View Full Version : 16 Classic ( sweet sixteen) Prop size

09-28-2013, 06:10 PM
Hi every one, I'm in the U.K. and have just bought a 1999 classic 16 fitted with a 4.3L Mercruiser/Alpha one, can any other members with the same set up tell me what props there running please, this one a 22" Mercury Enertia prop fitted at present and seems to go well,but wondered if it could swing anything a little larger ?
There are very few, if any, other 16's in the U.K. I had been looking for one to buy for the last 5 years or so, and there have only been three in total that I had found for sale in all of Europe over that time !!!... so I can't ask anybody here for advice... thanks.

09-28-2013, 07:00 PM
What is your WOT RPM?

09-28-2013, 07:05 PM
4800-to just under 5000.

09-28-2013, 08:04 PM
23" mirage plus

09-29-2013, 10:43 AM
21 Vengeance

09-29-2013, 12:18 PM
What is your drive ratio?

09-29-2013, 12:37 PM
Not sure what drive ratio, the boat is stored 150 miles away, I'm going down the weekend, I'll look then, thanks.

09-29-2013, 01:51 PM
The RPM you are turning is pretty much ideal, a 21 may put you over your torque band. A 23 might get you a little more top end but you will sacrifice some on the bottom. Spinning higher RPM's does not necessarily equate to more speed many times it is just the opposite, the trick is to get on top of your torque curve. When I finished up my 22 SB engine all I had handy was a Mirage 21 and a 23 Merc cleaver. The 21 made about 62, the 23 cleaver did 63. I borrowed heavy cupped 23 and turned 65, feeling I was on the right track I tried a 23 4 blade Turbo Ultima and got 65.5. Try to borrow a 23 before you spend any bucks, every boat/engine combo seems a little different.


09-29-2013, 01:56 PM
yes, thanks.

09-29-2013, 06:56 PM
I am gonna guess u have a 1.84 ratio. I had the same set up and a stock 23 mirage plus is a little too much for that set up. You are about dialed in right now. Do u have the 2bbl set up ?

09-29-2013, 07:36 PM
Not sure about the Carb, will also check that the weekend, thanks.

09-29-2013, 11:37 PM
My 4.3 dyno'd at 236HP. It has a 1.47:1 drive and I have a 19P high Five prop. It turns 4400 rpm at WOT.
My buddys 4.3 in a similar boat is a 205HP with a 1.65:1 drive and a 19p 4 blade Solas. It turns 4700 rpm at WOT.
We are 1.5 MPH different at WOT on GPS.
**note ** these are not Donzis but, the engine/drive/prop do not know what type of boat they are pushing


If you recreate This spreadsheet with these formulas you can have some fun manipulating the pitch and rpms to make a chart throughout the range. It's not real life but, you'll be surprised just how accurate it is. The key is...your engine has to have the ability to turn the rpms to get the number.

I used 4,800 as this is the factory WOT max figure. My engine pulls to 5,100 and yours may be diffent too....so you have to look at the variables that effect rpm. Cupping, diameter, # of blades, shape, surface area, etc... these will also change the slip number in real life but, don't be too concerned with this (I just used a constant for comparison purposes) to start. The rest is fine tuning and personal prefrence between props.

In my case one less blade will decrease surface area and increase rpms. I'm hoping for 3-400 rpm more by moving to a 4 blade. If I went to a 3 blade "speed" prop I could probably go up in pitch AND still get more rpms but, I'd trade off hole shot and possibly midrange.

09-30-2013, 08:19 AM
Thanks, I have done the maths on my outboard boats,and got some reasonable results, but this is my first stern drive, didn't know if being a big four stroke, with more torque, if it would be less 'load sensitive' than a two stroke.

09-30-2013, 09:38 PM
I did this .. I run a lazer11 25 pitch. its awesome... great top end , boat holds well very little walk when set up, have run this prop now for 10 years. 1.89 gear ratio in the alpha drive.
Gps with me and rider... 400 pounds 56

hold shot is fine with tabs applied if I have 2 extra riders. 23 is better with riders all the time.

10-01-2013, 04:47 AM
Thanks for information... I've watched your video many times.......it just captures the feel of the boat.......perfect..!!

10-01-2013, 08:52 AM
What are your goals? Top speed?
You're currently running in the right rpm range and the Enertia (a decent prop) seems to work well.

What's your speed on GPS?
With a 1.84:1, a 22p at 4950rpm (just under 5000) shows up at 56.0 MPH corrected to 50.4mph.
The same 1.84:1 with a 23p at 4750 (200 rpm per 1") reads 56.2 corrected to 50.6 so there's not a lot of bang for your buck (push for your pound) there.

Given this, maybe you don't really want to swing a larger prop...just one designed to maximize the desired properties... Cleaver?

10-01-2013, 09:24 AM
woobs may have an idea for you to try, I tried a cleaver on my 16. A cleaver is a stern lifting prop it tamed the porpoising a little. It did nothing for speed and it did not have the scary twitch while trimming that the one I tried on my 22 did.

10-01-2013, 12:50 PM
Thanks Woobs and Mop, I'm using the boat at the weekend, I don't have a GPS but a friend who will be at the meet does, to be honest, I have only used the boat once,and that was only for an hour or so in quite choppy water (Southampton water ) on the south coast of England, I only picked it up last week, so perhaps I am expecting to much to soon, your comment about a Cleaver is interesting as I did feel a twitch or two when trimming out whilst 'ringing its neck' so to speak,at full throttle, and it does porpoise a little, I was expecting it to feel a little more 'planted', still its early days, the sad thing is after this weekend it won't get used for 5 months or so.

10-01-2013, 05:57 PM
Se7en, I'm in Canada... I know all about putting your boat away for the winter!
2 runs left for me this year. Finish after Thanksgiving.
Have fun playing while you can.