Cavitation

[Watercadet]

Are there some applications where a certian types of props won't work no matter how you move them? Specificaly: I have a Pro Boat Miss Bud. I know, I know... just bear with me... I came accross a raw hull and have never even ran one as stock. That said here is the setup: .18 buggy motor MAC 2.5cc pipe, .130 flex (complety removed the existing stuffing tube and "skeg" that was arround it leaving a flat area) Hughley strut and rudder hung on the transom like a 'rigger. It is all adjustable and such as far as depth and thrust angle. I have tried a number of props and so far only the x series work with the x437/3 being the best. The x440 spins just as well but the X437/3 is smoother. I tried a 1735 and V937/3 to get the rear up and out of the water and both just spun and the boat didn't move. Where should I move the strut to maybe get these guys to bite? I have a Y536, X438, 1435 and 2035 from AB to try still.

Let me know what you think.

BTW Will and Mark, if any one has a sport 20 I would love to pace against it.

Adam

 

[shoboat]

Are there some applications where a certian types of props won't work no matter how you move them? Specificaly: I have a Pro Boat Miss Bud. I know, I know... just bear with me... I came accross a raw hull and have never even ran one as stock. That said here is the setup: .18 buggy motor MAC 2.5cc pipe, .130 flex (complety removed the existing stuffing tube and "skeg" that was arround it leaving a flat area) Hughley strut and rudder hung on the transom like a 'rigger. It is all adjustable and such as far as depth and thrust angle. I have tried a number of props and so far only the x series work with the x437/3 being the best. The x440 spins just as well but the X437/3 is smoother. I tried a 1735 and V937/3 to get the rear up and out of the water and both just spun and the boat didn't move. Where should I move the strut to maybe get these guys to bite? I have a Y536, X438, 1435 and 2035  from AB to try still. Let me know what you think.

BTW Will and Mark, if any one has a sport 20 I would love to pace against it.

Adam

67000[/snapback]

​

Adam,

I would try moving the strut deeper for those other propellers to bite. You may

want to try a cut down H-4 or a 40 X 52/3 from ABC. The M-435/3 and the Y-535

Would be other Octura choices.

Thanks,

Mark Sholund

 

[Watercadet]

Thanks Mark! What are the Dia and Pitch of the H-4, and what are its characteristics? Here is a pic of my set up: https://www.intlwaters.com/gallery/displayimage...tup&cat=1&pos=0

the strut is about 3/16 below the sponsons.

Adam

 

[shoboat]

Adam,

The H-4 is really a 21 Hydro propeller,but we have cut them down for tunnel

hulls,monos,etc. I think I would stick to 35mm props for that boat. The M-435/3

and the Y-535 are really the best propellers for that boat. Anyone else with some

suggestions? We are all ears. I have done a few Y-535's lately so they must

be working well. I just did a few M-435's so I will be getting some feedback real

soon on them.

Good Luck Testing,

Mark Sholund

 

[jayt]

Based on my experience with a stock boat owned by a clubmember, your prop is set way too high. Drop the strut another 1/4" below the bottom of the transom, and give it a couple degrees of down angle at the prop end.

The x437/3 is just too much prop for this boat; you will want to keep the rpm above 25,000 rpm. That's about 30-35 mph with a y535 prop and is pretty fast for that hydro. The y535 works well on the stock boat so it or the y536 would be my first choices.

This is a pretty large, heavy hull for the .18s and the small diameter props they require. Try to balance the model to minimize the weight on the prop - get the CG as close to the sponson transoms as possible. Sharpening the sponson bottoms will help it to plane off. Are you giving it a toss when launching, or just dropping it onto the water? We found that a good toss helps a lot. Lastly, some of these little motors take quite awhile to break in and won't develop much power until a pint or two of fuel has passed through them. Don't overprop the engine during break in or permanent damage can occur. Good luck, it is such a beautiful boat!

 

[Watercadet]

Thanks for the reply Jim. The boat is not stock and nor does it run like it. The .18 is turning props with dia's as large as 40mm. The motor has been "cleaned up" inside and is on 50%. The hull is as lite as it can be with no ginger bread. I was trying lifting props with less dia. and more pitch to try and get the back up. I didn't want to angle the strut too much and have handeling problems like hoping. The Y536 I think will be the right ammount of prop but it is not going to have the lifting characteristics I was looking for.

Adam

 

[Eric Perez]

Thanks for the reply Jim. The boat is not stock and nor does it run like it. The .18 is turning props with dia's as large as 40mm. The motor has been "cleaned  up" inside and is on 50%. The hull is as lite as it can be with no ginger bread. I was trying lifting props with less dia. and more pitch to try and get the back up. I didn't want to angle the strut too much and have handeling problems like hoping. The Y536 I think will be the right ammount of prop but it is not going to have the lifting characteristics I was looking for.Adam

67299[/snapback]

​

The stock prop on the miss-bud is a non lifting prop and it makes the hull go -Why are you looking for a lifting prop? Is it needed now because your prop is behind the transom? and at less of a negative strut angle?

 

[Watercadet]

The stock prop on the miss-bud is a non lifting prop and it makes the hull go -Why are you looking for a lifting prop? Is it needed now because your prop is behind the transom? and at less of a negative strut angle?

Yes. The stock one doesn't do too well....

Adam

 

[ClayGlover]

Hey Adam. I made a new link to your picture-

https://www.intlwaters.com/gallery/albums/userp...52/DSC00021.JPG

Recap.... What are you trying to do, gain speed, or correct a handling problem?

 

[jayt]

The stock one doesn't do too well....

...and it shouldn't be expected to. Plastic props work poorly for high rpm/surfacing applications, flattening out the pitch and sometimes folding the blades.
There is nothing wrong with angling the prop downward to increase lift - up to a point. This does not always induce hopping and on some hulls is the only way to keep the transom up in the corners. Reducing the weight on the prop will help considerably. Move the CG as close to the sponson transoms as practical and you won't need as much lifting force.

 

[Watercadet]

Hey Adam. I made a new link to your picture-
https://www.intlwaters.com/gallery/albums/userp...52/DSC00021.JPG

Recap.... What are you trying to do, gain speed, or correct a handling problem?

Clay thanks for the new link and redirection.

I want more speed without the ill handeling....don't we all. I noticed that the boat rides butt low and wanted to raise it with just the prop selection. I think that Mark answered that by lowering the strut it will help with cavitation. Maybe I just wanted a brain storm. Thanks boys, ya'll delivered!

Adam