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PostPosted: 31 Jul 2016, 18:46 

Joined: 16 May 2016, 09:41
Posts: 10
Location: AZ
Just looking for some advice, or other insight. I have a 2001 Lowe 160 with a 2001 40 hp Johnson on it(rated for a 60HP max). Boat and motor are in great condition. I also have a 96 Johnson 50hp outboard laying around. Both have tilt and trim. Not sure how many hours are on the 40 HP. The 50HP has about 8 hours on is since the rebuild. Right now with the 40hp I am hitting 28-30 mph with 2 people and gear. It has a 15P and is running about 5200 rpm WOT. I would like to get a little more out of this boat. Would switching to the 50hp and putting on a 17P prop be worth it? Looking to be around 35 MPH at WOT. Does this sound attainable? Is is worth swapping motors out? Thanks in advance.


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PostPosted: 31 Jul 2016, 22:08 
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If your RPM is correct you may be able to install the engine, stay with the same prop and get very close to what you are looking for. You have room in the RPM band to do this.


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PostPosted: 01 Aug 2016, 08:37 
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FWIW my 16' V-hull (16-degree deadrise) with full floor & raised bow deck, weighing an estimated 700-800 pounds before adding the OB motor would go 30mph when it wore a 40hp Merc.

I upgraded to a 60hp Johnson and theoretically it should push me to 40mph, but I have opted to run a Turning Point 4-blade 17" pitch prop that will carry a load of std gear (that's always on the boat) and up to 5 people, without lugging. With me alone she'll go 36mph, so I have no doubts she'd be up to 40hp if I had the right pitch prop (19" pitch per Turning Point's prop calculator - see here: viewtopic.php?f=4&t=37433) for just me or 2 people and the typical gear.

Can't say you'll need to change your prop or not, but I too think that getting to 35mph WOT with the 50hp OB is doable.



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PostPosted: 01 Aug 2016, 12:40 

Joined: 16 May 2016, 09:41
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Location: AZ
Thanks for the help. I am not sure of the rpm on the 50. I have the 40 on the boat now. The 50 is coming off another boat I am going to part out and I didn't have a tach on that boat. I guess I should just swap them and see where I end up. Then tweak it from there. I will let you know what I come up with. May be a bit as I have to get this all together on the weekends.


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PostPosted: 01 Aug 2016, 16:21 
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maximak2 wrote:
Thanks for the help. I am not sure of the rpm on the 50. I have the 40 on the boat now. The 50 is coming off another boat I am going to part out and I didn't have a tach on that boat. I guess I should just swap them and see where I end up. Then tweak it from there. I will let you know what I come up with. May be a bit as I have to get this all together on the weekends.


unless something is wrong with the motor the RPM will be dependent on the setup, the boat, prop, motor height, trim etc.



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PostPosted: 01 Aug 2016, 18:30 
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Shave .050" off the 40hp head, bend open the reeds stop to around 1/4"-5/16" at the tips install fiber reeds while your in there. Install 50hp carbs and you now have 2 50hp motors. You might check the sticker on the breather to see if there is a difference between timing on the 2 but the head, carbs, and reed stops are the 3 big differences between the 2 motors unless your talking about the 50hp 3 cylinders but those are few and far between. I'd just swap out those parts before I'd mess with swapping whole motors but that's just me.



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PostPosted: 03 Aug 2016, 09:50 

Joined: 16 May 2016, 09:41
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Location: AZ
Lil blue- I thought about that. But tracking down the carbs and getting the machine work done would be more costly than swapping motors. As it looks right now, I am looking at a half a days work to swap out the motors. Bolt holes should line up and the rest looks to be plug and play.

Perch- I am aware of the set up and how it effects performance. The 40 is set up correctly, I trim it out to get the last mile an hour out of it the only thing I could do is change the prop. But I don't think the 40 is going to push it any faster. Unless there is something that I don't know of, then I am all ears.


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PostPosted: 10 Aug 2016, 09:29 

Joined: 16 May 2016, 09:41
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Location: AZ
OK, I swapped motors and made it to the lake. I had the same load that I normally carry and had a solid 30mph with the 15p prop and an occasional 31 mph. But the 50 up is running at 5500 rpm wot. The lake was rough as I didn't get there early.I imagine if it was just me in the boat I would be at 31-32 MPH. Would the 17p prop get me to 35? Or should I look for a 19p?


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PostPosted: 10 Aug 2016, 09:54 
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Without knowing the MAXIMUM RPM rating for the motor ... you're guessing. I would prop it turn NO LESS than 200 RPMs off the max, so if a 6K motor, you want 5800 or better.



