Microplus 461 Floor

[Markb259]

Hi all,
I’m a newbie to this forum. There will be lots more questions but….I rescued a Microplus 461 last year. The floor had a series of holes drilled in it. It was left uncovered for a while and as a result the floatation layer is saturated. I have started to removed the floor area and remove rotten balsa. There are no stringers, would it be recommended to install new stingers and fibre glass them in? Regarding the floatation layer, any advice on a replacement. Once this part is done I can move forward in this project.

I will add some pictures if that helps?

Any advice or guidance would be hugely appreciated.

 

[colhel]

Welcome to the Forum. I had a Microplus many years ago but I can't remember any balsa in the construction. Not sure what a floatation layer is. Pictures are always welcome, we like pictures

 

[Markb259]

Welcome to the Forum. I had a Microplus many years ago but I can't remember any balsa in the construction. Not sure what a floatation layer is. Pictures are always welcome, we like pictures

Thank you for the reply. Apparently the 461s have a balsa layer and then fibreglass over the top. It’s approx 15mm thick. I may have used the incorrect name for the floatation layer, this is the balsa layer. I’m assuming a suitable foam can be used, re-fibre glass then 18mm marine ply on to to create the main floor? Photos now added

 

[colhel]

The hull looks different to mine so maybe the construction was different too.
Have you seen this?
Microplus 461 – Microplus – The getaway boat

This was mine (about 1988)

 

[dpb]

I am rebuilding an old Sea Ray. Just finished the new floor.
If no original stringers then the boat does not need them by design but does not stop you adding them if you wish. In your shoes I would strip the old foam out, install new 18mm ply (hardwood with class three glue minimum). Protect ply faces with product of choice as well as cut edges. I used poly resin. Glass ply to hull at edges. Drill holes in ply to pour 2 part expanding bouyancy foam in between hull and floor, plug holes and glass over. Job done. Plenty of on line resources to explain these steps. Its a messy job but once done the rest of the project should be comparatively easy!

 

[Markb259]

The hull looks different to mine so maybe the construction was different too.
Have you seen this?
Microplus 461 – Microplus – The getaway boat

This was mine (about 1988)
View attachment 163564

Thanks for the reply. Nice looking boat

 

[Markb259]

I am rebuilding an old Sea Ray. Just finished the new floor.
If no original stringers then the boat does not need them by design but does not stop you adding them if you wish. In your shoes I would strip the old foam out, install new 18mm ply (hardwood with class three glue minimum). Protect ply faces with product of choice as well as cut edges. I used poly resin. Glass ply to hull at edges. Drill holes in ply to pour 2 part expanding bouyancy foam in between hull and floor, plug holes and glass over. Job done. Plenty of on line resources to explain these steps. It’s a messy job but once done the rest of the project should be comparatively easy!

Thank you for the info. Just so I understand you correctly, Put strips of ply around edges, glasses in, then install 18mm ply as the floor, drill holes, fill with bouyancy foam, plug and glass.

Do you have any photos of this through the process?

Really appreciate the advice.

 

[dpb]

I glassed the ply floor straight to the hull but then i had stringers to fix and support the floor so your ply strips might help. I posted some pics on here a while ago
My 80's Sea Ray 197 Monaco Project
Otherwise this chap posted some vids that i found useful.https://youtu.be/kKgzheMHi5w?feature=shared

 

[colhel]

Thank you for the info. Just so I understand you correctly, Put strips of ply around edges, glasses in, then install 18mm ply as the floor, drill holes, fill with bouyancy foam, plug and glass.

Do you have any photos of this through the process?

Really appreciate the advice.

On my Microplus the hull was a different shape to yours and sloped to the centre slightly. It was slightly uncomfortable and I did consider adding a floor for added comfort, but never did. On yours I can see the need is much greater. However you only really need it for your comfort, the boat doesn't require any extra strength and the amount of extra buoyancy you'll be able to fit under the floor will have little to zero affect. I'm pretty sure too (need someone to confirm) that if if the hull was balsa cored this would be within the laminate, having it on top would add little to the strength or bouyancy.
My view there's no need to have a layer of anything between the floor and hull. Make a floor and leave the void underneath free, this will allow you to drain the hull and make inspection much easier.

