Prop choice for Chaparral deckboat

WJL24

Cadet
Joined
Jun 9, 2012
Messages
11
I bought a 2004 Chaparral Sunesta 236 deckboat with a 5.0 fuel injected Merc. When boat was clean and I put in the lake with just me, I got 45 mph with 4600-4700 WOT with the new 4 blade Michigan Wheel Vortex 14 1/2 x 18. . Now that it's been in the water over a month and has scum on it I am getting WOT of 4000-4200 , 38-40 mph with 4 people in boat. Barely pulled me out of water on slalom ski. It was a real fight.
Thinking I should change prop for skiing. Should I stick with 4 blade and go to 17"? Looking for some advise on what's best.
Also, how do I determine what gear ratio is in this Alpha One Gen II?
 

tpenfield

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Jul 18, 2011
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17,621
Clean the hull . . . Sure, try a 17" pitch 4 blade.
 

jimmbo

Supreme Mariner
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May 24, 2004
Messages
12,944
2nd on cleaning the Hull

Even with the hull clean you were at the lower end of the WOT rpm range which is 4600 - 5000, so you are over propped when loaded. A 17" might be your cruising Prop as it will get you a couple hundred more rpms, or possibley a 16"

You might want to try a 15 when skiing, a 23 ft boat is pretty big load for 5 liter when trying to pull up a Slalom Skier

The gear Ratio is listed on the Decorative Band on the Upper Gear Housing on the Outdrive

Myself, I would want a 6 or 7.4 liter in something that size, Nice looking boat
 
Last edited:

ahicks

Captain
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Sep 16, 2013
Messages
3,957
I would drop the pitch (to help get the engine in it's power band as quickly as possible) and stay with a 4 blade because of the size of the boat, and because you are looking for some low end performance (vs. emphasis on how fast it will go).
 

WJL24

Cadet
Joined
Jun 9, 2012
Messages
11
Thanks for the input. However, I always put my boat in the water in May and it stays in until October. A clean hull only lasts a week or two. I guess I can drop down to a 17". Would a 5 blade be better?
 
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