Category Archives: Higgins 78 1:16 build

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!

 

Torpedoes Part 2

Unhappy with the mechanical switch I had designed for the torpedo motor control, I did a little research and decided to change to a magnetic switch to control the motor.

The mechanical switch required a hole in the torpedo wall for the pin to protrude through and I felt that the pin would drag on the wall of the tube during launch and also probably allow water to penetrate the torpedo once it was launched.  In these snaps, you can also see the O-Rings used for water seal between pipe and turned wooden components.

I found some magnetic reed switches that could be wire “always on”, so that I could use a magnet under the front part of the tube to keep the motor switched off until launched.

 

Also, I decided to join and seal the three parts of the torpedos with vinyl electrical tape.  I had originally designed them with O-ring seals, as in the photos above, but the tape seemed to work as well or better.  And I could use a bit of the same tape to seal the hole in the torpedo wall originally for the mechanical switch and convert the first 4 torpedoes to the magnetic switches.

Buoyancy testing was successful, with the torpedo floating slightly nose up just at the surface of the water.  Since I hoped to retrieve the torpedoes, I wanted them to float and also leave an obvious wake when running.  The drive train worked well and the propeller drove the torpedo through the water at a suitable speed, although the torpedo did rotate, but not severely.

The only issue remaining was how long the torpedo would run.  I had built the first torpedoes with the mechanical switches using two AAA batteries for power.  I used alkaline batteries rather than rechargeable since I was not sure about retrieval.  When I changed to the magnetic switches, I also changed to AAAA batteries.  The flotation and propulsion testing was even better with these batteries, but I still had no idea how long they would run.  And since I would be running the boat in the rather large Bayou St. John, a long torpedo run might be a problem for retrieval.

The solution was to design a tubular slide switch and install it in the nose of the torpedo, where a detonator might be.  When the switch is pulled out, it is on, but the torpedo does not run because the magnet under the front of the tube keeps the power off.  Once the torpedo is launched away from the magnet, the motor runs until the batteries run out or until the torpedo strikes and object head on and the impact pushes the slide switch in, turning off the power.  This would mean I would have to be fairly accurate in aiming the torpedoes and solid targets, such as the concrete steps along some of the bayou, or a canoe.

This photo shows the slide switch installed in the nose of the torpedo.

 

 

 

 

 

These photos show the torpedo in the tube.  On the left, the slide switch is pushed in, turning power off so the torpedo can be slid into the tube and the retaining block engaged with the launching pin.  On the right, the slide has been pulled out, “arming” the torpedo to run.  The magnet just visible on the underside of the tube in front of the forward pedestal keeps the power switched off until the torpedo is launched, when it should run until it bumps into something and pushes the slide in.

Addendum:

All this seemed an elegant solution and worked well in testing.  On the second water trial of the boat, in February, I did fire two torpedos, which launched perfectly, but I had forgotten to pull the switches out (on position) so the torpedoes did not run.  They went about 5 feet from the boat at the launch and then floated for a bit.  The water was just choppy enough that we soon lost sight of them and they probably sank pretty fast.  So it goes.  No definitive cure for stupidity, but I now have a “pre-flight” check list including arming the torpedoes.

Torpedo Launch Mechanism

I followed the original plan for the torpedoes and made 4 prototypes, but was unhappy with the rather in-elegant switch and feared it would be unreliable.  It did work as intended in the tubes, but was pretty tricky and touchy to adjust.  More later on torpedo re-design.

The first step was making the torpedo tubes.  I used thin wall 1 1/4″ plastic pipe for the tubes.  The torpedoes ended up a bit thinner than true scale.  The actual torpedoes were 21″ in diameter or about 1.3125 ” in scale, and by using the 3/4″ PVC pipe, the torpedoes on the model a bit under 1.25 “, but I figured that is close enough.  Because the torpedos are launched by springs from the tubes, I had to make the tubes a bit longer (1″) to accommodate the spring.  I found some springs just under 3/4″ diameter at the hardware store and epoxied plastic disks to the end of eight springs.  I use two springs per tube by gluing the second spring to the disc of the first.  The springs are held in the tubes by small wire pins placed across the tube near the back to catch the spring.  This arrangement permits removal of the springs if needed

The torpedo tubes were detailed with various materials, using paper strips for the reinforcing bands, plastic for other details, 1/16″ plywood for the pedestals, and 3/8” copper for the compressed air chambers on the top of each tube.

