Intelligent Infusion

The first proa Rob built was sheet ply for the long hull, tortured ply for the short one.  The second was bendy ply, stiff in one direction, flexible in the other until it was glassed.  The next couple were strip planked.  They were all messy, sticky,  dusty, wasteful jobs requiring a lot of physical labour and a fair amount of skill.
The next three were from infused panels.  An improvement, but still a lot of hard, messy work. From this experience was born the idea of Intelligent Infusion, a boat building method that eliminates the complicated, dusty, sticky, physical parts of boat building while at the same time improving the quality of the build and reducing the weight and waste.

It is not a radical new technique. It is best described as an accumulation of tips to simplify the build process, using the characteristics of the harry format, 3D software and the benefits of infusion.

Conventional infusion is a relatively straight forward technique, and there are plenty of You Tube videos explaining it.  However, most of these are for conventional moulded parts or flat panels.  Intelligent Infusion uses the same basic technique, but simplifies it for one offs and adds many more options, to the point that harrys can be built with zero to minimal hand laminating or cutting and grinding of cured laminate.

Intelligent Infusion requires a half hull/deck mould made from mdf or similar sheet material. The mould is a self supporting box section with curved rectangular sides supporting the mould bottom. They require minimal measuring and cutting. The mould sides are then bent around the bottom and screwed in place, the edges filletted and the surface sealed.  The mould is self fairing. Two mouldings are produced for each hull.

The rest of the boat is infused on an mdf table sized to the largest component.

Sanding, polishing and mould release are not required for either the mould or the table.

The full laminate, including the foam, is laid out dry.  The only tools are scissors,  straight edge, tape measure, hot melt glue gun and a jigsaw or utility knife, depending on the foam thickness.

All the measurements and details are laid out pre infusion.  Slot locations for bulkheads and interior parts etc. are easily measured and repeated.  Many of them are determined by the feature itself, so no measuring is needed. eg doors and hatches are made from the cut outs they will be filling.

Once everything is laid out it is prepared for infusion with low cost plumbing and a vacuum bag.  The bag is sealed, resin is mixed and the job infused.  The infusion takes about 40 minutes and ensures a perfect laminate, with no excess resin or voids.  Apart from mixing the resin, all the builder does is watch and go WOW!

Once cured, the peel ply is removed from the areas to be bonded and the components are glued into the slots or landings in the half hull. The other half hull is then glued to this.  Bonds are glass to glass, which is stronger than conventional glass to foam fillets and tabbing.  Everything is aligned, matching and very strong.  Any mistakes can be fixed using conventional boat building techniques.  After the glue has cured, the rest of the peel ply is removed and the boat is ready for painting, inside and out. The hull and fitout are inherently fair, so no sanding is required.

Intelligent Infusion is an evolving technique. It works for harryproa hulls, beams, all the flat and single curved items in the boats and most of the small compound curves.  ie everything on the Tenders and almost everything on the Cruiser series. We are working on rudder blades,  parts of the rudder drums,  large compound curves (Cruiser cabin tops) and masts. These are currently infused, but we are still simplifying the process and making it mess free.

The details that are included in the infusion process are:

– Both skins and the core
– Landings or slots for bulkheads, shelves, benches, steps, furniture, etc
– Self aligning edge joints, including for the two half hulls
– Perfectly fitting hatches and doors, plus their surrounds
– Rebates for windows, hatches, seats, doors, fittings, etc
– Accurately placed variations in foam thickness and density, including no foam in areas it is not required.
– Variations in laminate, including all local beefing up for high stress points
– Accurate, edge sealed holes for skin fittings, beams, masts and rudders
– Solids for attaching fittings
– Curves for seat backs, furniture edges, etc
– Sealing all exposed edges
– Plumbing, gas and electric cables, pipes, etc which can be concealed in the laminate or run along dedicated closed in channels.
– Variety of finishes such as formica, veneer, woven carbon, etc.

