Whats the difference between a speedboat and a powerboat ?

[Gav]

Originally posted by SplitPin
You're doing very well to acheive 12% slip.

so my 5% is very unrealistic then?

[SplitPin]

Originally posted by Gav
so my 5% is very unrealistic then?

With modern prop and boat designs, it may well be acheivable. As I said I was told this many moons ago.

[Burty]

Originally posted by SplitPin


I suppose the only way to find the true slip factor of a prop is to usegps to get the speed. note revs and work formula backwards!!

Graham.

Erm no not really cus gps doesn't take into account tides and currents.

The only true way to know your speed is by going to conniston this week or the pier to pier records or maybe a speed gun. you can maybe use gps if you do a run in all 4 directions and take an average but the calculations aren't that great because........

How accurate is your rev counter?
How do you know its exactly a x pitch prop

[RossM]

Originally posted by SplitPin
You're doing very well to acheive 12% slip. Do you use SuperGlue on the blades? lol.

I was once told that the slip factor was at least 15%.

may be because we have 5" of setback which allows the prop to be run in "cleaner" water.

Gav, 5% may be right! its a completely different boat and much more modern.
Most Phantom 20's have about 10-12% slip, less if running offset.

Rob how much slip do you get with 8 inch setback?

[Jon Fuller]

A lot of 'sweeping statements' tonight!

Not sure this is the right section.

[RossM]

worked out that if Robs still got the 22" et at 9k he will have 10% slip at 90mph with the 8" of offset.

Thats a pritty "average" slip % for that setback possibly due to the small pitch prop and high prop revolutions.
meaning, if a prop slips .X inch every full rotation and Robs prop is a smaller pitch so needs more RPM to reach the same speed and as a result then slip will be higher.
no doupt Rob had the engine jacked right up too

Robs Propshaft at MAX RPM (9000) is 4812.83
Our Propshaft Rpm at MAX RPM(7500) is 4643.96

so in theory we should have very simular slip-
Rob having abit more setback to run the prop in cleaner water
And
prop slip per revolution X extra propshaft rpm so would be slightly more slip.

Just a thought ,
Some people in OCR changed their 1.87:1 ratio boxes for 2:1 to lower propshaft rpm from 4010 to 3750 possibly for the same reason where the prop slips X amount every rpm.

[MrRob]

Originally posted by Tony Davis
this ain't no speedboat!

This is my dream boat!

[Just4Fun]

Originally posted by Burty
Erm no not really cus gps doesn't take into account tides and currents.

The only true way to know your speed is by going to conniston this week or the pier to pier records or maybe a speed gun. you can maybe use gps if you do a run in all 4 directions and take an average but the calculations aren't that great because........

How accurate is your rev counter?
How do you know its exactly a x pitch prop

Try running both ways and take average.

[Just4Fun]

Originally posted by MrRob
This is my dream boat!

I don't fancy the mooring fees. 10M is expensive enough !

The way it presents a relatively flat part of the hull to the oncoming water, despite its sharp bow, looks like it might be more uncomfortable in a rough sea than its shapes first suggests ! But hell, one can't have everything !