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  1. #1
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    1961 Merc 800 FGS - prop advice request thread with photos

    Hi, I thought I'd create another thread, separate from my "BOUNCE" thread. I want to thank all the posters in my previous thread for the excellent advice and comments!

    Here are some details about my set up and some photos.

    My goal with this boat is to maximize the performance (top speed) with the current motor. I'm not super concerned with blistering hole shot, but don't want to lug the motor more than necessary when getting on plane. The boat is a shallow V bottom with pad.

    I've tried a couple of props so far, results below, and I think there is a better prop out there, just need to know what to look for. Maybe raise the motor too.

    Details of lower unit and set up are:

    Through hub exhaust
    Gear case diameter = 4.25"
    Prop shaft = 15 spline
    Center of prop shaft to cav plate = 7.5"
    7" set back with CMC unit and 5 deg wedge
    Cav plate 2 3/8" above pad

    Props used so far:

    1) 13" x 24" cupped bronze 2 blade 48-49614 A4 51 mph at 5000 rpm
    2) 14" x 21" non-cupped bronze 2 blade 48-31452 A3 50 mph at 5600 rpm (revved to 5900 by trimming further, no increase in speed)

    Photo 1 - lower unit side

    Click image for larger version. 

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    Photo 2 - lower unit rear

    Click image for larger version. 

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    Photo 3 - CMC unit with wedge

    Click image for larger version. 

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    Photo 4 - Cav plate relationship to pad (top edge of level up against bottom of pad)

    Click image for larger version. 

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    I hope I've included enough information to help get started down the right path to find the right prop. I really appreciate the advice and comments!

    Pete

  2. #2
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    Pete, I'm sure some great advice is coming from experts soon. I didn't realize your engine has a modern type lower unit.

    Basic info: get a chopper and raise your engine height. You'll have to remove that trim tab, and maybe block off the upper water inlets. You'll probably lose water pressure before it starts slipping, so monitor that water pressure. Enjoy the journey!

    Trace

  3. #3
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    I'd try a trophy or a high five. A chopper will be fine for wide open, but the overall driveability will suffer.

  4. #4
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    Quote Originally Posted by Capt.Insane-o View Post
    A chopper will be fine for wide open, but the overall driveability will suffer.
    I'm also hesitant to recommend a Chopper for the same reasons. The boat has already displayed a tendency to be a hopper even with a lame aluminum prop, so with the bow lift a Chopper will provide along with the poor holeshot it could be a disaster.

    51 mph with 80 horsepower is VERY respectable by any standard. The boat is a craftsmanship masterpiece and in my mind could not be a more perfect representation of a bygone era. It certainly can be made faster ( very possibly a lot faster) but it's going to lose it's "authenticness" along the way. If you are ok with that, and prepared to do a ton of work and testing then let's have at it.

    First order of business, forget about the cavitation plate. The important dimension is where is the centerline of the propshaft in relation to the pad? I would start with the propshaft 3 inches below the pad which will likely make your existing props useless, you'll need a new inventory of props with a lot more "bite".
    Living in the Freedom provided by Bud Conner and his fellow warriors.
    R.I.P. my Heathen Brother






  5. #5
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    In keeping with the old school train of thought.Take your 14x21 and put a good trailer ball cup in it.Slip will go down and speed,maybe up a couple,maybe even three.And cost nothing!

  6. #6
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    Quote Originally Posted by outasite View Post
    In keeping with the old school train of thought.Take your 14x21 and put a good trailer ball cup in it.Slip will go down and speed,maybe up a couple,maybe even three.And cost nothing!
    OMG, I didn't want to go that far back
    Living in the Freedom provided by Bud Conner and his fellow warriors.
    R.I.P. my Heathen Brother






  7. #7
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    Pete,
    I'm certainly not going to disagree with the Capn or Transomstand, BUT, I was thinking your goal was to get maximum speed, and a chopper will help in that department.

    As inspiration, on that other forum where you've been posting, if you do a little searching, you'll find a Mercury "Boathouse Bulletin". On a Raveau boat very similar to yours, they clocked what I believe was a MK 78 at over 60mph. It did have a Speedmaster LU, but still, kinda neat to get that kind of speed in a pleasure boat way back then.

    Trace
    Last edited by cyhuff; 03-11-2015 at 12:12 PM.

  8. #8
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    Quote Originally Posted by transomstand View Post
    I'm also hesitant to recommend a Chopper for the same reasons. The boat has already displayed a tendency to be a hopper even with a lame aluminum prop, so with the bow lift a Chopper will provide along with the poor holeshot it could be a disaster.

    51 mph with 80 horsepower is VERY respectable by any standard. The boat is a craftsmanship masterpiece and in my mind could not be a more perfect representation of a bygone era. It certainly can be made faster ( very possibly a lot faster) but it's going to lose it's "authenticness" along the way. If you are ok with that, and prepared to do a ton of work and testing then let's have at it.

    First order of business, forget about the cavitation plate. The important dimension is where is the centerline of the propshaft in relation to the pad? I would start with the propshaft 3 inches below the pad which will likely make your existing props useless, you'll need a new inventory of props with a lot more "bite".
    Thank you for the advice, I would love to go faster, but, as you both mention (Capt. and Transomstand) it will take work to do it right. Sounds like the consensus at the very least is to raise the motor.

