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Old 20-08-2016, 18:11   #61
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Re: Engine Size

So after reading all this, my repowered 35 ft warrior with a 3gm30 yanmar has enough motor for coastal cruising and blue water?

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Old 20-08-2016, 18:37   #62
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Re: Engine Size

What HP does the Yanmar produce?

Since it's a 3cyl it's probably somewhat overpowered. So you're fine.


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Old 20-08-2016, 18:56   #63
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Re: Engine Size

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Originally Posted by EWOL Props View Post
The vibration above a certain rpm number is an hydrodynamic effect due to misalignment of blades.
If you like get in touch with me privately on CF or write me at info@ewoltech.com and I will tell you more.....
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Old 20-08-2016, 19:11   #64
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Re: Engine Size

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Originally Posted by Milfordadkins View Post
So after reading all this, my repowered 35 ft warrior with a 3gm30 yanmar has enough motor for coastal cruising and blue water?

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That engine should likely work fine. Definitely not overpowered though as the 3GM30 is not 30 HP. And not even remotely near 30 HP at reasonable rpm.
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Old 20-08-2016, 19:16   #65
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Re: Engine Size

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I read somewhere that a Perkins 4-108 would/should burn about .85 gallons/hour.

Mine seems to burn slightly less than that and I run it over 50% power.

1.4 gallons/hour at 50% seems very high.
Mine burned about .62 gal per hour avg in a 44 ft boat for the life of my having the boat. I never ran over 2800 rpm .
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Old 20-08-2016, 19:19   #66
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Re: Engine Size

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Two motors, both rated to run a max continuous RPM of 3600, both engines propped to just barely reach 3600 at full throttle.
One run 99% of the time underway between 2,000 and 2,200 RPM, (58%) the other run 99% between 2,800 and 3,000 (80%)

The one run at the lower RPM will outlast the one run harder. That is my experience, engines run between 50% to 75% seem to do the best, Ones run much lower do well also assuming they are run up at higher power ever so often.
Example a Sport Fisherman may troll at not much above idle all day and night, but almost always will run them up on the way out and on the way home.

But it's load more than RPM, but we are assuming properly propped and if so load and RPM are pretty consistent.
Yep, in fact commercial engine sellers rate the same engine at different rpm depending on it's use, recreational up to continuous. Commercial or continuous are rated at lower rpm.
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Old 20-08-2016, 19:30   #67
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Re: Engine Size

With an 80-horsepower diesel engine in my fat, 14-ton boat, fuel consumption more than doubles from one knot below hull speed (less than 2 gph) compared to hull speed (nearly 4 gph).
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Old 20-08-2016, 19:31   #68
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Re: Engine Size

One HP per 750 pounds should be good. Use the largest diameter prop with a large reduction gear. The reduction ratio is also the torque multiplyer. A 3:1 reduction gear and 200 foot pound torque motor delivers 600 foot pounds to the prop.
HP isn't the only thing to consider. Prop diameter, number of blades, prop DAR or surface area, gear ratio, etc, all contribute to the effectiveness of the propulsion system. An example of this concept is the high thrust outboards or outboards made specifically for sailboats.
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Old 20-08-2016, 19:40   #69
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Re: Engine Size

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With an 80-horsepower diesel engine in my fat, 14-ton boat, fuel consumption more than doubles from one knot below hull speed (less than 2 gph) compared to hull speed (nearly 4 gph).
That sounds about right. Speed is expensive.
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Old 21-08-2016, 00:13   #70
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Re: Engine Size

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Originally Posted by markpierce View Post
With an 80-horsepower diesel engine in my fat, 14-ton boat, fuel consumption more than doubles from one knot below hull speed (less than 2 gph) compared to hull speed (nearly 4 gph).
This is because the propulsion resistance correlates to the 3rd power of speed as to prop thrust.
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Old 21-08-2016, 08:04   #71
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Re: Engine Size

Thank you !

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That's very good of you. I'm seriously impressed. Separately I found your attitude to displaying pricing on your website very professional. It is great to see a vendor who not only listens but offers assistance to the boaters.
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Old 05-09-2018, 19:55   #72
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Re: Engine Size

Interesting thread as i am faced with repowering a Colvin 40’ Doxy in the next few years. Currently it has a Volvo md17C which only needs 1800 rpm to do 5kn. And flat out gives me 7. Looking at Beta 25 or 30 to go in before cruising full time (5 yrs) or rebuild the volvo ( I have a spare with 600 hrs on it) but I don’t want to be encumbered by rare + expensive parts in the future. Consider that a beta is half the weight ( about 300 lbs less) and the fuel tanks are two large heavy steel tanks that could be swapped out for two sensible size plastic tanks, I could easily shed 1000 lbs.
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Old 05-09-2018, 19:59   #73
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Re: Engine Size

k--if your Colvin is steel, the weight savings will likely be incidental. Still, I'd go for the Beta 30.
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Old 05-09-2018, 23:57   #74
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Re: Engine Size

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Originally Posted by kristjan View Post
Interesting thread as i am faced with repowering a Colvin 40’ Doxy in the next few years. Currently it has a Volvo md17C which only needs 1800 rpm to do 5kn. And flat out gives me 7. Looking at Beta 25 or 30 to go in before cruising full time (5 yrs) or rebuild the volvo ( I have a spare with 600 hrs on it) but I don’t want to be encumbered by rare + expensive parts in the future. Consider that a beta is half the weight ( about 300 lbs less) and the fuel tanks are two large heavy steel tanks that could be swapped out for two sensible size plastic tanks, I could easily shed 1000 lbs.
You don't have to do both to reduce deadweight. Change the tanks and rebuild the Volvo. Remember your ballast ratio. And do not enlarge your future prop too much, this would add considerable drag while under sail. Cheers
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Old 06-09-2018, 06:24   #75
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Re: Engine Size

Terra and K.Michael, Thank you for the input. I should have clarified, I meant I could carry a more useful 1000lbs in another form. Would be great to build compact tool storage in centre of vessel to get more out of the apartment.
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