 

[Markb259]

On my Microplus the hull was a different shape to yours and sloped to the centre slightly. It was slightly uncomfortable and I did consider adding a floor for added comfort, but never did. On yours I can see the need is much greater. However you only really need it for your comfort, the boat doesn't require any extra strength and the amount of extra buoyancy you'll be able to fit under the floor will have little to zero affect. I'm pretty sure too (need someone to confirm) that if if the hull was balsa cored this would be within the laminate, having it on top would add little to the strength or bouyancy.
My view there's no need to have a layer of anything between the floor and hull. Make a floor and leave the void underneath free, this will allow you to drain the hull and make inspection much easier.

Thanks for the information and advice. I think once the balsa mess etc is removed I may add a series of stringers (glassed in) to enable an 18mm ply floor to be added. The current buoyancy is only 10mm thick.

The other question is regarding the drain hole. Would you keep this or glass over it? I have read that some people glass over it as they can let water in? If this drain hole is below the floor line, and the 18mm ply floor is glassed in. Do you need to cut an inspection hole out of the floor? And how is the best way to seal it to prevent water ingress? Hope my waffle made sense? If not I will sketch it out.

Thanks guys

 

[colhel]

I would definitely keep the drain plug if you're glassing in the floor. Mine never leaked but if yours does I'm sure it could be made watertight. Regarding an inspection hole, could you just rest the ply on the stringers so you could lift the whole floor?

 

[Markb259]

I would definitely keep the drain plug if you're glassing in the floor. Mine never leaked but if yours does I'm sure it could be made watertight. Regarding an inspection hole, could you just rest the ply on the stringers so you could lift the whole floor?

That’s an option but I’m not keen just resting the ply. May introduce some quick release fixings.

Definitely gives me some more ideas now to move forward….I think. I will post pictures once I make further progress

Thanks guys

 

[Restoration man]

That def looks to me like a balsa cored hull , if so you must replace the balsa core like for like ,same thickness balsa and re glass over with same thickness fiberglass , the strength of the hull will be seriously affected if you don’t, you can’t just rip the inner layer of fiberglass off scrape out the rotten balsa and a pop false floor over it and expect that to be job done , that would be suicide , the boats strength comes from the core it’s like having an
I beam , I’ve been replacing my boats balsa deck cores as it was rotten just like yours , if you any advice let me know.

 

[Markb259]

That def looks to me like a balsa cored hull , if so you must replace the balsa core like for like ,same thickness balsa and re glass over with same thickness fiberglass , the strength of the hull will be seriously affected if you don’t, you can’t just rip the inner layer of fiberglass off scrape out the rotten balsa and a pop false floor over it and expect that to be job done , that would be suicide , the boats strength comes from the core it’s like having an
I beam , I’ve been replacing my boats balsa deck cores as it was rotten just like yours , if you any advice let me know.

Thanks for the information really is appreciated. If stringers are introduced to assist with strengthening the hull or ply layer glasses over with introduction of marine type foam, would this not strengthen?

I intend to strengthen the hull, not just leave it as it’s very thin. I want to strength then introduce a floor.

Just out of interest why does the balsa have to be replaced like for like? I have read on other sites to use ply or stringers as an upgrade?

Thanks for the information

 

[dpb]

If you have removed the inner grp layer and the balsa core then restoration man makes a good point.
However, if you increased the thickness of what is left of the hull to compensate for removed inner layer and balsa, build some stringers then fix and glass floor, then foam the gap that should work out ok i think. If you do rebuild the balsa floor and inner skin you need to be sure your work is watertight or the new balsa will eventually get wet and back to square one!

 

[Restoration man]

Thanks for the information really is appreciated. If stringers are introduced to assist with strengthening the hull or ply layer glasses over with introduction of marine type foam, would this not strengthen?

I intend to strengthen the hull, not just leave it as it’s very thin. I want to strength then introduce a floor.

Just out of interest why does the balsa have to be replaced like for like? I have read on other sites to use ply or stringers as an upgrade?

