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[Jerry Hill]

Probably nothing new here, and probably not seen because there's a better way, but, I'm playing with a slight twist to my existing setup.


I currently have a skeg under the rear of the hull, and a strut rudder in line. I get on with that fine, directing thrust from the prop gives me super tight turns rather like the full size boats, and it's fun trying to make it act 'real' on my 'sports' use boat. Not as efficient as an offset rudder though, so here I'm trying two rudders just outside of the thrust cone, and a skeg much further aft which has the profile of an out board leg for the fun of it.


Here's my basic idea:





I though I'd get the awkward bit out of the way first, so got on with the 'leg'. First I transferred the design on to some 10x60mm T6 aluminium, drilled the bearing hole and rough shaped the outline, hacksaw and files:







Using the bearing hole a dowel was used to square the part up on a mill and rough out the webs to thickness each side. The bolt slot and tongue cut on all but the top edge where the lump will remain for now, for helping with more processes:







Next a while spent with my favourite shaping tool, a Black & Decker Powerfile. After the rough stage in this pic it was run over again with finer grit:







But the only way to check the shape and finish of these things is to polish them. There's a few surface defects and notches to sort out, but as it's being satin anodised I won't be too fussy. The bearing hole will be reamed to final size after anodising, bearings will be Pb Bronze:







Next I'll move to the strut. I want that to include the appearance of an outboard transom brackety type thingy. And there's a sort of pseudo cavitation plate in there to support the rudders. Some thinking to do.




 

[Umi_Ryuzuki]

Wow, that polished up nicely.
I would have thought a U-joint between on the shaft, between the transom and the "outboard" would
have giving you a nice steerable outdrive. Just hinge your outboard to the transom, and it acts
 like a functional outboard.
 




 But maybe that's sort of what you already have...


.

[Martin (Admin)]

Wow, not seen that drawing for many a year!!!
( http://www.modelboatmayhem.co.uk/My_models/04%20hydrospeed.htm )

Nice work Jerry! Not often you see a shinny piece of aluminum!! 

[Tim_M]

Argh! the dreaded UJ. A Hook's joint WILL cause loads of vibration. Avoid 'em like the plague! 

[Mad Scientist]

Here's another variation: http://www.modelboatmayhem.co.uk/forum/index.php/topic,51509.0.html

The shaft is fixed to the hull; the steerable 'outboard' is the rudder. No universal joints required.

Tom

[Jerry Hill]

Moved this a little further forward. Weight is still OK, hoping to be no more than a regular setup, but I have a few routes to making it lighter if needed.


T6 Strut, Dural Cavitation Plate and Delrin rudder bushes added (threaded through the plate and nutted). The bushes will retain fixed rudder shafts, running in PTFE top hat bushes in the rudder Yokes. I get better use out of this arrangement where water can be the lubricant, an existing single rudder arrangement has the brass bearings pressure washed under way, along with any lubricant, so wear is high with those. The top hat bushes are a cinch to change, but to date wear rate is nowhere near brass.


Diverting from my drawing above the rudder shaft bushes are lower but wider, I'll shift the freeplay control from the bore to the face of the top hat bushes to keep the profile of the tiller arms as low as I can simply.


I'll probably feather the topsides of the Cavitation Plate.

[Jerry Hill]

Weight was beginning to nag me so I've taken thickness out of the underside of the cavitation plate, enough to make a difference but still keep stiffness it needs to support the rudders:







A polish on the plate's topsides followed after a tapered chamfered edge was added to just help to loose some of the slab look it has:







Also made a start on the transom bracket. It's a bit meaty at the moment but there's a bit more to be done to it. I'll be adding dummy web brackets to each side of it in rebates which will knock the bulkiness out of its appearance, something like my drawing all being well. The rubber mount is for the Outboard Cowling:







To ensure good torsional resistance on the strut I'll be mortising the transom bracket next, then on to the rudder yokes. In the mean time I need to lay up some Carbon/Glass laminate for the rudder blades.

[Jerry Hill]

Just enough time today to mortise the strut in and make up the dummy brackets:

[Jerry Hill]

Got the rudder yokes out of the way today. Here they have been propped up with temporary bushes, PTFE is on order which will bring the top hat rim to the same diameter as the cavitation plate bushes:

[Martin (Admin)]

Extraordinary!!!   

    Do you have a thousand tiny elves with buffing machines?!!?!?

[Jerry Hill]

Extraordinary!!!   

    Do you have a thousand tiny elves with buffing machines?!!?!?

Just a couple of decent pro quality mops with a bolt through them to hold in a drill press or milling machine chuck. The correct abrasive bars give results quickly and easily. From something like 240 grit emery cloth  to 600 wet and dry with oil then straight on to the mops. I like to anodise alloy parts, and that is only as good as the finish you start with, in this case parts will be etched to a satin finish on the leg in natural colour to shiny black on everything else, the polishing shows up flaws you can't easily see with an abraded finish, which will show up horribly when anodised, so everything is polished first.

