Contra-rotating surface drives

[yipster]

here a pic of apearantly normal DPX volvo surface props
amazing your faster on regulars

[longliner45]

verytricky..I think they are going on physicis,, and not boat application,but phyisics does requir the entire equasion to get a true answer,,,,,,I hope I spelled physicis right....longliner

[jehardiman]

Originally Posted by Verytricky

Ahem... I have just set the UIM Class V24 world record with a standard Volvo engine driving a standard Volvo DPX drive with E2 props( worked ) at 80mph, ( 70 knots ) average speed two ways between Bournemouth and Boscombe piers ( ie in the sea, not a lake! )

It is my understanding that given more power the Duoprops would give more speed. I know as fact I was hitting the engine limit, not the drive limit. Duoprop allows me to be very stable in the sea. When you get air, you back off slightly to bring the nose down, and as you hit the water again you power on to prevent a harsh bump. With any other drive I would have tourque effect on the boat, with the DPX drive I can be as silly as I want and the boat is stable.

I am investigating a 650Hp engine for a new race series in the UK, and I will definately have the DPX drive. Our initial calculations show a speed of over 100mph (87 knots ). We do not see the drives only being effective to 40 knots (46mph)!!

Pictures show the boat being 'driven silly' which I dobt you can do for any length of time on a non-duoprop setup.

Not to take away from your truly laudable achievements, but the V24 class is designed around stock components for cost reasons, not overall efficency which was the start of this thread. A lot of speed problems can be solved by throwing horsepower at it, i.e. why the really fast guys run GT's.

If we compare the modern V24 class (24', ~1150 kg multi-step, 320 nominal hp, 80 mph) with the original circa 1980 developmental Arneson (18' Arena Craft, ~1000 kg no step, 260 nominal hp, 78 mph) we can see that the single prop Arenson is slightly better in the efficency department ( 0.55 R/W vice 0.58) , even using a non-chopper blade. Big reason is that the Arneson can turn a bigger wheel, which always improves efficency. CR props are only advantagously used when it is needed to deliver more power with a fixed prop diameter, which is not the absolute case here.

[Verytricky]

Originally Posted by longliner45

its my understanding that duoprops are only effective untill they reach a speed of 40 knots,,,then they fall on their face,,contact volvo for the facts though,dont even know about wave piercing props ,,,,longliner

Found it...
On Volvo Pentas website. They claim the DPX was designed for speeds over 50 knots.....

http://www.volvo.com/NR/rdonlyres/E1...97_1996_en.pdf

[Verytricky]

Originally Posted by jehardiman

If we compare the modern V24 class (24', ~1150 kg multi-step, 320 nominal hp, 80 mph)

1490kg....

[jehardiman]

Originally Posted by Verytricky

1490kg....

Wow, you're way over class weight....Have you ever considered leaving the trailer off....it might let you go faster....

Class website (www.v24powerboats.co.uk) reports 1150 kg dry with a on trailer weight in the box of ~1500 kg. Ok so add in the 180 ltrs fuel for a wet weight ~1350kg

[Verytricky]

Originally Posted by jehardiman

Wow, you're way over class weight....Have you ever considered leaving the trailer off....it might let you go faster....

Class website (www.v24powerboats.co.uk) reports 1150 kg dry with a on trailer weight in the box of ~1500 kg. Ok so add in the 180 ltrs fuel for a wet weight ~1350kg

UIM rules since 2004.
Since Pascoe got the rights to build, he could not get the strength required on the canopy by the UIM unless he made the boat heavier. So in 2003 the change was made, effective January 2004 that the weight of the boat as raced, at the end of the race, dry of water should be 1490Kg

I actually lost a second place in Sweden in 2004 by being 4 Kg underweight, and was disqualified! The official results show 1486Kg ( DQ )



The class website is (www.v24Club.com)

The website (www.v24powerboats.co.uk) is a marketing website by the people who sell the boats.

Both are out of date, but the class website (www.v24Club.com) has at least the 2005 rules.

The latest rules are on the UIM website, but they list 1490 as the required weight.

( FWIW, I was weighed at the record attempt and was found to be exactly 1500kg! Exactly, not over nor under.. )