Do I need riser extensions?

D

Darylle

Member
Jan 21, 2011
53
Australia
Boat Info
1994 230 DA '03 f250
Engines
5.0 mercruiser alpha1
Hi everyone
As the title states I am curious if I need riser extensions as I have just replaced an engine due to water ingestion and cannot rule out the possibility that the swim platform with people sitting on it effects the water level in the "y" pipe whilst not underway.
Thanks in advance for your comments
 
You need 13 inches minimum
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Thank you again for the replies, I will check those dimensions tomorrow but I reckon there is no way I would have 13" above the waterline.
 
As expected, I do not have 330mm or 13" above the w/line I have about 50mm or 2"
With 2 adults on the platform (which is flush with the hull/deck join) the water sometimes washes over and this means the riser outlet is BELOW THE WATERLINE! What are my options to ensure I do not experience this again with my brand new engine? Even without the platform, water washes over the OEM rear deck area at times with people seated at the table if a boat goes past.
 
The engine hatch cover will be your limit for extensions and if that isn't enough, you need a bigger boat
 
you can install a 'water lift' style muffler....this type of muffler is commonly used when the engine is mounted at or below the water line....Sea Ray used these mufflers to correct a design flaw in the 1999 - 2001 era boats that had a very serious issue with water ingestion...

cliff
 
Thanks for the replies.
After checking I found there is no space for any riser extensions, so here and now it seems the "water lift" is the only way to go. Does this mean the "Y" pipe becomes redundant and I can plate over the transom hole? So the exhaust exit pipes above the water but in the long term is this a viable modification and would anyone have an photos of this set up in a similar size boat?
 
Water lift muffler are mostly used on inboards. On IOs use what you got merc spacers come in 3 and 6 inch on a 230 with a 5.0 you should have plenty of space between risers top and water check your boat to see if you have water in hull.
 
vandal is right that the water lift mufflers are normally used on inboards....I failed to notice you have an Alpha outdrive.....the first thing I would check/replace are the flappers in the exhaust....these flappers act as a one way valve that lets the engine exhaust out but closes off the exhaust when the engine is not running.....they are designed to prevent water from back flowing into the engine....

cliff
 
O.K
No space for riser extensions and I noticed upon removal of the risers one of the less than 12 month old flappers sticks open and it doesn't take much for the other to "stick" as well. They in my opinion are no guarantee in stopping water flowing back. I know it is a long shot but what about the "valve system" available with car exhaust (mufflers) that control a butterfly similar to a throttle plate?
 
Nothing like that will be water tight, less people or more boat, probably not what you want to hear.
 
Thank you again for the replies I am having great difficulty believing in this day and age there is not a better system available!! So a brand new searay will have this same exhaust design?
 
I'm going to give this a shot. Believe it or not there is some science built into the exhaust system. Try this, fill a clear drinking glass with a flat but thin bottom(one without any design so that you can see through it) with 4" of water and put a straw into the glass and bottom it out in the glass. Hold the straw in a straight up and down orientation then place your finger on the open end of the straw to capture water in the straw. Remove the straw from the glass of water (try not to lose any water from the straw) and place it next to the glass and you will see that the level of the water in the straw is lower than the level of water in the glass (even when you account for the thin bottom of the glass).

As a result of this experiment one can conclude that the level of water in the exhaust system (the straw) will always be lower than the boat's water line level where the water that the boat is sitting in (the glass of water) enters the exhaust system.

Now, the exhaust system "Y" is also curved at or above the water line and continues to bow out (it bows out as wide as the engine is wide) as it makes its way up to the elbows. The "bows" in the exhaust system means that the level of the water has to rise even more for the water in the exhaust "Y" to travel up to the elbows. If those bows were not there the water would have a shorter distance to travel upward to reach the elbows. In other words if the exhaust pipes were straight the water would have a shorter distance to travel before reaching the elbows, by putting the bows in the system you turn an approximately 2' straight shot to the elbow into an approximately 3' journey on up to the elbow.

The flaps are also there to help stop water from cresting the joint before the elbows.
 
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Iam a little confused before I suggest some help. An alpha drive draws raw water through the leg and then cools the motor and then exits back through the leg with the exhaust gas. Your boat design differs ?
 
Goose1, I believe you are correct except the water and exhaust are discharged through the propeller (leg) but also through (2) two additional holes (one port and one starboard) at the bottom of the gimbal ring
 
I had the 4.3 l with alpha on my previous boat and did not have two places it exhausted. Although exhaust configuration is designed by the boat builder not engine builder so anything is possible. The 13 inch riser clearance isn't applicable here I don't think but flapper sticking is. Google Mercury service bulletin 2001-13 it explains the many reseaons water can get into engine maybe that might help you, I can't figure how to attach a pfd or I would post it.
 
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