Mast step tube broken at the top end

I capsized downwind without any cunningham in a bad spot just windward of an "bathhouse pier" a windy evening without having tied the mast retainer .... and continued to mess up ...
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The deck and the connection to the hull seems Ok!

There is a hatch on deck back att the centerboard but I can't reach the frontside of the tube from there. One idea is to somehow fixate the out side of the tube from inside the hull and then grind away enough inside the tube to build it back from there, but I don't have any experience with this kind of work.
 
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The main purpose of the tube from below the deck to just above the plywood base is to keep water out. The load from the mast is handled at the deck and plywood base. So if you don't have cracking/delam/core failure on the deck, the repair is is mainly to just get the tube watertight again.

If it were me, I would be working inside the hull, remove any splintered pieces of the tube, sand it/rough it up and then layup 3 layers of mat around the tube in the damaged area. You could also use something like 1708, which is mat stitched to 2 additional uni layers - a single layer (wrap) of 1708 would be stronger then the 3 layers of mat, but it's a little more expensive. You can buy in widths, such as this http://www.jamestowndistributors.co...Fiberglass+Biaxial+Cloth+Tape+-+6+inches+Wide. Whatever direction you decide to go, mat should be the first layer against the existing tube as it will conform to the irregular surface.

You may also want to add a few "tabs" the tie the deck to the tube if you do suspect any issues right at the tube/deck (similar to what has been described in tieing the tube to the hull in other threads..

Once the tube is reinforced, cleaning up the inner portion is next - break away/remove the damaged gelcoat, roughen it and fill it with mat or bog. The purpose here is to simply bring the laminate back to the same level it was before, better to under-fill then over fill (and the sanding down that comes with that). It doesn't need to be re-gelcoated, just smooth (taping sandpaper to the lower section works well as method for sanding the area smooth/flush with the existing tube)
 
First you need to install a 5" inspection port. You can find details on the preferred location here on the Laser forum.

Second take a disc grinder(4" or 4 1/2") with a 80 grit disc and be aggressive grinding off all of the splinter glass. This does not have to be pretty. You will replace the missing glass and adding another 50% more. Also rough up the deck about 3" all around the tube.

I would do the repair with epoxy and cloth. Cut a bunch of strips about 3" wide at 45 degrees. This will look like tape but the fibers will all be running 45/45 instead of 0/90. This will allow the glass to easily follow the curves. Mix up some epoxy filler the consistency of peanut butter and make a fillet all the way around the tube at the tube/deck intersection. This makes a nice round transition instead of the hard 90 degree. The glass likes this.

Run the strips of glass vertically up the tube(it only has to cover the broken area)and at least 2" onto the deck you roughed up. Go all around the tube. After you do the vertical pieces. Take more strips of the cloth and starting at the deck wrap the repaired area at an angle so that the tape is covering itself with a 50% overlap. Run it down at least 2" past the damaged area.

It is important to use the bias(45 degrees) cut glass. Regular cloth is hard to use and typically half of the fibers are always oriented in the wrong direction.

Then take a Dremel tool or a die grinder and remove the disturbed glass and gelcoated part of the tube. Fill in the big voids with an epoxy filler like silica . Keep it shallow because you need to finish the repair with atleast 1/16" of gelcoat.

After this repair is done, do not ever think about it again. It will be fine.
 
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A late Thank You for the advice above. The dinghy was on the water again in the beginning of August last year. I got a lot of help from an old-timer in the Club here.
We did chose to repair from the hatch back at the centerboard, and that did cost us some extra hours of work I guess. First we worked it from the inside of the tube grinding away everything that was delaminated.
We tied a thin piece of sheet metal temporary on the outside of the tube and built it back up with polyester resin and small pieces of fiberglass. Then we reinforced the outside of the tube with more mat and also made some extra connection to the deck.
It was good to tape sandpaper to a piece of a broken bottom section to create some finish to the inside of the tube.

Been happy sailing since then.
 
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The main purpose of the tube from below the deck to just above the plywood base is to keep water out. The load from the mast is handled at the deck and plywood base. So if you don't have cracking/delam/core failure on the deck, the repair is is mainly to just get the tube watertight again.
Haven't posted in a while and noticed your comment. It is fundamentally accurate, but the deck load diminishes linearly as a function of distance from the deck to the inside of the hull bottom. This is why you see a lessening level of adhesive wear on the tube going downward. Therefore, in this case it is best to reinforce probably 4 to 6" below the deck in order to make sure that transition area is structurally sound; because you can't phool physics.
 
Haven't posted in a while and noticed your comment. It is fundamentally accurate, but the deck load diminishes linearly as a function of distance from the deck to the inside of the hull bottom. This is why you see a lessening level of adhesive wear on the tube going downward. Therefore, in this case it is best to reinforce probably 4 to 6" below the deck in order to make sure that transition area is structurally sound; because you can't phool physics.

"This is why you see a lessening level of adhesive wear on the tube going downward"

Can you explain that a little more.
Also would be interested in your explanation of the direction(s) of the forces of the mast against the deck.

I don't disagree that in any glass repair, extending beyond the damaged area by some distance is nec.
 
Be happy to oblige. Consider the mast to be like a seesaw with the fulcrum being the top of the mast tube. The bending force above the tube is the vang and the main sheet. What opposes the force is the force is the wooden block glassed into the hull. this is a shearing force and is resisted by the bonding of the block to the inner hull and the bonding of the tube to the block. More later.
 
RE: Vang, you are absolutely correct! My apologies, I was multitasking and not paying attention and then called away. The main sheet curving the mast via the leech creates the bending force on the mast. there also laterial forces caused by the force of the wind against the sail, but judging from the wear patterns at the top of the tube, I would assume these to be less than what is created by the mechanical connection. Otherwise the forces on the tube are as described before, with the after part of the top of the tube and forward most of the bottom of the tube subject to the most the most wear. The bottom is actually subject to more than the top because of almost single point contact. The end of the tube will literally scrape off the gelcoat and dig into the glass and eventually cause a leak. I once made a probe out of a coat hanger to determine how deep this groove was on a mid-70s boat and it was over .125" deep at it's greatest point.

As for the direction of the forces, if you consider that you are two-blocked (close hauled) going up wind, and therefore, the force is greatest and is very close to the centerline of the hull. The bottom line is that those Teflon strips that APS sells are worth the money.
 
I'm not sure those Teflon strips are a good idea. Maybe they are OK if you sail only where there is absolutely no sand, but I removed the ones I had on my mast when I found that they picked up sand despite my best efforts to keep them clean. There is lots of sand where I sail. The sand gets imbedded in the Teflon and actually increased the damage to my mast hole. Note that it is quite difficult to get all of the adhesive off, which is essential, if you do remove them.
 
We have some sand where we sail, but I haven't noticed this happening. Definitely possible. I have noticed that with the tape, the wear at the top of the tube hasn't gotten any worse. I use one on the bottom, but don't know if it does any good.
 

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