Help with best Prop for Alpha 1 Gen 2

[CJ0920]

Hi all, I have a 1992 Chaparral 1800SL with the 3.0 Mercruiser and an Alpha 1 Gen 2 outdrive. Purchased the boat early spring (first boat) and took it out a few times. It had a new 15"x17P Michigan Wheel XHS aluminum prop on it the previous owner put on but never tested it out.

Took it out 2 times and at WOT his about 38mph and was in the mid 4k RPM ranges. It took for ever to plan off and at one point had to have a buddy sit up in the bow to get it to plane off. During this time didn't really pay too much attention to the RPM as I was already overwhelmed with being new to boating.

Second time out, hit something probably a rock and completely damaged the prop making it unrepairable. We limped back to shore. Searched around and was recommended by a local shop to switch up to a 4 blade. So I purchased a Quick Silver Diamond 4 blade aluminum 14"x18P. Took it out and noticed it planed off much nicer and liked the performance of it, however was noticing some sputtering from the engine every so often on acceleration. Also noticed lower RPM at WOT and reduce in speed.

I had the carb rebuilt and looked over, so its running much better. Took it out again and noticed my max RPM is about 3800-3900 trimmed up. Am I over propped? It feels like this prop is much smoother than the previous 3 blade as there is no vibration when trimming up, and now takes a few seconds to plane off, however just worried my WOT RPM's are really low. Any suggestions on what prop to try next?

Thanks in advanced!

 

[steelespike]

Re: Help with best Prop for Alpha 1 Gen 2

Sorry to here about your prop. Your numbers don't quite add up.Of course your original rpm may not be accurate.
Is your speed by gps?The only way to be sure it is accurate. The calculator says that with a 17" prop with a 2.00 gear ratio
the motor is turning about 5300 at 38.Not good I believe your wot rpm should be around 4800.
It would be normal for your motor to over rev with a 17" prop. When going to a 4 blade prop it is normal to reduce pitch 1 inch.
You need to verify your tach. Get us your wot rpm and gps speed with the 18".
With a 1.94 ratio 17" prop the motor is turning 5200 at 38 mph. Slow planing with a 17" is troubling
doesn't go with a 17" that struggles to plane?
It should jump up with a 17".With the 18" you increased blades and pitch on a motor that is all ready struggling with a 17" prop'
We need you to again test the 18" 4 blade get us the lightly loaded wot rpm and gps speed.

 

[CJ0920]

Re: Help with best Prop for Alpha 1 Gen 2

No the 3 blade did not rev up that high. I believe at most I was at about 4600 at its max range (4200-4600). 38 was verified with GPS on my phone and my gauges are pretty accurate.

With the the 4 blade 18 pitch, I can not hit 4k rpm but sort of close. Figure I'm about 3850 rpm and about 30-32 mph. I have not verified my speed via GPS with the 4 blade.

I don't think this is a 2.0 gear ratio, from my research I thought it was a 1.94.

 

[CJ0920]

Re: Help with best Prop for Alpha 1 Gen 2

Suggestions?

 

[jestor68]

Re: Help with best Prop for Alpha 1 Gen 2

Adjust based on 150-200 rpm change per inch of pitch. You obviously need to go down in pitch with the 4 blade.

Sticking with the same brand, material, and number of blades makes things more predictable.

 

[Slip Away]

Re: Help with best Prop for Alpha 1 Gen 2

And, Michigan Wheel does not make an Aluminum XHS propeller. The XHS II is their hub kit for the Vortex and old Rapture (SS) propellers.
You might like a Mi Wheel Vortex 15 x 16p 4-Blade Alum. Part # 992202.

 

[CJ0920]

Re: Help with best Prop for Alpha 1 Gen 2

Your right the old prop was a Michigan Vortex.
What about other brands?

Another question, if I wanted to switch to a stainless prop what recommendations would I be looking at?

