Propeller Choice on 2005 Chaparral 180ssi at high altitude

[sms1976]

I have a 2005 Chaparral 180ssi that will be mostly operating on a lake at 6400 feet in elevation, but sometimes on a lake at 3700 feet. The boat has a Volvo Penta 3.0GLP-C with SX outdrive and currently has a Michigan Wheel Vortex 4 blade 14x20 prop (992204) that is dinged up pretty good. I am working through the process of re-jetting and other carb adjustment(s) for the high altitude would like to find out three things:
1. What is a good starting point would be for that boat, which will be less powerful than its prior life at sea level?
2. Is there a difference if we want to pull a tube or a wakeboarder?
3. Does that propeller have a hub that would allow for easy prop changes if I stick with Vortex?

Thanks everyone! This boat is about ready to have some fun with (I hope).

 

[imrem]

I bought the turning point hub today with a 14x13 prop for my dad's (now mine) old '75 Glastron v-179. It has the volvo penta AQ130C/270. I am also at altitude running on lakes between 5000-8500 ft.

If you have an opportunity, I would suggest getting the standard setup on the lake to do some performance tests to see where you are at now then adjust based on those numbers. My dad ran the boat at 2500 feet with a 14x15 prop which pulled tubes and skiers fine and could hit the 5100 RPM redline no problem.

I had it out at 8500 feet last weekend and at WOT with a light load achieved 27 @ 4500 RPM. Same weekend I had it at 4600 feet and it did a little better 28 @ 4700 RPM WOT light load, but barely 15 @ 3600 with a full load and couldn't get up on plane or pull a tube or skier (unless it was skier, spotter, driver only).

I am dropping to a 14x13 which at 4800 RPM (cruise RPM) should give me 25-26 mph which is fine for me and will help pull a tube and skier.

mercury racing website has a prop slip calculator that calculates any value you want from RPM, slip, speed, pitch, etc. very useful.

 

[fishrdan]

You need to figure out where you are to get a good recommendation on where to go. Do you know the WOT RPM of the engine with it's current prop, with a lightly loaded boat, at what elevation?

You want to shoot for the top end of the engine's RPM range (4400-4800RPM?) since the engine will be down on power, 6500' is about 18% loss. I would stick with a 4-blade prop for hole-shot. If I had to offer up a SWAG on prop selection, I'd go for a 16P 4-blade (or a 17P 3-blade), though I bet you'll have to watch your RPM at 3700'.

Does Volvo offer up recommendations on rejetting the carb? I have a Merceuiser 140HP, basically the same engine with a different carb, and they say to not monkey with jetting up to 5000', and if you re-jet don't go down in elevation unless you re-jet. Rejetting is a pain, so I'd jet for 4000' and deal with the rich condition at 6500'.

Sorry for not being specific as I don't have the exact same boat, and your rig will probably run different than mine does.

 

[sms1976]

I went ahead and jetted for 4000' today for a closer lake at 3800' and the boat ran pretty good. The Volvo Penta guideline is to reduce one jet size per 2000' of altitude, so I went from 72 to 70 on the Port Main Jet, and 71 to 69 on the Starboard Main Jet. I didn't do any other changes but I did double-check to make sure the accelerator pump was not clogged. That was confirmed by gas all over my neck and shirt.

Still a bit of a stumble as it accelerates but I was able to get up on plane somewhat quickly and even pull a tube with a couple of kids on it. That's two adults, 3 kids, so medium load of around 600 lb. including gear. I have a digital tach/timing light and used a GPS speedometer. We were at 4650 RPM and consistently at 35 to 36 MPH, adjusting trim for fastest speed at WOT. It's hard to say how dinged up that 14x20 4-blade prop is, but it has a football shaped chunk about 1/2" x 2" out of one tip and some other smaller dings.

Anyone want to take a stab at what prop would be good on this boat? Or is there a better way to calculate that? I've heard to stay with a 4 blade on that boat and it will be up at the 6400' lake almost all the time.

Lastly, is there something that will stop this motor at redline (fuel cutoff or something)? I ask because the built-in tach is off (read ~3200 when it was at ~4600) and I don't want to have the digital one hooked up all the time.

Thanks for your help!

 

[Scott06]

On a 17 ft Sea Ray with mercruiser 3.0 I used an 18" vortex 4 blade for general use and tubing, a 16" vortex 4 Blade for skiing, at 600 ft elevation. This was with a 1.98 ratio in the drive, not sure what yours is as this will affect needed pitch. The 18" would hit 4600 maybe more if lightly loaded, 16" would over rev 5000. I always thought the vortex props worked great, an excellent value. I'm 260 lbs and it would pull me up no issue with a couple passengers, tubing with the kids I'd have 2 on the tube and 4 in the boat, that 3.0 would be at 4400-4800 for an hour straight. Amazed me how tough the 3.0 is, didn't owe me a thing after 20 years...

Be honest at altitude your numbers look pretty decent for the size boat/engine. At sea level and lightly loaded I don't think I did much better than 38 may be 40 or so in a smaller boat (2300 lbs dry).

No way a nick out of the prop that big isn't hurting you. If you want more holeshot at altitude try an 18" vortex, if you have a local prop shop they can fix you 20", hubs interchange so you can swap props depending on use and altitude. You can also buy the plastic hub sleeve separate from the hub kit for like $20 so you don't have to knock it out each time.

