buying new prop going from alum to ss

[nailem]

history: 1986 20' sunrunner with a 5.0l alpha 1 gen 1 drive 1.5:1 gears.
4600-4800 tarket rpm
all rpm is verified with a digital tach
i have tried a 17p cant remember diameter 3 blade alum 4000rpm
current set up is a 14.75x15 4 blade alum turns 4600rpm solas amita4

i would like to try a ss prop.
my buddy has a 19pxD? ss prop and his boat turns 4500rpm so we tried my alum 17p prop and it turned 4200rpm. after asking i was told that some times ss will turn faster even with a higher pitch

so taking this into consideration i would like to try a 16px15 4 blade apollo ss prop. do you think i will lose rpm, gain rpm or stay the same?

side note: i have done a full tune up plugs, wires, cap, rotor ext. the only thing i want to do this fall is a carb rebuild. im not sure if that will make much difference in total rpm but if anything it may go up a little not down?

thanks in advance

 

[markins]

Re: buying new prop going from alum to ss

There are things to consider when you go for a different prop.
In-short:
increasing a number of blades - aiming for lower RPMs with higher pitch gives you great torque at pre-set speed. Not too good for fast acceleration. The heavier the boat - more blades are better for steady performance.
less blades higher performance on higher RPMs, better acceleration and higher efficiency.
You'd need to calculate the blade for the power on a shaft, boat weight, RPMs, type of water and desired speed and/or torque.
Most of the original props average those numbers and in many cases come out with pretty good performance.
You'd need to find someone at your marina who knows marine props. In many cases it's trial and error typa-thin' and takes time to come-up with a prop that's good for your ship Captain.
Write a log of tried props that include all the data you can gather and analyse it later-on.

Good luck!
http://www.ReadManual.Com/stern.drives/mercury/

 

[nailem]

Re: buying new prop going from alum to ss

thanks markins, i live off of lake erie and have tried to call and ask around with very little help. no one around here that i can find will let you try props out. so trial and error can get costly. most or all of what i have learned is from this site and others.

i was trying to find more technical specs on the prop i have and the prop i am looking for and came up with nothing. i have been reading about progressive pitch and how most props have it but i can find the numbers for the 2 props. if anyone knows it would help.

if the apollo 16p ss kept the same rpm it would be ok but it would be nice to get it up to the 4800 mark.

 

[nailem]

Re: buying new prop going from alum to ss

i was also looking at the solas rubex. does anyone have any experience with these props? are the better tuned than the solas amita? do they typically turn higher RPM?

 

[hwsiii]

Re: buying new prop going from alum to ss

Nailem, I can tell you that the Solas Amita is a stern lifting prop and the Apollo is a bow lifting high rake progressive pitch prop. In my opinion you will lose a few hundred RPM and find the boat will ride with the stern lower and the bow higher with the apollo. You might gain a mile or two an hour, but I am not sure.


H

 

[nailem]

Re: buying new prop going from alum to ss

thanks hwsiii, i am not really that concerned with top end mph. boat is mostly used for wakeboarding and family cruising.

could you suggest a SS prop that would spin up a little fast than my amita but still staying within the same pitch? or even an alum. prop that would be a 15 or 16 that would spin a few rpm fast than my amita. thanks

 

[hwsiii]

Re: buying new prop going from alum to ss

Nailem, I am lost on what you are trying to accomplish. You are mentioning a bunch of RPM but yet no mention of speeds at these RPM so we can see what your prop slip is with the different props. Trying to get the exact prop to turn your motor at 4,800 RPM is probably going to be expensive. I try to pick props that fall within a couple of hundred RPM of the maximum recommended manufacturer's RPM, but trying to get it exactly right is verrrrry hard.


H

 

[nailem]

Re: buying new prop going from alum to ss

sorry thought i covered ll the bases then reread my original post and no mph.
speeds with me, wife and 2 small kids and GPS

the 17p 3 blade that came on the boat (i think michigan match ???) takes a long time to plane wot 4000rpm at 35-37mph

the 15p 4 blade amita 4400rpm at 33-34mph

i have money and would like a new prop that works for me and sell the 17p. i would like to go to SS but dont have to. if im spending the money i would like to get a prop that is going to help pick up the last few hundred rpm. but more than that i do not want to lose any putting me out of my range. your info on the apollo is exactly what i was looking for. sounds like it is not the prop for me.

that is why i was looking for some experience on a prop that "may" spin a little faster than the amita i have. again i know there is no guaranty but your info on the apollo was great and any other tips may help. worts case i just buy another one just like i have but would be nice to try something different.

thanks again

 

[ramster]

Re: buying new prop going from alum to ss

If this helps, I have used an four blade 21" Amita on my boat and could only spin it to 4200-4400 rpm, switched to a SS 20" Apollo four blade and I spin it to 4800 rpm. I don't know if it will be the same for your boat but I found the Apollo to work much better than the Amita on mine. Maybe a 16" Apollo will actually turn a few more rpm than your 15" Amita. One way to find out.

