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Old 27 September 2005, 08:36   #21
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Thanks Charles. I went to the Volvo site and read just that but there's no explanation of how they function or what movement the blades make. From what I can tell, it appears the blade protrudes down from the transom about 50mm. The pictures appear to show two blades, one on top of the other. I wondered whether there was a pivoting action as they moved downward. I can't suss it.
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Old 27 September 2005, 08:58   #22
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It got me intrigued too, so I looked at the site and could find nothing informative

So I rang my local dealer, clueless wasnít the word, I quote, 'Volvo make what.....oh.... I didnít know that'

So I rang Volvo they knew a bit more but not a lot. Full vertical stoke is 35mm (not much) by 300 or 450 (two width sizes)

it works by inducing lift at the back of the boat, me 'do you mean lift or thrust ' Volvo '.......Iíll send you some literature'.
Volvo Couldnít answer what effect they had on speed or what comparative work they had done but did say (several times) that they were very good, based on what I donít know.

I'll wait for the Info and see because if they are good Iíd be interested Des.
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Old 27 September 2005, 09:54   #23
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The blades just move in and out about 2" - not a lot but it creates quite a bit of lift to the stern by creating a "step" of water ashead of them - this obviously lifts the bow and pushes down the stern - just like a normal trim tab.

The advantage is they are so neat and ahve very little chance of going wrong - they also seem cheaper than most!!!

control panel £42

9m 6 core cable £50

control unit £58

other cable £28

Interceptor £83 each

£344 ex vat for a system using the 2 biggest interceptors. Up to 4 can be used on bigger boats - this is from Volvo's retail price list!!!

One clever part of the system means you can actually steer the boat if your main steering fails.

Volvo could be onto a winner with this but they just aren't bothering to market it!!!
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Old 27 September 2005, 09:59   #24
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Interceptors aren't really new.

For more info see this

They are used on quite a lot of fast ferries etc - can also be used to dampen roll etc - from the companies conclusions they aren't as effective as normal trim tabs but a lot easier to install and cause less drag etc. Also they are far harder to damage - no problem with grounding etc.

http://maritimedynamics.com/mdi_msi_brochure.pdf

http://www.maritimedynamics.com/index.htm
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Old 27 September 2005, 10:59   #25
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Quote:
Originally Posted by codprawn
The blades just move in and out about 2"......
Volvo say 35mm which is 1.4Ē

Quote:
Originally Posted by codprawn
..... creates quite a bit of lift to the stern.....
I think you will find it is thrust, lift is what you get going into a low pressure area such as above a wing.

Quote:
Originally Posted by codprawn
......this obviously lifts the bow and pushes down the stern - just like a normal trim tab......
It's the other way around.

Not getting at you Codders it just helps to get the facts right.

You are right that it is cheap and looks low maintenance Additionally it doesnít clutter the transom area with horrible sharp SS blades that bend when hit


Des
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Old 27 September 2005, 11:19   #26
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Quote:
Originally Posted by Scary Des
Volvo say 35mm which is 1.4Ē

I think you will find it is thrust, lift is what you get going into a low pressure area such as above a wing.

It's the other way around.

Not getting at you Codders it just helps to get the facts right.

You are right that it is cheap and looks low maintenance Additionally it doesnít clutter the transom area with horrible sharp SS blades that bend when hit


Des

Of course that is what I meant - currently have about 15 windows open and 3 phones going - I need to get a grip!!!

I
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Old 27 September 2005, 11:21   #27
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Not sure that lift and thrust mean quite the same thing in hydrodynamic terms - water being incompressible. If trim tabs or these fin things raise the back end (and lower the nose) - it must induce some drag rather than thrust. Thrust implies that they accelerate you, which they can't.

I can see how they could level the hull out and therefore give more speed, i.e. the additional drag of the tab could reduce the overall drag of the hull. The tabs must induce drag though - otherwise they wouldn't/couldn't have any effect.

...all IMHO ...

D...
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Old 27 September 2005, 11:30   #28
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of course they cause drag - stick a match into the water and it will cause some drag - a step of water will build up under the hull at the back which will lift the stern and drop the nose - call it lift - call it thrust - it is pretty simple really - words just complicate it!!!
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Old 27 September 2005, 11:33   #29
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Quote:
Originally Posted by codprawn
of course they cause drag......... - call it lift - call it thrust - it is pretty simple really - words just complicate it!!!
Fair enough - but it is much easier if people use the same simple words.........
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Old 27 September 2005, 11:37   #30
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Actually thrust doesn't imply they accelerate you!!! Depends which direction the thrust is coming from!!!
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