Performance Data/Numbers

[jdupree]

John,

On my 81 200 XF which is the same hull as your ccp I'm running a 14.25 x 17 aluminum prop on my 200 HP Merc right now.  I get about 5400 WOT and 40 MPH top end and 3600 RPM cruise is about 25 MPH and 4000 rpms put me in the 30MPH range.  I'm thinking of trying out the 14.5 x 17" stainless turbo prop from Dale for $185.  What year model is your 200 Merc?  is it a 2.5L ?

My Mercury is a 1992 Offshore 2.5L.  Looking at your numbers, sounds like you are right where you need to be but it never hurts to try other options.

[GoneFission]

[Capt. Bob]

Mod. Edit: 31 Dec. 2010
Originally posted in Discussions forum by Member Fitz73222

Basically do a calculation of crankshaft rpm's divided by gear ratio = net propeller rpm X pitch minus 10% for average slippage = net inches per minute divided by 12 = feet per minute X 60 divided by 5280 to get miles per hour.

Here is my 60 bigfoot Merc on the flats boat speed calculation.
5500 rpm (WOT) divided by 2 (2:1) gear ratio = 2750 propeller rpm X 15" pitch = 41250 inches per minute minus 10% average slippage = 37125 inches per minute divided by 12 = 3093.75 feet per minute X 60 minutes = 185625 feet per hour divided by 5280 (1mile) = 35.15 mph. This is confirmed by GPS.
Your rpm's seem way to low even if the engine is down an inch or two.

See if your numbers jive with this calculation method.

A "Tip o' the Hat" to Fitz73222 for posting the formula.

[flounderpounder225]

WOW! I sat down and followed the formula, and the result was almost dead on with my GPS MPH reading, about .5 MPH off (low), which probably equates to this Enertia prop which feels like it has very little slip.

[fitz73222]

There is also a formula as to how to calculate slippage; I saved it from a Bass and Walleye boats article about 8 years ago but it is in a stack about 3 feet thick of past issues and I will try to find it (Someday!). just for reference that publication is the best I`ve seen about new engine testing, performance set up, etc. I let the subscription lapse some years ago; I just checked, they are still in existance! If you want to find out anything pertaining to engines and performance check them out; just google Bass and Walleye Boats magazine. Sometimes they will occasionally test big ole boats like ours; the great lakes can make our waters look like a little pond somtimes!

Thanks guys; its fun to help and get help...Thats what we do!

[Newbie25]

Marc,

Ken actually recommended me the same prop that he sent you from Mercury and its a 15 x 15. This was when we were just guessing at the info. I will be posting my results in April. I hope to get the boat to a cruise speed of 30 and a WOT at 40.

[flounderpounder225]

Marc,

Ken actually recommended me the same prop that he sent you from Mercury and its a 15 x 15. This was when we were just guessing at the info. I will be posting my results in April. I hope to get the boat to a cruise speed of 30 and a WOT at 40.

Yes, that's the Enertia Prop, 15 X 15, it was made for heavy boats, see my post on here, that prop stood out above any other I tried, in every aspect from take off, WOT, hard turns with no Blow-Out.  For my boat, it was worth the money.  Honestly I don't know if you'll see 40 MPH WOT with a 305 (5.0 Liter), you should see mid to upper 30's though, with a comfortable cruise around 28 or so, at a decent fuel burn.

[Newbie25]

Them speeds sound good to me. Its a  fishing boat if I wanted to go fast I would have bought a race boat. I happy at 28 and 30 because the farthest out that I ever go is 12 miles anyway.

[Glock Diver]

WOT with less than a half tank of gas, 1 person onboard, gets me 5200 RPM, 42mph.
97 225 Osprey, with 200hp Johnson 2-stroke

Prop: stainless 3-blade SST.
I know nothing about props, but its stamped 14 3/4 x 17....   Probably stock original?

Think a different size would push a few more MPH out of her?

[LilRichard]

I'm running the Powertech OFS4 on a 150 'Zuke.  Wanted greater bow lift (FBs tend to bow steer as you know).  I think *think* I'm running a 21P, I'll double check.

Getting just over 40mph on a good day WOT.  Loves 25mph cruise (at about 6gph) around 4200RPMs.  Will cruise up to about 29/30MPH around 4600RPMs and 8gph.  In no way is it a go fast boat, but it will jump on plane with the motor almost fully jacked up!

