Prop close to what i need?

starsnstripers

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Joined
Nov 30, 2007
Messages
1,330
24' 3500lbs 260hp Alpha 1 Mercruiser 1.50:1 Have a 15 3/4X17" any thoughts? Try it and see or?
 

starsnstripers

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Nov 30, 2007
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Re: Prop close to what i need?

Also, how much difference would a 14.5 x 19" compare to what i have 15 3/4 x 17"?
 
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hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: Prop close to what i need?

Stars, welcome to Iboats prop forum and I will try to help you as much as I can but without more information no one can help you, and I will tell you I need more information than anyone else. But if you would like my help fill this form out and I will help you as much as I can.

, You might try reading this for a better understanding of changing props for better performance, and for the major differences between aluminum props and stainless steel.

http://forums.iboats.com/showthread.php?t=369057


If you would prefer to not go to this much trouble there are many other people who will come along and gladly help you.

1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
2a.What is the maximum recommended HP for your boat
3. Number of people and gallons of gas normally on boat and what do you use the boat for
4. Year, make. manufacturer and model of motor and recommended Wide Open Throttle (WOT) range
5. HP and gear ratio of motor IMPORTANT
If you don?t know the ratio, you need to pull the plugs out and put a piece of tape across the prop and the lower unit and then cut it between the prop and the housing then do the same thing on the flywheel and turn the motor until the tape lines up with each other on the prop, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor
6. Anti-ventilation Plate height above keel of boat if it is an outboard in inches, use a straight edge under the keel and sticking out to the anti ventilation plate for a reference
Motor Transom Height
AntiventilationPlateStraightEdge-2.jpg


When the boat is running in the top 20% of your speed you should be able to see the anti ventilation plate very clearly at the top of the water and have water just splashing over the top of it.

Correct Anti Ventilation Height

correctheight.jpg

7. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. Make sure you trim the prop up until it starts ventilating and then just trim in until it quits ventilating.
RPM _________ Speed ______ GPS ______ No. of people ______ Gal. Gas ________
8. Make, model, diameter, pitch, number of blades and whether SS or aluminum prop and does it have a hydrafoil, dolefin or trim tabs
9. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way by just pushing the throttle at the helm and not at the carburetor, checked compression, and looked at the plugs and checked spark as well as timing and advance, all of the foregoing could be the reason your prop is not attaining full RPM
10. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations and does the prop show any damage that you can see

REMEMBER, The numbers I give you will be NO better than the information you give me. I use a computer program I designed to find the correct pitch and then knowledge to pick a Better prop design for your boat.

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.



H
 

starsnstripers

Lieutenant
Joined
Nov 30, 2007
Messages
1,330
Re: Prop close to what i need?

Thanks for all the info hwsiii My boat is a 1969 Old Town Atlantis 2560 that weighs 2900 dry. Is 8' Beam 7'6" at the transom Has a 260 hp Mercruiser with an Alpha One, Mich. Wheel 031036 1.5:1 Drive 15 3/4 Dia - 17" pitch 40 gal of gas two ave. people. I haven't used the boat yet it's a drive from another boat. I am just wondering how close i am from the get go? Oh, 27* deadrise
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: Prop close to what i need?

Stars, I can't imagine that boat having a 27 degree deadrise, that would make a big difference in my calculations. Would you please verify that.

The 17" pitch should be close.



H
 

starsnstripers

Lieutenant
Joined
Nov 30, 2007
Messages
1,330
Re: Prop close to what i need?

I was told that and had doubts too. I have a 233 formula in the yard and i know it has a 24* deadrise i checked and compared and by god it does. 27* thats correct.
 

starsnstripers

Lieutenant
Joined
Nov 30, 2007
Messages
1,330
Re: Prop close to what i need?

It had these side homemade fins on it in the pic but here's a pic of the stern dead rise. Can't wait to try her out! See pic, thanks
 

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hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: Prop close to what i need?

That is one major deadrise, but with that weight I still believe it will be close with the 17, try it and then get back with me and we will get it setup very good.



H
 

starsnstripers

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Joined
Nov 30, 2007
Messages
1,330
Re: Prop close to what i need?

Here's a copy of her specs, neat boat i just hope she can handle a sea, hehe
 

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starsnstripers

Lieutenant
Joined
Nov 30, 2007
Messages
1,330
Re: Prop close to what i need?

It's a heck of a deadrise but i'm going to add trim tabs.
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: Prop close to what i need?

Stars, if you will run it with the 17" pitch you have now and get us a WOT RPM and GPS speed we will see how what you you have now is working for you.

My theory on the extra plates on the side is he tried to slow the roll down when he was drifting side saddle in seas, because with 27 degrees that thing will roll bad in side seas when you are drifting.



H
 

starsnstripers

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Joined
Nov 30, 2007
Messages
1,330
Re: Prop close to what i need?

yeah thats what i was thinking too about those side fins, think they helped? I am leaving them on this season. I resealed and coated them, they seem to be on there tight. Their rust pited but whole. Do trim tabs help against the roll? A friend said the large Dia at 15 3/4 is for like pontoon or housr boat slower power, which makes sense. thinking a 19-21 pitch X 14 1/2. I'll try it whith this prop and see what happens. Thanks again.
 
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