alum to SS prop Johnson 130HP in a 20 cuddy cabin

[feles99]

EXPERT HELP NEEDED: I rebuilt a Renken 92 cuddy cabin 20' in which previous owner added a platform and a Johnson 130HP V4 looper 1996. Short engine very close to the water, becafull when trimming and turning. Still runs fine. Initially had a 14 1/2 x 17 aluminum with WOT of 4600 (did not have speedometer). I cut the prop with a grinder to 13 1/2 diam x 17. I did not sharp the edges so I do not know if I am loosing too much performance. I have been using that prop for months and at WOT gives 5500 rpm and 30 or 31 mph. Cruises at about 23 miles and 4400 rpm. I want to change to SS to get a little more top speed or performance specially when cruising. I only cruise or idle in canals. Do no sky. QUESTIONS: 1) Should I get an SS 13 1/2 x 17? 2) What if I get 13 x 18 or 13 3/4 x 17? 3) How can I know the potential difference in speed and rpm before buying the used SS prop? 4) I rarelly go above 4400 rpm or cruise. Is it OK for a couple of minutes run engine at about 5000 rpm or it reduces life quickly?

 

[steelespike]

Re: alum to SS prop Johnson 130HP in a 20 cuddy cabin

With a chopped down prop it shouldn't be hard to improve your performance.
Usually converted I/Os don't do well with an outboard considering your prop
your performance is admirable.
I like the Turning point Hustler props.Close to ss performance at al. prices.
based on your rpm with the original 17" pitch I would go with a 15 inch prop.
would put you about 5,000.A solas amita 4 blade should help it plane easier and stay on plane at less power.There is no way to be sure about changes when going from one material to another with perfect props let alone those that are chopped up..Its important that the motor can operate
within its design rpm range Doesn't hurt the motor to run at its max rated rpm though obviously cruising is less stress.Operrating a correctly propped motor at lower rpms is fine.

 

[Brew2]

Re: alum to SS prop Johnson 130HP in a 20 cuddy cabin

Not sure, but I think max RPM on that motor is about 5800-6000. I'd check and if so, you might want to adjust prop pitch such that your WOT RPM moves from 5000 up closer to that range. "Lugging" the engine at too low an RPM will do way more damage than running at WOT with a properly pitched prop. As Steelespike said,

"Its important that the motor can operate
within its design rpm range"...that includes getting the RPMs at WOT in the right range.

Do a search on "Lugging" in the forum and you'll find plenty to read up on it.

Put 23 years on my 1986 Evinrude 140, often at WOT. Still running great when I sold it this past spring.

 

[junior1113]

Re: alum to SS prop Johnson 130HP in a 20 cuddy cabin

had a 93' 140 great motor. i ran it at 5600 all day long. first thing to do is make sure engine hieght is perfect. where is cavititation plate in relation to bottom of hull? hopefully a little above. i would suggest looking into a 4 blade prop with big boat small motor setup. they put out more low end torque. 4 blade 15" pitch would probably do the trick.



93 2000cc hydra-sport vector
93 200 evinrude ocean-pro
turbo ultima4 14.25x17 48mph@5900

 

[feles99]

Re: alum to SS prop Johnson 130HP in a 20 cuddy cabin

Guys Thanks for the feedback. I found out Redline for the 2.0L V4 Looper is 6000 RPM. I though 5500. I have 500 to play with. If redline is 6K, WOT of 5800 is OK? This weekend, I am going to do a nw test of WOT, and will measure everything again. Attached is a picture to look how the engine and bottom looks like. When idle or low speed I can trim. When getting speed trim is at the lowest. At cruising, if the water is calm I can trim up a little and speed goes upabout 2 miles. In the ocean 2 feet waves or in the choppy canal at trim should be at the lowest, or engine makes different noises and rpm changes. When cruising and turning prop loose grip. Going to 4 blades sounds great. For the first trial of 4 blade what do you guys suggest considering my alum prop: 14 1/2 x 17 WOT 4600rpm. Then 14 1/2 grinder to 13 1/2 x 17, 5500rpm.
NOTE: Boat weighs 2K lbs. Adding extra weight of people or diving tanks do not make too much difference in getting it to cruise. In fact is better as prop stay more in the water.

