What plywood and timber?

[saltylegs]

I used 12mm marine ply about 4 coats of varnish the sefl addhesive stripes and about another 7 coats, I find there is normally at least 1 good looking side of the ply that comes up well.

see link below

http://i1143.photobucket.com/albums/n630/saltylegs/66369837175F7C0AB.png

 

[ianat182]

Just a thought , as you are buying Marine ply anyway is there a possibility of using epoxy to make the stringers from this timber - might assist in the bending of them and could be done in two or more 'laminations' of the 12mm that you're getting, and might waste.? At least it would all be 'Marine quality'.

ianat182

 

[rbcoomer]

Just a thought , as you are buying Marine ply anyway is there a possibility of using epoxy to make the stringers from this timber - might assist in the bending of them and could be done in two or more 'laminations' of the 2mm that you're getting, and might waste.? At least it would all be 'Marine quality'.

ianat182

Hi Ian,

I had considered that, but as there are 6 'main' sections that run the length of the main cabin/cuddy floor, the length will exceed that of the ply sheets. Whilst I could overlap and taper joins, the current stringers are wood and have held up well given they have obviously been wet for some time. They would probably still be good if they had been sealed originally, but although still solid the decay process has clearly begun at the ends and on the surface. Thus I aim to replace with a similar hardwood which should last at least another 30 years! There isn't much bend in them as they run the length of the hull and effectively taper out towards the bow, so once cut/planed into shape I aim to resin coat prior to glassing in. The originals were sealed in top, bottom and sides, but not the ends. I'll probably use ply offcuts etc for the short bits between the stringers to form the box sections of the floor support however - still resin coated of course and glassed in.

The only issue I currently have still to overcome is that the engine and out-drive are still in place and will be a major problem to lift out - height, weight and lack of access/space. I had planned to complete the cockpit area floor and then lift the engine forward so I can strip and refurb the aft section! Whilst the stringers run the full length to the transom, they are cut down to around 3/4" aft of the engine bay bulkhead. Thus I don't believe they offer much structural rigidity and considered a 'join' at the aft bulkhead. The more I've thought about this however the less I like the idea - given the hull is a deep-v capable of 80mph! Whilst I don't envisage traveling at such speeds myself, the job needs to be right and I imagine hull stresses could be immense and not worth shortcuts.

Plan B is now to rig some kind of frame over the stern and lift the engine onto this as I'd then be able to replace stringers complete. Then of course there's the transom and I've no idea what to expect there yet...

The picture below shows the largest of the stringers and the decay at the end (arrow). Red line illustrates where the ply bulkhead was (rotted away).

I'm running a thread over on the Mobo forum where there are other images that better illustrate the layout: http://www.ybw.com/forums/showthread.php?t=285958

Regards,

Robin

 

[Captain Coochie]

There are many grades of marine ply and the £40 one has voids in it .
I looked a while ago and if i am correct the best Lloyds approved ply is Anchor marine ply but it is around £100 per sheet at trade prices so will retail at alot more .
I wouldnt use Meranti for a boat , in fact i wouldnt even use it for external joinery and have burnt all the Meranti i had in the workshop as i think it is rubbish . Sapele would be a better timber but Iroko is around the same price so that would be better .
PM me a cutting list of the solid timber you need ( The shorter they are the more likely it is that i will have it in stock )
It wont be free either but at trade prices

 

[Twister_Ken]

Hi Ian,

the current stringers are wood and have held up well given they have obviously been wet for some time. They would probably still be good if they had been sealed originally, but although still solid the decay process has clearly begun at the ends and on the surface.

Have you considered the possibility of scarphing or doubling new ends onto the existing stringers? Something Cuprinolish (or a plane) should sort out the surface rot. Could be a considerable time and money saver.

 

[Boo2]

I looked a while ago and if i am correct the best Lloyds approved ply is Anchor marine ply

Is that this stuff ?

Boo2

 

[rbcoomer]

Have you considered the possibility of scarphing or doubling new ends onto the existing stringers? Something Cuprinolish (or a plane) should sort out the surface rot. Could be a considerable time and money saver.

Hi Ken,

Yes I did, but they are capped with fibreglass the entire length and where I have removed sections of this to check, the wood is saturated. Thus even if I could expose and dry it, I'd still need to glass over and probably wouldn't be confident in it's strength. The guys who provided the fibreglass reckoned it would only be there for structural shape anyway and that the resin provides the strength, but to my mind it would be a bodge to cover up and not replace? There is also some rot along the bottom edge, but this could again just be at the ends as I've not removed one entirely.

Cuchilo - Thanks, I'm a fair distance from London but will send you measurements once done (hopefully during the week after work one evening) - I fear they won't be off-cut sizes, unless you are building some very big stuff!

Thanks all,

Regards,

Robin

 

[Tresner]

A bit late in replying to the thread, but if you can find it use Okoume ply. It has 50% more plys and will serve you better than most of the other marine grade plys. Listen to Little Ship when he talks about the apoxy sealant. Over in the colonies we use a product called Restores-It. It is a clear penetrating epoxy sealand (CPES). It has a lower viscosity than water and will wick into the wood. CPES is a wood fiber based product and will move with the natural movement of the wood. Apply at least two coats. If you apply varnish or paint over the wood before it is completely cured, you will gain the extra advantage of the chemical bond. I use it on all bare wood, both inside and out.

It is a bit expensive but will save you from having to do a job over again after a few years. But then I will let LittleShip tell you about that................. ;D

 

[ianc1200]

I built a plywood pram - the Woodenboat "Nutshell" - back in 1988-1990 out of Jewsons marine ply, with two coats of West Epoxy inside and out. Over the years had several areas of rot, but 2 years ago it was close to the bankside and a small branch punched a neat 2" diameter hole through.
My conclusion is whatever the encapsulation, moisture will find a way through, so if you want it to last build using the best ply you can buy. I thought this was the Robbins Super Elite, and have bought this to replank the Nutshell (hadn't heard of the Anchor ply).

A bit OT, but there seems to be a movement in the States of building with less than perfect ply in the knowledge it will last a few years, and then you can break up.