Merc 888/898-Merc 1 prop size survey.

[Boomyal]

All you guys that have the above combination, in 17 to 19 ft runabouts, what prop sizes are you running?

I am confused. The appropriate Merc Manual shows that I should be running a 15 1/4 x 21p-15 spline prop. Yet I have two examples of the above combination that apparently have 13 1/2 x 21p props. As I am not near my boat, I am not even sure if there is room for a 15 1/4". For some reason, the prop diameter is not stamped on the Merc aluminum props, only the pitch.

To arrive at the diameter of my Merc prop, I put a dot on the garage floor, centered the prop over it, then ran a square along the floor to the tip of each blade and marked it on the floor. I then just measured the radius from center dot to tip of blade dot.

My OMC runs a 15 x 17 and that prop is monsterous compared to the props on my two Merc examples.

 

[Haut Medoc]

Re: Merc 888/898-Merc 1 prop size survey.

Depends on the weight of the boat & it's lines....
I run a 14.25 X 17 on my '22 foot Sea Ray....
It is an 888......JK

 

[ziggy]

Re: Merc 888/898-Merc 1 prop size survey.

"Boat length can be used to select a propeller for initial trial. Correct propeller allows engine to trun recommended RPM and gives best performance. Because of the many variables of boat design, only testing will determine best propeller"
that is the first statement in my mercruiser propeller recommendation chart. oem service manual #1 vol. 2.
so to me, first you must find a prop. that allows you to reach wot specs. then ya would fine tune from that prop to find the best performance. that would depend on what kind of performance you want. ie. speed. low end torqe for pullin watertoys etc.
so i guess ya use yer chart as a 1st best guess and go from there.....
i don't have yer 888, but i was spinnin a 21P fan blade type propeller (larger dia. but don't know what diameter) with my 165hp on a 19' v-hull. i could not reach wot spec very well. top end was fine, no hole shot so to speak. got me a 19P flo-torq II type prop(less dia. than my 21P but don't know what dia. that one is either, just less than the 21P i had) and now have a hole shot, and have not lost my top end. with a pace boat gps top speed was about 43mph with both. the 19P i reach the top end of wot spec, the 21P i was lucky to reach the bottom end of wot spec. wot spec is the most crittical aspect of choseing the right prop from what i read, and trying to reach the top end of that spec is what i understand is what ya should shoot for. so for me this is what i am gonna run. if i was to experiment, i recon my next step might be a 19p SS. i'm happy with my aluminum and ain't rich so ain't gonna experement right now....i reach the top end of my wot spec and have good performance for my boat. so that must be what i need.......good luck in findin yer niche.........

 

[Boomyal]

Re: Merc 888/898-Merc 1 prop size survey.

Yeah ziggy, all good prop poop. My real quandary, however, is over prop diameter, that's why I've really asked the question for those who have similar boats and who still have the prop that the boat came with.

 

[Haut Medoc]

Re: Merc 888/898-Merc 1 prop size survey.

Ya might get some better answers in the prop forum, Boom....
For your shorter length & lesser weight, I would estimate a 14.25 X 19 or 21......

 

[Boomyal]

Re: Merc 888/898-Merc 1 prop size survey.

Ya might get some better answers in the prop forum, Boom....
For your shorter length & lesser weight, I would estimate a 14.25 X 19 or 21......

Haut, I wasn't so much asking for an actual perscription as I was about actual real life prop diameters. I have the two examples that do not match the manual diameters for boat length and weight.

Although the props on the '76 888 and the '78 898 are both apparently Merc supplied props, the are both the 13.5" diameter variety (21p). Now bein as old as they are, anything could have been put on them.

I had a chance to buy a 15.25 x 21p Appollo SS prop on ebay for $145.00 shipped. That agrees with the manual but not what is currently on the 888 and 898.

As far as the Prop Forum, I was just trying to find out from the general populace that might not get over that way.

 

[ziggy]

Re: Merc 888/898-Merc 1 prop size survey.

boom, i'd think ya'd be better off in the prop topic too. some sharp prop cats over there.....
from just thinking about it. and no expereince other than what i'd said. "i think" a smaller dia. prop is gonna move less water than a larger dia. prop of the same pitch. therfore "i'd think" the larger dia. is gonna slow down yer engine, put more load on it. the guide in the book seems to be a general application guide line. + there's new tech. out there that may mean better prop design. i assume that the newer flo-torq II i got is better prop design than the fan blade style i had + the flo-torq wasn't even invented when my manual was written. so no basis from the book at all on what i put on it. for what it's worth. i still had the old style thick thrust washer in front of my 21P X 15, maybe 15 1/4. so to me it could have been what my boat came with in 75, though no way of knowing for sure. i still think it's about being able to get the top end of wot. that is what is crittical. what is yer wot right now. are ya with in spec? what's yer goal in changeing props? mine was to be able to achive the top end of wot so i didn't overload my engine.... a ss prop aint gonna flex as much as a aluminim one either the way i understand it. though i'm not sure of what the ramifications of the less flex are. i think more load, as the prop don't flex and let the water slip by. now where's the pros to set my notions stright. ........have a good one man.....

went to the lake for a visit again today..... 6 or 7 folks in boats that were out enjoying the 80* day we had today.....and i'm winterized,,,,,,

 

[Tail_Gunner]

Re: Merc 888/898-Merc 1 prop size survey.

