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Author Topic: 30% extra thrust?  (Read 7009 times)

toesupwa

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30% extra thrust?
« on: August 27, 2007, 10:44:00 PM »

Mobile Marine Models are claiming 'an extra 30% thrust' from one of their Kort nozzles over a reduced scale full size Kort.

http://www.mobilemarinemodels.com/PDF/Korts.pdf

Has anyone out there used one of these Korts?... and do they appear to 'add' any more power? :-\
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DavieTait

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Re: 30% extra thrust?
« Reply #1 on: August 27, 2007, 10:52:58 PM »

In the real world the new Kort Nozzle / Propellor combo's are giving 25-30% increase in efficiency over an open propellor with the latest LIPPS Propellor / High Efficiency Nozzles 15% more efficient than a Kort. Its possible to get very high power "gains" with an accurately made anf fitted propellor/nozzle but your not doing any more than harnessing the power your putting into the water far more efficiently.

With a good set up you should get 30% more run time out of the same battery / motor combination provided you stick to the same speed on the water.

Here's the latest LIPPS/Nozzle combo as seen on the Rebecca FR143 in June 2007



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toesupwa

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Re: 30% extra thrust?
« Reply #2 on: August 27, 2007, 11:00:16 PM »

Yes davie, i understand the increase in power a matched kort / prop can give over an open propeller and rudder.

I've made a few Korts to match the Marin 19A profile..

But MMM seem to be infering that their Korts are even more efficient than the full sized (reduced to model size) Korts
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ministeve

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Re: 30% extra thrust?
« Reply #3 on: August 28, 2007, 12:06:31 AM »

hi all what i think mmm mean is you loose efficiency when you reduce to model size so they tinkered with the design a bit to compinsate
not 100% sure but will ask mmm next time we talk
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HS93 (RIP)

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Re: 30% extra thrust?
« Reply #4 on: August 28, 2007, 12:19:43 AM »

I think you may find that they now use an aerofoil section that allows the flow to speed up From what I have read about full size they use parallel and aero section

http://www.harringtonmarine.com/stdnozzleshapes.htm

Peter
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DavieTait

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Re: 30% extra thrust?
« Reply #5 on: August 28, 2007, 12:22:57 AM »

And just to confuse things the new LIPPS Nozzle has a raised lip inside of the nozzle 1/2 aft of the line of the propellor blades high enough to cover the tips of the blade which gives it its increased performance ( the Rebecca in the photo's has had a 22% increase in thrust over a good quality Kort Nozzle so these things work !! )
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toesupwa

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Re: 30% extra thrust?
« Reply #6 on: August 28, 2007, 12:38:42 AM »

Having made Marin 19A Korts (as per full size), I'm trying to figure out how MMM can claim..

"...as much as 30% more power over conventional tubes"

I dont see any facts and figures to back up these claims...

Davie, Where did you get your information from about the increase in Rebecca's performance increase of 22% in thrust?.. do you have a link about the LIPPS Prop / Kort please
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DavieTait

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Re: 30% extra thrust?
« Reply #7 on: August 28, 2007, 01:04:43 AM »

There was a write up about the increase in performance of her in the Fishing News ( industry newspaper ) a couple of months ago i'll see if I can find it. The prop's are wide bladed towards the tips and seen head on follow the curve of the inside of the nozzle. The LIPP's nozzle has a raised ( vertically by 2" ) area 1/2" aft side of the swept area of the blade tips with an aerofoil section towards the aft end. These are fixed ONLY with a seperate rudder as with the LIPP they can't be used as a steering nozzle.

I can't find any direct links but I think its a KORT Nozzle and the LIPPs is the special design of the propellor

Davie
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toesupwa

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Re: 30% extra thrust?
« Reply #8 on: August 28, 2007, 01:15:53 AM »

There was a write up about the increase in performance of her in the Fishing News ( industry newspaper ) a couple of months ago i'll see if I can find it.

I can't find any direct links but I think its a KORT Nozzle and the LIPPs is the special design of the propellor

Davie

Thanks Davie, your information is much appreciated...

