# Do hydrofoils help with prop blow out?



## firecat1981

I was asking in another thread but I figured this would help others.

Does it help? My thoughts would be yes since it forces some water back down, but I could be wrong. I was trying to decide between a se200 and smart tabs for my boat, but if the foil will help then it's an obvious choice for me. 
Also I see that Bob's machine shop has an aluminum one out, anyone tried it?


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## Brett

Not really, if you've elevated the outboard to it's highest running position,
then you have the anti-ventilation plate above the bottom of the hull
and as a result lifted the foil above water level also.
What you are looking for is something to hold the water in contact with the blade tips.

http://www.microskiff.com/cgi-bin/yabb2/YaBB.pl?num=1306375989


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## Flyline

Have u thought about making one for your motor?

It's on my tohatsu 8hp and love it so far.


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## firecat1981

ok here is my boggle, I fail to see the difference. Is the compression plate just aluminum that is rolled on the sides? Now forget I said hydrofoils cause I can see why some wouldn't do anything since they just stick out of the sides of the cav plate. I am now specifically referencing the SE200 like I had before. The shape under came down an inch or so around the edges of the prop the length of the foil, so wouldn't that do the same thing?


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## firecat1981

I guess it would have made sense if I looked on there site first wouldn't it have, lol.



> 11. "Will it help with prop cavitation?"
> 
> Yes. Prop cavitation/ventilation where the propeller takes in air on turns is damaging to your motor and lower unit. The crescent-shaped of the SE Sport helps to hold water more firmly around the prop than any other foil on the market.


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## noeettica

I like the SE sport on motors over 20 HP 

Fastglass built a tunnel and runs the SE Sport


I also have a fab shop that knocks out ones like blake posted 

(mine is a permatrim clone)


All boats are different Some guys like tabs


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## firecat1981

Ok I have been looking up compression plates and other hydrofoils.......... 
From what I can see from the pic above and the permatrim site a compression plate is just basically an extension of the cavitation plate. Here is a few pics.


















As you can see there is no real profiling or anything, just usually a flat piece of aluminum plate that is folded on the sides that extends backwards to capture the spray and force it down making it into added thrust.
A hydrofoil on the other is a wing made to add lift like an airplane wind does, it usually extends outward from the cavitation plate. Here s a picture of a doel-fin.









From what i can see the SE200 sport is a mixture of both of these designs. It extends the cav plate, but also has a wing profile for lift. That being said shouldn't it help with getting on plane, as well as help with blowout?



















I've more or less made up my mind, but I still like to hear different opinions. I figure this will be good for others who are looking at this in the future.


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## Brett

A compression plate does not just hold the shape of the water it cuts through,
it actually squeezes and channels the water to the blade tips to prevent blowout.
That is what allows full use of a tunnel hull with the prop above the bottom of the hull.
That inverted U shape actually needs to start forward of the prop
and carry back past the anti-ventilation plate for best results.

note the shape of the plate below and how it will squeeze/de-aerate the water
that will be coming in contact with the cupped prop.


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## firecat1981

Brett the picture you show does look like it would work well, but all the other plates I looked up were just straight sided. Even if it doesn't squeeze the water wouldn't it still redirect it downward and help with blowout? Remember I'm not running a tunnel or jacked up super high, I'm 1.5 inches above the hull bottom with a 5.5 inch setback, just looking for a little more trim adjustment when running.


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## Brett

Not enough knowledge of the SE 200 to be able to help you decide, FC.
Sounds like it's time for a test ride with what you have.
See if it gets the job done, or if something else is needed.
Maybe as simple as dropping engine height back down a 1/4 inch.

:-?


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## firecat1981

The prop improved the situation, even when loaded down, but I still need a foil or tabs to get that best out of that little motor. I'd also like to be able to trim up further in a chop to keep dry. I have no way to lower the motor without redrilling and cutting the transom down. It's much easier to adjust higher then lower.


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## WhiteDog70810

I've seen these mentioned before on here for running super shallow, often in conjunction with power tabs. From what I understand, tabs on a flat bottom boat can be adjusted downward to make the water hump up higher under the motor and then you have the compression plate to keep that hump around the prop. Sooooo depending on how "too" high your motor is, you may need tabs to make the compression plate work or you may be fine with just the plate.

...or if you really get ticked off, you can flip it over and put a tunnel in this hull!
;D

Nate


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## firecat1981

Power tabs with a compression plate maybe, but usually not with a hydrofoil as they do similar jobs. There is no way I am cutting a tunnel into this boat! I learned my lesson last time and if I were to do another tunnel I would design the boat around it, instead of building a boat and then adding the tunnel.


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## WhiteDog70810

I thought you were thinking of a compression plate instead of a hydrofoil after going back and forth with Brett earlier. You are absolutely correct, tabs and a hydrofoil are redundant.

I know your opinion on tunnels.  That is why I had to suggest it. This way no one will suggest it seriously.

