Slo mo Shun

[Phil Winks 1Participant @philwinks1]

Bob I do believe you are “the glass is half full” kind of a guy (not a bad thing)  approaching 1/2 hp yes (I think) but actually only just over 1/3rd init ?

[Bob Abell 2Participant @bobabell2]

Just looked it up, Phil!

 

I HP equals 746 Watts……so a half `orse is……373 watts…….and that is approaching……What I said!….360!…lol

 

We had a day out at Barmouth today……….first time out this year…….not much snow about now

 

Bob

[Phil Winks 1Participant @philwinks1]

Touche BoB I did say “I think”. I was labouring under the illusion a kilowatt was 1hp shows how wrong one can be

 

Not a flake of snow  left here mate all dissapeared by tue/wed started thawing straight after my good lady slipped on the ice last sat and broke her ankle promoting me to chief cook/bottle washer and gen nurse maid

Edited By Phil Winks 1 on 17/01/2010 21:27:46

[Rick DevonshireParticipant @rickdevonshire]

Have yo ant pics of SlowMoShun doing it’s stuff on the water yet bob?

Rick.

 

[Bob Abell 2Participant @bobabell2]

Sorry Rick…….Not received the prop shaft stuff yet!……….and in any case……..the lake is still frozen over!

 

Just sorting out the rudder servo mount and motor base at the moment

 

There`s no rush!…………………Thanks for your post

 

 

Bob

[Phil Winks 1Participant @philwinks1]

Posted by Bob Abell on 21/01/2010 08:27:08:

Sorry Rick…….Not received the prop shaft stuff yet!……….and in any case……..the lake is still frozen over!

 

Stil frozen Bob! We’ve been fully thawed for about a week here in somerset still mucky weather though, luckily we missed the snow yesterday. It came within about 40 miles of us

[Bob Abell 2Participant @bobabell2]

Decided to paint the rudder etc

 

Still waiting for Mr Postman to bring the prop stuff

 

And our lake is still frozen over……..Bob

[Phil Winks 1Participant @philwinks1]

Just like we all knew at the start Bob this has become an A1 quality model an absolute credit to you and here’s hoping it moves well enough on the water to do its authentic appearance justice. mind you with D.M. involved in the powertrain design its bound too.

 

Seriously Bob well done and I seriously hope the oppourtunity arises to see it in person on  the water

[Bob Abell 2Participant @bobabell2]

Thank you , Phil, for those very kind words of appreciation and you`ve followed the build all the way from day one, your presence is very encouraging

 

I really am surprised that other readers out there have not got involved……..Your comments are always welcome

 

Still a long way to go…………………Bob

 

 

[ashley needhamParticipant @ashleyneedham69188]

Bob. You are covering multiple bases here with this build, and thus promoting maximum interest.

 

Despite it starting life as a KIT you are essentially scratch-building a lot of it, and modifying it along the way (to personal taste),  decorating it in impeccable fashion and demonstrating your annoying penchant for RUST, or at least wear and tear…and then there is the propulsion dilemma, whereby we all get a chance to chip in with conflicting and sometimes quite useless advice (sorry).

 

So far the job is absolutely top hole 100%     but I think

 

..the sternest test has yet to come.

 

Will it perform……

 

Ashley

[Bob Abell 2Participant @bobabell2]

Thank you, Ashley

 

I`m in no rush to get it on the water, but if the two MMB900 motors develop nearly a 1/2 HP each…………….then a good turn of speed should result……………I`m sure it will be alright on the night!

 

As a matter of interest, the props I`ve ordered, are available LH only! ………The man says it won`t be a problem?………………What do you think about that?

 

As these boats normally run about in straight lines, he`s probably right!

 

Bob

 

[Bob Abell 2Participant @bobabell2]

Would you believe it?

 

The prop stuff is lost in the post!

 

It was despatched on the 15th Jan

 

Now what?……..Bob

[Len OchiltreeParticipant @lenochiltree67043]

Make some, you did it before for another boat.

Your water is still frozen! crikey it must be cold oop your way.

 

A belated Happy New Year.

 

Len.

[Bob Abell 2Participant @bobabell2]

Thanks Len….and a Happy New Year to you too!

 

We`ve had it rough this year, the water has been frozen since before Christmas…..No club Frostbite sail either

 

I couldn`t really make a pair of high performance props, I made one for The Great Eastern, but that was only a chuggalong!

 

I`ve spoken to the suppliers and they will send a second shipment on Monday

 

Thanks for your post……..Bob

[ashley needhamParticipant @ashleyneedham69188]

If you have to use props of the same hand, as there are two shafts, then at least it will not be quite so bad as having just a single prop and I would have thought been ok..

 

Not that my Fantome is as fast as yours (will be…. 1/2 a horse!!  my word) but it was supplied with two x50 props, both same hand . and I didnt notice any handling quirks, other than it turned very slightly better one way than `t other. reversing was a washout though, as the thing would turn hard one way as soon as you even THOUGHT about applying reverse thrust…

 

I had George Sitek make a pair of maximum pitched L/h and R/h 3 blade brass props, and straight line performance seems to be the same, and it still reverses like a banana!!     what ho.

 

I would like to try one of these props on the 850 engined Seahawk, just as a comparison, as this is a higher power and revving beast, but of course one is a 5mm shaft and the other 4mm. I suppose I ought to try a standard brass prop on it just to see what the difference is….

