Hull Repairs

[alb40]

In the spring, I will need to be thinking about sorting out a few soft spots in the hull of my boat. From the waterline upwards, she is built from plywood which is either 10 or 12mm in thickness.

Due to a few leaks in the decks under previous owners, a few spot areas have developed in the hull. I havent done anything with them yet, seen as though most of these areas are well above the waterline.

My question is... what sort of plywood should I be using? Is the standard grade Robbins Elite Plywood upto the job? or should I be using a higher grade (and even more expensive) wood? I plan to coat all the sides and end gain with epoxy prior to fitting.

Much of the wood is fixed using copper rivets. Ive never had to replace any before. Can anyone give any tips on how to use them? Or shall I just use countersunk bolts instead for ease of use?

Any other tips in this (fairly major) operation would be gratefully recieved.

Thanks, Alex

 

[aztec]

marine ply is BS1088.

the money comes in when you want "face" sides.. A-A means good timber face sides both sides.... A-B is one side.... B-B is less quality etc...

i use C-C quality for structural work if it's going to be covered or painted. get mine from sydenhams at about 40 odd quid a sheet. but then all my interior is laminated epoxy/T&G then varnished.

if you want good face sides, you might consider veneer... looked at some decent stuff on ebay recently, although i have a friend who could probably get some.

on the rivet front... visit your local ship/boat builder/repairer, they'll give you some tips, but i found it really easy.... two man job though if you can't get to both sides at once... you can make the tool yourself.

steve

 

[burgundyben]

Well covered.

I think also BS1088 specifies the glue and that each of the layers contains no voids as can be found in cheaper plywoods.

 

[fluffc]

As I understand it

'Marine Ply' is constructed with waterproof glue, and as you say, no voids in the laminate the could potentially weaken it. Use for structural repairs.

'Exterior Ply' is the same stuff, but is not void-free so unsuitable for structural repairs.

'MDF' ain't waterproof.

 

[alb40]

Looks like the robbins stuff would be suitable then. Its their standard grade marine ply to BS1088.

It claims a 15 year guarantee with good quality faces. The more expensive grades have mahogany plies inside, and thats why their more suitable. They claim a 25 year guarantee on that stuff, but its not far off double the cost. I would plan to coat each sheet on all sides and soak the end grain in epoxy after all the holes are drilled, which would really protect it, and give a good base for painting.

The standard marine ply is just over 40 quid a sheet. Ill be buying in half sheets, cause the panels on the boat are exactly half a sheet wide. You can probably just make out each join on the picture below:

The first 3 to 4 panels on each side will need replacing for sure. Most of the panels towards the stern appear sound, although the ones ajoining the transom appear to have been replaced with a sheet of B&Q /forums/images/graemlins/crazy.gif It wont replace them yet though, as their still solid.

Anyone got any tips on sealants? Ive had good luck with 'boatlife' sealant before, which is a polysufide type.

 

[oldharry]

<< a sheet of B&Q. wont replace them yet as they are still solid.>>

What a shame - but they are not likely to be solid. There's an awful lot of rubbish around nowadays with BS1088 stamped on it, ands which would not pass the test for wbp or exterior grade ply.

Marine ply has all laminates same thickness of hardwood, including facings (unless specially veneered with eg teak finish), is glued with epoxy resin, and where internal laminates join, there should be voids of not more than a specified size, so they do not weaken the board.

Exterior grade and WBP will have 'hardwood' external veneers, which may be very thin, but will have much thicker internal softwood veneers, so there is much less strength. It has no guarantee about void width, so there may be areas of substantial weakness, but worst of all if (when) water penetration occurs the softwood laminates will rot, leaving the thin covering veneers unsupported. It effectively rots from the inside out, so that on superficial inspection all is well, but the sheet is substantially weakened without showing any external symptoms! Nasty!

A few years ago I was checking out a 22 foot plywood 'Seamew'. The transom had been replaced at some point, and appeared sound from the outside. The deck had rotted a little above it, but when we were cutting back the damaged timber, we discovered we could insert a probe right through the transom from top to bottom! The rudder fastenings were all that was holding the outer skins in place!!

So check your B&Q sheeting a bit more carefully, you may well find you only have around 2 - 3mm of solid timber!

 

[ThreeSummers]

[ QUOTE ]
Marine ply...is glued with epoxy resin

[/ QUOTE ]

Is it really? Just curious... (say me building a boat with marine ply...).

 

[alb40]

I think the crappy ply is ok at the moment, if i tap about all over it with a small hammer, there is no noticeable deflection in the wood. Some of the marine ply at the front though has some badly rotted spots near the top which your can put your finger through easily. Some of that in other places can deflect about half an inch under moderate hand pressure. Its all these pieces that will end up being replaced.

 

[burgundyben]

Thats a fine boat you have there.

Tell us more about her?

 

[alb40]

Why thank you very much.

Unfortunately, theres very little I do know about her. She was sold to me as a 'Robbinson Classic Cruiser' being one of two built for the MOD.

But my findings point more to her being a fast broads cruiser, prehaps build by Jack Powles of Wroxham - she has similar lines to some of their fiberglass boats.

Shes built from Ply down to the waterline, then has a conventional carvel built bottom. I dont know why wood was used here. Shes sheathed in epoxy from just above the waterline down. On the top, she has leaky teak decks, and a varnished wooden cabin side. I replaces most of the cabin top in standard WBP ply over the summer, and epoxy sheated that to protect, waterproof and give a nice finish.

She powered by two perkins T6354 engines, with direct drive gears, and V drives which give a 1.5:1 final drive. This can get her to 18knots on a good day.

Further work to complete - Damaged sterngear was replaced last year, but she still requires a new rudder on the starboard side as its got a slight kink in it. The rudder shaft log also appears to be suffering from rot, so that will need replacing. Im hoping that work be too difficult to do. I start sheathing the decks in epoxy, so this will be continued. It is at least, now watertight for the winder apart from a couple of minor leaks which have been difficult to trace. The wheelhouse roof will also be replaced next year to complete work on the topside.

Thats about it really. Another wooden boat being saved /forums/images/graemlins/grin.gif

Lots of Pictures HERE

 

[burgundyben]

Ah yes, I remember her now. Did you ever get a response from Byron on Mobo chat forum, he's more likely to know about her than anyone else I think.

Remember now telling you to get some clamps in place on those injector pipes, did you do it? ( I know from messy and smelly experience that those clamps are important!)

Little bits and bobs like that for 6.354s can sometimes be sourced from commercial vehical breakers who may have the odd one lying around or form ASAP supplies.

Good luck with your repairs.

 

[alb40]

Oh yes i remember now. Those injector pipes are now clamped and hopefully wont be breaking!

I didnt have a response from Byron, but i cant remember whether or not i contacted him TBH