TOPIC: Prop Confusion

Hi guys,

I'm searching for the right prop. My motor is fresh with just two hours from being broke in, so very soon the operational restrictions are lifted, and I get to run a normal fuel mix.

My setup is a short shaft Merc 850, mounted on a CMC where the motor is mounted 3-1/2" above the stock G3 transom top. The cav plate is just shy of 2" above the keel... The CMC sets the motor back about 5" behind the transom. I took a lot of time to fair in the final 24" of the boat's bottom, so its perfectly straight.

Of the props I've borrowed to test (24P, 23P, 21P, 19P, 17P); with my 2:1 gears, I am happiest with a Michigan 19P non-cupped prop... I am seeing only 7-8% slip on flat water, which i understand is very good... and am in the mid-5000 RPM range. I may be zeroing in on the optimum pitch, but the available prop styles are still really confusing to me.

I realize different prop styles and pitches have different purposes. My '63 90 cu. in. 850 has lots of low end torque. With the 19P it just jumps out of the water. I plan to keep a 17 or 19P for water skiing or hauling people around... But what I am after is an optimum high speed prop. Can anyone offer suggestions or insight?

Thanks in advance,

Dean

Dean, you need to find an 18p chopper, have it cut from 14" dia. to 13 or even 12.75" have it cup'd close to fact specs, you should see spds of 50mph, you can also add the 100hp carbs and it will be a 100hp.

Thanks Jeff,

I've seen the 14 x 18P mercury chopper props. What happens if its not cut down? Will it work?

Sure, if you can get your rpms, I run a 22p chopper on reggie and it has the 4cyl 850. its a very different engine and the gear ratio is different,2.3:1, yours should be a 2:1 so the 18 should be a good fit, note that Ben runs a merc 100hp and had his cut to fit his setup.Idont remember how much he had it cut though.

For the fastest speed, pick a stainless steel or bronze prop. At your elevated height, cupped would work the best. For starters, I would try a 19" Ballistic SS, a 21" Ballistic SS, a 20" Quicksilver Laser II, and a Quicksilver 2-blade bronze 21" 48-49630-21.

Have tried all of these on my Glastron V-153 with 115 HP Merc and 2-blade bronze fastest. 53 MPH at 5,400 RPM. Told by PowerTech support it had 100% efficiency.

FYI adding just the 1000 carbs to your motor will not result in 100 h.p. you would need to also add the larger reed stops and the exhaust deflector that the 1000 has.
As far as props I am surprised that the non cupped prop is doing the best. The plate allows higher running heights and trim where cupping would be needed to prevent cavitation, just an observation that there may be a lot more you could be getting with a more modern prop and cupping. Maybe that 19 cupped?
You may run into interference with the trim tab with the SS props available, If yours is the Zinc type which it should be for that year, you can run with one that is flat and has no tab. This gives more blade clearance, you can modify yours or get one from Merc. this is what was used with the choppers as the prop blades raked back quite a bit and would hit the tab.
You might check on the site here but, I would bet that mid to high 40's would be about it speed wise with that motor. Maybe you are there now?
Randy

Id say a 19 or 21 pitch prop. I ran a 21 cupped brass prop just like DPANKY's and got low 50's with my 1965 900. The same basic engine as yours.

Conrad

hey, just come on by and try some out

Thanks VERY MUCH guys, you have given me a lot to think about.

Jeff, WOW do you think you have enough props there? You're just a little too far out (I mean in miles...heh) to come and try your collection. I am going to try your recommendation however.

Conrad & Dpanky, I had tried an old Kiekhaefer two blade 19" bronze prop I borrowed from Thom, but it was not cupped and cavitated easily on take off and while turning. I had better luck with his Michigan Wheel 19P aluminum (no cavitation and two more MPH)

Randy, no cup at all... with the 19P Michigan I see 46 mph GPS @ 5500 RPM on glassy water. I havent tried any cupped props yet... Thom loaned me a Mercury 17P cupped, but I've yet to run it.

Read the Merc service manual, it said for over 45 mph speeds with a regular prop, by changing to a high performance prop and dropping 1" of pitch I can realize a 1-2 mph increase. It also says I can realize 1-2 more MPH for each inch I raise the motor (not to exceed 20-1/2" for a short shaft motor) it looks like my motor clamps are now 18-1/2" above the keel... with the CMC it is set back about 5" too, so I could theoretically go up 2 more inches?

