Replacing A Michigan Wheel Rapture

[AguaSki]

I just returned from picking up my boat at the local J/E dealer after having my spring maintenance completed. The first thing I noticed was that my 1 year old Rapture prop was missing. The prop was in new condition and had no dings or scratches. After questioning the owner and the mechanic that worked on the boat, it was determined that a thief must have reached through the fence to where my boat was parked to steal the prop. The owner is a stand-up guy and offered to replace the prop at no cost to me. After he made a few calls, he could not find another Rapture. He told me that he would make some more calls, and also said he would reimburse me if I was able to find a prop on the internet. He was also open to replacing the prop with something other than a Rapture. So now the research begins.

I don’t see a Rapture here on Iboats, but I do see Apollo and Stiletto. I seem to recall from a previous thread that Michigan Wheel was replacing the Rapture with the Apollo line-up. Is that correct, and is an Apollo prop an equivalent replacement? To be truthful, I was not happy with the performance of the Rapture, but because the shop owner has been good to me in this instance, and previous instances, I don’t want to take advantage of him in this situation. I only want a prop of equivalent technology as the Rapture. I figure it is shops responsibility to replace what was stolen on their property, and it is my responsibility if I want a prop that is above and beyond what I already had. Any thoughts on where to find a Rapture or something of equivalent technology?

These are the details on what I had:

• 15 pitch Rapture
• 140 hp Johnson, 1978
• Glastron SSV-188, 1978
• WOT RPM 5,280 (I have had 3 tach’s in the last year and all had the same reading. The current tack is a digital OMC.)
• 37 mph verified by GPS
• Smart Tabs
• The motor has been raised two holes, I have one hole left to go if needed
• Good hole shot for skiing and tubing
• The boat is mostly used for water sports

My RPM’s are too low, so this may be an opportunity to correct things a bit.

Please share thoughts on what might be a suitable replacement prop that will be fair to me and the shop owner.

 

[walleyehed]

Re: Replacing A Michigan Wheel Rapture

i'D SAY GO WITH THE STILETTO IN 15 BUT YOUR r'S ARE TOO LOW, AND WITH THE ENGINE IN THE THIRD HOLE, SOMETHING IS WRONG...
Sorry for the caps...I know that boat well...had 2 of them with the same engine as demos...we ran 15P's on both at about 5600RPM. I feel you have some possible engine trouble there.....we run 13P's on 115's/24ft pontoons and get 5500-5600..something else is wrong...I gotta think on this a bit.

 

[AguaSki]

Re: Replacing A Michigan Wheel Rapture

Before I took the boat in for the maintenance I checked the compression. All four were 120 psi. I received the same report with the annual maintenance. I also have been thinking something is wrong with the motor, but the motor runs really well. It starts right up and idles at about 800 rpm. There does not seem to be anything obvious with the way the motor runs.

FYI - The motor was rebuilt with a new power head in the spring of 2005. I purchased the boat from this same shop immediately after the rebuild with a 1 year warranty. The shop that rebuilt the motor is also a J/E dealer. I followed the break-in procedure exactly. Because the motor is technically new, and it runs so well, I keep coming back to my tach as the problem, but now that I am on my third tach, I don't know that a fourth tach will be any different. The shop also verified that my tach was within 100 rpm.

 

[walleyehed]

Re: Replacing A Michigan Wheel Rapture

I don't want this to sound like a stupid question...but 100RPM off from what? 1000RPM...6000RPM?
Anyway...I don't think the tach is the problem...
What altitude are you running at...you may be higher than I think...

 

[AguaSki]

Re: Replacing A Michigan Wheel Rapture

Yeah, I am not sure exactly what the 100 rpm is. I don't even know if I was over or under the shop tach. This shop does have a nice test tank that has been dug out of the ground and lined with concrete. It is kind of like a bad dirty swimming pool with a ramp entry. The technicians can back the trailer in past the top of the wheels during testing, so it is my hope any comparison of the tach would have been done at a high rpm. I really don't know for sure how my tach was tested against the shop tach.

I run in the central AZ desert lakes. These lakes, including my primary lake, are about 1,700 feet above sea level. I have not taken the boat to Powell, which should be considerably higher. I think the Colorado river lakes on the CA/AZ border are about sea level, but I have not been there with this boat yet.

Is 1,700 feet considered high enough to alter motor performance? I know that I am higher than most boaters at sea level, but I never thought of this as an issue.

 

[98SeaArk]

Re: Replacing A Michigan Wheel Rapture

Aquaski, I work for West Marine and i know we carry them and i was doing a little reasarch earlier at work and we do carry michigan wheel rapture props. you can check them out on westmarine.com and i dont' know exactly what size you need but one of the model #'s for west marine is 6685077 so check it out and let me know what you find.

 

[AguaSki]

Re: Replacing A Michigan Wheel Rapture

Thanks SeaArk. I have a West Marine close by, and I use their website frequently. No offense intended, but I have a lot of loyalty to the Iboats store, and use West Marine when Iboats cannot supply my needs. If possible, the shop owner prefers to replace my Rapture with another Rapture, but if his sources cannot locate another Rapture, an alternative will have to be found. This is how I might get a Stiletto or Apollo, but I think the shop owner will eventually find another Rapture. A new Rapture would be the most fair to everyone, even if I would prefer experimenting with a new prop.

One other thing I did not mention about my rpm's. When I am raising my trim at WOT, I have never had the prop blow out. It sounds like it is getting close, but I have never blown out on a straight run over smooth water. If I go into a sharp turn at full throttle, I do blow out, and have to ease up on the throttle to get hooked again, but no blow out when driving a straight line over smooth water. This has me wondering if I should raise the motor to the last hole.