Don't know on the rev limiter works assume there is one but you might post that in the VP section for a clear answer.

 

[sms1976]

I forgot to add that my drive ratio is 2.18:1. I found that Michigan Wheel makes a Vortex that is 14.5 x 18 that is the next step down in pitch. From the formula I found over at the Chaparral forum:
[FONT=&quot]Pitch / Drive Ratio x RPM X 60 / 12 / 5280 x Slip Factor (actually 100%-Slip Factor%)
I am getting a slip factor of about 11% based on my digital tach reading of 4650 RPM and GPS speed of 36 MPH. That seems pretty good (too good?) for a dinged up prop based on what I've read. That was at 3700' so I decided I should do that test again, lightly loaded at the 6400' lake where I'll be spending most of my time. I'll hopefully be able to do that this weekend.

I'm really interested to know what the stock prop is for that boat, but can't seem to find that.

Thanks everyone for your help![/FONT]

 

[fishrdan]

You're right in the ballpark at the 3800' lake, I wouldn't change a thing except for repairing the prop. The 6400' lake is most likely going to be another story, and you'll need to drop pitch for best performance. 18P 4-blade that you found should work well.

I'm running a 14.5x18P 4-blade Alpha4 prop that's a fantastic match for my boat, strong hole-shot and lifts the stern out quickly. I run also run 16P 4-blade Michigan Vortex when needed (heavy load or altitude) and don't like how the prop lifts the bow high for a couple seconds before getting on plane. The Alpha4 seems to quickly pop the boat up on plane level, while the Vortex pops the boat on plane quickly with the bow pointing to the stars...

Check the back of your tach as it may be set to 6cyl or 8cyl.

 

[Sea Rider]

Before playing with less pitch props, engine needs to be re jetted for high altitude boating. Check if there's altitude kits for that engine. Usually comes in 3K Ft increments, then go for a prop maximization. If that combo will be taken back to sea level operation will need to re jett it back again along propping it right for sea level operation.

Happy Boating

 

[jkust]

That is one of the great benefits of the MPI engines...no rejetting. The good news is that that Chaparral is a holdover of their SSE line from several years prior which for that boat then became the 180SS then the SS badging was ditched by Chaparral for the SSi moniker though it weighs 1000lbs less than the actual 18 foot SSI known as the 190SSI which was called the 183SS (which were 18'3 inches) for two years being 2002 and 2003. The 190SS and it's previous name the 183SS also had a 3 liter option though they were 3000+lbs and struggled with a 3.0 but did well with the 5.0MPI optional power. Point being be glad you don't have one of the much heavier 18 footers and a 3.0 at high elevation.
The stock prop was whatever the dealer outfitted it with, generally would have been an aluminum Black Max which is a no frills prop. Betting it would have been a 19".

 

[sms1976]

Thanks everyone. The next boat I get will definitely be fuel injected since I go between these different lakes. I was able to do a run on the higher lake, still with the dinged up propeller, and we got to 33-34mph at 4450 rpm, with pretty slow acceleration and it took awhile to get up on plane. I'm not feeling too bad about that but I think I will try that next Vortex 14.5" x 18P. I don't see a way to make that timing light change from 4- to 6- to 8-cylinder mode--just 2- or 4-stroke mode--so that must be okay. Cylinder 1 should fire the same number of times per rev no matter how many cylinders, right?

That was also still jetted for the lower lake to see how that would go, and it seems like I need to re-jet. When we were sitting still, the exhaust was pretty smoky. I couldn't find my plug wrench so I couldn't look at the plugs, but next time I think I'll try the jets for higher altitude.

 

[fishrdan]

The switch (8-6-4) should be on the back of the tach, tach reads from the coil, so if it's set to 6 on a 4-cyl engine, it would read slow, 2/3 speed.

Re-jetting from the 3800' to the 6500', I wouldn't monkey with it for 1 day... I go for several days when at altitude, so it's worth it to re-jet, performance wise. Boat just feels like a slug until the carb is re-jetted and prop swapped. I've had a couple multi-day trips where I was hopping altitude and just re-jetted for the lowest lake, 5000'. The more times the carb is apart, the more times to mess something up, loose a part, strip threads, wear out gaskets. I don't swap the top gasket every time I re-jet, but if it's been a couple of years I'll replace the gasket.

If you were running 4450RPM with the 20P prop, the 18P should put the engine at the top of it's WOT RPM range, which is a good thing.

 

[Leardriver]

Part of the slow acceleration is the lower power output at altitude, and all your prop can hope to do is get whatever HP is left to propel you.

My boat uses a 26 pitch Bravo III at sea level, 24 pitch at Lake Powell, 3600 feet, and 22 pitch in Colorado at 6000 feet. If I were to make some kind of chart, it would show one degree of pitch change for every 1500 feet of altitude, or 4 degrees for 6000 feet change.

I have all of those expensive props, because your boat is a pooch without the correct prop, and boating days are too valuable to accept good enough as the standard.

 

[sms1976]

fishrdan, that was the problem on the tach; I had thought you meant on the shop tach, but your follow up made it clear. Thanks for that tip! With less loading and a half-full tank of gas, the boat performed much better at the higher lake. I will still try that vortex 14.5" x 18p soon since that should help with the early acceleration, but overall I think the boat is shaking off some of its rust/cobwebs as it gets some more time on the lake.