Installing Motor Using Plastic Padding

[shipwrightParticipant @shipwright]

I am constructing a pilot launch nearly from scratch but I am using the Kingston Mouldings glass fibre hull.

The 600 size Mabuchi motors (RS-555PH-3255) are mounted on standard motor brackets (MFA 540/550/600 Motor Mount Bracket). The gap between the base of the bracket and hull is not flat (because the hull is curved). I was wondering whether I could use Plastic Padding to fill this gap – will Plastic Padding bond firmly to the inside of the glass fibre hull? Has anyone on this forum had experience of using Plastic Padding inside a glass fibre hull ?

I have made an album of photos of a motor "lashed up" inside the hull – I hope that it is accessible to the forum. The plastic tape and cardboard are there simply to allow me to take the photographs.

Ian

[shipwrightParticipant @shipwright]

Using Plastic Padding to form a base for a motor inside a fibre glass hull

[shipwrightParticipant @shipwright]

An Update,

This morning went to a small ship chandler/repairer in Gloucester. They were very helpful. Suggested that I use Plastic Padding Glass Fibre Filler (tougher and more flexible than the Marine Plastic Padding). Roughen the area with coarse abrasive paper. Dampen with acetone (nail varnish remover though you need to check contents label as not all use acetone) the internal surface of the hull in the area where I want to install the motor. Gently raise a few fibres to assist with bonding to the Plastic Padding and then apply the filler in layers sanding as required. To ensure that the brass mounting plate bonds to the Plastic Padding ensure that the surface of the brass is abraded with coarse emery paper.

I've purchased the Plastic Padding and will see how it works out.

Ian

[Dave MilbournParticipant @davemilbourn48782]

My own preference is these circumstances is to bond a 6mm ply plate into the hull using David's Isopon P40, which is a polyester-based filler paste which contains chopped strands of glass fibre. The filler bonds better to wood than it does to metal and will take up the gap between the curved hull and the ply. The hull should be roughened to provide a key for the paste. The motor is then screwed to the plate which means that both mount and motor can be removed later if required.
I also favour P40 for installing prop shafts, rudder tubes and bow thruster tubes into GRP hulls. If using acetone on GRP then be very careful as too much will soften the hull and may distort it permanently.

Dave M

[shipwrightParticipant @shipwright]

Hello Dave,

Thank you for your very useful advice. I'll certainly take on board the need to be careful when using acetone – obviously use very sparingly. As I have already purchased Plastic Padding Glass Fibre Filler I will use that (otherwise I would have followed your advice and purchased David's Isopon P40).

Ian

[Dave MilbournParticipant @davemilbourn48782]

Ian
You never know – the PP product may be even better for this job than P40. Keep us all posted, please!
DM

(Ref  the acetone advice – you're most welcome; Robin Whitmarsh would never forgive you for 'melting' one of his beautiful hulls!)

Edited By Dave Milbourn on 05/05/2012 16:43:05

[ashley needhamParticipant @ashleyneedham69188]

I have never used acetone,, as long as the hull is roughed up a bit I think p38 or 40 will be ok, not had a problem yet.

When I made the Fantome I bought special marine quality filler and Silicone sealant to stick the hull and motor bits together. It certainly seems to have stuck 100% and better than p38/40…but it was much more expensive..

Ashley

[shipwrightParticipant @shipwright]

I have now installed the proptubes. However, there is a small angular error in the Starboard Proptube – I estimate error at about 2 to 3 degrees. My inclination is to continue with the construction and ignore the small error. The effect of the starboard tube misalignment is to bias the boat to Port slightly – but in practice I could compensate by using a small amount of rudder to Starboard.

I am very reluctant to remove the Starboard proptube because it is solidly installed using epoxy and if I try to remove it there is a real risk of damaging the hull.

Does anyone knows what magnitude of proptube angular misalignment is generally considered acceptable (eg +/- half degree, +/- 1 degree etc) ?

One probable contribution to the misalignment is the struggle that I had to construct perfectly identical "A" brackets from 1mm brass sheet – I did my best (I experimented with cardboard templates to get the right shape) but obviously not quite good enough

I have put 4 photos into an album under shipwright.

