Model Boat Mayhem - Forum

Please login or register.

Login with username, password and session length.
Pages: [1] 2   Go Down

Author Topic: Propulsion advice  (Read 5764 times)

cdsc123

  • Guest
Propulsion advice
« on: May 16, 2007, 02:41:08 PM »

Gents I've been asked to help out with this query;

Hello All

Just been given a model Brave Class? Circa 52" long with fibreglass hull and single electric motor. Plans that came with it say "Modav PRECEDENT .... KD Perkasa Class, designed B Ayres  Jan1976" Could that be the age of the model?

The model is not very detailed but better stay that way, cos of kids ages. Now for the important questions where I need a bit (lot) of guidance really:

1. Could it be based on a real boat given that it is marked P47 and had some big missiles on the stern?

2. It has s a single 6v 9000rpm electric motor, will that be sufficiently powerful?

3. Any good (and cheap) books/guides out there as to how to set these things up including RC etc...

Any thoughts most welcome.

Thanks


Any help with questions 2 and 3 please?
Logged

Shipmate60

  • Global Moderator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,235
  • You bark - I will bite!!!
  • Location: Fareham
Re: Propulsion advice
« Reply #1 on: May 16, 2007, 03:25:46 PM »

Is the 6volt 9000 rpm motor a Jonson with a fan inside the casing?

Bob
Logged
Officially a GOG.

DickyD

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 9,497
  • www.srcmbc.org.uk
  • Location: Southampton UK
    • SRCMBC
Re: Propulsion advice
« Reply #2 on: May 16, 2007, 05:24:01 PM »

The PRECEDENT .... KD Perkasa Class, is made by Metcalfs but is only 49" long.

Richard ;)
Logged
Richard Solent Radio Controlled Model Boat Club http://www.srcmbc.org.uk

boatmadman

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 2,721
  • Location: South Cumbria
Re: Propulsion advice
« Reply #3 on: May 16, 2007, 05:34:00 PM »

I beleive, and stand to be corrected, that the Perkasa was a development from the 'Brave' class gas MTB's. I think she was built for the Malaysian Navy, possibly in the 50's or early 60's.

Ian
Logged
if at first you dont succeed.....have a beer.....

cdsc123

  • Guest
Re: Propulsion advice
« Reply #4 on: May 16, 2007, 08:22:35 PM »

Thanks for the response you guys, I have redirected the owner to this site as ours isn't so good with technical modelling questions

  http://www.bmpt.org.uk/forum/forum_posts.asp?TID=340&PN=1&TPN=1

Regards, Christian
Logged

Shipmate60

  • Global Moderator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,235
  • You bark - I will bite!!!
  • Location: Fareham
Re: Propulsion advice
« Reply #5 on: May 16, 2007, 11:03:47 PM »

To get real performance from this large model I would suggest 2 x Graupner 700BB Turbo Motors.
These are fairly power hungry, but will get this large model planing well.

Bob
Logged
Officially a GOG.

tigertiger

  • Global Moderator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 6,933
  • Location: Kunming, city of eternal springtime, SW China.
Re: Propulsion advice
« Reply #6 on: May 17, 2007, 02:53:42 AM »

Thanks for the response you guys, I have redirected the owner to this site as ours isn't so good with technical modelling questions

  http://www.bmpt.org.uk/forum/forum_posts.asp?TID=340&PN=1&TPN=1

Regards, Christian

Be fair Christian,

You hadn't given us folks 6 hours to respond before you redirected.
There has been a lot of proplulsion advice on PT boats on this site in the past.
Try a search of this site as well.

I don't think 1976 is necessarily the age of the model, it is the year the design was produced.
Good book guide is https://sslrelay.com/s84068217.oneandoneshop.co.uk/sess/utn;jsessionid=15464bb50324a0d/shopdata/index.shopscript
Hugh Brights book 'The Complete Marine Radio Control Manual' 12.95 pounds
Logged
The only stupid question is the one I didn't ask

DickyD

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 9,497
  • www.srcmbc.org.uk
  • Location: Southampton UK
    • SRCMBC
Re: Propulsion advice
« Reply #7 on: May 17, 2007, 08:06:32 AM »

TT he means he has redirected the owner to this site [Mayhem] as his site[http://www.bmpt.org.uk/forum/forum_posts.asp?TID=340&PN=1&TPN=1] is not so good with technical modelling questions.

Richard ;)
Logged
Richard Solent Radio Controlled Model Boat Club http://www.srcmbc.org.uk

kendalboatsman

  • Guest
Re: Propulsion advice
« Reply #8 on: May 17, 2007, 10:41:18 AM »

Intriquing ???