 

[CaliBoatBoy]

Re: Help with best Prop for Alpha 1 Gen 2

Hey there, I've done a ton of research. And something is not adding up here. Your original prop was a 3 x 17" Going to the new 4 x 18" should have only cut your RPM's by 200-400RPM maximum. What you reported was an RPM drop from 4500 to 38-3900RPMs? YIKES.

The normal rule of thumb is when you go to a 4 blade, drop DOWN in pitch 1". So really, you should have purchased a 4 x 16" prop, if not even a lower pitch like 14". It will most commonly be a 14.5 dia prop. The diameter diff should not and will not have a dramatic effect.

If you want hole shot and you aren't trying to be a speed boat (or you should have purchased something else) you need to pitch down and go to a 4 blade.

For example: My boat is a Wellcraft Eclipse 182S with the 4.3 V6 Alpha One outdrive. Stock prop is a 21 pitch prop. AWFUL however, I do get almost 50 mph with two people trimmed out WOT. My "cruising" prop is a Stainless Steel 19" and I use the Attwood Hydrostabilizer. Works pretty good with 4 people, with 8 it is a little slow on the hole shot. I just ordered a 4 blade 17" Solas Amita prop and I will gladly report back in.

Hope this helps some. I am still getting used to NOT having my Moomba :-(

 

[CJ0920]

Re: Help with best Prop for Alpha 1 Gen 2

Thanks for the info. I agree in dropping in pitch. I've been playing with a prop calculator online. I went with the 4 blade 18 pitch as a recommendation from a local shop. He told me a 15" diameter is too much for the 4cyl and is better on a 6 cyl. He also mensioned that the boat probably came with a 19 pitch prop. So I took his suggestion. I thought about returning it to him after this last time out however I must have hit something in the water because there is an inch of paint chipped of two of the blades. Nothing is bent but it is now considered used I guess.

 

[CaliBoatBoy]

Re: New prop test results

Re: New prop test results

As promised, I received my new prop today. The Solas Amita 14.5" d x 17 pitch 4 blade. I left work early and waited around. Removed the SS prop, greased the spline, hooked up the boat packed and made my family sit and wait on UPS to arrive. Well, they showed at 5:20p and by 5:27p we were on our way to Whiskeytown Lake.

From the get go, away from the launch, I could tell she had more torque and *****. Luckily, where we put in, the no wake is approx 100 yards.

I had my wife up front, (120 lbs and my son 105 lbs) and my daughter (65 lbs) to the left of me (220 lbs).

I slammed down the throttle and O>M>G>! It was AAAALLLLIIIIVVVEEE. We were on plane in less than 3 sec and I was quickly approaching the Max RPMs of 4,800. I pulled out my trusty iPhone and Speedometer App and we saw 36 mph, 4,800 RPM. I easily had more however, I chose NOT to ruin my motor. This is a drop of 5 mph with my SS 19 pitch. I slowed, sped up, cut corners and basically felt like a Porsche on rails at LeMans. It was so responsive!

Next, the true test. My wife and son (225 lbs total) on a tube. Ripped them right out, took deep corners, slowed, sped up etc, boat and prop were flawless.

Quite honestly, I could not be happier. I seriously considered putting the boat up for sale to get a straight inboard. Now that said, I probably could have gone with the 18 pitch instead to keep a couple mph on the top end but my hole shot is reminiscent of my dads Moomba. Not bad for a 4.3 V6 ehhhhhh?

 

[CJ0920]

Re: Help with best Prop for Alpha 1 Gen 2

Update, dropped down to a Michigan Wheel 4 blade 15x16p and now the motor is running much better. Engines recommended max range is 4200-4600 and she is now running about 4300rpm trimmed up a little bit. Gets on plan nice and has a pretty good top end speed. My speedo seems to be not working so haven't been able to verify my speed yet.

I did snug something again I've been told to just file down the ends a bit and I should be good. I seriously need a depth finder....

 

[CJ0920]

Re: Help with best Prop for Alpha 1 Gen 2

So filed the blade down a little with a grinder to smooth out the rough edges. Took her out, and was running great. Saw 35mph via GPS with 4 adults on board running about 4100rpm. Ended up snagging something else again! FML.

