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Old 23-10-2015, 13:54   #1
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Yanmar engine choice

Hi guys,

I'm looking to replace my engines & saildrives in my FP Bahia 46.
I've got the 40hp 3-cylinder bolted to SD31 drives now, however the boat had 4 cylinder engines before.

So my options are now again the 3-cylinder or the 4-cylinder with SD60 saildrives.
But also I'm a bit interested in the 4-cylinder turbo engine... since the difference in price is not that big.

I'm thinking to get the 75hp turbo and to overprop it.
My thoughts are to calculate the prop to take 30kw at 1800rpm engine speed.
This will be exactly 75% load (engine delivers max 40kw at 1800rpm).
In order to have cruising speed at around 1800rpm and max rev at around 2400rpm.

Is there anything wrong with my thoughts?
Share your opinion please.

Thanks
Bahia
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Old 23-10-2015, 14:12   #2
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Re: Yanmar engine choice

Bigger is better but do not overprop it.
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Old 23-10-2015, 14:39   #3
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Re: Yanmar engine choice

Hi,

why not overprop? If I leave the "standard" prop
the engine will run with higher rpm and little load only.
I want to run it at lower revs (like a genset) and with 75% load
to avoid carbon and to have the best fuel economy.
I don't see any other solutions than overpropping to achieve this.

Best regards,
Bahia
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Old 23-10-2015, 15:06   #4
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Re: Yanmar engine choice

I think you have a different definition of the term "overprop".

Usually refers to have a prop so large that max RPM can't be achieved at WOT with clean hull.
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Old 23-10-2015, 15:20   #5
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Re: Yanmar engine choice

Quote:
Originally Posted by Bahia View Post
Hi,

why not overprop? If I leave the "standard" prop
the engine will run with higher rpm and little load only.
I want to run it at lower revs (like a genset) and with 75% load
to avoid carbon and to have the best fuel economy.
I don't see any other solutions than overpropping to achieve this.

Best regards,
Bahia
I see no problem with your logic, but those sound like you are buying a lot of engine for nothing. How many HP were the originals? I'm guessing 50 HP more than enough. Turbos are less trouble free. Some logic says: buy the lowest HP in the biggest block. A turbo is usually the opposite. Just some random thoughts.
I thought Yanmar preaches high rpm to avoid carbon?
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Old 23-10-2015, 15:26   #6
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Re: Yanmar engine choice

What about weight?
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Old 23-10-2015, 15:53   #7
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Re: Yanmar engine choice

Hi,

difference in weight is not noticeable. Cat has ~14 tons, when traveling.
So 3 or 4 cylinders does not really matter. Space is available, too.

I wanted the turbo to run a low rpm setup and to enjoy the turbo whistling...
...but at the end the turbo is still a potential source of problems.
Not really what I need on a commercially used boat.
So I will probably go for the 4JH5E. I'm happy that it's DI already.

Now it's time to rob a bank or save some money... and to find a cheap supplier

Re the carbon... If you look at Yanmar commercial engines used for gensets... same engine just without the watercooled manifold... having specs to run at 1500/ 1800rpm. It's all about the load.
Many skippers confuse load with throttle, which is not the same.
WOT does not necessarily mean 100% load.

Cheers
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Old 23-10-2015, 16:39   #8
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Re: Yanmar engine choice

Myself I love turbo's, they are more efficient and run correctly combustion temps with a turbo are actually lower than a NA engine, Turbos are thought of as high RPM, high output, but they also increase torque at low RPM if correctly sized for that, but they are more complicated, often with aftercoolers etc.
If you want a turbo, do it. But if others run the boat, I'd rig the injection pump so that it can't be run at full throttle if you overprop it.
But then I'm one of those that believe if an educated engine guy is at the helm, a little overpropping doesn't hurt.


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Old 23-10-2015, 23:16   #9
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Re: Yanmar engine choice

No. Please don't do this. Turbos don't belong on a sailboat. You need to run them hard, or they will carbon up. Ask me how I know.


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Old 24-10-2015, 04:40   #10
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Re: Yanmar engine choice

I would be wary using a turbo on a boat unless it was necessary to get high hp in small size. Simply something else to go wrong.

I love turbos, don't get me wrong, but a sail boat should be kiss.

Also, what about a tractor based marine motor for cheaper parts and servicing. Is that possible?
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Old 24-10-2015, 06:31   #11
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Re: Yanmar engine choice

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Originally Posted by Moonos View Post
Also, what about a tractor based marine motor for cheaper parts and servicing. Is that possible?

Almost all Marinized engines are tractor or auto based. I really can't think of one currently made that's not(with the exception of ship propulsion).


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Old 25-10-2015, 05:27   #12
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Re: Yanmar engine choice

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Almost all Marinized engines are tractor or auto based. I really can't think of one currently made that's not(with the exception of ship propulsion).
I thought that some engines like kubota/Beta were cheaper for parts than Yanmar as they were easily obtained from machinery suppliers without the "marine" tag on it.
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Old 25-10-2015, 05:35   #13
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Re: Yanmar engine choice

Quote:
Originally Posted by Moonos View Post
I thought that some engines like kubota/Beta were cheaper for parts than Yanmar as they were easily obtained from machinery suppliers without the "marine" tag on it.
FWIW, John Deere mini tractors use Yanmar engines...
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Old 25-10-2015, 06:14   #14
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Re: Yanmar engine choice

I have the Yanmar 4hj4-te 75hp turbo on my 47 mono.. Gets to hull speed and then some!

Don't listen to others that say turbos don't belong on boats, they have been in the marine industry for years. If they had problems it's because they don't know how to run a diesel engine properly. You can't lope around all the time, you have to get a load on it(like you already know) and get the temp and exhaust flow up. It doesn't have to be there all the time, but that's with any diesel engine. They are meant to be ran at a load. Most commercial fishermen use turbo diesels with thousands of hours on them because the run them like their supposed to.

I picked the Yanmar because it was the lightest, smallest of the bunch in that hp range. Had I more room and didn't mind the weight I would have gotten a non turbo Beta for sure. Not sure on price, both great engines though. If you have the money to swing get the 4jh4-te, it's non common rail and non after cooler (which I agree adds complexity and added maintenance).

Oh, qnd the turbo DOES sound sweet when it spools up! wink

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Old 25-10-2015, 23:29   #15
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Re: Yanmar engine choice

Sorry, but turbos do NOT belong on sailboats. The need to be run hard, and often. Are you aware that the Yanmar recommendation on the use of turbo way is, get this, "weekly". We sail. We use our engine just not enough.


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