AIR 40 – WIP

The AIR 40 is unique in many ways. The prime requirements were for a low cost, easily handled boat that would sail well in light air, be safe and easy to sail in heavy air and be suitable for the client and his wife to live on for extended periods. Secondary requirements were an open saloon that could be closed up and the ability to fit in a mono slip, a container or onto a trailer. Plus a tender that was capable of long trips at high speed in adverse conditions.


Length Overall: 12m
Beam Overall: 6m
Length Windward Hull: 9m
Draft Boards up: 250mm
Draft Boards Down: 1.1m
Sail Area: 60 sq m
Weight of composites: 820 kgs
Weight ready to sail: 1,000 kgs
Payload: 1,000 kgs (This can be increased if the excess goes in the lee hull)
Bruce Number at full payload: 0.61

(inc masts, beams, rudders and booms.  Does not include wastage, paint, consumables or safety gear)
400 gsm double bias fibreglass: 406 sq m
600 double bias fibreglass 180 sq m
440 gsm unidirectional fibreglass: 38 sq m
300 gsm uni carbon: 251 sq m
6 mm H80 foam: 9 sq m
12 mm H80 foam: 58 sq m
15 mm H80 foam: 32 sq m
20 mm H80 foam: 82 sq m
25 mm H80 foam: 19 sq m
Epoxy or methacrylate glue: 25 kgs
Carbon tow: 1 kg
Infusion resin: 178 kgs

Length Overall: 40′
Beam Overall: 20′
Length Windward Hull: 30′
Draft Boards up: 10″
Draft Boards Down: 44″
Sail Area: 645 sq’
Weight of composites:1,800 lbs
Weight ready to sail: 2,200 lbs
Payload: 2,200 lbs (This can be increased if the excess goes in the lee hull)
Bruce Number at full payload: 1.5

(inc masts, beams, rudders and booms.  Does not include wastage, paint, consumables or safety gear)
12 ounce double bias fibreglass: 4,360 sq’
18 ounce double bias fibreglass 200 sq’
13 ounce unidirectional fibreglass: 410 sq’
9 ounce uni carbon: 2,700 sq’
1/4″ H80 foam: 97 sq’
1/2″  H80 foam: 630 sq’
5/8″ H80 foam: 350 sq’
3/4″ H80 foam: 880 sq’
1″ H80 foam: 205 sq’
Epoxy or methacrylate glue: 55 lbs
Carbon tow: 2.5 lbs
Infusion resin: 390 lbs


The low cost was easy. Intelligent Infusion and the simple layout will allow it to be built very quickly, with little waste. The basic structure weighing about the same as a racing cat helps as well. Even the hinged beams, which would normally be very complex and stressful to build are “just another infusion” which happens to include the accurately aligned hinges.



Easy handling is a Harryproa trademark. The novel seating allows for three people to sit side by side on sheltered, comfortable, padded seats with all round vision, out of the sun and the wind and centrally located to minimise the motion. These seats rotate to face the table when it is time to eat. When the boat is folded, they sit in a recess in the lee hull. Steering is by tiller and the two mainsheets are close at hand. Shunting is far less onerous than tacking or gybing, particularly in adverse conditions and reducing sail is a simple task performed without having to leave the area between the beams. If required. it can be done with both sails completely eased, so the boat is stationary. This is far less stressful than trying to take in a reef when the boat is sailing upwind or the crew is on the pitching, exposed foredeck with flogging sails out of hearing range of the helmsman.



Light air sailing is frequently a lost pleasure in modern cruising multis. The Air 40 has 60 sqm of sail in two easily handled mainsail only rigs. These are self vanging and self stacking (no lazy jacks to catch as the sail goes up) due to the wishbone boom. The lightly loaded sheet controls the angle of the sail, the combined outhaul/vang and the flexible, unstayed mast control the shape. As long as the boat is kept reasonably light, it will ghost along in very low winds. In strong air, the unstayed shunting rig comes into it’s own. No scary jibes while surfing down monstrous waves with the mainsail crashing into the shrouds, no starting the motor and backing the headsail to ensure the tack is completed. Simply release the sheets, rotate the rudders, sheet on and sail off in the other direction. Sailing becomes the enjoyable, low stress affair it should be.



