SO 40DS Performance with Yanmar

[erkan]

Dear All,

This is my first post in the forum but I have read quite a number of subjects so far. I am so glad to be a member of such a forum.

I have a 40DS from year 2003 with a 56 hp Yanmar 4JH3E. I bought it last year. It has an original 18*13 prop. I am disappointed with the speed of the boat even with that much power. Even at 3000 rpms I can hardly reach 6 kn. But it has a very good performance under sail. I changed the prop with a folding volvopenta 2 blades 19*13, very good increase in sailing speed but no change under motor power! I strongly believe that the given prop diameter (18") is too small for this engine.

I would appreciate if you share your thoughts on the subject.

But I have to admit that the sailing performance is above my expectation and I am quite happy with my boat. My previous boat was a cyclades 39 which was fast with 40hp Yanmar but terrible under sail, I believe I cannot have everything in one boat .

Best regards,
Erkan
Urla, Turkey

[hoppy]

I have a SO40 with the 4JH3E and a Flexold 3-blade 18x13-3R. I have no problem getting to 7 knots at 2800 rpm. I never used it with the original prop so I cant compare.

[gene]

I also have the SO40 but same hull and engine. I do 8 knots at 2800 rpm with a 3 blade folding 16x10. I have a power curve on my web site here.

santosha.info/html/power_curve.html

Gene

[hoppy]

Gene, interesting that you went to the trouble to measure that all. I just know that my speed is usually 7 something at 2800.. I don't think I have ever seen 8. Never really gone beyond 2800.

"According to the experts, Continuous running below 80%, or 2920 can cause glazing of cylinder walls. " my engine and I guess that of most private owners will have the glazing I'd bet. How did you work out the economy. I have figures between tank fills but that is only a average for all kinds of usage..

erkan. was the folding prop you bought designed to work for your engine and gear ratio? When I bought my flexofold they made it clear that it was important that I told them the gear ratio so they would give the right prop. It's more than just size that's important, it's also the pitch of the blades as well.

[juanluis]

I do 7 knots at 2800 rpm. The engine is a Yanmar 40hp and the propeller is the original folded blade equipped by Jeanneau (SO409 Performance).
Juan Luis

[erkan]

Thanks for your replies.

Dear Gene, It is interesting to hear that 16"*10" prop gives 7 knts! Should be high rpm at the shaft. What is your gear ratio?

Hoppy, 1.5" increase in pitch means around 1" increase in diameter. So I consider the pitch as well when I say the size of the prop. Original one was 18*13 3 blades. I was not happy (clean bottom). Needed high rpm to move. So I bought the folding one +1" in dia without changing the pitch dimension. Actaully 3 blades are better in high seas and Agean sea is not a calm sea. Maybe I will go for a 3 blades maxprop. So I can change the pitch as well...

I chekced with the gearbox manufacturer Kansaki and they reccommend max 21" for my gearbox.
First I have to measure if I see the correct rpm. Maybe my gauge is defective. Because it goes as high as 4000+ at the full throttle in gear. The spec is max 3800 in the book.

Ayway, I am hopefull after learning that I can do 7 kn at 2800 rpm, and I will find a way.

Brgds,
Erkan

[gene]

This is interesting as the numbers don't add up for my prop size.
I got them off the survey and looking at a picture I took it looks more like 15x10R.
So I will check carefully when I haul next year. I would assume we all have the same gear box. I did my speed test as I had a 4 hour motoring trip in calm seas so I needed something to do.

As far as glazing goes if I have a long run I finish off at 3200 or higher for about 5 min. This process is supposed to minimise glazing.

Gene

[hoppy]

I have the Kanzaki with a 2.63 ratio

erkan, the "max" of 3800 is the rpm that maximum power occurs and you will be able to rev beyond that.

[sitara]

Getting the right size prop for a boat is quite an art. The variables that must be considered are waterline length, displacement, available shaft horsepower, maximum engine RPM and gearbox ratio. As I understand it the propeller pitch is the main determinant of hull speed and that increasing pitch at a given RPM will increase speed at that RPM. The diameter of the prop is determined by the power of the engine and is not closely related to speed through the water.

I am not a prop expert so I hope these ideas are correct.

[MartyB]

Sitara,

Ypu've explained props about as well as I can. A bit better or more info....ie an 18x7 allows 7" forward movement in one prop rotation, as I understand it, an 18x8 would allow 8" forward movement. So the OP going from an 18 to a 19" prop, keeping the pitch the same, did nothing for speed, only potential bite in the water. I would see an 18x14 as a possible better bet for additional speed, and going with a three blade for more power/bite in rough water.

