Help me find the right prop size. Hwsiii is this the prop you recommended?

[scbackpacker]

I have a 1995 Monterey 196 Montera running an alum. Solas Amita 14.3-21 pitch 3 blade prop. I would like to get a better hole shot for skiing and general cruising around. After boat planes I can trim up just a little and hit 42 mph on gps at 4400-4800 rpm but I'm having a lot of porpoising. At 5000 rpm it smooths out but I don't run it at this speed.
The stats I know on my boat:

1. length- 19' 6"
2. width- 8' 2"
3. weight- 2700lbs
4. engine- 4.3 LX. alpha generation 2 outdrive 1:84R 180 hp
5. fuel- 30 gal.
6. passenger capacity- 8 but will normally carry 2-6 people.
7. hull- I'm going to say a deep V..sport boat.

I'm staying with an alum. prop for right now.
I hope this is enough because it's all that's in the owners manual.
thanks.

 

[scbackpacker]

Re: Help me find the right prop size.

Re: Help me find the right prop size.

 

[Bondo]

Re: Help me find the right prop size.

Re: Help me find the right prop size.

After boat planes I can trim up just a little and hit 42 mph on gps at 4400-4800 rpm but I'm having a lot of porpoising. At 5000 rpm it smooths out but I don't run it at this speed.

Ayuh,.... Donno what to tell ya,... You're already Under-propped...
Rpms at WOT is 4800 for your motor,+ you're already Over that....
And,...
A 19' boat with an Under-propped 4.3l Should be Slamming you into the seat at hole-shot Now....

 

[propper_advice]

Re: Help me find the right prop size.

Re: Help me find the right prop size.

Completely agree with Bond-o regarding your RPM's. Have you considered adding a hydrofoil or switching to a 4 blade?

 

[scbackpacker]

Re: Help me find the right prop size.

Re: Help me find the right prop size.

Yes I have considered a 4 blade. What do you mean by underproped? That the prop is to small? I'm new to boating. Only had it in water twice.

 

[propper_advice]

Re: Help me find the right prop size.

Re: Help me find the right prop size.

Hold out, Bond-o may still answer you and explain his thoughts in more detail.

Meanwhile, you are basically correct. When RPM's are too high, we correct the problem by increasing your pitch. A 23 pitch would bring your RPM's back into the proper rev range.

You could move into a 4 blade, making a pitch adjustment to correct RPM's, and also improve the hole shot / handling.

EDIT When your company establishes a business contract with iboats we can then permit soliciting!!

 

[scbackpacker]

Re: Help me find the right prop size.

Re: Help me find the right prop size.

So maybe a 23 pitch will help solve the porpoising. Is there a thread that explains props where a newbie could understand?
What do you think about the Solas Amita 14" 23 pitch 4 blade to get the rpms down and be a good performer? iboats have them on sale.

 

[642mx]

Re: Help me find the right prop size.

Re: Help me find the right prop size.

So maybe a 23 pitch will help solve the porpoising. Is there a thread that explains props where a newbie could understand?
What do you think about the Solas Amita 14" 23 pitch 4 blade to get the rpms down and be a good performer? iboats have them on sale.

A 23p will take off slower and have more top end than the 21p. All boats porpoise a little bit, you may not have it trimmed correctly. Try playing around with the trim a little. Most folks trim to fast and don't give the boat enough time to react before they start trimming it more..... try getting up to 30-35 mph before you start trimming it.

A 4 blade is a good prop for cruising and holeshot. They lack a couple MPH that 3 blades can achieve.... but it depends on what you like. And if your going to spend money on a prop.... get a SS prop like a Hill Marine or a Mercury prop. (A Mercury Revolution 4 would be a good choice for your needs).

 

[scbackpacker]

Re: Help me find the right prop size.

Re: Help me find the right prop size.

642mx you are probably correct. I've been watching the trim gage and rpms. The trim gage is out and I'm going to watch rpms and speed. I'll use the prop I have now to learn the ropes of trimming out. I'm not going to get a SS until I learn how to read the lakes and buoys. Made mistake the other day and wiped out a blade on a new prop. I'm having it repaired right now and will be back at it this weekend. The boat goes plenty fast for me and planes good.
Thank Yall for the help

 

[Bondo]

Re: Help me find the right prop size.

Re: Help me find the right prop size.

What do you mean by underproped? That the prop is to small?

Ayuh,... The Whole Idea of Props,+ their Pitch is to properly load the motor so that the rpms at WOT is within the rpm range listed by the manufacturer...
Your motor Tops out at 4800rpms.... The acceptable range is 4400/ 4800rpms...
You need a prop Pitched to keep the rpms to a 4800rpm MAX...

You state it'll spin to 5000rpms +.... That's Underpropped.... More Pitch is the cure...
That said,... It's hard to believe the Hole shot is Bad,...
Raising the Pitch, lowers the torque available at the hole shot...

 

[scbackpacker]

Re: Help me find the right prop size.

Re: Help me find the right prop size.

