Hole in my boat

[goldscoter]

quick problem.I am removing the fittings of an old inboard engine on my boat, having changed over to an outboard.where the inboard once was i am now putting in storage. the water inlet filter has a tap about three inches high, so i started to remove it. it basically came away in my hand, leaving a hole of about 3cm dia directly through the hull.there are also four more holes of about 1mm dia where the screws used to be.any ideas on the best way to plug these?i was thinking of just glassing in a piece of wood and taping it over.dont know what to do with the outside though, taping over would look terrible, and it still has to be antifouled there.

 

[aitchw]

Is it a GRP hull or wood/marine ply. If GRP it's easy if a little time consuming.

 

[Talbot]

I am assuming that your hull is wood. I would chamfer the edge of the existing hole with a 45 degree router, then cut out a fill-in piece of appropriate wood, again with a 45 deg chanfer. Glue the two parts together with a waterproof glue, and glass over on the inside. This should provide a good strong waterproof plug. The screw holes I would fill with an underewater waterproof filler. Once these have been faired, there should be no sign of the repair after the antifoul has been applied.

 

[PaulJ]

This may seem obvious but whether the hull is wood or Gf, work from the outside and ensure that the outside of the plug is larger than the end/side which goes inside. If time, vibration, moisture and temperature changes were eventually to cause the bond to weaken, we wouldn't want the plug to be able to blow inwards!

Paul.

 

[goldscoter]

its grp.sorry i should have specified.is a bond of filler strong enough with it taped on the inside?

 

[cliff]

O.K. now it is easy to repair.
take a grinderette (4" or 4½") fitted with an emery disc say 40 grit or 60 grit and working from the OUTSIDE of the hull fair the edge of the hole back maybe 2" or 4X hull thickness to give a gentle slope (1:8) nb only grind in ½ hull thickness. Now go inside and repeat the process. You will now have a hole with tapered edges and in the process you will have removed most of the screw holes.

Working from outside apply a piece of woven mat over the hole and apply resin round the edge stippling the resin well into the mat. Keep the mat tight. Once the resin has set (10 mins?) build up more mat and resin from the outside stippling the resin well into each successive layer of mat. If tou have a mat roller all the better as you do not want lots of resin and no mat. Once the level is nearly upto hull level you can repeat the process on teh inside having first filled the remains of the screw holes with resin. A couple of layers of mat resined onto the inside of the hull should be sufficient "reinforcement. Make sure all surfaces to be resined are clean of all paint. oil etc and are dry.
Finally apply gelcoat to the outside and cover with cling film (or use wax in the gel coat). Once the gel coat has hardened it can be cut back and polished. depending on how good your work is will determine how easy it will be to obtain a good finish on the gelcoat.

Please note that Gel coat filler is not gel coat - it is only a white polyester resin and not as good as proper gel coat.

Hope the above helps.



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[oldsaltoz]

G'day Goldscoter,

Repairing the small hole in you hull should be straight forward and well within DIY capacity of most.

You should only use epoxy resin and cloth designed for use with epoxy, so no chopped strand mat.

All contaminants must be removed form areas to be glassed, including paint, and wash down with acetone to remove any grease/oils.

Grinding the inside and outside to form a tapered edge midway is good, we normally start on the inside as the sag in the glass will not be a problem; so, the first patch is cut to fit close to the edge of the newly ground area, I prefer to wet this out on a board first then place it as it's a messy job trying to wet out glass that has nothing behind it. place this first bit and let it cure overnight.

Now from outside build up layers of glass and resin to fill the void, cut the glass to shape to fill low areas first then use larger patches to cover them. Only mix small batches of resin in shallow containers and keep a finger on the job after about 5 layers in case it starts to heat up; sop if it does and wait till it cools.

When the outside hole is filled to within 3 mm move inside and do the same thing, let this cure overnight.

Curing leaves a residue that will reduce the bonding, so you need to wash this off prior to sanding or applying more layers, it's just fresh water and a plastic kitchen scourer, wash and rub till the water no longer forms beads, this will take about 10 minutes tops.

When the inside is flush, put 3 coats of just resin over it, this can be done as each coat gets very tacky, saving the wash and sand.

Now mix some 'closed cell' Micro-Balloons or 'Q cells' with your resin and fill / fair the outer hole, a plastic ruler held at about 10* is good here. Let this cure and wash as above then sand to final finish, 120 grit then 200 is ok. Now apply 3 or 4 coats of resin wet over tacky as above or wash and sand between coats.

Tools needed, 1 x small threaded cloth roller, lots of shallow conainers, ice cream containers or plastic milk cotainers cut longways are ok. White Vinegar to start cleaning tools, Acetone to finish cleaning. Rubber gloves, latex disposable type are good and cheap buy a box of them. Scissors and cutting board with a suitable knife or blade. Large fan to ensure good ventilation when working inside. Plastic ruler to smooth out filler. Paint brushes, half inch with plain wooden dandles, not painted or plastic, they will contaminate. Eye protection. A good respirator, not a doctors mask please. A Grinder, I use a 4.5 inch fitted with a concrete grinding wheel, will not clog and is fast.

I think I have covered it, if I have missed anything please take into account that it is the festive season and very very hot here at the moment (Hic) ..

Avagoodnewyear............

