Prop diameter effect and planing trouble

[timharper89]

So I've been having trouble with planing since I bought my 1987 four winns 195 with a 4.3L. It had a 23 pitch prop when I bought it, which was way too high, so I bought a 4 blade 14x19, which was better (33mph wot with 2 adults and full tank of gas @4600 rpm), but with a loaded boat (5 or 6 adults and maybe 2 kids under 7, it would take a full minute or more to plane. You can imagine how good it is to ski behind. Anyway I just bought a 4 blade 15x15 prop. I took it out yesterday, and it may have seemed faster to plane, but I couldn't HOLD it on plane under 4k rpms. Granted there was 1-2+ chop, but I've been out in that before with less trouble. I didn't get a wot/speed, but the rpms were higher at similar throttle positions. Is maybe the 15 diameter to big? Seems I should have much easier time planing going down I pitch and up in diameter, but maybe not? Any extra knowledge of there that could help me out?

 

[Bondo]

Ayuh,..... My guess is, yer over-loadin' yer boat with that many people onboard,.....
Skiing with that many in the boat is just plain ole ridiculous,....

Diameter plays very little, it's got the most to do with blade design,....
The lower the pitch, the larger the diameter, so it don't slip as badly,....

Pitch is what you shop,...

 

[alldodge]

^^ Agree
I would not use a 4 blade prop on the boat, it takes more HP to turn and you don't need all the stern lift. Your 4 blade 19 is like a 3 blade 21

Look for a 3 blade 19

 

[timharper89]

^^ Agree
I would not use a 4 blade prop on the boat, it takes more HP to turn and you don't need all the stern lift. Your 4 blade 19 is like a 3 blade 21

Look for a 3 blade 19

I thought 4 blades helped plane faster and hold it better. Is that wrong? Planing is the issue I'm trying to fix

 

[timharper89]

Ayuh,..... My guess is, yer over-loadin' yer boat with that many people onboard,.....
Skiing with that many in the boat is just plain ole ridiculous,....

Diameter plays very little, it's got the most to do with blade design,....
The lower the pitch, the larger the diameter, so it don't slip as badly,....

Pitch is what you shop,...

The overloaded boat is a few times a year thing, but still trying to pull a skier out is challenging with 3 on board. I thought going down in pitch would make that better, and the 4 blade design even more so. But it seemed to not be the case with 2 adults and a 7 year old yesterday.

 

[alldodge]

I thought 4 blades helped plane faster and hold it better. Is that wrong? Planing is the issue I'm trying to fix

Yes and No
If (note the if) the motor has enough low end torque for the size, weight of the boat then yes. No if there is not enough HP. Your not able to quickly get up on plane so you don't want to loose any more hp turning the prop then necessary.

The other side is also once on plane if there is to much lift then it won't stay on plane as you noticed

 

[airshot]

Is the motor running at peak effiency?? Almost sounds like your engine nay need a tuneup!! Gotta have the engine on song before you play with the propellor or your results will be false!!!

 

[timharper89]

Yes and No
If (note the if) the motor has enough low end torque for the size, weight of the boat then yes. No if there is not enough HP. Your not able to quickly get up on plane so you don't want to loose any more hp turning the prop then necessary.

The other side is also once on plane if there is to much lift then it won't stay on plane as you noticed

Never heard that perspective, but it makes sense. So maybe a 17p 3 blade for towing sports? To much lift? Ugh! propellers are so complicated lol

 

[timharper89]

Is the motor running at peak effiency?? Almost sounds like your engine nay need a tuneup!! Gotta have the engine on song before you play with the propellor or your results will be false!!!

I know it is performing poorly. Low compression in one cylinder, but we are saving for a different boat and don't want to dump a bunch of money into this one. Was hoping to get some compromise on performance with a prop change to get us by a season or two.

 

[jimmbo]

Merc's High 5 was popular with Skiers and other Watersportsters. It has 5 small blades, and doesn't appear to be all that large in the Diameter.

With 1 weak cylinder, you are effectively running a 4 cylinder engine, as the power of the 5th is being used to carry the dead one. If it takes a Minute to plane, it is not going to be a boat to ski behind, in any Stretch of the Imagination

Instead of putting good money into bad, get rid of this one asap, cancel the Insurance, and you although you won't be boating this year, money saved by not doing so, will bring forth a replacement sooner

 

[timharper89]

Merc's High 5 was popular with Skiers and other Watersportsters. It has 5 small blades, and doesn't appear to be all that large in the Diameter.

