Outboard Prop

[boatman]

Anyone know much about props?

 

I have a 20hp Johnson with a 10x13 OEM prop that takes a long time to get my boat on plane when I have 2 +200lbs guys in it. Its ok when I'm alone. I'm thinking of switching to a 10.5x11 cupped prop. Do you think this will get me on plane quicker without too much loss of top speed? The motor is (manually) trimmed to the best setting and the skeg is about 1/2 - 1" below the bottom of the boat.

 

I'm only considering a new prop. I am not going to get a hydrofoil, trim tabs or a new motor.

[BITEME]

Boatman

 

I had the same setup on a 14 foot springbok not bad once you get up by a dog to get up same issue with weight the prop switch will not do much good in fact i steered clear as i was told by numerous shops it would stress the motor more than its worth its up to you whether you do this or not

now on to the part you dont wish to do I had some favourable results with a foil turning and on plane were enhanced plane not so much as turning

 

hope this helps

peter

[Bernie]

You need to gear down. Going to a larger diameter with less pitch u may end up being close to what you are running now.Suggest reducing pitch -same diameter when you are loaded up. An engine is stressed more overpropped. It puts more load on bearings/gears. An anology is like when you try to start to pedal a bike uphill in 10th gear.Puts more stress on your body. Gear down and see how easy it becomes. Just dont go as fast. What you then have to be careful of is over revving no load.

[boatman]

Thanks guys,

 

My boat is a 1987 Springbok so its probably the same as your old rig, BITEME. I just want to get on plane a little quicker. Top speed and turning are still ok. I really don't want to put a foil on my motor. I'd sooner use my 1954 25hp motor than do that.

 

The 10.5x11 is an approved prop for my motor. I don't think there is a 10" prop with a pitch less than 13" available for my motor. I thought by increasing the diameter my RPM's wouldn't change too much so it wouldn't over stress the motor, while the decreased pitch would give me the extra torque I need to get on plane. Is my thinking wrong?

[POLLIWOGG]

This is where you really need a tach.

 

The rule of thumb if I remember right was 2" of pitch = 300rpm and an " of dia. = 200 rpm so your not making much of a change other than the cupped prop might not slip as much.

 

If you can get your hands on a tach and find what it revs now and find out what your WOT rpm should be you can get a good idea as to drop 2 or 4 '" of pitch.

[Chris Cross]

Boatman, yes the 10.5X11 will improve your take off.

It will drop your top speed about 10%.

You will still corner the same.

You will have more power in rev too.

I sell props for a job.

Any questions you can PM me.

CX

[glen]

10X13 seems like the wrong prop to me.

 

I have a 20 evinrude and it has a 10X9 or is it 9X10 and it works great on a heavy boat.

[boatman]

Thanks, Glen.

 

The 10x13 is an all purpose prop and I think it is the standard prop for my motor (1984-97 14 tooth spline) although my parts manual shows numerous other choices. There is an approved 11x9, which might be what you have. Either way, I think a 9" pitch would be too much for me. I just need a little extra push. I'm not pulling skiers or anything.

 

Out of curiousity, what type of boat are you running and what is your top speed? I consistently get 34km/h (21mph). I found no top speed difference between a 1993 15hp Evinrude or my 1987 20hp Johnson, but the 15hp won't get me on plane with two people.

[glen]

My boat is a 14'5" starcraft side console. The boat is about 500lbs on its own. The motor is a 1976 evinrude 20hp. I get 20mph with two people. My boat will plane with three people.

 

Hull shape may be part of the problem for you.

 

What prop is on the 15hp you have?

[boatman]

Sorry Glen,

 

I haven't been here for a while.

 

I'm not sure what prop is on the 15hp. It is just the standard all-purpose prop. Its a motor I borrowed from work while my 20hp was being serviced. My boat is in my avatar. It has a modified V hull - deep and wide. Its rather flat from about midship to the stern so it has lots of surface area. You'd think it would get up with little trouble, but obviously it doesn't. The hull doesn't look much different from the new Princecrafts utilities.

 

Also, your motor would have a 9" prop. Its a completely different animal than mine. Nice motor, though. Glad to know people are still running those old girls.

 

I bought the 10.5x11 cupped prop and I'll let you know how it turns out this spring.

[boatman]

UPDATE:

 

I finally got the boat out on the water yesterday. The new prop performed exactly as I'd hoped . I got up on plane in 3 seconds. Top speed didn't seem effected, but I didn't have a GPS with me to know for sure. Turning was a little better as there was much less ventilating and I found I have a lot more power and control in reverse.

 

The prop I chose was the Rascal prop by Turningpoint ($100 total with universal hub). It is a cupped aluminium prop designed for small hp motors. If anyone is looking for a new prop I'd recommend it.

 

Thanks everyone and especially Chris Cross for the advice.

Edited April 21, 2007 by boatman

[Guest lundboy]

Oops too late to suggest putting some of those fins on the cavitation plate. They will put you on plane in no time! Keeps you on plane at lower speeds as well. They work wonders and often are cheaper than a new prop.

 

http://www.basspro.com/webapp/wcs/stores/s...0002000_200-2-7