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Author Topic: Propping correctly & how to test props.....  (Read 262256 times)
Glen
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« on: March 13, 2008, 06:57:26 am »

THIS APPLIES TO EVERY ENGINE AND BOAT AND IS NOT VERADO SPECIFIC

Before you start messing with props, you must get the engine height right. New props are WORTHLESS if they are not given the opportunity to do what they are designed for. And your engine height is probably not at optimum now. It is due to a little known fact about how mfr's rig: they "bury" them a little. Most mfrs rig the engine lower than optimum so they can keep themselves out of liability due to spinouts or blowouts. And raising to optimum won't cause blowouts. Forget all that stuff about using rulers and how far the hull is above/below the prop/plate. It's easy to tell if your engine height is right: with normal load (50% gas) ,get someone to take it up to cruise, trim it normal, and go back and  look at the big anti vent plate above the prop on the lower end. It should be OUT of the water at speed, getting splashed is ok, but out of the flow. If it's totally dry in all seas, you're probably too high. If it's "buried" under the water, you need to raise your engine and then start testing props. A buried cavplate is like dragging a bucket on a rope behind your boat: total drag that hurts performance and puts pressure (pull) on the transom. Sorry, not an artist but a really crude pic might help:


An additional advantage in raising is the powerhead 1 -3 inches higher off the water is it reduces the salt/water mist, that gets in the motor and causes corrosion.
Courtesy of Ken at propgods.com, here's an E-tec that is "buried":



and here's the same engine mounted at the proper height:



a Verado at proper height:


and how the merc racing team sets the height - a perfect shot of the cav plates getting splashed, but not in the flow. This is not a "racing" setting, this is how everything from a 12 foot to a 42 foot boat should be:



Now back to propping....

Someone writes:

“I don’t think I really need to test my props by going to WOT, I don’t run fast and just like to cruise”

A common misconception is if you are not a full throttle user (WOT), that the props that came with your boat are the proper ones. Running at full throttle is not something that any of us do often, but just like your car transmission selects the right rpm, a good prop does that too. Too big a prop and you will be “lugging” the engine in cruise. But the testing requires WOT (wide open throttle) to see if you are propped correctly for long engine life.

Here is how to tell if you are propped correctly. This may rattle you to cavitate your engines but it'll be OK....

1. Load the boat down with 50% gas and a light load for fishing cruising, etc
2. Find a very flat piece of water a mile long and bring your trim tabs all the way up.
3. Trim your engines "in" and take it up to full WOT and start trimming up
4. Keep trimming up SLOWLY a bit at a time, letting the boat catch up to the setting...until the engine starts cavitating  - losing speed ( you can't hurt it - all new engines have rev limiters)
5. Now drop it back down a bit until it "bites"
6. Now look at your rpm...- it should be in the top half of the mfr's recommended top end rpm. For example, the Verado’s range is 5800-6400 rpm. Therefore I should be at least 6100, 6250 would be ideal. But don't get hung up here, anything over 5900 rpm is ok, you won't be hurting the motor. A few more hundred rpm may get you a bit more speed though. But less than 5800 is going to do long term damage to the motors. It will cause the motor to add gas to the oil, raising the oil level and diluting the protection the oil gives the motor. Eventually the crank will fail and it will not be warranty.
7. Fill out the PDF sheet below so you can compare after you are completed.

compare the results on a prop slip calculator -  at WOT and cruise you should be less than 10%---> go here: http://www.rbbi.com/folders/prop/propcalc.htm

It should be noted that prop changing is not a magic cure-all - all you can do is try to get your props up near the upper range of  mfr WOT and that's about it. Too many people think changing props is like adding Nitrous or 50 more HP...not so....it's fine tuning in my opin, and for me never been worth more than a few mph or gph when changing a pitch up or down...However, many props are different.... some are smoother than others..others allow you to dock better ....it's not just all about hard statistics....I personally run a prop that gets a bit worse mpg and less top end but it "feels" better than all the others I tried....Don't get hung up on specs searching for the "holy prop grail".

Size depends on what you find above, but three of the best props for < 35 feet are Merc’s Tempest Plus, the Revolution 4 (4 blade) and the new Enertia. Most boats come with a Mirage plus as it is a good all purpose prop.

Discuss your results with our prop expert here - Ken Reeves of Propgods.com. See his site.

Click here for a PDF version of a blank test sheet. (Nice and big so you can write at speed.)
« Last Edit: June 03, 2012, 01:05:51 am by Glen » Logged

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Ken2
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« Reply #1 on: May 06, 2008, 04:38:59 pm »

When you guys are looking at the plate at speed. Get to a mid to fast cruise and trim your motors like you normally would.
If they are trimmed all the way "in" they will look lower.

So trim them up to where the boat rides well, like you would normally drive it.
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Ken - Propgods.com & Veradoclub prop expert
redhearts
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« Reply #2 on: June 09, 2008, 03:08:30 pm »

I read this very informative article on Friday and decided to run the test this past weekend. Fortunatley the water was like glass on Lake Ontario Sunday so i think my results were very accurate. Please provide your recommandations.

