Ouch – Biff on the nose

[Tim RoweParticipant @timrowe83142]

My NitroHammer has been a shelf queen since a bath test run maybe 5 years ago. It has a 12 size glow engine with a neat little pull start. The test was successful in that the motor started easily. It was unsuccessful in terms of the amount of bath water emptied onto the floor. Fortunately for the sake of my continued existence my better half found it very funny.

Wind forward to a couple of weeks ago and I had the opportunity to run the boat in a large open water cistern. Large in terms of about 50m long and 35m wide. You might say predictably the nose of the boat ended up like this:

The result of a head-on collision with the stone walls of the cistern. My pals, once they had picked themselves off the floor suggested a bit of tape would be fine and we should keep going to run in the engine. Fortunately my better instinct told me it would be better to pack up for the day.
When I got home to check the boat out and that nothing had moved internally I found that the bolt had fallen out of the tiller linkage of the brand new outrigger rudder.

Drastic cut required to get back to sound material.

As I am using epoxy the bow was masked up. Taping also helps to stop the gelcoat breaking away while sanding the edges true.
The hole was roughly blocked up with two small shaped pieces of mahogany (won't delaminate if it happens to get wet). The wood was coated with Araldite and manoeuvred and held in position while setting with the stick. The stick was fixed to the wood insert with a tiny drop of superglue so it could be easily broken off later.

Here the top piece is being fitted. You can't do it with one piece because of the taper at the bow.

Once in place and firm, the inserts and opening was sealed with epoxy thus completing the structural part of the repair.

The epoxy sits slightly under-flush with the cut line so I can fill the remaining space with polyester. Just to note that polyester is OK on top of epoxy but the other way around can be a problem unless the polyester is absolutely cured.

I don't mind sanding polyester filler whereas I don't much like sanding epoxy unless it has a very high ratio of micro-balloons.

Nest stage to make the pattern.

Tim R

[Tim RoweParticipant @timrowe83142]

How to make a silicone replacement

[ashley needhamParticipant @ashleyneedham69188]

Ooo er Tim. That looked painful.

i am a foam man nowadays and would stick a lump of styrofoam on the end, sand easily to shape, EzeKote and paint.

Ashley

[Tim RoweParticipant @timrowe83142]

Hi Ashely

I did try some rubbery foam but it was difficult to cut and carve to shape. The silicone bumpers I made for the the Boxkite were OK. Funnily enough the first one came out better than the second but that's often the case isn't it?

I need some more practice I decided and once you have the mould making spares is a doddle.

Tim R

[Tim RoweParticipant @timrowe83142]

The pattern is made from softish balsa.

I do have some balsa blocks but for this tiny item is was less wasteful to stick two bits together.

Stuck onto the flat bow with double sided tape and roughly sawn to shape.

A bit of careful sanding and the pattern begins to take shape. I have a habit of always putting a centreline on things as a reference and it always comes in handy.

The tape is to protect the gelcoat from the sandpaper. When the tape gets roughed up a bit it is time to stop.

Pretty much there now but I have made the bow very slightly less pointy than the original.

That's it and we have a new nose. The temptation is to leave it there and paint it. No, we have to stick to plan.

First coat of high build spray primer and a light rub down. Two more to go and then we have the pattern.|

Tim R

[Tim RoweParticipant @timrowe83142]

Next to make the mould.

I know it's OTT but it's just stuff I have to hand.

Bits of pine chopped up to make the mould case.

Here the waxed pattern is stuck (with wax) to the waxed glass.

The mould case is placed over the pattern.

The pattern and mould is partially filled with epoxy thickened with micro-balloons to a consistency that will just flow.

When the epoxy has cured sufficiently (but not fully cured) the rest of the mould is filled with random bits to glass in epoxy to provide a strong back-up to the mould surface.

A quick coat of fast drying sealant and the recess waxed and the mould is ready for pouring.

