DIY Test Prop

[spybot]

I am trying to track down some problems on my OMC outboard. The boat lives 75miles away from me so i am looking at bring the engine home and try to find/fix the issues i am having. To do this successfully i will need a test prop. I have searched locally and nationally for one but cant get my hands on one. (I stay in Scotland)
So i thought there may be a away to build a hacked version of a test prop from a few bashed props i have lying around. Both props are 13 3/4 alu. One is a 15 pitch one is a 17 pitch. Is it possible to cut - bend - hack these into a load test prop ?
If so how do i go about it ???
Do i just cut tips of the blades making them 2/3rds the length they are just now ??
Do i bend the blades to try and make more of a paddle wheel rather than a prop ??
Is the 15 better as it has more torque to start with ??

Iam stuck here guys any and all ideas taken on board.

 

[Sea Rider]

Test props are special ones, cutting blades off from a standar prop will not work, motor will overrev babdly, no bueno. Are used to test motors to their max wot range along a tach in large testing tanks while motor is geared forward. Fix whatever was the issue and test motor in open waters at wot, it's same.

Happy Boating

 

[jimmbo]

There several test wheels listed on E-bay. However, they are HP specific.

I do recall seeing a listing of them, just have to find it

 

[Sea Rider]

Prop wheels for wot tank tests are similar to this one..



Be aware that each motor manufacturer has their own test wheels and all of them varies in shape between HP models. So buy one that matches 101% your current brand motor and HP model.

Happy Boating

 

[Faztbullet]

Test props are special ones, cutting blades off from a standar prop will not work, motor will overrev babdly​

Wrong again...Below is pic of my 21P V-6 test prop..I can run a 200Hp on trailer @5000RPm with no problems or over rev...
Spy start with the 17 and cut 1 inch off tips and test if you need more rpm remove 1/4 " at a time it will get you close. Service shops have been making and using em for years, my old dealer shop had close to 60 handmade one we used on the wall. Note it will not work in a tub or tank as it will blow the water out!!!!

 

[Sea Rider]

If OP doesn't count with a test tank it's useless. Should have replied much before to the OP's post with your argument and not quote and critizise someone elses's post. It's not the same chopping all blades off which will overrev any motor than chopping them at different blades lenghts which will give different rpm through wild guessing and testing.

Happy Boating

 

[TunaFish389]

Why not use a prop as is for testing? Is there a reason to cut it down?

 

[ahicks]

Wrong again...Below is pic of my 21P V-6 test prop..I can run a 200Hp on trailer @5000RPm with no problems or over rev...
Spy start with the 17 and cut 1 inch off tips and test if you need more rpm remove 1/4 " at a time it will get you close. Service shops have been making and using em for years, my old dealer shop had close to 60 handmade one we used on the wall. Note it will not work in a tub or tank as it will blow the water out!!!!
[IMG2=JSON]{"data-align":"none","data-size":"full","src":"https:\/\/www.iboats.com\/sites\/default\/files\/styles\/ideabook_teaser_big\/public\/images\/gallery\/test_0.JPG?itok=e2NGE90k"**[/IMG2]

If not in a tank, it would be nice if you'd share a little more detail regarding how that prop is used.

 

[Faztbullet]

Well Sea ...When you state it will not work gotta call you out as its not so.This has been done for years and it does not cause engine to over rev. That prop in picture will hold a V-6 at 5000RPM with a load on engine.It will also try and push boat/trailer and truck up the launch ramp....some study on prop design and types could help ya out.

Why not use a prop as is for testing? Is there a reason to cut it down?​

The reason it cut is to allow it to slip and build RPM and still have a load on engine,,sort of a poor mans dyno.. When you cut the tips off you take away part of the progressive pitch and rake of the blade unloading the prop.

 

[QBhoy]

Hi
where in Scotland are you ? I’m part of a pretty big boating community there. Can likely offer help or put you onto someone with a load of props to try. Is it an Evinrude ? Johnson?

 

[Sea Rider]

Before continuing with this discussion, OP has not said a word about which OMC HP motor it's all about including its wot rpm range factory stated. Issues to consider.

