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Old 07 October 2006, 19:22   #21
Country: UK - Wales
Town: West Wales
Make: Vipermax 5.8, SR4.7
Length: 5m +
Engine: 150 Opti, F50EFi
Join Date: Sep 2005
Posts: 6,298
I was referring to the worn paint on the skeg and propeller, rather than the damage. The water must be shallow where you use it!
As it's only had use this season, I wouldn't think you've got a loss of power, but this may be worth checking - it may have left the factory with a problem.

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Old 07 October 2006, 20:14   #22
Country: USA
Town: Punta gorda Fl.
Boat name: War Machine
Make: Falcon U.S.A.
Length: 9m +
Engine: twin 250 Yamaha
Join Date: Jan 2006
Posts: 936
re Medline underpowered

I might suggest trying a smaller wheel with your motor. As an example I am running 14 inch by 19 pitch propellers on my Yamaha 250 Hp motors, You are running a 14 by 21 (higher pitch) prop on a motor with quite a bit less power.
With a 13 1/2 inch prop you would be pushing less water reducing the load on the motor, which should increase the rpms, performance. It is just my guess but I would think possibly the wheel you are running is too large with a bit too much pitch, you might check with Suzuki and see what they recommend for the engine. Yamaha has a website with performance bulletins on boats with info on propellers for given h.p. motors, perhaps Suzuki has something similar, good luck!!

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Old 08 October 2006, 13:30   #23
Country: UK - England
Town: West Sussex
Make: zodiac
Length: 6m +
Engine: suzuki 115
Join Date: Jul 2006
Posts: 101
The correct wot for your engine is 5600-6200 and you are using the correct prop (14x21) My df115 swings the same prop as yours to 6000rpm so there is no reason why the bigger motor should not do the same .There is obviously a reason why it will not rev higher but your current prop is not the cause.
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Old 26 November 2006, 05:36   #24
Country: Ireland
Town: Co. Cork
Boat name: AmyClaire
Make: Zodiac
Length: 6m +
Engine: Suzuki 140 hp
Join Date: Jan 2006
Posts: 34
Update - Underpowered Zodiac Medline II with Suzuki DF 140

I have a new (Dec 05 – approx 40 hours) Zodiac Medline 2 (6 Metre) with a Suzuki DF 140, 4 stroke engine.

My problem is that she will only rev to 5,000 RPM at a max speed of 30knots at WOT.

We have checked the throttle cables - both at the hand control and at the engine and they appear to be o.k. – no restrictions, fully extended!

We have disconnected the throttle cables and operated the throttle lever on the engine with the RIB in the water - using a screw driver and hanging on tight! - Yet we can still only get the above figures at WOT - which eliminate the cables!

We have disconnected the throttle cables and revved the engine in neutral and we can get the engine to rev to the recommended 6,200 RPM - so now we know that the engine is capable of revving to that figure – but it will not rev to more than 5,000 RPM in motion.

I have emptied the bilge – it contained about 10/15 litres of water.

I am running a 21” x 14” Alloy prop and have tried a 19” prop which gave me an increase of about 200 RPM but no real speed increase.

On trying a 20” stainless steel prop the revs remained at 5,000 but the speed increased by one knot to 31 knots

When I tried a 17” aluminium prop, the revs increased to 6,000 and the speed went to a maximum of 34 knots (one way – 30 knots the other) giving an average of about 32 knots – two people and a quarter tank of fuel

The Engine has been trimmed fully out (until cavitating!) and has been tried in all different trim positions

We have dropped the engine by one notch Ύ” without any variation in speed or revs. The bottom cavitation plate is exactly inline with the base of the hull.

Speed is measured with a Garmin 198 C Chart plotter. This has been checked with a hand held Garmin and at worst was 1 knot out in speed (it varied up and down – sometimes my Garmin was quicker other time it was slower)

The RIB is trailered and always washed down and the engine flushed after each use. The hull is spotless.

My local Suzuki Distributor has put the engine on the computer (or visa versa!) and he is convinced that the engine is operating correctly.

I have removed all extra weight from the RIB (i.e. porta pottie, extra life jackets, oars, snorkeling gear, etc

Does anyone have any suggestions? Can you help? Surely this setup (Zodiac Medline II with a 140 HP four stroke DF Suzuki outboard) should be achieving at least 40 knots at a minimum of 6,000 RPM?