 

[walleyehed]

Re: Replacing A Michigan Wheel Rapture

That IS an indication of being a bit low yet...If you're not blowing out at full trim in the third hole, I don't think you'll have any water pressure issues in the 4th hole.
The SSV-176/115 and the 2 SSV-188's/140's were all mounted in the second hole, but third would have been better.
At your elevation (1700ft), you've lost about 5% of your sea-level HP. We've played with these quite a bit at 3600ft., and based on that, I'd say you could drop 1 size in main jets...example, if it has 65C's go to 64C's, but before doing so, Make sure the jets that are in it are factory sea-level. Make sure your timing is about 1 deg retarded static....this will put it about 1 deg advanced at WOT max advance.
I ran a 115 set up for 3600ft (2 sizes smaller mains and 3 degs advanced at 700ft) with no trouble at WOT, but I won't tell anyone to set it up that way.
I just think it should be closer RPM-wise with a 17P than it is..and you're running a 15P...should be an easy 5600 with a 15P at 1700ft.
This engine does have the bubble-back exhaust, right?

 

[AguaSki]

Re: Replacing A Michigan Wheel Rapture

Thanks for working with me on this.

I have to admit your advice is a bit above my comprehension, but I do have a manual, and I will dig into this issue. My father is much more mechanical than I, and should be of assistance in trouble shooting this.

I went to the lake today with my spare prop. The spare is a 17p Hustler. The Hustler ran at 5,150 rpm and 39.5 mph. I guess the drop in rpm and increase in speed is to be expected with increased pitch. Probably already known, but the Hustler is aluminum.

Also, what is bubble-back exhaust? The model # is 140TL78C. Not sure if that helps or not.

 

[walleyehed]

Re: Replacing A Michigan Wheel Rapture

The bubble-back is just a round exhaust chamber insted of the flat chamber on the back of the engine between the cylinders..It should look like a drooped "bubble" on the back...just want to make sure someone didn't slip a 115 flat exhaust plate in on ya...
Also, the Hustler is a very hard pulling aluminum prop, but the loss of RPM doesn't show up in speed with this prop.
Your slip ratio figures out to about 7% with the numbers you give....I "think" that's a bit too efficient, and not actual...If the speed is GPS verified, I think the tach is reading about 200-250 low...if the speed is pitot or speed wheel, we can't really figure too close because accuracy of these are usually a bit off.
Any way you could get your hands on an OMC 13-1/4X17P? Or possibly a Stiletto advantage in a 17P?

 

[AguaSki]

Re: Replacing A Michigan Wheel Rapture

I think I have the bubble-back exhaust. See the picture below.

All speed is GPS verified. Technically my GPS says my max speed was 41 mph, but I never saw it, and 39.5 mph at 5,150 rpm seemed to be the most consistent reading I saw. This was also across some really smooth water.

Since I am already working with my shop to get another prop, I will see what I can do to get an OMC or Stiletto to replace the missing Rapture. I may have to kick in some extra $, but thats OK.

I am also going to look into my main jets and timing. How do I tell if my jets are factory sea level?

 

[walleyehed]

Re: Replacing A Michigan Wheel Rapture

A factory service manual for that year and model will give the specks on jets, timing, etc...
If that's GPS speed, the tach is off, or the prop has been worked/reworked. I just feel like 7-8% slip is too low for that prop.
The only way to know for sure is to run a prop of known pitch in excellent condition, and with 1700ft in this equation, I think something in a 15P needs to be tested.

 

[AguaSki]

Re: Replacing A Michigan Wheel Rapture

I purchased the spare Hustler prop new from Iboats, and only used it once before my most recent outing. Because this Hustler is new, it is in great condition and has never been worked on. It should be a true 17p. Perhaps I still have a tach problem? The tach is a digital OMC.

I have a Clymer's manual. Not sure if that is the best manual, but it is what I have. The Carburetor Elevation Orifice Chart say's there is an "early" 1978, and a "late" 1978 for the 140 hp. I am not sure which one I have, but the sea level for the "early" 1978 is 61C, and the "late" 1978 is 65C. If I were to guess, I think I have the "early" 1978. Stamped on the back of my hull is "GLA744980377 - 1978 Model". From this I interpret that the boat was built in 1977 (last two digits of the ID), but it was 1978 model. If the motor was rigged to hull at the same time, it would have been done in late 1977 or early 1978. I am guessing here, but the evidence seems to point the "early" 1978. I also wonder if this is part of my problem. Perhaps there was a carburetor rebuild in the past, and the wrong parts were used.

There does not appear to be an early/late differentiation in the timing specifications. Full Throttle Spark Advance degrees BTDC is 28, and Throttle Pick-up degrees BTDC is 0-3.

 

[AguaSki]

Re: Replacing A Michigan Wheel Rapture

Is there a way to tell by model/serial number if this is a early/late 1978?

140TL78C/J4988734

 

[walleyehed]

Re: Replacing A Michigan Wheel Rapture

Mid year changes are hard to track in person, so Here's what I'd do...pull a bowl cover nut off of 1 side of 1 carb and remove the main jet. inspect the sides of the jet until you see the number...get that number and with that amount of variation, we can tell which it is.

Edit: the reason I asked about another prop is because the Hustler gives numbers that don't show with any other prop..it pulls hard, doesn't go as fast as it should for the blade design and it's in a field of it's own...
For best Data, we need a 391198 or 391199 or a 176214 OMC, all of these are alum, and should be a ton of them around...I've got some priceless data on these props.

 

[AguaSki]

Re: Replacing A Michigan Wheel Rapture

I did not have enough daylight when I got home from work to try getting to the main jet. Maybe tomorrow. I added a few props to my Ebay watch list matching the part #'s provided. Most of the auctions have a few days left, and with shipping time it will be about 1.5 weeks before I can get one of the props to test.