Prop / Speed Equation Recent Comments

re: Prop / Speed Equation

2010-03-19 07:33:16

posted by: walynut.

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

re: Prop / Speed Equation

2010-03-18 19:37:07

posted by: luveyes. nope... they dont matter at all.

re: Prop / Speed Equation

2010-03-18 19:18:58

posted by: Captain Ahab. Mr. Obvious says......is there any variable for boat size and weight?

re: Prop / Speed Equation

2010-03-18 17:59:54

posted by: luveyes. 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??

re: Prop / Speed Equation

2010-03-18 17:17:58

posted by: YarcraftStorm. 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

2010-03-18 16:56:24

posted by: dwmaster. 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

2010-03-18 16:35:34

posted by: walynut. Odd, it shows my slippage at 0.1527298245614035.

Something must be wiggy with my numbers cause I dont even belive that.

re: Prop / Speed Equation

2010-03-18 16:31:51

posted by: YarcraftStorm. 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

2010-03-18 16:25:51

posted by: YarcraftStorm.

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

2010-03-18 13:56:17

posted by: sweeney. probably off because your amount slip is not corrected into the equation