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Dr. David Fleming
09-17-2010, 01:30 PM
Just tore up my lab finished 30P on the 22ZX - water level is down a foot in the Detroit area - hit something near beacon hill marina in Lake St. Clair.

Occured to me I never seen this topic on this site - does the Merc Bravo/Alpha stern drive kick up if you hit an object like an outboard motor does? Have seen a number of stern drives on performance boats with the skeg missing or broken - any opinion on how this effects performance? Another question - the skeg fin is fairly blunt from Merc - 1/16 radius edge - anyone filed this to a point for any performance increase?

Some Johnson racing outboard motors in the 1920's removed the skeg fin entirely and just ran the bullet - inboard shaft drive has no skeg below the prop. Wonder if this would reduce the rudder effect of the drive - course a shorty reduces the rudder effect also.

gcarter
09-17-2010, 01:40 PM
Does NOT kick up.
It's all hydraulic, therefore pretty rigid.
You can easily add one of those SST sheet metal fins.
I don't know personally what difference the performance is, but they're present on all high performance outdrives I've ever seen.

Last Tango
09-20-2010, 04:08 PM
Funny you should mention getting a SkegGuard. I have always wanted to try that on my Donzi's. I will gladly be the test boat for that on 22ZX's. I just saw one on the rack at our newest boat stuff store on Saturday, and remarked again that it was time to try it.

No kick-up on the Alpha or Bravo One drives on any of my Donzi's past or present. Plenty of chunked out skeg fins will attest. LOL!

mrfixxall
09-20-2010, 04:40 PM
Just tore up my lab finished 30P on the 22ZX - water level is down a foot in the Detroit area - hit something near beacon hill marina in Lake St. Clair.

Occured to me I never seen this topic on this site - does the Merc Bravo/Alpha stern drive kick up if you hit an object like an outboard motor does? Have seen a number of stern drives on performance boats with the skeg missing or broken - any opinion on how this effects performance? Another question - the skeg fin is fairly blunt from Merc - 1/16 radius edge - anyone filed this to a point for any performance increase?

Some Johnson racing outboard motors in the 1920's removed the skeg fin entirely and just ran the bullet - inboard shaft drive has no skeg below the prop. Wonder if this would reduce the rudder effect of the drive - course a shorty reduces the rudder effect also.


Bummer, if you need it fixxed try out the guy the does my props..

http://www.dahpropellers.com/

he knows his chit and is reasonable on repairs thats if you want it done rite :)

The Hedgehog
09-20-2010, 06:38 PM
Bummer, if you need it fixxed try out the guy the does my props..

http://www.dahpropellers.com/

he knows his chit and is reasonable on repairs thats if you want it done rite :)

Give him a try. I have heard good things about him.

I would just get the skeg fixed. Been there and done that. It is not too bad

Carbo
09-20-2010, 09:42 PM
Mercruiser rams DO kick up. I have resealed dozens. In salt water the end caps corrode up and tighten up on the chrome shaft. They trim up and get stuck. There are spring loaded balls in the piston assy just like an outboard. They will allow fluid transfer through them on impact.....it is more or a drag up but they are NOT fixed. They will trail up on grounding or impact.


in this pic #11 spring pushes plate#10 against the #9 balls that seal against #8...........under impact the balls unseat and allow fluid transfer as the rams extend.

http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=880951%2000&ivar=images/COMMON/1623.png&inbr=5398&bnbr=150&bdesc=POWER+TRIM+CYLINDER+REPAIR+KITS

Planetwarmer
09-20-2010, 10:33 PM
Mercruiser rams DO kick up. I have resealed dozens. In salt water the end caps corrode up and tighten up on the chrome shaft. They trim up and get stuck. There are spring loaded balls in the piston assy just like an outboard. They will allow fluid transfer through them on impact.....it is more or a drag up but they are NOT fixed. They will trail up on grounding or impact.


in this pic #11 spring pushes plate#10 against the #9 balls that seal against #8...........under impact the balls unseat and allow fluid transfer as the rams extend.

http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=880951%2000&ivar=images/COMMON/1623.png&inbr=5398&bnbr=150&bdesc=POWER+TRIM+CYLINDER+REPAIR+KITS

They sure did a piss poor job designing that setup! I have heard of people sinking their boats because they hit a mostly submerged floating log, and ripped the drive off.

The Hedgehog
09-20-2010, 10:37 PM
They sure did a piss poor job designing that setup! I have heard of people sinking their boats because they hit a mostly submerged floating log, and ripped the drive off.