    I took a look at my setup and I'd have to modify the CMC unit - turns out the bolt that would go through the lower port-side mounting slot on the motor bracket will interfere with the hydr. fluid sump. Also, the upper holes in the motor bracket would be above the CMC clamp plate. The solution for raising the motor may be a future project (integrated tilt/trim perhaps or remount the CMC).

    Despite my desire to go faster, I'm very satisfied with the current speed, and just happy the package (boat and motor) seems to be working well

    I really appreciate ALL the advice I've received, it's going into a file for future reference!

    Pete

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    Hi Trace,
    I always want to go faster Looks like I'll need to do some work, though, to get the motor higher (see my response to Transomstand and Capn above) and I may wait 'til later to do that. It appears that the way I rigged everything when I built the boat (not knowing a thing about where to set the prop shaft or cav plate height with the set back) I managed to build in some constraints that'll require some thought to get around.

    I've poured over those Boat House Bulletins over the years!! It's wonderful to have access to that kind of information. Your're right, the speeds some of those boat achieved is amazing. Did they have any kind of dynamic tilt/trim back then? I'll bet it was fun to test the rigs.

    Pete

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    Pete,

    Any guy who can build such a nice boat will have no problem whatsoever figuring out how to get that motor higher!

    And more pics... that machine needs to be seen by all!

    T

  11. #11
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    Quote Originally Posted by cyhuff View Post
    Pete,

    Any guy who can build such a nice boat will have no problem whatsoever figuring out how to get that motor higher!

    And more pics... that machine needs to be seen by all!

    T

    ^^^ With some experience at wasting a BUNCH of money on props, you may find it much simpler and cost effective to make some changes on the bottom of the boat with a set of forward strakes to provide lift where the boat needs it at it's transition speed.

  12. #12
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    Quote Originally Posted by peter1708 View Post


    I've poured over those Boat House Bulletins over the years!! It's wonderful to have access to that kind of information. Your're right, the speeds some of those boat achieved is amazing. Did they have any kind of dynamic tilt/trim back then? I'll bet it was fun to test the rigs.

    Pete
    If you find a thread on here called "Life at Lake X in the sixties" you can read the stories and thoughts from the people who actually did it.
    Living in the Freedom provided by Bud Conner and his fellow warriors.
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  13. #13
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    Quote Originally Posted by Capt.Insane-o View Post
    ^^^ With some experience at wasting a BUNCH of money on props, you may find it much simpler and cost effective to make some changes on the bottom of the boat with a set of forward strakes to provide lift where the boat needs it at it's transition speed.
    Hi Capt., interesting you bring up lifting strakes. The designer of this boat built a one-off for a guy. He deepened the V a little and added lifting strakes. I believe the motor that was put on it was a racing motor, with power tilt/trim and a power jack plate. I guess it ran into the low 70's. Ultimately, an older inline was put on it because no one else but the owner was able to drive the boat!

    Pete

  14. #14
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    Quote Originally Posted by transomstand View Post
    If you find a thread on here called "Life at Lake X in the sixties" you can read the stories and thoughts from the people who actually did it.
    I just read the first couple of pages and I think I've found my reading material for the next few weeks! Great stuff!

    Pete

  15. #15
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    Pete..(and guys he lives north me and Doc Frankenmerc about 100 miles) but was going to post ya the FG thread, but saw this new post you, so I'll stay here for now. I had to go out back shed and look for stuff needed my old Shovelhead HD. Well, stack of props there and had to take a look the Flatbottom ones that did not work as well as the SS 2B cupped 12x24. But you know what meant that prop on FG. But I have a 2B 13x23 Alum, no cup prop that simple will not work my Flatty. Its a thru hub, and blows out without a easy throttle so useless to me. The Flatty likes the over hub more 2 blade as more prop in the water, as seems exhaust it a zero problem. But from another guy out here us, owns a small island and a Merc freak too, but "other side the water us, Seattle" that had no use for it and sent me for free when me and Doc built the Flatty project.

    If ya think ya can use it, I'll box it and get it your way. Send me PM addy. If it works? Its yours. (What goes around, comes around) and "playing with props NOT borrowed, but bought?"..well ya get a expensive stack like the rest us!

    But be nice in summer ya drag it down here to the "Doc" and lets play with props as he has more props that Billary's lost emails! He keeps bugging me to drag the Flatty out to his lake, but as I'm Private HOA, private boat launch and marina, and cost bucks for getting plated trailer, and toss a light bar on. But I "never say never", so who knows.

    Tried one his 12x24 3B, and yep trim tab has to come off (we got same L/Us), and like said FG, torque steer was a "gorilla grab", and simple scary. But all boats are diff.

    Ever been at the "Docs"? Ya simple gotta see all the collection HE has in parts, blocks, built IL6 and WAY more. Plus a hell of a nice guy, even if hes a retired (gearhead) cop!

    And the "other Pete", TS...?...yes as ya older than ya think as you know that "trailer ball cup!"

    Tell ya a fast "prop work a hammer"..midnight back 70's on my XS Swit. Had the 3b bronze ski prop on and hit something and bent a blade. Back the lake house, and pull it off and start banging the hell out it on the house deck. Some how the neighbors (all owned boats, so understood) didn't tell me to KNOCK IT OFF AND DO IT TOMORROW! But heard about it next day as "could you wait until morning to spend a hour banging a prop from midnight until 1AM? Glad it stopped, prop on and ya left a water test and we finally got some sleep!"

    But I'm a type that will NEVER crash out "when on the brain.."I gotta fix this NOW!"
    Last edited by Robby321; 03-11-2015 at 08:06 PM.

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