Max Speed Attainable with These Fgures

ima75man has hit the nail on the head.

they cheat themself.

hank i understand you had a prop 4mph, but at what speed are we talking about ?
in this case the prop just has to be 8 miles per hour different on just a theoretical 32 mph ?
have you gone past theoretical maximum speed EVER and had a boat with no drag or slip at all ?..


omc stratos
do you think its possible to get 10mph more than a maximum possible speed with given factors ?????

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Originally Posted by phillnjack

Ahhh yes, i agree with the testing
but theory when given figures can only be right in the maximum possible.
to get to that figure is where the testing comes into play.
all the testing in the world cannot get you past the maximum possible attainable speed. !!!! the testing is trying to get as close as possible to this speed is what its all about.

we all like to think our boats and cars are farster than they are, ive raced car down the drag strip years ago.
and the amount of times i beat cars that were supposed to be sub 9 second cars was unbelievable.
I never got to maximum theory, neither did donald cambell, neither has anyone who has broken the
landspeed record or air speed record.
No boat has ever gone past or even too its maximum mathematical speed, !!! this is due to many factors.
the boat being the main factor in this case, the absolute perfect boat with zero drag/slip has yet to be invented.
there is no boat anywhere in the world that dont have a certain amount of drag.
And there has not yet been a propeller invented that is 100% perfect, they all have a certain amount of slip and drag to them.

but given a set if figures like revolutions per minute, and a gear ratio and a given size propeller, there is a
maximum speed, there is not getting around it with testing and raising the engine, lowering the the engine or filling
the boat up with helium,the max speed is max speed and that is the target, it cannot possibly be passed.

now anyone who thinks there boat is faster than the maximum calculated speed given the figures of rpm's, gear ratio, and prop pitch is a fool who is lying to himself.
and he is not fooling anyone.

at the top i gave figures, the figures are easy to calculate or to use on a formular, the speed reached can never ever possibly be faster....its just a fact.

test as much as you like with a gps, but dont take ya gps as gosple, no world records rely on gps they use a set length
and a timer, its far more accurate than gps.
with gps you are relying on the satelites , gps is great for pin pointing, but even then not 100%.
gps is a signal sent from a device to a set of satelites and then bounced back, this again takes time.

but in this particular case, the gps is way off target by around 20%.... or the figures quoted of pitch,rpm and gear ratio.
the gear ratio is not suspect in this case as its not going to be different.

33mph with a very good tail wind (hurricane strength) COULD be possible on a race boat.

but what a boat that would be



phill

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and that my friends is the LESSONS for today, stay tune more to come.

do i take it you have more than the max possible speed on your boat mike ?

lets hear your cliam on what it is and the revs etc etc etc.

Quote:

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Originally Posted by phillnjack

ima75man has hit the nail on the head.

they cheat themself.

hank i understand you had a prop 4mph, but at what speed are we talking about ?
in this case the prop just has to be 8 miles per hour different on just a theoretical 32 mph ?
have you gone past theoretical maximum speed EVER and had a boat with no drag or slip at all ?..


omc stratos
do you think its possible to get 10mph more than a maximum possible speed with given factors ?????

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TO be totally honest I have never used prop cal.i have always done my testing on the water and never thought about max speed cal. I can tell u for sure no two props run exactly alike two major factors in how fast my boat is are how much trim u put in the motor and how much chop is on the water I can easly scrub off 10 mph by not trimming enough the rpm's will be the same but not the speed. the three props that I was talking about were 20 pitch mercury clevers lab finished at mercury the fastest ran 74 the slowest ran 70 all about same rpm. all I am saying it is impossible to tell someone exactly how fast their boat will run on a given day with a calcalater.i would rather race to find out. u were in the infield at the ballpark on my speed.

The ban is for harassing members via PM. When one signs up on BRF, one agrees NOT to engage in such behavior.

Quote:

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Originally Posted by phillnjack

hi folks
can somebody on here please state the maximum attainable speed with the figures below
lets say for example with a zero amount of slip (yeah i know) and lets say the boat is the best possible
for speed and drag etc.

revs 5500.
gear ratio..2.09 to 1
propeller 13 inches of pitch
diameter 10 inches.


this is not a joke its a serious question


phill

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Well, you indicate that this would be a very dynamically designed hull (best for speed/drag etc.) so lets go with an 80% efficiency. 5500/2.09=2631.58 RPM 2631.58RPM x 13 inches = 34210.526 inches/minute 34210.526in/min x 60minutes = 2052631.579inches/hour 2052631 in/hour / 12 inches= 171052.632 ft/hour
Now that we have feet per hour, lets divide it by 5,280 feet,which is a mile.................... 171052.632/5280= (32.4 MPH)
32.4 MPH x (80% efficiency) = ----25.92 MPH-----
Your rig will likely run between (24 and 29 MPH) give or take......... And thats a wild guess!!! LOL!!

champ im with you all the way on this one, seems you have the same conclusion that were made previously.
but others for some reason think this boat with these figures can be running at 40mph !!!!!!!!!!!!
I say its a total impossibility with these figures.
it seems champ that you and me are the only ones who can see there is a maximum speed attainable with any set up.
once you know the maximum revs and the prop size and gear ratio, the maximum possible speed is very easy to see, but no boat will ever reach its
theoretical maximum due to water drag/slip etc.
I don't even think a boat exists that is 95% drag free yet, even the most powerfull drag boats don't allways get the same top speeds time after time after time.
there is not even a race car or aeroplane that can run 100% efficiency.

I think 80 to 85 % is a pretty reasonable target for the average recreational speedboat, and 93% is very good even for a race boat.

could be wrong !!!

I believe you are correct

What would be max speed on 16p, 1.83 gears and 7400rpms?

maximum possible speed with those figures would be 61mph, but that would be impossible to reach with a boat on water,
it would be nearer to 56mph with a slip of just 8%
that would be a good figure to attain without spending a fortune on getting the perfect racing hull and being ultra lightweight.