That is usually what happens down here too. I mean rips them clean off.

Carbo
09-21-2010, 12:20 AM
I didn't say it was a good system....only that it is there.:)

Dr. David Fleming
09-21-2010, 01:45 PM
Anyone know if the Volvo drive kicks up any better?

Anyone ever trimmed the leading edge and or trailing edge of the skeg to a razor point and observed a performance increase? or welding it for repair? Anyone ever remove the skeg to cut down on the whetted surface and reduce drag - seems like a lot of attention is paid to the nose cone for performance increase.

Wonder if it would help reduce the asian carp population?

Conquistador_del_mar
09-21-2010, 02:40 PM
Anyone ever trimmed the leading edge and or trailing edge of the skeg to a razor point and observed a performance increase? or welding it for repair? Anyone ever remove the skeg to cut down on the whetted surface and reduce drag - seems like a lot of attention is paid to the nose cone for performance increase.

Wonder if it would help reduce the asian carp population?

I don't know about the fish, but I did break off the rudder on a slalom ski when I was young after hitting a turtle that I saw at the last second before I crashed.
Yes, whenever I have repainted an outdrive, I have always sanded the leading edge of the skeg to a sharp edge to help reduce drag along with air filing the drive sides to get them as straight as possible to also try to eliminate drag. Concerning those stainless rudders, my understanding is that they simply add drag by their added width. A good welder can repair or replace a broken skeg rudder with a new one. A good welder will heat sink the drive hub with a wet towel or such to keep the extreme heat from transferring. Running without a skeg can lead to problems from my experience. Bill

Dr. David Fleming
09-22-2010, 10:11 AM
You didn't say if all the filing and filling and sharpening of the skeg gave any measurable performance? Thanks for the response.

mrfixxall
09-22-2010, 10:33 AM
I'm going back 25 yrs ago when i first got my donzi.the boat had a trailer with tiny wheels and the old owner didn't put the safety lock on the drive..on hes way home the drive had wend down and ground the skeg down to about 2'' left of it..he ran the boat like that for years,then when i bough the boat i had put a bigger engine in it (LT1) and the only thing i noticed was that the boat would lien really bad under hard throttle..i would also notice that if i ran a aluminum prop and where i boat it would get tore up that day because of the shallow water and the crap that floats down river..

since then i welded a new skeg on and trimmer some of it back away from the prop so the prop could get clean water.. i also thinned out the leading edge of the skeg but not to a sharp edge..the twisting of the boat went away after i welded the skeg back on.

Conquistador_del_mar
09-22-2010, 12:56 PM
You didn't say if all the filing and filling and sharpening of the skeg gave any measurable performance? Thanks for the response.

Almost all the drive work that I used to do was for customer's boats back when I did boat repair/restoration work professionally up to about 1995, so I really don't have an apples to apples comparison. I also restored many boats on the side that I sold with no before and after speed comparisons after restoring the drives. Sorry. I did pick up 2-3MPH on my 36' Cigarette after restoring the TRS outdrives, but I also installed nose cones and changed from 22" Hydromotives to 24" Hydromotives so it is not a good comparison. There have to be many guys who could chime in about skeg/drive work and how it affected speed/performance. Bill

Planetwarmer
09-22-2010, 11:16 PM
I am willing to bet that filing the skeg to a point would have negligible gains, if any. I wouldn't think there is significant drag caused by the added material. If anything, I would imagine that the square edge would slightly screw up the flow of water on its way to the prop. Im sure that a lab could find a problem with the squared off metal, but I bet it wouldnt make that much difference due to the side and forces of the boat and drive.

That is my 2 cents. I am talking out of my a$$. Sorry to waste your reading time.

OH! I sure hope OU can pull out a national championship this season. BOOMER SOONER!

The Hedgehog
09-22-2010, 11:45 PM
Almost all the drive work that I used to do was for customer's boats back when I did boat repair/restoration work professionally up to about 1995, so I really don't have an apples to apples comparison. I also restored many boats on the side that I sold with no before and after speed comparisons after restoring the drives. Sorry. I did pick up 2-3MPH on my 36' Cigarette after restoring the TRS outdrives, but I also installed nose cones and changed from 22" Hydromotives to 24" Hydromotives so it is not a good comparison. There have to be many guys who could chime in about skeg/drive work and how it affected speed/performance. Bill

I agree. It works. Keep those edges clean. I do it too.