Prop Question???

Manos · 19 August 2005, 08:40

I am wondering if any one can with finding thje right prop for my RIB.

When I put the 200VMax (2-stroke 2002 model and had it from new) on it I changed the prop from 14 x 21" Yamaha Pro to 15 1/4 x 17" Yamaha Saltwater Series II. The boat weight fully laden is 2900 kgs, the boat length overall is 8.5 mtrs and length of water line 7.50 mtrs. I set up the engine with a power lift also.

The the engine at 4200 revs gives a cruising speed between 25 to 28 knots (not MPH) depending on the sea state. At WOT the engine does not rev more than 5000 (it should be between 5500 and 6000) and the boat has a top speed of 30 knots. When the boat is empty i.e. with about 50 ltrs opf fuel no fresh water etc the engine revs up to 5300 and I get a speed near to 35 knots mark.

I do not think that the boat lagging on acceleration and it planes quite fast what ever the weigth on it.

I have now ordered a new prop 15 3/4 x 15" Yamaha Saltwater Series II. Do you think this is the appropriate prop or should I exchange it for something else which will fit my 200VMax like 16 x 17" and what make?

Any replies gratefully received.

Many thanks

If you have not seen the video, you can see the boat with its current set up here (about 4minutes)
http://www.neptune.com/users/manos/videoWMP/manos338620.wmv

Phil Robinson · 22 August 2005, 15:16

Sorry to say it, but someone once told me that prop choice is a bit of a black art. I've tried various prop calc tools. The last one told me to use a 17p, however trial & error showed me that a 15p was the best for the job.

The best option is to try & borrow a few used props to trial from your local dealer / boat breaker. Sorry, not the easiest method, but it's been the best way for me to get it right so far.

dykkeren · 23 August 2005, 12:50

There is 2 factors that will influence on performance. Larger diameter gives more trust,not speed, an cost a bit to turn around. Pitch gives the speed of the propeller acording to rpm of the propeller.

But why go from a Yamaha pro to an saltwater series II this prop is designed to give more trust than the pro serie and less speed.

Seaharrier · 23 August 2005, 15:19

Manos,

What is the recommended HP for your RIB. 2900kg for 200 hp seems like underpowerd. 14,5 kg/hp.

Paul

Manos · 23 August 2005, 16:01

First I would like to thank you all for the ninfo you provided.

It all makes sence and I also agree with your views.

@ Phil
The boat is in Greece. Hench is quite difficult to find the props (especially the 15 3/4 x15 Saltwater Series II which I have now ordered and is in the post) to test.

@dykkeren
I decied for this prop 15 1/4 x 15 Series II because it was recommended to me by a good friend who is an engineer in the US who has spent hundered of thousands of hours with Yamaha engines, racing them, tuning and re-tuning them and upgrading them. Also after I gave all the data to Yamaha USA they recommended the 15 1/4 x15 Saltwater Series II

@ Paul
MAR.CO the builders recommend minimum 225 bhp 4 strokes with 15 1/4 x 17 Saltwater. I have discussed the issue of putting a 200VMax on the boat and after making a few calculations and taking in to consideration the different (I suppose gear ratio and torque of the 200VMax compared with the 225) they advised that it was an OK combination.

Is only that the engine does not pull the revs at WOT. The boat accelerates very well and comes to the plane very quickly even with 500ltrs ful, 100 ltrs of water and 8 people on board, it also pulls OK from the waves. However at WOT it does not give the appropriate revs (5000 max instead of 5500-6000 as recommended by Yamaha).

BTW this is a slow motion video clip when in a flat sea were going behind the wash of various crafts to see how the boat handles waves
In the real situation (we hit forse NNE 6 to 7) it coped more than well both boat and engine doing between 15 to 17 knots without any problem what so ever.
Click here to watch GATO DI MARE SLOW MOTION.wmv 4MB

The set up on the film is:

Gato Di Mare @ 4200 revs e 26 to 28knots
Trim @ 2.7
Power lift full up
6 persons
300 ltrs fuel
100 ltrs water
Prop 15 1/4 x 17" Yamaha Saltwater Series II
Yamaha 200VMax XL 2-srokes

The consumtion I got for the boat during cruising it was also good (I think)

First fill ............................ 400 ltrs
First trip to Milos ................180 ltrs
2nd Trip to Milos................. 200 ltrs
plus another ...................... 200 ltrs
Trip to Poros 200 ltrs ............200 ltrs
Fill again ............................ 150 ltrs
Trip to Kithnos, Serifos, Sifnos 250 ltrs

Total 1580 ltrs plus 35ltrs of oil and done about 40 hours which averages at about 39.50 ltrs of fuel /hour at 25 knots average speed per hour is about 1.58 ltr/mile

codprawn · 23 August 2005, 16:12

Did you get the CMC jack??? What do you think of it and does it help with speed and acceleration if you use it properly??

Looking at your revs for unladen it does seem as if you are nearly there - only about 300 short.

Prop selection does seem to be very much a case of trial and error - ideally you want to be able to vary the pitch depending on load as most aircraft do. Unfortunately nobody seems to be able to offer a good vari pitch prop at a good price.

Manos · 23 August 2005, 16:32

Yes Cod I got the CMC jack plate.

Is very good and had no problems with it. I think it will last for years. It lifts the boat quite high up and with a little trim (as low as 1.3) you get the bow out of the water at all times. The only thing that I see may be replacing in two three years are the plasctic (kind of plastic any way) washers.

Unladen the boat is fine. Is only when is loaded. I put on a lift and had a look at the weight with full fuel and water and it showed without people on it 2678kgs and something kgs!!!

So if you add 4 of us on it is near to 3 tonnes even more I recon.

Manos · 23 August 2005, 17:29

Quote:

Originally Posted by dykkeren

But why go from a Yamaha pro to an saltwater series II this prop is designed to give more trust than the pro serie and less speed.

Correct but the pro series I have has 21" pitch. I think too fast for this boat

Jono · 23 August 2005, 18:22

Quote:

Originally Posted by Manos

a good friend who is an engineer in the US who has spent hundered of thousands of hours with Yamaha engines, racing them, tuning and re-tuning them and upgrading them.

So he's worked on them, without a break, for 6 hours every single day since they Yamaha started making outboards in '59? related to Genichi Kawakami,by any chance? Manos your capacity for exaggeration astounds me even after all this time.....

You need to cover your head more in that fierce Greek sun

Manos · 23 August 2005, 18:46

Whatever Jono.

Jono · 24 August 2005, 09:00

Quote:

Originally Posted by Manos

Whatever Jono.

Manos, Whilst you continue to post shit, I will continue to post sarcasm...

I have followed various claims and statements of yours that have always been found somewhat lacking in substance. By all accounts, you are a personable and intelligent individual who appears to be reasonably successful, so why continue with all this stuff?

Manos · 24 August 2005, 11:25

.

codprawn · 24 August 2005, 13:59

Quote:

Originally Posted by Jono

Manos, Whilst you continue to post shit, I will continue to post sarcasm...

I have followed various claims and statements of yours that have always been found somewhat lacking in substance. By all accounts, you are a personable and intelligent individual who appears to be reasonably successful, so why continue with all this stuff?

Can't you allow the bloke a bit of poetic licence??? Or have you never been a fisherman????