PT Boat prop shaft angle?

[kenb]

I'm scratch building a 4' long aluminum-hulled R/C replica of an 80'
ELCO PT boat, and I am attempting to verify the true downward angle of the
propeller shafts to ensure this boat has a hope of planing-out properly when
it's underway.
I have a couple of sets of mediocre plans for this boat, but the
downward angle of the propeller shafts differs between the two, leading me
to believe that someone has altered the true geometry on at least one of
them for one reason or another.
Would anyone have plans or kit drawings that might clear up this
discrepancy for me before I build a masterpiece that doesn't work in the
water?

--
Sent to you by Ken at
kenwho?@sympatico.ca
Replace "who?" with "b2" for e-mail

[dpharant0519]

Ken,
Scale looks on a model are fine, but true scale in the drive is not. If you
put "Scale" props on the boat it would barely move. If you put "Scale" power
in it, it might just move at a slow, slow walk if you are lucky. For that
matter, scale speed would be far from on a plane.
You will want to pick your power system first, then match your drives and
props to that.
You may even want to have 2 sets of props. One for scale show, and the
others for actual running.
If you set up a true drive angle, it is unlikely that you will have enough
room for a prop that will drive the boat anywhere near planing.
These are things you have to work with as a scale modeler. Unfortunately you
can not scale the water the boat rides on.
If you get enough power in the boat, it WILL plane. If you can give us an
idea of your intended drive set up, IE. motor types, gas or battery, number
of cells ect, we can help you find some good props for that drive.


Visit climateboatworks at:
http://www.climateboatworks.com

[kenb]

dpharant0519 <dpharant0519@rogers.com> wrote in message
news:t_9M9.7965$F2h1.3557@news01.bloor.is.net.cabl e.rogers.com...
> Ken,
> Scale looks on a model are fine, but true scale in the drive is not. If
you
> put "Scale" props on the boat it would barely move. If you put "Scale"
power
> in it, it might just move at a slow, slow walk if you are lucky. For that
> matter, scale speed would be far from on a plane.
> You will want to pick your power system first, then match your drives and
> props to that.
> You may even want to have 2 sets of props. One for scale show, and the
> others for actual running.
> If you set up a true drive angle, it is unlikely that you will have enough
> room for a prop that will drive the boat anywhere near planing.
> These are things you have to work with as a scale modeler. Unfortunately
you
> can not scale the water the boat rides on.
> If you get enough power in the boat, it WILL plane. If you can give us an
> idea of your intended drive set up, IE. motor types, gas or battery,
number
> of cells ect, we can help you find some good props for that drive.
>
>
> Visit climateboatworks at:
> http://www.climateboatworks.com
>
>
>
>

[kenb]

Sorry about the previous post that got away before I had time to reply to
it, Outlook does some weird things sometimes.............

dpharant0519 wrote in message:

> If you set up a true drive angle, it is unlikely that you will have enough
> room for a prop that will drive the boat anywhere near planing.
> These are things you have to work with as a scale modeler. Unfortunately
you
> can not scale the water the boat rides on.

That's my main concern at this point, it would be a shame to set up the
prop shafts in such a way as to inhibit the boats true potential by
inclining them too shallow or steeply, thus affecting the nose-up or
nose-down behavior when underway. The ELCO drawings I've seen indicate the
angle to be in 4-8 degree range downhill toward the stern, while drawings
I've seen for the 60's era Patrol Boats (twin Delting Engines w/18 degree
v-drives) are closer to 10-12 degrees slope downwards toward the stern.

> If you get enough power in the boat, it WILL plane. If you can give us an
> idea of your intended drive set up, IE. motor types, gas or battery,
number
> of cells ect, we can help you find some good props for that drive.

I have a lathe and mill and some other nice toys out back, so I have a
bit of artistic freedom to work with here, but here's what I have in mind.
The jury is still out on some details, but it's looking like twin screws
(4 inches apart) in a 48" ELCO PT driven by a gearbox with forward/reverse
capability. This gearbox will be mounted about 18" back from the nose, with
twin prop shaft tubes extending back and downwards through the bottom of the
hull approx 35" back fom the prow (exact distance and angle to be
determined).
The engine, probably from a new chainsaw (30-45 cc), will sit behind it
in a 12" long compartment centered approx 28" back from the prow, connected
to the gearbox with a u-jointed driveshaft through the centrifigal clutch.
I have kept the engine and drivetrain components separated by a driveshaft
so that I can change balance and engine types without having to modify the
boat itself too much, I just have to pick a spot and make up a driveshaft to
join them up. I have heard of four-stroke options that may present some
worthwhile benefits, so I want this design to remain flexible.
I am expecting to need at least 2" props on it, maybe bigger, but I
still have some gearbox ratio determinations to make before I will be able
to determine the desired pitch for the props. Any additional comments on
prop details and shaft angles are most welcome.
--
Sent to you by Ken at
kenwho?@sympatico.ca
Replace "who?" with "b2" for e-mail

[MIDEMETZ]

Nothing to do with shafts but you might like to take a lok at this PT model.

Mike

[Allan]

That's not necessarily true.... The props that are supplied are usualy not
much help- flat bent bits of metal - if you profile the prop correctly it
will work twice as good. For example I Have a dumas Chris Craft Cobra - It
has a 29mm scale prop and it planes correctlt (2ft 6 long) - power is
supplied by a 6 cell nicd pack and it runs on a 545 motor with a gearbox-
run time is between 10 and 20 minutes.

Mostly the problem with scale models is that the prop is not scale and the
boat is over heavy. Also remember that water does not scale so you will have
to run faster than actual scale to get scale appearance - look up froudes
laws for an explanation.



--
For Radio Controlled Model Boats Visist our website www.astecmodels.co.uk

Fast Electrics a speciality

Allan

"kenb" <kenwho?@sympatico.ca> wrote in message
news:afpN9.342$oW.124775@news20.bellglobal.com...
>
> dpharant0519 <dpharant0519@rogers.com> wrote in message
> news:t_9M9.7965$F2h1.3557@news01.bloor.is.net.cabl e.rogers.com...
> > Ken,
> > Scale looks on a model are fine, but true scale in the drive is not. If
> you
> > put "Scale" props on the boat it would barely move. If you put "Scale"
> power
> > in it, it might just move at a slow, slow walk if you are lucky. For
that
> > matter, scale speed would be far from on a plane.
> > You will want to pick your power system first, then match your drives
and
> > props to that.
> > You may even want to have 2 sets of props. One for scale show, and the
> > others for actual running.
> > If you set up a true drive angle, it is unlikely that you will have
enough
> > room for a prop that will drive the boat anywhere near planing.
> > These are things you have to work with as a scale modeler. Unfortunately
> you
> > can not scale the water the boat rides on.
> > If you get enough power in the boat, it WILL plane. If you can give us
an
> > idea of your intended drive set up, IE. motor types, gas or battery,
> number
> > of cells ect, we can help you find some good props for that drive.
> >
> >
> > Visit climateboatworks at:
> > http://www.climateboatworks.com
> >
> >
> >
> >
>
>

[1Ironhorse]

I am doing a 1:12 scale 80' Elco boat. The center prop shaft angle is 11 degrees and the wing prop shafts are 9 degrees. I got this information from ELCO engineering drawings (purchased from www.ptboats.org).

I would like to know how to figure what size prop & what power is required for my boat?

[jeepers1940]

How is your Elco model doing? What power and prop did you decide to use?