 

[steelespike]

Re: alum to SS prop Johnson 130HP in a 20 cuddy cabin

That looks like a great job.Motor has a tremendous setback.Should get the prop in really clean relatively undisturbed water.
5800 wot is fine.
I think your present venting problem is most related to the chopped down prop.You will be very pleased with whatever prop you get.If you want improved planing,hole shot and low end handling and performance the 4 blade will do very well.With your chopped down prop and your unusual boat setup its difficult to do any kind of accurate prediction.I do feel the prop will turn your boat from adiquate performer to an exceptional performer.

 

[feles99]

Re: alum to SS prop Johnson 130HP in a 20 cuddy cabin

GUYS MY APOLOGIES. SOME CHANGES TO MY INTIAL POSTING: Yesterday I took out the prop and find out it was Mich 15x17. Months ago, at WOT 4600 rpm and I decided to cut 1 inch with a grinder so I make it 14x17. Yesterday, i sharped the edges to cut the water (not professionaly). Yesterday, I also checked that the vertical distance between the keel to the prop axle (mid or horizontal trim) is no more than 2". Means prop is very high and that is why I cruise at the lowest trim. Horizontal distance between keel and prop about 28" because platform. Today I retested, lowest trim as it was choppy. 3700rpm 18mph, 4500rpm 26mph and 5600rpm 32mph. Means 20% slip.... I am planning to take this week my 3 blade 14x17 alum prop to a technician to balance and change pitch from 17 to 19 and thus gain 300 - 400 rpm. DOES IT MAKE SENSE??? I think I will be cruising at 29mph and 4600rpm. SOUNDS CORRECT???? Besides, I am planning to get a 4 blade aluminum prop and tested. If changes are required I will take it to a techinician. WHAT SIZE AND PITCH DO YOU GUYS RECOMEND FOR THE 4 BLADE PROP??? I only want to idle or cruise under 5000 rpm, do not care for top speed.... Great to get more grip with 4 blades considering the hign engine..
Thanks for reading and answering......

 

[feles99]

Re: alum to SS prop Johnson 130HP in a 20 cuddy cabin

I wanted to add to today's test: 3 people, 16 gal of gas, 12 gal of water, choppy 1' - 2' waves. RPM vs MPH: barely cruising 18mph 3700 rpm. Crusing: 22mph 4000 rpm, 26mph 4500rpm, 29mph 5000 rpm, and WOT 32mph 5600rpm.
Thanks again and again..

 

[steelespike]

Re: alum to SS prop Johnson 130HP in a 20 cuddy cabin

While it appears you did a wonderful job of cutting down your prop but I feel it is a comeplete waste of money to have it worked on.Just save it as a spare.
Your motor is high but has a tremendous setback which allows more height.
Setback is usually measured in inches It looks like yours is in feet.Wave action may affect venting some because the motor moves through a wider arc.
Again if your chopped prop is sensitive Its my feeling its the prop not the setrup. I feel a good 4 blade will eliminate your venting issues.
The 4 would normally lower your max rpm and speed.Normally you would drop an inch in pitch with a 4 blade.To me its difficult to determine a prop size
from your performance with the chopped prop.Its my feeling that a 17" pitch
should perform in your rpm range.