[Jerry Hill]

Out of interest here's one of my former rudders, this one is on on a 10cc airscrew hydroplane. I'm using the same bearing arrangement on the dummy outboard. The rudder shaft on the outboard though is fixed, and the rudder pivots around it, the bushes being a press fit in the rudder and minimal running clearance on the shaft. On the hydro rudder below the shaft is fixed in the rudder, the idea being to have maximum bearing surface, but it's a slightly different design. I always make spare bushes, but whilst it will happen in time after a couple of years use there's no sign of wear yet. Here the parts were pulled from the anodising dye quickly to give a nice deep blue shade:







Incidentally the rudder blade is a home made carbon/glass laminate, just a sandwich moulded under pressure between two glass surfaces. I'll be doing the same thing with the outboatd rudders. They flip up in an impact but there is no shear bolt, simply friction adjusted by tweaking the slot the rudder sits in. The blades are laid up so that the carbon weave is on the surface, this is self lubricating and means the rudder can be squeezed in tight without pickup, whilst keeping enough friction to stay there unless hit. I've certainly clouted the odd buoy or two with this type and it all works as it should.

[Jerry Hill]

On to the fiddly stuff. Two shortened glass filled nylon spherical control rod ends fixed to the rudder yokes to form the tiller arms, and made up some clevis' to suit (to be anodised black). Control rods will be 3mm stainless steel, which I'll heat shrink in black as I want all of this stuff to be discrete looking:

[craig dickson]

Hi Jerry


You have a superb thread here, and I have to say your workmanship is absolutely outstanding!


 


Cheers
Craig

[Jerry Hill]

Thanks Craig, much appreciated 


Some more progress. The control rod material arrived so they've been added at the rudder end for now, I'll detail routes and linking during the build of the boat.


To divert a little here's the CF layup for the rudders as it's formed, under weights between flat boards wrapped in silicone release paper:







This gives a nice sheet of material at far less cost than it would be to buy commercially. Here there's five layers of twill weave CF in epoxy resin, the weighting process leaves a good resin/mat ratio that's far lighter and stiffer than aluminium:










A couple of starter rudder shapes have been cut, then double sided taped together for match shaping:







After some foil shaping and fitting to the rudder yokes they pretty much stay as they are from here:















Next I want to make up a little skirt thing to stop the leg from looking too, well, leggy. And, I've to fit the GRP engine cowling moulding via a bracket of some sort. I want to route the engine's exhaust out through the scale position if possible, I'll come to that. I've come across some PTFE rod that's carbon filled, so it's black. That'll go well on the rudder bushes so an order is in.

[essex2visuvesi]

That's some proper Bling you have there Sir!

[Jerry Hill]

Hmm, too much for now, the look is the whole point of this and I've got to decide on a few things shortly that have come to light. I'll explain where I am........


Most of the metalwork is done, apart from a couple of bolts that need to go it to hold the cavitation plate (it's currently held by the leg alone in the pictures). There's a couple of pieces to go on to the dummy bracket, which I can make now as the cowling needed to be in position.


The cowling is a moulding from Daz Elson, and I wanted to mount it with some flexibility, so I made up an aluminium channel to hold a second rubber mount, the first being at the front lower section. Having cut out clearances to drop over the strut the cowling was propped up and the beam bonded in with JB Weld:








It seems strong enough. With some additional neoprene packing either side of the strut it's got the right sort of resilience I'm seeking. This part is quite a lever for fixings and I've had to keep an eye on an existing boat with this cowling, this way should give me a setup that won't mind the odd push or knock. With the best will there is the occasional airborne occurrence with these boats, hitting the water at 40 mph+ can have an effect on such a part. This video gives an idea of the possible conditions, with an inversion at 4:40 :  https://www.youtube.com/watch?v=tNjMbFMqpgs


And in this video a view of the outboard cowling on the same boat, it's quite a hostile place to be back there  : https://www.youtube.com/watch?v=1GIi7zsz0iE


Anyway, it seems fine, much happier with that arrangement.


With everything propped up so far I want to decide on what gets coloured what when anodised. Originally I thought black strut, cavitation plate, control links, transom bracket and rudder yokes, with a satin natural colour on the leg. In my head the cavitation plate is too big so needs to be knocked back I'm wondering if the cavitation plate should also be natural, so that anything alien to a true outboard is knocked back visually. What do you guys think? 

[martno1fan]

Fantastic work Jerry  .
Mart

[Jerry Hill]

Thanks Mart.


With the anodising now out of the way I can make up the bushes and bearings next, from there we can move on to build the boat it belongs to.


Whilst the leg and the cavitation plate were in the anodising bath the rest of the parts can be seen here in a holding bath, this is after re-polishing and the etching process is done to give a satin finish. It's a mild acid bath just to stop and neutralise the Caustic etch bath action, I can only fit so much into one session so parts queue up behind:









Being very much a 'Fred in the Shed' setup here's the same parts crammed into the anodising bath, lots of fiddling to ensure continuity, and safety:









The leg fully finished, with added notch to clear a fixing bolt for the cavitation plate:









And with the rest of the parts dyed black, less the cavitation plate which I've decided to keep the natural anodised colour:









A few parts are on their way from Model Marine Supplies, and a visit to my local model shop Nimrif RC tomorrow, will secure all of the rest of the parts needed to build the boat, so this will be up and running over the next couple of weeks. The next pic will be the finally assembled dummy outboard ready to fit.

