Ribcraft 5.85 with a Suzuki DF140 - Page 2

gingercoastie · 13 August 2005, 12:35

If you trimmed the engine up a bit, you may get some more knots.

roycruse · 13 August 2005, 13:04

I dont think they are actually doing 42.2 knots when the photo was taken - if so then its bloody impressive at 2000 rpm - not to mention very steady camera work

I assume that 42.2 was max speed and 6.2 was the current speed.

roycruse · 13 August 2005, 13:10

Thanks robin - are those trim tab switches in the centre of your console.

did you have those fitteb when the boat was built or did you get them rero fitted.

dod you use them much - what difference do they make - do you recomend them...

robin · 13 August 2005, 16:25

Quote:

Originally Posted by gingercoastie

If you trimmed the engine up a bit, you may get some more knots.

If that was for me Alex....
Yup...did that

The 42.2 knots is the max speed attained on the run.
Having come down to a more stable speed to take the picture (6 knots as per the current speed indicator) the leg was trimmed back in again otherwise we would have been going uphill.

robin · 13 August 2005, 16:41

Quote:

Originally Posted by roycruse

Thanks robin - are those trim tab switches in the centre of your console.

did you have those fitteb when the boat was built or did you get them rero fitted.

dod you use them much - what difference do they make - do you recomend them...

Left hand switch is nav lights, right hand switch is bilge pump.

No trim tabs.

Personally I wouldn't bother with trim tabs on a boat this size.
You are able to deal with fore/aft trim issues using the outboard leg. Any lateral balance issues can be dealt with by judicious distribution of weight (move the lardies about).
That really doesn't leave the trim tabs much else to do except on a larger craft (leaning into the wind issues) ....or....to assist with planing on a poorly balanced or wrongly set up boat.
Keep it simple.
All in my humble opinion of course

robin · 13 August 2005, 16:46

Quote:

Originally Posted by roycruse

I dont think they are actually doing 42.2 knots when the photo was taken - if so then its bloody impressive at 2000 rpm - not to mention very steady camera work

I assume that 42.2 was max speed and 6.2 was the current speed.

Spot on.

At 42.2 knots I had one hand on the throttle and the other on the wheel.

randski · 14 August 2005, 08:53

Quote:

Originally Posted by Kernow

Now my Ribtec 5.35 with a 90 hp will touch 40kts ( 38, 4 up)

What am I doing wrong? My Zodiac 550 with Suzuki df115 will only reach 34kts HELP!

roycruse · 14 August 2005, 13:38

Quote:

Originally Posted by randski

What am I doing wrong? My Zodiac 550 with Suzuki df115 will only reach 34kts HELP!

I presume you have the leg trimmed right out at the time in calm conditions.

What prop are you using?
What RPM are you doing at 34 knots?
How much fuel / passengers are you carrying?
How are you measuring 34 knots - paddle wheel speedo or gps?

I would have thought you should be going quicker than that - my humber with its DT55 could manage 33 knots but it was a much smaller boat,

Kernow Buoy · 14 August 2005, 13:53

Quote:

My Zodiac 550 with Suzuki df115 will only reach 34kts HELP!

Yes agree with Roy, think you should be going a bit quicker than that, he's asked all the relevant questions, lets see how much of your money we can spend!

randski · 15 August 2005, 12:14

Quote:

Originally Posted by roycruse

I presume you have the leg trimmed right out at the time in calm conditions.

What prop are you using?
What RPM are you doing at 34 knots?
How much fuel / passengers are you carrying?
How are you measuring 34 knots - paddle wheel speedo or gps?

Have not had the leg trimmed right out
Standard prop that came with the motor
about 5500 rpm
full tank 80lt/2 passengers
gps

I am just going out now for a couple of hours will try with the leg trimmed right out & see what it will do.

randski · 15 August 2005, 12:15

Quote:

Originally Posted by Kernow

Yes agree with Roy, think you should be going a bit quicker than that, he's asked all the relevant questions, lets see how much of your money we can spend!

OH NO not more money!

roycruse · 15 August 2005, 12:27

Quote:

Originally Posted by randski

I am just going out now for a couple of hours will try with the leg trimmed right out & see what it will do.

you should find that buy the time you get the engine trimmed to about 3/4 up you have gained several knots in speed as the hull lifts out of the water and reduces friction.

the boat should continue to gain speed as you trim up until one of 3 things start to happen.

1. The prop starts to ventilate (this is most likely)
2. you raise the bow too much giving the boat too high an angle of attack (thus slowing you down a bit)
3. the boat starts to chine walk (this is less likely)

randski · 15 August 2005, 17:05

Water wasn't totally calm but still only managed 34.9 knots.

I have got slight damage to my prop, (did I fail to mention this?

) so I assume a new prop is the answer?

Any advice on where to go or which would be best? (Ok Kernow, I've got my wallet out)

Did chine a bit but have adjusted the trim tab.

Kernow Buoy · 15 August 2005, 17:24

Any idea what rev's you were getting flat out?

randski · 15 August 2005, 18:34

He's not here at the mo but I think it was about 6

Kernow Buoy · 15 August 2005, 18:52

Crikey, assuming thats 6000 rpm according to the net your at the top of your rev range ( which suggests the engine is fine

)
Any idea what size prop your using? look for something saying 14x17 or similar stamped on it and let us know

randski · 15 August 2005, 19:02

Ok, I exaggerated slightly. Apparently it was about 5800 revs.

It says 3x14x21 on the side of the prop

Kernow Buoy · 15 August 2005, 19:28

Hmmm. I would have thought a 21" pitch prop was about right, I've fed the details into a prop calculator ( had to guess your gear ratio) and it came up with 45 knots !!!
How bad is the damage to your prop?

randski · 15 August 2005, 19:41

When the engine went in for a service the fella said the damage wasn't too bad but there are a couple of 1 centimetre chunks of metal missing from one blade and a few scrapes on others.

We got a chain wrapped round it

roycruse · 15 August 2005, 21:01

Quote:

Originally Posted by randski

there are a couple of 1 centimetre chunks of metal missing from one blade

crickey

- not that i have much experience in these matters but a couple of 1 centimeter chunks sounds bad to me. I would certainly be looking to get that one repaired.

I( would be worried about balance and the vibration it causes damaging the bearings in the drive shaft of the engine, especially if the damage is near the edge of the prop and not near the centre.

Please correct me if im wrong someone - may be 1 centimeter chunks missing is perfectly normal. but i would guess its gonna cost you a knot or two...