Prop/Speed calculator

[Ben]

This looks useful.

http://www.rbbi.com/folders/prop/propcalc.htm

[Hydrostream]

I like this one,
This is a downloadable prop slippage calculator that is designed to easily calculate changes to speed and slip by changing variables such as engine rpm, horsepower, and prop pitch.

http://www.hydrostream.org/Prop.htm

[Jono]

I tried the prop calc and it told me that it "thought I was a lying bastard and to get me GPS checked"....:cry:

[Tony Davis]

Originally posted by Jono
I tried the prop calc and it told me that it "thought I was a lying bastard and to get me GPS checked"....:cry:

How long have you owned a Falcon?

[Burty]

dont understand that entered all the info and with my laser it said i had 0.08 slip. but with the chopper it said it was impossible as the slip was a minus
explain that please boffins
speed was gps'd over quite a distance
pitch of props measured by prop reveloutions
:confused:

[Jon Fuller]

was the gps speed taken in one direction only?

[Burty]

was in boat on my own, did 2 or 3 runs then looked at max speed.
does that mean that i havent actually done 76mph then
:(

[Burty]

look

[JamesM]

My boat had negative prop slip too. Cye must be one amazing genius boat rigging dude :D

Your GPS seemed pretty much bang on next to your mondeo (shiney and new, but it is a ford) speedo when we tried it out if you remember. And that was in all sorts of dierctions and at lots of speeds ranging from bugger all to over a ton.

hmmm go figure :confused:

[JamesM]

The tide moves pretty fast at weston :D

[Jon Fuller]

I'm not trying to belittle your speed, Just pointing out that your 'max' speed would have been the highest 'speed over ground' that you attained, this would have been your actual water speed, plus the speed of the tidal flow you were traveling in, which could be 4 or 5 mph, depending on where you are and point in the lunar cycle it was (tide height etc)

However, a P20 with a 2.5 efi ought to do circa 75-80, mebbe more, you should'a gone to windermere, you might be going even quicker than 75!

[Jon Fuller]

Originally posted by Johnny Boat Dude
The tide moves pretty fast at weston :D

but that's unlikely to affect the speedo in your mundane-o

[Burty]

that was my old sharpe havent tried my P20 yet
:D

[Burty]

it affected it for a while didnt it johnny:laugh:

[Jon Fuller]

Originally posted by Burty
that was my old sharpe havent tried my P20 yet
:D

Ah!

[Burty]

even if i take 7mph off speed it still only says 0.8 whats that 8%?
what would you expect prop slip to be Mr F?
6" setback
20" mid

[JamesM]

That 76 was in his sharp 19 with a mildly tuned 200 merc probably about 210hp at the prop. Enigine was on a 5.5" setback plate running a worked 26" chopper (mine but I'm to scared to use it) which we were told is now 24" by prop revolutions. It was a lovely flat day and he came past me on one of his runs. It looked awesome that chopper picked the whole boat up, it was running with only a palm sized contact point between the hull and the water, big rooster tail too. Looked well twitchy though, most excelent :D

[JamesM]

Originally posted by Burty
it affected it for a while didnt it johnny:laugh:


erm :bang:

[Hydrostream]

Originally posted by Burty
dont understand that entered all the info and with my laser it said i had 0.08 slip. but with the chopper it said it was impossible as the slip was a minus
explain that please boffins
speed was gps'd over quite a distance
pitch of props measured by prop reveloutions
:confused:

Thats good slip no's, should be around 8-12% if set up right, you need slip, without it you have no thrust. Without thrust youre stopped!

Is your chopper a diferent pitch to the laser? Whats the pitch of the two props? Did you change the speed when you put in the pitch of the chopper?

Whats the pitch of both props and the speed with each?

[Burty]

Is your chopper a diferent pitch to the laser?

Yes

Whats the pitch of the two props?

chopper is a 24 laser is a 22.75

Did you change the speed when you put in the pitch of the chopper?

yes

Whats the pitch of both props and the speed with each?

chopper 76mph @ 6200rpm

laser 72mph @ 6800rpm

[JamesM]

Originally posted by Burty
Is your chopper a diferent pitch to the laser?

Yes

I didnt know you had a chopper :D

In that case you wont need to borrow mine anymore ;p;