Sanger dlx prop at altitude?

[viscose]

I recently purchased an 02 Sanger dlx with the 315 Mag MPI motor and the 1:1 velvet drive. The prop on it is a 4 blade but I'm not sure of the diameter or pitch. I bought the boat out of Texas, a few hundred feet above sea level, where it had lived since new. I live in Utah and boat at the lowest about 3600' (Lake Powell) and the highest 6250' (Flaming Gorge).
With the prop it has now at WOT I am at about 45-4600rpm, and I believe that 46-5000 is the recommended WOT. Speed at 6250' was 38.5 mph on glass and at about 4500' 42 mph in semi rough water. I haven't tested the speed at 3600' yet but may get a chance this weekend. I am a little bit disappointed with the hole shot when pulling me from a deep water slalom start (225 lbs).
I have read that 3 blade props will give more top end and 4 blades more acceleration; however that the acme 3 blades outperform their predecessors in both speed and acceleration. That being said I am thinking of a new prop. I have found an application chart that shows the acme 425 as the prop for the SangAir which is my boat with a tower and ballast. The 425 is a 3 blade 13x13 with .080 cup.
I would like any suggestions that people may have.

 

[viscose]

Re: Sanger dlx prop at altitude?

I downloaded a prop calculator from http://www.castlemarine.co.uk/pitch.htm which with my details, 4000 lbs (incl gear people and gas) recommended an 11.78" diameter and 11.66" pitch. With 10% slip it said I should get 51.64 mph @ 5000 rpm. If I change the max rpm to 4800 it gives the same mph but a prop of 12.06" by 12.13". If I go to 4600 rpm the prop changes to 12.36 x 12.63".
If I change the weight to 3700 lbs (~800 lbs of people gear and fuel) it tells me 53.68 mph at 11.78 x 12.12" at 5000 rpm and 53.68 mph at a 12.06x12.61" prop at 4800 rpm; and same mph but 12.36x13.14" at 4600 rpm.
these numbers all seem a bit high and outside of the propellers actually made for my boat. I am a little bit more confused.

 

[viscose]

Re: Sanger dlx prop at altitude?

I was mistaken, acme does make the
779 12.50 12.625 .050 cup 3 1 1/8" LH
489 12.50 13.00 .080cup 3 1 1/8" LH
three blade props and
1467 12.50 12.125 .060 cup 4 1 1/8" LH
1469 12.50 12.50 .080 cup 4 1 1/8" LH
four blade props. but are these really where I want to be?

 

[viscose]

Re: Sanger dlx prop at altitude?

I got down to Lake Powell last weekend, top speed was about 40 mph. I'm a bit confused. Can anyone help?

 

[walleyehed]

Re: Sanger dlx prop at altitude?

#1, you're dealing with too many different props....and, the info you have obtained is based on sea-level performance.
Pick a brand and stay with it unless you intend to do what I have done and became a prop tester for all manufacturers.....nearing 500 props now...of course this would be impractical to "Test" this number of props to see what you need.
ALWAYS test with a normal load-that's rule #1..
Do this at each altitude at which you intend to be running.
on most rigs, it works out to "about" 1" less pitch for every 1500ft above sea-level...to get near the same RPM.

p.s. Speed is only a "result" of efficiency which includes boat design, hull condition, prop condition and type..... and balance is critical on this design as you are limited in control of bow-lift.

 

[viscose]

Re: Sanger dlx prop at altitude?

I have spoken with Sanger and Acme. Sanger said Acme 911, Acme said Acme 653. I'm going to try to 653 as soon as I get a spare $500. thanks for the help!