I am still running 25:1 oil, just 2 hours away from completing the break-in... then I am dropping the mix to 50:1. Is there a performance hit running 25:1?

I found a 14 x 18" Chopper that I picked up... Mercury part# 48-75766-18, I am going to give it a test this weekend and let you know how it goes.

Dean

Dean,
No performance loss at 25-1. Many racers run that much oil and they wouldnt if it slowed them down.

Nice 14x18 chopper! PS that link on ebay for the 19 pitch prop I posted above is a cupped 2 blade. For the price it would be worth trying. (not my sale fyi)

I run my stock lower units pretty high. I have run the prop shaft 1 inch under the bottom of the boat and got cooling. BUT YOU NEED A PSI GAUGE TO DO THIS SAFELY.

Conrad

Ponyboy wrote:

hey, just come on by and try some out

Dang!! I need to buddy up with this guy so I can find the prop I need for the Challenger!!

Nice shiney chopper......MMMMMMMMM. LOL. remember they like LOTS of air, and hit it hard outa the hole then back off after plane is reached....if ya wanna....lol, see the movies I posted for explanation of take offs! though they will work at a slower hole shot it strains the engine more......or maybe it strains me? remove the trim tab also as the chopper has much more rake than most any other props.
Oh and the bronze 2 blade in the first pic is a 12x26p, untried as of this time, but it sure looks cool

Where are these movies poste?

over on the G3 glasspar section, fastest in the MID west & 2nd fastest, see deans movie also while your there under fastest g3 in the west.

As yet untryed 14" x 22" Chopper for Glastron V-153 with 1988 Mercury 115 HP.

With 1974 Mercury 115 HP and 21" bronze 2-blade 52.9 MPH GPS.

I have A 2-blade cupped brass prop that is either a 19" or a 21", not sure of the markings. WILL IT WORK on my "new" 1969 Merc 1000!!!

I have A 2-blade cupped brass prop that is either a 19" or a 21", not sure of the markings. WILL IT WORK on my "new" 1969 Merc 1000!!!

I have A 2-blade cupped brass prop that is either a 19" or a 21", not sure of the markings. WILL IT WORK on my "new" 1969 Merc 1000!!!

If your motor is elevated off the transom, the newer designed props with rake will not lose grip like the 2-blade bronze props. My 21" 2-blade bronze prop with motor about 1/2" off the transom loses grip fairly easy but will "come back" by backing off the throttle or trimming in.

You may have to use a surface prop - Laser II, Ballistic, chopper, etc. that grips better.

Dean,
I am running a Merc 1000 shorty without any raise or setback. I'm using a 20" chopper that was cut down to 13 1/4 inches. It was originally 14, but it wouldn't move past the ventilation/cavitation plate or the zinc trim tab. I'm seeing speeds of about 50 @ 55-5600 RPMs.
Best of luck in your prop search!
-Ben

Well, I tried the 14x18 chopper... didnt like it. Boat was squirrelly when it was flying. In fact, when the boat was up out of the water it was crabbing (stern coming to port) so I had to hold the wheel to the left about 120 degrees to go straight. The first time I dropped the throttle and landed the boat back in the water... it jumped from side to side... I think it was due to the keel wasnt parallel to the direction of travel. Anyway, that prop is gone... did some horse trading with Dr. Frakenmerc. My next prop was a Quicksilver# 02036-17. What a difference! Handled great and beat my fastest speed by 3 mph on my GPS.

If your running 49 mph with a 2:1 lower unit and under 5800RPM that prop has to be bigger than 17p.

More like 19-20pitch...

And yes the more you run out of the water the more it will crab. you have to be ready to straighten your wheel when you get out of it.

Good work It looks like it is riding very well! The bow is up nice, but your probably loosing a bit of speed due to being so far trimmed up. A prop with a bit more rake will hold the bow up without ecessive trim angle.

Thanks for the vid
Conrad

Hey Conrad,

Yeah, well i wasnt ready the first time, scared the U-KNOW-WHAT out of me! After that I sure to slow down slowly.