[Atlantic Mouldings]

Superb 
Great finish

[martno1fan]

Love the anodized finish i was going to try this on some hardware a while back but havent got round to doing it yet but youve given me some inspiration so watch this space lol.
Next you will have to have a go at making a real scale outboard  that would be something .
Mart

[Jerry Hill]

Anodising is an easy process, rule one has to be about observing safety. Nasty Caustic and Acid chemicals involved. But, with care and through learning what can and what can not be anodised a domestic route to the process is easy to obtain. Fancier methods are also accessible, but not a requirement. Have a go 


As an Engineer I can tell you that scale outboards are possible, plenty out there, but they are all doomed to failure far in advance of flexishaft versions, unfortunately Physics will not allow such a thing to work for very long, unless you just wanted one for a scale Fletcher or something. In essence, such a thing is only as good as the bevel gears required, and to keep profiles sensible the gear tooth contact patch and shear strength of any suitable material will not tolerate a 7HP+ gas engine for long, given the lever moments and torque requirements. A few folk have had a good go, but they've all disappeared as far as I know. Closest thing at the moment is the Dragon drive, known to fail, or the MHZ, also known to fail but less so (apparently). I guess if you take it as the bevel gears, seals needed, and shaft bearings are a consumable then it can be done, not my way to be honest. I'd love someone to completely take the carpet away from under me on that one as I'd love a scale OB.


This project now needs to be tested. The Carbon PTFE material is interesting stuff. I would describe it as chalky to machine, the carbon content was stated as 25% as I recall, which leaves you with an even worse problem than PTFE gives machinists, holding the stuff. By definition this already self lubricating plastic is very slippery indeed with the Carbon added. To match machine the rudder bushes I make one side then tweak the other to make a correct fit, this normally means remounting the top hat bush to face off. I could just about do that without the part simply popping out of the chuck as soon as a tool contacted it. So all is well, but something to keep an eye on, single setting part production is best. I.e. hold on to a goodly portion of bar and make the part in one go without remounting it. Resetting could be achieved using a few special work holding methods, but applying the KISS principle means single setting is best for sure. Glad I used it though, with a no slop transition fit on the shaft the friction is very low, like PTFE alone but visually better in black for this application:







I used some of the same material to make a couple of spacers to help stabilise the cowling and complete the dummy transom bracket look I wanted:





The shaft bearings have also been fitted, the hole reamed to 8.00mm and the bearing OD made to 8.00mm, so a light press fit. I've added some Loctite shaft lock for surety. The bearings were going to be drilled for oil retention, but instead I've left a gap between the fwd and aft bearings for that purpose. Lubrication will be total loss oil feed, using biodegradable chainsaw chain lube with added ZX1, this is what I've turned to on all my boats now as as much as I understand flexishafts are the best thing to achieve the best thrust angle they are all horrible in my view and a pain in the backside to service most types. Total loss oiling means no more shaft removals after every session.




So that's it! I've got to get hold of a couple of grub screws for the rudder shaft retention, but from hereon it needs to be fitted to the boat. I've delayed the skirt idea mentioned above until the prop height is established.


Going back to first post, the idea of two rudders is something of an unknown in this configuration, the backup plan is to revert to a single rudder by simply making a new cavitation plate with a single bearing, but I've made up three sizes of rudder pairs to give myself a chance, the ones shown are the smallest. I'll dial in offset to keep the turning radius right for each rudder.
We are running an engine a third of the power of my existing boat. This is all being done for my son, who's fairly new to RC Boats and following a concept of a much lighter boat with a smaller engine I hope it will be manageable for him, we can up-rate the engine later as the build will allow that. Having said that it's a CMB 65 in a 44" boat, so no slouch, it's for sports use remember. We'll see. Next update will either be a report on success, or notice of the return to the drawing board.
But for me, the enjoyment has been had in making it, if it works that's a bonus 

[martno1fan]

Ill def have a go mate have the acid and some dye will test it out soon. I know what you mean about the gears involved in the outboards and i agree 100%.I like the idea of the flex shat versions without gears but not as scale looking but might be a good compromise. I know TFL sell a few small electric versions but havent tried them as yet.
Anyway i dont want to take your thread off track,carry on with your good work and hope the testing goes well. As regards your double rudders i think they should work very well,you could always make some longer ones if need be  .
Mart

[Jerry Hill]

Always an interesting shape to produce on a lathe, I couldn't resist making a bullet nut for this thing. I'll be threadlocking it on, but methinks some nylocs and spare props will be in the tool box at the lake just in case 

[martno1fan]

Ive had good success using a very thin slither of silicon tubing between the prop nut and prop,i did lose a bullet nut but the silicone saved my prop lol.
Mart