 

[nailem]

Re: buying new prop going from alum to ss

how is the tuning on the solas rubex 15p 4 blade
or
michigan wheel vortex 16p 4 blade
both compared to my 15p 4 blade amita

 

[hwsiii]

Re: buying new prop going from alum to ss

Nailem, if you will fill this out I will try and help as much as I can.

Iboats Boat and Motor Info
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 recommended HP for your boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make and model of motor
7. 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 and turn the motor until the tape lines up with each other, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor
8. Manufacturer?s recommended Wide Open Throttle (WOT) range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches
10. Is it a bass boat or does it have a pad bottom
11. Does it have a hydrafoil, dolefin or trim tabs
12. Make, model, diameter, pitch and whether SS or aluminum prop
13. 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. If you do not have a tach you can buy a Tiny Tach for $ 50
14. Are you at sea level or a higher elevation, give us the elevation in feet
15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark, all of the foregoing could be the reason your prop is not attaining full RPM
16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop
17. Does the prop show any damage that you can see
18. 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
19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.

REMEMBER, The numbers I give you will be NO better than the information you give me

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

 

[nailem]

Re: buying new prop going from alum to ss

1. 1986 Sun Runner 220cv
2. 20? long I think 8?wide and NADA calls it 3000lbs
2a ?????
3. 2 adults and 2 small kids 18gals of fuel
4. mostly cruising and wakeboarding
5. ?????
6. 1986 Mercruiser 5.0L
7. rated at 220hp 1.5:1 ratio
8. 4400-4800rpm
9. ????
10. no
11. hydraulic trim tabs
12. 14.75x15p 4 blade alum
13. WOT 4400rpm (digital tach) 34mph (GPS) 2 adults 2 kids 16gal of fuel
14. 571 feet above sea level
15. Replace: plugs, wires, distributer cap and rotor, set timing to about 8 or 8.5* BTDC, new oil, clean fuel filters, butterflies are open. Rochester Quardrajet (sp) Good squirt of fuel from pump. I do want to do a carb rebuild this fall.
16. 1 year. Prop works good but im buying another and would like to try a different prop instead of have 2 of the same.
17. no
18. would like to try a different prop and it would be great if I could pick up a few RPMs but I certainly do not want to lose any. I would like to stay with a 4 blade

bottom is clean

i have also tried:
17p 3 blade alum = 4000rpm 37mph long time to plane and a lot of tab needed
15x19p 3 blade stainless michigan match SS = 4000rpm and 37mph felt about the same as the 17p alum

 

[hwsiii]

Re: buying new prop going from alum to ss

Nailem, the numbers you gave me for these props makes no sense to me. You have an aluminum 3 blade 17" prop turning the same RPM and speed as a 19" SS prop and it even has less prop slip than the SS or the 4 blade amita, and I find that hard to believe. I think you are not remembering the orret RPM and speeds, beause this is not logial. an you tell me what was so different about the 17" 3 blade aluminum prop.


H

 

[nailem]

Re: buying new prop going from alum to ss

all tree props where run the same day. I next trip out to the boat i will look to see the make of the alum 17p. but i have the numbers right. with in maybe 100rpm between the 19p ss and the 17p alum. there was one less kid when i ran the ss but she only weighs about 40lb. and speed was by gps. SS prop took a little more trimming but those were the #s. thats why i have some confusion about the SS prop. i do not think it mater's but the SS took the old style thrush washer and both my alum take the new style.

those same two props on my buddies boat the 17p alum spun slower than the 19p ss by 100 or so rpm.

SS 19p part # 033008

 

[hwsiii]

Re: buying new prop going from alum to ss

The SS prop is a Mihigan Wheel prop but I don't know whih model. There is sometjhing wrong with either the SS or the 17" aluminum beause there is no way they ought to turn the same RPM.


H