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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

Propeller Pitch

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T O P I C R E V I E W
canadiansailorkid	Posted - 06/03/2021 : 12:49:34 I have a 2003 6hp 4stroke Mercury long shaft outboard, but I'm unsure of the propeller size on it as I can't find the stamping. It came with the my 1978 C25 when I bought it. But I suspect it has the standard 7.8"diax8"pitch 3 blade propeller on it. Although looking at the parts catalog for my motor it recommends a 8.5diax6" pitch for sailboats. My question is how much of a difference would this actually make? Is it worth the $250 my local store is charging for a replacement prop? Or would I not see a noticeable difference in performance? I do have a bit of a tight docking situation in my marina, maybe it would be worth it, I just don't have experience with different props. Thoughts?
9 L A T E S T R E P L I E S (Newest First)
JanS48	Posted - 06/14/2021 : 20:31:34 I have a 2003 Mercury 15 on my STD rig C25, 2 years ago I 'spun' the std 3 blade prop and replaced it with a shallow pitch 4 blade prop. It did not change the top speed of the boat at all but maneuvering at low speed especially when throwing it in reverse and gunning it a little to bring the boat to a dead stop was much improved. On an extended outboard run, if keeping the speed under 6k the fuel consumption improved slightly. The prop is a Solas from defender at a cost of $ 85. It took all of 10 min to change the prop.
Stinkpotter	Posted - 06/11/2021 : 19:45:09 For tight-space maneuvering, there's something else to be aware of--"prop-walk". This is the sideways thrust from some of the water coming off the prop--you experience it particularly when starting from a stop, accelerating hard at very low speed, or switching from Forward to Reverse. The way I describe it, in Forward (at low or no speed), the motor SHOVES the stern to STARBOARD (turning the bow to PORT), and in reverse, it PULLS the stern (and the boat) to PORT. A higher pitch prop does this more, a "high thrust" prop somewhat less. But understanding it can help a lot for maneuvering in tight spaces, and it can help you plan a way to do a maneuver. I use it by coasting to a space about in front of my slip, shifting to reverse, and letting prop-walk rotate me in place as it stops the boat, turning my bow to starboard to enter the slip. This is with my powerboat, but I did a similar thing with my C-25. You can demonstrate it to yourself by, at rest, putting the motor in gear (F or R) pointed straight ahead, and gunning it a little. The stern will move as I described. And it can help or hinder your attempts to steer the boat at low speeds, even as you're turning the outboard to do it.
canadiansailorkid	Posted - 06/07/2021 : 19:40:46 Thanks for the info everybody! I've been busy this week and got her in the water finally after many years on dry dock. Since I haven't really had much experience with the 7.8dia x 8" standard pitch prop I'm going to try it out this summer and see gain some experience with it. If I do change it out it will be next summer so that I have something to compare it too. I agree with Steve and Leon that I shouldn't rely on my motor for absolute precision. I understand learning the 'feel' and using the inertia to get it close then a well placed midship line or boat hook to reel myself the rest of the way. Like I said, my marina is tight and up against a bit of a steep hill/cliff that likes to backwind your sails when you least expect it. Sailing it in would require four 90 degree turns (right/left/right/right)in a busy water way with no more than 30' open water between docks on both sides. I'm sure a skipper could do it, but I happy to admit when I have reached my limitations. I also haven't shopped around on price, I went to the only mercury parts dealer in town and they are known for being pricy. I will certainly try searching for Tohatsu or other compatible brands if I do go that route next season. A view of the only 2 sailboats in my marina, very nicely placed by management as far into the harbour as possible where there is the least amount of depth, no more than 4 feet to float my swing keel. https://i.ibb.co/tCTMsTq/20210606-162624.jpg
Stinkpotter	Posted - 06/05/2021 : 20:20:46 How big an investment is a little aluminum prop? I know a stainless steel prop for my big motor is in the $500-$700 range, but forging, machining and balancing a big hunk of stainless is a whole different thing from molding a little piece of aluminum. I also know that our little high-thrust, lower pitch, 4-blade aluminum prop on our C-25 was amazing for maneuvering (compared to a predecessor)... maybe less so for long-distance mileage, but that wasn't an issue for us.
Voyager	Posted - 06/05/2021 : 06:58:04 What their return policy? You can always try it out and if it makes no difference, you can always return it. I�m going to wager that it will change your docking performance considerably.