Maybe I'm misunderstanding the term hole shot. It does pop right up when accelerated which I like. What I would like to have is a prop that will keep it in the correct rpm range and keep the getup and go that I have. From what you're saying is that there is a give and take when changing pitch like changing gear ratios in a gear box. Give me a little time I'll learn.

 

[hwsiii]

Re: Help me find the right prop size.

Re: Help me find the right prop size.

Packer, buy the Solas Amita 4 blade ALUMINUM prop in a 21" pitch and it will lower your RPM to where they ought to be as well as increase your hole shot and acceleration through your whole RPM range, and should get rid of your porpoising as well, because it is a stern lifting prop. Porpoising can be created by the wrong weight distribution in the boat, or a boat bottom anomaly or the wrong prop for that particular boat, normally having not enough rake and blade surface area to hold the bow up when running, but as you see on yours when the prop turns enough RPM it is able to carry the bow high and quits porpoising.

Porpoising is actually caused by the center of lift on the boat being moved back and forth form the center of gravity of the boat, a lot like chine walking. On some boats if you throttle up slower when you come on plane it will slow the effect down a lot, but on others it doesn't matter if you do it slow or fast it still happens. It is a basic instability in the boat that can be caused by many reasons, including hull features but more often it is caused by weight placement in the boat. Moving some weight forward or backwards some of the time can totally cure the problem, but not always. This problem can be exacerbated at times by using a prop that has some rake but not enough to lift the bow as required, and at other times it is best to use a zero rake prop that lifts the stern only and thus eliminates the tendency of the boat to porpoise because it keeps the center of lift on the boat in the stern and it never passes the center of gravity farther forward in the boat.On some boats you can give it more speed and it will actually stop porpoising. I know that is a very lengthy and detailed explanation, but that is the root of the problem with porpoising.


H

 

[scbackpacker]

Re: Help me find the right prop size.

Re: Help me find the right prop size.

Hwsiii I wish had all the info to fill out your form but what I gave on 1st post was all I could find. So you think a 4 blade 21 pitch will help out and not stepping up to a 4 blade 23 pitch. With 2 people me 250 lbs and my wife 150 lbs. I had her sit up front on the bow and it would porpoise. Setting in the passenger seat it also porpoise. I'm sure I'm trying to trim to fast so I'll be working on that. Around 3000 rpms and 30 mph she runs like a champ. The main thing I'm after is keeping it in rpm range and being able to pull skiers. The only Solas 4 blade 21 pitch prop I saw on iboats was the hubex 14" prop.
Hopefully they will continue their free shipping a little longer.

Fellas I sure appreciate the help. I can see that boating people are good and helpful people. Thanks

 

[hwsiii]

Re: Help me find the right prop size.

Re: Help me find the right prop size.

Packer, you will lose about 300 Rpm just changing to a 4 blade Solas over the 3 blade, and if you changed to a 23" pitch you would lose about another 400 RPM, which theoretically brings your RPM down a total of about 700 RPM and that would bring your WOT RPM down to about 4,300 or 4,400 and that is too low, as I show your motor should turn 4,800 RPM at WOT throttle. Also you would lose a good bit of your hole shot as well as acceleration. The Solas Rubex ALUMINUM 4 blade in 21" is the same prop as the Amita, the difference is the Rubex has an interchangeable hub, so it can be used on many different models of motors and the Amita has a normal rubber hub that is not interchangeable. Bond-o is very right, when you increase the pitch of a prop you lose some low end thrust for hole shot and acceleration.

From what you're saying is that there is a give and take when changing pitch like changing gear ratios in a gear box. Give me a little time I'll learn.

Think of it like just like you are, as you lower the pitch you lower the rear end gear ratio, because on a boat the pitch, diameter and blade geometry of a prop is the final GEAR.

If you will read this it will give you a better idea of some of the different blade geometries and what they actually do and how they perform on some hull forms.
http://forums.iboats.com/showthread.php?p=2037486#post2037486


H

 

[scbackpacker]

Re: Help me find the right prop size.

Re: Help me find the right prop size.

I picked up the prop that I damaged from the "prop man" I can't even tell where the repair was made. He had a Mercury 3 blade ss laser2 with hub in 23 pitch for $200.00. Do you think this will work to help with porpoising and rpms or will the alum. 4 blade 21 pitch be better?

 

[scbackpacker]

Re: Help me find the right prop size.

Re: Help me find the right prop size.

Hwsiii is the correct prop that you recommended for my Monterey 4.3l?
Solas RUBEX 4 #9513-140-21 Aluminum Boat Propeller
Mercruiser Alpha One 4.3L Sterndrive 155 - 210 HP

 

[hwsiii]

Re: Help me find the right prop size. Hwsiii is this the prop you recommended?

Yes, That is the correct one.


H

 

[scbackpacker]

Re: Help me find the right prop size. Hwsiii is this the prop you recommended?

Thank you very much... I gave the info to my wife so the kids can get it for me. You have a good day.

 

[hwsiii]

Re: Help me find the right prop size. Hwsiii is this the prop you recommended?

I will be glad when you get to use it, you will be very happy.


H