I sold on my Perkasa many years ago, to a shop in Preston, it had a 6v motor and I made a missile launcher for the stern deck using missiles from an aircraft kit. Apart from the length that sounds like it. That motor might be an MFA Marlin as they powered up those kits nicely, I ran mine on two 7.2v racing packs connected in parallel for a greater run time.
Logged

DickyD

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 9,497
  • www.srcmbc.org.uk
  • Location: Southampton UK
    • SRCMBC
Re: Propulsion advice
« Reply #9 on: May 17, 2007, 11:59:01 AM »

Any chance of some photos Christian ?

Richard ;)
Logged
Richard Solent Radio Controlled Model Boat Club http://www.srcmbc.org.uk

cdsc123

  • Guest
Re: Propulsion advice
« Reply #10 on: May 17, 2007, 01:57:27 PM »

Hi Richard
I'm trying to encourage the owner to join in on Mayhem himself, in the meantime I'll work on it via the bmpt page.
Rgds, Christian.
Logged

DMSmith

  • Guest
Re: Propulsion advice
« Reply #11 on: May 17, 2007, 09:57:15 PM »

Hello All
Christian (big thank you) has pointed me in your direction. What an excellent site!!
Firstly I'm not really a modeller or boat expert so excuse me for any faux pas. However as an engineer I'm not too bad at putting things together and making them work. What would really help me is a good interior shot or two of some boat electrical intallations to give me a pattern to follow.
Anyway, about the boat:
Actual hull length 47.75" plus a 2" platform at the stern. (Previous measurement taken with 6 year old holding the other end of the tape measure.)
It has 3 turbine outlets at the stern so I guess it could be based on a Perkasa. The hull and superstructure are spot on, its just the armament that confuses me.
The motor is made in Germany, has Marx moulded into the base plate and a paper label on top with the following info: Decaperm-5pol;6V=leer60A9000u/min;load7A7000u/min;350cmp;20W;90degC;.5ohm; Jmax 1h 7A 5' 10A
I've now got a 6V 4ah sealed battery to go with the motor, but rather think I'd be better off with two in parallel. Perhaps one mounted each side to balance the boat. (A local model shop (in big village just north of Oxford) seemed happy enough to take over 100 from me in gear to get the boat working but disinterested in offering advice to the point of rudeness!!)
Sorry no photo available but the boat is cream (or v.v.pale grey) with a green deck. A cluster of four side by side rockets on a plinth at the stern with metal mesh around it. On the foredeck there is a gun with a curved shield around the breech and loader's seat.
It would be great to find the guy who built it, its nice to know the history of things.
Thanking you all in anticipation.
Cheers
Dave


 
Logged

Shipmate60

  • Global Moderator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,235
  • You bark - I will bite!!!
  • Location: Fareham
Re: Propulsion advice
« Reply #12 on: May 17, 2007, 10:23:50 PM »

DMSmith
While the deccaperm is a good reliable motor, but overpriced, at the gearbox outlet it only runs at about 2750 rpm. You would need a huge prop to make her go well.
Sorry to say that this motor isn't really suitable for a fast patrol boat.

Bob
Logged
Officially a GOG.

DickyD

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 9,497
  • www.srcmbc.org.uk
  • Location: Southampton UK
    • SRCMBC
Re: Propulsion advice
« Reply #13 on: May 17, 2007, 10:28:01 PM »

I would think he would probably need larger batteries too Bob.
 
Richard ;)
Logged
Richard Solent Radio Controlled Model Boat Club http://www.srcmbc.org.uk

boatmadman

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 2,721
  • Location: South Cumbria
Re: Propulsion advice
« Reply #14 on: May 17, 2007, 10:37:16 PM »

Hi,
I scratch built a 36" Brave Borderer a few years ago. I put in 3 electric motors, port and starboard for cruising, with the centre motor kicking in at full throttle at full speed only. The ESC (electronic speed controller) drives the port and starboard only.

This set up gives a reasonable scale speed - see pic below. As a note of interest, the borderer was the first fully armed and loaded British warship to exceed 50 knots! (needed 3 gas turbines to do it!

Hope this is of interest to you

Ian
Logged
if at first you dont succeed.....have a beer.....

boatmadman

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 2,721
  • Location: South Cumbria
Re: Propulsion advice
« Reply #15 on: May 17, 2007, 10:38:18 PM »

dunno how i did that twice! lol!
Logged
if at first you dont succeed.....have a beer.....

kendalboatsman

  • Guest
Re: Propulsion advice
« Reply #16 on: May 17, 2007, 10:38:48 PM »

Hello,

If you live near Oxford have you tried Howes? They always seem to offer good prices and have been around a while.

Clive :)
Logged

DickyD

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 9,497
  • www.srcmbc.org.uk
  • Location: Southampton UK
    • SRCMBC
Re: Propulsion advice
« Reply #17 on: May 17, 2007, 10:43:06 PM »

dunno how i did that twice! lol!

