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Author Topic:   Routinely changing props
Disco Stu posted 08-05-2003 09:26 PM ET (US)   Profile for Disco Stu   Send Email to Disco Stu  
I have not heard it suggested before and I am wondering if it is ever practical to own two props and swap them out based upon daily conditions. For example many days I will go out with 5 people, a fairly full load for my 17í hull, while other days it will be just myself. I havenít had to replace a prop before, but from my reading it does seem like a fairly quick operation. Does anyone do this, or are there limitations to this idea that I am overlooking?
Sal DiMercurio posted 08-05-2003 11:31 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Stu, if your running a 19 pitch prop by yourself & turning the maximum rated rpms, when you put 5 people in the boat, your going to drop down maybe 400 rpms.
If you know your going to have that many people it only takes a minute to change to a 17 pitch prop which will allow your engine to again reach it's max rpm rating & run much easier.
If your now running a 17 pitch then use a 15p with a big load, but be aware that if your running alone & have the prop with 2" less pitch, your engine will over rev by 400 rpms so don't open her up if your load is alot less then the original 5.
Sal
WHALETEX posted 08-06-2003 12:48 PM ET (US)     Profile for WHALETEX    
I do change my props depending on how I feel I will use the boat. The only caution I have is to not overly reuse the cotter key (if your engine uses one) and if you are doing the change the prop while the boat is in the water be sure you have a spare for everything that attaches to the prop shaft. For my engine this includes the cotter key, the prop nut, washer under the prop nut, prop, the thrust washer behind the prop, the pliers to remove the cotter key, and the wrench or slot pliers to remove the prop nut. Over the years I have dropped or tried to drop all of these parts overboard changing a prop whether I was changing it for performance reasons or because I had hit something and damaged the prop. My caution on the cotter key was a lesson learned the hard way when I was in college. I lived in an apartment without a secure area to park my boat so I would take the prop off and carry it inside. I had reused the cotter key 15-20 times trying to save a little money and ended up feeding the prop and all the hardware to the fish one afternoon when the old cotter key finally failed. I now keep a bag of standard stainless cotter keys and only use them once or twice before installing a new one. I still save the old ones just in case I get real clumsy.
5 mi E of Milwaukee posted 08-06-2003 09:24 PM ET (US)     Profile for 5 mi E of Milwaukee  Send Email to 5 mi E of Milwaukee     

I change my prop back and forth all the time.

I got one of the four bladed plastic replacement props with two inches less pitch than my "running about" prop for trolling because it gave me more precise control of slow speeds since I can move the throttle some off the stop. Out on Lake Michigan I rarely see WOT anyhow, so there's not much danger of over revving without beating myself silly. In fact, I have a dedicated prop changing wrench on the back garage wall, so the proceedure no longer even entails a trip to the tool box.

Maybe it's my imagination, but either the four blades, or the plastic construction, helps smooth the perceived engine pulses at slow RPMs. (Does anything sell four strokes as much as trolling? In the name of science, I'd sure like to hang one on the back of my Montauk and compare it to my "classic" 90 hp Merc. Might be hard giving it back tho...)

--scott

Tom2697 posted 08-08-2003 02:35 PM ET (US)     Profile for Tom2697  Send Email to Tom2697     
With small boats and small engines, heavy loading will destroy your performance. Consider this, say your boat (with just you) weighs 1500 lbs and you have a 90 hp engine. Your weight to power ratio is 16.7 lbs/hp. Now load you boat with 4 more friends (@ 200lbs each) and your ratio goes to 25.6 lbs/hp. To lower your ratio back to original, you would need a 140 hp engine. Understand my point? Changing props to match conditions such as these is definitely a good idea! On the bigger boats with massive engines, a few extra pounds does not matter nearly so much. You might even want to consider a smaller pitched prop than you originally thought...
where2 posted 08-13-2003 12:43 PM ET (US)     Profile for where2  Send Email to where2     
15' Whaler with 70HP OMC, Prop choices: 13-1/4"x19"SS cupped, and 13-1/4"x17" Aluminum cupped. Uses: Aluminum for skiing, SS for cruising. Hole shot on the SS with a slalom skier is very poor, however top end pushes 50mph with solo operator. Hole shot with Aluminum is acceptable for slalom skier, and top end goes beyond recommended RPM for WOT. Yes, I swap props...

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