[Capt. Bob]

WOT with less than a half tank of gas, 1 person onboard, gets me 5200 RPM, 42mph.
97 225 Osprey, with 200hp Johnson 2-stroke

You probably  can get about 300 + more rpm and still be in a very comfortable zone.

Prop: stainless 3-blade SST.
I know nothing about props, but its stamped 14 3/4 x 17....   Probably stock original?

You would need to reduce the pitch to around 15 (now 17) to get that 300 (might not get that much) but....

Think a different size would push a few more MPH out of her?

How much more do you want? You might want to consider a 4-blade in your current size but they are costly to experiment with. I love mine on my 200 Evinrude (will update this post with the size) and it produced 5500 rpm WOT with a constant 40 mph loaded.

Here's some basic reading to get you started.

http://theoutboardwizard.bizhosting.com ... eller.html

http://www.boatfix.com/how/props.html

EDIT: I ran a 4 blade Renegade on the 200 Evinrude  14-1/2 x 17

[Glock Diver]

Thanks Bob!
I am comfortable with my current top speed of 42mph, but it wouldn't hurt to go a little faster. However, if it would require dropping $250 on a new stainless prop, and I'd only get 2-3 additional mph, I'm not sure it's worth it!  It's rare that I run WOT anyways, since it hits the wallet pretty hard.

[Aswaff400]

tried another prop today,

an old OMC 3 blade stainless 15x17p spun 59-6000 at 49-51 mph, with a full tank of fuel, full livewell, 2 people, and fishing gear... jumped out of the hole and down the drag strip like you wouldnt believe... reached idle to WOT in less than 30 seconds

i was told to try the powertech OSF4 15-1/4x20P and the numbers chould get me close to 5500 with the top speed and hole shot that im looking for

heres the old OMC

[Coverhill]

Here is some info that may be of help on the subject of what HP for a 17 foot Aquasport.

I have a 1988 17' Aquasport that I've owned since "new". Originally the boat came with a
90hp Yamaha carburetted engine, which was very reliable but which gave me only about
3.5 statute miles per gallon at 3400 RPM and a speed of roughly 22 statute miles per hour.
I know that these figures are accurate because I kept a record of this info.

In January 2012, I repowered my boat, mainly because the new fuel injected motors are
SO MUCH more fuel efficient. My main goal was to obtain maximum fuel efficiency.
After looking at all the manufacturers and technologies I decided to go with 2-stroke fuel
injected technology, rather than 4-stroke technology. Dusky Sport Center in Hallandale,
Florida gave me an excellent price on a 90hp Evenrude "E-tec" engine (model E90DSL)
and did the engine change out. I got $1,500 for my old Yamaha and its controls, which
they help me sell to someone who buys motors. Dusky did an excellent job rigging the
new motor to my boat, which included Evinrude's digital "I-Command" multifunction
gage that shows (1) GPS speed, (2) Gallons per hour fuel burn to the tenth of a gallon,
(3) Miles per gallon, (4) RPMs, (5) Engine temp, (6) Battery voltage, etc.

I also considered going down to a 70hp E-tec, which in my opinion is adequate power
for my 17' Aquasport. Ultimately I chose the 90hp E-tec since it is built on the same
block as the 70hp and the weight of both engines is about the same.

Because my highest priority is fuel efficiency I specified that when "propping" the
engine that I wanted to turn less than 5000 RPM at Wide Open Throttle. My new engine
turns up 4860 RPM at WOT. fully loaded for fishing. I cruise it now at 3100 RPM which
gives me a solid 20 statute miles per hour and 6.5 statute miles per gallon of gas.
That's a good 80% better fuel efficiency than the old 90hp Yamaha. My new top
speed is 38 statute miles per hour, faster than water conditions will allow 90% of
the time.

Below is a photo of the new "Performance Specs" card that I made up last month
on this new combination. All those RPM/GPS SPEEDS were done in slack water that
had only a light chop. The card also shows the boat weight during these tests as
well as the exact prop thats on my new motor.

Hope this will be of help to others.

Coverhill
North Palm Beach, FL

[Coverhill]

The 17 foot Aquasport

Here's the specs that Aquasport's manufacturer got back in 1970 with an 85hp Johnson
swinging a prop of 13 1/4" diameter and 17" pitch

HERE'S THE "PERFORMANCE DATA SHEET" OF COBURN & SARGENT, then the manufacturer.