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Old 05 January 2017, 14:33   #21
ncp
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I was always able to make over the rated rpm in my 7.3m Willard with the Cummins. I made 36 mph with 2 people at 2700 rpm and 32 mph with 14 people at 2700 rpm. If propped right, I don't think that you'll notice much difference.
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Old 05 January 2017, 15:27   #22
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Originally Posted by ncp View Post
I was always able to make over the rated rpm in my 7.3m Willard with the Cummins. I made 36 mph with 2 people at 2700 rpm and 32 mph with 14 people at 2700 rpm. If propped right, I don't think that you'll notice much difference.
What was the HP of the Cummins? I imagine well over 200hp since it could move u guys so fast at only 2700rpms. Unless I am just wayyyy underpropped. Are the Willard Ribs aluminum? Or lighter then a Fiberglass Hurricane?

Do you remember the Diameter & Pitch of the prop that you used?

I am very slow compared to you, I will only be doing 17mph at 2700 rpms! I have to be at 3200 rpms to cruise at 23 mph. I am currenty running a 15x19 Prop, not sure what the outdrive gearing is.
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Old 05 January 2017, 15:34   #23
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Im not sure underpropped is a good idea. The boat is designed to carry a lot of weight. You'll probably never have enough weight to really load it down. I can't really tell the difference between 2 people and 13 people with a single 250 outboard. The boat is rated for twin 150s When I talked to hurricane during my rebuild they were happy I was staying with a single 250.

A diesel boat is not a race boat so who cares if you're a tad bit slower out of the hole. Prop it for how it runs 99% of the time, at cruise.

Rated payload on your boat is like 2500 lbs. and the boat probably weighs less than 5000lbs empty.

The bow is a big thing. Odd question, how tall are you? My teenagers couldn't drive it until they grew some.

Jason

I am a smaller guy, 5'9 180lbs still growing sideways. Which will not help in any case because the console is literally 4 feet from the Transom.
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Old 06 January 2017, 22:40   #24
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What was the HP of the Cummins? I imagine well over 200hp since it could move u guys so fast at only 2700rpms. Unless I am just wayyyy underpropped. Are the Willard Ribs aluminum? Or lighter then a Fiberglass Hurricane?

Do you remember the Diameter & Pitch of the prop that you used?

I am very slow compared to you, I will only be doing 17mph at 2700 rpms! I have to be at 3200 rpms to cruise at 23 mph. I am currenty running a 15x19 Prop, not sure what the outdrive gearing is.
The Willard was all glass and pretty heavy.

Cummins, 5.9L, 6BT, 210 HP

1:1 Borg Warner 72C transmission

Konrad 520 outdrive (I think it was 1:54:1 but I'd have to check...I sold the boat about 2 yrs ago)

After many props, I settled on a 17 1/4 x 23, 3 blade Powertech. I also tried a ~18 1/2 x 19 and 21.

Minimum planing speed with the Willard was about 19 mph at 1900 rpm.

I guess we need to know the outdrive ratio of the Volvo. It sounds like you've got a lower gear ratio and you're running a lower pitch prop.
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Old 07 January 2017, 09:12   #25
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I am completely new to Inboard Motors, especially Diesels. But I am no stranger to Outboard Motors however. What i have learned over the years is that nearly 8/10 people over-prop their engines in hope of squeezing every last mph of speed from them. Then after the engine prematurely fails at only 1000 hours or less they go spreading horror stories giving bad reviews.

I would by far rather under-prop an engine to reduce the force/stress on the internal engine components & operate it at lower rpms at slower speed than go 10 mph faster and have the engine fail at 1500 hrs.
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Old 07 January 2017, 09:29   #26
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Your not comparing like for like with the Cummins and volvo.
The Cummins will be more torquey and won't rev anywhere near the max of the volvo
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Old 07 January 2017, 17:03   #27
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Your not comparing like for like with the Cummins and volvo.
The Cummins will be more torquey and won't rev anywhere near the max of the volvo

Mostly speaking of Outboards, but im sure same things happen with inbourds as well.

i have heard that the 5.9 Cummins are very reliable in heavy duty Trucks. Do they carry the same rep in the Marine Industry?
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Old 07 January 2017, 17:13   #28
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Yeh they have a reputation for being prety solid engines as there such a big engine at 210hp &5.9l there not exactly getting a sweat on
By comparison the volvo is 200hp and only 3.6l
Hence the need for the volvo needing to rev to produce the hp
Both have a good reputation but a totally different animal
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Old 07 January 2017, 17:31   #29
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Your not comparing like for like with the Cummins and volvo.
The Cummins will be more torquey and won't rev anywhere near the max of the volvo
Agreed. Max is 2600 rpm for that rating of the 5.9L.

It's a heavy lump (I think ~1100 lbs) and was no speed demon but worked as advertised!
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Old 07 January 2017, 18:42   #30
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That makes complete sense, it was the big old heavy low horsepower Diesel engines that bought diesels their rep for bullet-proof reliability. And manufacturers are betraying that rep by these "Lighter, More-Powerful" Engines.

Arctic-Cat (Snow-Machine Manufacturer) Has engines that weigh less than 300 pounds but produce well over 200hp) Funny thing is your lucky to see 100 hours of engine time on them before they grenade. Still cost 10k though.

I will look at a Cummins when i do a repower one day. I hear they are rather cheaper to rebuild, more availability for parts and overall better service than Volvo.
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