Hobbyking Osprey build

[Old School]

This has now moved on from a simple review to a build. I have removed all hardware and mounts to facilitate reinforcing the hull with carbon fibre. My initial grandiose plan was a big 56 series motor and 1/4" drive components, however, the wisdom of this site made me realise I would be better off with a 40 series drive with 3/16" flexshaft. I have decided to go with a 4092 series motor around 1300 - 1400 kv, a Swordfish 220 amp ESC, 6s lipo batteries in parallel, Speedmaster stinger and will commence with a prop around 45 mm and progress from there.

All removed components will be either refitted to this build or cannibalised for another smaller 70 cm mono that I am also constructing.

[martin]

Check the hull with a strait edge to see if theirs any hook ( concave or hollow ) at the rear of the hull bottom, if their is you might need to take the concave out of the hull. Otherwise excessive hook will suck the hull down to the water making the boat run wet & slowing it, my Osprey had a hook that I had to fill to get the bottom flat.

[Old School]

Martin,
on the starboard side 1mm depression mid-chine approximately 80 mm forward of the transom. On the port side any depression is less than 0.5 mm.

[ray schrauwen]

You could leave the hook alone until you are done reinforcing the hull. If you make a jig to put the hull into while the carbon dries adding weight to the inside you can sometimes remove hooks etc this way. Besides there is more material present after putting carbon in in case you sand through the hull.

Some hulls like Speedmaster and others purposely put hooks in the bottom so you don't need trim tabs. Don't overlook trying it without trim tabs first.

[Old School]

How drastic actually is a hook, please? I am only after a fun sport boat. Once reinforced I could weight the inside of the hull properly supported to hopefully relieve the depression. Sanding the gelcoat is not really my chosen path and I would preferably avoid doing it.

One thing I will definitely carry out is reinforcing the interior of the cab moulding and then clamping it to hopefully cure flat.

[Peter A]

My HK Pursuit had a warped bottom on it from new. It didn't really cause a lot of problem initially, however when I inlayed the hull I got some small ali channel and taped it to the bottom to flatten out the high spots. I have since blueprinted the bottom of it. My Q mono was as bad, so I used some 20x20x3 steel angle pieces and stuck them to the bottom of the hull with double sided tape then did the inlay to straighten the hull bottom, the carbon inlay when cured keeps it in place. You can choose whether or not to fill and finish the bottom further after that. Oh yeah you have to carefully pry off the taped on angles, a bit of heat from a heat gun on the steel softens the tape adhesive and makes this a bit easier.

[Old School]

Peter,
many thanks. I understand the need to "blueprint" the hull of a competition craft hull to gain every advantage, but wondering if such corrective action is essential on a "fun" boat. If I had not been informed I would never have checked the hull for fairness as it looked visually straight.

[Peter A]

It is probably worth taking as much distortion out as is practical while doing the inlay. It will not hurt the performance or handling, whereas any issues that may be there may become a problem if you decide to prop up later for some faster running. The setup you are going with is easily capable of cracking 100kph. The hull will perform differently at 100 than it will at 70-80.

[martin]

If theirs a hook in the hull its much easier to sort out at this stage, not only can excessive hook slow the boat it can also push up the amp draw. As Peter has said get any warp out before doing the inlay.

[Old School]

Peter and Martin,
many thanks

[Old School]

After completing several self righting boats I am now in a position to progress this construction. Like most Hobbyking hatches mine does not conform fully with the deck cutout showing distortion along the sides. To hopefully correct this as much as possible I have applied several layers of fibreglass cloth along the sides and across the width of the hatch moulding. I then clamped the hatch down onto the hull after firstly lining the deck opening with plastic film. The hull was then inverted.

I am hoping that the glass cloth will cure and hold the hatch in a better shape than when supplied. I will then apply some two part foam to the interior.

Edit: while the internal fibreglass bracing did help there was still some springiness in the hatch, so I have bonded a thin aluminium strip laterally midspan to hold the hatch at the width I hope is correct.

[Old School]

The part I detest but a necessary evil is the carbon fibre inlay. Even though the transom has a plywood doubler I also added a 2 mm carbon fibre plate stiffener as well.

The first image shows the garbage bags used to protect the hull during the inlay. The tape on the transom is temporary until the resin filler in the factory holes is cured.

[Old School]

Showing the underside of the hatch. The aluminium metal strip worked perfectly to hold the hatch flat so it sits neatly in the hull cutout.

Edit: a compression plate is now fitted to tie the foredeck to the hull. This reinforces the foredeck in a mishap.

[Old School]

While waiting for resin to cure, I have decided to modify my Speedmaster stinger to fit to the hull. Initially I intended using a 1/4" driveshaft but was convinced that a 3/16" shaft would suffice. Considering the short length of the stuffing tube also convinced me about running a 1/4" drive through the tube. Having previously purchased the 1/4" drive Speedmaster stinger I set about reducing it to accommodate a 3/16" rotating bushing. This was accomplished using several telescoping brass tubes which will be bonded inside the stinger bore.

The TFL eBay store "rcgenesis" had an 8 mm/4.76 mm (3/16") collet so this has been purchased.

[Old School]

With reference to thread relating to the centre of gravity problem -

https://forums.offshoreelectrics.com...rey-CofG-issue

After the carbon fibre inlay was carried out I temporarily placed the motor and batteries and other items needed in the boat. With the dual batteries beside and outboard of the motor the CoG is at 30%. With the batteries forward of the motor the CoG is 33%. During the build I will fit battery trays both beside the motor and in front of the motor to give me a choice.

The batteries I intend using are 4000mah 60C 6s. I feel given the size of the motor (56-series) that dual 4000mah batteries in parallel will be needed for a reasonable runtime.