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Old 17-10-2012, 21:44   #1
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Exhaust: Thru Hull? Not Thru Hull?

I am thinking of buying a 400hp 22ft cabin cruiser that has been converted (by proper mechanics) to thru hull exhaust. I would not make this conversion. Should I avoid this boat due to this conversion, or should I think great, this is an advantage?
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Old 17-10-2012, 21:52   #2
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Re: Exhaust: Thru Hull? Not Thru Hull?

Not sure what you mean by thru hull exhaust. Possibly a stern drive that diverted the exhaust to exit the transom instead of through the propeller hub?
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Old 17-10-2012, 21:53   #3
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Re: Exhaust: Thru Hull? Not Thru Hull?

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Not sure what you mean by thru hull exhaust. Possibly a stern drive that diverted the exhaust to exit the transom instead of through the propeller hub?
Right, converted from through the prop to direct through the transom.
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Old 17-10-2012, 21:58   #4
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Re: Exhaust: Thru Hull? Not Thru Hull?

I looked at a 19' boat that was rigged to go either way with some sort of diverter valve. Didn't buy it (wife didn't like the color) so didn't look closely at how it worked but results you run the exhaust through the prop and it was quieter, switch the valve and exhaust through the transom it had more power and a little better mileage but louder.

Other than a little louder (or a lot louder depending on the muffler or lack thereof) I don't know of any negatives to exhaust through the transom.
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Old 17-10-2012, 22:07   #5
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Re: Exhaust: Thru Hull? Not Thru Hull?

By the way, all the go fast boats are rigged for exhaust through the transom.
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Old 17-10-2012, 22:34   #6
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There is nothing wrong with thu-hull exhaust motor breathes easier will make a little more hp at top end but will loose a little on bottom end torque. It will be louder. You should check your boating are for noise restrictions and exhaust requirement ( lots of lakes won't allow above water exhaust ) that said you can get silent choice which is a diverter valve so you can direct exhaust thu-prop or thu-transom which is good way to go. Might aswell have the best of both.
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Old 17-10-2012, 22:37   #7
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Re: Exhaust: Thru Hull? Not Thru Hull?

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There is nothing wrong with thu-hull exhaust motor breathes easier will make a little more hp at top end but will loose a little on bottom end torque. It will be louder. You should check your boating are for noise restrictions and exhaust requirement ( lots of lakes won't allow above water exhaust ) that said you can get silent choice which is a diverter valve so you can direct exhaust thu-prop or thu-transom which is good way to go. Might aswell have the best of both.
This is only for the ocean. Also, I am not keen on investing more money, unless it is for safety!
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Old 17-10-2012, 22:52   #8
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No safety issues just check the exhaust hoses and clamps. All so a good idea to have some form of plug if a hose should ever happen to blow
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Old 18-10-2012, 04:34   #9
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Re: Exhaust: Thru Hull? Not Thru Hull?

Check out Silent Choice. I think they are still in business. Installed a few some years back.
No big thing.
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Old 18-10-2012, 04:54   #10
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Re: Exhaust: Thru Hull? Not Thru Hull?

Running the exhaust separately rather than through the stern drive is a good idea. Stern drives with large amounts of hp get warm, really warm. Yanmars with big diesels have been known to peel the paint off the upper part. So by routing the exhaust separately that is one heat source less.

The problem with the Mercuriser and volvo stern dirves is although they have gear oil in the leg it can't mix so the oil in the upper part can't reach the cooler oil in the lower part which is immersed in water therefore cool. Result is the upper part of the leg gets warm and if it over heats takes out the bearings.

There is a "shower spray" conversion available which takes a water feed from the front of the drive and sprays it onto the upper leg to try and help cool things down.

I have felt a stern dirve with 200hp through it go from cold to warm in 30 minutes of hard use and that was with a separate exhaust. How much hotter would it be with exhaust gasses going through the leg.

Something to consider perhaps.

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Old 18-10-2012, 05:00   #11
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Re: Exhaust: Thru Hull? Not Thru Hull?

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No safety issues just check the exhaust hoses and clamps. All so a good idea to have some form of plug if a hose should ever happen to blow
These systems are generally just a "Y", with a diverter flap from elbow to transom or leg.
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Old 18-10-2012, 18:22   #12
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Re: Exhaust: Thru Hull? Not Thru Hull?

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These systems are generally just a "Y", with a diverter flap from elbow to transom or leg.
Click image for larger version

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Here is a pic...
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Old 18-10-2012, 22:14   #13
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Quote:
Originally Posted by Blue Stocking

These systems are generally just a "Y", with a diverter flap from elbow to transom or leg.
The silent choice system yes is just a y with a flap controlled with a solenoid From your pick it looks ok
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