C'mon you 'teccies' - I need your help!
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Old 26 November 2006, 07:38   #25
Cypman's Avatar
Country: UK - Isle of Man
Town: Douglas
Length: no boat
Join Date: Aug 2006
Posts: 337
I have a DF140 on my Humber 6.3m Ocean Pro, and have tried a number of props over the last 18 months. The aluminium 21in pitch (all the props are 13 3/4in or 14 in diam) supplied with the engine gives me about 6,000rpm WOT and 39kts. I had hoped to get a faster top speed but recognising that the DF 140 is a relatively small cubic capacity engine, alledgedly only providing circa 128 BHP, the top speed is probably about right. I have also tried Suzuki's own S/S props, the 22in pitch only gave me a WOT of 5500rpm so I have now fitted the 20in pitch version. This gives me much better acceleration, a WOT of 6200rpm but a decrease in top speed to 38 kts. Nonetheless it is by far the best solution for this engine and my boat. Finally, it is probably fair to say that the DF140 is a fabulously smooth and economical power unit which lacks the "grunt" or the additional weight of the new DF150, horses for courses !!!
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Old 26 November 2006, 08:28   #26
Country: Other
Town: Oakley
Boat name: Zerstφrer
Make: Ribcraft
Length: 5m +
Engine: Suzuki DF 140
MMSI: 235050131
Join Date: Jun 2003
Posts: 3,931

I have a Ribcraft 585 with DF140. At the moment I get 40.5 Knots at 6000 RPM two up with half a tank. This is using the standard 21 inch alloy prop. And I haven't really tried to do any accurate speed testing yet, this result was achieved during a cruise.
I've just got my hands on a Suzuki 23 inch alloy prop that I'm hoping to try out this week.
My source tells me that Suzuki props aren't quite the ultimate design for that engine and when he gets some new props I'm hoping to try a custom 22 inch alloy prop. (Non Suzuki make).
I'm worried that although I may get some increase in top end speed with a larger prop I won't have the same acceleration lower down when I'm stuck in the rough stuff.

If I get out this week with all this rain and wind I'll post my results.
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Old 26 November 2006, 09:03   #27
Country: UK - Wales
Town: swansea
Boat name: Too Blue
Length: 8m +
Engine: Suzuki DT225
Join Date: Mar 2004
Posts: 12,791
That's not a bad speed for a 140 though!!! Makes me wonder about the true advantages of a stainless prop. A lot more expensive and more likely to damage your engine if you hit something - by the look of it not always better performance either.....
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Old 26 November 2006, 11:49   #28
Country: Canada
Town: Cowichan Bay
Boat name: Neptune
Make: Zodiac Hurricane
Length: 6m +
Engine: twin140 suzi 4stroke
Join Date: Oct 2005
Posts: 201
A few things. You definately do not want to lower your engine. You need to raise your engine the cavitation plate for suzukis needs to higher. Everyone on this side of the pond is finding that the 140's need to be rigged higher than normal(normal being the cavitation plate in line with the bottom of the transom) we are finding that the cavitation plate needs to be 1"-3" above the bottom of the transom. also the 140 is really a glorified 115 we have matched both motors on the same boat same conds etc etc and there was a 3 knot difference.

I had the same problem as you just not as extreme. I run twin 140's on a 6.4 m hurricane. The cavitation plate was iniatially set up level with the bottom of the transom and I was topping out at 5500 38 knots. We in the end raised the engines 2.75" I now top out at 6000-6100 and gained four knots.

A good indicator for engine placement is if the engine it too low you will get excessive spray and if it is too high you will cavitate in turns.

As for propping it seems you need to play around with it a bit. Is it possible for you to demo a few props from the the shop you bought the engine from.

The problem with the 140's is the gearing ratio it seems Suzuki is going to address this issue with the 2007 140's they have changed the gearing ratio in the lower end. I will be changing the gearing and it should help alot. A bit of extra money though. I was quoted about 400 pounds per motor should be available spring 2007.

It is amazing how small changes to the way your motors are rigged make such a big difference.

Good Luck; Simon
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Old 27 November 2006, 14:14   #29
Country: UK - England
Town: Wilmslow
Boat name: Serotonin
Make: Quicksilver
Length: 3m +
Engine: Mariner 15
Join Date: Feb 2003
Posts: 712
PM MeMe, he has the same outfit I'm sure his goes well over 30
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Old 27 November 2006, 15:03   #30
Hightower's Avatar
Country: UK - England
Town: Fareham
Length: 6m +
Join Date: Sep 2003
Posts: 7,855
Here's a longshot, but.......Have you checked the there's no water in the bilge, weight is a BIG killer of speed .


Looks Slow but is Fast
Member of the ebay Blue RIB cover club.
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