I made up some launching pins which are retracted by a servo.  One channel operated the port side tubes, and a second the starboard tubes.  Moving the channel control one way fires one tube, then the second direction fires the second tube.  The wire from the servo arm passes through a hole on the trigger and ends in a loop, so the trigger doesn’t move when “pushed” but retracts only when “pulled”.

The launching pins extend up through the deck, through the rear pedestal mount of each tube, and through the wall of the tube, protruding about 1/8 inch into the tube interior.  The pins engage small blocks on the torpedo.  When the pins are retracted by servo action, the torpedo is launched about 4 feet.

I used pretty beefy servos to make certain they were able to pull the pin when the torpedo was loaded in the tube against the spring pressure.

 

The loading process is pretty simple.  I use needle nose pliers to retract the pin on a tube, insert the torpedo with the retaining block down and slide it back against spring pressure until fully in the tube, then let the pin back up into the tube to engage the retaining block.

The launching system is simple and works well.

Drive Train

When figuring out the power system for the boat, I used several methods of scaling the power down from the original.  One method started with the horsepower of the original, another the displacement as a function of length, width, and depth.  Both methods resulted in an estimated power requirement of somewhere between 500 and 750 Watts.   Of course, the ultimate performance will be related also to the propeller size, pitch, etc and other factors affecting the RPM of the propeller shafts.  I thought that it would be smarter to run at a somewhat lower propeller shaft RPM and drive props that were larger than scale with a moderate pitch.

The boat is powered by three PropDrive 28 electric motors.  They are rated at about 1,100 rpm per volt and can handle up to 15 volts.  I had planned to use one large capacity 12 volt LiPo battery to power the boat motors and the air pump, but decided to start with lower voltage 7.4 volt LiPo batteries, one for each motor, figuring that the lower RPM might produce more realistic scale performance and that I could always increase the operating voltage if needed later on.  Also, having multiple batteries might avoid problems if one battery ran low and shut off.  The motors are small, smaller than a thimble of thread, just over an inch in diameter (28mm) and very powerful, rated at 189 W at 11.1 v (3S LiPo) and 290 W at 15 v (4S LiPo).  I estimated the power as about 110 – 120 W at 7.4 v (2S Lipo) for a total of 330 – 360 W for the boat, less than the estimated requirement.  But again, if the performance was lacking, I could up the batteries as necessary.

This shows the three motors installed in the hull and the stuffing boxes for the three props.  Aft of the center engine is a box built to hold ballast if needed.  In this picture, there is a one pound metal weight in the box, which can hold two such weights.   During initial buoyancy testing, I added two pounds of ballast in the box, but later, after addition of the torpedoes and other weight (crew figures), I could remove the ballast and the boat floated on the waterline.

I tried using a single ESC to control all three motors without success.  I found it might control two but not three motors.  In the end, I powered the boat with the three NTM PropDrive motors, each with individual battery and water cooled ESC.  For the ESC, I use the Turnigy AquaStar.  The center engine has an older version, and the two wing engines a newer version.

 

The air pump is powered by a separate 8.4 V NiCd battery.  And there are two 6 volt NiCd battery packs for accessories.

This picture shows the batteries installed in their boxes.  The three LiPo batteries for the motor are forward and run through the three toggle switches on the left.  The right hand toggle switch controls power to the air pump.  The slide switches control the accessory 6 v batteries on the left of the after battery box.

 

The props are plastic and rotate counter-clockwise, which is not to scale.  They are also larger than scale, which was done by design, hoping to compensate for lower shaft rotation speed with a bigger bite.  The props are inexpensive and easily replaced.  Since I will be running around in the local bayou, full of debris and hazards, replaceable props are a necessity.

The prop shafts are 3/16″ brass rod, running in stuffing boxes of 7/32″ brass tubing.  The prop struts were fabricated out of brass and copper and then epoxied to the hull.   The center prop shaft and engine mount are at a different angle than the outer shafts, which is consistent with the Higgins design.

