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Kit Guide

Some Tips on Slot Gasket Renewal

By 2nd October 2020

A couple of weeks back, Claire and I had a practice session in our RS200 in a reasonable breeze. Planing offwind it quickly became apparent that all was not well with the boat, with two fountains of water on either side of the centreboard. An inspection back on land identified two small tears in the slot gasket, one either side of the centreboard (in its upright position). The volume of water projected by the tears was enormous, the boat had to come back to my workshop for some fettling.

The internet gives some good sources of information for slot gasket replacement. In summary:

  • Get the old gasket and all old glue off
  • Cut the new slot gasket to size
  • Abrade everything that is going to be glued
  • Stick it on with contact adhesive

Having been through the process, I thought I'd write up a couple of notes for those who have yet to attempt it - there are ways in which to simplify the job.

The job starts with the removal of the old gasket, which on the face of it appears trivial. Not the case. Contact adhesive (or Sikaflex, if the old gasket was fixed by RS) takes time to remove properly. The only way I found to remove it effectively was with a very sharp chisel. Always have the edge of the chisel pointing toward the slot, that way you will not take gouges out of the surrounding gelcoat. Allow at least an hour to do the job properly.

Removing old glue

The key point is that the chisel needs to be really sharp, I ended up resharpening mine four times through the process. Once all the glue is removed, you may well find that there are little chips of gelcoat that need to be fixed along each side of the recess for the slot gasket. Of course you didn't create these chips with your chisel and you can tut at the previous owner or RS. So fix the chips using matched gelcoat.

Now that you have the gelcoat out, fix that scrape at the back of your boat where your crew rammed the stern up Slipper beach whilst sailing with her friend Emma (I'm going to be in so much trouble when Claire reads this).

Once all your gelcoat work is complete, it is time to shape the new slot gasket. Here is an easy way to cut the new gasket to shape. First, cover the front of the hull recess with good quality masking tape. Second, take a new stanley knife blade and cut the masking tape to the shape of the recess. Third, peel off the tape that is inside the recess and transfer to the new gasket, thus using it as a template. Then use very sharp scissors to cut the gasket to shape. You have the added advantage that you have also masked the hull to avoid messy clean up of glue later.

Slot gaskets are a surprisingly tough material, and it is much easier to cut down the centreline of the gasket before you stick it to the boat. So measure up the length and position of the cut from the old gasket, transfer onto the new gasket and cut using a straight edge with a new Stanley blade. The material seems to dull the edge of the blade very quickly, I ended up using both ends on two blades to make the cut. Note that the ruler for the cut has been taped to the gasket to make life easier and reduce the likelihood of the knife slipping. Once the cut has been made, use another strip of masking tape to rejoin both sides of the gasket, this will make the next part of the process easier.

Cutting the GasketThe gasket is bonded to the hull using a contact adhesive, I used Thixofix. The difficulty with using a contact adhesive is that the positioning of the parts to be bonded has to be very precise, there is no chance of repositioning once you have started. This is especially problematic when bonding something that is long and thin - if you start at one end of the gasket with a very small error, it is magnified by the time to get to the finish. An approach to deal with this is to make a sort of hinge out of masking tape that allows for exact positioning of the gasket. Something like this:

HingeThis lets you sort out any issues with positioning before glue is applied. The bottom of the hull is curved so there is a bit of lifting on the ends of the masking-tape-hinge, but it is as good a way as any to get it right. Next, abrade all areas that are to be bonded and have a cup of tea before starting the next stage. Your boat should be looking something like this (note that the centre of the new slot gasket has also been masked off to save contact adhesive getting on your newly polished centreboard):

Ready for BondingContact adhesive works by getting a good bond to each surface and it does not need to be put on with a trowel. I put a line of adhesive down each side of the recess and gasket and spread it to a thin covering using a decorators filling knife, discarding any excess (using Acetone to clean my knife). You need a complete covering without pools of excess adhesive.

Glue appliedOnce the adhesive is touch dry, take a deep breath and use your hinge to position the gasket within the recess. Systematically apply pressure to the gasket to ensure a full bond in all areas. Avoid the temptation to start lifting masking tape and leave the boat to cure for 12 hours, after which the gasket should look like this:

All donePush the centreboard down through the gasket to make sure that your cut is long enough - you don't want to stress the end of the cut at the front end of the gasket. Now comes the question of whether to fair in the new gasket. I didn't bother, the fit of the gasket to the recess is pretty good and fairing with Sikaflex would make for a difficult removal task next time round. I did refinish the hull though, she looks very smart.

Everything you need to do this job is available from Rooster!

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