-To air test any prop as in post 6 will need to count with a tachometer to start with in opt working state. If OP's combo doesn't count with one will need to install one as a starter.

-Can air spin a plain or chopped prop "safely" provided that you know which is the max rpm factory stated for that HP motor brand as not to overrev it beyond its safe max rpm.

-Air spinning a prop will achieve way more rpm than if spinning on water at same throttle setting, check it yourself with a tach. A chopped blade prop should rev higher than same plain prop due to less weight at same throttle setting.

-Large HP motors usually have overrev systems that kicks in after passing their max wot rpm range, so won't be able to full throttle them as the rev limiter will be kicking in prematurely.

-Air testing props at neutral or geared when at idle or at their max rpm range, is not same as when motor is tested at full load while pushing a boat on water and that's where motors starts to develop performance issues. Max load is all, neutral no load, geared or not is relative and useless, it's no indication that same motor will perform top when at full load.

OP should test his motor at load on water not out of water, no air nor water test will determine which component is the direct culprit if already having a mechanical or electrical issue on an old style non EFI motor. That's what troubleshooting guides are for..

Happy Boating

 

[jimmbo]

Out of Water testing requires a Dyno

 

[spybot]

Hi
where in Scotland are you ? I’m part of a pretty big boating community there. Can likely offer help or put you onto someone with a load of props to try. Is it an Evinrude ? Johnson?

Hi Q
I stay in Anstruther fife North of Edinbrugh
Your offer would be greatly appropriated
Thank You

 

[spybot]

Before continuing with this discussion, OP has not said a word about which OMC HP motor it's all about including its wot rpm range factory stated. Issues to consider.

-To air test any prop as in post 6 will need to count with a tachometer to start with in opt working state. If OP's combo doesn't count with one will need to install one as a starter.

-Can air spin a plain or chopped prop "safely" provided that you know which is the max rpm factory stated for that HP motor brand as not to overrev it beyond its safe max rpm.

-Air spinning a prop will achieve way more rpm than if spinning on water at same throttle setting, check it yourself with a tach. A chopped blade prop should rev higher than same plain prop due to less weight at same throttle setting.

-Large HP motors usually have overrev systems that kicks in after passing their max wot rpm range, so won't be able to full throttle them as the rev limiter will be kicking in prematurely.

-Air testing props at neutral or geared when at idle or at their max rpm range, is not same as when motor is tested at full load while pushing a boat on water and that's where motors starts to develop performance issues. Max load is all, neutral no load, geared or not is relative and useless, it's no indication that same motor will perform top when at full load.

OP should test his motor at load on water not out of water, no air nor water test will determine which component is the direct culprit if already having a mechanical or electrical issue on an old style non EFI motor. That's what troubleshooting guides are for..

Happy Boating

I have an Evinrude 120hp V4 Looper that i am trying to chase down a no power under load fault. It will rev no problem but as soon as its under load it dies. Plus at idle it will run rough then build up to normal rev then fall flat again. I need the test prop as i will have to work on it 75miles from the loch.

 

[Sea Rider]

As you have experienced already, any engine runing good at idle will miss when under load if already with hidden electrical issues. What's the use of testing props on air when you alredy know that the motor fully misses when at full load pushing you boat.

You better start throubleshooting each electrical component individually, one of them must be the culprit, which one, that's the issue. No prop tested on air nor a wheel prop submerged in water will spot an electrical culprit for you. Sorry, it's your homework.

Electrical components have 3 stages : works spot on, are dead kaput or misses intermittently your motor's sympthom is clealy associated to the latter stage. Heats, shorts misses at load repetitively.

Keep both props as spares can reapair them or even repitch them for future use. Get a Service Manual for said motor and troubleshoot each electrical component to their factory Ohm and Voltage specs, way to go and not keep losing precious boating time LOL!!

Happy Boating

 

[Faztbullet]

Sea.....Where in the world did you get the idea of air testing????? The test prop is used in water!!! A test prop in water will load the engine so it can be tested for carb/fuel and electrical problems as dealers have used them for years despite your inexperience with them and higher HP engines.
Spy...Cut the 17 as stated, install and take tools,manual,spare tank to closest boat launch and perform your troubleshooting on engine. From what you posted I would start with fuel side first.