Bumper boat build

[Chris EParticipant @chrise]

I am sure that Ashley will answer this but in general I would argue that having excess power is just giving the motor & electronics a hard time for no gain and might endanger the model if the excess power makes it unstable.

If an S35 gives all the performance that you want / the model can handle then why go for more?

Think of a propeller as a screw in DIY. As it turns it screws itself into the wood. A propeller works in exactlly the same way in water. As you turn it the prop is trying to pull itself through the water which it achieves by moving the whole model. What can vary is the amount that it tries to pull the model along. A number of factors determine the pull. Firstly the size (diameter) of the prop. Bigger props having more blade area try & pull more water than smaller props. Secondly how far it tries to pull itself with each turn. This is known as the pitch of the propeller. 'S props generally try & pull themselves by 0.85 of the diameter of the prop whilst 'X' props try and pull 1.6 times (eg – a 40mm 'S' prop tries to move forward by 0.85 x 40 = 34mm per rpm whilst a 40mm 'X' prop tries to move forward by 1.6x40mm = 64mm) .

Obviously how fast you turn the prop also makes fundamental difference as does how well it is designed and how it is mounted on the model..

Edited By Chris E on 02/01/2023 12:42:13

[Mike JParticipant @mikej]

Hi Chris, The prop part of my question was really about the difference between the X and S types and you've answered that – Thanks.

The first part of my question was about the motor location with regard to the support tube on the bumper boat. When going forward should the motor be in front of the post with prop right at the front of the boat, or motor behind the post putting prop nearer the centre?

Any answers appreciated!

Thanks

Mike.

[Chris EParticipant @chrise]

Good question. I can guess but as far as I can see there hasn't been a picture of the underside. It also looks like the prop was spaced as far from the motor as possible to reduce shadow effects.

[ashley needhamParticipant @ashleyneedham69188]

Mike. The props started largest/most pitchy first, as I was unsure as to how much power the motor would generate. As it happens, it was way too much. and prop sizes and pitches were reduced on an experimental incremental basis, arriving at an S35. There is no point in overpowering the bumper, it just makes it more difficult to control.

Difference between X and S, like wot Chris says.

The motor is mounted behind the pivot tube, and I will stick a picture up after typing this. 

Et voila!    in the snap, the front of the bumper is to the right and I think thats an X50 on there.

Ashley

Edited By ashley needham on 02/01/2023 16:56:02

[Mike JParticipant @mikej]

Thanks Ashley, the drawing in the mag shows the prop on the left as above but the front of the bumper is also on the left so I felt a need to ask. Surprised no-one else asked, or maybe it's just me missing something obvious.

I didn't want to get to the water and find Barbie was steering not me!

Already ordered S35 and X35 to try both.

I don't have any brass tube but do have some left over 15mm copper pipe from a plumbing job. Thought I might use a length for outer tube. Take another length, cut a slot lengthways in it, squish it in the workmate to close the gap then solder up the join – hey presto, inner tube! A bit of trial and error on the slot width and plenty of grease and in my mind it should work (maybe not in practice though). Could be shopping for brass tube soon.

Mike.

[ashley needhamParticipant @ashleyneedham69188]

Unfortunately the very worst person to proof read anything like an article is the author of said article!

Normally in an article i twitter on , and it doesnt matter if I get out of synch, or miss vital moments in the build, I mean….who will notice?? BUT the bumper article, different kettle of fish. I needed to write as if describing the build for a novice, without making it too boring for the experts.

The way to think of the power unit is like it was a rudder, but instead of a flat blade, there is a motor and prop.

Any sort of tube will do. If using 15mm pipe, you might have to seal the top of the pivoting inner bit ( inside the hull) with silicone or something to stop water ingressing.

Ashley

[ashley needhamParticipant @ashleyneedham69188]

Just noted Chris E post regarding prop spacing from motor…

The thread on the prop adaptor is long to enable an aircraft prop and nut to be used, it’s much too long to screw a boat prop on to, so I just grabbed some washers to use as spacers! I could/should have just trimmed the thread a bit, however there is some merit in having a bit of space between motor and prop, although at these slow speeds the benefit is probably only theoretical.

Ashley

[ashley needhamParticipant @ashleyneedham69188]

It’s been a while, so I want to know how many bumpers have been built for the summer season??

