Need help in buying new prop

[Vision91]

im looking at buying a new prop for my boat the one i have on it now is the aluminum factory one and it haves some dings in it from goin to the lake this weekend. i want to buy a ss prop but not sure what to go with or where to even start the prop i have now is a 13x19.. the motor is a 1972 mercury 1150..and the boat is a 1991 vision bass boat not sure on the weight but the length is 16.5 ft thats about all the info i have on the boat since its no longer made...o i also have a performance jack plate...i started a thread on this a while back and didnt get any help so maybe this time i will thanks for the help.

 

[sutor623]

Re: Need help in buying new prop

Vis you probably didnt get any help cause the boys on here need more info. First off we need a GPS reading of WOT. Next we need to know what RPMs your motor is spinning at at WOT. Without out these two facts we will all just be pissing into the wind.

 

[steelespike]

Re: Need help in buying new prop

The prop size and the wot rpm and speed by gps is very important.Some cells have a gps app.
If you boat where hard contact are likely you may want to reconsider a ss prop.
You could get your old prop repaired and get us the info needed.
Before selecting a prop we need to know if the present setup is working.
And what the wot rpm is both before and after a prop selection.

 

[Vision91]

Re: Need help in buying new prop

oops my fault forgot to add the speed and rpm in...anyhow the speed by the gps was 36 at wot and rpm 4900...i recently got the motor back from the shop and im not sure if they did a time and snyc...since they only replaced the ignition coil.

 

[sutor623]

Re: Need help in buying new prop

Is the gear ratio the factory 1.78?

 

[sutor623]

Re: Need help in buying new prop

Nevermind, in '72 they went from 1.78 to 2:1 ratio.

 

[sutor623]

Re: Need help in buying new prop

Your RPM range in that motor should be 5000-5500RPMs. It seems to me that you would want to drop down to a 17P prop. id say even a 16P but they are few and far between as far as selection goes.

 

[Vision91]

Re: Need help in buying new prop

yea as far as the gear ratio for it i aint got the slightest clue im still new to boat engines...a lot diffrent from diesel engines. ok ive been doing some reading about 4 blade rops and by the sounds of it they have their ups and downs that go along with them. but aslo from what i understand is that these engines have a torque curve around 3400 rpm. so what im trying to get at is if 4 blade would be better than a 3 blade for hole shots and speed. what are some good props that arent to much money

 

[sutor623]

Re: Need help in buying new prop

There are a ton of decent and high quality props available right here on Iboats. 4 blade props do have their benefits. Theoretically, they plane the boat at a lower cruising speed, and have a better hole shot, with the sacrifice of some top speed. (In your case maybe 2-4MPH) Another thing to consider is that from a 3 blade to 4 blade of the same pitch the rpms drop about 200 or so. So there is a lot to consider. Honestly I have never used a 4 blade, but Im sure Steele can give you some good advice on it.

My guess is that a 15P 4 blade would put you at around 5500RPMs ( I like being on the upper end when it is just me on the boat, so when I load the boat and engine down with extra people and the RPMs drop you are still in the factory spec) I would also say that a 17P 3 blade would put you at around 5300RPMs, and a 16P 3 blade at 5500RPMs. If you are willing to sacrifice a few MPH and want improvements in other areas go with the 4 blade. If you want to milk that motor for every MPH you can, get the 3 blade. Hope that gives you a better idea.

And Steele, feel free to correct me if you feel any of this is inaccurate.

 

[Vision91]

Re: Need help in buying new prop

i appriciate the info now i just need to figure out which prop im goin to go with theres quite a few of them to decide from

 

[sutor623]

Re: Need help in buying new prop

Yeah if you plan on banging it up by the end of the summer just get a little $100 aluminum one. I run through props on most of my boats (durn river!) so I tend to buy the Solas props. Works fine for me. And before you buy anything, let Steelespike chime in and give you a pointer or two. Im sure he'll leave a reply before morning. I'm confident with what I told you but he's the prop guru on here.

 

[Vision91]

Re: Need help in buying new prop

yea i know how it is running on a river stupid logs and sticks everywhere...and once again thanks for the info i look into solas props..and also wait and see if steelespike puts a comment or reply on here

 

[Vision91]

Re: Need help in buying new prop

started looking at the back of my boat and noticed that the anticavitation plate is about 8 in above the bottom of the boat..i added a sketch of what my boat in the back looks like sry if its small...now i was wondering if my plate has to be from the bottom of the boat or where it is now cause my motor is all the way down..

 

[sutor623]

Re: Need help in buying new prop

Wow! Have you even had that boat out on the water yet? I tried a shortshaft kicker on a boat similar to that (with the lower lip) and it cavitated and sounded like I was going to blow it up. RPMs going crazy.

 

[sutor623]

Re: Need help in buying new prop

What is that transom height all the way to the bottom?

 

[steelespike]

Re: Need help in buying new prop

The motor is on a jack plate is there no room to lower it if necessary. Are yoiu on the right plate? The one just above the prop.
Does the boat respond to up trim?Have you had any ventilation(cavitation)?
It does appear a 17" prop would put you and 5200 to 5300 rpm.
It also seems the a small bass boat might work with a 19.
Just checked the Vision only weighs 800 or 900 lbs dry weight.
I think theres a good chance the Merc can do better with a 19.
Is the 36 by gps?
You may want to have the timing checked I think there may have been bulletin about the timing some years back.Some time ago over on one of the merc forums there was a discussion about setting the timing right.Also with the 3 carbs you want to be sure the carbs are picked up right and opening all the way.

 

[sutor623]

Re: Need help in buying new prop

The motor is on a jack plate is there no room to lower it if necessary. Are yoiu on the right plate? The one just above the prop. Gotta run I'll be back after supper.

I think his top line is off. I think the cav plate is about 2" lower than his line.

 

[Vision91]

Re: Need help in buying new prop

yea the boat does respond to up trim when my trimp pump did work the brushes are now longer in the motor they got disenigrated a while back. and thanks for finding out the dry weight of the boat i couldnt find it anywhere...the boat is pretty much the design of the ranger boat not sure which one though..cause when ranger boat vision out they redisgned it to their liking. all three carbs do open all the way when the throttle is opened. ill try here in a few mins to get a few better pics of it i took those while taking the boat out of the water. and for vent and cav im not really sure. and for lowering the jackplate i have no way of doing it. ill measure the transom height to the bottom and let you know.

 

[sutor623]

Re: Need help in buying new prop

You may want to have the timing checked I think there may have been bulletin about the timing some years back.Some time ago over on one of the merc forums there was a discussion about setting the timing right.Also with the 3 carbs you want to be sure the carbs are picked up right and opening all the way.

http://forums.iboats.com/showthread.php?t=168855

 

[Vision91]

Re: Need help in buying new prop

quick update on this subject i managed to find a dealership that would lend me a 17p 3 blade ss prop a 18p and 19p ss as well to find out which one does the best. and my results where 40mph gps at 5300 rpm with the 17p...45 with the 18 and rpm at 5200 roughly and the same speed as before with the 19p so im goin with the 18p. and still couldnt tirm the boat up do to the trim pump not working need to fix it sooon.