what props

[william omelaszParticipant @williamomelasz10688]

[william omelaszParticipant @williamomelasz10688]

Hi guys,i recently bought a Model Slipway Sentinel..its been built to a nice standard,..what i want to find out is, what is the correct props,..at the moment she has 2 x 3 bladed props….but, whilst looking for info i,ve seen this model with 2 x 4 bladed props, and ..even 2 x 5 bladed scimitar type props…what are the correct one,s

[Dave MilbournParticipant @davemilbourn48782]

The full-size vessel has five-blade props, counter-rotating outwards (from the top). The prototype plank-on-frame model had geared 545 motors and so had no problem turning five-blade props. Unfortunately I've seen several grossly-overpowered examples – one even had 2-blade plastic X props! It really depends on what motors and what voltage your model is running. Do you know what type of motors you have and can you say what the voltage of the battery pack(s) is? You must appreciate that Sentinel is what Vosper's designers call a 'short, fat warship' so a model would move at a speed more like a destroyer's than an MTB's.

Dave M

[william omelaszParticipant @williamomelasz10688]

Hi Dave,thanks for the reply,..at this moment i don,t know the size of the motors,..but it comes with 2 x 9.6v 3700mah,…..i,m picking the model up on Saturday,…from Wigan…i got it on ebay…for a very low price i,d post some pics, but at this moment i don,t know how to

[Dave MilbournParticipant @davemilbourn48782]

You have to Create an Album first. Go to the Grey toolbar at the very top of the page and click on Albums, then Create an Album and follow it from there. You can load photos which are in JPG format by Browsing for them on your computer's drive. Once you've uploaded and saved them you can add a photo from your album to a posting by clicking on the camera icon above which says Insert Image from Album. It's not that difficult – even I managed it!

My money says the model has two Speed 600 motors, in which case a transplant will be required! 9.6v is quite definitely more than is required.

Dave M

[william omelaszParticipant @williamomelasz10688]

if it does need a transplant…do you mean the motors? or the batteries

[william omelaszParticipant @williamomelasz10688]

Hi Dave,

I now have an album…like you said it was easy

[william omelaszParticipant @williamomelasz10688]

Hi,Dave ..the motors are 540,s..linked to …4mm shafts and 40mm 3 bladed props ..will she need a transplant??

[Dave MilbournParticipant @davemilbourn48782]

There are 540's and then there are other 540's. Some would be hard-pressed to pull the skin off a rice pudding on 24 volts and others would happily pull your arm off on 6v. They look the same from outside. A 'standard' one is rated at no more than 7.2v, and 40mm x 3-blade props are on the large side. I would hesitate to run any on 9.6v unless I knew more about the motors. Is there a manufacturer's label on them (e.g. MFA, Graupner)?
Rule of thumb for direct drive (brushed motors) is not to use props which are larger in diameter than the motor case.

DM

[william omelaszParticipant @williamomelasz10688]

Hi Dave,

here,s a pic of the motors,..its not a great pic, but you might be able to recognize the motors…

[ashley needhamParticipant @ashleyneedham69188]

William. They look like MFA 540, seeing the black label. They are rated to 15v, but are weedy motors.

This is a weight concious model. Brushless would be good, something to give, say 12,000 rpm, at 9.6v for good performance. However will need two speed controllers, so a bit fiddly.

OR…possibly a pair of J.Perkins speed 480 motors and new 30mm or 35mm props. these are rated at 9.6v and a feisty little motors. I would also get some new flexible couplings from Model Boat Bits to suit.

Ashley

[Dave MilbournParticipant @davemilbourn48782]

Got 'em. These are the ones **LINK**

They are rated up to 15v although I wouldn't run them at that sort of voltage. On 9.6v they will still be revving at 12600 no-load speed, which is too fast for the model and much too fast for the props. I would recommend changing to 35mm dia props at the very most, and probably reducing the voltage to 7.2v to obtain a more realistic speed.

BTW the wire leads look too thin for the currents involved. I'd recommend replacing all the power leads with 16AWG silicon-covered cable **LINK**

Have you any idea what the object between the two couplings is?

