Diving Boat

[Rocky46]

I have a 12th scale boat that runs fine when it is thrown in. But when I stop, it will not come up to plane. It just dives down. I have tried to make adjustments with no luck. the CG is right on. I have even moved it back some. (tried to post a picture but didn't work)

[Jesse J]

Hi Rocky and welcome to the forum!
I Assume you are talking about a hydroplane hull, which is the only hull type i have seen do this.
The trick is to hit the throttle hard, and if it dives, let off and hit it again just as the nose comes up. You may also be under propped.
Need to know exactly which hull, prop size and yes photos and or video would really help us help you.

[Rocky46]

Thankyou for your quick response. I will include more information. Leopard 3670-2000KV, Hobby Wing SeaKing 180 v3, Battery 4 cell 5000mA 75c. I have tried different props. ABC 17-16 2 Blade, ABC 17-45 2 Blade, Octura 1440, Octura 1445, Octura m445. I have installed a RCM V2 Telemetry System to help with setup.
20210514_113551_resized.jpg20191006_123404 (3).jpg


PS: I'm 74 and love being called a Junior Member. LOL

[Fluid]

Can the OP answer a few questions so we can help him?

- Where is the CG in inches behind the sponson transoms?

- Set the model on a flat surface resting on the sponson transoms and the bottom of the strut (may have to remove turn fin and rudder). How far below the bottom is the prop centerline? Is the strut flat on the table or tilted up or down towards the table? A few photos* of the rear from straight behind and from the side would help.

- Most of the props he lists are probably not appropriate in that they may produce enough lift to drive the nose under. The x445 seems the best choice.



*Go to this forum - https://forums.offshoreelectrics.com...ips-amp-Tricks - and start a thread called ?Testing?. Make ten short posts with just a couple words in them. Now you have enough posts to upload a few photos.




.

[Jesse J]

Also Junior, what hull and how long is it?

[Rocky46]

The CG is 1-1/2 inches behind the sponson transoms. Hull length is 33-1/2 inches long. It was a kit boat that someone else built. I will take some measurements and post later.
20210514_144613_resized.jpg20210514_144539_resized.jpg20210514_144742_resized.jpg39441318_2175586996060742_2522115589187567616_o.jpg

[Jesse J]

Now I’m thinking under powered may also be an issue.

[properchopper]

As usual Jay nails it : " ...Most of the props he lists are probably not appropriate in that they may produce enough lift to drive the nose under. "

Look closely at the trailing edge of the prop pictured in post #6. Likely a huge contributing factor to "stern lift/nose dunk"

prop lift.jpg

[Rocky46]

Look closely at the trailing edge of the prop pictured in post #6. Likely a huge contributing factor to "stern lift/nose dunk"

I'm not a prop guy, What am I looking at?

Is there a thread here for prop science?

Been reading up on props.... found this: Low lift: a prop which does not have this tendency. With Octura props, the X series (an X before the number) indicates a low lift prop. Props without the X are high lift props.Ex.:X470 Octura prop.

So I need a Low lift Prop.

So maybe a Octura x445 oops they are out of stock!

Now I read the Octura M445 is even better. Wow---this prop stuff can be complicated.

New edit: Just put on the M445 prop. Adjusted prop shaft to be parallel with bottom of boat. Adjusted Center of prop shaft to be level with the bottom of the sponsons. How am I doing?
20191006_122804 (2).jpg

[Rocky46]

Does anyone recognize this boat kit?
20210515_151743_resized.jpg39441318_2175586996060742_2522115589187567616_o.jpg20210514_113530_resized.jpg20210515_151659_resized.jpg

[ezhitz]

The boat is a black Pearl designed by a gentleman in Michigan he goes by the name of shooter here on the forum. Search here on the forum under black Pearl for some builds. On my boat my strut is 1 1/16 deep from the bottom of the hull to the bottom of the strut.

[Rocky46]

OK, Mine is 13/16 so maybe I should go Lower. (Deeper)
20210515_183324_resized.jpg

[ezhitz]

Try going a little deeper on mine when I had it set so the boat was level on the table it would dive on take off.

[Fluid]

As requested in post #4:

“Set the model on a flat surface resting on the sponson transoms and the bottom of the strut (may have to remove turn fin and rudder). How far below the bottom is the prop centerline? Is the strut flat on the table or tilted up or down towards the table? A few photos* of the rear from straight behind and from the side would help.”

For clarity, take the photos with the boat upright on the table.


.

[Rocky46]

Pictures don't show well. What I need is a good starting point. What I have now is the sponsons are 13/16 below the bottom of the boat so I made the prop centerline also 13/16 and parallel to the bottom of the boat so it is flat. ezhitz suggested going deeper. Should the propshaft tilt up or down and how would that change the ride of the boat? If could learn what prop angle and depth change in ride of the boat it would be helpful.
20210516_125508_resized.jpg20210516_125607_resized.jpg

[Fluid]

The starting point is having the bottom of the hull parallel to the tabletop and the bottom of the strut flat on the table. Running the strut deeper usually makes the diving problem worse, unless there is excess cavitation running it shallow. Angling the strut down at the prop end will drive the bow down harder. Angling it up a degree or two at the prop end can help the diving, but it can make the boat unstable at speed. Try this setting with the x445 prop and see what happens.

As mentioned in a post above, how you apply throttle can make a big difference. I am not familiar with that particular hull, but some hydros are more difficult to launch than others. Since it was a kit boat the builder might have made changes to the sponsons, but likely not. Some hydros like a gradual application of power, some like full throttle, some need to be rocked with on/off applications. Some experimentation with starting techniques might help.




.

[Rocky46]

Thankyou Fluid, that's a big help. Looks like I need to get to the pond for some testing.