Yep, 49.1 on my GPS (it captures the max speed). The prop has a pretty pronounced cup on it, not sure what that adds to effective pitch. The run when that video was taken was over 48. When I was off camera, trying my hardest to stay ahead of Thom's Wild Thanggg... my GPS locked in the better speed... and the 850 was turning every bit of 5700-5800. I could use a gauge on my CMC so I can know where the trim is at... but for now, I just blindly trim based on feel and RPM.

It was an amazing difference, especially in the handling. It was solid like driving on wide-track radials. Whereas the chopper felt like driving on skinny ply tires on ice... heh.

Dean

Thats cool. I love that 90 cube 850! The other day I swapped a cleaver for a 24 pitch chopper for the fun of it. It holds the boat up at slower speeds . Under 65mph.

I ran the boat into a 20 mph wind on the river . It was a bit rough on the water and needless to say the boat got really smooth in the chop going into the wind. @ roughly 62 mph land speed (82mph wind speed) the boat was all but lifted out of the water and very light and squirrly.

Its a weird feeling when the boat suddenly gets smooth over rough chop... Its flying well at that point. My cleavers keep the boat low to the water.

Keep up the good work and play with as many props as possible.
conrad

Thanks Conrad, the problem is the weather is turning here in the Seattle area... probably not a lot of chances to run it over the next several months. Will keep everyone posted with the progress. I'm rebuilding a set of KC-1A carbs for the 850 tiger now... that could change the prop game.

Are you talking about your Carlson Contender? Arent you worried about getting too much air up under the tunnel? Holy cow.

Yep thats the Carlson. I ran the 24 to limit my speed that day. If I ran my 26 chopper into the wind, i dont think it would be so fun

My 25 and 26 cleavers on the other hand run really flat to the water and require a lot of speed to carry the bow. They are great on the top end for sure and make the boat feel safer. These are my fastest props.

Props Props Props.
Cornad

Dean....lookin GOOD!

I took ole Wild Thanggg out today and got back-to-back runs at 65 MPHgps. Then my Monster Merc broke loose from the transom - again - and the ride started getting pretty wild.
I'm pretty sure the transom wood is compressing and leaving the through bolts loose. This is the second time in the last couple outings - Not good.
I'm going to retire Wild Thanggg before something serious lets go.
Too bad too as I KNOW there is more speed to be had.
The tach was still climbing when I ran out of lake and had to shut down.
The small ear chopper I was running was picking up and carrying the bow real well with minimal trim. 14.25" x 26"p
Thom

Hey Dean looking great in the water running!

Be nice to that motor, LOL.

Darrell

Thom, is there any way to fix the transom? Have you determined the extent of the problem? Would a commerially made transom support that distributes the stress of the bolts be enough or do you need to take out the soft wood?

65 MPH in a Glaspar is fantastic. What is the horsepower of the Mercury?

"is there any way to fix the transom? Have you determined the extent of the problem? Would a commerially made transom support that distributes the stress of the bolts be enough or do you need to take out the soft wood?"
I don't know yet - I'm too disgusted to look closely, but I anticipate another deck off full work-over to make the G3 more solid. I'll know more this winter.
"What is the horsepower of the Mercury?"
It is an '87 Mariner 115 - a gray '87 Mercury 115.
It has been rebuilt with some minor changes made.
It is mounted on a '77 1500xs short shaft driveshaft housing and a 2:1 standard shorty lower unit. (not a low-water XS lower unit)
It is a BRUTE and it pulls up through the RPMs amazingly.
Stock, the '87 Mariner/Mercury had low dome pistons.
These have been replaced with high dome pistons.
The stock reed stops don't open as wide as the mid-'70s 850 4 cyl reed stops, so I installed 850 4 cyl reed stops.
The original carburetors on the '87 Mariner/Mercury used .072 or .074 main jets.
I replaced these carburetors with early 1500xs WMK-11 carburetors with .082 main jets. (this required installing the '87 Mariner/Mercury butterfly shaft & throttle pick-up link into the top carburetor so that the adi linkage would properly open the carburetors.
The '87 Mariner/Mercury came with adi (Alternator Driven Ignition) which I used in the build for several reasons.
The most obvious being that the '87 115 block has casting designed for the adi system, but more importantly because there is no 'rev limiter' like is commonly found on the older switchboxes used with the solid state distributors (triggers).
The only old school switchbox that was assembled without a rev limiter was the 1500xs & T2, T2x switchboxes with the part number ending in A-25. NLA and very rare finds.
I timed the beast to 20 BTDC @ WOT, which is the current factory recommendation for a stock '87 115 inline-6 running today's pump gas.
The timing is limited because of the poor quality and octane level of the gas available today.
I run 100LL with Amsoil @ 50:1 and turn the beast up to 6400 RPMs for extended distances on the bigger lakes.
I also put 4 oz of SeaFoam and 1 oz of StarTron in every 6 gallon tank of fuel.
How's THAT for an answer?

