Questions about props on fish/ski boat

[charleso]

I am in the process of purchasing(pending a clean bill of health from the local omc dealer) a 17 foot Bass Skier by Bassmaster with a 1988 Johnson 120 Horse. It has a 13x19 ss on the motor and a spare 13 X17 alum. My dealer does not like ss for our area c/o rocks and other obstructions(I had two bad strikes on my previous boat, ss would have taken lower unit both times.One was actually a huge alligator snapping turtle!!!! The aluminum just took it hard and had to be rebuilt, but everything else was ok. He suggest the 17 incher is not enough, anybody have any ideas about what should be a good all around prop, or should I have two props, one for tubing, the other for riding and fishing?

 

[walleyehed]

Re: Questions about props on fish/ski boat

The idea of having 2 props for each type of use is the best way to go.
My question would be "which 2" do you want...
The answer to that would be the cruise prop that puts you at about 5700-5800RPM at wide open throttle and the toy puller prop should get you in the 6000RPM range with a normal load at WOT.
Don't discount an SS prop just yet...There are other reasons that SS will out-weigh an aluminum prop, and the chance of destroying a lower unit does not go up as much as one may think.
At this point, the best thing to do is try both props with a normal load and post back with the max RPM achieved with both props.
Another item you may need to list is where is the AV plate in relation to hull bottom, ie, even with, 1/2" below, 1/2" above, etc...

 

[charleso]

Re: Questions about props on fish/ski boat

The motor is mounted on a real good jack transom plate, so I can move the AV plate up or down by adjusting. Will note current height when unit comes back from hospital. The motor has a stabilizer fin mounted on it. I have seen them on numerous boats in the past, never have had one myself, do they help or are they just something to get you to fork out a few dollars?

 

[charleso]

Re: Questions about props on fish/ski boat

I am new to site, got informed about no trade policy in forum area, how can I list items for sale/swap, does it cost?

 

[walleyehed]

Re: Questions about props on fish/ski boat

I believe you can list items in the classifieds for a small fee...should be able to locate it on the home page.
As for your rig, the fin is one of many tools that can be used to achieve a specific result. The fin will rob speed in most cases unless the engine is lifted high enough that the fin is out of the water when on plane.
The Total performance of your rig will be a combination of how high any certain prop will allow you to raise the engine. You'll be limited in heigth by using aluminum, compared to a good quality SS.

 

[charleso]

Re: Questions about props on fish/ski boat

Thanks tons for the advice, will check out speed/rpm/AV height on test run. The AV plate you are refering to is the plate the fin is mounted on? Also, on the first run should I let the trim all the way down, or have it about half-way and adjust up or down accordingly? All of my boating experience to this point has been on smaller boats and much smaller motors, not exactly sure what to expect as far as making the first hole shot with that much motor. I was not aware of the fact that you can trim a ss prop up higher than an aluminum, what could the expected difference be? I am leaving to go out of town for work now, will be back to check response this weekend. Once again, thanks so much for the advice.

 

[Ron G]

Re: Questions about props on fish/ski boat

not to but in,but yes thats the AV plate,trim all the way down when taking off and go from there on certain boats and props you dont have to trim all the way down .certain props are made to ride high even out of the water,with the ss you should have a smother ride depeanding on the prop again.Kenny can explain it better than i can.

 

[charleso]

Re: Questions about props on fish/ski boat

Don't worry about butting in, I need and want all the advice I can get, my boating experience to this point has been with small boats and small motors, I am chomping at the bit to get 'er back from the doctor and she what she is capable of doing.

 

[walleyehed]

Re: Questions about props on fish/ski boat

The Difference (one of ) between SS and alum is how the prop can be manipulated in the building process.
SS is usually thinner, blade-wise and the ability to "cup" and make the prop bite harder is one of the advantages without the blade-flex of aluminum.
The geometry of the blades can be made differently, allowing a much more efficient design.
I should also state I use the term "Cup" loosely...the placement of, the type and amount changes with each design..some are better suited to one type of hull, than another.

 

[charleso]

Re: Questions about props on fish/ski boat

Walleyehead,

You sound a lot like me. My wife quickly learned that if the motor was black, no need telling me 'bout the hull. I realy do appreciate the advice. One more? How big of a difference will it make on motor rpm's when the water actually warms enough here in S Georgia to put someone on a toy and drag them behind the boat?During the test should I actually look for a little over 6000 or just back off wot just a little, Until I started reading post and the faq's, I always thought you would back away from wot once the boat was on a plane, but it does make sense to keep her tach'd up

 

[Ron G]

Re: Questions about props on fish/ski boat

From my dealings you'll loose a little rpm maybe 100-200 from winter to summer,2 strokes are made to run wide open and they like it.

 

[Texasmark]

Re: Questions about props on fish/ski boat

I'm at bout 700 ft altitude. Was waiting for the loss as the weather heated up this year from January. Funny thing happened. I lost mph (2) but didn't loose rpm's as the weather heated up. Figure that one out!

Mark

 

[bassboy1]

Re: Questions about props on fish/ski boat

Funny thing happened. I lost mph (2) but didn't loose rpm's as the weather heated up. Figure that one out!

My guess is water density or air content in the water changed.