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Date Posted: - Thursday - 05/18/06 - 1:24pm
Author: Lawrence Killingsworth
Author Host/IP: slip-12-65-126-25.mis.prserv.net / 12.65.126.25
Subject: Perkins 4-107 RPMs

Just wondering if there is a consensus out there as to the optimum RPMs to run a Perkins 4-107. I run mine on Ta' Ata Ori at around 1500 RPM and that gives me almost 6 knots (with a clean bottom and flat water -- 18-inch prop).

Fuel consumption is frugal at that speed, of course. I only carry 70 gallons of diesel in my main tank, so I have to be sure I can get to the store and back...

Anyone out there run theirs faster or slower? And what's your experience?

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Replies:

[> Mine too -- Will Holoman, - Thursday - 06/29/06 - 7:41pm (host2.brwncald.com/65.198.3.2)

I run 1500rpm all day at ~5.5 knots.

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[> MAX RPMs? -- Mike Cox, - Thursday - 06/29/06 - 8:01pm (NoHost/72.24.202.31)

What is your 4-107s maximum RPM output while under load? My TM 36 with a 4-108 and a 1.91:1 transmission with an 18x10 3 blade fixed prop cruises best between 2200 and 2400 rpm (6.2-6.5 knots). It maxes out at over 2700 and over 7 knots.

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[> [> Perkins 4-107 RPMs -- Doug Wilson, - Friday - 06/30/06 - 1:09am (user-10cm9ou.cable.mindspring.com/64.203.39.30)

Made a trip to Catalina last week, I ran my newly rebuild 107 at 1300, made 5.8 Knts. This was a motor only trip to put some time on the machinery.
Don't know about fuel until I refuel before the next trip.
Also have no way to check how much fuel is in the tank as the fill takes a 90 degree turn aft.
But with 14 hours of time, I bet I didn't burn much.
Doug

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[> [> [> Seems too low -- Mike Cox, - Friday - 06/30/06 - 10:30am (cache-dtc-aa09.proxy.aol.com/205.188.116.13)

I fully understand that a 4-107 or 4-108 can be cruised (5.5 to 6 knots) at a lower that recommended rpm and save some fuel but I would be concerned that if the engine is set up (prop size and pitch and xmission ratio) to obtain a good cruising speed with a low rpm in no or light wind conditions, it will not be able to obtain or maintain its optimum power output when you really need it - powering into a strong head wind or strong current, or once the prop and bottom began to get fouled up. It will also load the injectors with carbon build-up. An additional problem with having a boat set up (prop size and pitch with xmission) to reach cruising speed at low rpms is that you sacrifice slow speed control needed for docking or other maneuvering. One of my prior boats would cruise nicely at low rpms in light wind conditions but would overload (heat-up and black smoke) when pushed to higher rpms in stronger wind conditions. I also had to kill quite a bit of speed when docking as it would make 2.5 to 3 knots when running at the lowest rpms. I personally rebuilt the engine and saw the effects of running at too low an rpm. The boat was carrying too much prop pitch.

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[> [> Symptoms -- Will Holoman, - Friday - 06/30/06 - 5:04pm (host2.brwncald.com/65.198.3.2)

So the symptoms of too much prop pitch are black smoke and running hot under load? What is the recommended rpm for cruising speed with the 4-107/108? I get white smoke at sustained rpms over 2000 (only). The temp is 150 at the front of the head so I hope that is the cause. Any thoughts?

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[> [> [> Perkins 4-107 RPMs -- Doug Wilson, - Friday - 06/30/06 - 10:32pm (user-10cm9ou.cable.mindspring.com/64.203.39.30)

Cactus Tree has the original 12X8 sailor two blade prop. Took it to Wilmington props for a tune up while hauled, in perfect condition.
My Wx conditiions were calm on the trip over, and 12-15KNTS on the quarter on the return.
I feel I had plenty of RPM's left, just breaking in, but am looking forward to putting more of a load on the engine on the next trip. Unless I can sail, of coarse.

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[> [> [> Recommended Cruising RPM -- Mike Cox, - Friday - 06/30/06 - 11:59pm (NoHost/72.24.202.31)

Will,
You will find varying opinions from diesel mechanics and other "experts" on the recommended cruising RPM for the Perkins 4-107/4-108. These opinions will be in the range of about 2300 to as high as 2900. In practice, I think you will find a lot of sailors cruising 4-107/108's between 2200 and 2500. The power curve graph for the 4-107 shows that with a typical propeller load the engine should top out with a continuous rating at 3000 RPM and be putting out about 36 SHP. The Average Fuel Consumption chart for the 4-107 shows .5 GPH @ 1500 RPM, .66 GPH @ 2000, .75 GPH @ 2250, .82 GPH @ 2500, 1 GPH @ 2750, and 1.3 GPH @ 3000. An overpitched or oversized prop will not be able to reach the max continuous rating of 3000 RPM. If a 4-107/108's actual max RPM is very far from 3000 RPM due to a prop mismatch, it will not be delivering anywhere near it's rated continuous output of 36 Shaft Horse Power. If a 4-107/108 is topping out at 2000 RPM, then it is really only able to put out about 15 to 20 SHP before it will overload. A lot of sailors only focus on the max hull speed. If their engine is getting them close to hull speed they're satisfied without regards to RPM, but it may not be good for the engine.
Mike

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[> [> [> [> Thanks for the comments -- Lawrence Killingsworth, - Wednesday - 07/ 5/06 - 5:16pm (NoHost/198.185.135.7)

Thanks for the comments, everyone. I don't have any of those power curve graphs, etc., so when the former owner said "Run her at 1500 RPM," that's what I did. I may just rev her up a bit more next weekend.

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