I have a Boston Whaler 205 Conquest with a 175 Verado. Typically when the lake has minimal chop i will cruise between 3900 and 4200 RPM running around 26-28 MPH with the trim tabs up and the engine trimmed @ around 6.5-7.0

My first test was to establish where my Engine height was situated and i found this a little difficult. I think it may be too low? it looks like it is mounted at its lowest setting and when i was at WOT i was able to trim it all the way up to 10 without cavitating or losing speed.

When i started the test on Sunday the boat was great to get up on plane and topped out at 40.6 MPH and 5960 RPM. I did this a few times and trimmed the engine up to 10 maxing out my RPM's @ 5960. Boston Whaler has a performance test on their website that shows the 175 verado with a WOT range of 6250 RPM and 44.1 MPH

http://www.whaler.com/rec/pdfs/performance/19.pdf

i am using the same prop 14.5 x 17 Vengeance. Is it possibile that the engine height alone has reduced my MPH by 4 and my RPM by 300? Can i raise my engine myself or do i have to take it in for service?

I had a good laugh at the Website Hypochondria, i don't want to create work for my self but i just want to make sure that i'm getting the most out of my engine. The 4 MPH would be nice too...

Justin
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Stevens
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« Reply #3 on: June 09, 2008, 03:43:29 pm »

The only way to tell if your engine is too low is to go back there while at speed and have a look.  Take a look at the pictures above.  But, yes, a buried engine could well slow you down by as much as 4 MPH and 300 RPM.

Now, having said that, you are also running a Vengeance prop, which is an entry-level basic SS prop without much cupping or anything.  You could probably gain several MPH by swapping it for an Enertia or another fast prop, reducing that slip figure from your current 12% down towards 5-6-7%.

Finally, keep in mind that the manufacturers' stated data often exaggerates, or their testing was done on light boats (i.e. empty tanks, no gear, optimal conditions, optimal rigging), whereas real-life conditions will be different.
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Flipper
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« Reply #4 on: June 30, 2008, 11:36:06 am »

A quick question to the experienced out there.

We've got a 150 Verado on a 20ft Flipper (a Finnish centre console). Going really well, but fuel consumption is a big concern.

I would like to try a 23" ali prop which I have (I think it is from a mercruiser) instead of the 21" Stainless currently fitted. However, the 23" prop does not have the holes in the propeller hub that the stainless one has, does this matter?

Long term plan is to see if there is big change is fuel consumption with the 23" and if so, then to buy a stainless version.

Any help / suggestions gratefully accepted.

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Ken2
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« Reply #5 on: July 02, 2008, 09:00:59 am »

The holes in the hub only have an affect while getting up on plane.

Once your on plane, they don't do much.
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Ken - Propgods.com & Veradoclub prop expert
teamlund
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« Reply #6 on: July 20, 2008, 08:53:54 pm »

I told my buddy to check his engine height. I told him how to test it and what it should look like and sent him this page. He is running a 16 ft alumacraft with a 70 hp yamaha 2 stk. He gained 3.5 mph top end with two people in the boat and 1/2 tank of gas!!!! His rpms were at 5200 wot and now they are at 5600 which is inside of the engines rpm range(max is 6000 rpms) I cant believe the difference it made with just alittle 70 hp motor. He is pretty pumped about it!!! Grin This is a huge diff in a 16 ft boat... He didnt notice any difference in holeshot.... Thanks for all the sweet info glen!!!
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midnightmagnumcorp
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« Reply #7 on: September 08, 2010, 11:43:46 pm »

if my props are only giving me 5800 rpm, how do I modify the props to give me 6100-6200 rpm? can they be machined? or do i need new props all together? any local help in the 954 area?
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Ken2
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« Reply #8 on: September 09, 2010, 12:01:11 am »

getting 150-200 rpm is ok, If you want 400 rpm, you just need to go to a lower pitch.
If you like everything about your existing props, just go 2 inches lower pitch, and you'll gain about 400 rpm.

Its normally easier for a shop to lower your rpm. (adding cup or pitch) then it is for them to gain you rpm.
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Ken - Propgods.com & Veradoclub prop expert
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« Reply #9 on: September 09, 2010, 12:05:31 am »

thanks for the reply, any idea on the relative cost a company might charge for this reduction in pitch for each prop?

 300-400 rpm gain will put my verado in perfect rpm range of 6100-6200
« Last Edit: September 09, 2010, 12:06:59 am by midnightmagnumcorp » Logged
Ken2
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« Reply #10 on: September 09, 2010, 12:52:19 am »

150 to 200 can be done without too much worry about ruining the props.
If you want 400 rpm, get a new set of props with 2 inches less pitch.

If you choose to have them redone by someone, it will probably cost 100-150 per prop depending on your area.
And if you don't like the results, your props will be very hard to get rid of.
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