U²)

Hence the ideal , or Froude efficiency :

ηF = W₀ / Wί = U ( V – U) ÷ ½ (V2 - U2)

= 2 ÷ 1 + (V/U)

For the Froude efficiency to be high, V should be only slightly greater than U, i.e. the increase in velocity necessary to produce thrust, should be a minimum. The cause of inefficiency is the jet energy of the wake; the useful thrust T is proportional to the increase of velocity (V-U), whereas the energy imparted to the fluid increases as its square, ½ u2jet , the energy rejected being ½ (V-U)2 per mass unit.

Thus the efficiency is a maximum when the increase of velocity is a minimum, so that it is fundamentally more efficient to obtain thrust by imparting a relatively small increase in velocity to a large mass flow.”

As all current water jets use a nozzle principle to accelerate a relatively small mass of water to high velocity, the inherent losses are high at low to mid speeds.

Following is a chart presented by a division of the US Navy (ONR- office of Naval Research) in 2006 comparing efficiencies between modern water jets and various propeller systems. At ten knots a waterjet has less than 50% propulsive efficiency compared to a conventional propeller. In the low to mid-range speeds water jets have very low propulsive efficiencies as predicted by the Froude model. It is not until relatively high speeds are obtained (35 knots and over) that water jets are able to begin to match propeller systems for efficiency.

The Contrapel propulsion system overcomes this problem by maximizing the mass output and minimizing the outlet velocity, through maintaining the lowest possible back-pressure in the outlet. The pleasant outcome was that equivalent high speeds have been achievable even though the gains I was expecting were mostly thought to be the slow-speed ranges.

Kevin, I've had Hamilton jets all my boating life (40 years) and am a great fan. I still have a jet-boat for hunting which is fitted with an alloy supercharged Toyota V8 (my creation which was built by me thirty years ago) The engine is coupled to a Hamilton three stage jet. I'm very fond of this boat as it has great memories for me. I've fitted 750 single and three stage units to alloy jetboats, which I started designing and building in the early 80's, so that we could explore Fiordland lakes, rivers and fiords. I built an alloy jet boat while living in London and fitted it with a 770 series 3 stage Hamilton powered by 350 cub inch Chev, and later purchased the 212 series unit to get comparative data against which to compare the Contrapel system. The 212 was powered by a 400 cub inch Chev. I'm not a boat builder, I've done this out of interest, so it's been quite a mission....so please excuse me if I appear a little short in my reactions at times.

To answer your questions, if I understand you correctly. The reaction forces of the two contra-rotating impellers not only removes the radial energy in the flow, they balance each other to produce a very quiet and extremely smooth unit. No vibrations can be detected. Not only this, the propellers are able to sustain massive damage to the leading blade edges, as well as huge clearances around the pump housing walls, with vitually no apparent loss of boat performance nor increase in vibrations. (This is not the case with pressure jets)

The propeller rotational speeds are extremely low, in fact we run them at less than half engine rpm! For example a 190mm diameter Contrapel running at 60mph has a propeller rpm of around 3000.

The 330 mm dia. units in the yellow boat featured on the TV clip are turning at 1,700 rpm @ 44mph. (That's an 8 ton boat)

I've never been a fan of the cutless bearing and the inability to dry-run in the garage before heading off on an expedition without removing the drive-shaft. There are no water lubricated bearings in my system. Furthermore the bearing supporting the inner shaft at the outlet is fitted behind the anti-ventilation cone and thus is not subject to flow or pressure. The units can be dry run for as long as you want by just putting the garden hose into a skin fitting which feeds the engine cooling.

Reverse in an enclosed system, particularly jets, is problematic, as the outlet becomes the intake...so it's like sucking through a straw. Reverse flow in a pressure jet only allows for "flushing" of the grill. The Contrapel system has two problems, the reduced outlet diameter which is still relatively very large compared to a pressure jet and the the hydrodynamic requirement of "balancing" the flow across the propellers (which are now going backwards). To overcome these issues the unit has a bi-pass gate which automatically opens underneath the propellers when the throttles are shifted into reverse. This enables the water to be drawn in from underneath the unit while in reverse, while an anti-ventilation cap "closes off the outlet" from the air, otherwise the units would draw in air and not reverse the flow. The result is a much more linear thrust force as a reversing bucket tends to lift the stern, and stir up the bottom in shallows. Tests that I've conducted show that I can expect in excess of 70% of forward thrust when in reverse. I'm still working on the system, however the mechanics and the way it works is very pleasing so far. A lot of what we know about boating will change from now on, as the Contrapel system gives so much more control over the boat at low engine rpm. At the end of the fishing season last year Paul and I trolled for trout all day long on one unit in the 8 ton yellow boat. We were averaging 1.2 liters of diesel per hour. At trolling speed the propellers are rotating at 300rpm and the boat has positive thrust and control.

I hope these explanations are of help Kevin and I'll pass them onto Tim who hopefully will post them for you to read.