I've raised my tugs pull from 2lb 12 oz to 2lb 14oz of pull with the replacement of a straight kort to a Marlin 19A shaped kort...
I've just built another tug with a bigger motor and prop together with a Marlin 19A kort that achieves 4lb 4oz of pull.
Having seen the claims by MMM i was interested in how they had achieved the 30% increase... But your information has sent me off in a new direction to increase the 'pull' of the new tug.. thanks..
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HS93 (RIP)

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Re: 30% extra thrust?
« Reply #9 on: August 28, 2007, 01:18:33 AM »

some other info. and some nice vidio

http://www.becker-marine-systems.com/index.html

Peter
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toesupwa

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Re: 30% extra thrust?
« Reply #10 on: August 28, 2007, 01:35:31 AM »

some other info. and some nice vidio

http://www.becker-marine-systems.com/index.html

Peter

Thanks Peter, but those are full size korts (probably 19A type) which i have already been studying for some time...

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HS93 (RIP)

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Re: 30% extra thrust?
« Reply #11 on: August 28, 2007, 03:55:49 AM »

Yes but I thought the information was scalable that why they use test tanks for full size boats ?

Peter
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Re: 30% extra thrust?
« Reply #12 on: August 28, 2007, 04:28:10 AM »

. as much as 30% more power over conventional tubes.

This does not mean 30% more than the best of the best available.

But it does mean that if you are using conventional tubes you can get a big increase in thrust for a few quid.

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toesupwa

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Re: 30% extra thrust?
« Reply #13 on: August 28, 2007, 06:30:26 AM »

. as much as 30% more power over conventional tubes.

This does not mean 30% more than the best of the best available.

But it does mean that if you are using conventional tubes you can get a big increase in thrust for a few quid.



"After much research in to the many real-live prototypes...
.. So what might work well in the real world does not always work right in the model world..."

Sounds to me as if they are claiming a 30% advantage over full size shape Korts that have been scaled down to fit models...
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toesupwa

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Re: 30% extra thrust?
« Reply #14 on: August 28, 2007, 06:50:30 AM »

Yes but I thought the information was scalable that why they use test tanks for full size boats ?


An interesting point there Peter
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Welsh_Druid

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Re: 30% extra thrust?
« Reply #15 on: August 28, 2007, 07:26:13 AM »

Going off topic a little ( sorry) but I notice in the photos of the Rebecca that the rudder is a simple flat plate ( with strengthening plates). It seems strange that with all the effort that has gone into the design of the Korts that they have not used an more efficient profile on the rudder ?

Don B.
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DavieTait

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Re: 30% extra thrust?
« Reply #16 on: August 28, 2007, 10:32:31 AM »

Believe me don that rudder is more than up to the task , the Rebecca has a very tight turning circle compared to the bulk of the fleet ( even those who had the Becker Rudder - straight rudder with  a movable tip section as seen on the Maggie M trawler model ). The Maggie M Mbe trawler that you can buy with a kit has even removed the Becker rudder she was built ( possibly due to maintenance issues but i'd need to check ). Even the large Pelagic fishing trawlers ( over 65m long ) have fairly standard rudders.

The one I have seen that isn't standard is a modified 1970's designed and built trawler called Shekinah INS155 hows this for a rudder..

and how she looks on the water
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cbr900

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Re: 30% extra thrust?
« Reply #17 on: August 28, 2007, 01:37:21 PM »

So your saying that better steering control is gained by not turning the nozzle but turning a rudder behind the nozzle............


Roy
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DavieTait

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Re: 30% extra thrust?
« Reply #18 on: August 28, 2007, 03:03:58 PM »

No Roy a steerable nozzle will always outperform a fixed nozzle/rudder combo in turning but with the newest LIPPS nozzles you just can't move it at all. There is only 1/2" of clearance aft before the vertical lipp which is 2" high and they are only this efficient because the designers can fix all of the variables ( they have to scan the hull with a laser and design each nozzle/propellor for each individual boat , they tend to be 5% smaller in diameter too with the Rebecca FR143 going from a 1.9m prop to a 1.8m prop and nozzle ). There are a lot of fishing vessels that use steerable korts but there are also quite a few that have removed the steerable kort in favour of the fixed kort / seperate rudder arrangement which has less stress on the hull and is easier and cheaper to maintain ( also more efficient nozzle shape by up to 20% ).

For manouverability a steerable Kort wins over a fixed Kort but for efficiency its always better to have a fixed nozzle. The best set up for a tug would probably be an azipod with the motor in a housing with a LIPPS/Nozzle which can be moved 360'
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toesupwa

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Re: 30% extra thrust?
« Reply #19 on: August 28, 2007, 08:35:58 PM »

I emailed Mobile Marine Models and questioned their claims asking for details of boat models tested and test data relating to their kort's...

