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Old 07-05-2014, 12:21   #1
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Boat: Gulfstar 50
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Perkins 4.236 HP ratings

Hi All,

Having a 4.236 in my boat I tend to read threads about them. We all have seen the 4.236 listed as having 67 or 72 or 85 or ?? Hp and I've often wondered about this.

The HP ratings that I did a quick google search for show that they all fall on the HP curve from the "Pleasure Craft High-Speed Rating" graph.

67 HP at 2000 rpm
72 HP at 2250 rpm
84 HP at 2800 rpm

So from this I presume that the engine regardless of the HP rating is the same and that the maximum rpm setting in the governor is what selects the rated HP. I presume that Perkins did not use an actual different governor. Can anyone confirm this?

It makes sense to me to limit the rpm to 2000 and call it 67 HP for an engine that is designed to run at WOT for ever in a heavy displacement work boat. All the while setting the governor to 2800 rpm and calling it an 85 HP engine for a taxi or delivery van.

The engine in my boat does about 2200 rpm at wot no load and is a bit over propped so it does only 2000 rpm in gear.

If there is any question here it would be can anyone confirm these presumptions? And has anyone changed the max rpm settings on their engine. I'm not planning to do so but I am curious.

Regards
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Old 07-05-2014, 13:09   #2
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Boat: Alden auxiliary ketch 48'
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Re: Perkins 4.236 HP ratings

I would add further inquiry to the question. I am currently rebuilding a 47' Alden auxiliary ketch which will displace somewhere in the neighborhood of 35,000lbs. It formerly had a Westerbeke diesel in it that was removed by the PO. When I try to calculate the hp needed for my vessel (4 hp for each ton) I end up with 68 hp. That would match up with a 4.236 (my intended engine) but I have read here that some folks are running a 4.108 with similar displacements.

I don't necessarily mind the extra capacity if it helps out in dire situations but I wonder if I am putting in too much power.

What type of boat do you have? What is the displacement?
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Old 07-05-2014, 22:52   #3
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Re: Perkins 4.236 HP ratings

Quote:
Originally Posted by crazyoldboatguy View Post
I would add further inquiry to the question. I am currently rebuilding a 47' Alden auxiliary ketch which will displace somewhere in the neighborhood of 35,000lbs. It formerly had a Westerbeke diesel in it that was removed by the PO. When I try to calculate the hp needed for my vessel (4 hp for each ton) I end up with 68 hp. That would match up with a 4.236 (my intended engine) but I have read here that some folks are running a 4.108 with similar displacements.

I don't necessarily mind the extra capacity if it helps out in dire situations but I wonder if I am putting in too much power.

What type of boat do you have? What is the displacement?
I've got a Gulfstar 50 at about the same displacement. 30,000 unloaded. Some of the G50 were powered with the 4.108 and they were noted for being underpowered.

The 4.236 is a good match for my boat. Having the extra power to push through adverse conditions could be a blessing. It is still economical to run at lower rpm. Plus many repowers use a 100HP yanmar so you will not be over powered.
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Old 18-05-2014, 21:12   #4
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Re: Perkins 4.236 HP ratings

The Perkins Manuals list the SHP at 72HP at 2500RPM.
Like you I have seen many numbers 80, 84HP etc.
I run my engine at around 1600RPM for economy motoring. Previous owners used 1800, but I find the loss of .2Kts more than made up for in fuel.
I get 6Kts at that setting in smooth water, that is a 22,000Kg, 4m beam, 42' Ketch - not too bad.
I have a friend that just sold their KP44, fitted with a turbo Perkins of the same HP rating as the normally aspirated 4.236 - much more fuel efficient than mine!
Unfortunately I cannot recall the model number.
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