Nate


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## noeettica

Yes fc is right Tabs and foil are redundant I did it with a Stern lifting prop ... Bow was stuffed down into the water ... had to try it though ...


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## firecat1981

Nate, I was, it will either be a compression plate with smart tabs, or a hydrofoil (SE200). I would perfer the SE200 as it would be cheaper and might do the job of both.
Now don't get me wrong, I don't hate tunnels in general, I just feel are absolutely useless on alot af boats. To use one correctly you really need a high horsepower to weight ratio, a seriously cupped prop, nose cone, and a hydaulically adjustable jackplate. In other words, on most skiffs it's pointless IMO.

I may revisit the tunnel issue in my next design to help compansate for what I have planned, but this hull is staying as is.


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## firecat1981

Damn forum crashed on me so I'm writing a shorter version of this post.

As you can guess I went with the SE200 hydrofoil. It says right on the package that it helps eliminates cavitation issues.









Here is a shot of the profile, you can see how and why it would work.









Here it is installed, It looks great thanks to the color matching.









Now here is the money shot. You can see how much it extends the cavitation plate both back and to the sides, from the cavitation plate back to the rear edge of the foil is about 5.5 inches.









I believe these foils are a much better design then the ones that just extend to the sides. There was one other foil I was looking at, I think it was a stingray XRPIII. It had a similar concept to mine, but the thing was HUGE! And they wanted like $150. For smaller motors I think the SE200 is the way to go. I'll let you all know if it really solves the issue.


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## Guest

> Damn forum crashed on me so I'm writing a shorter version of this post.
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> As you can guess I went with the SE200 hydrofoil. It says right on the package that it helps eliminates cavitation issues.
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> Here is a shot of the profile, you can see how and why it would work.
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> Here it is installed, It looks great thanks to the color matching.
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> Now here is the money shot. You can see how much it extends the cavitation plate both back and to the sides, from the cavitation plate back to the rear edge of the foil is about 5.5 inches.
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> I believe these foils are a much better design then the ones that just extend to the sides. There was one other foil I was looking at, I think it was a stingray XRPIII. It had a similar concept to mine, but the thing was HUGE! And they wanted like $150. For smaller motors I think the SE200 is the way to go. I'll let you all know if it really solves the issue.





Question? Why did you build a tunnel in your skiff with a jack plate, but still are using the stock prop?


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## firecat1981

Answer, I don't have a tunnel, or a jackplate, and that's not the stock prop, it's a TP hustler.


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## Guest

> ok here is my boggle, I fail to see the difference. Is the compression plate just aluminum that is rolled on the sides? Now forget I said hydrofoils cause I can see why some wouldn't do anything since they just stick out of the sides of the cav plate. I am now specifically referencing the SE200 like I had before. The shape under came down an inch or so around the edges of the prop the length of the foil, so wouldn't that do the same thing?



So this is not your current skiff?


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## DuckNut

Nope, that one met the front of an SUV. Current one is blue.


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## firecat1981

Yep that's my old rig. I was just using that picture as an example.


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## Guest

I ran my SUV17 with a powertech 3 blade cupped prop on the transome with my cavitation plate 3" above the bottom. No blow-out, but my hole shot sucked.

I'm now running at the same height, but I cut down the transom and added a jack plate. It runs 31mph solo, good hole shot and no blow out and I'm only using a Mercury 25hp 2 stroke.














BTW,

This cavitation type plate is way different from the one you are running. Most of these "foils" made in TX channel a ton of water to the prop and cost from $200-$400. They almost inclose the prop.


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## firecat1981

> This cavitation type plate is way different from the one you are running. Most of these "foils" made in TX channel a ton of water to the prop and cost from $200-$400. They almost inclose the prop.


please explain how it does any different a job? The foil pictured has straight sides and no dynamic shape, all it does is force water back down by extending the cavitation plate. With the straight sides there is no real compression. The se200 does a similar thing because it extends back but also has the dynamic wing shape to help with planing. I just dont see it enclosing the prop at all or channeling any more water.


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## Brett

Texas tunnel skiffs (aka: scooters) make every effort to get those props up high in the tunnel.
To prevent prop blowout, the water "hump" created by the tunnel is further shaped
by a long "eared" compression plate like the one shown below.
Without the compression plate, tip-wash would blow the "hump" apart,
resulting in loss of thrust and a useless tunnel hull.


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## firecat1981

I can see how the one pictured above would be needed with an extreme tunnel running the prop half out of the water, but I don't see how the permatrim types will do anything better then the SE200.

On that note, I did get out Sunday for a little while. I definately had more trimability as it didn't blow out at such a low angle, but did if I went more then a few degrees in the positive direction. It was a big improvement. 
It was hard to see any performance advantage as my boat was loaded down! I had a full tank of fuel, full livewell, full cooler, and 3 men aboard (230lbs, 170lbs, 160lbs), and 3 fishermen worth of gear. Even loaded down like that I was able to get 22.2mph per the GPS, but that was in fairly windy conditions. I think that is pretty respectable for a little 4-stroke 20hp.


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