 

[junior1113]

Re: alum to SS prop Johnson 130HP in a 20 cuddy cabin

GUYS MY APOLOGIES. SOME CHANGES TO MY INTIAL POSTING: Yesterday I took out the prop and find out it was Mich 15x17. Months ago, at WOT 4600 rpm and I decided to cut 1 inch with a grinder so I make it 14x17. Yesterday, i sharped the edges to cut the water (not professionaly). Yesterday, I also checked that the vertical distance between the keel to the prop axle (mid or horizontal trim) is no more than 2". Means prop is very high and that is why I cruise at the lowest trim. Horizontal distance between keel and prop about 28" because platform. Today I retested, lowest trim as it was choppy. 3700rpm 18mph, 4500rpm 26mph and 5600rpm 32mph. Means 20% slip.... I am planning to take this week my 3 blade 14x17 alum prop to a technician to balance and change pitch from 17 to 19 and thus gain 300 - 400 rpm. DOES IT MAKE SENSE??? I think I will be cruising at 29mph and 4600rpm. SOUNDS CORRECT???? Besides, I am planning to get a 4 blade aluminum prop and tested. If changes are required I will take it to a techinician. WHAT SIZE AND PITCH DO YOU GUYS RECOMEND FOR THE 4 BLADE PROP??? I only want to idle or cruise under 5000 rpm, do not care for top speed.... Great to get more grip with 4 blades considering the hign engine..
Thanks for reading and answering......

down in pitch results in increase rpm you got that backwards. 15 would give you 300rpms 19 will take away 300 and you will kill the motor luging it. recommend 4x15"p.

 

[junior1113]

Re: alum to SS prop Johnson 130HP in a 20 cuddy cabin

GUYS MY APOLOGIES. SOME CHANGES TO MY INTIAL POSTING: Yesterday I took out the prop and find out it was Mich 15x17. Months ago, at WOT 4600 rpm and I decided to cut 1 inch with a grinder so I make it 14x17. Yesterday, i sharped the edges to cut the water (not professionaly). Yesterday, I also checked that the vertical distance between the keel to the prop axle (mid or horizontal trim) is no more than 2". Means prop is very high and that is why I cruise at the lowest trim. Horizontal distance between keel and prop about 28" because platform. Today I retested, lowest trim as it was choppy. 3700rpm 18mph, 4500rpm 26mph and 5600rpm 32mph. Means 20% slip.... I am planning to take this week my 3 blade 14x17 alum prop to a technician to balance and change pitch from 17 to 19 and thus gain 300 - 400 rpm. DOES IT MAKE SENSE??? I think I will be cruising at 29mph and 4600rpm. SOUNDS CORRECT???? Besides, I am planning to get a 4 blade aluminum prop and tested. If changes are required I will take it to a techinician. WHAT SIZE AND PITCH DO YOU GUYS RECOMEND FOR THE 4 BLADE PROP??? I only want to idle or cruise under 5000 rpm, do not care for top speed.... Great to get more grip with 4 blades considering the hign engine..
Thanks for reading and answering......[/QUOT

never really had and experience with cutting props down. rule of thumb for v hull is 1' prop to transom =1" higher than level with motor. Ex. 3.5' prop to transom =3.5" cavitation plate above bottom of hull. this to compensate for water rising off the back.

 

[feles99]

Re: alum to SS prop Johnson 130HP in a 20 cuddy cabin

I researched a little about setback, ventilation plate and chopped down prop. Then, I took measurements with ventilation plate parallel to bottom of the hull: Setback: Keel to front of engine 35 1/2". Setback with trim up/down 40"/29". Ventilation plate to keel 6 1/2". I read that the standard measurement is when the anti-ventilation plate is in line with the bottom of the hull or 0". Setback of 36" means my engine can be 3" higher than other engines. That means my engine is 6 1/2" high - 3" for setback = 3 1/2" higher than standard.
Going back to props. I do not understand what you mean by chopped down prop.
The 3 blade will be spare and will not be serviced. Now, I am focus on getting a 4 blade. I will look for same diameter 14" and reduce pitch 2" to 15". The 2 inches decrease in pitch will increase my rpm about 400 but the change for 3 to 4 blades will decrease about 150rpm, so total increase will be about 250rpm. With 3 blades I was at WOT at 5600 and max is 6000.

I would appreciate if someone who knows about props and knows what I need gives me an advice in brands or models. Aluminum is the first option in case need to be modified + cheaper. A used SS is also on budget.

 

[steelespike]

Re: alum to SS prop Johnson 130HP in a 20 cuddy cabin

Chopped prop;refering to the prop you ground down.