 

Rudders are fabricated from copper sheet wrapped around 3/16″ brass rod and soldered to the rod and together.  Both the prop shafts and the rudder shafts are larger than strictly scale, again because of the operating environment.  The Higgins boats had two rudders unlike the ELCO boats which had three.  The rudders on the model are also oversize and extend deeper than scale to avoid problems with loss of rudder control due to prop wash/cavitation at speed, which had been a problem for me with earlier models using scale sized props and rudders.

Addendum: March 2017:

The boat had its first water trial in February and did pretty well.  The motors were coupled to the shafts using Dumas couplings and the nylon “dogbone” coupler sheared off its ears on two of the three motors.  There is a video of the boat running up to speed and you can see the loss of power as the couplings sheared.  Fortunately, the portside wing engine coupling held and the boat made it back to shore instead of drifting away into Lake Pontchartrain.

I reworked the couplers, replacing the nylon dogbones with soldered brass tubing.  This arrangement ended up working well on a second trial and produced pretty realistic performance, although the extreme torque and power of the motors caused problems keeping the drive coupling attached to the motor shaft.  The set screws loosened on two of the three motor shafts and once again, the boat made it back on a single engine.  I am still working on this issue, and will update on results.

Lights

The model is being equipped with LED lighting for things like anchor/mooring light, running lights, and searchlight.  The LED bulbs are installed in brass mounts fabricated from brass tubing and sheet stock.  Colored LED bulbs are used for running lights.  The lighting will be powered with a 5.5 – 6 volt power supply also used for Arduino, separate from the 12 volt power for the drive train.

Bow light:

img_0300a

Stern light:

img_0302a

Port running light:

img_0301a

Starboard running light:

img_0298a

 

 

 

Deck furniture and ventilators

The Higgins PT boats initially had 10 funnel ventilators as standard equipment plus powered fan ventilation in the engine room.  Ventilation was critical not only for the humans inhabiting the below deck space, but also for exhausting carbon monoxide and gasoline vapors that might accumulate in unventilated spaces.

In later boats, after the turrets were relocated aft, two of the tall funnel ventilators were removed and a smaller funnel vent added to the engine room hatch.

Funnel ventilators under construction.  The larger vents were built up using half inch plastic water pipe as a base and adding shaped card stock for the upper part of the vent.  These will probably be used for actual ventilation on the model, to provide cooling for the electric motors.  The smaller vents are made similarly but start with 3/8″ copper pipe as the base.  In this photo you can see some crew members being made from Sculpy clay, and several copper wire/aluminum foil armatures for more crew on the bench.

higgins_crew_ventilators_wip

 

 

 

Armament

Browning machine guns and turrets

The boat being modeled has the standard two turrets mounting twin Browning 50 caliber machine guns and a 20 mm Oerlikon auto cannon on the after deck.  For this model, all the guns are constructed with optical fiber in the barrels to simulate gun flashes when firing.  The fiber will be illuminated with LED lights controlled with Arduino modules/sketches.

50cal_brownings_construction_1

The gun barrels for the Brownings were made up from 1/16″ brass tubing for the barrels and polystyrene tubing for the cooling sleeves.  The holes in the cooling sleeve were drilled by hand using a jig made up from a 1/4″ hex nut on threaded rod as a jig/guide to spacing the holes around the tubing.  The brass tubing for the barrels will hold 1 mm optical fibre for the gun flashes.50cal_browning_guns

This snapshot shows the guns near completion with the gun cradle and turret mount in the background.  The ammunition cans and belt guides are also in place.  Details were made up from polystyrene sheet plastic, brass wire, and brass sheet stock.

50cal_brownings_crew_1

The guns ready to be mounted in cradles and the optical fibre installed.  The two “gunners” are ready to man their stations.

50cal_browning_gunner

20 mm Oerlikon auto cannon

This gun will be installed on the after deck, behind the engine access hatch. See part 2 for more information.

 

 

Torpedoes

The Higgins PT model I am building is of the earlier series and it is based on the Al Ross plans for the PT 265 class.  These boats were originally designed with torpedo tubes, but many had the tubes replaced with “roll off” torpedo rack/launchers before deployment or in the field.

