4 prop expresscraft 60inch

[Old School]

It is amazing what a little elbow grease can achieve. When received yesterday the interior was very dirty. An hour of scrubbing, removing loose 5-minute epoxy and RTV sealant and the surface is now much better.

The port side sponson tip had about 1/4" missing so this has been built up. The port side forward corner of the hatch cutout had a 1 cm crack. I sanded back through the gelcoat to the base fibreglass and the crack was still evident, so the area was ground out and now filled. I cannot detect the crack going all the way through the skin but will reinforce the underside later just to be sure.

[Old School]

Some progress has been made however a severe medical emergency in the family has meant that I have been visiting a close relative in the hospital most of the last four weeks. A carbon fibre inlay has been accomplished plus carbon fibre vertical struts fitted under the forward deck with install to be finished by my son (it is his boat).

Today I set about fitting the stuffing tubes. Perhaps by sheer luck, alignment is less than 5 mm apart over a distance of almost one metre, inferring that the tubes are parallel. I check with two lengths of one metre 6 mm carbon fibre rods shimmed inside the stuffing tubes and extending aft beyond the transom. After the motor mounts have cured then I will remove the motors and then finish the install on the stuffing tubes, cutting them to length.

When installing stuffing tubes I like to use the next size up brass tubing (in this case 3/8" O.D.) and bond this in the transom. Once cured this acts as an anchor to enable setting up the 11/32" stuffing tubes. I finish the larger 3/8" tubing sleeve flush with the transom outer face. The stuffing tube then extends approximately 2 - 3 mm beyond this, acting as a solid point to attach the Speedmaster nitro stinger. The stinger mount is drilled to accept the 11/32" tubing, still allowing the stinger shaft to be adjusted for either positive or negative attitude.

Before the stuffing tubes are finally installed I need to work out where the water cooling inlets will be fitted, whether mounted to the sponson aft lower surface or transom mounted.

The Turnigy T20 (Proteus) motors do look very tiny indeed in this hull. Hopefully, the motors will be run with a "Y" winding (730 kv) on either 10s or 12s. Balance (CoG) will be an issue with this hull due the long overhang at the bow and foredeck. I did add epoxy and two-part foam to the tips plus additional carbon fibre around the nose of the hull. The batteries will need to be located aft of the motors to attain a 32-34% CoG. Attaining a 40% CoG for speed runs should not be an issue. Unless parasitic weight is added to the aft end of the hull then I do not believe a 30% CoG to be possible.

[Old School]

I have progressed the drives with the stuffing tubes installed and the 1/4" flex drives cut to length and the cut ends soldered. A downside of the Turnigy T20 cooling jacket is that it is not able to be reversed and be able to positiion the cooling outlet nipple at the high end of the right motor because the inlet nipple would foul on the sponson inner wall. The jacket would need to be drilled and a nipple inserted at the 12 o'clock location. Given the difficulty removing and replacing the jacket without damaging the o-ring I do not wish to go there again.

My son has the stinger drives over 1000 klms away so I based the flexshaft length on the stinger installed on my Osprey build. The flexshafts are contra-rotating and are reduced to 3/16" at the propellor end. I have no idea what suitable props will be required but as I am doing just the basic build my son can research that at a later date.

While I do admire the beautiful all black interiors on the masterful creations of those master builders, I build more for functionality rather than aesthetics so do not pigment the epoxy used. The build has a long way to go yet but hopefully I have made the final task a little simpler for my son.

The view of the transom shows the battle scars this hull has endured in its previous life with the multiple strut drives.

[rol243]

as long as the water outlet on jackets are at the top [ 12 o,clock ] doesn,t matter where the inlets end up. not doing counter rotating props hey ?

[Old School]

Fortunately I was able to rotate the jacket to get the outlet almost at 12 o'clock with the inlet just above the tunnel floor. The left motor is set up with a reverse rotation flex and locking collet.

It is up to my son how he sets up the boat in the future. I believe inward rotating props give better directional stability at the expense of cornering speed. Since my son is a fan of outright speed then cornering speed is not that much an issue.