islander	Posted - 06/04/2021 : 10:40:25 To take an educated guess, Tohatsu makes Mercury engines 30hp and under so the 6hp Tohatsu Sail Pro uses a 8.375 Dia.X 6.0 pitch High Thrust prop. Looks like the Mercury 8.5diax6" pitch for sailboats is virtually the same. I would try it. (I like spending other peoples money)
Stinkpotter	Posted - 06/03/2021 : 21:36:04 We bought our C-25 with an older Honda 8 with its standard prop, I presume designed for getting a small inflatable or other boat on plane--not to horse a 4500 lb. displacement hull around in a slip. I replaced it with a 10-15 year newer "Power Thrust" Honda 8 (larger diameter, lower pitch prop and reverse exhaust directed away from the prop). I can say that the comparison was stark. Backing into our tight slip was easier, particularly when conditions required some speed, and stopping with just a flick of the shifter was like running into a pillow. The smaller the outboard, the truer it is that the right prop for horsing around a big displacement hull is different from the right prop for a dinghy. Higher pitch is more efficient at higher speeds--at low speeds or from a stop the higher pitch creates more "prop walk" (pushing the transom to one side or the other) and less of the thrust in the direction you want. I can't quantify the difference you should expect, so the question is, to what degree are you dissatisfied with what you have?
Leon Sisson	Posted - 06/03/2021 : 19:54:03 I agree with Steve's excellent points about not being too dependent upon your motor. "Arr matey! In my day, a true sailor could man the helm with his knees and haul the mainsheet with his teeth!� One hand on the rail and a bottle of rum in the other! These swabs what fancy themselves sailors now days can't leave port without roller furling, self-tailing winches and electronic charts! It's come to a sad state of affairs, I tell ya." Here's my experience with sailboat outboard prop selection. On my Catalina 25, I've used both an old Honda 10 hp, 20" shaft, with what I assume was the default one-size-fits-all 3-blade propeller, and a Yamaha 9.9 hp 25" shaft, 11-1/4"x9-1/4" dual/high thrust prop with 3 huge blades. The difference was dramatic. The deeper, larger, lower pitch prop and numerically higher gear ratio produced far more thrust. This is especially true in reverse, due to the way Yamaha routes exhaust with their "dual thrust" prop. On the Catalina 22 with a Yamaha 4 hp 20" shaft, I switched from the general purpose 3-blade prop it came with to one with 1" less pitch. � The lower pitch prop allows the engine to rev higher, thus delivering more power to the water. It still bogs down well short of full throttle due to being over-propped for the boat. Maneuvering at the slip is noticeably improved by the more efficient bite at low speed. Edited to add: Re: "...the $250 my local store is charging for a replacement prop?" That seems high. I suggest you shop around a bit on price. I paid under $30 w/shipping for a 4 hp Yamaha prop. I've seen 10hp Yamaha props listed for under $100.
Steve Milby	Posted - 06/03/2021 : 16:45:03 Most people rely on their motor to get their boat into the slip, and they think that, if they had the perfect motor with the perfect prop, it would be easier. Perhaps it would, but what would you do if your motor quit 100 feet from your slip? Most folks would panic. The better approach is to think about all the ways you can get your boat into the slip, with or without the motor. If you can get it into the slip without using the motor at all, then surely you can get it in there by using a less-than-ideal motor and prop. Here's a link to a thread where I described ways you can move your boat all around a marina and into your slip without using your motor at all. http://catalina-capri-25s.org/forum/topic.asp?TOPIC_ID=31545 My Cal 25 was in a marina with an extremely narrow fairway, and I found that the easiest way to get into my slip was to shut off the motor about 4 boat lengths from the slip, let it coast to the slip, and then use a boat hook to manipulate it into the slip, stern-first. Generally, sailboats with an outboard or a diesel inboard engine don't back or maneuver terribly well. They don't make it easy for you, so you have to learn techniques that make it easier. Rely on your motor to get you close enough to your slip, and then either use the motor to get it in, or use a boat hook to get it in, or even sail it in. With my C&C 35 diesel, I generally used the engine to get the stern between the outer pilings, and then pulled it in the rest of the way with a boat hook. Why? Because when I was singlehanding it, there was no crew to fend off a piling or a neighboring boat if I got akimbo to the slip. By using a boat hook, I was able to pull the boat into the slip with complete control. To answer your specific question, IMO you probably won't find a prop that will make docking as easy as you think it should be. Boats don't maneuver as precisely as your car, because they're operating in a fluid environment. Using your motor together with good techniques will make docking easier.

Association Forum

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.