Another Prop Puzzle!

[tyrantjon]

what I have: 1991 wellcraft eclipse 232, 5.7 ltr 350 magnum (260 hp) mercruiser, alpha 1 gen 1 outdrive. approx 4000 lbs. recommended WOT range is 4300 to 4800.

when I got this boat, it had a stainless 3 blade 14.5 dia, 17 pitch

with that I am only able to get about 4000 rpm at 40 mph WOT

I tried (recommended by a seasoned boat tech) an aluminum 4 blade 14.5 dia, 17 pitch

with that I dropped to 3800 rpm and 38 mph

so, with that being said, can anyone tell me what prop I could or should use in order to utilize approx 4500 rpm WOT and be able to get it to push approx 50 MPH?

thank you in advance.

 

[Starcraft5834]

Re: Another Prop Puzzle!

assuming your engine is sound... and it's not terribly waterlogged (soggy foam) and to heavy.. ( if i sits in the water- ie water line seems normal) your probably good. some experts will chime in.. 17 pitch for that engine should do the job.... going down in pitch should increase your RMP's

 

[tyrantjon]

Re: Another Prop Puzzle!

engine is in excellent shape! purrs and runs smooth as advertised! very sound hull, not water logged at all. entire boat is dry as the desert. the boats manufactured weight as is, is 3900 lbs, with my gear and whatnot, I'm over 4000 lbs, which is normal. which brings me to believe that the previous owner swapped the props and now I'm trying to find out what is needing to be on there to bring me up in RPM's and hopefully tweek it to where I can get more MPH's.

so what you are suggesting, is to put a 15 pitch on it, which will get me closer to my recommended WOT range. I agree with that. but would you be able to help with how I would be able to gain more speed? also, 3 blade or 4 blade?

 

[MikDee]

Re: Another Prop Puzzle!

Put the SS prop back on for speed! Now, are you trimming for speed? Here's how: At WOT, slowly trim up as your rpm, & speed go up,,, Then if you start to feel prop slip, bring it back down just a bit till the prop grabs,,, That's your best rpm, & top speed. If you haven't been doing this, you will get more rpm, & about 5mph more top speed.

If you've done this, and still not getting the right top speed, and rpm, Your engine is not up to snuff! Check, & reset your timing to factory specs. Also, make sure your throttle linkage is opening all the way (at the injectors)? Plus check that your flame arrestor is clean, & clear! Then your fuel tank vent, that it's clear? (it can only let in so much fuel at a time, if it's clogged any), you can just pop the fuel cap open when running to see if it's restricting any power?

Hows your fuel filters, have you changed them this year? How about the Distributor cap, wires, & spark plugs, are they in good shape, and Marine design anything else is not sealed for sparks, and is dangerous! I like AC Delco MR series spark plugs, whatever length, heat range, you need, either: MR43, MR44, MR45,? These are an alloy plug (no rusting), plus have a massive center electrode for the most secure spark.

This should get you to 50mph, or Plus!

Shoot I used to get 40mph on my old (heavy) 79'-24ft SeaRay cuddy with a (stock) 350/260hp Mercruiser at 4500 rpm, with a 14"X17" Black Max Aluminum prop!

 

[tyrantjon]

Re: Another Prop Puzzle!

Put the SS prop back on for speed! Now, are you trimming for speed? Here's how: At WOT, slowly trim up as your rpm, & speed go up,,, Then if you start to feel prop slip, bring it back down just a bit till the prop grabs,,, That's your best rpm, & top speed. If you haven't been doing this, you will get more rpm, & about 5mph more top speed.

If you've done this, and still not getting the right top speed, and rpm, Your engine is not up to snuff! Check, & reset your timing to factory specs. Also, make sure your throttle linkage is opening all the way (at the injectors)? Plus check that your flame arrestor is clean, & clear! Then your fuel tank vent, that it's clear? (it can only let in so much fuel at a time, if it's clogged any), you can just pop the fuel cap open when running to see if it's restricting any power?

Hows your fuel filters, have you changed them this year? How about the Distributor cap, wires, & spark plugs, are they in good shape, and Marine design anything else is not sealed for sparks, and is dangerous! I like AC Delco MR series spark plugs, whatever length, heat range, you need, either: MR43, MR44, MR45,? These are an alloy plug (no rusting), plus have a massive center electrode for the most secure spark.

This should get you to 50mph, or Plus!

Shoot I used to get 40mph on my old (heavy) 79'-24ft SeaRay cuddy with a (stock) 350/260hp Mercruiser with a 14"X17" Black Max Aluminum prop!

I've gone over the engine with a fine toothed comb. new plugs (MR44's) new dist cap, new wires, new rotor button, overhauled the original Rochester quadrajet carb, dialed it in perfectly, flame arrestor is kept very clean, I've routed (4) 3 inch clean air ducts to the engine and the bay is vented very well, fresh oil and gear lubes and grease everywhere, I go over this boat and engine every winter to ensure it's hassle free for the warm seasons. I will be resetting my timing tonight because I have not touched that in a while. one thing I have not experimented with is your recommendation with the trimming. I've always had friends and family with me so I didn't want to freak anyone out with me messing around with that.

