I have noticed that most small outboards don't back up well. Especially the through-hub-exhaust models (typically over 3.5 hp). What happens is that the exhaust washes over the prop blades in reverse, and the prop can't bite much water.
That has been addressed with modern High Thrust props on selected new outboards, but I was having trouble getting one to fit an old Merc 7.5. Couldn't find a listing on any prop selection charts to get the HT prop. It looked like the only option was going to be for me to bore out the leg of the outboard to relieve the exhaust just above the ventilation plate.
Every way I tried to get a solution, I was stopped "dead in the water". Then, I contacted Solas, and got the answer.
I traded emails and a phone call with Marc Feinman, the US marketing rep for Solas Science and Engineering. He came up with the correct Solas part number (1113-100-07) which is a 4-blade, high-thrust, 7-pitch prop to fit the old 8-spline prop shaft on the Merc 7.5 OB. No special hub sleeve needed. Retail is about $92.00 US. Our store can source it through Coast Distributors.
Marc is a great guy, very knowledgeable and quite helpful. I can't say enough about how he handled my customer service request. He's in their Tampa, Florida office. Bottom line is that he knows the applications very well. The prop selector charts didn't help me much. Most OB and prop manufacturers concentrate on the faster, bigger and newer motors, and go-fast boats. They tend to ignore sail applications. The correct part is in fact available for most small OB's -- IF you get Marc to help find it.
I know from experience that these props are excellent for sailboats -- I have one on a Nissan 9.8 on my boat. I was actually able to downsize from 15 hp to 9.8 hp, and still get better thrust, especially in reverse. Anyone who wants to improve the low-speed thrust on their outboard-aux sailboat may want to investigate these high-thrust Solas props.
Paul Van Voorhees
Certified Tohatsu TLDI Technician
Mgr, Obersheimer Sails
Buffalo, NY USA