Prop test prediction game for the prop experts !

[QBhoy]

Hi
So...my buddy has a maxum 2300 cuddy with a 5.7 carb and a 21" vengeance prop. Currently he is unsure whether it's a 1.62 or 1.47 ratio....I suspect the former.
Here is a wee competition for the prop experts amongst you...no prizes given except bragging right, I'm afraid ! The question is as follows...kudos to the one who guesses closest...

Current performance and data;
4200rpm @45mph gps with 21" vengeance
He has just bought a high 5 19" prop...what do we think the likely results will be, with regards to rpm and speed ?
No cheating with prop calculators now !

My predictions are that he will get further into the proper rpm range (4400-4800)...perhaps even at the top end or over and run about 47mph.

Over to you guys....results will be posted within the week

 

[jimmbo]

Speed will drop, and rpms will be within +150

 

[QBhoy]

Interesting Jimbo...
Fair play for going first !

 

[QBhoy]

Surely the rpm will rise significantly? 2" less pitch and 1" less diameter ? Just a thought

 

[Maclin]

Top rpm will be about 4500 rpm with top speed about the same, the boat won't be able to backup very good and will want to sell the high 5 soon after. Posting for a friend

The high 5 is tuneable, so if they don't like what happens at first there are always the port plugs to play with.

 

[jimmbo]

Surely the rpm will rise significantly? 2" less pitch and 1" less diameter ? Just a thought

Extra blade, more drag and higher slippage

 

[Scott Danforth]

gear ratio is 1.47:1 on the 5.7's

only getting 4200 rpm out of that motor and hull combo, I would do a compression check and weigh the boat.

 

[alldodge]

Current 21x13 3/4 @ 4200 rpm and 45 mph
with 1.47 drive = 20.80 slip
with 1.62 drive = 12.72 slip

Going to high 5 is 19x13 1/3
Will loose rpm and top end speed, have more lift which can cause the prop to blow out in turns

What you should have is a 19x13 3/4 3-blade to get your rpms up. Test boat shows it doing 46.7 mph, and this one does have some hours on it

If you really want to try another prop, try a 4-blade 17 pitch. If you must try a high 5, I would suggest going to a 15 pitch

 

[SkiDad]

my prediction is 46 MPH @ 4500 rpm

 

[QBhoy]

Some interesting theories...
It really is a friends boat, haha.
I had suggested a 19" standard stainless ages ago. He came across this for ?150 in mint condition, so thought it worth a try.
If it is a 1.47-1 ratio...I'm surprised he is even getting 4200 rpm with a big 21" (current prop).
He gets the prop tomorrow..results to follow.

 

[89retta]

42mph and its going to hit the rev limiter

 

[b.gagnon]

Can a High5 run close enough to the surface on an I/O to work properly????

 

[QBhoy]

Loving this. So many different theories. Postage delivery on Monday now. Hold tight....

 

[QBhoy]

First trial today...weather less than ideal with a fair chop on the Loch. He had to keep the full hood up too (spray hood type camping cover)

45mph gps @4600 rpm

I'll post more details when the weather is better and the hood is off. I've suggested he gets a laser 2 19". Should have the boat perfectly propped, I'd think.

 

[QBhoy]

Ski dad closest so far......wait until the hood is off her. Suspecting better performance. Not as good as a laser 2 though. We going to swap props on sat night