Regards

Barry Davies (Contrapel Ltd)

Tim, tell Barry THANK YOU for the reply , we will need more info. on this project as it comes up. Heck Barry just might have to send us a TEST boat to put some hours on it for him.

Barry actually gave me these numbers a while back but I have been too busy to post them up. The boat was fully fuelled, 2 up. Weight would have been around 8000kg.

RPM --- Knots --- Lph --- L/nm
1200 --- 5.99 --- 7.3 --- 1.21
1540 --- 7.82 --- 17.2 --- 2.2
1800 --- 9.5 --- 28 --- 2.94
2000 --- 10 --- 37.5 --- 3.75
2250 --- 15.5 --- 52 --- 3.35
2500 --- 17.6 --- 65.4 --- 3.7
3030 --- 29.7 --- 107 --- 3.6
3230 --- 33.5 --- 127 -- - 3.79
3500 --- 37.25 --- 164 --- 4.4

These numbers are on new gearboxes and still as-new motors. The motors still need to be properly broken in. The gear boxes were specifically designed for the units and motors. To be confident, the team need to do enough hours on them before removing them for a full inspection and bearing check. Once everything is signed off the numbers will be properly validated - and I will share (so long as I am allowed)

A (cough) glass Tiara 3200 Open running a pair of Volvo D6 310's running three blade 19,0 x 24,0 props(the Contrapel Stabicraft is running two D6 435's) got the numbers below. There are lot of hull differences and there is a heap of fendering to drag along with CP1. The Tiara is also beamer with a shallower deadrise.

These numbers came from
Performed by: Jason Hinkel
Test location: Holland, MI, USA
Test date: 2003-09-24

RPM --- knts --- L/hr--- L/nm
600 --- 4,3 --- 1,5 --- 0,3
1000 --- 6,4 --- 3,0 --- 0,5
2000 --- 9,7 --- 34,8 --- 3,6
2500 --- 15,1 --- 65,1 --- 4,3
3000 --- 23,4 --- 85,5 --- 3,7
3300 --- 27,3 --- 102,2 --- 3,7
3500 --- 29,4 --- 120,3 --- 4,1
3610 - -- 30,5--- 130,2 --- 4,3

So what do you guys think?

That looks pretty promising Tim! For comparison purposes, do you have performance numbers for the Victoria Coast Guard boats with twin 200 outboards? (those boats look to be about the same size/weight as the boat with the Contrapel drive)
thanks,
Mike

The Vic coast guard boats are smaller. The biggest we have sent lately was a 9.2m running twin BF250's. It weighs a lot less than the 10.2. Off hand it came in at around 3200kg so around half the 10.2's weight. I might be able to find the figures if you want? Honda were particularly interested in the boat as it was one of the first in Melbourne to get two 250's.

Tim.

StabicraftMarine wrote:The Vic coast guard boats are smaller. The biggest we have sent lately was a 9.2m running twin BF250's. It weighs a lot less than the 10.2. Off hand it came in at around 3200kg so around half the 10.2's weight. I might be able to find the figures if you want? Honda were particularly interested in the boat as it was one of the first in Melbourne to get two 250's.

Tim.

Hey Tim:

I was really looking for something comparable to the boat with the Contrapel drive--so we could compare the Contrapel drive to outboard power. But, that said, we always like facts and figures--almost as much as we like pictures!

Thanks,
Mike

Any more news on this system?

-How did that Floridian slip into AAB without me noticing...Welcome "Bonita Springs Fla."

We need more of us!

Not from me Welder.
To be honest, I have been dealing with a lot of in-house stuff for the last few months so haven't spoken to Barry in a while.
Last I did they were working with the gearboxes and trialling new things. My understanding is they have had a great deal of interest, some local, some offshore and are looking to commercialise the tech sooner than expected (remember, this was released as a work in progress).

Rest assured, when I know something, you will hear it.

Actually, there is one thing I heard about, they are looking at getting some press onboard for a test. It is scheduled for March I believe. I'm not sure if the detail you guys will want will come from it but time can only tell.

Cheers,
Tim.

Tim
Propulsion system looks promising, is there plans to take this commercial as viable alternative to I/O. Could be a market for someone looking into a better system then sticking a leg out of the transom, or a more reliable system than that.
If I did find a decent alternative for my rebuild I would consider it, and I am running a Volvo I/O diesel 290SP, also I am only one of many. where can more info be found?

Katoh wrote:Tim
Propulsion system looks promising, is there plans to take this commercial as viable alternative to I/O. Could be a market for someone looking into a better system then sticking a leg out of the transom, or a more reliable system than that.
If I did find a decent alternative for my rebuild I would consider it, and I am running a Volvo I/O diesel 290SP, also I am only one of many. where can more info be found?

That's the idea absolutely. The best place to start is on the Contrapel website http://contrapel.com/. It is fairly 'old school' and is written more as a white paper but it is a good place to start. When I hear anything, I post it here so here is probably the next best place.

Tim.