Prop blow out, needing help

[steelespike]

Re: Prop blow out, needing help

Yes; but a steered away from a foil because I don't think you need one. You need a little more size in the anti vent plate.
A doelfin may help if it doesn't mess up the natural planing of the boat.

 

[Scott Danforth]

Re: Prop blow out, needing help

could be a slight hook to the hull. that would cause a slight plow and possibly contribute

when the boat is running along, how is the attitude of the boat? level, or a slight plow to the bow?

the height looks good, however I am leaning toward steelespike's thought. I think that you need a bit more surface to the anti-cav plate since you seam to experience prop cavitation more when there is a light chop.

dropping the motor down slightly may also work, however at the expense of added drag.

 

[jbeener1]

Re: Prop blow out, needing help

could be a slight hook to the hull. that would cause a slight plow and possibly contribute

when the boat is running along, how is the attitude of the boat? level, or a slight plow to the bow?

the height looks good, however I am leaning toward steelespike's thought. I think that you need a bit more surface to the anti-cav plate since you seam to experience prop cavitation more when there is a light chop.

dropping the motor down slightly may also work, however at the expense of added drag.

The boat runs level or a slight lift of the front.

 

[jestor68]

Re: Prop blow out, needing help

Yes; but a steered away from a foil because I don't think you need one. You need a little more size in the anti vent plate.
A doelfin may help if it doesn't mess up the natural planing of the boat.

It's been used on all types of boats, including pontoons to address ventilation issues. By "covering" the prop, it appears to reduce or eliminate air being drawn down into the prop.

It'll cost ya about $ 37 to find out.

 

[dazk14]

Re: Prop blow out, needing help

Call your Prop shop and ask what they would charge to add cupping to a small 10" diameter prop. Post back.

The doel-fin may work, but you're AV plate is deep, so it'll likely scrub off speed.

 

[jbeener1]

Re: Prop blow out, needing help

Call your Prop shop and ask what they would charge to add cupping to a small 10" diameter prop. Post back.

The doel-fin may work, but you're AV plate is deep, so it'll likely scrub off speed.

The prop shop said between 30-40 dollars. My questions is if they do that does the pitch need to change? I have a tiny tacometer coming and will be in on Friday. That to should help a little on finding out what can be done on the prop part

 

[dazk14]

Re: Prop blow out, needing help

The prop shop said between 30-40 dollars. My questions is if they do that does the pitch need to change? I have a tiny tacometer coming and will be in on Friday. That to should help a little on finding out what can be done on the prop part

Let's see what the tach says. Often times the added trim out (or engine lift) allows a higher rpm, so overall, the cupping somewhat evens out and you just get added performance.

Since you didn't complain about hole shot, that suggested to me that your propped in the correct powerband - or least not lugging it - hence my suggestion.

Of course, I'm happy to spend your money to get a tach. Makes my/our life easier, but not all folks can afford it, so just working from decades of prop fitting when needed.

 

[jbeener1]

Re: Prop blow out, needing help

Let's see what the tach says. Often times the added trim out (or engine lift) allows a higher rpm, so overall, the cupping somewhat evens out and you just get added performance.

Since you didn't complain about hole shot, that suggested to me that your propped in the correct powerband - or least not lugging it - hence my suggestion.

Of course, I'm happy to spend your money to get a tach. Makes my/our life easier, but not all folks can afford it, so just working from decades of prop fitting when needed.

I agree with you and do thank you for all yours and everyone elses help on this,i should have the rpm readings on Saturday.

 

[jbeener1]

Re: Prop blow out, needing help

Gentlemen this is what i made out of an aluminum road sign, it has stop the prop blow out, it does slow the boat down some. As soon as the weather clears up i will run boat with this on to check speed,rpms at WOT then i will run it with it off to recheck.

 

[MikDee]

Re: Prop blow out, needing help

Good Job! But, it looks a bit too long?

 

[jbeener1]

Re: Prop blow out, needing help

Good Job! But, it looks a bit too long?

Thanks and i was wondering if it was too long.

 

[steelespike]

Re: Prop blow out, needing help

That looks great.
I'm thinking you could lose the folded edge unless you feel it needs the added strength.Or perhaps flip it over for a test.
Gradually reduce the size and refine the shape.
Perhaps an enlarged version of the original anti vent plate. I would assume the original designers felt that shape worked well
with the least resistance.

 

[jbeener1]

Re: Prop blow out, needing help

That looks great.
I'm thinking you could lose the folded edge unless you feel it needs the added strength.Or perhaps flip it over for a test.
Gradually reduce the size and refine the shape.
Perhaps an enlarged version of the original anti vent plate. I would assume the original designers felt that shape worked well
with the least resistance.

i will start re-shaping and see what happens,thanks for your help.

 

[dazk14]

Re: Prop blow out, needing help

If it was simply prop blow out that that you were trying to solve...with the a/v plate so deep.. the easy answer is add cupping to the prop (or a different prop) which will run in an aerated flow . You were going to provide tach data to confirm room for the plainly obvious and inexpensive solution.