 

The 850 revs to 9000 rpm approx, so,is this not high enough for best efficiency on a “racing” style 2 blade x pitcher, or is it on the limits for a 50mm standard 3 blader???

 

Ashley

Edited By ashley needham on 23/01/2010 17:05:03

[Bob Abell 2Participant @bobabell2]

Thanks, ASH

 

Don`t quite understand your last paragraph, but here`s the prop list, I`m using…

 

http://www.prestwich.ndirect.co.uk/mocompropellers.htm

 

I`ve selected ……..Prop 2227m

 

Will it do?

 

Bob

[Bob Abell 2Participant @bobabell2]

Big problem!……..Not enough room for the water cooling pipes!

 

But on closer inspection, the motor base has a cutout in the bottom. If I cut out the wooden base………….There`s just enough room for 3/16 dia tubing!…..Phew!

 

Saved again!…………………….Bob

 

 

Edited By Bob Abell on 24/01/2010 08:32:28

[ashley needhamParticipant @ashleyneedham69188]

Bob, I saw somewhere a list of various sizes of prop and the speed at which they start to cavitate, which i should have made a note of or printed out..but didnt.

 

The larger the prop the slower it has to turn, basically and 50mm is a largish prop in the scheme of things. However 2 blade “x” props behave differently at high speed, and you seem to have ordered some super duper ones tailored for very high revving engines.

 

SO.   the question is, at a 50mm sized prop and a 9000 rpm motor would a 2 blade be a better bet than a 3 blade standard? or is 9000 rpm not yet fast enough to upset a 3 blade prop….hence I would like to try a 3 blade brass prop on the Seahawk. And if it was to be ok then i might leave it on, as our pond is shallow in places and now full of small boulders that kids have chucked in after the ice last year, and a brass prop will be more hardy.

 

At 5000 Rpm, there doesnt seem to be any difference in the other boat, although an ammeter may show some variance. Several bods on our pond have the opinion that 2 blade props are more “juicy” at lower Rpm ??

 

When i fitted water cooling to the Seahawk, like you have found, there didnt appear to be any room under the motor for cooling coils. but those slots in the mount provide just enough clearance for said coils..however you have to take the motor off, fit coils, refit motor.

 

Ashley

[Bob Abell 2Participant @bobabell2]

Hello Ashley

 

You`re gonna like this!……….Because it`s easy and novel!…………Can`t wait….eh?

 

Get a selection of props and a high rev ving drill………..and try each prop in turn….and compare the difference in wind force!……Good eh?

 

You could have a standard target of say a cardboard box and see which prop blows the box furthest along the table!

 

What a super duper idea for a wet Sunday morning?….eh?….eh?

 

 

Full of great ideas!…………………..Bob

[ashley needhamParticipant @ashleyneedham69188]

Er…….yes     Ashley

[Dave MilbournParticipant @davemilbourn48782]

Ashley

A little research goes a long way, old thing. MMB’s website quotes a no-load speed of 6500 RPM @ 12v. One might reasonably expect something of the order of twice this @ 24v but the loaded speed will, of course, depend upon the size and pitch of the prop used.  Mo-Com props are I think the norm for geared IC motors rather than electric ones, but who knows? I would imagine Prestwich Models have forgotten more than I’ll ever know about props and motors, so I guess Bob has been as well advised as it’s possible to be.

HOWEVER

My Aussie mate John  Darke is something of an authority on operating high-voltage electric motors in large scale boats, and he always uses 3-bladed Raboesch Type A brass props.

One man’s meat etc etc.

 

Bob

Empirical beats theoretical every time in my book! “Bring it on, dude!”

 

DM

[Bob Abell 2Participant @bobabell2]

Thanks for the moral support, Dave

 

Although my prop stuff is lost in the post somewhere, I`ll carry on with the present selection…….and see how it goes……….I`m feeling very optimistic at the Mo!

 

Have you got anywhere with the battery harness`s yet?…….Will PM you shortly

 

Bob

[ashley needhamParticipant @ashleyneedham69188]

Dave, research.. whats that??  we have a forum full of experts to advise !!!

 

I like the “however”, and I might even get around to getting the meter out to see what effect different props have  at low speed, where, by and large, they spend most of their time, at least, on our pond. All these super props may be calculated for this and that, but when they are NOT running at their optimum speed..then what??

 

You cant beat a bit of empirical research, especially when there are so many variables with model boats. Bobs speed issue will be very interesting come pond time.

 

Ashley

 

 

[Bob Abell 2Participant @bobabell2]

Hello, Chaps out there!

 

Is there any sense in fitting an air fan to the motor coupling……..To avoid the water scoop method?

 

I`m a bit concerned about the scoops getting blocked up with duck muck or weed etc

 

It was normal for industrial motors to have fans built in as standard

 

Seems a good idea to me………Bob

[Bob Abell 2Participant @bobabell2]

Well Chaps…….The prop stuff has finally materialised!

 

I informed the supplier only yesterday, that the stuff still hadn`t been recieved …..and….Hey Presto!…….It arrived today!

 

Many thanks to Prestwich Model Boat Supplies…….Much appreciated

 

Just look at those beefy ball bearings and sharp lookin` props…..Just rarin` to go!

 

And the couplings look man enough for cooling fans to be fitted too

 

Now for some action!………………….Bob the Builder

 

 

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