Hey there Boomyal, most of the stuff you see in the prop forums is outboard related, having a I/O my self now and trying to maximize the boat's effeiceny i have found a few thing's to be true so far. Diameter really mean's very little, that is unless it redirects' the ehaust over the outer hub, that of course will create slip. As to tourqe flow id stay away for now, merc seems to using a new plastic washer for a better lack of terms that create's almost no forgiveness in hitting USO (Under Water Submerged object's)

Some thing's are very basic, I/O's are very stern heavy and using a high lifting 4 blade prop you get two things, less wetted surface (increasing speed and econ) And they are balanced better much smoother in operation......3 vs 4 ...Uyah ya think

Between the higher lift and smoother operation id try a Stilletto 4bl 20 or see Dahadley if you press him or walleyehed they really have a great grasp on these matters....... Anyway's good luck....

 

[ziggy]

Re: Merc 888/898-Merc 1 prop size survey.

As to tourqe flow id stay away for now

hum, guess i'd best have a spare onboard.....i run the missouri river, which has much debris on it...........thanks for the forwarning.......i've been takin my chance w/o havein a spare on board too.....mr. dangerous i guess. worse yet, i got several spare props, just not the tools to do it on the water in an emergency situation....i will before i go out next season........thanks,

 

[Bondo]

Re: Merc 888/898-Merc 1 prop size survey.

Boomyal,..... I Think you're measuring the Dia. Wrong,........

The Props that are in the 13" Dia. range also have a 4" Gearcase Dia.......
Those are the Mid-sized Outboard gearcase Props......

The I/Os use a prop in the 14"/ 16" Dia.s,+ a 4, 1/2" Gearcase Dia.......

I think that Old Manual you're reading is Wrong Again,.....
Maybe it's just Prop Technology has Changed that much.....

The Monster 15",+ 16" Dia. Props are Usually used on Houseboats,+ Extremely Large Cruisers......With Very Low Pitches,.....15"s or Less......

Btw,..... There's 8"s from the Propshaft centerline to the Cav-plate,......
You Can spin a 16" Prop.......But you Don't want to on Your Boat........

On Average,.....
Props for Your Boat will be from Mid-14" dia. to High- 14"s........
Pitch Could run from 17"s to 23"s..............
As Pitch goes Up,.... Dia. goes Down..........

 

[Boomyal]

Re: Merc 888/898-Merc 1 prop size survey.

Boomyal,..... I Think you're measuring the Dia. Wrong,........

I can't see any other way to measure it BUT I'm gonna take the prop off of my White drive and measure it the same way. Then I'll see if that measurement agrees with the stamped on diameter.

 

[BRG25]

Re: Merc 888/898-Merc 1 prop size survey.

19' Stingray with 4.3 alpha 1

Stock prop is 14x23

 

[Bondo]

Re: Merc 888/898-Merc 1 prop size survey.

Boomyal,..... I Think you're measuring the Dia. Wrong,........

I can't see any other way to measure it BUT I'm gonna take the prop off of my White drive and measure it the same way. Then I'll see if that measurement agrees with the stamped on diameter.

I guess I just don't understand the Framing Square in the process,......

If you measure from the Prop Center to the Outer point of the Blade,+ then Times 2,.....
That should be the overall Diameter.............

Like I said before,......
Most Merc. props in the 13" range are a 4" gearcase Diameter, which would mean the Prop Hub would be Too Small........

 

[Boomyal]

Re: Merc 888/898-Merc 1 prop size survey.

Boomyal,..... I Think you're measuring the Dia. Wrong,........

I can't see any other way to measure it BUT I'm gonna take the prop off of my White drive and measure it the same way. Then I'll see if that measurement agrees with the stamped on diameter.

I guess I just don't understand the Framing Square in the process,......

[colour=red]If you measure from the Prop Center to the Outer point of the Blade,+ then Times 2,.....
That should be the overall Diameter.............[/colour]
Like I said before,......
Most Merc. props in the 13" range are a 4" gearcase Diameter, which would mean the Prop Hub would be Too Small........

Maybe I was just taking the long way around bond-o. Essentially, that is what I was doing. I was just relying on marks of the floor to measure instead of measuring the prop itself. I just used the square, sliding it on the floor up to the outer tip of a blade, then putting a dot on the floor at the base of the square, then measuring from there back to the center dot. Whew!

