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Kit Guide

Hollows in Topper Hulls

By Dave Cockerill 2nd October 2020

Screen Shot 2015-09-20 at 17.59.42


Toppers are made of polypropylene, an amazing material because it is so tough. However it is not rigid and this can cause problems. If you want the hull to retain its original shape it is best to store the boat on its decks or on it’s gunwhale. If it must be kept on its hull then chose a trolley that supports the boat on the rigid points – under the back of the hull plate and under the mast cup bolt (just like the trolleys we designed and supply). The top racers often use our trolleys but even then their boats are stored upside down if left for long periods of time.


It is pretty much impossible to remove hollows completely. In fact some boats come with slight hollows from the factory! This is not an issue for beach boats and I remember my sons first Topper being more like a corrugated shed than a boat and he was pretty quick where the waves and the corrugations work in synch!

The technique is:

  • Inflate the hull (even lung pressure will do) through the bung hole.
  • Heat up the area around the hollow / depression. The best way is to use a hot air gun at full temperature but from a distance of perhaps 100mm and played across and around the problem area. A warm day or warm garage will make this easier. You are aiming to warm right though the 6mm thickness of the hull so it will take a fair bit of time.
  • Maintain the pressure in the hull.
  • Be prepared to re-heat a few times.


Be a bit wary. If a Topper is stored with the bung in during a hot spell it can expand. The end result can look like hollows but actually they are ‘expansions’. If the hollow is the hull plate area (an area that can’t expand) then the hull has expanded around it and the technique is different:

  • Remove the bung.
  • Turn the boat over.
  • Soften the whole of the hull by applying heat. A hot sunny day with the hull draped with black bin liners might work. A radiant heater suspended well above the hull and left playing on the surface for a number of hours might also work.
  • Plastic has a memory so it may go back to it’s pre-expanded state.

Of course the real trick is to leave the bung out.


The trick, of course, is not to get scratches in the first place. This takes real care with a Topper because even a finger nail can scratch it! Tough as old boots but soft with it; very strange!

I have never found a filler that works so to get rid of a 1mm deep scratch would mean removing 1mm of hull thickness over a large area. They are about 6mm thick but even so I wouldn’t want to weaken the hull by doing so.

The good news is that most 1mm deep scratches are actually only partly into the hull. There are sides to the scratch that stands above the surface (it’s a bit like a ploughed field).

The following is the best that can be done (unless you know better!)

The technique is:

  • Powerwash the hull, then clean with Cif and, if necessary, a plastic scouring pad. Only necessary if the hull is dirty.
  • Using a very sharp stanley knife blade, carefully scrape away the part of the grove that is above the surface of the hull. I almost caress the surface.
  • Use ‘wet and dry’ abrasive paper to smooth the area. The grade to use depends on how deep the scratches are. I’ve never used rougher than 80 grit and I have started at 1000 grit which is quite smooth. Use loads of water.
  • If you want a shiny surface go down to 2000 grade (grit) wet and dry and then heat the surface with a hot air gun (sometimes called a paint stripper).

Then don’t worry. Pretty much all Toppers have some scratches and a good start makes so much more of a difference, in fact a de-greased hull makes more of a difference (use a bathroom scouring paste, like Cif, and a plastic scourer if necessary). Get the worst out and then spend your time on the daggerboard and rudder. They are solid plastic and can be worked to a smooth shape and a smooth finish (see separate Tip sheet).

I hope this helps

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