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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

Propeller for my C25

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T O P I C R E V I E W
JanS48	Posted - 06/05/2019 : 13:38:44 Greetings everyone I need to replace the prop on my 2004 Mercury 15hp 4 stroke. Although this motor powers the boat along nicely, I'd like to have more thrust and control at low speed, like when rounding up. I'm contemplating going to a 4 blade SOLAS prop (great prices) but don't know which pitch would be best. They list: Hi Thrust: 10 x 7 or 10 x 5 the second # being the pitch Std 4 blades: 9.25 x 7, x8, x9, or x10 The standard prop on the motor was a 3 blade 9 x 9 Anyone have any experience with changing props? I'm told this would be a simiilar choice for those with a Mercury 9.9 4 stroke. I'm leaning towards a STD 4 blade 9.25 x 8 but honestly that is just a guess. Thanks in advance Jan
9 L A T E S T R E P L I E S (Newest First)
Voyager	Posted - 07/22/2019 : 13:04:52 And just to add to Dave Stinkpotter�s comments, the 8HP with a four blade prop (which I inherited) does so great in reverse. I learned to dock in a very tight marina on a river with wind, current and chop (frequently not in agreement), so I had no choice but to become virtuosic with an outboard engine. Today I�m at a easier marina but I back into the slip to dock so my move is to drive down the fairway, hug the right side then spin the boat on the keel until I�m pointing 180� and slam it into reverse and pull her alongside the slip. Then before crashing into the dock, flip it into forward and rev. Prop-walk is my friend sucking me against the dock. I put it in neutral then secure spring lines,then dockline. That Honda 8 and 4 blade prop is the bomb for bringing it home.
Stinkpotter	Posted - 07/21/2019 : 13:37:20 If you're concerned about fuel economy and/or noise, 6 knots and above is not going to help. "Theoretical hull speed" for a C-25 is 6.3 kts, above which you are pushing the boat up over its own bow wave as if to get it on plane, which takes a lot of power with that type of hull. That's why you see the "hump" behind you--the bow is up and the stern is squatting, using a lot of fuel for every additional fraction of a knot. My high-thrust Honda 8 could push past 6.3, but I stayed at or below 5.5 for a considerably quieter ride and better mileage.
JanS48	Posted - 07/21/2019 : 10:56:31 Followup: Greetings everyone, I ended up going with a SOLAS 4 blade 9.25 x 8 The prop seems to work quite well giving more control at low speed and slowing the boat quickly from forward to reverse. In traveling a distance (10 mi) I get noticeable better fuel economy moving at 6k. Speed wise it's about the same as the former 3 blade, it does however get to 6k easier. Top speed wide open is about 7.5 k if flat calm, with big 'bump' in back of the boat. All that said I'm pleased with the purchase.
JanS48	Posted - 06/07/2019 : 12:37:46 Greetings to BCG-Woodbury Funny you mention a Tohatsu 8, the previous owner had a 1998 Nissan 8 which I'm told was/is a Tohatsu. Both he and some friends said the motor pushed the boat along well in Narragansett bay (where the boat still resides). I'm curious did the motor prove reliable? I still have the Nissan 8 which I was keeping as a spare. I never attempted to use the old motor as I really wanted a 4 stroke electric start. Thanks Jan
BCG-Woodbury	Posted - 06/06/2019 : 19:21:56 Hi Jan - My boat came with a Tohatsu 8 which was working just fine on my inland lake. The big issue was I only had thrust up until 1/2 throttle and then flat from there. Probably cavitating. I wanted full range so I looked at the manual which had about 6-8 prop variations. Each one of them was for a weight range. It turns out that all the motors ship with a prop for light rowboats. When I switched the the correct pitch and size for the C25's weight range I gained full range and fine control at low speed. As for a quick change-up from forward to reverse, with all that mass, you have a much better chance with your 15 HP than I'll ever have with my 8 little ponies. Regards,
JanS48	Posted - 06/05/2019 : 22:00:45 Thanks for the comments, this Mercury 15 is exactly the same as a Yamaha 15, which I'm told is the same displacement as the 9.9 except for the cam and carb. Frankly the performance pushing the boat is better than expected, it does 6k easily at just over half throttle. In a dead calm sea I can get over 7.5 k at full throttle but with a big 'bump' in back of the boat. It doesn't get to a plane but it does lift the bow quite a bit. It however lacks the ability to quick reverse that was mentioned, that would be a huge help for me in rounding up in tight quarters when the wind is blowing. It's for this reason I'm looking at the prop change. Based on what was said, I'm now thinking of the Hi-thrust 10 x 7 four blade. This motor is a long shaft 20" model which I installed a 5" extension on. That helped a lot when motoring in a chop. Sounds like the extra blade with 2" less pitch may be the way to go [10 x 7] four blade. Thanks for the input. Please keep the comments coming... Jan
JanS48	Posted - 06/05/2019 : 21:56:06 Thanks for the comments, this Mercury 15 is exactly the same as a Yamaha 15, which I'm told is the same displacement as the 9.9 except for the cam and carb. Frankly the performance pushing the boat is better than expected, it does 6k easily at just over half throttle. In a dead calm sea I can get over 7.5 k at full throttle but with a big 'bump' in back of the boat. It doesn't get to a plane but it does lift the bow quite a bit. It however lacks the ability to quick reverse that was mentioned, that would be a huge help for me in rounding up in tight quarters when the wind is blowing. It's for this reason I'm looking at the prop change. Based on what was said, I'm now thinking of the Hi-thrust 10 x 7 four blade. This motor is a long shaft 20" model which I installed a 5" extension on. That helped a lot when motoring in a chop. Sounds like the extra blade with 2" less pitch may be the way to go [10 x 7] four blade. Thanks for the input. Please keep the comments coming... Jan
Stinkpotter	Posted - 06/05/2019 : 20:29:42 The Honda 9.9 Powerthrust (for displacement hulls) prop is 4 blades, 10" x 6.5" I had the same on my Honda 8 (same motor except for the cam), and compared to an older Honda 8 with a general-purpose 3-blade prop, the biggest advantage I felt was that reverse stopped the boat as if it had run into a pillow. 5.5 knot cruising speed was reached at about 2/3 throttle, so the pitch wasn't too low.
Leon Sisson	Posted - 06/05/2019 : 16:12:59 Jan, For a Catalina 25 or other displacement hull I would get the prop having the least pitch, most blades (also with the largest area per blade), and largest diameter available for your motor. You want the 'tug boat' option, not the hydroplane version. On my Catalina 25 I've used both a Honda 10 hp long shaft with 3-blade prop, and a Yamaha 10 hp extra long shaft 'high thrust' with 3-blade low pitch prop. The difference is night and day. Right now, I can't find the numbers on the Honda, and can't read the ones on the Yamaha. However, the Yamaha prop looks flatter and the blades appear to have a lot more area. I seem to recall that the high thrust Yamaha also has a numerically higher gear ratio, turning the prop slower with more torque. In unfavorable conditions, such as high wind, steep waves, and strong current, the Yamaha moves the boat with real authority. On my Catalina 22 with a 4 hp Yamaha, I went down 1" pitch from what it came with. Still can't rev out the motor before reaching hull speed, but very noticeable increase in rpm and thrust. And speaking of props, I suggest carrying the other one aboard as a spare, along with the tools and parts to change it on the water (pliers/wrench, cotter pin, shear pin, tab washer, nut, whatever), in case the one in use becomes damaged or lost. Perhaps not as critical as with a power boat, but still worth the small amount of weight and storage space. � Leon

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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.