The aforementioned often allows higher engine mounting, read more speed, less bow rise on take off, better mileage. From performance improvements, often times you can pickup the small rpm loss from cupping.

You should check your rpm's with the foil, which likely has been lowered, although you can try to "tune" the setup to recover the parasitic losses.

If you are looking for faster planing, lower planing speed, eliminating excessive porpoising, but increasing drag, then fine run a foil. The only concern with your design is that it is untested...

I would suggest that you are cautious doing your testing and in particular how those fins may dig in during a very sharp turn. If you were running in bigger waves in a following sea, that could be unstable. It doesn't sound like the latter would apply in this case.

Regardless, any solution that doesn't harm the motor(rpm wise) and gets you out and back safely is a winner.

 

[jbeener1]

Re: Prop blow out, needing help

If it was simply prop blow out that that you were trying to solve...with the a/v plate so deep.. the easy answer is add cupping to the prop (or a different prop) which will run in an aerated flow . You were going to provide tach data to confirm room for the plainly obvious and inexpensive solution.

The aforementioned often allows higher engine mounting, read more speed, less bow rise on take off, better mileage. From performance improvements, often times you can pickup the small rpm loss from cupping.

You should check your rpm's with the foil, which likely has been lowered, although you can try to "tune" the setup to recover the parasitic losses.

If you are looking for faster planing, lower planing speed, eliminating excessive porpoising, but increasing drag, then fine run a foil. The only concern with your design is that it is untested...

I would suggest that you are cautious doing your testing and in particular how those fins may dig in during a very sharp turn. If you were running in bigger waves in a following sea, that could be unstable. It doesn't sound like the latter would apply in this case.

Regardless, any solution that doesn't harm the motor(rpm wise) and gets you out and back safely is a winner.

As soon as the weather calms down i will see what the speed,rpms are doing with the fin on and off. the weather around here is a mess. As for now another prop would be around 100.00 and the foil i made for free, i know its untested for now but as i said before when the weather calms i will test. Is it in most cases the if you cup a prop that you drop your pitch?

 

[dazk14]

Re: Prop blow out, needing help

As soon as the weather calms down i will see what the speed,rpms are doing with the fin on and off. the weather around here is a mess. As for now another prop would be around 100.00 and the foil i made for free, i know its untested for now but as i said before when the weather calms i will test. Is it in most cases the if you cup a prop that you drop your pitch?

Yes, that is the general rule if you need identical RPM's and do not have a ventilation issue - which you have.

As I indicated, you can likely tune back some of the rpm's, with the added performance benefits and still be well within the full throttle rpm range. - if it was propped reasonably to begin with.

You sure seem spooked about a $30 mod. These sites have some GREAT cook book prop fitters that have worked tirelessly to assemble a sizeable Prop/Rig database and saved people a ton of money and aggravation. The problem is, none of them have ever been on a race circuit, so these "curveballs" have yet to be incorporated into their formulas.

Nobody bats a 1000 in prop fitting, and few people spend much time trying to max out the 35hp and under props/performance and many lament that they need more HP, when a properly setup prop/rig will do the job nicely.

Good luck.

 

[jbeener1]

Re: Prop blow out, needing help

Yes, that is the general rule if you need identical RPM's and do not have a ventilation issue - which you have.

As I indicated, you can likely tune back some of the rpm's, with the added performance benefits and still be well within the full throttle rpm range. - if it was propped reasonably to begin with.

You sure seem spooked about a $30 mod. These sites have some GREAT cook book prop fitters that have worked tirelessly to assemble a sizeable Prop/Rig database and saved people a ton of money and aggravation. The problem is, none of them have ever been on a race circuit, so these "curveballs" have yet to be incorporated into their formulas.

Nobody bats a 1000 in prop fitting, and few people spend much time trying to max out the 35hp and under props/performance and many lament that they need more HP, when a properly setup prop/rig will do the job nicely.

Good luck.

Im not spooked about 30 bucks but if i spend the 30 then have to drop a pitch then im out the 30 and the cost of another prop. That is my purpose of test my rpms and speed. Yes im just trying to maximize my boat and motor cause its all that i have.

 

[jimmbo]

Re: Prop blow out, needing help

Looking at the pics I suspect the keel is causing enough turbulence to cause the prop to vent. As mentioned before cupping might help. a prop with a smaller diameter might also help.
If the engine is not bolted to the transom relocate it a bit off side to see if not being behind the keel makes a difference. Be aware of risk to how the boat may handle at planning speeds

 

[jbeener1]

Re: Prop blow out, needing help

Looking at the pics I suspect the keel is causing enough turbulence to cause the prop to vent. As mentioned before cupping might help. a prop with a smaller diameter might also help.
If the engine is not bolted to the transom relocate it a bit off side to see if not being behind the keel makes a difference. Be aware of risk to how the boat may handle at planning speeds

Thanks and again as soon as the weather clears to where i can get out and run it i will.