40 Outrigger Props

[shoboat]

Andy,

We tried some 1718's cupped to 5.63" on a N/R 21 powered boat that weighs

3 1/2 lbs. and had no problem in the mid 70's for heat racing. Still testing the

1816 and 1818 props,but it looks promising to be racing around 80 MPH. We

have had a lot of good results with the 1714 and 1716 so far. I think we have

found more power for the MAC 21 also,still testing,but looks good so far. Over

in Australia we have had a lot of promise with pitched H-4's and H-10's. A few

21 boats over there are 75 to 80 MPH,so the old reliable propellers are still

doing the job though. We are always looking for more power and more speed

though,so we will keep on testing like you guys do. Mid to high 70's for the

average guy is our goal. We try to get 3 to 5 MPH every year. We are finding

that the smaller diameter is helping us a lot.

Thanks,

Mark Sholund

 

[AndyBrown]

Mark,

You really didn't tell us anything. Mid 70's is mid 70's, doesn't matter if you do it with 3.6" or 5.6". However all boats handle best with the least amount of cup possible, so if you could run 75 mph with 3.6" why run 5.6"?

 

[shoboat]

Andy,

We will just keep testing and when I have something better to contribute

I will post it. I can tell you this though the 40 boats are running in the 80's

and even with bad air densities. We have a LOT MORE testing to do. Our

testing is for real, so no B.S. here, just facts.

Thanks,

Mark Sholund

 

[Joe_Knesek]

Mark, for a 21 motor to pull over 5 inches, it must have some real slip or the motor's not turning up. If not, it would be doing a lot more than 70.

 

[TimD]

Could this be a case of mistaken terminology here?

 

[Joe_Knesek]

Mark, I ran the #'s through your little speed caclulator on your web site and something doesn't compute. A motor turning 30k at 1to1 ratio with 20% slip would run 77 mph. If you run the same numbers and increase the pitch to 5 inches, you should be going 113 mph according to your calculator.

To run the 77 with 5 inches of pitch, the prop has to slip 45% or only turn up 20.3k. If the prop is slipping that much, it must be real inconsistant and would handle like a tank. If your loading up the motor that much, you'd find yourself dead in the water a lot.

 

[ClayGlover]

Clay,
Not 100% sure, but from what I can see, looks like you have an original (1996) SG.  From the short view of the rears I can see a very high AOA.  5 degrees is what the 1996 SG had. 

This boat will run well, but the strut must be nearly level.  I can see the center rear has been added later.  That may be having an adverse effect. 

There is an original SG 67 racing and leading the points race in NAMBA dist. 9 using the same High AOA rears, but without the center. So the boat is still original and it runs well.

Anyway, my suggestions are: #1 Make the Strut flat.  If the boat continues to stuff you have two choices. A. remove the center rear.  or B. replace the high AOA rears with the new low AOA rears and maintian the center rear.

A. would be the no cost choice.  B. will cost a set of new rears.

Either way I would recommend our Anti-walk strut.  And yes it does reduce prop walk when running the big high pitched props.

Andy

I sure appreciate all the sound advice fellas. B)

Andy, thanks for taking the time help me out with this.

When I took the boat off the original owner's hands about 2 years ago, it was set up with the center ski and NO rear side sponsons. You might be correct about someone adding the center rear later on, I don't know the history of the boat. Now I know the year built is circa '96 . The thing looks near new though!

Anyhow, the outside rears you see in the picture were added by myself last year. I purchased them from CMD around early to mid last year to help the boat's rearend to hookup in the turns, so I'm assuming they are the newer design and AOA? The picture may possibly make them look different. I don't know... here is a brief description of the rear of the boat-

The outside rears I have here are 9.5" long measured at the ride pads, and they have approximately 4" of flat area from the transom before their front rocker curve begins. The outside rear's ride pads run approximately 1/32" deeper than the center ski bottom. Measured with my angle finder, their 4" flat rearmost running surface's AOA is approximately 1 degree relative to the setup table. I am either measuring different than you do, or don't understand? They don't have anywhere near a 5 degree AOA at the flat rear area of the ride pads relative to the water surface aka setup board.

The center sponson's flat bottom area extends much further forward to nearly 9" from the transom before the rocker curve begins, with its total length being 13.75". The bottom running surface of the center ski is 13/16" wide. The center's flat area AOA is the same as the sides, but 5" longer before curving to the tub's bottom.

If this doesn't jive or sound right, please let me know and the center ski will come off. I've leveled the strut, and the strut bottom runs about 3/64" above the rear outside sponson bottoms, and approximately 1/32" above the center ski's running surface. If it's necessary to get the strut bottom below or even with the rears, the center ski will have to come off or be notched to allow the travel.

Thanks again for your help-

 

[Dale0]

Andy,

Whats this about a new strut? I have been running my strut on my 20 SGX boat at 1.5 deg. Is there a longer one that can be run flatter?

Dale

 

[Mike G]

5" cup and 5" pitch are not the same thing!

 

[Ron Jefferson]

Andy: I've got a question for you. If the only thing you change on a boat is the prop and all the props are sharpened and balanced by the same person. What causes the amount of left rudder deflection to change to keep the boat straight?

