Going from a 40HP to a 50 HP outboard

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maximak2
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Location: AZ

Going from a 40HP to a 50 HP outboard

Post by maximak2 » 10 Aug 2016, 18:12

I guess I should ask what is stopping the motor from going past 5500 rpm the prop or the governor?

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DaleH
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Going from a 40HP to a 50 HP outboard

Post by DaleH » 10 Aug 2016, 18:16

maximak2 wrote:I guess I should ask what is stopping the motor from going past 5500 rpm the prop or the governor?
The prop ... as rigged/setup on the boat as tested. And these is no governor per se ...
#1) 1st tin rebuild, 18' Lund http://forum.tinboats.net/viewtopic.php?f=21&t=36583
#2) 25' Parker refurb from EMPTY hull http://www.classicparker.com/phpBB3/vie ... p?f=15&t=6
#3) 16' V-tin rebuild http://forum.tinboats.net/viewtopic.php?f=21&t=36465
#4 Procraft SV14
#5) 16' Starcraft entirely NEW Transom Skins http://forum.tinboats.net/viewtopic.php?f=3&t=37548

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Pappy
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Going from a 40HP to a 50 HP outboard

Post by Pappy » 10 Aug 2016, 18:35

I had the "Pleasure" of working with Dr. Solas around 15 years ago. Worked with him off and on for around 6 mos. or so during the time he was taking over production of OEM propellers. His propellers did not match what he was supposedly copying and the differences wreaked absolute havoc with the boat manufacturers and us (Engine manufacturer). We had him over in Orlando for a few days to give him his baselines/guidelines and then every few weeks he would ship me a couple pallets of propellers to run against our reference propellers. Very nice guy, unassuming, quiet and pretty darned smart. He did exactly what he had to do to satisfy our parameters as well. That was then, this is now and the props we were running were nowhere near what we talk about on TinBoats.

maximak2
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Joined: 16 May 2016, 09:41
Location: AZ

Going from a 40HP to a 50 HP outboard

Post by maximak2 » 10 Aug 2016, 20:10

OK, I get it. So in theory of I put a 17p prop on it I should see a decrease in rpm with the same boat/ load/ motor. Since I am not hitting the governor at this point.

My apologies if I am not clear. Hard for me to put into writing what I am thinking. I am trying to Max out the pitch on the prop without lugging the motor.. I am not sure by putting a 17p on if my rpm will actually decrease or will still be at 5500. In that case I could have gone to a 19p.

Reason being is that most of the lakes here are filled with skiers and wake boarders. And the lakes are typically filled canyons or valleys. This makes the long and sometimes narrow. Now the wake boarders are usually doing 20 or less and getting around is no issue. The skiers are in the 25 to 30 range and getting by them safely is a challenge. Most of the time I am stuck behind them a ways and have to wait for them to let go to get by. Following is kinda nerve wracking as you don't want to run them over if they fall. I keep a good distance from them but it only takes on little distraction to ruin a good day.

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Pappy
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Going from a 40HP to a 50 HP outboard

Post by Pappy » 10 Aug 2016, 23:16

What Dale is trying to tell you is that it takes horsepower to pull props. You are at the limit of what you can do with the 15" prop. Any more prop pitch (17") and the engine will be slower on acceleration to plane and be down on RPM. Even more so with a 19".
In short...you have the correct propeller on it now.
If your next question is about what happens to the engine with too much prop....the answer is that it becomes more prone to failure as the load increases.

maximak2
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Joined: 16 May 2016, 09:41
Location: AZ

Going from a 40HP to a 50 HP outboard

Post by maximak2 » 11 Aug 2016, 08:07

Got it. Thanks for the help every one.

nowgrn4
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Going from a 40HP to a 50 HP outboard

Post by nowgrn4 » 31 Aug 2016, 09:42

FYI.

My 1652 Weld-Craft w/pods and '03 50HP Johnson runs 35MPH @ 5,700RPM with OMC Prop #390851 (11.75-17").
17' Pro-Line 115HP DI Johnrude Bay rig
1652 Weld-Craft 50HP Johnrude fish camp rig
17' Grumman canoe 3.3HP Johnrude on side mount creek runner

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