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PostPosted: 10 Aug 2016, 10:24 
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Joined: 15 Mar 2014, 16:57
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This is only a rough reference:

http://www.kirschbaum.at/ki_prop/pdf/20 ... 0Chart.pdf

But it shows your max RPM's to be 5500 on both those motors, and a gear ratio of 2.42 which would put your 40hp somewhere at 2% prop slip at 30mph, which is unheard of, so something is wrong - either the ratio listed here is wrong or either your speed or tach reading, because we know your prop pitch is taken off the prop and its probably least likely that your prop was repitched.

Unless I'm looking at the wrong chart and you have a 4-stroke...in which case your max rpms are 5800/6500 for the 40 & 50hp respectively, and your prop slip with the 40hp was 8% which is much more reasonable but still excellent. Were you to maintain that efficiency at 5500 rpm your 50hp should be topping out at 32mph but you'd be operating well below the recommended minimum RPM range of 5900 (again, assuming the chart is correct...)

I'd try & find good info on the gear ratio for both motors and the recommended RPM ranges for your 50hp motor first (if you don't have it already).



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PostPosted: 10 Aug 2016, 10:37 
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Doesn't sound like you had the conditions needed for a good test.
Like we thought, your original propeller still allows the 50hp to operate within the RPM band. Wait for a better day and post results. Your baseline will still be intact since you haven't changed weights or load. Unfortunately, a larger propeller will bring the new engine down into the bottom of the RPM band so for now stick with what you have. Does the new engine have Trim&Tilt?


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PostPosted: 10 Aug 2016, 12:05 

Joined: 16 May 2016, 09:41
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Location: AZ
Here is what I know. The tach is a factory one in the dash. I believe it's made by faria? The 50 has trim and tilt. The gear ratio is a 2.42. GPS was taken by my garmin. I used 2 different 15p props. One solas that I bought new. The other was off the 40 up. It is labeled as a 15 p. Same speeds with both props. This is the 2 stroke version of the 50hp and the rpm range at wot is 4500-5500. So I am at the top of that range.


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PostPosted: 10 Aug 2016, 13:29 
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maximak2 wrote:
The 50 has trim and tilt. The gear ratio is a 2.42. GPS was taken by my garmin. I used 2 different 15p props. One solas that I bought new. The other was off the 40 up. It is labeled as a 15 p. Same speeds with both props.

Nice numbers! I ran them through my prop efficiency calculators (in Excel) and got 7.2% slip! FWIW, I gave you my performance with my 60hp Johnson and I too am getting SUPERB performance, also where slip is only ~7%.

I highly doubt one could get better on a tin boat!

... I remain surprised :shock: that you got that good a result from a Solas prop, I always thought 'Solas' was a Nordic word or slang for pure unadulterated crap :? ! Never, ever tested one worth buying ... :wink:


OMC 50hp OB Performance & Slip.JPG

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PostPosted: 10 Aug 2016, 16:07 

Joined: 16 May 2016, 09:41
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Location: AZ
I never knew that solas were a questionable prop. Good to know. I guess the question is what is holding me back at this point. Is the ignition governed to 5500 rpm? Is the motor just out of torque to spin the prop?


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PostPosted: 10 Aug 2016, 16:34 
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maximak2 wrote:
I never knew that solas were a questionable prop.

Don't get wrong ... they didn't work for me on V6 OB tests, but their smaller OB props sure appear to be fine! So maybe I should have re-worded my comments :oops: ...

Quote:
Is the ignition governed to 5500 rpm?

If like my 60hp OMC, it has the max RPMs listed as 6,000 but the rev limiter in the CDI/powerpack is 6200.

Quote:
Is the motor just out of torque to spin the prop?

Huh? Do you mean you are "likely" to spin out the hub as you are at the top of the RPM range? I'd say 'no'. If anything, with boat rigged as typically run, with 1/2 fuel and 1 person, I prefer to be at the top of the range! I personally do not settle for anything less than being no more than 200 RPMs off the maximum or high end of the WOT range.

To do so otherwise is to lug the motor if/when a heavy load is carried and say you were at the low end of the range to start ...



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#2) 25' Parker refurb from EMPTY hull http://www.classicparker.com/phpBB3/vie ... p?f=15&t=6
#3) 16' V-tin rebuild viewtopic.php?f=21&t=36465
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#5) 16' Starcraft entirely NEW Transom Skins viewtopic.php?f=3&t=37548
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