Was able to finish up the day on the water, but now thinking I should just keep this as a spare, because there is a slight vibration probably due to it off balance a bit.

So the equivalent 3 blade Michigan Wheel prop (aluminum) 15x17 ran great. Only issue is planning off and vibration when trying to trim up a bit. Was seeing 38mph. Would have to lower the trim all the way down and leave it there to not have any vibrations. The 4 blade Michigan Wheel prop (aluminum) 15x16 ran nice and smooth when trimming up, but also probably lost a few mph. Planned off really quick. A quick silver diamond 4 blade 14.25x18 (aluminum) prop dropped rpms down to 3900 and felt like it was bogging down the motor. Lost a lot of speed, and could barely do 30mph. Hub on that one was much longer and looked more aggressive than the Michigan Wheel prop.

Question, is it worth looking at a stainless steel prop? If I were to go to a ss prop 3 blade what size should I be looking at? Would it get better top end speed?

Thanks for your help.

 

[craze1cars]

Re: Help with best Prop for Alpha 1 Gen 2

So filed the blade down a little with a grinder to smooth out the rough edges. Took her out, and was running great. Saw 35mph via GPS with 4 adults on board running about 4100rpm. Ended up snagging something else again! FML.

Was able to finish up the day on the water, but now thinking I should just keep this as a spare, because there is a slight vibration probably due to it off balance a bit.

So the equivalent 3 blade Michigan Wheel prop (aluminum) 15x17 ran great. Only issue is planning off and vibration when trying to trim up a bit. Was seeing 38mph. Would have to lower the trim all the way down and leave it there to not have any vibrations. The 4 blade Michigan Wheel prop (aluminum) 15x16 ran nice and smooth when trimming up, but also probably lost a few mph. Planned off really quick. A quick silver diamond 4 blade 14.25x18 (aluminum) prop dropped rpms down to 3900 and felt like it was bogging down the motor. Lost a lot of speed, and could barely do 30mph. Hub on that one was much longer and looked more aggressive than the Michigan Wheel prop.

Question, is it worth looking at a stainless steel prop? If I were to go to a ss prop 3 blade what size should I be looking at? Would it get better top end speed?

Thanks for your help.

As you've already experienced, a 3 blade will increase vibration and decrease holeshot. If that's a good trade-off for you, it might gain 2 mph at best. Keep in mind you have a 115 hp motor (unless you have a 3.0 LX, which you did not say), so most likely you have the smaller valved 3.0 that was only produced for a few years in the early 90's, and not the typical 135 hp that most 3.0's actually are. 35 to 38 mph is the most you'll ever see out of that motor.

This is a difficult thread to read. It's a shame CaliBoatBoy decided to throw all of his results right in the middle of yours...I thought you were all over the place at first, then I realized I was reading results from 2 entirely different people and boats!

I think you have flawed numbers and advice cannot be accuarately given.

Using prop slip calculator with your recent reported results:
16 pitch, 2.0 gear ratio, 4100 rpm loaded, 35 mph....that equals NEGATIVE 13% slip. Not mathematically possible.

Change your ratio to 1.94 and you have NEGATIVE 9% slip. Again not mathematically possible.

So something is wrong. And if it's your tach, it means you are ALREADY spinning about 4800 rpm with a full load (which brings you to 7% slip...entirely possible), and my most likely recommendation to drop to a 15 4 blade will cause you to substantially over-rev your engine.

Now your other results, 18 pitch, 3900 rpm, 1.94 ratio, 30 mph...equals 12% slip. This is a very realistic figure. But why it is so inconsistent with your reported results from the 16 pitch I cannot understand.

You didn't share your rpm with the 17 pitch so can't check that one. And you didn't get a speed when you ran the 16 pitch with lighter load at 4300 rpm, so can't verify that run either.