Glad you said that, I nearly poured the last glass down the sink ???
Logged
Richard Solent Radio Controlled Model Boat Club http://www.srcmbc.org.uk

DickyD

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 9,497
  • www.srcmbc.org.uk
  • Location: Southampton UK
    • SRCMBC
Re: Propulsion advice
« Reply #18 on: May 17, 2007, 10:55:16 PM »

There are wiring diagrams on the Mayhem site accessable from the home page.
They are for twin engines but can be used for one.

http://www.modelboatmayhem.co.uk/Common/Electrics/Images/setupsA4JPG.jpg

Richard ;)
Logged
Richard Solent Radio Controlled Model Boat Club http://www.srcmbc.org.uk

DMSmith

  • Guest
Re: Propulsion advice
« Reply #19 on: May 18, 2007, 10:29:32 PM »

Thanks chaps for the pointers.
Went back to Howes today and bought a second battery and bigger (55mm) prop. This time had a different assistant so got more useful help!
On a budget so will have to keep motor for now.
Will spend a few days putting it all together and will see how she goes at our local Marina. I'll just have to avoid the full scale boats..
If performance is pitiful I'll try a three motor set up as that is what a brave and perkasa would have had for real. I think I can get away with leaving the centre shaft in place as is, although I note that the shaft is at a 14 degree angle from the flat aft hull section and may be steeper than original?
Cheers to all.
Dave
 
Logged

Shipmate60

  • Global Moderator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,235
  • You bark - I will bite!!!
  • Location: Fareham
Re: Propulsion advice
« Reply #20 on: May 19, 2007, 06:21:14 PM »

DMSmith,
There isnt any right or wrong way to power a model.
There are some more tried and tested ways though.
Motors are very rarely produced for model boats as the market is too small, so a motor labeled as a 550 can vary in speed and current consumption.
Here is a pic of my old "Perkassa-Type" patrol boat. She was 36 inches long but very heavy.
I found a 9.6 volt 550 motor in an old battery drill and used this on 9.6 volts.
As you can see she handled quite well.

Bob
Logged
Officially a GOG.

DMSmith

  • Guest
Re: Propulsion advice
« Reply #21 on: May 19, 2007, 09:13:24 PM »

Thanks Bob and forum members.
Spent pretty much all day refitting driveline and electrics and just road tested her in the bath (3") to spare. I reckon she'll go alright, hell of a force against the hand and nearly chucks the water right out over the side, jacuzzi style. Toyed with the idea of putting bubble bath in!!
Made little wooden boxes for the batteries and araldited them to the bottom, eitherside amidships. At rest waterline is spot on. Made a plinth for the rudder servo c. 5" ahead of the rudderstock. In the end the layout was partly dictated by the length of the wires supplied with the motor controller and the receiver.So with a bit of luck I'm there!  :D
Only remaining problem is slight water leak between shaft and elderly (polyfiller type?) sealant. Any good products out there I could paint on to seal and stabilize this sealant?
Thanks
Dave
Logged

Shipmate60

  • Global Moderator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,235
  • You bark - I will bite!!!
  • Location: Fareham
Re: Propulsion advice
« Reply #22 on: May 19, 2007, 10:25:45 PM »

Dig out and make a small box or use blu tak and pour in epoxy resin.
Will only take a few minutes

Bob
Logged
Officially a GOG.

DMSmith

  • Guest
Re: Propulsion advice
« Reply #23 on: May 20, 2007, 09:33:24 PM »

Will do thanks.
In the interim I painted over the porous sealant inside with epoxy and this has done the trick well enough to allow a "sea trial" at the marina. ;D
She went well, not planing, however she was moving swiftly and the bow wave looked good and to scale. She ran for over 1 1/2 hours, mostly full throttle, and only slowed down a bit towards the end. Motor was warm at finish too but no smells so I assume OK ??
I think I've got room for a 60mm prop. Are there any single engines out there that would spin that fast enough to lift her fully onto the plane?
I rather think I'm getting the bug!! :o
Cheers
Dave

Logged

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,500
  • Location: Blackpool, Lancs, UK
Re: Propulsion advice
« Reply #24 on: May 20, 2007, 11:26:40 PM »

Selection of a prop for maximum performance for a given motor/hull/battery combination is a "black art".  Conventional wisdom is that often, if the motor has more revs to give, a larger prop will not allow the motor to spin fast enough to increase speed, and may well cause the whole thing to slow down while using more current and overheating the motor.  It is possible that you may need a two blade prop to allow an easy increase in RPM, and eventually, speed.  Counterintuitive, but...........
Hopefully, someone with more experience in making heavy boats go fast will give some accurate advice.
Logged
"With the right tool, you can break anything" - Garfield
Pages: [1] 2   Go Up