Which prop angle at 5500 feet???

[Dream Weaver]

Just trying to figure out which prop would be best to run for my application. I live in Denver so the lakes I use most are around 5500 feet above seal level. I pull tubes and sometimes skiers. I have a 19' bayliner capri with a volvo penta aq125 (about 120 hp) / 270 outdrive running LH rotation with a hydrofoil. Last season I was using a 14 x 19 and I had a hard time plane-ing out when I was pulling a tube or when I had more than 2 passengers on board. Once I got going I would achieve maybe 25mph max at about 4000rpm. Unloaded I was able to achieve about 32mph at about 4200rpm with a quicker plane off the holeshot. With a new prop this season I would like A little more top speed but mostly I would like a better hole shot to make the boat plain out quicker when I am fully loaded or pulling a tube. Any advice will be greatly appreciated! Thank you!

 

[tpenfield]

Re: Which prop angle at 5500 feet???

Props are not measured in angle . . . they are measured in 'pitch' with is the distance that the prop would want to travel in 1 revolution. It sounds like you could go down a little in pitch . . like to 18" or 17" pitch. 14 diameter is probably fine.

 

[steelespike]

Re: Which prop angle at 5500 feet???

You did a pretty good job but we need the year and the gear ratio
usually on a tag on the upper gear box.As usual for me Volvo system numbers are a mystery to me couldn't find a 270 at all found some 120's which had 2.15 gear ratio.Using that ratio your numbers are pretty good except for the lack of power
Props are measured in inches; a 19" prop moves forward about 19" in one revolution. Diameter is a secondary consideration and usually simply follows the design.
You lose about 15% power at 5000ft.Your foil could be hurting your top spoeed a little though the numbers are pretty good.
I think a 16 inch 4 blade prop should give you about 4700 rpm and improved hole shot plus ability to stay on plane at reduced throttle and better response around the dock.Speed will probably be reduced .You may be able to remove the foil after a test.
A 16" may be hard to find especially in a left hand.
I believe you can change to right hand rotation and find many more choices.
A 17" may also work well and they could repitch to a 16 if necessary.