Need Help w/twin props
 

I just purchased a 2006 kachina 34 with 525's and lab 32... it had 30hrs.. w/xr drive.. The owner said it would do 85 @ 5200... and i have never seen that... even with me and my wife and 50gal fuel trimed out to the max.. i'm at 80 @ 5000 barely... I have tried to re-lab.. giving my numbers.. with no luck.. I am going to try 30 non lab.. but looking for some one with lots of knowledge in this field.. Shouldn 't i be able to get 85 @ 5200 with 525s... I can get the motor's up to 5200 but the drive will be too high and I loose mph..Thanks

Re: Need Help w/twin props
 

Are you boating in different water than he was ie: Salt vs. Fresh? This can cause an RPM difference. If not you need to get the RPM up. The 525 needs to run at 5350-5400 RPM at WOT. So you need another 350-400 RPM, to hit the peak HP.

Julie

Re: Need Help w/twin props
 

Thanks for your response... but he said he was at lake havasu and that is also where i was boating.. the temp was 100.. but i tried early a.m.. when it was about 85 with the same numbers... any suggestions...

Re: Need Help w/twin props
 

Well then, lets work with the numbers you have provided! You need to increase you RPM to 5300-5400, if peak top end is your goal. So we need to look at different propellers or working the propellers you have. The 32P props are to tall so we need to look at reducing the pitch for a gain of 200-250 which puts you closer to the RPM goal. This will give you good top end and cruise speeds. However we are still sy 100-150 RPM or so, if we want to hit peak HP. But when I run thru your slip calculations and you have alot of slip. I have calculated 18% which is very high. Unfortunately anything you do to the propeller will be a bandaid and you are leaving speed on the table. It is quite possible that you may need to install a drive spacer to control the propeller slip.
Here is what I think you should do, run the stock 30P Bravo I and let us look at the your numbers with a stock propeller and then we can formulate a plan of attach from there.

Julie

Re: Need Help w/twin props
 

is it the possible the prevoius owner was "padding" his numbers to help the sale? 85 is a nice round number... :cool: :D

Re: Need Help w/twin props
 

85 MPH @5200, slip is at 17%.
80 mpH @5000, slip is at 18%

Julie

Re: Need Help w/twin props
 

Well there is a great possibilty that he padded the numbers.. i would have still bought the boat, but you know that is what happens all the time.. just like when i race my sand rail.. everyone says.. oh i have 500 hp... but come to find out they barley have 300 or 400... But i guess that's the way life is...

Re: Need Help w/twin props
 

It's possible the previous owner may have seen 85, once. An outgoing tide, tail wind, perfect water conditions, low air temp, low humidity, a gps spike and you've got your 85 mph.

Speeds can vary considerably from day to day and throughout the day. When we test with a customer at the boat ramp we have a baseline set of props that we run on the first and last run of the day. That way we know what all the other props are doing.

I was testing in a cat last week and with the props I had we were getting 97mph. The owner was disappointed because his props ran 101 the day before. When we put his props on they only ran 96. That's a difference of 5 mph from one day to the next. That's why it's so important to have a baseline set of props. The faster the boat is the more surrounding conditions will influence the top speed.

Matt

Re: Need Help w/twin props
 

But if I can't even top the 5000 mark.. that will affect my top speed.... i'm going to try a set of stock 30s and see what kind of rpm vs speed i get..then i guess i'll go from there..

Re: Need Help w/twin props
 

Testing will always provide valuble data, I encourage you to do so. Post your results here and we will pick up were we left off.

Safe Testing!

Julie