Exhuast through the transom below the water line?
04-12-2007, 11:31 AM
#23
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Brad, I plan on using a variation of your design and would like to have your input and opinion.
I would prefer to have the tip double wall ( two pipes )through the transom. The tail pipe would connect to the tip with a rubber collar and double clamps on each end of the collar. A typical dry tail pipe jumper would connect the tail pipe to the tip. The tip would be turned down and wet. The tip would have a welded transom mounting flange drilled for fastening the flange to transom.
However, how would you get the tip through the transom with a standard jumper pipe welded in place ? Perhaps a recessed bung could fitted in the tip to provide for a screw in sweep elbow after the tip was installed (5 " OD )
The double wall tip would assure minimum exhaust heat at the transom and the collar would provide some protection for transom flex and motor mount shift. However, the tail pipe over hung load will increase as the collar may flex. Therefore, perhaps the tail pipes could be connected together with a strap. A strap should also reduce loading on the header and header bolts. Perhaps the strap would be located 6 to 8 " from the header.
I would prefer to have the tip double wall ( two pipes )through the transom. The tail pipe would connect to the tip with a rubber collar and double clamps on each end of the collar. A typical dry tail pipe jumper would connect the tail pipe to the tip. The tip would be turned down and wet. The tip would have a welded transom mounting flange drilled for fastening the flange to transom.
However, how would you get the tip through the transom with a standard jumper pipe welded in place ? Perhaps a recessed bung could fitted in the tip to provide for a screw in sweep elbow after the tip was installed (5 " OD )
The double wall tip would assure minimum exhaust heat at the transom and the collar would provide some protection for transom flex and motor mount shift. However, the tail pipe over hung load will increase as the collar may flex. Therefore, perhaps the tail pipes could be connected together with a strap. A strap should also reduce loading on the header and header bolts. Perhaps the strap would be located 6 to 8 " from the header.
04-12-2007, 02:34 PM
#24
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Brad, I plan on using a variation of your design and would like to have your input and opinion.
I would prefer to have the tip double wall ( two pipes )through the transom. The tail pipe would connect to the tip with a rubber collar and double clamps on each end of the collar. A typical dry tail pipe jumper would connect the tail pipe to the tip. The tip would be turned down and wet. The tip would have a welded transom mounting flange drilled for fastening the flange to transom.
[Why go to all the trouble if you are going to be wet exhaust any way? There are a lot of boats with through transom exhaust that never get to hot at the transom tip as it is wet at that point.
However, how would you get the tip through the transom with a standard jumper pipe welded in place ? Perhaps a recessed bung could fitted in the tip to provide for a screw in sweep elbow after the tip was installed (5 " OD )
Have CMI weld a screw in bung that will only be 1/2" or so and you could cut out a notch in the transom hole and seal it as you slip the tip through. The tip flange will cover that anyway on the outside.
The double wall tip would assure minimum exhaust heat at the transom and the collar would provide some protection for transom flex and motor mount shift. However, the tail pipe over hung load will increase as the collar may flex. Therefore, perhaps the tail pipes could be connected together with a strap. A strap should also reduce loading on the header and header bolts. Perhaps the strap would be located 6 to 8 " from the header.
I would prefer to have the tip double wall ( two pipes )through the transom. The tail pipe would connect to the tip with a rubber collar and double clamps on each end of the collar. A typical dry tail pipe jumper would connect the tail pipe to the tip. The tip would be turned down and wet. The tip would have a welded transom mounting flange drilled for fastening the flange to transom.
[Why go to all the trouble if you are going to be wet exhaust any way? There are a lot of boats with through transom exhaust that never get to hot at the transom tip as it is wet at that point.
However, how would you get the tip through the transom with a standard jumper pipe welded in place ? Perhaps a recessed bung could fitted in the tip to provide for a screw in sweep elbow after the tip was installed (5 " OD )
Have CMI weld a screw in bung that will only be 1/2" or so and you could cut out a notch in the transom hole and seal it as you slip the tip through. The tip flange will cover that anyway on the outside.
The double wall tip would assure minimum exhaust heat at the transom and the collar would provide some protection for transom flex and motor mount shift. However, the tail pipe over hung load will increase as the collar may flex. Therefore, perhaps the tail pipes could be connected together with a strap. A strap should also reduce loading on the header and header bolts. Perhaps the strap would be located 6 to 8 " from the header.
04-13-2007, 01:02 PM
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---what about piercing a hole in the tip instead of welding on a fitting that needs an over size transom hole....Then piercing a like size hole in the rubber collar....Then cap the collar hole with a split SS pipe that has the jumper pipe welded to the split SS pipe....The SS pipe would be fitted with two angles for bolting together causing a tight clamp at that end of the collar. The other end of the collar would get double clamps.
Water would flow through the jumper pipe, through the collar hole, through the pierced hole in the tip and out the wet tip.
Therefore the transom hole can be glassed in with a smooth surface
We have re-thought connecting the two tail pipes together. Instead of the SS strap ---maybe two ball ends screwed into a necked adjuster tube. The ball end method would provide finite adjutment that the strap would not.
Water would flow through the jumper pipe, through the collar hole, through the pierced hole in the tip and out the wet tip.
Therefore the transom hole can be glassed in with a smooth surface
We have re-thought connecting the two tail pipes together. Instead of the SS strap ---maybe two ball ends screwed into a necked adjuster tube. The ball end method would provide finite adjutment that the strap would not.
04-23-2007, 10:21 AM
#27
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Turns out CMI does not make a internal flap for the turndown tips. Installed them anyway. It works great. The 525 engines are very quiet at idle with the exhaust under water. Once on plane we were making some noise but less than normal as the exhaust is directed down near the drives. Zero reversion!
05-03-2007, 10:49 PM
#29
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Here are photos of the boat completed. Tails are in, the new hatches are painted (by me), and the old exhaust holes are now flap/vents with hinges. The Harlequin paint changes color from every slight angle green to purple. The material to paint the hatches and vents covers cost me about $1000.
Boat runs great. Even in hard reverse no reversion or scooping with tips underwater. Even when I was testing without the hatches and the vent covers no water came in the bilge. The engines have a nice deep rumble at idle with the exhaust fully underwater. No way the noise police will bother me.
Boat runs great. Even in hard reverse no reversion or scooping with tips underwater. Even when I was testing without the hatches and the vent covers no water came in the bilge. The engines have a nice deep rumble at idle with the exhaust fully underwater. No way the noise police will bother me.