Now is the time to build those Barbies/Daleks/Tardis’s/k9’s/R2D2’s or woteva.

Ashley

[Dave ReedParticipant @davereed72029]

Started but not quite finished yet…..

Splash of paint and it'll be fine

[ashley needhamParticipant @ashleyneedham69188]

Good man! Any issues, and there are not likely to be, just ask.

Just as an aside, as the top is 4mm ply, to cut out the access hole you can safely drill holes in the corners or your shape and use a jigsaw. Any splintering is not an issue as the combing reinforces the hole and in any case it’s well hidden under the top.

i used my small bandsaw and just cut through one end and then twiddled round to get the opening. A sliver of very thin ply and glue fills the outer cut easily. Make the sliver of ply stand proud of the surface and simply sand flat, no filler required and in any case only a tiny bit of this will be seen past the top. (but don’t squeeze the cut bits together as this may distort the top).

Ashley

[Dave ReedParticipant @davereed72029]

I'll be using the drill/jigsaw method to open the top as I don't have a bandsaw.

In fact, I'll be using all (drill and jigsaw) of my power tools to do that.

 

Cutting pulleys out of ply might be a bit of a challenge for me, but as long as I still have all my fingers at the end, all's well

Edited By Dave Reed on 04/06/2023 16:47:14

[ashley needhamParticipant @ashleyneedham69188]

You could use a hole saw to get circles of ply, I think thats what I did, then drill or file out the centres once the three layers are glued together, or cut squares..knock the corners off, then use a sanding block to round off the bits. It doesn’t have to be super accurate.

Ashley

[Trevor HollowayParticipant @trevorholloway99134]

I used a piece of broom handle, drilled the hole in the middle, mounted on a bolt in the hand drill and filed out the groove while it was spinning.

[Chris FellowsParticipant @chrisfellows72943]

It was Open Day at our club Knightcote and there was 8 bumper boats including a Harry Smith design one? All having great fun pushing a bouy from one end of the lake to the other (not very far!) and into the goal or dock by the winner.

Some boats had nice paint jobs, and one had flashing lights and played fairground music, as there was a best boat competition. Piloted by Barbies and other figures.

When I'm back home tomorrow I'll post a photo or two.

Chris

Edited By Chris Fellows on 11/06/2023 19:44:43

[ashley needhamParticipant @ashleyneedham69188]

Look forward to that Chris.

There was a.n.other bumper at the Kempton event, I think the modelboatbits one (sadly no driver on it) and there was a BIG difference in manoeuvrability between it and ours. I have seen Harry’s interpretation, similar to the MBB one sort of. Trouble is, Harry makes all his upside down….!

Ashley

[Chris FellowsParticipant @chrisfellows72943]

The yellow one is the Harry based design. Not sure about "Barbie" in the No. 2 boat!

Chris

Edited By Chris Fellows on 12/06/2023 19:30:06

[Trevor HollowayParticipant @trevorholloway99134]

Chris, that is exactly what they were meant for.

Fun for operators and onlookers.

All those cider fuelled design reviews paid off.

[ashley needhamParticipant @ashleyneedham69188]

Wow…that looks like a psychopath Barbie in no2!

Its very gratifying to see the mass production of (the only plan I have ever submitted) my bumper boat, I must say. The tops are all good and great to see that the ‘plan’ top has not been slavishly followed, but bods have done their own, which is to be expected.

Although driven by a killer Barbie, the No2 top is very reminiscent of a more modern bumper top. Like the blue one with a chequered bonnet..harks back to the first dodgem cars.

I always wonder how many craft have been built from the free plans, well, there’s 6 (?) Just there, and I know of 3 more, plus our 6. 

Well done chaps. Round of applause.

Ashley

Edited By ashley needham on 13/06/2023 07:58:55

[Chris FellowsParticipant @chrisfellows72943]

Thought you'd be pleased Ashley. It was the chairman's challenge for the open day to build the boats and score a goal with the buoy. No doubt the boats will be used on our Thursday morning get togethers for more fun!

There was a competition for best boat which is why they went above the quick and simple with first class paint jobs, flashing lights and sound boards! But good that it focussed minds and great models were produced. There were actually 7 of your design but one had problems during the first foray!

Chris

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