Prop help please... What I DO know!

[Xesvuli420]

Hi there! glad you stopped in to help. I'm trying to get as much as possible out of this boat. Any advice is appreciated

~~~~~~~~Intended Use~~~~~~~~~
I'm not expecting a high top speed out of this boat, but I was at least hoping for 35-40mph. However I would gladly sacrifice top speed to make my goals reachable. The main priority for this boat is for water sports, and fishing with grandpa, which isn't an issue. I want to learn to ski(combo mainly, but slalom would be fun to learn as well), Tube, wake board, wake surf, and Para sailing <---Ha ha just kidding!... or am I?!?!?. I would like to be able to do this even with 3 or 4 people inside the boat. The boat is getting worked on right now to put the motor in its tip top shape.

I hear that for what my intended use is a 4 blade prop would be more ideal

I also hear that for boats under 220hp, Composite props are really worth looking into. If so, the ComProp website says I need 4bladex12.7dx19p
http://www.comprop.com/omc.html

~~~~~~~~Specs~~~~~~~~~~~~~
*I know current Diameter, Pitch, and Material are recommended to help assist with figuring this out, however, the boat is an hour away at a shop.


200lb Operator wanting to learn watersports
1987 Dixie Bandit 170
17.5' Fiberglass open-bow deep V-hull
OMC/Cobra I/O
3.0L GM 4cyl 140hp
Holley 2 Barrel
"WOT range" (as per service manual) 4200-4600rpm
Currently hits red line before WOT (but better for Hole Shot right?)
3 blade prop. Pitch and Diameter unknown, (but Pictured below)
Max occupancy 6 person or 1000lbs
Top speed ~30-32mph before the overhaul
Anything else you need just ask.

So can you guys help me out? Thanks!

 

[steelespike]

Re: Prop help please... What I DO know!

Really can't do much without Prop size and max rpm and speed.
It does appear the prop needs repair or replacement.Try to get it repaired
do a couple test runs with a light load to get a baseline performance record.Prop size should be on the barrel or under the prop nut.
The 3.0 will be taxed trying to perform what you want.but with the info we can help get the best possible results.

 

[Xesvuli420]

Re: Prop help please... What I DO know!

Really can't do much without Prop size and max rpm and speed.
It does appear the prop needs repair or replacement.Try to get it repaired
do a couple test runs with a light load to get a baseline performance record.Prop size should be on the barrel or under the prop nut.
The 3.0 will be taxed trying to perform what you want.but with the info we can help get the best possible results.

The only ting on the prop is "P295"
I dont get how alot of people say they can pull with 75 or 90hp motors, but a 140hp motor will be taxed. Not saying your wrong, just saying its frustrating

 

[steelespike]

Re: Prop help please... What I DO know!

We used to ski with 25 hp with a 100lb adult spotter.It was fun but not practical.
NADA says Dixie Bandit 170 is 1875 lbs dry.(130hp?) 4 adults 600 18 gal gas 140 lbs Skier 150 various equipment battery etc 150. About 2165 lbs.I/Os are notorious for being a little sluggish out of the hole.
We can get you setup for sking and it will work ok but will limit your top end
And you will have to watch your rpm with a light load.Some change props for water sports or cruising.If you see if they can fix your prop they can tell you the size.You can keep the old prop as a spare.Its bad to guess on a prop.
But my guess is a 17" pitch will help you do better for water sports.Surely will overev with a light load.A 4 blade will help you out of the hole better.
And will reduce max rpm and top speed some.
Something like smart tabs will improve hole shot handling and ride.
Any changes should be done one at a time.
If your going to guess on a prop your better off being a little under propped
because you can use it by keeping an eye on the rpm.If you end up over propped you can't use it.Hopefully you can get the base line performance tests.

 

[Xesvuli420]

Re: Prop help please... What I DO know!

We used to ski with 25 hp with a 100lb adult spotter.It was fun but not practical.

Haha See, surely I should be fine

NADA says Dixie Bandit 170 is 1875 lbs dry.(130hp?)

http://boatpropellers.iboats.com/OM...r=1987&**********=448017538&*******=288100556

See the 4th one down. Not the only resource, but one of many saying the 3.0 is 140hp

4 adults 600 18 gal gas 140 lbs Skier 150 various equipment battery etc 150. About 2165 lbs.

