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>> Home > Boat Building Blogs > 20th Scale ELCO 80ft PT boat part 1
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20th Scale ELCO 80ft PT boat part 1 Print Booklet
Author: CB90   Posts: 12   Photos: 46   Subscribers: 4   Views: 832   Responses: 16   |   Most recent posts shown first   (Show oldest first)

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20th Scale ELCO 80ft PT boat part 9 - Posted: 10th Sep 2018
Installed the three out-runner motors, I hope I never have to replace them.

They have rubber mounting washers and nylock nuts and spring washers in M3.

They are about half inch apart took a few hours to install with full access as currently boat has not been skinned.

I hope to add small fans to the prop hubs to keep them cool

Now have received the rudders and water scoops. they will be installed after the bottom skins are on.

Attached Photos - Click To View Large

Response by RNinMunich on the 11th Sep 2018
Just when you think you've seen everything - up pops a boat with airscrew spinners ! 😲 But a good idea to use 'em as fan spinners👍
Nice work mate, Cheers Doug 😎
PS Looking at the first pic before expanding it I thought you were trying to build a 'Hover-chair' 😁😁
20th Scale ELCO 80ft PT boat part 8 - Posted: 18th Aug 2018
Added the three motor mounts and reinforcements, predrilled mounting holes and shaft exit before fixing into position.

Used a long shaft and a dab of paint on the end of it, to mark the points of the motor positions, the use a small right-angle to angle to set the mount 90 degrees to the shaft.

Now waiting for some nuts, bolts, spacers and washers


Attached Photos - Click To View Large
20th Scale ELCO 80ft PT boat part 7 - Posted: 13th Aug 2018
Have added reinforcing to the frame supporting the end of the shaft tubes, 3 pictures show dry fit.
and once dry glue in shafts with epoxy resin, 3 pictures of fixed shaft tubes.

Now looking at an extra part frame to support the three motor brushless out-runners.

Attached Photos - Click To View Large

Response by RNinMunich on the 13th Aug 2018
Very brave - fitting the shaft tube before the skin 😲
Rather U than me Gungadin! Have fun 😉
Or is that a dry fit just to prepare the shaft lines?
Response by CB90 on the 19th Aug 2018
Hi RNinMunich,

Should not be too bad as will cut ply slit/profile from tubes to the transom then reinforce inside under rudder compartment.
rest of the tubes length are already supported.

I really wanted to make sure the motors and shafts were in excellent alinement, and being able to see through the hull is a good advantage. (note. do not have facilities to make alignment tools).

In previous models I have left it towards the end of the build to fix motors couplings and have found alinement to be a bit difficult, especially on smaller boats.
20th Scale ELCO 80ft PT boat part 6 - Posted: 11th Aug 2018
Dry fitting pro-shafts (Note, all shafts parallel with the keel)
Drilled with an old prop-shaft which I modified to a cutting tool then finished with a round file and cut slots for propeller-shaft support bracket with a hacksaw, file and knife.
Note these shafts are lightweight aluminium tube with steel liners and steel shafts. props at currently 40mm but as with all things scale things are not always practical in scale size such as propellers and rudders and in this case the direction of rotation (not all going round clockwise).

Attached Photos - Click To View Large
20th Scale ELCO 80ft PT boat part 5 - Posted: 8th Aug 2018
After some calculations I find I need to extend the reinforcing for the port & starboard shafts forward towards the bow.
Created some wooden guides when drilling the prop-shaft holes
and glued them in position temporarily, as you make expect the drill needs to be rather long, so I made one out of an old brass shaft basically sharpening it so it could cut wood.

Next job will be to cut out for integrated shaft support brackets (2mm wide and minimum of 35mm long slot) and the tube shafts are 8.5mm in diameter.

