2008 chaparral 236 Volvo SX prop questions

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Bmroge711

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Hey y’all! My 2008 236 SSI with 5.7 Volvo and penta SX currently has a 14.25 diameter 19 pitch 4 blade aluminum prop. I believe the max rpm’s at 4000 and top speed at 42ish mph seem low. Spec sheets show 50 mph @ 5100 max rpm. Any advice on correct prop?
 
Props are all theory, because of many factors. What I did was found a prop design that I liked. I contacted them and gave them all the specs of how it preformed and how I would like it to preform. They gave me their recommendation, and I started with that prop. Some prop shops will work with you., mine did. I found a prop that hit the max rpms, but I settled for one that would not, because it preformed better at the low, middle, and high ranges. Good luck, pass on the info, it may help someone else.

P.S. My girl was 2 mph from hitting the 50 mark. However she has pulled, tubes, skiers, wake boarders, and an occasional air chair.
Now that she has out grown that era, she just cruises at about 20-22 mph and 2300-2600 rpms.
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Good pic. Was that taken by a helicopter?

Like you said no easy asnwer for a prop. Hopefully a shop will work with you trying one then another and let you zero in on what's best for your boat.

To be on plane at 2300 rpm. Unheard of for me. 2800 to 3000 is lowest rpm to be on plane for all boats I've owned.
 
contact Chaparral directly they will tell you what prop came on the boat to run 50 MPH at those RPMs, I would think a 19 3 blade but not sure of your gear ratio. Your not making much power at 4K RPM.
 
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I've been contemplating on whether to switch my prop to see if it would reduce the annoying yawing action my boat has. Any speed below plane [~21mph] its a constant back and forth.
 
Something is definitely wrong and not sure its the prop. Has something changed or has it always been like this? A 19" prop is fairly low for any larger displacement. What gear ratio is your leg? Have you done any engine diagnostics to ensure all is good there?
 
SST said:
I've been contemplating on whether to switch my prop to see if it would reduce the annoying yawing action my boat has. Any speed below plane [~21mph] its a constant back and forth.
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Do you have trim tabs?
 
Denny said:
Do you have trim tabs?
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No I never put them on. I don’t understand how trim tabs can stop or lower the left and right yaw movement. I thought the tabs were for bow up or down or leveling a list.
 
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SST said:
No I never put them on. I don’t understand how trim tabs can stop or lower the left and right yaw movement. I thought the tabs were for bow up or down or leveling a list.
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Sometime ago another Chaparral member posted that if you idle with them all the way done they will eliminate most of the yawing, and it does.
It brings it down to more of a fade.
 
Denny said:
Sometime ago another Chaparral member posted that if you idle with them all the way done they will eliminate most of the yawing, and it does.
It brings it down to more of a fade.
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I get it now. The drag from the tabs helps override the spill off the prop. What is the speed limitation on full down tabs? In most areas of the Erie Canal is 10mph.
 
SST said:
I get it now. The drag from the tabs helps override the spill off the prop. What is the speed limitation on full down tabs? In most areas of the Erie Canal is 10mph.
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I run with my tabs full down most of the time which allows me to plane at lower speeds. Only when I go to the higher speeds will I start to raise my tabs.
 
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Doc said:
Good pic. Was that taken by a helicopter?

Like you said no easy asnwer for a prop. Hopefully a shop will work with you trying one then another and let you zero in on what's best for your boat.

To be on plane at 2300 rpm. Unheard of for me. 2800 to 3000 is lowest rpm to be on plane for all boats I've owned.
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Yes, we were crossing Lake St. Clair and this helicopter was coming from The Detroit River after filming a boat race there. So I see this helicopter flying just off the surface headed straight for us It swung out to my left and circled behind us, I thought nothing of it, figured they were sight seeing. In January the next year I get this large envelope with 3 photos in it, front, side, and rear views.

He probable figured to make some extra money while he was in the neighborhood.

Also the reason I am able to plane at such low rpms is, if I had 2 people in the jump seats I had a hard time getting up on plane with the Bennett tabs that were on her. I would have to run at 2600-2800 rpms to keep her on plane which was too fast and not a comfortable ride.. So I gave Bennett a call, and asked them what is the largest tab I could run with 1 cylinder, they told me 12" X 18", and that is why I can get her up and keep her up at those rpm's. ( on smooth seas).By myself and or 1 other person, I never get into my 4's to get up on plane.
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IMG_5684

This is "IMG_5684" by denny wenger on Vimeo, the home for high quality videos and the people who love them.
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In this video I am somewhere around 18-20 mph, and 2300 rpms against a small current.
 
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Thanks. Good info. Makes sense.
Unfortunately the video would not open for me.
 
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