Altho if the prop is over pitched, ie the 13 is too big, then going with a 12 or 11 might be the way to get more rpm so that it can go faster. One has to work the pitch both ways!

marty

[erkan]

The pitch has the role in the boat speed as long as you have the correct diameter. In my case 2800 rpms should give 11 knts! (2800rpm/2.63)*13"*60 minutes= 82600"/hr= 11 knots (aproximately). I have almost 50% loss.
Another empiric (correct spelling?) formula says; max loaded rpm should be 100-200 rpms less than engine max rpm spec. In my case this does not work either (if I am reading the correct rpm).

So I conclude as I have to increase the diameter in order to make use of the power from the engine.

What looks strange is why original Jeanneau prop spec is small for my boat and/or why I am the only one complaining about the speed?

[MartyB]

"COULD" please note quote, as you mentioned earlier, could the tach be reading incorrect? I did not see an actual yes it has been tested etc. Along with, "COULD" the knot meter be reading correct too?

Only throwing these two items out, as it appears based on a few other posters, with similar sized/same boats and motors with similar or the same prop that they are doing within what I and they would call correct speed for the rpm etc.

You may not have a prop issue!

Marty

[hoppy]

erkan, have you checked that your gearbox is 2.63? Maybe it's no, although I cant imagine why it would not be....

What speeds do you see when sailing? I see 7 easily, 8 at times and occasionally get into the 9's with enough wind. Maybe the problem is your log. Have you compared with a GPS?

Good luck solving this...

[super g]

Same boat and engine and I had the same issue with a 19"x R11 3 blade prop, so I imagine 18" would exacerbate further.

I felt I was running at too high a revs for 6.0knots cruising, with fuel consumption to match. It felt like the engine hardly noticed the prop was attached, similar to blipping the throttle on a motorbike in neutral.

In the end I fitted a 20" feathering Max Prop, cannot recall the pitch setting, and have a much more sedate engine note, though I'm revving well below the recommended 80%. Every now and then I open her up for a while to reduce the risk of glazing.

If your interested in trying a 19" I have a spare.

[sitara]

MartyB
Re your comments about pitch and for example an 18 x 7 prop allowing for 7 inches forward motion per revolution. Prop slip also comes into play here - this is the stream of water we see being propelled away from the stern of the boat - so forward motion is quite a bit less than the theoretical 7". Prop slip is 1.4/(Knots raised to the power 0.57). At 7 knots there is 43% slip according to this formula.

I had a rev counter on one boat that was out by 500 rpm at max engine speed. This cause a lot of problems until the mechanic checked the rpm with another meter.

Erkan - I believe you a right about the prop reducing unloaded revs by about 200 rpm so it sound like the pitch of your prop is too small. The danger of too much pitch is an overloaded engine blowing black smoke.

[erkan]

MartyB, I did not check the tach yet, will do it next week. But I don't "believe" it is problematic.
I use Garmin gps and my iphone for the speed, I am sure of it.

Hoppy, yes I am sure that it is 2.63. I read it on the gearbox plate and I also checked it with the manufacturer:) by the way, I asked if I can use both right and left propellers as my folding prop was left one (just by changing remote connections) and the answer from Kanzaki was: yes. So this is an extra info for km4a1 users.
I have no complaints when sailing with the wind, esp after folding prop it is much better now. My log is already problematic, it shows "zero" after one week in the marina, I use gps to measure the speed.

Clouds, thank you very much for your comments. I fully agree with them. I am experiencing exactly the same things! I see that I am not the only one having this problem...
So, I have to go for a 20" maxprop. Thanks for your 19" offer, but my boat (and I) are in Turkey, it cannot be practical to ship it overseas:) And my existing volvopenta folding prop is already 19*13.

Erkan

[erkan]

An update about the situation:
2 weeks ago new 3 blades 20" maxprop was installed with 20 degrees (=13.7") pitch (thanks clouds!) and now I do 7 kn at around 2600 rpms :-) Max rpm is 3500 which is a little below the spec.
Why the original prop was 18*13, I have no idea!
Erkan

[oceandiamond]

Replaced my original prop on my SO40 ( 2000 ) with an autoprop from Bruntons.
Easily do 7 knots at 2,500. Also noticed more consistent thrust when heading into the wind under power
Easy to install and improved performance under sail

[so40gtb]

Erkan, your results with the MaxProp match the performance of my '00 SO40 with the MaxProp and the 4JH3E. You have probably discovered by now how good the "bite" of the MaxProp is in reverse and you will soon begin the learning curve of how to most effectively use its characteristics, forward, reverse, and sideways, when docking. Since the MaxProp was on our boat when we acquired her, I can't compare it to a fixed propeller. 6 kt is normal around 2000 rpm and 7+ kt is normal at 2500 rpm. We don't run the rpm higher unless an exceptional, short-term need arises. Have a great summer on a great boat with a great prop!

[cpetku]

just did a 6 hr trip. 8 knots at 2800 rpm with max prop on a 2004 40ds.