Ian

[shipwrightParticipant @shipwright]

OK – I have now had time to reflect on my comments made yesterday. I made a "ruler" (photo in my album entitled 'Plan View with Template' ). It clearly shows that the error is in the alignment of the Port proptube (not Starboard as I stated yesterday). I have decided I can't ignore this error (about 4 mm laterally/across the beam) so I am going to take a risk and remove the epoxy that attaches the Port proptube to the hull. I shall use a mechanical method – far too risky to use chemicals or heat both of which are likely to damage the hull. I'll start removing the epoxy this morning – I anticipate that it will be a lengthy task but I think that the effort is worthwhile. I'll report results idc.

 

Ian

Edited By shipwright on 07/05/2012 08:49:42

Edited By shipwright on 07/05/2012 08:50:09

[ashley needhamParticipant @ashleyneedham69188]

Ian. I think practically speaking this misalignment will not have much bearing on the running of the boat. You may need to set the rudders a bit to compensate, and obviously there will be some loss of effiiciency, but it is only a model.

Does it LOOK odd? If you cant see that there is a horrible misalignment with the naked eye, without casting a rule over it, I say leave it, but I am only a bodger.

If you want a show model, then get the saw out…

Ashley

[shipwrightParticipant @shipwright]

Ashley – whilst I am not a perfectionist by any definition I didn't like the look of it inside the boat (you couldn't observe the misalignment from outside the hull ). I have now completed the removal task – proptube removed from hull with no damage to hull or proptube. I used a power tool with flexi shaft and used small grinding bits (like dentist's drill – I wore a face mask to protect against the dust). Took just over an hour including the cleaning up (I used a Stanley knife to remove the araldite from the proptube). So, if anyone is faced with removing a proptube it is feasible but needs patience ! Also at this stage of the build I had complete unobstructed access to the inside of the hull – it would much more difficult if the deck was on. The moral of this story is …………………… get it right first time !! Also use only a small amount of adhesive to "tack" the proptube in place and check and double check the alignment until you are absolutely sure it is correct – then apply the adhesive to completely secure the propshaft. I've learnt this the hard way!

Now I need to realign the proptube, double check, tack with a small amount of adhesive, check and then apply full amount of adhesive.

Ian

[shipwrightParticipant @shipwright]

Another update – I've completed the realignment (see my album for photos) and used epoxy again to fix the Port tube. My next task is to make a solid replica of the plasticine wedge that I made to assess the shape of the gap between the hull and the brass motor baseplate.

For Dave Milbourn – is this too much detail ? I haven't written a build log before. I can easily do less for the log. Your advice please.

Ian

[Dave MilbournParticipant @davemilbourn48782]

Ian
Search me, guv. All I ever write is Instruction Manuals and it seems that you can't have enough detail in those! If you're happy with doing lots of photos and details then it has to be more useful than less.
Dave M

[ashley needhamParticipant @ashleyneedham69188]

Ian. I usually "tack" the propshaft tubes to the hull with a few drips of superglue, before glueing them permanently with filler or epoxy. One set, they are held in place securely and you can measure and eye them up. but no so securely as to be too dificult to break and re-set if required.

Previously I was going to say, do what your concience tells you to do….once done,the boat will sit on the shelf for 30 years and you will only ever see the bit you wished you had altered during the build!

Ashley

[shipwrightParticipant @shipwright]

Another Update – I have now completed the installation of the motors. The construction of the mounting blocks was a bit of an adventure. I used the fibre glass Plastic Padding (PP) and I made some "shuttering" (as you do for construction with concrete) using 2mm styrene card and experimenting until I got the correct geometry. I then filled with the PP and waited until it had set. Then using a combination of hand sanding with a wood block and a grinding bit mounted in a chuck with flexible shaft, I shaped the blocks to fit – regularly trying the fit with the motors and propshaft coupling until it looked and felt correct. The holes/indentations in the PP blocks are there to provide clearance for the nuts on the underside of the brass motor baseplates. Finally, when I was 100 % confident that the fitting was OK I permanently fixed the motor baseplates to the PP blocks with epoxy (the motors were attached to the baseplates so that I could ensure correct alignment. Then I filled the proptubes with oil and connected a 12 volt battery and let the shafts "run in". I have put a few more photos in the album.

A couple of points. The resin & hardener react while setting and that reaction is "exothermic" (gives out heat). Not ideal for the fibreglass hull! No serious damage but you can just see very slight ripple on the outside of the hull. So I would be slightly wary about recommending this method for making motor mounting blocks. It might have been better to build up the blocks in two or three layers – that way the temperature rise would have been less. My conclusion is that this method would be ok for a wooden hull. An alternative is to create the block in wood and fix that with epoxy.

