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Ventilation prob with my 2007 25Sport Contender (nka 28Sport)

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Ventilation prob with my 2007 25Sport Contender (nka 28Sport)

Old 02-12-2019, 08:03 AM
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Default Ventilation prob with my 2007 25Sport Contender (nka 28Sport)

Hope someone can give me some advice here....
I have a 2007 Contender 25 Sport with twin Yamaha 150 XLs. The boat ventilates (commonly termed cavitating) in all sea conditions, and with every possible trim/tab combination. The engines are currently mounted on the top hole #1- so as low as they can go. There is evidence that they were originally on #3 -- which is where the factory says they should be mounted. However, every dealer that has seen it out of the water tells me the 25" shafts are the problem, and that the engines are too high. They are citing the fact that the cavitation plate on the engines is higher than the MAIN hull.... not the step at the rear. We have also tried multiple props with no luck at curing the problem. Anyone out there with a similar rig? Or just another Contender that you can tell me what your plates line up with on the hull? Hoping to decide whether to move the engines up while it is out of the water this week.
Thanks!
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Old 02-12-2019, 08:21 AM
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what props have you tried ?

Mercury Enertia is normally a good one on that hull.

Yamaha 2 strokes or 4 strokes ?

Both motors ventilate, or mainly one of them?

Anything mounted inline with the motors, high speed water pickup, or transducer ?
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Old 02-12-2019, 08:26 AM
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Both ventilate -- even in calm seas and on a straight course.
4 Strokes, 3 and 4 blade versions -- sorry don't have the numbers handy on them. I have another boat with twin 150s, so lots of props.
Nothing mounted to be fouling the water.
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Old 02-12-2019, 09:39 AM
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I would try 17 pitch Mercury Enertia's if you load up with lots of fuel, gear, and people for fishing.
19's if you don't run very heavy.
I'd expect low to mid 40's. Some guys say they crack 50 with that setup, but load is obviously a big part of it.
The Enertia's normally have plenty of bite, but sometimes you still have to have cup added to get them to hook up strong.

Depending on what props you have, maybe you can have some cup added to your existing props to give them a little better traction.
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Old 02-12-2019, 09:54 AM
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Ventilation IS NOT Cavitation, those are two completely different problems and mostly its ventilation not cavitation.

However, ventilation on a boat can have different reasons, mainly three things
1° wrong weight distribution aka as sternheavy (thats why you need more tabs when going over the hump and propellers ventilate then)
2° wrong propellers, particularly too small diameter or too low pitch (but then thy break loose and not ventilate
3° portusions in front of the lower units disturbing the waterflow to the propellers or the famous "hook" in the hull

First test to do is put more weight to the bow to level the boat ans see if that helps, sternheavy boats have more ventilation issues than leveled ones due the different angle of the waterstream
Second is to check accurately your hull and if there are transducers, thru-hulls, antifouling drops, trim tabs or any other thing making a uneven surface
Third would be to check different propellers (but you already did that without solving the problem)

Did you have this problem after repowering with more heavy engines? if so, weight distribution is most likely the culprit

Chris
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Old 02-12-2019, 09:58 AM
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Originally Posted by AdMel View Post
..... every dealer that has seen it out of the water tells me the 25" shafts are the problem, and that the engines are too high.
This doesn't add up...no way in heck that hulls needs 30" shafts.

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Old 02-12-2019, 10:47 AM
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Originally Posted by ChrigelKarrer View Post
Ventilation IS NOT Cavitation, those are two completely different problems and mostly its ventilation not cavitation.

However, ventilation on a boat can have different reasons, mainly three things
1° wrong weight distribution aka as sternheavy (thats why you need more tabs when going over the hump and propellers ventilate then)
2° wrong propellers, particularly too small diameter or too low pitch (but then thy break loose and not ventilate
3° portusions in front of the lower units disturbing the waterflow to the propellers or the famous "hook" in the hull

First test to do is put more weight to the bow to level the boat ans see if that helps, sternheavy boats have more ventilation issues than leveled ones due the different angle of the waterstream
Second is to check accurately your hull and if there are transducers, thru-hulls, antifouling drops, trim tabs or any other thing making a uneven surface
Third would be to check different propellers (but you already did that without solving the problem)

Did you have this problem after repowering with more heavy engines? if so, weight distribution is most likely the culprit

Chris
Knowledge-filled post right there and good advice!
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Old 02-12-2019, 11:52 AM
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Originally Posted by ChrigelKarrer View Post
Ventilation IS NOT Cavitation, those are two completely different problems and mostly its ventilation not cavitation.

However, ventilation on a boat can have different reasons, mainly three things
1° wrong weight distribution aka as sternheavy (thats why you need more tabs when going over the hump and propellers ventilate then)
2° wrong propellers, particularly too small diameter or too low pitch (but then thy break loose and not ventilate
3° portusions in front of the lower units disturbing the waterflow to the propellers or the famous "hook" in the hull

First test to do is put more weight to the bow to level the boat ans see if that helps, sternheavy boats have more ventilation issues than leveled ones due the different angle of the waterstream
Second is to check accurately your hull and if there are transducers, thru-hulls, antifouling drops, trim tabs or any other thing making a uneven surface
Third would be to check different propellers (but you already did that without solving the problem)

Did you have this problem after repowering with more heavy engines? if so, weight distribution is most likely the culprit

Chris
. What is the famous hook in the hull? Thank you
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Old 02-12-2019, 12:41 PM
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Originally Posted by ebert View Post
. What is the famous hook in the hull? Thank you
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Old 02-12-2019, 06:36 PM
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Originally Posted by UncleLuke View Post
well I have the famous hook ,and if I trim up it will start to vent? You can here it but no loss in speed. We are talking 19 kts. I thought it may of come from the keel? Thanks
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Old 02-13-2019, 05:40 PM
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Thanks to all for the thoughts. When my boat is ventilating (and yes, I knew that is what's happening -- not cavitating -- but it amazes me how many people don't realize they are two totally different things. Didn't want to lose anyone on it) the RPM's on that engine will soar into the high 4Ks plus. It's not just a noise issue.
I did get somewhat of an answer from Contender. They insist the engines should be mounted in the third hole (mine are at #1--as low as you can get the engines). The engineers say that the cavitation plate should be level with the step transom, rather than the main hull. Still waiting on their thoughts on props, as a mechanic who worked on the boat for the first owner mentioned "oversized props" to me -- they were on it when I bought it and literally give the only decent ride right now.
In the middle of replacing both pivot bushings, so will try raising the engines to #3 before we launch.
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