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10 Replies | Page 1 of 11 | Top of Page | Bottom of Page

Prop / Speed Equation

by walynut , Posted to Fishing Buddy on 03/18/2010 1:18 PM \| "Quote" \| "Quick Reply" \|
walynut Joined: 01/08/2003 Location: ND	Found this and thought that I would share it with you. In order to find out the rough speed that a prop will give you. Pitch x RPM / Gear Ratio x .000946 equals speed I ran my numbers and I found it to be a 1 MPH high 19x5200 / 1.86 x .000946 equals 50.2 MPH and I am running 49 to 49.6 Kinda cool! Does it work out for anyone else? SUPPOSABLY, if your numbers are way off you could have a vent or cavitation problem, or trim / motor mounting to high or low.
	Good Luck and Good Fishin' Eric T
<a href="http://mas.midkotamedia.com/www/delivery/ck.php?n=a4e5439a&cb="><img src=">http://mas.midkotamedia.com/www/delivery/avw.php?zoneid=177&source=%7Csite~fbo%7C%7Cch~other_content%7C%7Ccat~the_other_off_topic_category%7C%7CsCat~%7C%7Cgeo~minnesota%7C%7Cp~prop_speed_equation%7C%7Cpos~centerCol_forumTopicFirstPost%7C%7Cac~ForumsAction%7C&target=_blank&cb="></a>
Re: Prop / Speed Equation by sweeney on 03/18/2010 1:56 PM \| Reply #1 \| "Quote" \| "Quick Reply" \|
sweeney Joined: 03/07/2002 Location: ND	probably off because your amount slip is not corrected into the equation
Re: Prop / Speed Equation by YarcraftStorm on 03/18/2010 4:25 PM \| Reply #2 \| "Quote" \| "Quick Reply" \|
YarcraftStorm Joined: 07/14/2003 Location: ND	It off by 7 mph on my boat and I know that my boat runs right where it should. The real key is to determine the Slip %. A well tuned walleye boat will probably run around 12% while the bass rigs can get down below 8%. It really comes down to effiecency. FYI, my rig runs around 13% depending on the prop. There are a pile of prop calculators that will do this stuff for you if you do a little searching. Mercury has an excellent propeller site that has all kinds of good info. Here is some technical reading, have fun! http://sites.mercurymarine.com/portal/page?_pageid=126,48572,126_49291:126_49315&_dad=portal&_schema=PORTAL This will get you to the prop selector, which of course is going to reccomend a mercury prop but you can find similar prop styles from other manufacturers. http://sites.mercurymarine.com/portal/page?_pageid=126,53050,126_53052&_dad=portal&_schema=PORTAL Here is a speed / pitch selector / MPH / Slip calculator. http://www.csgnetwork.com/marinepropcalc.html Remember when using high end cuped stainless props to add 1 degree of pitch over the actuall pitch to make up for the agressive cupping and rake. Same goes for props with more than 3 blades.
Re: Prop / Speed Equation by YarcraftStorm on 03/18/2010 4:31 PM \| Reply #3 \| "Quote" \| "Quick Reply" \|
YarcraftStorm Joined: 07/14/2003 Location: ND	Here's my example: 21 x 5700 / 1.75 x .000946 = 64.71 mph (theoretically) My rig runs between 56 to 59 mph depending on conditions. It makes it worse when I add 1 degree for cupping! 22 x 5700 / 1.75 x .000946 = 67.78! I only wish it would run like this. Now, if you take 13% of slip into acount that brings it back down to .............................................58.97mph, go figure! (0.13 x 67.78 = 8.81 mph so 67.78-8.81 = 58.97)
Re: Prop / Speed Equation by walynut on 03/18/2010 4:35 PM \| Reply #4 \| "Quote" \| "Quick Reply" \|
walynut Joined: 01/08/2003 Location: ND	Odd, it shows my slippage at 0.1527298245614035. Something must be wiggy with my numbers cause I dont even belive that.
	Good Luck and Good Fishin' Eric T
Re: Prop / Speed Equation by dwmaster on 03/18/2010 4:56 PM \| Reply #5 \| "Quote" \| "Quick Reply" \|
dwmaster Joined: 01/05/2009 Location: ND	You can't put this stuff out there now when people tell me they go 65 or 70 mph and I ask them what prop they're running, they will know better than say 19 or 21 pitch. And now I am going to have less occasions to be smile and be amused. :-(
Re: Prop / Speed Equation by YarcraftStorm on 03/18/2010 5:17 PM \| Reply #6 \| "Quote" \| "Quick Reply" \|
YarcraftStorm Joined: 07/14/2003 Location: ND	When I put your numbers in I get 1.5% to 2.3% slip. Boy would I love to own a boat that can run those kind of numbers, ahh just puliin your leg. You must have atleast one of you're numbers wrong. Don't worry though, soft water is on it's way!
Re: Prop / Speed Equation by luveyes on 03/18/2010 5:59 PM \| Reply #7 \| "Quote" \| "Quick Reply" \|
luveyes Joined: 08/16/2004 Location: ND	Wow, Im supposed to get 74.59..... Hit 61 last year; but prop work, weight transfer, and motor height changes I should see 64-68 fully loaded. I must have alot of prop slip!! Walynut...... we gonna use my boat for the Chamber!!!!! Hope you have $$ for fuel??
	YES, I am that foolish!
Re: Prop / Speed Equation by Captain Ahab on 03/18/2010 7:18 PM \| Reply #8 \| "Quote" \| "Quick Reply" \|
Captain Ahab Joined: 12/01/2008 Location: ND	Mr. Obvious says......is there any variable for boat size and weight?
	"Diligence is the mother of good luck." Benjamin Franklin
Re: Prop / Speed Equation by luveyes on 03/18/2010 7:37 PM \| Reply #9 \| "Quote" \| "Quick Reply" \|
luveyes Joined: 08/16/2004 Location: ND	nope... they dont matter at all.
	YES, I am that foolish!
Re: Prop / Speed Equation by walynut on 03/19/2010 07:33 AM \| Reply #10 \| "Quote" \| "Quick Reply" \|
walynut Joined: 01/08/2003 Location: ND	luveyes Said: Walynut...... we gonna use my boat for the Chamber!!!!! Hope you have $$ for fuel?? Just say the word and I will send you some cash; as for gas, i'm not scared because when we win it, we'll still be ahead!!! lol
	Good Luck and Good Fishin' Eric T

10 Replies | Page 1 of 11 | Top of Page | Bottom of Page

Posted By: walynut
Posted On: 03/18/2010 1:18 PM

356 Views, 10 Comments

Tags: speed, prop, equation, found, 000946, numbers, equals, pitch, gear, ratio
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Region: Minnesota

Categories: Other > Other Off-Topic

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