Underpowered Zodiac Medline 2 with DF 140 Suzuki

[Merox]

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.

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 - yet we can still only get the above figures - 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 am running a 21 º x 14” Alloy prop and have tried a 19º prop which gave me an increase of about 200 RPM but no real speed increase.

Speed is measured with a Garmin 198 C Chart plotter.

Does anyone have any suggestions?

Martin

 

[JUSTINTIME]

Re: Underpowered Zodiac Medline 2 with DF 140 Suzuki

way over pitched prop

 

[JB]

Re: Underpowered Zodiac Medline 2 with DF 140 Suzuki

Moving to the Prop Forum

 

[Merox]

Re: Underpowered Zodiac Medline 2 with DF 140 Suzuki

Lads and Ladies - I'm in trouble - can anyone suggest a solution to my problem?

Thanks,

Martin

 

[Crownie2]

Re: Underpowered Zodiac Medline 2 with DF 140 Suzuki

I couldn't see your pics, but...

Actually, with the 19" pitch wheel your slip calculates at 12.2% - and that's not bad. I would say try a 17" pitch prop to get the RPM's up more. IMO you want to be around the 5,800 area.

I think the 21" was not the right prop as the slip calculates at over 17% with that one - if your speed is accurate...

Bob

 

[Silvertip]

Re: Underpowered Zodiac Medline 2 with DF 140 Suzuki

Reving the engine to 6200 RPM with no load means absolutely nothing. Chances are it would rev that high if only two cylinders were firing. And -- you run the risk of destroying it.

 

[Merox]

Re: Underpowered Zodiac Medline 2 with DF 140 Suzuki

Thanks Bob,

I've now tried the 17" prop which increased my revs to 6,000 and the speed came up from a max of 30 knots to 34 knots (Garmin Gps).

Yes, its faster out of the hole but I'm still not satisified with the top-end speed.

Any further comments?

Regards,

Martin

 

[JUSTINTIME]

Re: Underpowered Zodiac Medline 2 with DF 140 Suzuki

are u using stainless or aluminum prop?
u are in the range, if u went to 18 u will be around 6200
3 blade will give u a faster top end
4 blade will give u the hole shot

 

[deejaycee_2000]

Re: Underpowered Zodiac Medline 2 with DF 140 Suzuki

It sound to me like your motor might not be set up correctly, a 6 meter inflatable with a 140hp should give you at least 50 mph at WOT, the correct prop should be 17" or 19" prop ..... check that your anti-cavitation plate is inline with the bottom of the boat ......

 

[Merox]

Re: Underpowered Zodiac Medline 2 with DF 140 Suzuki

Update .....

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. The bottom cavitation plate is level with the base of the transom.

We have dropped the engine by one notch ¾” without any variation in speed or revs

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?

 

[JUSTINTIME]

Re: Underpowered Zodiac Medline 2 with DF 140 Suzuki

u need a 17" no matter what
i would use aluminum

what diameter are u using
3 blade top speed
4 blade hole shot
raise the motor also will make u faster

 

[Merox]

Re: Underpowered Zodiac Medline 2 with DF 140 Suzuki

Its a 14" diameter aluminium

 

[Merox]

Re: Underpowered Zodiac Medline 2 with DF 140 Suzuki

14" - 3 blade!

 

[Crownie2]

Re: Underpowered Zodiac Medline 2 with DF 140 Suzuki

What does your dealer think about your top speed?

He should have a good idea as to what to expect.

To me it doesn't sound that far off - but I have no experience with large Zodiacs.

Are rour expectations based on information you gained from boat tests or some other reliable source?

 

[tommays]

Re: Underpowered Zodiac Medline 2 with DF 140 Suzuki

http://www.hotribs.com/05ribreviews/01zodiac/medline.asp

i googled around a bit and there are reviews of the boat showing about 45 MPH with a 150Hp 2 stroke


Tommays

 

[Crownie2]

Re: Underpowered Zodiac Medline 2 with DF 140 Suzuki

Hmmm... well 40 knots may be a little optimistic but according to the test linked above it seems it should be a little faster than 34 knots.

As mentioned above, you could try raising the motor one hole on the transom and perhaps an SS prop, in that order...

 

[walleyehed]

Re: Underpowered Zodiac Medline 2 with DF 140 Suzuki

Get the engine up...as crownie said.
If you moved it down a hole, you went the wrong way.
We're talking about the bolts that hold the engine to the transom here.
I've got a DF115 here on a 24ft pontoon that will make 33mph...I was amazed to say the least. we also went up 2 holes from where it was(dealer set-up) and went to a stainless prop.
Also, the Evinrude DFI isn't really a good comparison to a 4-stroke 140, and I'll bet they had it set up for max performance.
Did you have your 25hr inspection done?