Mercury 3.5hp Convert Long Shaft to Short Shaft

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LCBrandt's picture
LCBrandt
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Joined: 6/26/07
Posts: 1282
Mercury 3.5hp Convert Long Shaft to Short Shaft

After a 6-hour run yesterday getting my dinghy from home to the mother ship, I'm of the belief that I need to convert my new long shaft Mercury 3.5 (a new 4-cycle) to short shaft. As it is, the O/B extends nearly 16 inches below the dinghy keel, and that will seriously limit my ability to get ashore in the Pacific Northwest's rocky shoreline and to have access to some shallow waterways.

Has anyone done a conversion like this? 

Larry Brandt
S/V High Flight #2109
Pacific Northwest, PDX-based
2002 C-36 mkII SR/FK M35B
 

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TomSoko
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Joined: 2/15/07
Posts: 978

Larry,
I don't have a conversion kit, but I agree completely with your desire to convert to a short shaft.  Everything I have read says that you should NOT use a long shaft OB on an inflatable or any other small dinghy-type craft.  The torque/stress on the transom is too great, even with a relatively low HP OB.

 

Tom Sokoloski
C36/375IA Past Commodore
Noank, CT

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Catboat Willy
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Joined: 12/22/14
Posts: 387

Larry;
 Several years back we tried the conversion the other way around, that is from a short shaft to a long shaft. In the end, the cost of parts was far more than anticipated and it would have been cheaper to just scrap the engine. It was only two years old. You will most likely find that you will need special internal parts (shafts etc)
My response to your question would be; Try and sell it as is and don't mess with an attempted with conversion. Use the proceeds from the sale to get yourself a newer short shaft engine.
Bill Dolan
Punta Gorda, FL
C-36 # 1041
 

Bill Dolan 1990 Catalina C-36 MKI - Hull #1041  'Williwaw'
Std. Rig, Walk Through, Wing Keel
M35, Oberdorfer Conversion,
Home Waters; Charlotte  Harbor & The Gulf Islands of Florida
'You are never out of work if you own a boat'

 

pierview
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Joined: 9/27/09
Posts: 598

Larry...

 I'm guessing, but I think if you did try the conversion you might invalidate any warranty you might have on your new long shaft. I agree with the comment about just selling it and going with a short shaft.

Chuck Parker
HelenRita 2072 Mk II
2002 Tall Rig - Winged Keel
Atlantic Highlands, NJ

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cussy
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Joined: 9/9/14
Posts: 25

Hi Larry   We had the same problem as you  and same engine , we bought a used engine that had been ran dry of oil so power head was gone and swapped everything below the head it took me around 45 minutes to change over you would not believe how easy it is to do , the ruined engine cost me £55 as it would have cost the lad i bought it off a small fortune to repair it , I made mine short shaft and ( being a scotsman) put everything else on ebay and yes made a nice little profit , I did keep the coil , carb ect for spare parts  

cheers Kenny 

Geileis
Hull 1489
1995
Fin Keel 
U shape Lounge 
Westerbeke M35 engine 
Mikuni heating
Second best thing that ever happened to me 

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