The MFA Spearfish is a very popular model boat that relies on silicone rubber to join its 36” long hull and deck together.

Using silicone to join these two halves together works well - and of course - also makes a good watertight seal!

Most of these boats are quite old now, so when one comes along for restoration and needs taking apart to gain access, the first job is to cut into this seal to separate the joint and clean it up ready to be resealed after any necessary work is completed.

Cutting away the old silicone with a sharp Stanley knife is not at all easy as it makes a formidable bond that many years later is usually very much secure, so I have seen no evidence to date that silicone rubber is not a good adhesive/sealer to use in a model boat.

Obviously the strength of the bond depends on good preparation and how well the silicone was applied, but for joining the two glass fibre halves of the Spearfish together, silicone rubber appears to be a very good choice.

I have no experience of bonding wood and brass tube together (as in sealing a prop shaft into a wooden hull) but it sounds like it also works well and may be worth a try as it could also dampen some transmitted vibrations and make for a quieter boat.

…but taking note of RodC’s caution, no electronics should be added to the boat until after all the vapours have disappeared completely to avoid damaging them.

Bob.

Most of the silicone sealers smell like vinegar whilst curing. Those fumes are deadly to electronics. There is one version intended for electronics, sorry but i cant recall the name tho. Next time i am in at my supplier i will look it up & edit this post.
I used it for 20yr when i was a calibration tech repairing NASA-quality RF front ends incl 2.4 GHz, & hi-end digital multimeters.

Personally I'd be wary of using silicone bathroom sealer. Whilst I have used top quality in both the kitchen and bathroom I do notice that over time, behind the sink and basin the sealant has been affected by water and has peeled away from the worktop.

This has been after some years though and obviously boats aren't in the water for long periods.

My other concern is that whilst some sealants can take paint they usually don't do it very well and the paint can fail at the sealant/hull joint.

I prefer to use putty or P38 on the outside to plug the hole and hold the prop shaft in place before surrounding the prop shaft with epoxy on the inside.

But there is usually more than one way to do the job and if you are happy and confident with it then why not.

Hi Roy,

Setting the prop shaft in silicone bathroom sealer is not something that I have ever considered, but it sounds like it could be a really good idea for some models and its use should certainly insulate the shaft against some resonance to make the boat run more quietly.

I am also extra fussy when fitting the prop-shaft (and later when aligning the motor mount and coupling assembly), and have always used 24 hour Araldite to do the job.

Hi Bruce et al, I am very careful with prop tubes and I used to set them in place using P38.
Now I have moved on and use bathroom sealer, the white one is a stronger glue than the clear one. It insulates a lot of noise and never quite goes hard. Been doing that for the last 4 or 5 model boats, never let me down.

Back to the ring net fishing boat from the Scottish Isles, the epoxy makes the bare wood very shiny just like they are fullsize.

See below my 2 'Mary Anns' They are both the same inside. They say a picture tells a thousand words, but I never noticed!
If you look you can see that the near one is lower in the water, it was sinking! When I got her back there was an inch of water in her, traced yesterday to a sprung plank. Being treated with epoxy as I write.
Roy

Thanks Guys for all your replies. I ordered Ezy Kote which arrived yesterday and my fishing boat has had 3 coats, that was yesterday. Today after allowing time to harden, it was into the bath and she went 90 minutes without a drop of water coming in.
So the fitting out of the motor and radio commences tomorrow and then testing and then the complex superstructure with rigging.
I will post pictures when done.

Thanks to all,
Roy

Hi Roy, I would go straight to West systwm epoxy. It is a 2 part product but easy to mix and has a good pot life. Your biggest problem will be painting over the enamel paint that is on the craft so maybe google West System and ask the question what you need to do to cover this. They may suggest priming first ?. The epoxy will give you a very hard and durable surface that will counter a lot of damage. You can actually add pigments to the epoxy to give you a color and that is what I did on my Venice water taxi model for a white bottom. Cheers and good luck Ian

Have you thought about using a marine Spar varnish? try it on an area that is not visible about 1" square if it affects the paint. other is an epoxy resin. another method is to pour resin inside and let it flow around as you move the boat around twisting and turning making the resin flow into all the cracks and crevasses. Are you sure it's not your prop rudder shafts leaking. do you have stuffing boxes for you prop shafts? are your rudder shafts above the water line?

Hi Zooma, all good points you have made. My experience in purchasing ex-kit models that were built as decorative models and following the less than perfect glue joints has me thinking "Never again"!

But I got sucked in again and this was a bread and butter construction against P on F. I thought that will just mean extract the prop tube sort out the rudder operation etc. I did not want to go into a re-paint as the model was a period piece and I wanted to preserve rather than refurbish.

Many modellers build a model and the constructed wooden hull is just a former for the glass fibre covering, this is not my thing. I like to think of the builder maybe 60 years ago creating something for himself, proud of his acheivment and then I come along preserve his work but put her where she belongs on the water.

So I am expecting delivery of the Ezy kote reccomended and just go to the seal it all in place without further action. Incidently in this case it took 30 minutes for the leak to become apparent! So sweep the problem under a coat of sealer for me.

I want to get on the water and send feedback to the very kind seller on Gumtree who so genuinely packed it and sent it from Cumbria to Herts for less than her cost.

There was a very helpful contact after I contacted the Scottish Fishery Museum, there was a registration number CN992 painted freehand on the model and a name "Providence" on the model and base. I asked if this was a known registration and a curator came back to me and said that number was never reached.

But with additional information she told me about the fishing boats this registration letters refers to, Cambletown off the west coast near Bute and some links to videos of the boats at sea. Recommended a local model boat club and sent me a copy of as she said, "very similar plans".

They were indeed similar plans as when increased in size, revealed the very registration I had enquired about, which took me to Harold Underhill plans and in Plank on frame models book volume 2 in the adenda were the plans in general arrangement already on my book shelf!
When all is finished I will feedback to the above ladies.

Thank you for responding
Roy

Hi Roy,

If you wanted to treat the exact source of the leak before the blanket covering of epoxy you could try some bright coloured food colouring that can be dripped onto the suspected area to identify the track of the water leak.

An alternative is to thin the epoxy to a water like consistency for its first detail application in this specific area before the final overcoat(s) so you know the source of the leak has been blocked.

Bob.

Bob

Thanks Doug all the info I wanted!

I agree with your weak wood checks, I use a very bright torch inside the hull and the lights off.
cheers
Roy

Ahoy Roy😉
Same situation I had with an ancient Gina 2 Fish Cutter Model I inherited from an Aunt (you can see it in my Blogs).
I used Deluxe Materials EzyKote inside and out. Reinforced inside with FG tissue, simply because my hull was plank on frame, very thin and brittle.
Had no reactions with the remnants of the old oil based paints I had removed, was ca 2mm thick in places🙄Removed with heat gun and 3/4" chisel
EzyKote is water based and one part. Dries in warm weather (like now 'Phew'🤕) in 20-30 mins. AND - Doesn't stink the house out🤗
Not cheap, but very good.
Cheers, Doug😎
PS to those going to drastic lengths to find hull leaks like filling with water-
For the a.m. hull I turned it upside down with some bright white LEDs inside.
Turned off the shop lights and then simply marked rings round any places I could see light shining through. Subsequent Domestic Tank Facility tests were passed with dry bilges😊.