PT 305, the boat being restored by the WW2 museum in New Orleans is of the 265 class, but in the field carried roll off torpedoes and gradually increased armament including the 20 mm, 37 mm, and 40 mm cannons typical of the late stages of the war.  I do not know whether the PT 305 ever had torpedo tubes installed at the time of construction, as PT configuration changed and evolved continually and rapidly during the war.

img_0306aThe 265 class was an intermediate stage in the evolution of the Higgins PT boats.  Because the boats were originally designed to carry torpedo tubes, the gun turrets were attached to the cabin at the aft corners and had short tails extending aft.  Once the tubes had been abandoned and the roll off racks were being installed on boats during construction, the gun turrets were moved aft about 30 inches to improve visibility from the cockpit, and the later boats had extensions from the cabin tho the turret and still maintained the short tails aft of the turrets.

The plan is for the model to have working torpedo tubes that launch working torpedoes.

img_0311aThe tubes are being fabricated using 1 1/4 “thin wall PVC pipe, the type used for under-sink drain pipes and the torpedoes will be launched with a compression spring.  The torpedoes will be pushed into the tube, compressing the spring and held in place with a pin extending up through the forward pylon holding the tube.  When the pin is retracted by servo action, the torpedo should launch.

The torpedoes are fabricated from lengths of 1” PVC water pipe with turned wooden head and tapered tail.  The propulsion system is a small electric motor, which just fits in the plastic tube, two AAA batteries in series and a switch that is held open by a pin extending through the wall of the plastic tube.  When the torpedo is in the tube, the pin is pushed upward and the switch is open.  As the torpedo leaves the tube, the pin drops down and the switch closes, starting the motor.

img_0308aIn developing the switch, I made up several prototype knife switches of brass using elastic bands to provide the closing mechanism.  These worked but were too tall to work well in the small space available, so I converted to a switch of spring steel, which has a lower profile and seems to have solved the problem of space.

In the photo, you can see the component parts of the torpedo, one of the initial prototype drive units, and the “new and improved” switch.

At present, I need to fabricate the four torpedoes, get them painted and sealed, do some buoyancy and water testing, then see if they will launch from the tubes as planned.

Deck Part 2

The second layer of deck planking was laid longitudinally.  First, the large access hatch was planked separately, and the planks were extended out from the frame of the hatch along its length to form an overlap along the side, and also extended from the rear of the hatch to the edge deck plank along the transom.

img_0133a

Once the hatch was planked, it was replaced into the opening and the remainder of the deck planked.

 

Hatch coamings were built up using wood for the forward hatches, and laminated card stock for the engine room cabin hatch.  This hatch coaming also had wooden blocks placed so the hatch cover can be screwed down during operation.  This hatch is planned to be the main access for batteries, receiver, motors, etc at later stages of construction.

img_0131a

Planking was carried around the cabin and turrets.  Planking was glued down and also secured with wooden pegs.  The pegs were made by splitting wooden tongue depressor sticks with a knife and then tapering them to a point.  These wooden pins were then dipped in glue and gently hammered into a hole in the deck plank and deck beam drilled with a #65 drill.

 

img_0142a

img_0141a

img_0145a

Deck part 1

 

higgins_hull_5Once the hull is free of the building board and on the cradle. the next steps included trimming the upper parts of the ribs and preparing to plank the deck.

higgins_hull_6The first step was installing deck beams on alternate frames, using the deck beams to also frame up the various hatches to be added or created later.  I used the same plywood for the deck beams as for the ribs, supplemented by hard maple for some of the areas needing reinforcement, such as the position of the Samson Post.  Then I added the perimeter board/rub strake to the deck, using hard maple, the same thickness as the deck planking to be added later.

higgins_hull_cabin_1The deck was also planked in two layers, as the hull, with the first layer laid on diagonally and the second layer longitudinally.  The area of the main cabin was left un-planked and the cabin framing set up as shown as a guide the planking, which was stopped at the forward edge of the cabin.

Once the first layer of planking was in place, the main access hatch was laid out, running aft from the cabin.  This was not a hatch as on the original, but designed to give easy and full access to the hull interior during the rest of the construction and after completion.  higgins_hull_cabin_2Once this hatch was cut, trimmed and fitted, the cabin was sheathed in plywood, turrets made up from Creole/Cajun seasoning cans (of paper) and the second, longitudinal layer of planking could be laid.

higgins_hull_cabin_3