The simple layout has double cabin for the owner and his wife and another double for guests or storage. A large toilet space was chosen over 2 cramped ones. The galley is in the saloon, close to the table which will seat 8. The saloon has a raised roof with roll down clears so it is comfortable in winter and summer. The roof can be lowered if required for security or reduced windage. To lee of the saloon is the full length ‘toybox’ where fenders, lines, anchors, fishing fear etc are stored.

A 40′ cruising multi that can be traillered and fit in a shipping container is a challenge. As is fitting into a mono berth in a marina. The solution was to fit folding beams. These fold in the horizontal plane so could be made very strong, without struts etc adding drag and complexity. The hulls are not affected, so staying in a marina, without the long walk from an end tie, becomes more enjoyable. And cheaper. The folding mechanism is stronger then the beams, but only requires pulling 2 pins and pushing/pulling the hulls together to fold or unfold the boat.

The tender is not the usual blow up, impossible to row, difficult to stow, 3 adults max load at 2 knots inflatable. It is 5m long, with a powerful outboard capable of long trips at high speed in adverse conditions. It also serves as the motive power for the mothership. The tender lives between the beams, which is a much better location than davits on the stern. It is held in place by pins across the bow and stern. The stern ones are removed to lower the outboard into the water. The tender becomes a “sled”, with the advantage that it contours to the waves, so the prop never leaves the water. When the boat is folded, the tender fits under the bridgedeck. When the tender is away, the space is covered with slats, which roll up when not required.



Custom 18m – AUSTRALIA

The 18m/60’ter in Melbourne Australia is quite unique.

It is the first infused flat panel harry built and the first harry built without Rob’s direct input. In many ways, it was the inspiration to have a closer look at the KSS build method. The owner, who had previously owned power boats, bought a set of Visionarry cruiser plans and used them as the basis for his boat, which he build pretty much single handed, including the rig.

APRIL 2016

Rick Willoughby – The bows on the lw hull are now almost plumb with much finer entry at the deck. At 15kts the attached flow does not go higher than the deck now.




The helm has been relocated to the cockpit rather than off the side of the lw hull. This change makes steering considerably more intuitive. Each wheel is fitted with an orbital pump/motor operating in closed loop with the same size orbital pump/motor at the rudder gearbox. The 1:3.3 gearbox was retained to ensure the hydraulic pressure is low. The orbital pump/motor has the torque rating to be directly connected to the rudder but the operating pressure would be higher and that would increase bypass and require high pressure fittings and pipes. The whole system as installed required around AUD1100 in parts and materials.

Removing one of the gearboxes has made the steering much more direct and is now a tad heavy for the small diameter wheels. With hindsight it would have been better to use lower displacement pump/motor on the wheels to give about 1:6 overall rather than the previous 1:10.

We were contemplating providing automatic make-up in the hydraulic circuits using an air over oil accumulator with a feed in check valve and pressure relief to cater for thermal expansion and leakage in the circuits but the simple closed loops are working fine and orbital pump/motors are getting smoother with more use. Both circuits are leak free at this stage.





Rick Willoughby – We sailed Peter’s boat from Port Phillip to Western Port on Thursday.

We had a good northerly until we got up into Western Port then the wind died. It came back up to about 8kts, allowing us to work up to Hastings. Peter plans to slip the boat in a yard at the top end of Western Port. That will happen sometime in the next week.

The wind started out around 15kts but built quickly to 20kts and gusted to 25 knots at times with us running almost dead square. Downwind we averaged better than 10kts once we got going and nudged over 13kts in the gusts.

