Notes on Sea Trials

The PT 277 model had the first sea trial, in the Bayou, in mid February and did well.  It floated just about on the waterline and after I removed a pound of ballast and added torpedoes and crew, it was pretty much exactly right.

On the first run, two of the three nylon couplers (“dog bones”) in the Dumas connectors I had used sheared off the “ears” but one held and I made it back to shore safely.  There are some videos posted on YouTube and in the one, you can see the boat accelerate and start to plane then slow down, as it lost the couplings.

 

I rebuilt the couplers using brass tubing soldered in place instead of the nylon connectors, which I could do since the prop shafts and motor shafts were pretty well aligned and needed only slight tweaking.

On the second trial, several weeks later, the boat again lost power on two of the three engines as the set screws failed on the motor shafts.  The set screws were ordinary 6/32 screws and the much harder steel of the shafts polished them off quickly under power.

On that trial, I also tested out torpedo launching, which worked well.  One side failed due to a loose connection between the servo wire and the extension needed to reach the receiver.  The other two launched, but did not run, as I had forgotten to arm them, so they floated for a while and then vanished.  We did not have a boat to use to retrieve them.

Back in the workshop, I filed flat spots onto the motor shafts, used harder steel proper set screws and added Locktite to all set screws.  On the third trial, the couplings held.  The boat was in the water about 20 minutes and had plenty of battery left.  Nothing overheated.  Performance was as hoped, with the hull planing nicely and a fairly accurate wake and rooster tail effect under full power.

The torpedo launching went fairly well.  One torpedo hung up in the tube and ran the battery down.  (Pretty realistic outcome).  The other three launched well.  Two ran in circles, and one ran fairly straight.  Another realistic outcome.  This time we had a canoe and retrieved all three torpedos that launched.

 

Also on the third trial of the 277,  I took out my smaller 1:32 scale Higgins, PT 462,  for its first run.  This one is powered by a single 550 brushed 12 T motor, powered with 8.4 v NiMH battery running through Dumas gear sets to three propeller shafts.  The boat ran well, planed at speed, but lost one prop and stopped partway through due to engine overheating.  The overheating was likely due to high resistance in the gear train and weeds fouling one prop.  The loss of the prop was due to lack of Locktite.  The above issues have been taken care of and both boats are ready to go back in the water.  Canoe at hand.

Both the 277 and the 462 were video’d using a drone.  Videos coming soon.

The third sea trial of the 277 was on April 9th and included the first test of the 1:32 scale model of an early ELCO 80′ boat, the 103 class, which included the 109.

On floatation testing at home, the model of the 77 ft. ELCO boat floated a bit too low in the water to suit.  Although the same drive train and battery are used in all three of the smaller hulls, the wetted surface area is different.  The 80 ft model also floated a bit low, but did just barely plane at speed, as in the video below.  It was running with only two props, the third one scavenged to replace the one lost from the Higgins, and may perform better with three.  But since I am reconfiguring the drive train for the 77 foot ELCO model, using lighter motor and battery, I will adapt both ELCOs to use the new system and leave the 550 motor in the smaller Higgins boat.

The 109 model benefitted from the re-configured gear train and there was no overheating on this run.

The 277 performed well.  It was loaded with 4 torpedoes and the crew figures but the weight must be just about right, as it floated on the marked waterline and planed at about 2/3 throttle.

The torpedo launching also went well.  And all torpedoes recovered!