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Old 23 April 2022, 11:20   #1
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Ribcraft 585 / Suzuki Df140 - 13Ē diameter prop OK?

I have just acquired a 2016 585/DF140 setup which is great but I am not sure if it is correctly propped.

Standard alu prop seems to b a 3 x 14 x 21 and Iíve read quite a few threads where people have changed to SS of various sizes.

The prop on my boat is a stainless steel Apollo 3 x 13 x 21 which seems like it is too small based on Suzuki propeller charts.

I donít have a lot to compare against but the hole shot seems OK and I get about 38-40knts at 6200 RPM but it does seem quite fast to get there as if itís a little too easy for the engine and it would rev higher.

I read varying opinions about the effect of diameter on RPM but surely having a smaller prop than standard is not great?

Any thoughts or recommendations would be appreciated!

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Old 23 April 2022, 11:28   #2
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6200rpm is at the top end of the rev range. The limiter cuts in at 6300. 21p is about right for that setup, so going up in diameter would give you a bit more grip. Does it blow out in the turns or when trimmed up in the rough?
Iím a big fan of 4 bladed props on RIBs, I find they grip better & keep you planing at lower speed.
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Old 23 April 2022, 12:17   #3
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Ribcraft 585 / Suzuki Df140 - 13Ē diameter prop OK?

Thanks for the reply Dave. Iíve only had it out for a few days on short trips in relatively good weather so hard to say if it lacks grip. It feels as if itís a little too easy for the engine to rev and hit that 6200 rpm if that makes any sense which led me to question the prop.

Would a larger diameter 3 blade help hole shot?

4 bladed sounds interesting, we will use it for family activities mainly so low speed planing for inflatable toys and general manoeuvrability would be prioritised over outright top speed.

Iím half tempted just to find an original aluminium prop so we have a baseline.
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Old 23 April 2022, 13:02   #4
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Originally Posted by cdbxyz View Post
It feels as if itís a little too easy for the engine to rev and hit that 6200 rpm if that makes any sense which led me to question the prop.
............
Iím half tempted just to find an original aluminium prop so we have a baseline.
I have the alu prop as originally supplied by Ribcraft and get 38-40 knots but I think at much less than 6200 rpm. I'll check next time out, maybe next week. I don't get any sense that it's particularly easy for the engine to rev but I've no experience with any other props.
I'll post here next week after checking max revs.
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Old 23 April 2022, 13:33   #5
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Quote:
Originally Posted by cdbxyz View Post
Thanks for the reply Dave. Iíve only had it out for a few days on short trips in relatively good weather so hard to say if it lacks grip. It feels as if itís a little too easy for the engine to rev and hit that 6200 rpm if that makes any sense which led me to question the prop.

Would a larger diameter 3 blade help hole shot?

4 bladed sounds interesting, we will use it for family activities mainly so low speed planing for inflatable toys and general manoeuvrability would be prioritised over outright top speed.

Iím half tempted just to find an original aluminium prop so we have a baseline.


The DF140 needs to be able to rev, itís not a particularly torquey engine so overpropping is a no-no. You need to be able to hit 6k rpm wot with your normal load. Iíd be tempted to find a larger diameter prop in the same pitch to try. How high is the engine on the transom?
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Old 23 April 2022, 20:16   #6
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I had the same setup - RC 585 with DF140, albeit older. I tried a few props with mine and the best one I settled for was a Mercury Laser 2, 3 blade, 20" pitch, stainless prop as per below. Note this prop requires a slightly different thrust washer to make it fit but otherwise I found it entirely compatible

Mercury Laser II Propeller 48- 16990A46- 13.25 x 20 RH SS 3 BLADE

Having said that I didn't get to try any 4 bladed props on it.
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Old 24 April 2022, 20:22   #7
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Originally Posted by Pikey Dave View Post
The DF140 needs to be able to rev, itís not a particularly torquey engine so overpropping is a no-no. You need to be able to hit 6k rpm wot with your normal load. Iíd be tempted to find a larger diameter prop in the same pitch to try. How high is the engine on the transom?

Yep, I am leaning towards trying a 14Ē alu or 13 7/8Ē diameter SS prop - I think the 21Ē pitch is fine and itís not like the boat is slow, but Iíd really like to see if I can get better low and mid range with the bigger diameter.

Not sure how high the engine is really - have added a pic below

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Old 24 April 2022, 20:24   #8
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Originally Posted by scrambler View Post
I have the alu prop as originally supplied by Ribcraft and get 38-40 knots but I think at much less than 6200 rpm. I'll check next time out, maybe next week. I don't get any sense that it's particularly easy for the engine to rev but I've no experience with any other props.

I'll post here next week after checking max revs.


Thank you, that would be useful
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Old 24 April 2022, 20:32   #9
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Ribcraft 585 / Suzuki Df140 - 13Ē diameter prop OK?

Canít tell clearly, but on first impression it looks low.
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Old 24 April 2022, 22:23   #10
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Canít tell clearly, but on first impression it looks low.
Here's a pic of mine for comparison.
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Old 24 April 2022, 22:25   #11
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I'd say it depends what you want from the boat.
I have an RC585 with a DF140 with the standard ali 3 blade prop.
I cruise comfortably and economically at 27kts @ 4500 rpm...have topped out @40kts.