Last but certainly not least – whilst grinding and sandpapering the PP block I always wore a filter facemask – the process generates a lot of very fine dust that is a potential health risk – also I did this work in a garage with the door open.

Next task is to "fair in" the proptubes and "A" frames. Then to fit the rudders.

Ian

[shipwrightParticipant @shipwright]

Progress report. I have fitted the rudder tubes – photos in my album. I used a plumb line and spirit level with a long brass rod inserted in the proptube to assess verticality fore & aft and also port & starboard. I have yet to "fair in" the proptubes to the hull – I can now combine that task with sealing round the proptube-hull joint. One of the next tasks is to fit the servo shelf.

I am now thinking about how to make the working parts of the boat easily accessible when the deck is on. In my HMS Biter there is one removeable section of deck that allows access to the motors/proptubes and some rather poor access to the rudders. I am thinking about making the whole of the deck removeable – put a wooden ledge (there is a correct name for this but I cannot recall it) round the inside of the hull which will support the deck. Reinforce the deck with wooden beams running longitudinally. Insert a number of wooden frames/bulkheads to provide lateral support. Of course there would be a lot of screws to undo. Anyone got views on the design of removeable decks ?

As an aside, I make extensive use of used cereal cardboard cartons to make patterns – I find that I need to have several attempts to get the profile right before committing to make the part (eg a frame or bulkhead if you don't have those details about the boat's transverse sections).

Ian

[ashley needhamParticipant @ashleyneedham69188]

Ian, as the boat is of a reasonable size and so is not particulary strapped for topweight, for deck fastening, you could use some of that magnetic strip that you see on the back of (for instance) fridge magnets. You can get it in rolls, it is about 8 or 10 mm or so wide….have one lot on the deck ledge and another on the underside of the deck edge and bobs yer uncle. It would only amount to about 4mm or so thickness for the two strips.

It would hold the deck very easily without being too grabby. Having loads of screws to undo would be tiresome and inevitably leads to damage and/or unsightly holes everywhere.

OR you could have sections aroiund the deck, rather than a continuous strip.

I have been using nylon rudder tillers lately, use 5mm rod for the rudder post, and nyloc nuts on the clamp bolt. These then simply push on the rudder post, hold it firmly enough, but are easy to adjust. Put a chamfer on the post and you dont have to be able to see too much to re-fit them, just slide and push them on. Adlustment becomes a doddle then, as with a firm grip on the tiller and the rudder , adjustments are easy to carry out.

Ashley

[shipwrightParticipant @shipwright]

Ashley – thank you for your helpful reply – I hadn't thought of magnetic strip and I'll look into it. I didn't quite understand your description of rudders/tillers etc – not quite sure how your use of nylon makes it easier to install and adjust.

I have laid out a full size trace of the hull deck edge and laid that trace on a calibrated board (basically white melamine coated chipboard shelving material with pencil lines drawn along and across at 10 mm intervals). Lined up the hull trace on the centre line of the board. Then I have drawn on the internal components (motors, proptubes etc) and the superstructure. This shows where you need the deck openings and then where to put the frames and the stringers. So I now have the information needed to start making the frames – fiddly job with trial and error until I can get the cardboard templates to fit. Then use those templates to draw out the frames on thin ply – then cut ply and file/sand to fit. Of course, if I had the dimensions of the boat's transverse sections I could make the ply frames directly without making templates. And I musn't forget to finish off what I have already started ! – ie fair in the proptubes and rudder tubes and construct the "shelf" for the servo.

Ian

(model boat building is more of a marathon – not a sprint)

[ashley needhamParticipant @ashleyneedham69188]

Ian. The nylon tillers are split and clamp on to the rudder post, metal or metal/plastic ones have a hole the the tiller and a grub screw of some wort, You put the tiller on to the post and then do up the grub screw to stop the tiller turning. IF you need to adjust it, you have to loosen the grub screw, move the rudder and re-tighten. This takes three hands normally as it is difficult to get very small changes, and very difficult if you cannot access the grub very easily.

The nylon ones grip the post tightly, but not so tightly that they cannot be moved for adjustment. Google them and it will become as clear as mud.

Ashley

[Author]

Posts