How did you get 2165? even at your weights I got 2915. But just for fun lets use these weights 800lbs in people, 25 gal gas(160lbs)(always fill up before I go), 200lb skier(my weight) 150 equiupment....
3185lbs is more realistic for the amount I carry. I guess I will have to throw a few guys overboard =o)

I/Os are notorious for being a little sluggish out of the hole. We can get you setup for sking and it will work ok but will limit your top end And you will have to watch your rpm with a light load.Some change props for water sports or cruising. If you see if they can fix your prop they can tell you the size.You can keep the old prop as a spare.Its bad to guess on a prop. But my guess is a 17" pitch will help you do better for water sports. Surely will over rev with a light load.A 4 blade will help you out of the hole better. And will reduce max rpm and top speed some. Something like smart tabs will improve hole shot handling and ride. Any changes should be done one at a time. If your going to guess on a prop your better off being a little under propped because you can use it by keeping an eye on the rpm.If you end up over propped you can't use it.Hopefully you can get the base line performance tests.

I like the idea of having 2 props. I may just do that. I am looking at a 4 blade comprop for the water sports, and maybe an aluminum or SS for speed. I will use the prop on there now for a emergency prop. I already have to watch for over reving now. The Tach goes past redline before the throttle is ever wide open. I guess i just need to find out whats on there now so I can get you guys to help me decide. I should have posted this yesterday while I still had the boat!

I wonder if the service manual tells the OEM prop sizes. its over 400 Adobe pages so if you think so tell me where to look and we will keep digging.
Thanks for your post!

 

[steelespike]

Re: Prop help please... What I DO know!

As far as weights typically they use 150lbs for an adult I used 8lbs per gallon
for fuel just threw out a figure.Probably didn't add right. Adding in my head
apparently no room there lol.
Its been my experience the I/Os come with a prop best for top speed,
Again guessing a 21 for your setup.Your dinged up prop may be allowing it to over rev.Of course it could be a 17 which would surely over rev.
On your manual; there must be an index. Look for something like prop selection ,performance specs anything that might bring up prop info.

 

[propper_advice]

Re: Prop help please... What I DO know!

My best selling composite prop for this application is a 17p and I do have many customers enjoying water sports. Those who like speed move into the 19p. When shopping composites, know that they are not all created equal. Be sure to shop around and check the reviews

 

[Xesvuli420]

**********update**********

**********update**********

Ok hey everyone. I got you guys the specs of my CURRENT prop...
Michigan 3x13.25x17

I am under propped pretty bad
My spec WOT range is 4200-4600
My CURRENT RPM range at WOT is somewhere between 5000-5500, although I haven't taken it that high to find out. it starts missing around 5000, so I always back the throttle out and try to keep it around 4800 (I just found out that my spec WOT is 4600 max)

I was thinking of getting a 21p prop for all around performance, because I hear that for every inch of pitch, you loose 100-200 rpm. So to go from a 17p to a 21p is 4inches, 400-800rpm loss. so if I am hitting 5000-5500rpm now, It would bring it down to around...
4600-5100wot if 1 inch = -100rpm (still slightly under propped)
4200-4700wot if 1 inch = -200rpm (Almost Perfect spec WOT range)

I guess I need to know the truth about how much RPM loss occurs to better figure this out. Also how much "load" (say 500lbs of people) will effect the WOT range. Props are not cheap, so I really need as much detailed information as you can tell me to help me come to a informed decision.

***Also just ordered a new Ski Prop "ComProp" 4x12.8x17. Not what I expected (in a good way)!, Haven't used it yet, but I expected a flimsy plastic prop. I know the pitch is the same meaning I will still be under propped, but with the 17p, and the 4th blade, I should get the best results when pulling, or under load. I just have to watch my RPM range.

Thanks Everyone!!!

 

[steelespike]

Re: **********update**********

Re: **********update**********

pitch change rpm is strictly an estimate 200 rpm/inch.
could be more or less.When you change material; and brand all bets are off
I saw one the other day that lost rpm with less pitch.

 

[Xesvuli420]

Re: **********update**********

Re: **********update**********

ok, getting ready to order my speed prop. need last minute help!

Ski Prop
13 1/4x3x17 (under propped)
3/4 throttle at WOT range (4200-4600 rpm)

Speed Prop
3 or 4 blade?
Aluminum or SS (I hear SS is only superior (performance wise) after 50mph)?
Smaller, same, or bigger diameter?

Thanks everyone!