The Proper Prop - Chaparral 21' Bowrider

[LambChop]

So, yes, I get it... the proper propeller question is probably the most asked question on any boat forum. But... I'm still going to ask it. What good is a boat forum without a virtual cornucopia of screw threads? Everyone loves to ad their 2? (I've got a mac, so making the "cents" sign is as easy as pressing option + 2) to the prop threads.


First, my current boat specs:

• Year: 1998
• Make: Chaparral
• Model: 2130 SS (Limited Edition - I think that got you some faux wood trim, a compass, and a depth sounder... how does that make it "limited"?)
• Length: 20' 6"
• Beam: 8' 4"
• Engine: GM 305 V8 w/ Throttle Body EFI - 240 HP
• Stern Drive: Mercruiser Alpha One
• Drive Ratio: 1.47 Drive Ratio
• OEM Weight: ~ 3150 lbs
• Current Prop: Mercury 21 Pitch Vengeance 3 Blade Stainless(don't know the diameter)

And the current Performance:

• Full Laden Specs - 6 adults: ~ 1020 lbs
• Gear: 100 lbs
• Full Laden WOT Engine RPM: 4,400
• Full Laden WOT GPS Speed @ 4,400 RPM: 45 mph
• Minimum Laden Specs - 2 adults: 350 lbs
• Gear: 70 lbs
• Minimum Laden WOT Engine RPM: 4,700
• Minumum Laden WOT GPS Speed @ 4,700 RPM: 49 mph

The boat came with a Mercury 21 pitch aluminum 3 blade prop installed. The stainless steel prop came as a spare and was a bit chewed up. I had it reconditioned and tried it on the boat. Performance seemed damn near identical, but at slightly lower RPMS (engine speed probably dropped by 200 rpm with the ss prop). It may have jumped out of the water just slightly quicker (perhaps more noticeable when heavily loaded). The difference certainly wasn't night and day.

When I ran the numbers through a prop slip calculator, I came up with 23%, which seems a bit on the high side to me.

After evaluating my needs, I've decided I want a good balance between top speed, cruising, and watersports. From what I've read, a stainless steel four blade prop is probably the best overall choice. I haven't eliminated the High Five, but it's cost and benefits may not align perfectly with what I want.

Any opinions on how the following props compare with each other (with respect to my hull)?

• Mercury Revolution 4
• Mercury Vensura
• Turbo 2+2 TH
• MIchigan Wheel Apollo XHS 4 Blade
• Solas HR Titan 4
• Other suggestions are welcome...

 

[JimMH]

Re: The Proper Prop - Chaparral 21' Bowrider

I have the Michigan Wheel XHS 4 blade 14 X 20 on my boat. Larson LXI 208, Volvo 5.0 GXI 270 HP very similar size and wieght. I had an Aluminum 3 blade 14.25 X 21. with the aluminum the following were the performance specs:

WOT RPM 4900
Top Speed: 59

4 blade Stainless:
WOT RPM: 4800
Top Speed : 56

Time to plane decreased by about 40% over the aluminum. A big increase in performance for water sports.
The boat also remains on plane at a much slower speed.
I would also suggest Smart Tabs as they really help with plane time and fuel economy.

 

[jestor68]

Re: The Proper Prop - Chaparral 21' Bowrider

My vote goes to the Solas HR Titan 4 in a 20 in pitch.

I am wondering why Jim's Larson 208 is 7-8 mph faster than all the other Larsons of similar size and power tested by Boat Test.COM?

Examples are: LXI 208 with 260 Mercruiser=52 mph. The 206 Senza with 260 Mercruiser=51.2 mph. The LXI 218 with Volvo 280 hp=52 mph.

You may be able to lay claim to having the quickest Larson 208 in Georgia, if not the country.

 

[steelespike]

Re: The Proper Prop - Chaparral 21' Bowrider

I wonder about LCs 23% slip. Is his speed by gps? Perhaps the reworked prop is not so good.
At 10% slip a 21" prop calculates to about 57 mph.

 

[LambChop]

Re: The Proper Prop - Chaparral 21' Bowrider

I wonder about LCs 23% slip. Is his speed by gps? Perhaps the reworked prop is not so good.
At 10% slip a 21" prop calculates to about 57 mph.

I used a GPS speed application on my iPhone to get top speeds.

 

[the riddler]

Re: The Proper Prop - Chaparral 21' Bowrider

I'm definitely not an expert, but I happen to have the same boat. Mine is a 1994 2130 with a carburated 305. I have an aluminum 4 blade 18p and my spare is a 3 blade 19p. The 4 blade is considerably better for water sports. The boat jumps out of water with that prop. I lose about 5-7 mph on the top end but since I'm not really racing anyone it doesn't matter to me. I use the 4 blade pretty much all the time and the three blade as a spare. When I can afford it I would like to get a 4 blade stainless prop.

 

[Tail_Gunner]

Re: The Proper Prop - Chaparral 21' Bowrider

•Full Laden Specs - 6 adults: ~ 1020 lbs
•Gear: 100 lbs
•Full Laden WOT Engine RPM: 4,600
•Full Laden WOT GPS Speed @ 4,600 RPM: 45 mph
•Minimum Laden Specs - 2 adults: 350 lbs
•Gear: 70 lbs
•Minimum Laden WOT Engine RPM: 4,700
•Minumum Laden WOT GPS Speed @ 4,700 RPM: 49 mph

Here's a conflict look at the rpm with a full load...100 rpm difference. I have a lighter boat and more power...6 people will drop me from 5000 to 4200...I wish i had paid more attention i simply went from a 20 to a 18 when i knew there was going to be a number of people on the boat that day...

