Suzuki DF90 propeller for a 5.2 m RIB

[Valiant Knight]

I had a Solas Rubex 3*13.25*17 aluminium propeller on my 5.2 m Valiant PT520 RIB. When I bought the boat, used, in 2011, it was already equipped with that propeller.
Since one of the blades got damaged, I bought a Solas Amita 3*13.875*19 aluminium propeller.
With the Rubex 17 propeller, the engine, at WOT, exceeded 5500 rpm and went into plane easily, even if heavily loaded.
Now, with the Amita 19 propeller, the engine runs slower: at WOT, under light load, stays between 4500 and 5000 rpm (maximum recommended for the engine is 5500), but will not go into plane with 5 people on board.
Should I go back to a pitch of 17?
What is the expected impact of the increase in diameter? Original Suzuki propellers have a diameter of 14 inches.
Any hints?

Thanks

Antonio Manuel Carrapatoso

[Colin D]

Good to hear from someone with another Valiant PT 520 .My previous boat was the Ribcraft 4.8 and I think the Valiant is a far better rough weather boat .I'm looking to change from my 2013 Suzuki df60a to the new Df 90a .I'm very interested in your post and any information you can give me about top speed , fuel flow, and any changes you have done to your boat .is there any place over in Portugal where I can purchase accessories for the Pt 520 .looking forward to hearing from you
Regards
Colin

[paintman]

What did you base your prop selection on?
Did you speak to either Suzuki or Solas or just buy a prop?

[Valiant Knight]

I chose Solas because I had good references. The options were SS or Aluminium, 3 or 4 blades, 17 or 19 inches pitch. Diametres vary from 13.25 to 13.875 depending on model (Rubex, Rubex + or Amita - all 3 blades).
I moved from 17 to 19 inches pitch because rpms at WOT were above the maximum recommended for the engine (6 k when max rpm is 5.5 k)

[Valiant Knight]

I chose Solas because I had good references of the manufacturer. The options were SS or Aluminium, 3 or 4 blades, 17 or 19 inches pitch. Diameters vary from 13.25 to 13.875 depending on model (Rubex, Rubex + or Amita - all 3 blades).
I moved from 17 to 19 inches pitch because rpms at WOT were above the maximum recommended for the engine (6 k when max rpm is 5.5 k)

Antonio Carrapatoso

[beamishken]

Your clearly overpropped now which is far more harmfull than previously where you were maybe slightly underpropped
Possibly dropping back to a 17" larger diameter prop will get you where you need to be

[Valiant Knight]

Originally Posted by ribcraft4.8

Good to hear from someone with another Valiant PT 520 .My previous boat was the Ribcraft 4.8 and I think the Valiant is a far better rough weather boat .I'm looking to change from my 2013 Suzuki df60a to the new Df 90a .I'm very interested in your post and any information you can give me about top speed , fuel flow, and any changes you have done to your boat .is there any place over in Portugal where I can purchase accessories for the Pt 520 .looking forward to hearing from you
Regards
Colin

My Suzuki DF90 is a 2006 model, not a DF90A.
Top speed with the Rubex (3*13.25*17) propeller was around 30 kts at around 6000 rpm.
With the Amita (3*13.875*19) propeller the top speed is lower (between 25 and 30 kts at less than 5000 rpm).
I needed 20 liters per hour with 4 people on board and cruising at 20 kts, and 15 liters per hour with 2 people on board and cruising at 20 kts in a 400 km trip up and down the Douro river, with the Amita 3*13.875*19 propeller.
If you want to find accessories for the Valiant, try Vanguard Marine. I use them for tube and hull maintenance. They are located in the north of Portugal.

Antonio Carrapatoso

[Colin D]

Thanks for the feed back . With the Df 60a that I currently have im getting 31knots and 2 miles per litre of fuel when im on my own going fishing.I was expecting to increase the speed by 5 to 6 knots to 36,37 .keep in touch

Colin

[jeffstevens763@g]

I had on a 6m boat df 90 2009

14 x 19 Ali
13.5 x 21 SS
14 x 20 SS

All worked well 4 adults & dog 120 lts of fuel

[jonp]

I've recently sold a 5.2 boat with a Suzuki 90fa. It came with a 19 inch prop and like yours wasn't getting into the high rpm, spoke with the solas guys here in Aus who recommended their 17 alloy which got me up to 6000 rpm (the newer engines rev higher).

If going to stainless I would of needed to of dropped to a 15 inch. Even though I dropped in pitch my overall cruise speed stayed much the same. I did however raise my engine 2 holes which then made the whole outfit more responsive without cavitation in tight turns etc.

