another prop ?

[flatboy]

O.K !! A couple weeks ago i posted for prop advice.I dont have the everyday boat you can buy at the local boat shop.(that could be my problem) anyway its an aluminum 18ft. flatbottom (built by a cajun boats back in 94) It has a 115 merc 2-stroke just overhauled last week! Bored out 15 over the works. My problem before the overhaul and now is what people seem to call blowout.I was runnin 5900 w.o.t at around 48-50 mph (gps) my complaint is it will not jump on step.If i hammer down i sounds like its slipping and i can dam near see the prop when that occurs.Once on step the boat rocks. When taking off im trimmed all the down and i do have stationary trim tabs. I was suggested to go to a 4-blade prop i have a 3 blade 20 pitch quicksilver.Any and all advice wiil be appreciated. If there is something i missed for more info let me know! Thanks.And the boat is used for fishing.

 

[Randybeall]

Re: another prop ?

Perhaps you need to lower the engine one notch. If you are pulling air into the prop it will most certainly slip. Since you have what seems to be an over powered boat perhaps a 4 blade prop would better transfer the execess energy to the water. However, basic set up applies to all props, if you can see it I would suggest lowering it just a bit and try again. Being too high might not pull enough cooling water into the intake and be the cause of your recent rebuild as well!

 

[flatboy]

Re: another prop ?

thanks i will try that to.I see the hustler prop is what everyone perfers.I will change my prop,the shop that built the boat said my prop is flat the cups are straight on it and he tested the boat and suggested to run a 4-blade but drop down on my pitch to around 18-19 verses the 20 im runnin now?

 

[HighTrim]

Re: another prop ?

You may in fact need a new prop, have you tested it for slipping? Also may be cavitating or ventilating as mentioned. Can you further describe your setup or a pic of the stern?

 

[CaptAhab]

Re: another prop ?

That pitch seems low, especially if it's an aluminum prop. I have an 18 foot aluminum with a Merc 90 pushing a 3-blade stainless 22 pitch prop close to you'r speeds, 47mph but at lower rpm's, my buddy however with the deeper v bottom of a Ranger 17 ft but same motor as you 115hp runnin a 5-blade gets the same speed, 47-50mph. I would think you could prop-up with a flat bottom.

 

[mthieme]

Re: another prop ?

If i hammer down i sounds like its slipping and i can dam near see the prop when that occurs.

I assume the motor revs up at this point and you don't go anywhere.
When you say you can see the prop - does this mean you can see it not spinning or you can see just below the water?
Sounds like a spun hub, but want to make sure.
Could be the motor sitting too high like someone else mentioned.
Sounds like one of the two.
You're rpms are good and your speed is flying. Personally, I wouldn't change the pitch. (although a 20P is an odd # - might have to replace with 21P).

 

[flatboy]

Re: another prop ?

when i hammer down the motor will tack out and no i dont move the bow of the boat rises up.I have to let off alittle to let what i guess for the prop to catch some water.When i say i can see the prop i mean that when i try to holeshot it pushes the water away from the prop then i can hear the exhaust like its not in the water anymore.I will try to get some pics posted.

 

[flatboy]

Re: another prop ?

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[steelespike]

Re: another prop ?

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In the picture from the stern it appears the motor is about 3" to low.
Is the anti vent plate (just above the prop)about even with the bottom?
From the side it appears the motor is trimmed in all the way.I wouldn't think it would run right there.If your present prop is flat with no cup the Hustler turning point should solve your blowout at minimul cost and no doubt improve overall performance.With that setup I would think you could go up 2" and not over prop.

 

[flatboy]

Re: another prop ?

Funny you should say that! The gentleman that rebuilt my motor said the cupping in my prop was bad! And the cav fin is dead even with the bottom of the boat.

 

[Randybeall]

Re: another prop ?

At least on my computer the darkness of the pictures makes it hard to tell the true height. With the engine trimmed in all the way you are lifting the stern and trying to pull water down, not what you want. Trim it out till at least the leg is truly vertical or one notch beyond that. Give that a try first. Yes, the Hustler can make a difference since it is a cupped prop and yours is a flat design. Start moving that trim out first. You will be surprised pleasently.

 

[flatboy]

Re: another prop ?

thanks alot! Ill try that.I will change my prop,do you recomend me going up in size/pitch or should i stay the same? The mounts on the motor i can see where it was before,the motor was up about 2-3 inches i dont know why it was dropped down seems that i have a couple of options to try.Again i appreciate everyones help!!!

 

[Randybeall]

Re: another prop ?

I too would suspect you could go up 2"in pitch and not be over propped. However, I would first suggest working with the trim and see if you can get the aireation problem worked out.

 

[flatboy]

Re: another prop ?

Im getting my prop reworked at the local prop shop(very respectable) the prop i have the shop showed me its a vented performance prop and expensive new. I was thinking bout the tp hustler but its aluminum thats a problem here in south louisiana with the marsh and bayous we have. I will try the prop when i get it back to see the difference the cups where completely flat. And i still have the option to raise my motor. I will repost with the results. Again thanks to everyone the input gave me a better understanding of prop set up.

 

[CaptAhab]

Re: another prop ?

Like others have suggested I also think you could go up in pitch at least 21 or for top end a 22 pitch, stainless would be you'r best bet on a boat like your's.
More blade area, more cupping and higher rake then you have on the quicksilver aluminum,that stock aluminum prop has to go!