Microplus- Wet balsa hull

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Mattbarker97

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Hi all,
I've recently been given this boat for free. The boat has been left in a yard for around 3 years, and accidentally tipped on its side in recent months. My plan was to refurbish the boat and keep it for myself. It has microplus signs on the sides however I cant figure out which model it is as it doesn't look like any of the models on the microplus website. Anybody have any ideas?

I did some work on it this weekend getting it upright clearing it out and fiberglassing a hole on the side of hull. Which led me to discover this hole on the bottom of the hull. Through research online it looks like a wet balsa core. So I did a knock test and the dull sound was 2ft around the hole. My plan is to work from the top; grind out the fibreglass above then pull/ chisel out wet balsa; then repair the hole and replace with new marine ply; And finally relay the old fibreglass ontop.

Other than this the hull looks in good condition, and it will be a nice boat once reconditioned. Any advice would be much appreciated as this is my first boat project!

Cheers.
 
Welcome to the forums.
Its ok - pictures can be a pain to post sometimes.
I'm sure you'll get some good advice once you get them posted.
 
Welcome to the Forum Matt.
The photo of the hole is rather blurred - do you have any others that you can post?

Re fixing the hole, and replacing the rotten balsa core - you mention 'working from the top and grinding the fibreglass' - I think this means working on it from the inside of the boat, with the boat right ways up?
II guess that you have marked out the 2' area around the hole that 'sounds' rotten by knocking - it might be easier to then cut out the inside skin with an angle grinder along the marked out area?
Re fixing the hole, approx how large is it? It would be easiest to attach a temporary mould surface on to the outside of the hull, and then lay everything up in the hole and on to the mould surface from the inside. Chamfer the outer skin to get a nice taper.
Re a new section of core, how thick is it? Rather than using plywood, it might be better to use some balsa again, or foam?
 
Last edited:
Bajansailor said:
Welcome to the Forum Matt.
The photo of the hole is rather blurred - do you have any others that you can post?

Re fixing the hole, and replacing the rotten balsa core - you mention 'working from the top and grinding the fibreglass' - I think this means working on it from the inside of the boat, with the boat right ways up?
II guess that you have marked out the 2' area around the hole that 'sounds' rotten by knocking - it might be easier to then cut out the inside skin with an angle grinder along the marked out area?
Re fixing the hole, approx how large is it? It would be easiest to attach a temporary mould surface on to the outside of the hull, and then lay everything up in the hole and on to the mould surface from the inside. Chamfer the outer skin to get a nice taper.
Re a new section of core, how thick is it? Rather than using plywood, it might be better to use ome balsa again, or foam?
Click to expand...
Thanks for the reply bajan, I took a video of the hole so this is just a screen shot from that, you can see the basics. Fibreglass outside skin, black rotten balsa, then inside skin.

Yeh I'd like to work from the inside of the boat, it makes much more sense in my head. It will be far easier to get a good finish on the inside and I dont want to chance cutting too much out of the outside skin of the hull. Yeh that is the plan, the hole is around 20cm in diameter but some of the fibreglass on the outside is weak and flaking away so I think I'll have to make the hole bigger.

I've ordered 9mm marine plywood, this is a total guess as the boat is in north wales. There are plenty of wood shops and boat shops around there that I will be able to pick up the correct material if I am wrong. What do you mean by foam? I havent seen anything online about this which is where I've been getting the majority of the information.
 
Righty ho re the plywood - my only concern about using this is that it is much stiffer than balsa, and might create a localised 'hard spot' in the hull? Whereabouts in the hull is the hole - if it is aft of amidships then there would be less impact stresses when on the plane and going into waves, compared to if it is up near the front.

Re the logo for Microplus, if it is just an 'M' it might stand for 'Marina' rather than Microplus?
 
The hole is around 10cm back from the cabin, it's going to create much more work removing the cabin so I'm going to try to attack it from both sides. It's a 16ft boat so probably around 8 to 10 ft is where the wet balsa is.

The logo actually says microplus, then on the back where it has a little tab saying microplas and the issue number 876
 
PCUK said:
Look at any fibreglass suppliers and you will find foam sheet in different thicknesses for exactly your purpose, and at low cost!
Click to expand...
Thank you so much for the advice! I've attached the link, is this what you're talking about?

Core Materials | GRP UK LTD

Also, is this the same procedure as marine ply. So sand then polyester resin, hardner and filler. Finally, foam then fibreglass cut out ontop?
 
Matt, in view of how this is a relatively small area to repair, and taking into account the age of the boat (old polyester has to be well prepared before you apply new polyester on it to repair it), then it would be well worthwhile carrying out your repair with epoxy instead of polyester.
And this free manual in the link below gives you comprehensive details re how to go about doing this.
https://www.westsystem.com/wp-content/uploads/Fiberglass-Manual-2015.pdf
Yes, the epoxy will probably cost a bit more, but not much more, and it should be a stronger repair.
 
Bajansailor said:
Matt, in view of how this is a relatively small area to repair, and taking into account the age of the boat (old polyester has to be well prepared before you apply new polyester on it to repair it), then it would be well worthwhile carrying out your repair with epoxy instead of polyester.
And this free manual in the link below gives you comprehensive details re how to go about doing this.
https://www.westsystem.com/wp-content/uploads/Fiberglass-Manual-2015.pdf
Yes, the epoxy will probably cost a bit more, but not much more, and it should be a stronger repair.
Click to expand...

100%, Epoxy is the way to go if repairing a polyester boat. Its apparently an old fashioned and outdated view that cheapo polyester resin is ok to repair old polyster

i recently had a crack repaired by David Johnson of West Systems. I had cheaper quotes as low as £100 to repair with polyester by non boat rights but by general fiberglassing companies, but instead went with the more costly epoxy route for piece of mind
 
Could you gouge out the rotten wood between the skins then fill with foam? If you think it is quite a large area how about cutting round it with an angle grinder inside so you can keep the inside skin intact to glass it back in?
 
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