The manual does list a 13.5 x 23 and a 13.75 x 21 for up to 17' on the first and 17' to 19' on the second. They are both for the 888 but it appears they are for stainless.
They state [colour=red]3-S. Steel[/colour]

I have been assuming that the slightly chewed up spare prop that I have at home was the same size as the ones on both the 888 and 898. I need to get across town and acutally measure the ones that are on the boats.

Maybe this 'spare' I have has been cut down. That happened to me once when I sent a 15" OMC prop out for repair. It came back considerably shorter in diameter.

 

[Tail_Gunner]

Re: Merc 888/898-Merc 1 prop size survey.

Boom you must be norweigan. Christ that manaul is 20+ years old ....... thing's have chnged my freind

 

[Boomyal]

Re: Merc 888/898-Merc 1 prop size survey.

Boom you must be norweigan. Christ that manaul is 20+ years old ....... thing's have chnged my freind

What's with Norweigan TG. A factory manual is a factory manual, or so I am constantly told on the forum.>o

 

[Tail_Gunner]

Re: Merc 888/898-Merc 1 prop size survey.

I will just get myself into trouble if i answer that, so i will say this, can you find a 14.25 hub and see if it fits on the 19 spline shaft and does it allow the exhaust to flow into the hub and not over the hub. Or just ask Dhadley what type of prop would fit on that leg and give the best results, probably tell him the exact rpm & speed @ wot and what yor expectation's are and he will find you a prop that just rock's

Ummm im pure Norwegian i wish i could share a joke, but in today's world there is no humor, If it's for that new boat you have id really shoot for a 4 bl stilletto, fast smooth and a soft ride. That's a really good hull for speed and smoothness.

 

[Boomyal]

Re: Merc 888/898-Merc 1 prop size survey.

I will just get myself into trouble if i answer that, so i will say this, can you find a 14.25 hub and see if it fits on the 19 spline shaft and does it allow the exhaust to flow into the hub and not over the hub. Or just ask Dhadley what type of prop would fit on that leg and give the best results, probably tell him the exact rpm & speed @ wot and what yor expectation's are and he will find you a prop that just rock's

Ummm im pure Norwegian i wish i could share a joke, but in today's world there is no humor, If it's for that new boat you have id really shoot for a 4 bl stilletto, fast smooth and a soft ride. That's a really good hull for speed and smoothness.

When I can get that thing up on it's chine, then I'll know I can whip ya. Guess I'd have to invest in another set of smart tabs though.

I do have a post in props, but I want to find out what exactly that 888 came with. I know the current 13.5 x 21 runs it up a little past redline (5000 rpm?) but I won't be satisfied until I try the manual specified 15.25 x 21 to establish a basis.

I do have that capability as I bought a 15.25 for my friend for his 898. When the opportunity presents itself, I'll just borrow it and see how it goes.

 

[Tail_Gunner]

Re: Merc 888/898-Merc 1 prop size survey.

If your pushin 5000 with that prop and if your not off the chine's its a very whimpy prop, that's a heavy old cast iron 302 probably pushing 180-220 hp, If i was a bettin man id say it's a bit A@@ heavy and you need a stern lifting prop or maybe a overall lifter,,,,,,, 5000 rpm? what is your speed....... no prop guru here but it sure sound's like ya need some traction.......o

 

[Bondo]

Re: Merc 888/898-Merc 1 prop size survey.

The design of the blade has more to do with tip placement than diameter...
I still see MANY people getting hung hard on diameter. .

Trying to get a clarification on this very point. 'twould seem that diameter (blade shape aside) would be as equal a part as pitch. Where am I wrong?

There was a time when I was trying to turn a 1.5/1 ratio outdrive with a 3.0l,......
It Don't Work........
I stumbled around Trying to find a prop Small Enough,......
I found that an Outboard, 4" gearcase prop will Slide right on,+ Bolt Up,......
'Cept the Big Gap around the 4, 1/2" gearcase of the Outdrive Ventilates,... Sooo Bad,....
Ya don't go Nowhere.....
15" pitch wasn't Nearly Small enough,.....
So,.....
I Tried This,.........

That was a recently rebuild prop,... Without Dings.....
The 3.0l wouldn't pull maybe 2500/3000rpms........
I figured if I Cut enough Diameter off it,.... I Should be able to find the RPMs......

Nope,.......
I Shaved a Full Inch off the blades of this prop with a jigsaw.......
That's a Full 2"s Reduction of the Diameter......
And,...... The 3.0l pulled the Same anemic RPMs,......

That was the End of the "98" season,...... 1999 started out with the 4.3LX,+ the Alpha I......

I suggest that everybody should Just Forget about Diameter,............
It's danm near Totally Irrevelant..................