Reaching across from the rip to Cape Schank gave the best speed I have seen on the boat. The wind during this period was 18 to 20kts. We touched over 17kts a couple of times. Wind was just aft of beam. We may have coaxed a little more speed if the course was 10 degrees higher.

Waves hitting under the cockpit knocked the speed. The highest waves were no more than 1m because we were only a couple of mile off the shore with wind from the north. The best speed, consistently above 15kts, was as we approached Cape Schank where the fetch was reduced and waves less than 1m. We then hardened up a bit and speed dropped to around 13kts. After that the wind dropped as we got further into Western Port. I was surprised by the difference in wind speed as we got into Western Port because it was like that most of the day according to the various weather reports – only 20 mile apart but totally different conditions.

A short video where we are doing around 15kts:


The modified bow does not lift the water as much as the full flat face so not quite as spectacular looking but probably less drag associated with it.

We managed a short shunt pinching up to make the channel past Cowes where the angle between tacks was 79 degrees. However that was very much tide assisted. The usual loop at the shunt looks like a smooth U-turn.



Rick Willoughby – We tested a swing-up dagger board on Peter’s boat today.

Winds were very light 3 to 4 knots according to Fawkner beacon data. Irrespective of the light winds we could maintain control right up to about 45 degrees true. In these conditions we made best VMG by dropping off the wind a little but were sailing higher than nearby deep keeler.

The board is fitted through a slot that has been cut in the deck. It has a 25mm pivot pin on one and and an 8mm shear pin in the other. There is a 60mm diameter stainless brace up to the longitudinal beam The board is 80mm thick, 500 chord and immersion just under 2m. It is cambered. The long slot is to cater for a collision situation when the shear pin fails by theta end of the board being forced upward.

The hull is near clean at the moment. It is 3 weeks since it was on the hard for some work so fouling is light. At present we can get over 8kts with the electric motors meaning it is about as smooth as it has been since the electric drives went on. On a reach with the board up we managed boat speed above windspeed. That was coming back in 5 to 6knots of wind doing 6.5 to 7 knots through the water.

The combination of relatively small but very solid rudders under the hull combined with a swinging dagger board looks good.



The owner/builder is no Russ Brown. He knew nothing about infusing,flat panel building or sailing before he started, but has a wonderful capacity to have a go and try stuff. To put together a 60’ter,including building the mast, boom and rudders yourself is an amazingfeat. To build a boat using a new technique (infused flat panels)and to experiment on a 60’ter takes a huge amount of perserverence. With all this, he is extremely relaxed, quick to own any errors andan all round pleasure to sail with. He also makes a great cup oftea.
The boat is not finished, but the bits that are (the galley area), areto a high standard. Like my boats, the rest of it is workmanlikerather than show room. The time, money and weight savings from thisapproach are appreciable.
It is a big, undercanvassed cruiser and this was only the third timeit had been sailing.
The first impression is how large it is.

I am no Beken. The photos don’t give any sense of how large, airy and spacious the boat is. 7of us on board could walk round the bridgedeck easily and safely. Plus the ww hull deck. Equally easily, we could have sat around inthe saloon. The galley has lots of space, there are 2 double queen bunks and a toilet in each end of the ww hull.

The attributes of a harry are low cost, easy to build and sail and fast. 
These are met on this boat as follows:

Low cost: Very. It is built from infused Polycore honeycomb flatpanels with curved hull bottoms. 4 tons weight including the rig and motor (according to the launch crane), with minimalist layout. The basic boat seems very stiff and strong (no big waves, but no creaks or groans), although a few fittings are too light, but this is easily fixed. There is probably another couple of hundred kgs of fitout (table, fridge, etc) to add. 7 people was a good load, but it made no trim difference where anyone stood.