I tested on the weekend with 3 different stock props and one of your own modified props. H4, H7, 1450 and a reduced and pitched 1450 that Joe Knesek lent me for testing (a prop purchased from you). The H4, H7 and AB 1450 prop all hopped and required substantially more left rudder than the stock 1450. The stock 1450 was real smooth but the motor reved and the boat was down on MPH. I bent on the stock 1450 till the launch took all the way around the back of the course to unload. When it did the boat remained smooth and picked up speed.

So, I decided to reduce the amount of pitch I put in the blade until I was confident with the launch and lived with the mph. If I want a real prop from you for this boat. Do I send you the prop I bent on? Or can I measure the prop myself and send you the numbers?

 

[AndyBrown]

O.K. Clay the rears are all good. The only problem is the high angle on the strut.

Also the bottom of the strut must be the same depth as the center rear slightly deeper. You can simply notch the center rear till you get what you need or get a new strut.

If the strut is too high, the rears will bounce off the waves and stuff the front.

Dale O.

The struts have been the same for several years now. Clay's boat is eight yrs. old and built before we had the Anti-walk struts.

Ron J.

Get back to you later.

Andy

 

[Ron Jefferson]

Andy...

Don't forget about me.

Ron J.

 

[shoboat]

Hey Ron,

If an H-4 and H-7 hopped, you will need to level your strut more. This will

also help on the launch and the top end performance. If you are running

your MAC 21 you should try a 1714 or 1716 they won't hop. I think you will

be surprised how well they work. Just a suggestion .

Thanks,

Mark Sholund

 

[Ian Inverarity]

Mark,

Are you modifying the ABC props? I have back cut 3018's for gas riggers and it improves the acceleration and seems to work pretty well. I tried a back cut 2718 on my 90 rigger and the handling coming onto pipe was tricky.

Ian.

 

[AWaddle322]

Ron J.,

If the only thing you change on a boat is the prop and all the props are sharpened and balanced by the same person. What causes the amount of left rudder deflection to change to keep the boat straight?
Look at the leading edges of these props and I believe you will find your answere.

Sincerely,

Allen Waddle

 

[Ron Jefferson]

Mark: Thanks for the feedback. I am trying to understand why the strut needs to be adjusted to accomodate certain props. Is it the profile of the blade, the diameter or the overall design? And, what does changing the prop do to the boat to cause a substantial change in left rudder deflection.

I understand that changing the strut will more than likely take the hop away but want to really understand why. The way the boat is set-up now with the 1450 I have almost zero left rudder and the boat is real smooth. I guess what I'm really saying is, I usually can find the set-up but don't always understand how I got there. I was hoping Andy could give me some theory behind props and there effects on ride attitude. I'm hoping I'm waiting because the answer is long and detailed.

Ron

 

[shoboat]

Ian,

Yes, we are testing a multitude of different propeller modifications and I will

share some of the results as I get them in.

Ron J,

I think you have really quite a few questions that you want answered.

Your question on left rudder deflection, I think has to do with quite a few factors

that are involved. The pitch of the propeller,the prop torque,the acceleration rate,

and the most important factor, the entry angle of the water onto the blade face.

I think this is probably the most important thing that you do when you make a strut

angle or depth change. I can tell you there is a lot of physics behind propeller

design, and I am still learning a lot about the different factors that effect our

setups. I would be very interested too, if Andy would share his many years of

knowledge on propeller design and the way that they effect our boat setups.

Great question Ron,I hope we get some more responses?

Thanks,

Mark Sholund

 

[AndyBrown]

Yes Ron it is long and my 2do list is very long.

Hopefully tonight or over the weekend I'll get down to it.

In the mean time: What is the bottom of the strut and rear sponsons relationship, width of rudder blade and depth of rudder below the bottom of the strut?

The 3 props that hop; are they from me for a particular hull? Are they direct from me or did they come to you through a different channel?

 

[Ron Jefferson]

Andy: Thanks for getting back to me. I'll try to explain the best I can so you're not chasing a problem that doesn't exist.

-width of rudder is 150thou at the rear

-Depth of rudder below strut is 1 5/8"

-strut is flat bottom

-rears are swept back like a roadrunner and the center of the drive dog is about even with the rearmost surface of the rears, placing the front of the prop hub slightly back from the ride surface of the rear sponsons.

-H4 and H7 props are Randy Rapedius and the reduced diameter and pitched 1450 is the Joe Knesek prop you did for his roadrunner.

-the stock 1450 is from Randy also. I bent it myself and runs smooth and quick.

Let me explain the "hop" so know one is confused. The boat isn't bouncing up and down in the rear. It's more like the prop isn't engaging fully. More of a wiggle I guess. The rooster tail is choppy and the boat doesn't look smooth. This is all in the straight's as the boat sits down and looks good in the turns. Let me know if you want the prop or just a measurement.

Thanks again, Ron

 

[Joe_Knesek]

just to clearify, the prop Ron is using from me has 3.8 inches of pitch and is reduced to 49 mm.