Thom

Thanks Thom for the very informative answer. I hope to mount the 1988 Merc 115 HP in my profile picture on a Glastron V-153 and hope to reach 55 - 58 MPH, a far cry from your 65 MPH. But you must be pulled over 115 HP with the dome pistons and carbs with bigger jets. Plus the short shaft and chopper prop help the speed also.

Soft transoms can be hard to fix. I looked at a 1984 Glastron CVX 16 in great condition save for the transom which was rotten and caved in from the motor's mount. Boat restoration place wanted $3,000+ to repair. Another shop quoted $2,200 to fix it from the outside. There is alot of information on how to fix transoms correctly. Plus in your case with the extra horsepower, you may want to put in knee braces for additional strength. Good luck with the transom redo.

My outboard mechanic is rebuilding the 3 carbs of the 1974 Merc 115 HP because of a hesitation problem. Informed me that he found a piece of a broken razer blade and a spray can extension tube in the carbs. Motor should run better now.

Hey Thom, now you have me thinking, maybe I am running into a rev limiter on the 1500/adi/high dome Tinkermerc!! Did any of the ADI switch boxes have limiters in em?

I am of the belief that the answer would be no, but I'm not positive.
Maybe Master JeffG knows for sure??
T

Its funny you mention the rev limiter. My factory box from my 1500j was toast when I got it. It had the RPM written on it back. (could not read it)
So I put a standard 1974 1500 long shaft box in it. It turns close to 7000 RPM so far

I get my 28 pitch cleaver back from the shop in a week or so. Its super thin and razer sharp. Hope to see past 75 mph It should. My crusty 26 cleaver pushes the boat 74 mph.

Conrad
Conrad

Conrad

Thom, have you considered Sea Cast for your transom? Hear it cures rock solid. Hate to see you take the "wild" off the "thangg".

Thanks Darrell!

I always baby the 850, until the need for speed hits me. Seriously, the motor is running great and only this current tank I took it from 25:1 to 50:1. I have a big 11 hours on the motor. Thom kept me in check during the break-in... but now all bets are off...heh.

Today I installed my freshly rebuilt KC-1As. Hope to get it out for test next weekend if our NW weather holds out.

Dean

Thom, have you considered Sea Cast for your transom? Hear it cures rock solid. Hate to see you take the "wild" off the "thangg".

I almost used SeaCast and didn't. I agree that the Wild Monster Merc belongs on Wild Thanggg, and it sure is a great adrenaline rush when that bow starts to fly and the tach is knockin' on heaven's door.
I have taken a close look at things this week and think that the transom is actually solid and I just need to use some larger washers to stop the shuffling, but for now I'm retiring the set-up.

The strakes I added to the bottom of the hull are always out of the water when I need them to be working, so most likely before Wild Thanggg returns the strakes will be moved closer to the pad and the transom's loco-motion will be under control.
I'm hoping to get those strakes to develope water pressure between them and the pad that will stabilize the hull when it is trying to balance on about 2 square feet of surface.
Any thoughts??

Now,...If GLASSPAR NUT was to come back to the forum and start ribbin' the Dark Side like he used to do so well,...WildThanggg will only be,...EIGHT NUTS AWAY!!!
Muu-Wah-Haa-haa
Muu-Wah-Haa-haa
Muu-Wah-Haa-haa

You tell Nut like it is!!! Thats good. He is alive, as he e-mailed me three times last night.
Sent him the video of the new mercs and he said it made him sick!!!! Too bad!!!

Here is a pic for him too!!!!


The only time a OMC engine has ever been that high was when they were flown out over the ocean and pushed out of the plane!!!!