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Old 10-15-2020, 07:09 PM   #1
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Default Twin 4.3 prop

So, here it starts. I have -05 2900se with twin 4.3 carb, 190hp engines. I think props are not correct, due WOT is 5200rpm, but top speed is only 31kn. Getting plane takes only 3-5 seconds.

I don't know specs for props, so can you recommendate good setup. Boat is equipped with generator and lead piece, so it got quite heavy rear end.

Todays setup in pic.
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Old 10-16-2020, 01:04 AM   #2
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Are those Bravo 2 drives?
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Old 10-16-2020, 03:41 AM   #3
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Yes, but no idea of ratio
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Old 10-16-2020, 12:11 PM   #4
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I suspect there are 1.8:1 since you have 4.3. You can take the props to a prop shop and they measure to let you know the size as well as a recommendation.
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Old 10-16-2020, 12:20 PM   #5
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What are you expecting?
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Old 10-16-2020, 05:39 PM   #6
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Less rpm, and more top speed.
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Old 10-17-2020, 04:14 AM   #7
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Ok then..
You are underprop’d a bit just by your WOT.
190hp 4.3’s have a WOT range of 4400-4800.

That’s why the hole shot is so good.
Just based upon rough math, adding 2” of pitch would be needed to get the rpm down to the recommended rpm range. This will add a little to the top speed, but will take a bit more to plane. As Mike suggested, get a shop to check the props so you have a true baseline to start from.
With the extra weight you mention, the props may have been reduced to help her get up.
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Old 10-21-2020, 01:51 PM   #8
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Quote:
Originally Posted by Orange2900 View Post
So, here it starts. I have -05 2900se with twin 4.3 carb, 190hp engines. I think props are not correct, due WOT is 5200rpm, but top speed is only 31kn. Getting plane takes only 3-5 seconds.

I don't know specs for props, so can you recommendate good setup. Boat is equipped with generator and lead piece, so it got quite heavy rear end.

Todays setup in pic.
1) Max RPM is 4400- 4800, so you're under-propped and over-revving the engines.

2) I'm unclear what you're referring to regarding the 'boat is equipped with 'lead piece'. This sounds like ballast. Ballast in the stern doesn't make sense. Ballast is typically used for lateral trim, so is placed toward the the gunnel to correct for a list.

3) You're missing the zinc's in the anti-ventilation plate.

With lead at the stern and under-pitched props, it sounds like someone tried to set-up the boat to be a wakeboard boat. The under pitched prop would get them on plane faster while towing and the weight could add to the size of the wake.

1) Measure how much space between the tip of the prop blade and the bottom of the anti-ventilation plate.

For Prop diameter sizing you want the space between the anti-ventilation plate and the tip of the prop blade to be 15% -20% of the prop diameter (20% being ideal). I'd start with how much you have now and calculate what that value with be with a different diameter prop.

2) Record the pitch of the prop (it should be written on the hub).

As prop diameter increases OR Prop Pitch increases, max RPM decreases and Max Speed increases. However, Time to plane (hole shot) also decreases.

Ideally your target is to be able to reach (but not exceed) 4800 RPM regardless of what your top speed is.
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