 

[William_H]

There is some excellent advice already given. I think polyester resin would be satisfactory because the chamfer outside and inside give a lock. I would suggest fibreglass cloth rather than chop strand mat as it is easier to mange in small pieces but you will need many layers. I think it is important to lay up the resin in one sitting so that there is a good chemical bond between layers from the outside to the inside. You might find that a bag of sand or even rags in a plastic shopping bag or covered with cling film on the inside will enable you to lay up the initial layers against the film from the outside. The plastic or film enables a quick release from the resin so that you can lay new cloth Or better you may be able to mount the sandbag from the outside against the hole so that you have something to lay the cloth on from the inside. The whole job is quite easy and satisfactory. On a fibreglass aircraft wing a properly done patch (as desctribed) can be regarded as having structural strength as good as original (usually using epoxy or vinyl resin) so because you are only filling a hole you really can't go wrong. Just make sure the area and job is warm enough. regards will

 

[PaulJ]

All seems good advice to me but just one query..... Maybe it's an "old wife's tale" but I was told many years ago that epoxy will "stick" ok to polyester but does not form a chemical bond. Therefore, for a repair to a polyester hull you should use polyester resin....... It seemed to make sense to me.

Paul.

 

[Guest]

First you have to clean it all up around the holes ..... oven cleaner is a good one for it - then a good fresh-water rinse off and dry.

Materials : marine play pad - does not have to be 'thick', micro-balloons filler, epoxy glue, polyester resin and chopped strand mat, acetone .....

Now cut the pad to be oversize and sit nicely in place covering the hole and mating with surface around.
Using acetone soften the resin grp around the hole ready for epoxying the pad in place. Generous amount of epoxy to hold and seal the pad over the hole.
Now really roughen up and prepare the area around the pad and the pad itself for glassing over. Acetone on the hull grp again to make sure its softened to bond well with the matt and resin you will apply.
Now lay up layers of chopped strand mat and resin building up a good strong uniform area covering the pad and surround .... the matt being eased out to spread load out from the pad area.
Finish off with a few extra coats of resin to make sure all sealed well.
Let it cure off.

Outside requires a little ingenuity ..... taking a thin piece of plastic that is not affected by polyester resin / harderner .... you cut to oversize of the hole area. You also rig ready props etc. to put in place to hold the plastic in place duriung curing .....
Mix up a generous amount of resin, hardener and micro-balloons into a thick filler paste ....... trowel into the holes and before it drops out ...... fit the plastic plate in place to hold and fair the filler .... reducing the amount of sanding etc. required once cured.
Letr it all cure and remove plastic .... you should have a reasonable surface that may just require a little cosmetic touch up .... finally paint over with good quality primer and anti-foul or whatever is your fancy .....

You can in fact put screws through hull into the pad - suiatbly countersunk into hull ... but shouldn't be necessary.

Of course this is my suggestion and in no way a professional answer .....

 

[snowleopard]

research by a designer with many years of grp construction gives bond strength figures of 80% of the strength of original material with polyester-on-polyester and 70% with epoxy-on-polyester.

the big benefit of epoxy is that it will bond with a much wider variety of substrates than polyester.

 

[PaulJ]

Interesting, so it wasn't complete rubbish! Thanks Chris.

Paul.

 

[goldscoter]

much thanks to all!!saved me from a slow and wet demise.a couple of questions:
1:how warm does it have to be?its freezing all day long and the forecast doesnt look much better for the next few days, tops of about 12 degrees.does this just affect the rate of curing, or the quality of the finished patch?will i need to set up a heater in the boat?
2:when the patch is done, and all is cured and sanded, is it enough to just use a primer, and then antifoul on top of that, or do i need to apply a gelcoat like some were saying?
apologies if im asking questions that should be obvious to most, but all of my previous experience is with plywood ie. dinghys
thanks again
Dan

 

[oldsaltoz]

G'day Goldscoter,

You will need some heat at low temperatures to get the curing chemistry going, I have used 1500 watt lamps and fan heaters in the past without problems, just make sure the 'area to be glassed' is warm prior to adding any resin rather than applying heat after lay-up.

Re final underwater protection, assuming you have a protective layer of resin, just sand the shine off and coat with any suitable primer; when cured give it a light sand and apply antifoul as normal.

Andavagoodnewyear........

 

[T_S]

Just a point to mention with all this sound advice. Make sure you use a Lloyds approved resin, the crap out of the local car spares shop won't do. And before anyone questions me on this...Yes there is such a resin!

 

[T_S]

P.S Myself if I was undertaking this job after sanding the sufaces to provide an appropriate key for the area, I would use a piece of Formica with releasing agent on it fitted with wide tape to the outside of the hull, then apply two thick coats of Gelcoat from the inside then as the gel coat became tacky lay up with glass and resin until the hole could be sanded flush using a light grinder, then finish off with two layers of matt and resin over a larger area.

 

[Guest]

Be careful to 'warm' the area and curing - not HEAT ...... you can literally cook resin .... causing brittleness and less adhesion. Most resin companies will quote similar to paint requirements ..... 15 C or more for optimum. Below this and curing slows down significantly.

FYI - when repairing cracks and other limited access repairs .... you can use a hair-dryer to reduce viscosity of the epoxy / polyester to get it to run into the cracks etc. - but care as it sets quickly !! I used to repair model Helicopter tail-booms with this system .... works !!