Bunging up holes in the hull

[c4pt]

Hi.
Can anyone give me some advice on filling the holes left by an inboard instalation and a sea toilet. I'm not replacing either so see no need to have the relevant holes in the hull. The prop shaft hole is the main one followed by the exhaust and toilet outlet. Do they need glassing from both sides or just from the inside and use a filler?

 

[vyv_cox]

You can do it from the inside, but don't expect good adhesion without appropriate preparation. You need to fair the internal edges of the holes until the hull thickness approaches zero. The angle of the fairing (outside of hull to new surface) should be not much more than about 30 degrees. Remove any gelcoat, polish and dirt on the internal surface of the hull to which the new layup will be bonded. Tape a piece of aluminium or similar to the outside of the hull to act as a mould. The aim is to use as little filler as possible. Epoxy resin will adhere better to the old GRP. Overlap the new layup by at least 3-4 times the hull thickness plus the faired part, more if possible.

The relatively small holes that you are filling should pose no problems at all. I have filled the hole left by a drive leg, about 10 x 12 inches, using this method without any problems.

 

[Avocet]

Will the polyester filler you put on the outside stick to the epoxy?

 

[stamfordian]

Agree with what,s said see one for real at the link below

<A target="_blank" HREF=http://www.arweb.co.uk/argallery/stamfordian>http://www.arweb.co.uk/argallery/stamfordian</A>

 

[oldsaltoz]

G'day Stuart,

Glassing them up is no big project but you note the following. Only use epoxy resins as it's all but impossible to get a secondary bonding on poly resin. Also, only use fibreglass fabric designed for use with epoxy resin, (No chopped strand), you are looking to get a ratio of 2 parts fabric to one part resin with epoxy: poly resins can have up to 3 parts resin to one part fabric.

Make sure the area to be glassed is clean, that means grinding off all paint and contaminants: feather both sides of the hole/s.

When laying up, do not apply more than 4 layers wet on wet or you may generate too much heat and boil the resin. Start with a large patch about 6 inches wide to cover a 2 hole, the next patch should be about 5 inches and so on down till the hole is level; this will prevent a 'hard spot' in your hull.

Also note, epoxy resin leaves a residue when it cures, so before you start sanding it, wash it with fresh water and a scourer till water no longer forms beads, then sand.

Tip: Adding a very thin layer of closed cell balloons to the inside or the mould plate (On the outside) and letting it go off, then sand the inside and apply your glass. This will make final clean up and fairing a simple task.

Hope this helps

Avagoodweekend Old Salt Oz /forums/images/icons/cool.gif

 

[vyv_cox]

I don't entirely agree with your statement about epoxy v. polyester resin. I have made many repairs using polyester in the days when epoxy was far less available than now. I understand that polyester to GRP can only form a mechanical bond, whereas with epoxy there is some degree of chemical bonding in addition. It follows that good roughening of the surface will help to make a good bond. However, nowadays I would use epoxy for this type of job, e.g. bonding the thrust bracket for my Aquadrive last winter.

A practical detail that I omitted in my first post. Taping an aluminium sheet or something on the outside of the hull only provides a weak support. I usually put a single layer of glass and resin on first and let this go off, before putting on more layers.

There is a good deal of general information about GRP repairs and construction at <A target="_blank" HREF=http://www.cyb-glassfibre.co.uk/grpdoc.html>http://www.cyb-glassfibre.co.uk/grpdoc.html</A>

 

[Strathglass]

I would agree with your posting apart from one minor change. When applying layers of fabric I always put the smallest bit on first. Then each following piece I make slightly larger thus it bonds to a new part of the hull. This is easier to do and gives a smoother inner surface but still gives a good taper which ,as you have stated, is essential.
Iain

 

[c4pt]

Hi All
Thanks for the advice, I feel more confident in tackling the holes now. Happy Sailing
Stuart Morgan (c4pt)

 

[oldsaltoz]

Re: Sheeting order

G'day Iain,

When repairing a hole from inside the boat, I place the large sheet firt to avoid exposing raw fibreglass ends to the wetted side of the repair.

This helps to prevent water ingress at a later stage. If repairing from the outside, the smallest sheet is applied first, the final sheet is cut so that it's edge does not extend outside the damaged area, and faired with closed cell balloons, then given 3 coats of resin.

Hope this helps

 

[AvanLoon]

Why should you mess around with polyester and glass fibres? Just a blind flange bolted in the holes will do the same watertight job. With the advantage that you can easily change your mind and replace a new water toilet on the same openings. Above all, you can do this in winter as well, which is less easy with the polyester an fibre job.
Kind regards