Need help picking a prop for speed

[DirtyOldBoat]

I have a 1973 Glastron/Carlson CV-16 (16 foot) with a Mercury 1500. I've currently got a 19p aluminum 3 blade prop and the last time I had it out I could hit 50MPH on the GPS at around 6300 RPMs. I know the motor is spinning too fast, and since then I have removed a ton of soggy foam and plywood from the back, so it should go faster now.

What do you guys think about a 2 blade bronze prop? I'm told this might help with torque steering, and this hull can be a bit hard to handle above 50MPH. What pitch should I be looking for...maybe 22? I think I'm looking for around 5600-5800 RPMs.

 

[steelespike]

Re: Need help picking a prop for speed

They say the 2 blade produces good results leaning toward speed over power.
I do wonder if todays technology might have as good or better results.
Do you know the gear ratio?Is it a 73?

 

[Chris1956]

Re: Need help picking a prop for speed

A 21P prop should drop your max RPM to about 5900, which is still pretty fast. You should pick up a bit of speed as well. I normally ran my 16' Avenger with a Merc 1500 on a 21P aluminum. You might consider a Hustler prop. They are aluminum and have some rake, which is usually good.

I found the power curve of my Merc 1500 to be too flat for a 23" P prop.

 

[GCarlover]

Re: Need help picking a prop for speed

If I were you I would buy this prop in a heartbeat. 2 days left (May take offer) I think he sold 2 others $25 shipping.
They also come in a 14" dia; don't recommend it.
Mercury Outboard 2 Blade Bronze Prop 24 Pitch | eBay
Specs here: Mercury Nos Racing Props [Archive] - Boat Racing Facts Forums (13x24) Part # 48-49614A4
The 73 150 is engine, not propshaft rated, but uses premium gas.
Should be 2:1 gears. The prop above is a high performance high rake which is supposed to out perform the standard 2 blade bronze. I have a 2 blade worn to 13 1/2 x 23' with a high cup converted to my 87 140 Johnson , Runs about 53 at 5700.
It gets a lot of slip when trimmed up. You will need to cut down your trim tab or get a special one.

 

[DirtyOldBoat]

Re: Need help picking a prop for speed

Hmmm, I'll definitely have to think about that. You don't think 24p is too much?

 

[GCarlover]

Re: Need help picking a prop for speed

Hmmm, I'll definitely have to think about that. You don't think 24p is too much?

Your engine is smaller than my 140 looper but should run higher comp (135-145) With domed pistons the Mercs rev well. Find out it the rebuild changed anything to use lower octane. I've been around two 135 Mercs. Pretty sure 150's will rev higher (Iboats boat specs are 48=5800. The prop I have without cup ran 52 on a gt 160 (71-135 hp @ 1.78:1, 3rd hole, no trim unit). Appx over 800 lbs two people 1970 115 Merc on a CVX 16 @ 50 ish. Not sure, my speedo read high. 47 on a v163 w/ 135 Merc.
I'm mainly going by what you get(6300 w/19 Al) Your 2:1 would be the same as 21" for a 23". If you use the prop slip calculator set at 14% slip it computes 51 just above 5000. I used 25" because it has a slight cup. Normally I use 2" more on a 2 blade. Your CV 16 is lighter than all I mentioned. My guess you would go about 54 @ 5300.(light load) At best it will increase your mileage just for crusing. Don't need to high rev unless you have a heavy load. Not for skiing, too much slip. If you want that prop it's not a bid, shows make offer. I might offer on it. There was a Johnson hub on Ebay. Will check for I-6 150hp on this forum.

 

[DirtyOldBoat]

Re: Need help picking a prop for speed

I might offer on it

Feel free to take it if you want. I spent too much on deep cycle batteries and fiberglass today. :lol: Thanks for all the info...I think I'm going to wait until I can get the boat out on the water again and see exactly where my RPMs are at with my 19p, a lot has changed since the last time I had it out. (And that was 2006!) I need to burn a bunch of gas to break in before I can even go WOT since I've got a rebuilt powerhead.

 

[GCarlover]

Re: Need help picking a prop for speed

Did you check if your engine was de-tuned or are you still using premimum? Your specs are right at 10% from the Prop Calculator site. Just Google and fill in the blanks. Here is a pic of my prop. You have to register on GCOAMN to see it:
Another Prop to the Collection
Screan & Fly posts:
brass 2 blade prop?
Bernie writes:
Two Blade Brass Props
With the right application, they can be interesting. I have a '77 Hydrostream Viper with a '73 Merc 115 jacked up around 2 inches - I run a 13x24 2 blade bronze elephant ear Merc prop - it gives a tremendous cruise - 42 GPS @ 4000 and still runs 57-58 @ 53-5400 trimmed out. And then overtrim and it throws a great roostertail although the speed drops off. It performs almost as good as my usual 20" Laser II. And polished up it looks tough on the trailer also. (I think this shows 12% slip. These boats are light and very efficient.)
Prop recomondation
Bigbroadjumper writes:
Prop recomondation
I am looking for a recommendation on a spare prop. I have a 1974 Mercury 1500, and a 16' Magnum Merauder. The weight is about 750 lbs dry and without motor. Currently I have a bronze 2 blade 23 pitch prop and I am turning about 5500 and about 57 mph on the GPS. What I am looking for is a prop for more all around use. Something the kids can use to ski, and just run around. Currently the boat starts to chine walk at about 55 and I don't know if that is a product of the 2 blade or somthing else.
Ebay went off but probably be back:
Mercury Outboard 2 Blade Bronze Prop 24 Pitch | eBay
He won't drop much and his shipping is $25 (too High)
There's one just like it on Scream & Fly for $195.

 

[cr2k]

Re: Need help picking a prop for speed

Basic Rule Of Thumb on prop size with a 2 stroke. Don't prop so low that you over rev this is hard on the rods.
Don't prop so high that you lug this will cause carbon build up on the pistons/heads and soon the two will start tagging each other and this will blow both the rods and the pistons.