With 1 weak cylinder, you are effectively running a 4 cylinder engine, as the power of the 5th is being used to carry the dead one. If it takes a Minute to plane, it is not going to be a boat to ski behind, in any Stretch of the Imagination

Instead of putting good money into bad, get rid of this one asap, cancel the Insurance, and you although you won't be boating this year, money saved by not doing so, will bring forth a replacement sooner

Insurance for me is $140 for the year. I do my own maintenance. Very little cost aside from fuel and towing fuel to be on the water.

 

[Scott06]

I know it is performing poorly. Low compression in one cylinder, but we are saving for a different boat and don't want to dump a bunch of money into this one. Was hoping to get some compromise on performance with a prop change to get us by a season or two.

You won't be able to prop around these issues. If it was healthy and you were getting 4600 wot with a 19" 4 blade, then I would suggest a 17" 4 blade... But you have a dying engine unfortunately.

I run 4 blades for loading watersports performance works well but my engine is in good shape. If you are handy get a junkyard truck 4.3 engine and swap it in. If nothing else when you sell this boat it will a greater value

 

[timharper89]

You won't be able to prop around these issues. If it was healthy and you were getting 4600 wot with a 19" 4 blade, then I would suggest a 17" 4 blade... But you have a dying engine unfortunately.

I run 4 blades for loading watersports performance works well but my engine is in good shape. If you are handy get a junkyard truck 4.3 engine and swap it in. If nothing else when you sell this boat it will a greater value

We are looking and ready to upgrade when the right boat comes along. When that happens, I'll just list it for next to nothing to get it out of my driveway. Considered doing just this, but decided against it because it is a big job, and I don't really know what I'm doing. I've got the inclination, just not the experience with that.

 

[Chris1956]

Probably not helpful for you, as you want to be rid of it, but those 19 footers with V6 Sterndrives are pretty butt heavy. They plow some water when accelerating, even with good motors and props. A mitigation is power trim tabs. With tabs down, she will pane at lower speed and therefore faster. she will also stay on plane at a lower speed. Tabs up and she will get top speed.

The spring loaded tabs may help, but I always wanted full control, so I never tried them.

 

[Chris51280]

Merc's High 5 was popular with Skiers and other Watersportsters. It has 5 small blades, and doesn't appear to be all that large in the Diameter.

With 1 weak cylinder, you are effectively running a 4 cylinder engine, as the power of the 5th is being used to carry the dead one. If it takes a Minute to plane, it is not going to be a boat to ski behind, in any Stretch of the Imagination

Instead of putting good money into bad, get rid of this one asap, cancel the Insurance, and you although you won't be boating this year, money saved by not doing so, will bring forth a replacement sooner

that is true. I had spark plug wires crossed once so it ran on only 4. I was barely able to ski behind it.

 

[achris]

..., so I bought a 4 blade 14x19, which was better (33mph wot with 2 adults and full tank of gas @4600 rpm),

Still too low. Yes the recommended is 4400-4800 and you're right bang in the middle, but the 4.3 lacks to bottom end to comfortably carry a prop that only makes 4600.

but with a loaded boat (5 or 6 adults and maybe 2 kids under 7, it would take a full minute or more to plane.

Not surprised in the least! You are going to kill that engine operating it like that...

Also, read the manual, the bit where it says that if you're planning on skiing (any towsports really), find the right prop when not skiing, and then use the next size (2") lower when skiing...

So, use a 4 blade 17" or 18" for your normal operations, and when you want to ski, swap in a 15" or 16" prop... 3 blade or 4 blade is your choice.

Chris........

 

[timharper89]

Probably not helpful for you, as you want to be rid of it, but those 19 footers with V6 Sterndrives are pretty butt heavy. They plow some water when accelerating, even with good motors and props. A mitigation is power trim tabs. With tabs down, she will pane at lower speed and therefore faster. she will also stay on plane at a lower speed. Tabs up and she will get top speed.

The spring loaded tabs may help, but I always wanted full control, so I never tried them.

The sad thing is the boat has Bennett trim tabs. Maybe I'm using them wrong. They were on the boat when I bought it, but I push them both down. I don't know that I have verified that down is actually down

 

[timharper89]

So, use a 4 blade 17" or 18" for your normal operations, and when you want to ski, swap in a 15" or 16" prop... 3 blade or 4 blade is your choice.

Chris........

I used a 15p prop, and it wouldn't stay on plane very well after coming up on plane in rough seas. Will this not be a problem if on calm water but pulling a skier?

Also with a full boat would going down in pitch help?

 

[jimmbo]

deleted

 

[Scott06]

I used a 15p prop, and it wouldn't stay on plane very well after coming up on plane in rough seas. Will this not be a problem if on calm water but pulling a skier?

Also with a full boat would going down in pitch help?

Yes heavier load go down in pitch