– Going Hard –
There is no right way of designing and building a hardtop for your cruising multihull. Soft top bimini’s are common because they are light, protect you from sun and rain, and less expensive to manufacture.
Commonly many transition to a hard top bimini which provide better protection, the ability to be walked on (with good boom access), solar panel mounts and water catching systems. I have added a hardtop to every one of my cruising catamarans (Magic Happens, Chaotic Harmony, Whim and now Favourite Child). There have been some hard lessons learnt along the way.
My build techniques have all been in foam and glass. Initially I bought pre glassed panels, slotted them together, edged them and mounted the relatively flat hardtop to the existing aluminium frame. For the last two hardtops I have designed and built them with the goal to have them appear as if they were part of the original design. Here are a few tricks and lessons learnt.
The hardtop is usually close to the cabin top in size. I have chased up the original building plans and copied the foam material, thickness and density and then replicated the same layup and type of glass. If the cabin top was stiff then your hardtop bimini will be also.
Original softtop bimini.
To replicate the cabin top shape, I copied the curve with stiff cardboard to make a mould. I then using flooring chipboard to shape the curve and make a jig.
Measure three times, cut once. The foam is expensive.
I nailed the foam to the jig with thin bullet-head nails. When you have shaped and glassed one side the foam is easily pulled off, leaving the nails in the jig and with holes barely visible and easy to fill. Thick foam may not bend readily (I used 30mm for this job). To get a smooth curve I scarfed out slots and filled them when the foam was nailed down to the jig.
Around the edges I double the foam thickness which enabled a track to be routed out for thick-walled electrical conduit (the orange one) to be laid down and glued in. When the area is shaped and glassed this can be then slotted for clears to be fitted. Always sand the conduit first to increase adhesion. Mark the slot line carefully prior to cutting it out either a router or multitool. A router is not very forgiving and a multitool is slow but easy to use if you have marked the slot out well.
All angles covered.
Around the top edge of the hardtop I ran similar conduit but this time only half buried it so that it created a line for water to travel for fitting a collecting system. This conduit was to carry the solar panel cables and I ran a thin cord mouse through the cable before I glued it into place. I also set up the exit points which tracked thought the supports so that all wiring was hidden.
Never try and glass over a hard edge. Cove everything. (eg no right angles – just curves).
Always use peel ply. This stuff is expensive but saves hours of filling and sanding. By using peel ply your filling and sanding will be to cover overlaps and bumps rather than fill the weave.
I used microballons as a filler. Always apply more than you think, and you will be able to work down to a perfect level. If you apply them thinly you will inevitably have to fill twice. A light bar laid flat and shining laterally across the job will readily highlight the areas you need to get right.
A sanding system with a vacuum attachment is a godsend. I used a Festool sander. Damned expensive, worth every cent. I set up a fan and vacuum when using the torture board. I made my own board with sticky back velco, sticky back sandpaper rolls, flexible ply and added handholds and a weight. Because you will be working on a horizontal surface you can achieve a flat level quickly with the right gear.
Spray painting. There are restrictions on what you can do so you might need to check with your local council. I bought a cheap wedding marque, set it up inside my shed. Don’t go cheap on the protective gear though – good masks, disposable overalls and goggles all essential. My spray equipment is a $200 kit and a good air compressor. Gravity fed on the gun. If you can spray the high build paint you will get a good finish quickly. I am the son of a housepainter. There are three rules to getting a good finish. Preparation, preparation and preparation. You cannot cover anything with a two pot high gloss epoxy paint. It will show every dent and dust particle. Make sure your spray area is immaculately clean. I wet wiped and hosed it out twice before spraying.
The support struts for my hardtop I made in the shed, but they were not fitted until the hardtop was mounted on the boat. This meant I had to glass them on, fill, sand and paint them aboard. Not an easy task and to get a good finish it meant a mountain of taping and covering and the perfect day to spray – early, dry morning, no wind. One of my favourite things is to apply lots of bog to awkward above head positions and then sand most of it off. Not ...
I initially planned to mount the clears onto the boat with flexible sail track. I fitted them and then decided that it made the job look like an addition, so I very tentatively took out the grinder and added a glassed-in conduit track around the sides and across the front. A lot more work but now an integral part of the boat.
Ready for final strut painting.
I fitted the solar panels in the shed – it was easier to do this while out of the sun and in a dust and dirt-free environment. I used semi flexible panels and mounted them with 4.5mm very high bond tape. I was after a flush appearance, but solar panels stuck directly to fibreglass have issues in the tropics – basically they cook the glass and eventually will crack or delaminate it. Elevating them might reduce this and the tape creates a gap for water and air to flow. Time will tell.
Of all the hardtops I’ve made this one was the biggest – three metres long and five wide. I needed to hire a car moving trailer and organise a crew of mates to help with the fitting. It was light enough for four to easily carry but bulky in size. We strapped it to the main halyard to raise and support it in place. Ever useful milk crates held it in position while I worked on the struts. I had already mounted the middle front strut to the boat. This was a fixed point that could not be varied, and it was from here that I could position the top accurately.
Finished with clears.
The build was done part time over five months. Materials cost – foam, glass, fill, paint and disposables (not including solar panels and clears) was a bit over $14,000. I didn’t count the hours (on purpose).
Weight is always a critical issue on multihulls. The hardtop in the shed (painted with panels on it) weighed in at 114kg. I had removed two back deck mounted fuel tanks, the second 10-man life raft, a 120kg generator and the stainless and material of the original Bimini. The completed job raised the stern raised by 2cm over original so I have ended up with a lighter and better all weather functional boat. The hardtop is as stiff as the cabin. I feel as if I’ve successfully gone hard.