Easy to build: Simple shapes, flat panels, with very few deck fittings. The lee hull is 3m/10′ longer and a little narrower than the Vis and the ww hull a little longer with fewer curves than the Viscruiser (Rare Bird). The only slightly complex area is the motor arrangement which has an electric lift for the 60 hp motor. The well can’t be closed off underneath so waves hit it and leak onto the bridgedeck. There are plans for electric motors and/or two smaller outboards. Under motor the boat steers well and picking up the mooring was easy with 2 rudders and a steerable motor, aided by the picker uppers being within easy earshot of the helm.

Easy to sail: It will be, once the systems are sorted out. The rudders steer well, the connection and the wheels are ok once you know them, but took me a while to learn (others were quicker) and at night in an emergency would need a clear head. The system uses independant wheels mounted on the lee hull either side of the mast and 2 right angle gearboxes. There is a little play in the boxes and the rudders are only just balanced so there is occasional slop. Steering upwind with the front rudder worked a treat. The aft rudder was set to give a little lee helm. This had the effect of eliminating leeway,which was very obvious when looking at the wake whensailing upwind. Occasionally there would be negative leeway, with no obvious loss of speed, which is something I have tried but not achieved on other harys. My photos don’t do this justice, but itwas quite noticable.

Sailing hands off was no problem. The near enough 2 ton of windwardhull and 8m beam did not have significant weather helm once the boat was sailing, but in light air is a problem. Shunting was slow (maybe a minute from dump sheet to back on course when it went well), but once the systems are sorted out it should be a quick single handed operation, the same as on the other boats with ballestron rigs.

The underhung rudders are about 2m (11%) from the ends and judging by how well they steered, could have been a lot further inboard. They are not liftable, but making them so is on the to do list.
Fast: The long, light hulls are very easily driven.

The bows are over half a metre/20″ wide at deck level and throw up a lot of water above about 10 knots which slows the boat, albeit quite spectacularly. They are shaped foam blocks, so easily fixed. The below the waterlineshape is pretty good, judging by the wake.

Top speed was 14 knots in 18 knots of wind. Best was 13 knots in 14 knots of breeze.
 The sails are not right, nor are the systems to trim them. Both are easily fived. The unstayed mast is very stiff up to the hounds,flexes off nicely in the puffs.

One of the people on board was Peter Eagles, who does the harryproa engineering. He reckoned the mast would bend about 30% (~5m) at the tip before it broke. This probably makes the boat impossibleto capsize from wind loads.
The tacking angle was poor, due in large part to lack of main leech tension and hence jib luff tension (a turning block pin was on the verge of popping out, so we did not tension things as much as we could have), and jib sheet tension (no block or jammer). Despite this, upwind speed and hence vmg was impressively good, compared to the mono racers that were around at the time.

Conclusion: As with any one off boat there are some bugs to iron out,but once they are, this will be a very comfortable cruiser, easily capable of sailing at wind speed. 
The boat is not finished, but the bits that are (the galley area), are 
to a high standard. Like my boats, the rest of it is workmanlike 
rather than show room. The time, money and weight savings from this
 approach are appreciable. 

It is a big, undercanvassed cruiser and this was only the third time 
it had been sailing.





Proas do not tack, they shunt – meaning they go in both directions sailing forward and… well, forward. It is a fairly simple process of letting go the main sheet, turning the rudders, sheeting in and away you go…

Shunting like this is not as quick as tacking, and a lot slower than gybing. However, it is generally easier and much safer than both, and the worse the conditions, the more obvious the difference is.





A quicker way to shunt has been developed by the racers. Instead of bearing away, the boat is luffed head to wind. When the vmg drops, the sails are sheeted on to the new tack. This stops the boat and the rudders are rotated. As the sheets are pulled on, both rudders steer the boat back to the new tack. On a schooner, the aft rig is sheeted on first. If crew are available, they move forward on the windward hull to speed the turn. Similarly aggressive use of rudders, sheets and crew will also speed up a gybe/shunt. Both procedures could be sped up further by the use of an easily deployed brake such as legs or buckets in the water, or a simple flap.