Thanks for the information

It was made at the factory with balsa core it’s for a reason,it would also have been more labour intensive to make the hull that way , im sure if it was as easy as throwing in some extra stringers they would have done it when it was manufactured , the factory would have done a lot of stress calculations and testing , before to deciding to do it that way , If you only plan on using the boat on the canal then it might be ok to do it the way you want to do it but I wouldn’t want to buy it off you when your finished with it , and i certainly wouldn’t go to sea in it , also what you don’t want is hard spots on the hull ,all boats are designed to flex a certain amount, look at it another way I assume your trailer has some kind of rollers on it ? The bounce off the trailer going down the rod might cause crack to set up between hard spot and part of the hull that’s intended to flex a little bit ,hence think carefully about fitting stringers etc where they weren’t designed to be fitted,
it’s not as easy as saying “Dave” off Facebook says it’s ok to do it like that so it will be fine , just fix it properly and do the job once ,it’s not hard to grind down and clean up where the balsa was and stick some new balsa down with epoxy let it set and put few layers of fiberglass over the top, ok there are few more steps than that but you get what I’m trying to say , there are plenty of videos showing you how to fiberglass on you tube it’s not rocket science, best of luck Nick
Ps you could potentially swop the balsa for man made product like divinycell or pet foam I’ve done this in my side decks , but if my hull was cored like yours I would be still be inclined to replace like for like

 

[Markb259]

It was made at the factory with balsa core it’s for a reason,it would also have been more labour intensive to make the hull that way , im sure if it was as easy as throwing in some extra stringers they would have done it when it was manufactured , the factory would have done a lot of stress calculations and testing , before to deciding to do it that way , If you only plan on using the boat on the canal then it might be ok to do it the way you want to do it but I wouldn’t want to buy it off you when your finished with it , and i certainly wouldn’t go to sea in it , also what you don’t want is hard spots on the hull ,all boats are designed to flex a certain amount, look at it another way I assume your trailer has some kind of rollers on it ? The bounce off the trailer going down the rod might cause crack to set up between hard spot and part of the hull that’s intended to flex a little bit ,hence think carefully about fitting stringers etc where they weren’t designed to be fitted,
it’s not as easy as saying “Dave” off Facebook says it’s ok to do it like that so it will be fine , just fix it properly and do the job once ,it’s not hard to grind down and clean up where the balsa was and stick some new balsa down with epoxy let it set and put few layers of fiberglass over the top, ok there are few more steps than that but you get what I’m trying to say , there are plenty of videos showing you how to fiberglass on you tube it’s not rocket science, best of luck Nick

Cheers Nick, thanks for this great info and advice. I want to do this once and correctly. I was also speaking to chap local to me yesterday and he said literally the same as you….what you take out, replace. Designed like that for a reason.

I will strip out all the rotten balsa, get the hull to a decent condition.

Any recommendations on where to get the balsa from?

The other question is, once the balsa is glassed in. Would you then sit 18mm marine ply directly on top of the new balsa/fibreglass layer?

Thanks again for the advice. Much appreciated

 

[Restoration man]

Cheers Nick, thanks for this great info and advice. I want to do this once and correctly. I was also speaking to chap local to me yesterday and he said literally the same as you….what you take out, replace. Designed like that for a reason.

I will strip out all the rotten balsa, get the hull to a decent condition.

Any recommendations on where to get the balsa from?

The other question is, once the balsa is glassed in. Would you then sit 18mm marine ply directly on top of the new balsa/fibreglass layer?

Thanks again for the advice. Much appreciated

I buy most of my fiberglass supplies from east coast fiberglass they sell end grain balsa ,
without seeing more photos of the cockpit floor I can’t really comment on the best way to fit a floor/sole , but you don’t want to do is screw anything into the balsa once it’s been replaced ,that’s prob what caused the problem in the first place water getting into screw holes , the new core needs to be sealed 100% or it will rot again ,
on my boat I’ve swapped the balsa core in the side decks to pet foam it’s not got quite as good structural qualities but it’s cheap easy to cut and doesn’t rot ,the side decks aren’t quite as critical as the hull so I should be ok in your case this being a cored hull I would stick to what was originally used