I suggest you personally/physically verify your outdrive gear ratio...turn the motor by hand while someone counts the propeller revolutions. Outdrives are swapped out regularly and your boat is now 21 years old and could have anything slapped on it, so any research is meaningless...just verify it by physically counting. And also test your tach with another known good tach. It is an indisputable fact that something is wrong with your data from the 16 pitch test (unless you dinged it in such a way from hitting something that you actually added a couple inches of pitch to the prop), and it is not possible to give safe/good recommendations with bad data.

 

[CJ0920]

Re: Help with best Prop for Alpha 1 Gen 2

Craze1cars, I agree this thread has bounced around a bit.

To get back on point. I know for a fact I don't have a 2.0 gear drive ratio. I had a shop look at the serial numbers and he knew the gear ratio and I believe we were at 1.94 as you stated. Everyone said the 18p blade should be just about right on this boat, but when I took it out with my wife and two small kids (2,7) and it felt like we were dragging something behind us. I had the carb rebuilt and the engine looked over by the same mechanic.

Now since then, my gas gauge has not been reporting in and my speedo stopped working. I've been using my phone for the gps speed. I forgot to bring my docking holder for my phone these two times and was hard to watch the phone when looking at the water. That said, the 3 blade 17p, ran fast. The first time I took it out was our first time on the water so I was more focused on saftey than the rpm. The second time was when we ruined the prop. So I didn't get great data from that run. But I remember looking at the rpm gauge and seeing it 44-4500ish rpm.

 

[CJ0920]

Re: Help with best Prop for Alpha 1 Gen 2

How do I verify my RPM gauge is accurate? It seems like its fine but with the gas and speedo gauges all of a sudden not reporting in, kinda leave me a little suspicious.

Craze1cars...my 3.0 is in fact the 115hp, which is why reading everyone else's suggestions or experience is different because they are most likely running the 135hp...The boat is 18' and weighs 2100lbs dry and has a 19 gallon tank.

 

[craze1cars]

Re: Help with best Prop for Alpha 1 Gen 2

How do I verify my RPM gauge is accurate? It seems like its fine but with the gas and speedo gauges all of a sudden not reporting in, kinda leave me a little suspicious.

Craze1cars...my 3.0 is in fact the 115hp, which is why reading everyone else's suggestions or experience is different because they are most likely running the 135hp...The boat is 18' and weighs 2100lbs dry and has a 19 gallon tank.

Verify by hooking up another known good tach. I have an Actron multi-meter/engine analyzer with a tach feature, they're usually $50 or less. Point-n-shoot optical tachs are available on Ebay for less than $20 shipped and very accurate, but you have to point it at a reflector you stick to the flywheel under motion while someone else drives...sometimes difficult/sometimes not depending on your boat/motor configuration.

I once owned a boat like yours. Same 115 hp motor, roughly same size/weight boat (mine was a 1992 Rinker 181). I remember it obtained best performance with a Hustler Turning Point 3 blade aluminum 17 pitch. Mine had a 1.98 gear ratio. With that prop it would run 4500 to 4600 rpm all the time with normal load, and could do about 36-ish MPH on GPS. Holeshot was excellent it had no problem pulling 200 pound slalom skiiers out of a deep water start in about 4 seconds. I never tried a 4 blade on it, as I was very happy with the Hustler. So that might be worthy of trying since they don't cost all that much, but my experience with it on a different, but very similar boat, might be entirely irrelevant. 17 pitch Hustlers have smaller diameters and are much more aggressively cupped and raked than 17 pitch Michigan Wheels. So the Hustler will probably bite the water better and spin slower than a Michigan Wheel.

 

[eavega]

Re: Help with best Prop for Alpha 1 Gen 2

How do I verify my RPM gauge is accurate? It seems like its fine but with the gas and speedo gauges all of a sudden not reporting in, kinda leave me a little suspicious.

Easiest way is to run your motor with a good shop tach or an optical tach. That will verify if your dash tach is inaccurate.

As to switching to a SST prop, it may be a good idea given that you have dinged up a couple of Aluminum ones. The SST will be sturdier than Aluminum. The recommendation I have always been given is to step your pitch one inch down for stainless steel .



Rgds

Eric