Pitch?

[hotinnv76]

I have a 1989 Four Winns 160 Freedom. I need a new prop but not sure witch pitch the prop should be. My options are from 11 to 23. What would be the best and why? Want more take off speed but dont want to have a big loss in top speed. New at this whole boating thing so any help would be greatly appreciated.

 

[Silvertip]

Re: Pitch?

The first step in this process is to determine what diameter and pitch you have now and whether it is aluminum or stainless. The numbers are usually stamped into the hub of the prop. Next, unless you tell us what engine you have, I/O or Outboard, and what the current maximum speed and rpm are at wide open throttle with the normal load, we don't have a clue what to recommend unless someone stumbles by and happens to have exactly the same boat, exactly the same engine, and uses it exactly like you do. What you try to ensure is that the engine can reach is recommended wide open throttle rpm. If it can't with the current prop, you need a prop with less pitch. If it can, you already have the optimum prop. If the engine tends to rev higher than its recommended WOT rpm then a prop with more pitch is required. Google "Prop Selection" and read some articles on this topic.

 

[hotinnv76]

Re: Pitch?

The first step in this process is to determine what diameter and pitch you have now and whether it is aluminum or stainless. The numbers are usually stamped into the hub of the prop. Next, unless you tell us what engine you have, I/O or Outboard, and what the current maximum speed and rpm are at wide open throttle with the normal load, we don't have a clue what to recommend unless someone stumbles by and happens to have exactly the same boat, exactly the same engine, and uses it exactly like you do. What you try to ensure is that the engine can reach is recommended wide open throttle rpm. If it can't with the current prop, you need a prop with less pitch. If it can, you already have the optimum prop. If the engine tends to rev higher than its recommended WOT rpm then a prop with more pitch is required. Google "Prop Selection" and read some articles on this topic.

I have no clue what the WOT rpm is for my boat. I bought the boat used and didnt get any info on it. The engine is inboard 3.0L. I got the boat while the engine was taken apart due to the previous owner not draining the water and cracked the block. I had it welded and put the engine back together without a book. It runs great. Not sure if i am getting enough rpms though. 3500 seems about it at full throttle.

 

[Silvertip]

Re: Pitch?

3500 RPM at wide open throttle is not my idea of running great. However, the prop, load, condition of the boat, can all have a bearing on that. That motor should be running at about 4400 - 4500 RPM at wide open throttle. Now if your boat is full of water logged foam it may be a bunch heavier than it should be. Trapped water in the hull can add weight as well. Poor tune up on the engine can obviously result in poor performance. Prop changes should only be made after everything else has been investigated. If you put the engine together without a book, how did you adjust the valves, set the dwell and ignition timing, carb adjustments, etc? If everything is as it should be, then you need a prop with less pitch to get the rpm up where it needs to be. Right now you are lugging the engine.

 

[hotinnv76]

Re: Pitch?

Not sure on the foam. However I did get a printout on Valve adjustments and timing. Found one person in my area that knew that a 3.0l four cylinder was a boat motor." He build engines for a living." However I will go back through with a tune up and get back to you with the prop size and pitch that is currently on the boat. Noticed a couple things that might need attention.
I appreciate the help you've given me so far.

 

[hotinnv76]

Re: Pitch?

Here we go. got prop size. The prop is a Michigan Wheel 13.75x15. model # is 011002. gave the boat a tune up but cant put it in the water just yet. The prop has to be replaced due to a rather large gouge in it. What i want is a little more power for pulling a skier out of the water. As far as the water logged foam, how do you check for that? Props? Need more pitch or less?
Once again I thank you for the help.

 

[Silvertip]

Re: Pitch?

To check for water soaked foam you obviously need access to it so you'll need to check any hatches, access ports, or possibly remove floor boards if that's possible. Without any speed and WOT RPM data I can't suggest what pitch you need. If the engine does not reach its upper RPM band with a normal load in the boat, you need less pitch. If it is at its upper rpm band you should not decrease pitch as the engine will over rev. You can of course decrease pitch but you will have to pay attention to the tach and throttle back a little at WOT. Less pitch is required for hole shot. Right now you do not have enough data to be making prop changes.

 

[Silvertip]

Re: Pitch?

The more I think about this, the more I'm convinced the engine is not performing up to par. A 15P prop on that boat should provide good hole shot. 13P on that boat would certainly over rev the engine. My son-in-law had a similar boat (same engine) and as I remember there was either a 17 or 19P on it. I suspect the iginition timing and/or valve adjustment was not done properly. Have you done a compression check on the engine? Compression testers are $25 at any auto store.

 

[Bondo]

Re: Pitch?

3500rpms, at WOT, with a 15" prop. sounds to Me,...
Like Either the motor is running Very Poorly,...
Or,...
It's turning the Wrong Outdrive Gear Ratio........

 

[hotinnv76]

Re: Pitch?

Valves were adjusted per printout from mechanic. Also performed compression test on all four cylinders. 105 in all cylinders which I was told is normal for a engine thats been broke in. I think I'm going to go ahead and order the same prop that was on the boat. And purchase a 17p later to see if there is a big difference. I Thank You for all your help and will post again whan I have a little more info to give you.

 

[walleyehed]

Re: Pitch?

This is an OMC outdrive, Right?
Throttle butterfly straight up and down with throttle at wide open?