What's with the wish for set up to max speed?
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Old 24 April 2022, 22:49   #12
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sounds to me like its near perfect for that boat, I would leave things be.
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Old 25 April 2022, 07:09   #13
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I donít really have a wish for the top speed to be higher, Iím more wondering if the Ďcorrectí diameter prop ie 14Ē would give better characteristics in low - mid range.

It seems odd to change a prop diameter from the manufacturer standard size from reading various articles on the subject.

Next time Iím out I will take readings of rpm / knots through the rev range as well.
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Old 25 April 2022, 07:10   #14
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Originally Posted by scrambler View Post
Here's a pic of mine for comparison.


Thank you. Iíll take a better pic when Iím at the boat next. Itís hard to tell from the different angles and my one is trimmed up a bit on the land.
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Old 25 April 2022, 08:31   #15
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Hi,
As others have mentioned I don't think you're far wrong and as you say you've just bought the RIB, I'd enjoy it this year, get to experience the performance the current prop is giving you in various conditions then make a decision on changing the prop.
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Old 25 April 2022, 09:28   #16
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Next time Iím out I will take readings of rpm / knots through the rev range as well.
This link has the official test data and an image of the boat they used. However it doesn't say when the test was carried out although the pdf document was created in August 2021. It's possible the data is quite old and not with the current version of the DF140. The image and the oilskins certainly look a bit dated.
https://ribcraft.co.uk/uploads/2021/...Spec_Sheet.pdf

With all due respect to PD's experience, I think the engine height issue may be a red pike, sorry herring 🤣. Ribcraft are not going to vary the height and it just seems unlikely that anyone would change it from the standard, why would they?
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Old 25 April 2022, 10:42   #17
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I'm pretty sure we aren't getting those speeds at lower rev points but we do have a full 180L full tank and 2 adults/2 kids on board.

I've phoned around a bit this morning, Suzuki themselves were not much help but directed me to my local dealer who were excellent.

They think running a full inch lower diameter probably helps top end a bit but probably not beneficial throughout the rev range which is what I'm more interested in when towing inflatables or cruising on longer trips.

When I take the boat over for servicing at the end of the summer they will test it with different props for me. In the interim they have a standard one spare so I'll try that when I get a chance to see how it compares, I'll report back
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Old 26 April 2022, 20:18   #18
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Originally Posted by scrambler View Post
I have the alu prop as originally supplied by Ribcraft and get 38-40 knots but I think at much less than 6200 rpm. I'll check next time out, maybe next week. I don't get any sense that it's particularly easy for the engine to rev but I've no experience with any other props.
I'll post here next week after checking max revs.
Well I was completely wrong. I went out today and got 38.8 knots at 6400 rpm. I may have got more speed but I backed off pretty quickly. I think I may even have seen 6500 rpm but I can't be sure as I was only making quick glances at the plotter for obvious reasons.
I was single-handed with 65 litres of fuel in a 100 litre tank.
There was less than a knot of tide against and a 10-15 knot breeze veering around the starboard quarter so maybe assisting slightly.
Sea state was a slight chop.
At 4000 rpm I saw 22 knots and at 5000 rpm 30 knots.
Oh and btw according to my plotter the maximum speed I've ever done was 41.5 knots. I hope that wasn't in the same place I did today's run (Southampton Water) as that would mean I'd broken the 40 knot speed limit🤭.
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Old 26 April 2022, 22:42   #19
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I'd say it depends what you want from the boat.
I have an RC585 with a DF140 with the standard ali 3 blade prop.
I cruise comfortably and economically at 27kts @ 4500 rpm...have topped out @40kts.

What's with the wish for set up to max speed?

My 585 with the Mercury 150, propped with a REV4 14 5/8dia 19P I am cruising at the same speed but at 3600rpm.


The 150 has bags of torque and the WOT is 5000 - 5600, so 4000 rpm is a little over 30knts and 5000rpm is about 42knts, and the engine runs out of puff at 5300-5400 rpm which is a brown trouser 45knts ish ..... I don't go there very often as at that speed you need 1000% concentration and eyes like a hawk !
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Old 27 April 2022, 06:12   #20
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Quote:
Originally Posted by scrambler View Post
Well I was completely wrong. I went out today and got 38.8 knots at 6400 rpm. I may have got more speed but I backed off pretty quickly. I think I may even have seen 6500 rpm but I can't be sure as I was only making quick glances at the plotter for obvious reasons.

I was single-handed with 65 litres of fuel in a 100 litre tank.

There was less than a knot of tide against and a 10-15 knot breeze veering around the starboard quarter so maybe assisting slightly.

Sea state was a slight chop.

At 4000 rpm I saw 22 knots and at 5000 rpm 30 knots.

Oh and btw according to my plotter the maximum speed I've ever done was 41.5 knots. I hope that wasn't in the same place I did today's run (Southampton Water) as that would mean I'd broken the 40 knot speed limit🤭.


If those RPM figures are correct, which they shouldnít be as the rev limiter should be cutting in at 6300, youíre well under propped. Iíd like to see an engine printout to see the RPM profile.
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