The mould is filled with liquid silicone catalysed at 5%. This particular silicone will give a Shore hardness around 25 which is nicely squidgy. This time is very very careful to mix the liquid and catalyst very gently to avoid trapped air. I was also very careful with the filling to bring it just to the edge. On the Boxkite bumper I underfilled one so it ended up with a thin wobbly edge. The second I overfilled and both gave me a really hard time trimming.

This one is as-poured and you can see, the top is nice and flat. Another observation is that there are tiny "ears" on the silicone. This is where there were tiny pinholes in the epoxy mould. If you look closely you will see some black dots and these are where more prominent pockets were filled with polyester and dressed to shape. Having female features in a mould (ie small recessed blemishes) is not the end of the world as they will be male features (bumps) in the product and can be easily trimmed out. Have male blemishes in a female mould is not good as it will leave hollows that are much harder to deal with. I am sure there is a metaphor in there somewhere!! When I was learning to be a pattern-maker we were taught a lot about genders!!

So here we have the faithfully reproduced product – another metaphor!! and complete with a little ear to be trimmed.

It is very bright white so I looked up to see if there where pigments for silicone imagining there had to be. I found an American company that do a fluorescent orange which would be perfect. Many full sized racing boat have day-glo orange bows because they are designed not to sink but float with only the bow sticking out above the water. Lots of photos on the internet.
I am thinking of ordering some pigment as the same system will work on the two Cigarettes I am building to Ray Woods design.

And here we have it. Nitrohammer with its nice new shiny white nose.

Look out stone walls of cisterns as we can now drive it like a hooligan.

Tim R

[Chris FellowsParticipant @chrisfellows72943]

First class repair Tim, carried out with your usual precision.

Funnily enough when doing my first test of my new race boat, ScottFree, a few weeks ago, one of the bolts securing the rudder had dropped out and the other was loose!

Chris

[Tim RoweParticipant @timrowe83142]

Hi Chris

Thanks as always for your encouraging comments.

What happened was that as I set of for a second run, one of my pals stepped in front of me. For a moment I couldn't see a thing but knew that the wall was coming up so steered to port, or so I thought. When my view cleared it was heading straight for it. I only had time to cut the throttle but that made little difference. I just put it down to bad driving. When I found the disconnect later I realised that I had actually tried to turn but that wasn't happening!

I found a new bolt in my spares box and it is fixed with Loctite. The version that you need heat to disassemble.

Can't wait to try it again and get the engine fully run in and tuned. I made a few mods to make it faster and they worked!

Tim R

[Kev.WParticipant @kev-w]

To save yourself all this work and expense , my suggestion, is to teach your right thumb, a little more moderation on the throttle stick

A bit of 'self control' goes a long way to extending the life of ones boat.

[Richard SimpsonModerator @richardsimpson88330]

Incredibly interesting thread. Many thanks for taking the time to share it with us, I enjoyed following your process.

As regards the incident, hindsight is a wonderful thing and we all sometimes fall foul of a momentary loss of concentration or a bad choice when we cannot see what is happening. I was once trying out a new model tug that I had just purchased ready built. I knew the thing sat a bit on the low side, I knew the motor was too powerful for a scale tug and I knew the coaming around the superstructure was not very high. I was distracted by a youngster chatting and took my eye off the boat. When I looked again I thought she was sitting a bit lower but ignored it. Next time I looked the tip of the stern was sticking out of the water!

Unbelievably luckily I recovered the model with a grappling hook from a dinghy with just a few bits missing. After 20 minutes under water the motor was still turning!  She went through a complete refurbishing and detailing process and a conversion to a Navy Tug and I still use it. I have extended the coaming and removed a few pounds of lead from it though!

Edited By Richard Simpson on 22/05/2021 22:53:08

[neil hpParticipant @neilhp]

very nicely done…………..superb repair

[ashley needhamParticipant @ashleyneedham69188]

Yes, good job. Not quite invisible, but…..

Ashley

[Tim RoweParticipant @timrowe83142]

Thank you gents, one and all. It was fun doing it.

Tim R

[Ray Wood 3Participant @raywood3]

Hi Tim,

Great job, It almost guarantee's you will never hit the bank again ! and if it does it will bounce off

Having the steering fail didn't help .

Regards Ray

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