Hobbyking Pursuit self-righting

[Old School]

Motor and shaft installed. Motor is mounted forward to enable the 6s battery to be fitted. Cooling lines to fit.

[rol243]

looks like a very neat set up in the hull.

[Old School]

Many thanks, just awaiting some water outlets from Joe (RCBB).

[R2315]

Looks great! Really nice work, maybe post a vid once you get her in the water.

[Old School]

Many thanks.

[Old School]

The flip test was a success (eventually)!!!!!!!!! It will flip back over reliably within three seconds of placing upside down in the water. to get there however required a bit of head scratching. Now one would think that with several holes in the bottom of the hull and a big hole in the transom then something should happen.

Alas, I had a small design flaw in the flood chamber with it not being tapered towards the bow and the vent holes as far forward as possible. My chamber, for simplicity, was blunt nosed toward the bow and while the vent holes were as far forward as possible a small air pocket had developed. As built the hull would turn to about 75 degrees to the vertical. I decided to drill two inlet holes in the upper deck (first photo) to allow more water into the chamber. It seems odd that a hydraulic lock seemed to form in the chamber restricting the amount of water that could enter. The chamber has a capacity of 1.5 litres and yet only about 0.5 litres would pour from the chamber when the boat was lifted from the water when inverted.

The upper inlet holes did help but the hull would not flip that last little bit. I drilled a further vent hole on the hull lower surface which helped but just not enough the throw the hull the last few degrees over vertical. Pushing on the inverted hull showed that just a small weight increase would do the trick so I added 100 gms in wheel balance weights to the flood chamber upper surface (second photo). This did the trick and the boat reliably flipped.

Note: the yellow wire holding the battery secure is just for the flip test. I am awaiting battery straps to arrive from China. Alas, OSE was out of stock of the size needed.

[Bp9145]

Tim, you've done a great job. I'm sure you've inspired some people to do something like this. I know I am. . .perhaps I'll do one. . .thanks for the build thread for me to follow.

[rol243]

how does this hull now balance laterally ? just curious about the extra lead used on port side plus the battery pack as well.

[Old School]

Many thanks. As regards lateral balance, a flip boat relies on prop torque to straighten the boat in operation. When at rest the port side will obviously droop as the flood chamber fills. When power is applied the hull launches onto plane allowing the chamber to empty. As soon as the boat comes to rest the hull will droop down on the port side again.

Without lateral imbalance I seriously doubt a largish flip boat would right itself. Even with the weight of the chamber plus the relatively heavy 6s battery, I still needed additional weight to flip the hull. If my chamber was tapered at the bow then that air pocket would not have formed thus the additional 100 gms of weight needed.

Smaller hulls rely on oversize canopies and prop torque to right themselves. Perhaps these smaller hulls may have lateral balance.

[rol243]

no i meant dry lateral balance check. this would indicate how the hull would ride when moving at some speed with the chamber empty of water.

[Old School]

no i meant dry lateral balance check. this would indicate how the hull would ride when moving at some speed with the chamber empty of water.

The hull will always be out of balance laterally. A balanced hull would not right itself unless the hatch was grossly oversized. The hull relies on prop torque to keep the hull level in operation.

[rol243]

so if prop torque is the method used maybe its not a bad idea when setting up this type of boat would be to position both the motor and drive line including strut over to the left [ port side ] by approx 1/4 inch as this will certainly assist in letting the hull raise on the port side without the total need of the props torque to do this. lower pitched props can then be used for better run times etc etc. what do you think ?

[Old School]

From the three hulls that I have built with chambers finding enough volume for the chamber takes up a lot of the left side hull interior. I do not know the impact of placing the driveline to the left. Given the number of self righting boats in Europe with lateral imbalance and centred drivelines, the setup must be satisfactory to not feel the need to investigate moving the driveline position.

[rol243]

maybe the port side offset is not required but i am sure if this was done the left port side would lift alot easier than relying on prop torque to do this so the hull could run evenly. there are many mono hulls around that do not require any strut / prop offset to compensate for torque roll as i found out with one of my 53 inch deltaforce monos which runs lateral level with no need for trim tabs compared to older monos hulls that did require right [ starboard ] strut offset to run level.