HP Question

[czuniga]

thanks,,
i was actually really impressed with the performance of this 9.9 really did a good job...

 

[czuniga]

i will look into another prop once i fix this idle problem im having!!!!!

 

[czuniga]

Hello

Fixing to order a new prop solas amita seems to be what fits my budget at tis time. After removing the one I have right now. Its a Michigan 012111 which happens to be a 9.5 by10 pitch. Solas makes a 9.25 by 8 wondering if I should go any lower or higher since they also make it in 7 pitch?

 

[bbstacker1]

Did you get the idle issue fixed and the engine raised as Pappy suggested? I would get those things taken care of first before I ordered a new prop, you might find you don't need one. At any case, I would not go lower than an 8 pitch.

 

[Johny25]

Your motor can be made into a 15hp as someone mentioned above. I did the mod on my 87' 9.9 and it made a world of difference! I did the mod after I added 150lbs or so of custom flooring and seats in my 14ft lowe. We went from not getting on plane to planing without a problem after the conversion. Carburetor and exhaust horn/tube was all that I had to put on it. But if you are not comfortable with working on your motor I would not advise it. The exhaust tube required the removal of the powerhead. But the HP gain was substantial. I also made a jack plate to raise the motor almost 2" which also made a big difference.

 

[czuniga]

So I changed my prop to a solas 8 pitch. My engine revvs up nicely. Seems its fine up in it's power band. But does not quite push the boat like it used go. Seems like it creats an air pocket. The prop is about one inch under the lowest portion of the boat. Will a whale tail help?

 

[Pappy]

Going down in pitch in your case means that the engine will be revving quite a bit to maintain a good cruise speed. You may like the original prop better. If you can explain your issue better about the air pocket I may be able to guide you a little better.

 

[czuniga]

Yes,,

when it gets up on plane ans engince is reving at its full rpms eems to suck air from the surface and seems like the propeller slips,, i and wondering if an whale tale would help. Also could de be fabricated out of plane old aluminum or is it a product that needs to be purchased.


thanks

 

[bbstacker1]

Sounds like you raised your engine as suggested? Maybe you went up a little to far.

 

[czuniga]

Hello,

yes i did.. i made a homemade bracket. ill try to post a pic, but it worked fine with my 10 pitch prop. i did not have this problem before. My guess is the 8 pitch prop is spinning faster thus creating some kind of suction from the surface. I am wondering if a hydrofoil would help. since my bracket is bolted and i would really hate to drill more holes in my transom.

 

[czuniga]

i was able to get the pic up,, you can see the bracket

 

[Johny25]

Have you tried trimming the motor down one more slot and see if that helps? It should put the prop another 1/2 inch into the water. I should have mentioned that when I jacked mine up I test ran it before putting holes in the transom. A 1/2 inch up or down can make a world of difference.

And if you are sure your prop is 1 inch below the bottom of your boat it shouldn't be sucking air. I think you may be under propped which can also make it sound as though it is sucking air. The last little bit of throttle turn will make motor will rev higher but the boat won't go any faster.

 

[Johny25]

czuniga make sure when doing any changes to motor height and prop changes that you run the boat exactly the same each time so you know what results are happening from what. If you had 4 people in your boat before then put 4 people in again when testing the new prop. Lesson the amount of variables in the equation and you will have a much easier time

 

[czuniga]

If I'm under propped a hydrofoil wouldn't help right?

 

[czuniga]

If I'm under propped a hydrofoil wouldn't help right?

 

[czuniga]

My engine is in its lowest slot. I think my next step would be to try a9 pith prop. Or removing the bracket for a test run. But without bracket sits well underneath water.

 

[Johny25]

I am not a fan of hydrofoils myself. And no, if it is over reving because your under propped then a hydrofoil won't help. Put your 10 pitch back on and see what happens. Make sure the weight of the boat is the same. Play with all the trim settings and see what happens.Yes even the other way. Take tools to remove jack plate also and remove it if you cannot get it to stop slipping or whatever. Then test props again.

I have a hard time believing that your 9.9 is spinning so fast that it is sucking air. This is a photo of where I had my 30 hp motor, about 1 inch under the water and it wouldn't do what you are saying. And that is 3 times the HP. The only way I could get prop blowout is if I had it trimmed to the very back slot. And when you get blowout it is very noticeable. Prop spins, motor revs really high and boat goes nowhere or stops accelerating.

 

[bbstacker1]

czuniga, Looking at Johny25's picture is your setup about even with his, ie is your lowest plate pretty much even with the bottom of your boat or slightly lower? I can't really tell from your photo but it looks like you have a short shaft engine and I am guessing you raised the motor about 2 inches maybe a little more? If you are even or a little above the back of the boat with your engine you might have to lower it a little bit. My next thought would be to the prop itself, have you tried running the boat with the 10 pitch and the 8 pitch under like conditions, if so and this only happens with the 8 pitch then I would wonder about the prop. I am not familiar with Solas props (maybe one of the other folks on here can inform me/us) but my question would be does this prop have a rubber "slip" bushing between the hub and outer prop body, if it does could this be slipping? I know it is a new prop but that doesn't mean it can't be defective. If you suspect the prop is slipping find a way to mark the inner and outer sections then take it out and try it, after it seems to slip then check the marks to see if they have moved if they have the prop is bad.

 

[czuniga]

I ran about the same amount of weight the first time with the 10 prop. I did really good speed wise it was just that the engine seem to be having a difficult time sounded like i was straining the engine too much. When i placed the 8 prop it reved up really nice however i ran into this problem. It was about the same amount of weight. Three of us and some added weight of mods I will try to take a picture of my set up so i can post as soon as possible. It sounds exactly like Johnsons said the last bit of throttle is where is sounds as slipping or sucking air and it doesn't go any faster. Im guessing that i might be under propped. maybe i went too low with an 8. The thing is i can put my 10 back in there but i would be over stressing my engine. I need to try to borrow a 9 and give it a try see how it performs. I am just trying to get the best setup possible until a good deal for a 25 of 30 hp outboard comes along.

 

[Pappy]

The 8" prop has very little rake (angle that the blade is attached to the hub, not the pitch angle) compared to the 10" propeller. If you are high enough on the transom then the prop may very well be aerating at higher RPMs. Rake, among other attributes, helps to hold water on the blade better as the rake angle increases.
Best way to measure your current engine height is to make the cavitation plate parallel to the bottom and measure with a straight edge to the bottom and tell us where it is. The bottom of aluminum hulls have all kinds of junk on them to obstruct and feed air into a propeller. As I said earlier, you may be better off using your stock prop.