The rib I now have came with 15 inch yam prop which I changed to a 13 stainless solas. Even though I now have less pitch the better designed solas gives better all round performance. I also raised the engine on my current hull as manufacturers often mount engine to low.

Any engine needs to be propped so that it gets within close range of max rpm or you can end up doing damage with than an oversized prop not getting to the right rpm. If you are often carrying heavy loads then a smaller pitch will be needed. Many people seem to think they are saving fuel by having a wrongly propped boat because their rpm is less, this is far from true.

If in doubt speak with experts such as solas or fill in their online spec sheet to find what they recommend.

Jon

[MatFromPoland]

Originally Posted by Valiant Knight

I had a Solas Rubex 3*13.25*17 aluminium propeller on my 5.2 m Valiant PT520 RIB. When I bought the boat, used, in 2011, it was already equipped with that propeller.
Since one of the blades got damaged, I bought a Solas Amita 3*13.875*19 aluminium propeller.
With the Rubex 17 propeller, the engine, at WOT, exceeded 5500 rpm and went into plane easily, even if heavily loaded.
Now, with the Amita 19 propeller, the engine runs slower: at WOT, under light load, stays between 4500 and 5000 rpm (maximum recommended for the engine is 5500), but will not go into plane with 5 people on board.
Should I go back to a pitch of 17?

Don't you have any boat service who can lend you some prop to test ?
If not I would suggest go back to 17" and 4 blades.

You have mentioned that you damaged prev. prop. Are you sure that everything is OK with gear case ?

Please find mentioned below guide (this one is for Evinrude but rules are common):

https://www.youtube.com/watch?v=esQqJNIXLOc

http://www.evinrude.com/Content/Pdf/...ide_766315.pdf

Usually one pitch more is 200-300 RPM less so I do expect 5400 as minimum when you jump into 19".

I do have 19" (3 Blades) and 20" (4 blades)
I do have 100-200 RPM less on WOT (normal load)
but better consumption in average range.

I do suggest to check again 17" and RPM.
If you have much lower RPM than before go and check gear case.

They suggest to test RPM use load which you usually have.
If you go always alone, test it with single person.
If you go with family test it with family.
Hope it helps

[beamishken]

I can't imagine the gearbox is damaged causing your loss of rpm but if you continue to use the boat as is you are in danger of damaging the power head , valves etc can burn out due to overloading
If the engine can't make max revs it's overloaded not just at wot but through the entire rev range.
You need it prop so the engine can make just over max rpm with moderate load (during testing but don't run over max rpm) this can be achieved in various ways ss props 4/5 blade combinations different diameters etc there are dozens of prop combinations available.
The important thing is to let the engine rev to max rpm or its overloaded through the entire rev range with the potential for engine damage
A good dealer will often loan you several props for testing purposes to get the correct combination for your boat

[Valiant Knight]

Dear all:

Thanks for the hints.
I am going to try a Solas Amita 3*13.875*17 (17 instead of 19).
I will let you know the results as soon as I am able to test the solution.

Regards

Antonio Manuel Carrapatoso

[MatFromPoland]

Hope it helps:

https://www.youtube.com/watch?v=CFF6yL9lX9A

[Valiant Knight]

After a long struggle with the performance of the engine, I decided to change the shop I did the maintenance of the engine.
After an ECU replacement, I got back to 6.2 k rpm and 32 knots with just the driver or 6.0 k rpm and 30 knots with 2 on board, with a 17*13.875 propeller.
Should I go back to a 19 inch propeller?

Antonio Manuel Carrapstoso

[Valiant Knight]

Apparently the engine was running on 2 cylinders instead of 4...
Hard to understand how that was not noticed in the yearly maintenance.
:-(

Antonio Manuel Carrapatoso

[jeffstevens763@g]

On my 5.85 rib with a Df 90 I had a 14x 19 Ali prop and a 13.5 x 21 SS prop both doing around 45 mph at WOT perfect conditions

[Valiant Knight]

Thanks for the info.
Just a few extra questions:
When you state 45 mph, do you mean 45 knots?
What RPM did you get at WOT? Under what load?

Antonio Manuel Carrapatoso

[MatFromPoland]

I think it was 45 miles so it be about 39 knots.

Based on this website Suzuki Marine - Product Lines - Outboard Motors - Products - DF90 - 2012 - DF90A
RPM range is 5300 - 6300 so you do not exceed it.
If you plan to make fast trips with 2 people you can try to use 19"

But if you plan to go with more people and max is not so important maybe you can stay at this prop

[Valiant Knight]

Thanks for the info.

My engine is from 2006. DF 90 and not DF 90 A.
Recommended max. RPM range is 4.5 k - 5.5 k (Suzuki manual)

Antonio Manuel Carrapatoso