Running HDWR for SK-40?

[Flying Pilgrim]

I have a Dumas SK-Daddle .40 which I cannot seem to get "set up" correctly. I originally had the straight shaft hardware (sub-surface) but it cavitated REALLY bad, and I could not put a larger prop on it due to clearance problems. I then re-fitted it with a Marine Specialties HBR double rudder outdrive. It was no better. I fooled around with different props (plastic and metal), different angles and depths of prop. All props cavitated. Engine is a K&B sport 40, props run were prather 230, octura 2050, 1250, 1450, and Z 50. The prather 230 was too much, as it not only cavitated, but it would not get any rpm past half throttle. Should I use a lifting or surface piercing? I am thinking of using a flex drive on it with adjustable strut under hull (in front of transom). Any ideas?? ???

 

[Chris Attebery]

Howdy Pilgrim ;D

I have only seen one SK run about 10 years ago, but the guy had is set up pretty well.

Run a flex drive, set the shaft parallel with the bottom of the boat, and run that prather 230 or a 447 fully submerged. Don't run a lifting prop, they will lift the transom out of the water and cavitate.

Dual rudders seems excessive to me. Isn't there a skid fin on the bottom of the hull? It should be set right in front of the CG.

Flatbottoms aren't easy to setup, but they can be fun on smooth water.

Good Luck,

Chris

 

[Flying Pilgrim]

Chris,

Thanks for your reply!!

I was planning on trying a flex shaft setup this time .150 dia. cable. Yes, I put a fin right under the engine, it helped the turning tremendously!! I know these boats are not common, but they have to be nearly identicle to characteristics of the more popular cracker boxes. When I ran the Prather prop I listed, it would not rev past half throttle, as the sport .40 does not have the "umph" to turn much of a prop.

I know the boat would be a ball to skid around turns and bounce around. I only hope I can get it set up before I lose patience. I like to build a boat as per plans and then run it. I didn't think it would be this much work trying to get it to perform correctly.