Here i go again...Id bet that tach is off by a few hundred rpm at higher rpm...Enertia are fast props and fairly agressive...id go thru a few numbers ..ok here

Nope something (Tach) is off 21' boat....240hp (TBI) motor....1.47 gearing??? 21p ss???? Greg8255 had a very similar boat but a 383 stroker 375-400 hp and a 21 was just a tad shy...

 

[LambChop]

Re: The Proper Prop - Chaparral 21' Bowrider

•Full Laden Specs - 6 adults: ~ 1020 lbs
•Gear: 100 lbs
•Full Laden WOT Engine RPM: 4,600
•Full Laden WOT GPS Speed @ 4,600 RPM: 45 mph
•Minimum Laden Specs - 2 adults: 350 lbs
•Gear: 70 lbs
•Minimum Laden WOT Engine RPM: 4,700
•Minumum Laden WOT GPS Speed @ 4,700 RPM: 49 mph

Here's a conflict look at the rpm with a full load...100 rpm difference. I have a lighter boat and more power...6 people will drop me from 5000 to 4200...I wish i had paid more attention i simply went from a 20 to a 18 when i knew there was going to be a number of people on the boat that day...

Here i go again...Id bet that tach is off by a few hundred rpm at higher rpm...Enertia are fast props and fairly agressive...id go thru a few numbers ..ok here

Nope something (Tach) is off 21' boat....240hp (TBI) motor....1.47 gearing??? 21p ss???? Greg8255 had a very similar boat but a 383 stroker 375-400 hp and a 21 was just a tad shy...

I originally typed those figures when I had the aluminum prop on... I forgot to change the full laden RPM. However, my WOT engine speed certainly didn't drop by 800 rpm when under the full laden load. The fully laden was around 4,400 to 4,500 rpm. I'll call it 4,400 rpm and edit it above.

Either way, I'm really not trying to figure out pitch. I'll experiment with that on my own. I'd rather hear opinions on the different props mentioned above.

 

[Tail_Gunner]

Re: The Proper Prop - Chaparral 21' Bowrider

I am by no means trying to critical here...a 21p ss and 1.47 gearing is very very tall cotton for a 240 hp 21' boat. 50 mph sounds like a good number..You may want to redoulbe the gearing and pitch..just a thought..mistakes happen all the time...even by me.........every day.

http://forums.iboats.com/non-repair...-my-383-stroker-winter-project-524489-21.html

Have a read http://forums.iboats.com/non-repair...-my-383-stroker-winter-project-524489-21.html

http://trailtech.net/tto_tach-hour.html Cheap little tach

 

[LambChop]

Re: The Proper Prop - Chaparral 21' Bowrider

You may want to redoulbe the gearing and pitch..just a thought.

When I bought the boat, I never checked the ratio on the drive. It worked, so that was all I was concerned with. Later when I did check out the ratio, I was surprised at how tall it is given the motor and hull.

Also, I was wrong about the model of prop that is currently installed. It isn't an Enertia, it's a 21p Vengeance:

With the original aluminum prop, I saw just over 5,000 rpm at WOT, so I wondered if the tach was on given the prop pitch (21) and drive ratio. I did check my tach at idle and 2,000 RPM with a handheld tach and it was on. No idea if it's accurate at higher RPMs though.

Repainting the stern drive and replacing the gauges (my tach intermittently spikes to 5,000+ rpm every once in a while, even if the motor isn't running) are on my list of things to do before I put the boat in next year.

 

[Tail_Gunner]

Re: The Proper Prop - Chaparral 21' Bowrider

Well a few thing's

1. If it is a tbi motor you have a mefi ecu that cutoffs the engine at about 4900 rpm it will not spike to 5000..it sounds like very high speed misses....you engine cannot reach 5000 its electronically limited.
2. It looks like that prop is badly deformed on the blade area and some damage on the leading edge more than enough to cause the high slip..

3. There is a known way to check the gearing on your leg... ive just lost the link someone should post it.

Boat tachs are known for being inaccurate happens all the time and from what your describeing you have a short somewhere in the system....tach line.

Now if the leg is 1.98 gearing with a damaged prop along with the tach being a bit off.. the number's begin to make sense.

 

[LambChop]

Re: The Proper Prop - Chaparral 21' Bowrider

Yeah, that deformation happened after hitting a stump (or rock, no idea...) the first time out after having the prop reconditioned. I really didn't notice a difference in performance after hitting the stump. Still, I want to replace that prop, hence this thread .

 

[90stingray]

Re: The Proper Prop - Chaparral 21' Bowrider

I would look at something like a hustler turning point 4 blade 17p. The aluminum variety can be had for around $100. You need to get those rpms up when loaded down. I think if you can get 4800 with that ratio and a 17p prop your top speed should remain the same and holeshot should be a great improvement.

 

[Tail_Gunner]

Re: The Proper Prop - Chaparral 21' Bowrider

Here is how you can determine your final gear ratio

http://www.ehow.com/how_7597079_determine-ratio-merc-out-drive.html