 

[Starcraft5834]

Re: Another Prop Puzzle!

engine is in excellent shape! purrs and runs smooth as advertised! very sound hull, not water logged at all. entire boat is dry as the desert. the boats manufactured weight as is, is 3900 lbs, with my gear and whatnot, I'm over 4000 lbs, which is normal. which brings me to believe that the previous owner swapped the props and now I'm trying to find out what is needing to be on there to bring me up in RPM's and hopefully tweek it to where I can get more MPH's.

so what you are suggesting, is to put a 15 pitch on it, which will get me closer to my recommended WOT range. I agree with that. but would you be able to help with how I would be able to gain more speed? also, 3 blade or 4 blade?

you wont generally get more speed with less pitch........pitch correlation means...each #16-17-18-19 etc.. one prop turn= distance travelled.. so you see, your engine turning faster with say a 16p wont necessarrily mean your going to go faster.. you need to get a prop that operates in the recommended rpm range first..4400-4800 rpms. trimmed out as mentioned above,, once you are there, stop worrying about going faster.. you wont... if you put more pitch on... say 21p prop, (in attempt to go faster) your rpm's will likely bog down again...that's generally how it works. once you get to say 4500rpms, you will be able to tell by sound of engine that's the "sweet spot", not over reving, you will know when you hear it.. also, a 4 blade will absolutely cost you a mile per hour or two, in exchange for more hole shot, thrust, up on plane quicker, and maintain plane at slower speeds than needed with a 3 blade..

 

[eavega]

Re: Another Prop Puzzle!

engine is in excellent shape! purrs and runs smooth as advertised! very sound hull, not water logged at all. entire boat is dry as the desert. the boats manufactured weight as is, is 3900 lbs, with my gear and whatnot, I'm over 4000 lbs, which is normal. which brings me to believe that the previous owner swapped the props and now I'm trying to find out what is needing to be on there to bring me up in RPM's and hopefully tweek it to where I can get more MPH's.

so what you are suggesting, is to put a 15 pitch on it, which will get me closer to my recommended WOT range. I agree with that. but would you be able to help with how I would be able to gain more speed? also, 3 blade or 4 blade?

Well, by the numbers, you are looking at a ~9% slip on your 17P prop, meaning if your motor could spin it into its correct RPM range, you would be looking at about 50 MPH. With a 15P prop, you are not going to hit 50 MPH even if you could get the motor to spin at 4800 RPM. A 2" drop in pitch will increase your RPMs by approximately 400 RPMs (200 RPM per inch of pitch, but that is a rule of thumb, not a hard and fast fact) which would get you into the right RPM range (albeit the lower end of the range), but even at with no slip, it looks like your highest maximum speed would be in the 45 MPH range.

Stay away from a 4-blade if you are looking for top end speed. a 4-blade will give you more stern lifting which will get you on top of the water faster, but it will cost you top end speed.

Rgds

Eric

 

[tyrantjon]

Re: Another Prop Puzzle!

thank you

with what i gather from the responses im leaning towards believing that I will be able to gain up to my recommended WOT RPMs of 4500 +/- by utilizing a 15 pitch. also, in order to maximize in speed i'll need to toy with the trim to find the "sweet spot". is that about right?

 

[MikDee]

Re: Another Prop Puzzle!

Don't dare go down on pitch till you try this!
Trimming for speed is something us seasoned boaters know about, usually not "beginners, or rookies". Do it just like I said, and it will work like I said, & don't be afraid, it will become like second nature to you, you'll be able to tell by the sound, & feel of the boat,. Sort of like "Flying by the seat of your pants"!,,,lol, Once you come down off plane, you'll hafta trim down though, again you'll notice this due to the feel of the boat. We I/O, and outboard owners are lucky to have this, inboard motors don't have this advantage

 

[QC]

Re: Another Prop Puzzle!

This is NOT a 50 MPH combo. Work on trim, but this is a heavy combo and it is just not going to be much faster than 45 no matter what you do. I almost bought one of these and it had duo-prop and Big Block. They have high deadrise, and lots of freeboard. Also, with slip that good, I would double check the tach. I doubt that a 15 was ever used on these unless the gear ratio has been changed. Anytime I see a single screw where the owner complains of top speed, but not planing time, I suspect tach.

 

[Tail_Gunner]

Re: Another Prop Puzzle!

This is NOT a 50 MPH combo. Work on trim, but this is a heavy combo and it is just not going to be much faster than 45 no matter what you do. I almost bought one of these and it had duo-prop and Big Block. They have high deadrise, and lots of freeboard. Also, with slip that good, I would double check the tach. I doubt that a 15 was ever used on these unless the gear ratio has been changed. Anytime I see a single screw where the owner complains of top speed, but not planing time, I suspect tach.

Bingo while not a 50 mph boat is does have a ride that is very comfortable in a chop. I have a 22' footer similar design with a 454 and it struggeled to do 55....and yes tach's are worse than polotician's for accuracy..that polotics

 

[MikDee]

Re: Another Prop Puzzle!

That Wellcraft Eclipse is a lot more streamlined then my old 79'-24ft SeaRay Cuddy,, and probably lighter too, and I got 40mph out of that with a 17" pitch alum prop, fully trimmed out, and that was an old technology small block, not a Magnum, nor did I have a SS prop. So, IMO, there's no reason he couldn't get at least 45mph out of that Eclipse with a healthy engine if set up right, (nice looking boat, by the way, very beamy). Once I saw one, I longed for the Eclipse myself, but didn't have the dough at the time!