Swap a saildrive for an outboard - SailNet Community
 
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post #1 of 7 Old 11-14-2011 Thread Starter
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Swap a saildrive for an outboard

I have an 82 Cal 2-25 with the OMC saildrive. I have not had the boat in the water yet but have had the motor running with the adaptor described in the manual for running on the hard. I have rebuilt the carb and replaced the water pump impeller but keep going back and forth with keeping it or pulling it and mounting an outboard.

With how scarce and expensive parts are and the high fuel usage of the saildrive, Iíve read upwards of 6 gallons an hour, I only have an 11 gallon tank. Iím thinking of doing this this winter. Any thought on this idea would be great.
I am also wondering what size outboard everyone would recommend.

I will be sailing on Lake Superior out of Duluth, MN and I know waves can be an issue with outboards popping out of the water. Anyone see this as a reason not to swap the saildrive out?
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post #2 of 7 Old 11-14-2011
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I think those units were a 35HP de-tuned to about 18HP. I would guess fuel consumption would be a little less than 2 gals / hour at WOT. I don't think you would have to run it WOT to achieve hull speed, maybe only when bucking a real stiff headwind and chop? I had a 35HP Evinrude for years, ran great with no problems. If the Sail Drive is in sound condition I suggest you give it a try.
The incremental difference in fuel consumption should' be that great compared to the cost of removing the Sail drive, buying a new OB and mounting bracket, and the possibility of having to re-inforce the transom, and even with a long shaft the motor it may still pop out in choppy conditions.
Then it would be too late to go back to the Sail Drive. You need to get the "power to the ground" regardless of where it comes from. If the Sail Drive was previously used in fresh water it shouldn't have any corrosion problems.

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post #3 of 7 Old 11-14-2011
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Is it broke?

Seriously, if it is still functional, then I'd leave it until forced to do something.
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post #4 of 7 Old 11-14-2011
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I least try it. The 2 gallon/hour could be accurate and 18 HP is about twice the power recommended for the rule of thumb of 3 to 4 HP per ton of sailboat so you should be able to buck those waves and the wind. Maybe you should carry extra fuel though. This rule of thumb is for 18 to 24 knot wind making at least 2 knots into the wind. When there is no wind a 5 HP four cycle would be economical at half a gallon per hour, but not sure what would happen if you burned 2 cycle fuel. Maybe that would work if you used a 2 cycle spark plug. The efficiency of a 2 cycle falls off at part throttle much more than a 4 cycle. On a calm day see if you can get some fuel consumption values for the OMC, perhaps by weighing the fuel tank before and after a run at constant speed, maybe measured by GPS.

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post #5 of 7 Old 11-14-2011
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If the unit has always been used on a freshwater lake its pretty unlikely its had all the issues a saltwater unit would have had as the wear and tear between salt and fresh water is HUGE

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post #6 of 7 Old 11-15-2011
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My 37 foot 20,000 pound sloop has a 38 hp Beta that was a replacement for a 35 hp Volvo a few years back. It powers a Volvo saildrive. I cruise at 1800 rpm (6 knots) and burn 0.5 gals per hour. My fuel consumption go up if I really push the Beta to get the last 1 knot from it, so I don't do it.

Keep the saildrive. It makes getting into and out of tight spaces a breeze.


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post #7 of 7 Old 11-15-2011
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The rule of thumb for 2 stroke outboards is 1 gallon per hour for every 10 applied horsepower. I've had 3, 4, 6, 7 1/2, and 150 hp OB motors over the years and this rule seems to hold. I have a 4 stroke 9.9 hp and a 150 hp direct injection 2 stroke, which get better fuel consumption, but nowhere near that of my 27 hp inboard diesel.

If you are concerned about range, stay below your displacement speed (1.25 x sq. rt of your waterline length).

So, I agree with dabnis: if you are operating at full throttle with an 18 hp motor (2 stroke?) you should be getting about 2 gal/hour and be pushing your 25 ft boat past displacement speed of ~6 kts, assuming you are not pushing into high winds and seas. You should do quite well at half throttle.
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