Attached Photos - Click To View Large
ELCO 80ft PT boat Jumping the gun - Posted: 6th Aug 2018
Yes, jumped the gun and brought the motors.
Already have 3 light weight Aluminium prop-shafts that I intend to use:
Tube Length:25CM/9.84inch
Tube diameter:8.5mm/0.33inch
Shaft diameter:4mm/0.15inch Stainless steel
Weight:67 g

The Motors will run on 3s -11.1v

Three of these (one as spare):
High Performance 2808 1400KV 14 Poles Brushless Motor
Max Watt: 350W
Voltage range: 7-15V
Max amps: 35A
No load: 1.2A

One of these as centre motor or my swap for spare of above:
High Performance 2826 900KV 14 Poles Brushless Motor
KV(RPM/Volt): 900KV
Max Watt: 1000W
Voltage range: 7-18V
Max amps: 60A
no load : 2.2A

Attached Photos - Click To View Large

Response by RHBaker on the 6th Aug 2018
They look good motor choices. Where did you buy them? I might need some
Response by CB90 on the 18th Aug 2018
Sorry about delay in reply,

Yes I did buy them from Amazon : big Un =£17.17
Little Un £11.82

Paste above into browser

Next purchase shown in picture brought three of them a bit OTT
20th Scale ELCO 80ft PT boat part 4 - Posted: 6th Aug 2018
Added some strength to the Bow also act as glue points for the bow strips of ply or planking.

Created a template of the first section of ply to go on, thought I would mark out the rudders, prop-shaft supports and shaft exit points.

Unfortunately due to cost restrictions I cannot afford to buy or have the facilities to make the correct layout of brackets and supports for the shafts, which I feel may not be up to the job when coping with the high outputs of brushless motor, (still that my excuse)

So to use my poor-mans prop-shafts (with integral support skeg) I have had to reconfigure the layout slightly but will keep the original 3 prop-shafts and 3 non-scale rudders, but may shape them as per the originals.

Attached Photos - Click To View Large

Response by RNinMunich on the 6th Aug 2018
Hi CB,
Looks pretty good so far👍
Attached some pics of a restored ELCO 80 at Battleship Cove USA.
Showing the props and rudders; Port, Centre, Starboard.
If you need any more detail pics just let me know😉
Cheers, Doug 😎
20th Scale ELCO 80ft PT boat part 4 - Posted: 5th Aug 2018
Finished gluing in stringers a total of 8 in all, started profiling stringers and rudder and stern tube (prop shaft ) supports.

An important piece of advice from my Dad is to "make sure every thing is fair to the eye." Meaning it must look straight or the curves must flow, no kinks or unsightly lines.

Thus some of my frames had to be adjusted by perhaps padding out or moving the position of the stringer in the frame.

Added gluing supports around the bulkheads and other frames this is to support the 0.7mm ply joints until I get to the Bow when I intend to use small strips of ply or wood.

Attached Photos - Click To View Large
Part1 research information - Posted: 1st Aug 2018
From the construction hand book:-
Decking shall be single layer of mahogany plywood, approximately 9/16 inch thick, installed in general accordance with plan, BuShips No. PT486-S1106-411193, subject to development of satisfactory material.
Note. I have seen photos of some perhaps later ELCO 80s with planked decks.

62 degrees hull planking angle not 45 degrees as many have used.
stern transom at 12 degree angle approximately.

Prop shafts of real boat.
All three propellers turned in the same direction clockwise looking from rear, not the greatest configuration for a model boat.
propshaft angles are around 10 degrees.
The centre shaft is at a larger angle to the side ones.
The centre prop shaft angle is 11 degrees and the wing prop shafts are 9 degrees.
Using these angles may restrict your propeller selection.

The centre shaft appears from hull further aft than the side shafts but the propellers are all at the same distance from the stern or transom.

Attached Photos - Click To View Large
20th Scale ELCO 80ft PT boat part 3 - Posted: 29th Jul 2018
Have been soaking the 6mm square sectioned stringers in the bath for a length of time, over night in cold water or 2 hrs in hot water seems to do the trick.

Put stringers in place held by plastic ties or string until dry (24hrs) then remove and refit with glue and the plastic ties to hold in place.

Please note, don't glue a wet/damp timber as it will shrink as it dries and pull the boat out of alignment.

The blocks at aft are for the three propeller shafts, will be shaped (one has in a later photo) to hull profile. The wood is a very light like Obechi.

Please note. The Models main priority apart from cheapness is to produce a light weight hull that is large enough not to disappear on a pond but light enough for me to carry to a pond/lake as my back is not what it used to be.

Attached Photos - Click To View Large

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