I received this back...  ???

" I'm sorry, but under the laws of this land, I cannot divulge names etc. of specific models etc. we tested....  ( apparently 'it' comes under " unfair-trading" !!! ) ........... However, as you know, water is water, and will not scale down... hence if one scales-down a 1:1 kort, obviously the power output will not be the same ( in relation ) to the scale of the 1:1................ Over the two year period that we researched / developed / tested our Power Korts, we found that each size had to be individually designed to achieve the maximum thrust from each sized kort...... Hence the reason we are so confident in the output"

So, No... they wont divulge their test results..  >:(
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HS93 (RIP)

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Re: 30% extra thrust?
« Reply #20 on: August 28, 2007, 10:24:32 PM »

So why over the last hundred or so years have they spent millions on test tanks ? or do these people at ship builders and universeties just like "playing boats"

Peter
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DavieTait

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Re: 30% extra thrust?
« Reply #21 on: August 28, 2007, 10:32:43 PM »

What they mean is they've been making them more accurate so the propellor is as close to the inside of the nozzle as possible and the pitch of the prop is adjusted with the wider shape at the tip. I'm willing to bet that if you look closely at one thats all it is.

Large scale prop/nozzle models in test tanks are still used to verify computer testing results. Its a cop out that they say they can't name the models/etc show their results..BAH nonsense. Just an excuse to not back up their claim with facts thats all. I'd be willing to bet that one of their nozzle/prop combo's would be no more than 5% more efficient than an accurately made normal nozzle. No way they could get 20% more thrust unless they have gone down the LIPPS/High Efficiency nozzle route.

Be good to know if they sell this as a fixed nozzle or as a steering nozzle , if its fixed only then i'd bet its a LIPPS type if not then there's no way to get a 20% increase in my opinion.

Davie
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HS93 (RIP)

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Re: 30% extra thrust?
« Reply #22 on: August 28, 2007, 10:52:53 PM »

If you look at the link in the first post it shows that they are a steering nozzle , I think they have made them work as they where supposed to in the first place. Ive seen loads of boats with korts but most have the wrong type of prop or one with a gap of 1/4" from tip too nozzle

Peter
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DavieTait

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Re: 30% extra thrust?
« Reply #23 on: August 28, 2007, 11:04:40 PM »

A lot of the fishing fleet put on basic kort nozzles around their existing propellors 10-15 years ago. They found they got about 10-15% increase in efficiency but whe they started fitting custom designed nozzles/props they found an immediate 20% over that again so around 25-30% more efficient than the bare open propellor.

A proper propellor for a kort nozzle has a wide tip shaped to the inside of the nozzle not the rounded off profile on a normal prop. With a steerable Kort you cannot make the nozzle as efficient a shape as optimum just due to the amount of the nozzle that needs to clear the prop compared to a fixed nozzle.

Davie
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tigertiger

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Re: 30% extra thrust?
« Reply #24 on: August 29, 2007, 01:59:05 AM »

I emailed Mobile Marine Models and questioned their claims asking for details of boat models tested and test data relating to their kort's...

I received this back...  ???

" I'm sorry, but under the laws of this land, I cannot divulge names etc. of specific models etc. we tested....  ( apparently 'it' comes under " unfair-trading" !!! ) ........... However, as you know, water is water, and will not scale down... hence if one scales-down a 1:1 kort, obviously the power output will not be the same ( in relation ) to the scale of the 1:1................ Over the two year period that we researched / developed / tested our Power Korts, we found that each size had to be individually designed to achieve the maximum thrust from each sized kort...... Hence the reason we are so confident in the output"

So, No... they wont divulge their test results..  >:(


Hi Toesup

Perhaps your enquiry was too specific. Perhaps not.
But it is not legal to directly compare your product with the competition.
However under trading standards a claim must also be verifyable.

But if the could publish results as in an anonymous table as below.

Boat     Nozzle A   Nozzle B  Our Nozzle

Boat A     10kg       10.3 kg    13kg
Boat B      10.2kg       -          12.9kg

So Mobile Marine Models, if you are reading, there are people who are intersted in the results. If you have over-egged the pudding the truth will out with this lot. If not don't hide the test results. This could be a PR boob if you are not careful.
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