Author Topic: Choosing the right prop... a different kind of problem  (Read 254 times)

Racklefrack

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Choosing the right prop... a different kind of problem
« on: March 09, 2018, 05:13:50 PM »
Boat info: 2012 MX185 / 4.3 MPI 220 hp / 1.81 Alpha One / 23P prop

As this boat is new to us, we've been trying to dial her in for how we'll use her. It'll most often just be my wife and I, full fuel and very little equipment. I originally questioned the wisdom of putting a 23P prop on a 1.81 stern drive, but a conversation with Glastron helped me figure it out why they did: The boat was originally purchased in Colorado at about 4500' elevation... hence the 1.81 drive and 23P prop, to make up for the altitude.

But for here at most lakes in AZ, 23P might not be optimal. It seemed like it was performing ok, though it felt like it might be struggling at slow-to-mid speeds just a little bit. It popped up onto plane ok under near-full throttle, but to hold 20-25 mph seemed like it was chugging a bit. I was thinking of either dropping down to a 21P or going to a 4-blade 23p, but...

Unfortunately, we're also simultaneously experiencing an issue with the tach reading way too high so I don't know what WOT speed and rpm readings really are so I can't tell for sure what pitch the prop should be. I made a new post about the tach problem separate from this one, so I'm still working on that part.

So here's the real problem:

I just chewed up my prop on the bottom of the Colorado river. I can't run it like it is and I really don't want to spend the money to fix it -- especially if it's not even the right prop -- since it's just an aluminum screw. Instead of spending $120 to fix the prop and a new hub system, I'd much rather just buy a new Spitfire 4-blade for $160. The question is, what pitch?

I need a new prop, no doubt about it, and a spare prop isn't the worst idea. I'm not totally against the idea of buying both a new 21P and a 23P and use one / keep one for a spare, but it's not exactly the smartest use of money. So, if this were your boat and you had a busted prop, a malfunctioning tach and no idea what the pitch should be, what would your next step be?

I know, it's a mess. I appreciate any input you might have.

Thanks!
2012 Glastron MX 185, 4.3 220HP
2004 Newmar Mountain Aire 4302

Merlin16

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Re: Choosing the right prop... a different kind of problem
« Reply #1 on: March 12, 2018, 04:12:36 PM »
It's really tough to answer your question without the proper tach readings. Your first step should be to figure out the tach. If you've confirmed the setting on the back side, the only other thing is to check all the connections.
Then tackle the prop issue, but since you can't run the original prop to check rpm's, again, you're going to be guessing.
And for trivia, is your elevation higher or lower than the 4500' in Colorado?

FWIW, I've been using the Nemesis 4 blade aluminum and happy with the performance.
2016 GTS 185
4.5L MPI 200hp
Phantom Grey w/Sunburst Orange

Racklefrack

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Re: Choosing the right prop... a different kind of problem
« Reply #2 on: March 12, 2018, 09:20:50 PM »
It's really tough to answer your question without the proper tach readings. Your first step should be to figure out the tach. If you've confirmed the setting on the back side, the only other thing is to check all the connections.
Then tackle the prop issue, but since you can't run the original prop to check rpm's, again, you're going to be guessing.
And for trivia, is your elevation higher or lower than the 4500' in Colorado?

FWIW, I've been using the Nemesis 4 blade aluminum and happy with the performance.

Yeah, I know it's tough... it's why I came to the experts for help! I was really hoping it was just me and that someone here would have a better idea :)

I fixed the tach today. Well, "fixed" might be an overstatement... Mercury confirmed for me that the engine is programmed to idle at 625 in neutral / 650 in gear. The "correct' setting on the back of the tach should have been 2 but on that setting it read idle at 1000. The next couple settings were either too high or too low, but setting number 6 read the idle speed perfectly, so I left it there. The next time I take it in for servicing I'll have it double checked and calibrated, but this should be close enough for prop purposes -- assuming it reads higher rmp's as accurately as it does idle.

I'm fixing the 23P I dinged up to use as both a starting point to figure out rmp/WOT and to use as a spare after I buy a new prop. It's only $65 to fix; that's a lot cheaper than spending $150-$300 on a prop that might not be the right pitch and probably wouldn't be returnable. I know the 23p works, I just don't think it's optimal... it'll make a fine spare.

We're much lower than CO. We boat on lakes Havasu, Mohave and Mead which is the highest at just under 1100 ft. The lower Colorado River between Laughlin and Lake Havasu is where I dinged up my prop. They'd let the river run much lower than the release report lead me to believe... it was 2 1/2' when it should have been closer to 5'. Lesson learned :)

I'm leaning toward the nemesis/Spitfire 4-Blade as well, the only question is pitch.

Thanks for replying!
2012 Glastron MX 185, 4.3 220HP
2004 Newmar Mountain Aire 4302

The Canadian Guy

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Re: Choosing the right prop... a different kind of problem
« Reply #3 on: April 30, 2018, 04:39:21 PM »
I have a 2006 SX 175 and recently put on a 3 blade PIRHANNA prop.  It's made of carbon fibre and I bought it from Canada Prop here in Ottawa.  It's an awesome prope and comes with three spare blades that cane be changed in the water without having to remove the whole prop, just the damaged blade.  If you get a chance, check them out, you will not be disappointed I got an extra 5mph out of my boat with it.  The blade also has some small ribs in it to help efficeiently feed the prop more water.  I use a 21p and my boat tops out at 47 mph (engine 135hp) with the Pirhanna Prop 42 without.

I've tried to attach pics here, but with no luck.  Send me your email and I will be happy to send you a picture.

Safe boating,
Marc
2006 SX 175
Lives In Ottawa, Canada