Dave M

Edited By Dave Milbourn on 16/04/2015 08:53:32

[Dave MilbournParticipant @davemilbourn48782]

Ashley

The Perkins 480 motors on 9.6v will be turning at 22000RPM no load. As J P McEnroe once said, you cannot be serious! With luck you'd just boil the lake away while the model sits in a froth of cavitation – until the bearings burned out. If you're unlucky the wiring would catch fire and destroy the model as well.
Sentinel is NOT a "performance" boat. The full-size spent most of her time in trolling gear or loitering on the waterjet at less than walking pace, tailing suspect yachts which were just over the horizon with her clever-clever electronics. Maximum speed was used only during short-dash intercepts within territorial waters; in transit from one mission to another, or back to Gosport if Chris Pratt, the captain, had promised to buy the drinks……. Top speed is still classified but I can reveal it wasn't much over 30 knots, and the hull is described only as "semi-planing" – whatever that means. For information my original Sentinel had 6mm less freeboard than the kit version and used one pack of six D-sized 9AH NiMH cells for everything. It was rock-solid in turns without working stabilizers.
As the designer of both kits I've always found it puzzling that folk will grossly overpower Sentinel and yet load down Huntsman with SLA batteries until it sails like a narrow-boat. Can anyone enlighten me?

Dave M

[ashley needhamParticipant @ashleyneedham69188]

DM. Fair enough. I dont have one, seen one other nipping along fairly quick. didnt realise the 480`s revved that much !!! the ones on a couple of mine dont seem that buzzy.

The Sentinel I have seen is fairly tender, and heels over readily…was built as per instructions…Nimh batteries.

re…. huntsman….big boat…big batteries !!!

Ashley

[william omelaszParticipant @williamomelasz10688]

Hi Ashley & Dave,

now that i,m more wiser than i was at the beginning,.some modification is needed,if i go with..e.g. a pair of 30/35 mm props,..what configuration should i go for…3 blade, D-Type..perhaps… or some other configuration….i,m new to all of this and your expert knowledge is most appreciated.

[Dave MilbournParticipant @davemilbourn48782]

Hmmm. My model of Nellie was very different from yours so I can't say what props would be best with your model. I'd be tempted to obtain some plastic 3-bladed 35mm props for a start and try those. They generally have a fairly small pitch so they won't overload the motors. These props are much cheaper than the brass ones so you can afford to experiment a little. Try 4-bladed 35mm and also 30mm if you like. Also try them on a lower voltage if possible. You should eventually find a compromise which suits you, drives the model at a sensible speed and doesn't overheat the motors or flatten the battery packs quickly.

Ashley
JP Power 480 here **LINK**
Huntsman…big batteries…..big mistake!

Dave M

[william omelaszParticipant @williamomelasz10688]

Hi Dave,

thankyou for the info..its very much appreciated,…As you will no doubt have guessed, i,m new to all of this…i,ve had a few models, but, i,m not a builder,..well, not model boats,…and i have to rely on buying boats that are either ready to run..or need the minimum of work…as i posess 10 banana,s masquerading as my fingers…i,m happy that i won,t need to replace the motors,…as for the batts, well i,m getting 2 x new 9.6v 3700mah with the model, ..i,ve already got 2 x 8.4v …from another model..and ..i,ll get 2 x 7.2v…will i be better fitting them in parallel…for a longer running time,.

[Dave MilbournParticipant @davemilbourn48782]

…will i be better fitting them in parallel…for a longer running time,.

That again depends on what the electrical setup of the model is. If each motor has its own speed controller (best) then use a separate pack for each. If the motors are connected in parallel to one ESC then you would, in theory, get twice as much running time by connecting the packs in parallel, too. This doesn't happen in practice and you also risk one pack discharging into the other if they aren't charged and discharged at exactly the same rates. ACTion do a little board which will stop this from happening **LINK** This would be a wise investment.

Any clues about the mystery object between the couplings yet?

DM

[william omelaszParticipant @williamomelasz10688]

the mystery object….is a small block of wood with a piece of velcro stuck to the top of it…

[Dave MilbournParticipant @davemilbourn48782]

Thanks! Sounds like it had something mounted to it.

[william omelaszParticipant @williamomelasz10688]

yeah….i,m thinking it might have been the receiver,or possibly a speed controller,….as these are not with the boat,i,m going with 2 x speed controllers,as i bought a 10 cheap and cheerful,s from last year from China ..and to date i,ve used 5 without mishap…they worked out at £5.95each, they,ve got a little fan attached to them for cooling ..and they are rated up to 15v…

[william omelaszParticipant @williamomelasz10688]

[Dave MilbournParticipant @davemilbourn48782]

Good luck with those.

DM

[william omelaszParticipant @williamomelasz10688]

No luck needed,….i,ve had more trouble with Mtronic Vipers,…than i,ve had with these,..

[william omelaszParticipant @williamomelasz10688]

I,m knackered,…i went to collect the Sentinel yesterday,…654mile round trip….on the hottest day of the year so far…we left here yesterday at 7.30am..and got back at 12.30am this morning….but it was all worth it…due to the joys of ebay,,,,i paid £107 ….for the model…and am delighted to say that its even better in the flesh..than it was in the pics,and the guy threw in 2 x brand new 9.6v batteries, + 2 x brass 35mm props, and a lighting system…yet to be fitted…

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