Hobbyking Pursuit self-righting

[Old School]

With the completion of two Arowana 32 inch self-righting hulls which did require quite a lot of alteration to make usable, I thought to myself that making a self-righting Pursuit hull should present no additional challenges. The Arowana and the Pursuit share the same basic hull with each having a different deck and hatch moulding. Additionally, the Arowana has a slightly canted transom requiring either a very thin wedge under the rudder mounting face to keep the forward edge vertical or in my case I slightly modified the hole for the breakaway bolt in the rudder blade to enable the rudder to sit vertically.

Hobbyking had a sale on the bare Pursuit hull with free shipping from my local Australian wharehouse and the hull was delivered the next day after purchase. The Australian Hobbyking staff are brilliant when it comes to preparing goods for shipping and getting them picked up by the courier. All up cost was less than $120.00 Aud ($92.00 usd).

Yesterday I stumbled upon an old OSE thread from mid-2015 in which TFL announced it was after expressions of interest in a factory self-righting Pursuit hull. I understand the pros and cons presented by both sides and apparently the degree of negativity to the proposed project killed it off. Not having an inclination to go racing, I did side with the sporting crowd who understood the practicality of the design. I also understand the negativity from the American racing fraternity who believed it gave the racer an unfair advantage, plus the danger presented should a boat flip, self-right itself and then have to travel against the flow of racing to turn itself around.

I have purchased a quick change 40 mm motor mount from OSE plus a stuffing tube mount. I liked the idea of the quick change mount as I can place the inner flood chamber wall right up to the left side rail of the mount. With my Arowana build I had to space the wall out a little to allow access to the front motor mount ring retaining bolt. This did limit the water capacity of the flood chamber, however, in hindsight the modified Arowana hull will flip itself back immediately it is flipped over so obviously there is more than enough port side bias to unsettle the boat when flipped over.

While awaiting the mount to arrive I can proceed with a carbon fibre inlay in the hull. I need to install the motor mount rails before commencing the flood chamber install as I need to see how close to the centre of the boat I can extend the inner wall. Also part of the design will be to provide clearance to enable at least one 6s battery to be fitted to the rear port side wall of the chamber. On my Arowana builds there are rails the full length of the hatch opening and these restrict the available height under the hatch restricting me to two 3300 mah 3s batteries in series. Hopefully, I will be able to fit two 6s batteries in parallel and get some usable runtime.

I already have a spare Pursuit bare hull plus fittings from a previous Hobbyking sale to make a non-self righting hull. Having the quick change motor mount in the self-righting hull will enable easy transfer of the motor and ESC between each boat until I source another motor/ESC combination.

Hopefully I learned enough from the two Arowana builds to avoid some of the traps in making the hull water tight on the Pursuit.

[Old School]

Some progress today with a "kit" of carbon fibre inlay panels made. I also drew up the template for the forward flood chamber wall and cut from 2 mm carbon fibre plate. For the moment I can continue with the CF inlay, but cannot progress the flood chamber as I need to fit the motor mount (enroute from OSE) to determine the position of the inner wall.

Not everyone's choice but I do like West System G-flex 650. It is a lot more expensive than a typical West System 205 type resin but I like it as it mixes in a 50/50 ratio which I roughly judge for volume accuracy. The 5:1 West System 205 type resin requires a scale and for me a lot of stuffing around as quite often I will mix just a very small quantity and the 1:1 mix G-flex is so simple. It has less rigidity than the 205 mix but has the advantage of flexibility, but alas is a little heavier.

I also strongly recommend the West System 403/413 filler. It easily mixes in the resin with the quantity added giving varying thicknesses of resin. This is particularly important if using as a filler or adhesive as resin minus the filler material will simply run out of the join.

Another advantage of the G-flex is that uncured resin is easily removed with white vinegar, particularly important when reusing brushes and metal rollers.

[rol243]

Have you tried Micro Balloons mixed in the epoxy ? makes and excellent / light and easy sanding filler. i use this mix for glueing in the flex shaft log to hull floor with a 30 minute epoxy mix.

[Old School]

While working in the aircraft industry I did use micro balloon often as a filler. I have not tried it as yet on boats. I am sure West System have it, however, my last G-flex purchase I went for the 403 filler as it was available. Buying it in one litre bags (around $10.00 Aud) is a lot cheaper than the small quantities that Great Planes and an English eBay store sell the powder for.

[rol243]

actually the micro balloons are about the same cost at approx $10 au per bag from what i remember, it lasts me for years.

[Old School]

In preparation for the carbon fibre inlay, rather than tape up the whole hull to protect the surface from stray resin, I sealed the hull inside the original heavy plastic bag the hull was shipped in, cut out the hatch opening and then taped it. This way no actual hull outer surface has tape applied. Since the whole process may take a week or two I do not want masking tape sticking to the hull surface and being difficult to remove.

The inner surface has been sanded and wiped with acetone in preparation for the inlay.

Edit: carbon fibre inlay now done. Now awaiting the motor mount to determine the mount location and position of the flood chamber inner wall.

[srislash]

That is a slick idea. Awesome thinking. Are you thinking forward or rearward for the motor?

[Old School]

That is a slick idea. Awesome thinking. Are you thinking forward or rearward for the motor?

The plastic bag cocoon actually worked perfectly yesterday while applying the inlay. Hopefully, I can leave the bag on until I have finished the flood chamber. I am thinking a similar motor location to that used on the two recent Arowana builds. On those hulls the motor was placed with the rear mount basically on the CoG. I need to place a battery to the aft port side of the hull so need to allow distance between the transom and the motor mount for a 6s battery to lay against the flood chamber inner wall to get a weight bias to the left. On the Arowana I used 2 off 3s batteries but due space/height limitations was restricted to 3300mah each, which considering the motors were TP Power 4050 and a TP4060 will not give much runtime. On this hull I am hoping a single pack 6s may be a better choice with a Leopard 4092.

[boatsrnew2me]

this guy has a 3 part video series on his pursuit flood chamber build .thought maybe you would like to look at it .

[Old School]

Many thanks.

[rol243]

great info there.

[Old School]

Some progress while awaiting my motor and mounting. The flood chamber is constructed from 2 mm carbon fibre plate and has an offset at the rear to accommodate a 6s battery or if balance proves to be an issue a 3s will be paired with a 3s forward of the motor location.

The hull has a carbon fibre inlay plus two-part expanding foam in the bow section. I can now progress with fitting the stuffing tube, stinger, rudder and trim tabs and R/H turn fin.

Edit: I had thought the flood chamber to be quite large, but surprisingly on a leak test it only held 1.5 litres. That will be enough volume but was hoping for around two litres.

[Old School]

Most of fittings attached, just awaiting the motor mount. I have a Leopard 4092 1390kv 3y to run on 6s with a Turnigy 180 amp ESC. The battery will mount at the aft port side, retained by straps.

[hughb]

Looking good! I especially like the “Lithium” stickers

[Old School]

The quick change 40 mm motor mount from OSE arrived yesterday afternoon and is now installed. It would seem that the mount is designed for a flat bottom hull so to get a more suitable shaft height I drilled a new mount hole approximately 5 mm lower than the existing rear mounting hole. This dropped the motor lower into the vee of the hull. The mount is shown on the site with a Leopard 4092 with 68 mm cooling jacket. This is the option I chose, however to fit this combo did entail a little fettling as it is a tight fit.

[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.